Regulation of adrenocorticotropin secretion from cultured canine anterior pituitary cells.

Pituitary cells, collected from five healthy dogs, were cultured and treated with various doses of ovine corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), oxytocin (OT), or angiotensin II (AII) to determine which of these hypothalamic peptides affected adrenocorticotropin (ACTH) secretion. Of the 4 peptides, only CRH significantly increased ACTH secretion from cultured canine anterior pituitary cells. The lowest dose of CRH tested, 0.01 nM, significantly stimulated ACTH release. Co-addition of AVP, OT, or AII with CRH did not increase ACTH secretion beyond that caused by addition of CRH alone. Similarly, neither co-addition of AVP with OT, AVP with AII, or OT with AII significantly stimulated ACTH secretion. These results support a role for CRH in the physiologic regulation of ACTH secretion from the canine anterior pituitary, but do not support regulatory roles for AVP, OT, or AII.     

Effect of mitotane on pituitary corticotrophs in clinically normal dogs

OBJECTIVE: To evaluate the effects of mitotane administration on the function and morphology of pituitary corticotrophs in clinically normal dogs. ANIMALS: 12 clinically normal adult Beagles. PROCEDURES: Dogs were randomly assigned to the control group or the mitotane treatment group. In mitotane treatment group dogs, mitotane was administered for 1 month. In both groups, ACTH stimulation testing and corticotrophin-releasing hormone (CRH) stimulation testing were performed. Magnetic resonance imaging (MRI) of the pituitary gland and brain was performed in mitotane treatment group dogs before and after administration of mitotane. After CRH stimulation testing and MRI, dogs were euthanatized and the pituitary gland and adrenal glands were excised for gross and histologic examination. RESULTS: ACTH concentrations in mitotane treatment group dogs were significantly higher than in the control group dogs following CRH stimulation. Magnetic resonance imaging revealed that pituitary glands were significantly larger in treatment group dogs after administration of mitotane, compared with before administration. On gross and histologic examinations, the adrenal cortex was markedly atrophied. Immunohistochemistry revealed hypertrophy of corticotrophs in pituitary glands of mitotane treatment group dogs. CONCLUSIONS AND CLINICAL RELEVANCE: These findings indicate that inhibition of the adrenal cortex by continuous administration of mitotane leads to functional amplification and morphologic enhancement of corticotrophs in clinically normal dogs. In instances of corticotroph adenoma, hypertrophy of individual corticotrophs induced by mitotane may greatly facilitate enlargement of the pituitary gland and increases in ACTH secretion.     

Integration Between Different Hypothalamic Nuclei Involved in Stress and GnRH Secretion in the Ewe

This study investigated possible integrated links in the neuroanatomical pathways through which the activity of neurones in the paraventricular nucleus and arcuate nucleus may modulate suppression of gonadotrophin‐releasing hormone (GnRH) secretion during stressful situations. Double‐label immunofluorescence and laser scanning confocal microscopy were used to examine the hypothalamic sections from the follicular phase ewes. Noradrenergic terminals were in close contact with 65.7 ± 6.1% corticotrophin‐releasing hormone (CRH) and 84.6 ± 3.2% arginine vasopressin (AVP) cell bodies in the paraventricular nucleus but not with β‐endorphin cell bodies in the arcuate nucleus. Furthermore, γ‐amino butyric acid (GABA) terminals were close to 80.9 ± 3.5% CRH but no AVP cell bodies in the paraventricular nucleus, as well as 60.8 ± 4.1%β‐endorphin cell bodies in the arcuate nucleus. Although CRH, AVP and β‐endorphin cell terminals were identified in the medial pre‐optic area, no direct contacts with GnRH cell bodies were observed. Within the median eminence, abundant CRH but not AVP terminals were close to GnRH cell terminals in the external zone; whereas, β‐endorphin cells and terminals were in the internal zone. In conclusion, neuroanatomical evidence is provided for the ewe supporting the hypothesis that brainstem noradrenergic and hypothalamic GABA neurones are important in modulating the activity of CRH and AVP neurones in the paraventricular nucleus, as well as β‐endorphin neurones in the arcuate nucleus. These paraventricular and arcuate neurones may also involve interneurones to influence GnRH cell bodies in medial pre‐optic area, whereas the median eminence may provide a major site for direct modulation of GnRH release by CRH terminals.     

