Influence of catecholamines, prostaglandins and thyroid hormones on growth hormone secretion by chicken pituitary cells in vitro

In young chickens plasma concentrations of growth hormone (GH) are depressed by prostaglandins (PG) E1 and E2, epinephrine, norepinephrine, alpha 2 and beta agonists or thyroid hormones. A primary culture of chicken adenohypophyseal cells was used to examine the direct effects of these agents at the level of the pituitary as evaluated by GH release in the presence and absence of growth hormone releasing factor (GRF). Following collagenase dispersion and culture (preincubation, 48 hr) cells were exposed (incubation, 2 hr) to test agents, except for thyroid hormones which were added during the preincubation, and incubation period. Growth hormone release was increased (P less than .05) in the presence of PGE1 (10(-8)M by 34%; 10(-7)M by 54%), PGE2 (10(-8)M by 29%; 10(-7)M by 29%), PGF2 alpha (10(-8)M by 28%), and the beta agonist isoproterenol (10(-7)M by 46%). Basal GH release from chicken pituitary cells was not affected by dopamine, norepinephrine, epinephrine, thyroxine (T4), triiodothyronine (T3), or alpha adrenergic agonists. Growth hormone releasing factor stimulated GH release was not affected by the presence of prostaglandins E1, E2 or F2 alpha in the incubation media. However, GRF stimulated GH release was reduced by high doses of catecholamines: dopamine (10(-6)M by 34%), norepinephrine (10(-6)M by 74%), epinephrine (10(-8)M by 47%; 10(-7)M by 41%; 10(-6)M by 89%), and by the alpha 1 adrenergic agonist, phenylephrine (10(-7)M by 52%), the alpha 2 agonist, clonidine (10(-8)M by 34%; 10(-7)M by 83%) and the beta agonist, isoproterenol (10(-7)M by 64%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal interrelationships in postpartum suckled dairy cows.

Three cross-bred cows calved in March and April and were followed until day 62 after parturition. Each animal was suckled by 2 calves ad libitum. All calves were removed from the cows on day 55 after parturition. Blood was collected 3 times per day from the jugular vein by venipuncture. On 4 occasions after parturition--i.e. days 7-8, 21-22, 35-36 and 49-50, the cows were bled through a jugular venous catheter every 30 min during the 24 h. The plasma samples were analyzed for the content of 15-keto-13,14-dihydro-PGF2 alpha (main PGF2 alpha metabolite), LH, prolactin, cortisol and progesterone by radioimmunoassay methods. The concentration of PGF2 alpha increased from 280 to 730 pmol/l within the last 4 days before parturition. The highest geometric mean was 3106 pmol/l on the day of parturition. Thereafter a steady decrease of PGF2 alpha metabolite concentration was seen until day 21 when it reached plateau at 148 pmol/l. In all cows plasma LH concentrations increased significantly (P < 0.05) from about 1.6 micrograms/l on days 7-8 to 2.4 micrograms/l on days 21-22 post partum. The frequency of LH pulses showed no tendency to increase as the postpartum period progressed and averaged 6.5 pulses/24 h. Mean plasma LH concentrations increased from 2.1 micrograms/l 2 days before weaning to 3.2 micrograms/l 2 days after weaning (P < 0.05). LH peaks occurred less frequently in association with prolactin and cortisol peaks than in their absence. A partial positive correlation between PGF2 alpha metabolite and cortisol (r = 0.30) was found on days 7-8 post partum. Correlation between prolactin and cortisol on days 7-8 and 21-22 post partum was also positive (r = 0.20 and r = 0.27, respectively). There was a negative correlation between LH and cortisol on days 7-8 (r = -0.27) and days 49-50 (r = -0.21) post partum. The first and short progesterone increase observed after weaning was terminated in conjunction with PGF2 alpha metabolite peaks.     

Contractile effect of PGF2alpha and PGE2 on isolated branches of uterine and ovarian artery in different days of estrous cycle and early pregnancy in pigs

The contractile effects of PGF2alpha (3 x 10(-6) to 10(-4) M) and PGE2 (10(-7) to 10(-5) M) were examined on isolated branches of ovarian artery (OA) and extramyometrial branches of uterine artery (UA) collected from pigs in the luteal (day 10-12) and follicular phase (day 17-20) of the estrous cycle, and during early pregnancy (day 10-12). Strong contraction was demonstrated in both arteries during all investigated periods in response to PGF2alpha, which was significantly higher (P < 0.01) than to PGE2, being negligible in the follicular phase. In UA, the effective dose of PGF2alpha (ED50) amounted 7.9 x 10(-6) M and 6.3 x 10(-6) M in the luteal and follicular phase, and 5.0 x 10(-6) M in early pregnancy. ED50 for PGE2 reached 5.0 x 10(-7) M in the luteal phase, and 4.1 x 10(-7) M in early pregnancy. For both prostaglandins, the contraction was much stronger (P < 0.01) in OA than in UA branches. In OA, the ED50 for PGF2alpha was 1.2 x 10(-5) M in the luteal phase and was significantly higher (P < 0.05) than in the follicular phase (3.1 x 10(-6) M) and early pregnancy (2.7 x 10(-6) M). ED50 for PGE2 amounted 7.3 x 10(-7) M in the luteal phase and 1.7 x 10(-7) M in early pregnancy. Studies showed the influence of the estrous cycle and early pregnancy on OA branches sensitivity to the contractile effect of PGF2alpha and the lack of this effect on UA branches, and the influence of the estrous cycle on UA and OA branch contraction in response to PGE2.     

The effect of progesterone on oxytocin-stimulated intracellular Ca2+ mobilisation and prostaglandin secretion in porcine endometrium

We have studied in the porcine endometrium the expression of oxytocin receptor (OTR) mRNA and the effect of progesterone (P4) on oxytocin/oxytocin receptor (OT/OTR) function concerning intracellular Ca2+ mobilisation ([Ca2+]i), prostaglandin F2alpha (PGF2alpha) and E2 (PGE2; PG) secretion. Tissue was taken from cyclic and early pregnant pigs (days 14-16). A higher expression of OTR mRNA (P < 0.05) was observed in the endometrium of cyclic than pregnant pigs. The stimulatory (P < 0.05) effect of OT (10(-7) M) on [Ca2+]i mobilisation was noticed within 15-60 s and 30-60 s in endometrial stromal cells of cyclic and pregnant pigs, respectively. In the presence of P4 (10(-5) M) basal and OT-stimulated [Ca2+]i concentrations decreased in stromal cells during luteolysis and pregnancy. In stromal cells P4 delayed mobilisation of [Ca2+]i in response to OT by 15 s during luteolysis and had no effect during pregnancy. In cyclic and pregnant epithelial cells OT stimulated mobilisation of [Ca2+]i in 45 s and 60 s, respectively. Oxytocin increased (P < 0.05) PGF2alpha secretion during luteolysis and pregnancy and PGE2 during luteolysis from endometrial slices. Progesterone did not inhibit this stimulatory effect. During luteolysis OT increased (P < 0.05) PGF2alpha in epithelial and stromal cells and PGE2 secretion in epithelial cells. In the presence of P4 this effect of OT was reduced only in stromal cyclic cells (6 h culture). The presence of P4 decreased the effect of OT on [Ca2+]i mobilisation only in stromal cells. We found that, in most conditions, P4 did not inhibit the OT-stimulated secretion of PG in the porcine endometrium.     

Effects of prostaglandin F(2alpha) and nitric oxide on the secretory function of bovine luteal cells

The objective of the present study was to investigate the influence of prostaglandin F(2alpha) (PGF (2alpha)) and nitric oxide (NO) on production of steroids and PGs by culturing bovine luteal cells obtained from ovaries on days 8-12 of the estrous cycle with a nitric oxide (NO) donor (Spermine NONOate), and a NO synthase inhibitor (N(G)-nitro-L-arginine methyl ester dihydrochloride: L-NAME). When the cells were exposed for 24 h to PGF(2alpha) (10(-7)-10(-5) M), production of progesterone (P(4)) increased significantly at all doses used (P<0.05). Moreover, PGF(2alpha) stimulated PGF(2alpha) production (P<0.01), depressed testosterone (T) production (P<0.05), but did not affect synthesis of prostaglandin E(2) (PGE(2)). Spermine NONOate decreased P(4) production to 66%, 47% and 34% of the control concentration after treatment with 10(-5) M, 10(-4) M and 10(-3) M, respectively, but did not affect T production, and increased PGF(2alpha) synthesis (P<0.05) and PGE(2) (P<0.01) at all doses used. L-NAME increased production of P(4) (P<0.01) but did not affect (P>0.05) secretion of T, PGF(2alpha) and PGE(2). Estradiol-17beta (E(2)) was detectable on the level of sensitivity of assay and was not significantly altered by any treatments. The overall results suggest that PGF(2alpha) and NO produced locally in bovine CL play roles in the regulation of the secretory function of the bovine CL as auto/paracrine factors.     

Correlations between presence of spontaneous lesions of the pituitary (adenohypophysis) and plasma prolactin concentration in aged Wistar rats.

The predictive value of elevated plasma prolactin concentrations for the presence of spontaneous pituitary lesions was studied in 40 male and 38 female Wistar (Cpb:WU) rats, all 30 months old. The pituitaries were examined light microscopically and stained for prolactin using immunohistochemical methods. Plasma prolactin concentrations were measured by radioimmunoassay. Pituitary lesions were classified on the basis of their morphology in hematoxylin and eosin-stained sections as foci of hypertrophic or hyperplastic cells and hemorrhagic, pleomorphic, or spongiocytic adenomas; no carcinomas were found. There were significantly (P = 0.001) more female than male rats with pituitary adenomas (58% females, 33% males) or without any pituitary lesions (21% females, 5% males); however, there were less female (21%) than male rats (63%) with foci of hyperplastic and/or hypertrophic cells but no adenomas in the pituitary (P = 0.001). Elevation of plasma prolactin concentration above the upper 99th percentile value in age-matched rats without lesions was predictive, but not conclusively, of the presence of pituitary hemorrhagic adenomas in both sexes. It was, however, not predictive of the presence of foci of hypertrophic or hyperplastic cells. Elevation of plasma prolactin concentration above 10 ng/ml in male and 60 ng/ml in female rats was conclusive for the presence of hemorrhagic adenomas. Using multivariate analysis, significant positive correlations (P less than 0.01) were found between plasma prolactin concentration and presence and size of hemorrhagic adenomas and their prolactin staining intensity (correlation coefficients between 0.392 and 0.652). Foci of hyperplastic cells stained positively for prolactin, whereas hypertrophic cell foci and pleomorphic and spongiocytic adenomas did not stain for prolactin. There were no correlations (coefficients of less than +/- 0.189) between plasma prolactin concentration and the presence of hypertrophic or hyperplastic cell foci and pleomorphic or spongiocytic adenomas in the pituitary. The morphologic criteria developed to distinguish spontaneous hypertrophic, hyperplastic, and neoplastic lesions of the rat pituitary corresponded well with their prolactin immunoreactivity and/or ability to elevate plasma prolactin concentration. These criteria constitute a biologically meaningful classification system for these rat pituitary lesions.     

Endocrine,metabolic and clinical effects of intravenous endotoxin injection after pre-treatment with meloxicam in heifers

Meloxicam (M), a non-steroid anti-inflammatory drug for use in animals, reduces prostaglandin (PG) synthesis by inhibiting cyclooxygenases-1 and -2. The aim of this study was to evaluate M's capability to prevent the inflammatory response elicited by endotoxin (ET). Furthermore, we wanted to evaluate a possible effect of M on delta13-reductase and 15-hydroxy prostanoate dehydrogenase, enzymes responsible for the initial metabolism of PGF2alpha. Four heifers acting as their own controls were used in the study. The heifers received an i.v. injection of either saline (S) or M (0.5 mg/kg) at 1.5 h before an i.v. injection of ET (50 ng/kg b.w. i.v.). The trial lasted 57 h after ET injection and blood samples were withdrawn for analyses of 15-ketodihydro-PGF2alpha (PG metabolite), cortisol, white blood cells (WBC), Fe, Zn and Ca. Clinical examinations were performed throughout the trial. In the S + ET trial, ET injection elicited a rapid increase of the PG metabolite, a prolonged cortisol release and reduced levels of WBC, Fe, Zn and Ca. General appearance and body temperature were affected. In the M + ET trial the PG release was totally abolished, the cortisol release was reduced and the clinical effect was milder, also effects on Fe, Zn and Ca were milder in the M + ET trial, but M did not prevent the pyrogenic effect of ET. In the next two trials, we injected PGF2alpha (500 ng/kg i.v.) with and without M pre-treatment. After PGF2alpha injection, plasma samples were collected for measurement of the PG metabolite. M had no effect on PGF2alpha metabolism. In conclusion, M effectively suppresses several of the inflammatory reactions seen after ET injections and has no major influence on the PGF2alpha metabolism.     

Endometrial Oxytocin Receptor Concentration and Activity in Prepubertal Ewe Lambs

We have measured endometrial oxytocin receptor concentrations during prepuberty in ewe lambs, and have investigated the effect of progesterone on the activity of these receptors. In the first study, oxytocin receptor concentrations were undetectable in 2-week prenatal lambs but had increased immediately following birth and were then maintained throughout prepubertal life. Despite the presence of oxytocin receptors animals showed no prostaglandin F(2alpha) (PGF(2alpha)) release in response to exogenous oxytocin challenge at either 3 or 5 months of age. In a second study in 4-month-old ewe lambs treatment with exogenous progesterone resulted in the appearance of PGF(2alpha) release in response to oxytocin after 10 days of treatment. Thus, during the prepubertal life, ewe lambs possess the prerequisites of a luteolytic mechanism in that they have a dormant population of oxytocin receptors in which progesterone can induce oxytocin-stimulated PGF(2alpha) release.     

Regulation of mitogen- and TCGF-induced lymphocyte blastogenesis by prostaglandins and supernatant from equine embryos and endometrium

Immunosuppressive substances which interfere with lymphocyte blastogenesis are released in vitro by embryos and endometrium from mares in early pregnancy. Immunosuppression was not evident when tissues were cultured in the presence of indomethacin (a prostaglandin-synthesis inhibitor). Various prostaglandins (PGs) were added to equine lymphocytes and lymphocyte proliferation was measured after the addition of concanavalin A (Con A) or phytohaemagglutinin A (PHA). PGE2 and PGF2 alpha inhibited Con A-induced blastogenesis down to final concentrations of 1.8 x 10(-9) M and 1.3 x 10(-6) M, respectively. Other PGs tested (6-keto-PGF1 alpha and 13,14-dihydro-15-keto-PGF2 alpha) did not affect Con A-induced blastogenesis. PHA-induced blastogenesis was inhibited by concentrations down to 1.8 x 10(-9) M PGE2, 3.3 x 10(-7) M PGF2 alpha and 2.8 x 10(-4) M 6-keto-PGF1 alpha. At all concentrations, 13,14-dihydro-15-keto-PGF2 alpha only slightly reduced PHA-induced blastogenesis. Therefore, PGE2 was the only prostaglandin tested which, at physiological concentrations, significantly inhibited incorporation of [3H] thymidine. The mechanism of PGE2-mediated suppression was studied by adding PGE2 and T cell growth factors (TCGF) to TCGF-responsive lymphocytes. PGE2 reduced the TCGF-mediated blastogenic response in a dose-dependent manner. Furthermore, culture supernatant from embryos and endometrium from 14-day pregnant mares inhibited lymphocyte blastogenesis induced by TCGF. These results show that PGE2 interferes with lymphocyte blastogenesis by TCGF-dependent mechanisms. It is suggested that the PGE2 present in the uterus of the early pregnant mare may be one of the factors involved in immunosuppression at the time of maternal recognition of pregnancy.     

Effect of prostaglandin F2 alpha on hormone concentrations in dairy cows after parturition

This study was designed to evaluate the effects of exogenous prostaglandin F2 alpha (PGF2 alpha) on hormone secretion in cows without a corpus luteum. Blood samples were taken from 10 Friesian dairy cows at frequent intervals from a jugular vein and the caudal vena cava starting between nine and 20 days after parturition. PGF2 alpha (25 mg dinoprost) was injected intramuscularly into five cows after the first eight hours of sampling. Plasma concentrations of 13,14-dihydro 15-keto PGF2 alpha (PGFM) increased rapidly but had returned to baseline by 14 hours after injection. There was no significant effect of the treatment on the time taken by the cows to resume ovarian cycles, and it had no consistent effect on plasma luteinising hormone (LH) patterns; however the amplitude of pulses of LH was temporarily suppressed in two cows and the frequency of pulses of LH was immediately increased in one cow. Treatment with PGF2 alpha had no significant effect on the concentration of oestradiol in blood from the vena cava. It is concluded that any enhancement of the reproductive performance of cows treated with PGF2 alpha after parturition is not due to a direct effect on pituitary-ovarian function.     

Effects on plasma endotoxin and eicosanoid concentrations and serum cytokine activities in horses competing in a 48-, 83-, or 159-km endurance ride under similar terrain and weather conditions

OBJECTIVE: To determine plasma endotoxin concentration in horses competing in a 48-, 83-, or 159-km endurance race and its importance with regard to physical, hematologic, or serum and plasma biochemical variables. ANIMAL: 3 horses. PROCEDURE: Weight and rectal temperature measurements and blood samples were obtained before, during, and after exercise. Blood samples were analyzed for plasma endotoxin concentration; serum antiendotoxin antibody titers; thromboxane B2 (TxB2) and 6-keto-prostaglandin F1alpha (PGF1alpha) concentrations; tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) activities; WBC, plasma protein, lactate, serum electrolyte, and calcium concentrations; PCV; and creatine kinase activity. RESULTS: Detection of plasma endotoxin increased during exercise for horses competing at all distances but occurred more frequently in the 48- and 83-km groups. Plasma lactate concentration was significantly greater when endotoxin was concurrently detected. Endotoxin in plasma was not significantly associated with success of race completion. Plasma TxB2 and PGF1alpha concentrations and serum IL-6 activity significantly increased with exercise. Horses that had an excellent fitness level (as perceived by their owners) had greater decreases in serum antiendotoxin antibody titers during exercise than did horses perceived as less fit. In horses with better finish times, TxB2 and PGF1alpha concentrations were significantly greater and TNFalpha activity was significantly less than that of slower horses. CONCLUSIONS AND CLINICAL RELEVANCE: Endotoxemia developed during endurance racing, but was significantly correlated with increased plasma lactate concentration and not with other variables indicative of endotoxemia. Plasma TxB2 and PGF1alpha concentrations and serum TNFalpha activity may be associated with performance success.     

Prostaglandin and thromboxane concentrations in plasma and lung lavage fluids during sequential infection of vaccinated and nonvaccinated calves with bovine respiratory syncytial virus

The potential action of immunologic reactions and mediators released during the course of bovine respiratory syncytial virus infection in pathogenesis of the ensuing disease process was examined in an experimental infection study. Prostaglandin (PG) E2, PGF2 alpha 6-keto-PGF1 alpha, and thromboxane B2 (TxB2) concentrations were quantitated in plasma and lung lavage fluid by radioimmunoassay at 3- to 4-day intervals during a primary and secondary virus infection of vaccinated, nonvaccinated, and control (mock-infected) calves. A significant increase in the plasma PGE2 concentration for the nonvaccinated calves was noticed on day 3 after primary infection and on day 7 after secondary infection. The PGF2 alpha plasma concentrations increased significantly for the nonvaccinated groups on day 10 after primary infection. Plasma 6-keto-PGF1 alpha concentrations increased for nonvaccinated and vaccinated calves 3 days after the secondary infection. Plasma TxB2 concentrations during the primary exposure did not vary significantly. However, 14 days after the secondary exposure, both experimental groups had concentrations significantly greater than did the control group. Lung lavage fluid concentrations of TxB2 had peaks of activity 7 days after primary and secondary viral infections for the nonvaccinated group. Increases in plasma PG concentrations corresponded variably with disease expression, whereas plasma TxB2 concentrations did not have any correlation with disease expression. However, there was a significant correlation between TxB2 concentration in lung lavage fluid of the nonvaccinated group with disease expression 7 days after primary and secondary virus infection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of domperidone and thyrotropin-releasing hormone on secretion of luteinizing hormone and prolactin during the luteal phase and following induction of luteal regression in sheep

Effects of domperidone, a peripheral dopamine receptor antagonist, on secretion of LH and prolactin were studied during the luteal phase and following administration of PGF2 alpha. Since hyperprolactinemia has been reported to inhibit secretion of LH in ewes, effects of thyrotropin-releasing hormone (TRH) also were examined. Ewes 8-10 days post-estrus were assigned to be treated with: 1) vehicle (n = 5); 2) 0.3 mg domperidone (n = 6); 3) 1.0 mg domperidone (n = 6); 4) 3 micrograms TRH (n = 6); or 5) 10 micrograms TRH (n = 6) every 4 hours for 60 hr. Luteal regression was induced with PGF2 alpha at 12 hr after initiation of treatments. During the luteal phase, pulses of LH were more frequent (P less than .05) and the amplitudes of these were higher (P less than .05) in ewes treated with domperidone or TRH than in control ewes. These changes in LH occurred even though each treatment elevated markedly concentrations of prolactin in plasma. After induction of luteal regression, mean of LH and frequency of LH discharges were similar in all groups. However, in ewes treated with the 1.0 mg/4 hr dose of domperidone the pulse amplitude was greater than in the other groups (2.3 vs 1.1 ng/ml). Dose-response relationships and the magnitude of the prolactin release following domperidone or TRH varied with time. Treatments did not affect the timing of the LH surge or the increase in progesterone associated with the subsequent cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of Tumour Necrosis Factor α in Stimulation of Prostaglandins F2α and E2 Release by Cultured Porcine Endometrial Cells

The present studies were undertaken to examine the effect of tumour necrosis factor (TNF) alpha on prostaglandins (PGs) F(2alpha) and E(2) release by cultured porcine endometrial cells harvested on days 13-16 after oestrus in comparison to stimulation with oxytocin (OT) and luteinizing hormone (LH). A time-dependent effect of TNFalpha (10 ng/ml) on PGF(2alpha) release was observed in stromal and luminal epithelial cells. Moreover, TNFalpha increased PGF(2alpha) secretion from both endometrial cell types with effective concentrations of 1 (p < 0.05), 10 and 50 ng/ml (p < 0.01). The effect of TNFalpha (10 ng/ml) on endometrial PGF(2alpha) and PGE(2) release was compared with OT (100 nmol/l) and LH (100 ng/ml). All factors affected PGF(2alpha) secretion from stromal cells, however, the stimulation tended to be more potent after OT and LH (p < 0.01) than after TNFalpha (p < 0.05) treatment. In epithelial cells, only TNFalpha was able to stimulate PGF(2alpha) release (p < 0.001). PGE(2) secretion from stromal cells increased after incubation with TNFalpha and OT (p < 0.05). Only LH stimulated PGE(2) release from epithelium (p < 0.001), and its action was very effective when compared with TNFalpha or OT (p < 0.01). Summarizing, TNFalpha induces both PGs secretion from cultured porcine endometrium, but preferentially stimulates PGF(2alpha) release from luminal epithelial cells. Therefore, similarly to OT and LH, TNFalpha may be considered as a potential modulator of endometrial PGF(2alpha) production during luteolysis in the pig.     

A cooperative action of endothelin-1 with prostaglandin F(2alpha) on luteal function in the cow

Prostaglandin F(2alpha) (PGF(2alpha)) is the primary luteolysin in the cow, and luteal endothelin-1 (ET-1) interacts with PGF(2alpha) during the process of luteolysis. In contrast, a developing corpus luteum (CL) is refractory to exogenous administration of PGF(2alpha). Thus, the present study was aimed to investigate the functional relationship between ET-1 and PGF(2alpha) in the mid-CL (PGF(2alpha)-sensitive) and early-CL (PGF(2alpha)-refractory). In the mid-CL model, cows (n = 6/treatment) were assigned to receive one of five types of treatments on day 10 of the estrous cycle: (1) an injection of saline; control, (2) a 500 microg of PGF(2alpha) analogue (sufficient dose to induce luteolytis); full-PG, (3) an intraluteal injection of 0.25 mg ET-1; ET-1, (4) a 125 micro g of PGF(2alpha) (insufficient dose to induce luteolytis); 1/4PG or (5) an intraluteal injection of 0.25 mg ET-1 after administration of a insufficient dose of PGF(2alpha) analogue; 1/4PG/ET. In the early-CL model, cows were assigned to receive one of two types of treatments on day 5 of the estrous cycle: (1) a sufficient dose of PGF(2alpha) analogue; PG (n = 5) or (2) an intraluteal injection ET-1 after a sufficient dose of PGF(2alpha); PG/ET (n = 7). In the mid-CL model, 1/4PG/ET resulted in a rapid reduction of progesterone (P) concentrations similar to that in full-PG from the next day. However, the levels of P in 1/4PG/ET (1.5-2.5 ng/ml) kept significantly higher than that in full-PG (< 0.5 ng/ml). ET-1 or 1/4PG did not decrease plasma P concentrations (4-6 ng/ml). The plasma ET-1 levels increased with the full-PG administration. In the early-CL model, both treatments had no effect on plasma P increase and ET-1 levels. The overall results indicate that the intraluteal ET-1 injection after administration of insufficient dose of PGF(2alpha) induces the depression of P secretion in vivo during the mid luteal phase in the cow, supporting the concept that ET-1 is one of a local mediator of functional luteolysis in the cow. The result further indicates that the early-CL is not only PG-refractory but also ET-1-refractory.     

Effects of the perfusion of beta-, beta2-, or beta3-adrenergic agonists or epinephrine on in situ adipose tissue lipolysis measured by microdialysis in underfed ewes

The effects of isoproterenol (ISO, a non-selective beta-agonist), terbutaline (TER, a selective beta2-agonist), CL316243 (CL, a selective beta3-agonist), and epinephrine (EPI, beta- and alpha2-agonist) on in situ lipolytic response of s.c. adipose tissue were investigated in vivo, using a microdialysis method to measure glycerol release, in 12 adult nonlactating and ovariectomized, underfed Lacaune ewes. All the adrenergic compounds were perfused for 120 min at 10(-6), 10(-5), and 10(-4) M. They had no lipolytic effect at 10(-6) M. Isoproterenol and EPI at 10(-5) and 10(-4) M enhanced, in the same way, maximal response and area under the concentration curve (AUC) of dialysate glycerol, thus suggesting that involvement of alpha2-adrenoceptors in the control of in situ lipolysis is of minor importance in underfed ewes. Terbutaline had only a slight lipolytic effect at 10(-5) M. This low effect could be due to a lower affinity of TER than of ISO for the beta2-adrenoceptors. The beta3-agonist, CL, had no lipolytic effect whatever the concentration perfused. Further studies are needed to prove the putative presence of beta3-adrenoceptors and their possible role in the ovine adipose tissue.     

Maintenance of the corpus luteum of early pregnancy in the ewe. III. Differences between pregnant and nonpregnant ewes in luteal responsiveness to prostaglandin F2 alpha

The effects of pregnancy and number of corpora lutea on luteal regression induced with prostaglandin F2 alpha (PGF2 alpha) were examined in 93 ewes. Bred and nonpregnant ewes were assigned randomly to receive a single im injection of PGF2 alpha: 0, 2, 4, 6, 8 or 10 mg/58 kg body weight. Injections were given on d 13 postestrus. The concentration of progesterone in serum 24 h after PGF2 alpha injection was affected by dose (P less than .001). The effect of pregnancy and the interaction of pregnancy with number of corpora lutea on levels of progesterone in serum were significant (P less than .05); therefore, data were partitioned according to pregnancy status and analyzed separately. There was an effect of number of corpora lutea on serum concentration of progesterone in pregnant (P less than .01) but not nonpregnant ewes (P greater than .10). Similar relationships among groups were observed for the concentration of progesterone in luteal tissue. In nonpregnant ewes the minimum dose of PGF2 alpha to produce a significant suppression of progesterone in serum (P less than .05) was 4 mg/58 kg body weight. In pregnant ewes with one or two corpora lutea, the minimum effective doses were 6 and 10 mg/58 kg body weight, respectively. The concentration of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum was related to the dose of PGF2 alpha injected. There were no differences in the concentration of PGFM in serum between pregnant and nonpregnant ewes either before or after injection. Corpora lutea of early pregnancy appear to be resistant to the luteolytic effect of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanism of action of noradrenaline on secretion of progesterone and oxytocin by the bovine corpus luteum in vitro

The present studies were conducted: (1) to determine which beta-adrenoceptor subtypes are involved in progesterone and oxytocin (OT) secretion, (2) to examine whether noradrenaline (NA) acts directly on the cytochrome P-450scc and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), and (3) to study the effect of prostaglandin F2 alpha (PGF2 alpha) on NA-stimulated steroidogenesis in luteal cells. The effect of NA on progesterone secretion from luteal slices of heifers on days 8-12 of the oestrous cycle was blocked by both atenolol (beta 1-antagonist) and ICI 118.551 hydrochloride (beta 2-antagonist). OT secretion was blocked only after treatment with ICI 118.551 hydrochloride (P < 0.05). Dobutamine (10(-4)-10(-6) M), a selective beta 1 agonist and salbutamol (10(-4)-10(-6) M), a selective beta 2 agonist, both increased progesterone production (P < 0.01) with an efficiency comparable to that produced by NA (P < 0.01). The increase of OT content in luteal slices was observed only after treatment with salbutamol at the dose of 10(-5) M (P < 0.01). Dobutamine had no effect on OT production at any dose. A stimulatory effect of NA on cytochrome P-450scc activity (P < 0.05) was demonstrated using 25-hydroxycholesterol as substrate. 3 beta-HSD activity also increased following NA (P < 0.01) or pregnenolone (P < 0.05) and in tissue treated with pregnenolone together with NA (P < 0.01). PGF decreased progesterone synthesis (P < 0.05) and 3 beta-HSD activity (P < 0.01) in tissue treated with NA. We conclude that NA stimulates progesterone secretion by luteal beta 1- and beta 2-adrenoceptors, while OT secretion is probably mediated only via the beta 2-receptor. NA also increases cytochrome P-450scc and 3 beta-HSD activity. PGF inhibits the luteotropic effect of NA on the luteal tissue.     

Effect of vasoactive intestinal peptide on the release of growth hormone in perifused pituitary and hypothalamus of the goat

The effect of vasoactive intestinal peptide (VIP) on the release of growth hormone (GH) from the adenohypophysis of the goat was studied in vitro using the perifusion system. Two perifusion systems were employed to differentiate potential direct effects of VIP on the pituitary from indirect effects mediated through the hypothalamus. The first perifusion system used single chambers housing only pituitary fragments. The second system used two chambers in tandem, one containing hypothalamus and the second the pituitary fragments, the flow passing through the hypothalamic chamber first. VIP (10(-6), 10(-7), 10(-8)M) stimulated significant GH release in both perifusion systems (P less than 0.05, P less than 0.01) in a concentration related fashion. The quantity of GH release induced by the 10(-9)M and 10(-10)M VIP groups were not significant. Further, the GH released from the system that perifused the pituitary alone (10(-8)M VIP) was significantly higher than that containing both the hypothalamus and the pituitary fragments (P less than 0.05). The relative lower GH secretory response to the same dose of VIP applied to the hypothalamus-pituitary suggests that the perifused caprine hypothalamus may release an inhibitory factor, such as somatostatin in vitro. These results suggest that VIP stimulates GH release by acting directly on the adenohypophysis of the goat.     

The Possible Involvement of Salsolinol and Hypothalamic Prolactin in the Central Regulatory Processes in Ewes During Lactation

Salsolinol, a dopamine‐related compound and prolactin‐producing cells were found in the ovine hypothalamus. This study was designed to test the hypothesis that salsolinol, acting from the CNS level, is able to stimulate pituitary prolactin release as well as prolactin mRNA expression in the anterior pituitary cells (AP) and in the mediobasal hypothalamus (MBH) in lactating ewes. The intracerebroventricular infusions of salsolinol in two doses, total of 50 ng or 5 μg, were performed in a series of five 10‐min infusions at 20‐min intervals. All infusions were made from 12:30 to 15:00 and the pre‐infusion period was from 10:00 to 12.30 h. The prolactin concentration in plasma samples, collected every 10 min, was determined by radioimmunoassay; prolactin mRNA expression in AP and MBH tissues was determined by real‐time PCR. The obtained results showed that salsolinol infused at the higher dose significantly (p < 0.001) increased plasma prolactin concentration in lactating ewes, when compared with the concentration noted before the infusion and with that in lactating controls. In lactating ewes, the relative levels of prolactin mRNA expression in the AP and MBH were up to twofold and fivefold higher respectively than in non‐lactating ewes (p < 0.05). In our experimental design, salsolinol did not significantly affect the ongoing process of prolactin gene expression in these tissues. We conclude that in ewes, salsolinol may be involved, at least, in the process of stimulation of prolactin release during lactation and that hypothalamic prolactin plays an important role in the central mechanisms of adaptation to lactation.