Hormonal interactions within the hypothalamus and pituitary with respect to stress and reproduction in sheep

Endocrine systems may be used as indicators of stress in two ways. The primary role of a hormone may be as part of the homeostatic response to a stimulus (e.g., adrenaline, corticosteroids). The amplitude of hormone response may correlate with the severity of the stimulus and any change indicate that the body is responding. Alternatively, a hormone may have a key role in normal body function (e.g., reproduction) and stress may deleteriously alter the hormone signal prevent normal function. This demonstrates that the stimulus was sufficiently severe that homeostatic mechanisms were unable to maintain normal function. Stress may effect reproduction by reducing both LH pulse amplitude and frequency. The LH surge may also be delayed. Several mechanisms may account for these effects both at the hypothalamus and pituitary. Corticosteroids have a broad, yet fundamental, role in homeostasis and have been used as primary indicators of stress for many years. Excess corticosteroid can be detrimental so the concentration is controlled via the hypothalamus-pituitary-adrenal (HPA) axis by multi-level feedback mechanisms. Under field and experimental conditions, after an initial large response prolonged stimulation leads to a gradually reducing plasma corticosteroid concentrations. This has been interpreted as a reduction in perceived stimulus severity or habituation to the stimulus and the animal deemed "less stressed" and its welfare "better." However, this reduction may be due to the intrinsic control mechanisms designed to prevent prolonged increases in corticosteroid concentrations. The stress signal at higher brain levels may still be present and the animal may still be experiencing the stimulus as aversive. Thus, the welfare interpretation of a corticosteroid concentration may differ during the time course of a stress response. A greater understanding of the mechanisms controlling corticosteroid secretion at each level of the HPA is required to determine what is the correct interpretation at any time point. To address these issues, we have used mathematical modelling to produce representations of possible control mechanisms at each level of the HPA. The starting point was to measure AVP and CRH concentrations in hypophysial portal blood and ACTH and cortisol concentrations in jugular blood in conscious sheep during 2h road transport (a cognitive stimulus). Modelling identified the signal inputs that were most likely to explain the secretion rate of each hormone. Modelling suggested that the reduction in AVP and CRH secretion observed during transport was most likely due to a reduction in stimulus input, with a significant contribution from cortisol negative feedback only on AVP secretion. At the pituitary level, ACTH secretion was stimulated more by AVP than by CRH (ratio 2.3:1) and there was also a stimulatory effect related to cortisol concentration at the time of sampling. However, the responses to both stimuli were curtailed by cortisol negative feedback and an inhibitory effect of prior CRH concentration. These are complex effects, but the modelling does suggest that while "stress" inputs may reduce over time hormone negative feedback is a major factor reducing hormone responses. When interpreting hormone data for animal welfare purposes, it is important not to interpret a reduction in hormone concentration due to intrinsic hormone control mechanisms as a reduction due to a decrease in the stress stimulus.     

Studies on the functional relationship between thyroid, adrenal and gonadal hormones

In order to clarify the functional relationship between thyroid, adrenal and gonadal hormones, hypothyroidism was induced by administration of thiuoracil in adult male and female rats, and the effects of hypothyroidism on the adrenal and the gonadal axes were investigated in the present study. 1. The functional relationship between thyroid and adrenal hormones: Adrenal weights and corticosterone were lowered, whereas the secretion of ACTH, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) increased in hypothyroid rats compared to euthyroid rats. These results indicate that hypothyroidism causes adrenal dysfunction directly and results in hypersecretion of CRH and AVP from the hypothalamus. 2. The functional relationship between thyroid and gonadal hormones: The pituitary response to LHRH was lowered, whereas the testicular response to hCG was not changed in hypothyroid rats. Hypothyroidism suppressed copulatory behavior in male rats. These results suggest that hypothyroidism probably causes dysfunction in gonadal axis at the hypothalamic-pituitary level in male rats. In adult female rats, hypothyroidism inhibited the follicular development accompanied estradiol secretion, whereas plasma concentrations of progesterone and prolactin (PRL) increased in hypothyroid female rats. Hypothyroidism significantly increased the pituitary content of vasoactive intestinal peptide (VIP) though it did not affect dopamine synthesis. These results suggest that hypothyroidism increases pituitary content of VIP and this increased level of VIP likely affects PRL secretion in a paracrine or autocrine manner. In female rats, inhibition of gonadal function in hypothyroid rats mediated by hyperprolactinemia in addition to hypersecretion of endogenous CRH.     

Induced expression of c-fos in the diencephalon and pituitary gland of goats following transportation

To identify regions of the caprine diencephalone and pituitary gland related to transportation stress, the expression of c-fos protein was examined immunohistochemically as an indicator of neural activation. Ten castrated Shiba goats (Capra hircus), five transported and five controls, were used. Transported goats were trucked for 1 h and killed by transcardiac perfusion 1 h after the end of transportation. Control goats were housed in single pens killed in the same manner and at the same time as the transported goats. The diencephalon and the pituitary gland were removed after perfusion and used for immunostaining. Plasma cortisol concentrations during and after transportation also were investigated. During transportation, plasma cortisol concentrations increased (P < 0.05) compared with those in the controls. In the diencephalon, c-fos immunoreactive cells were detected in the subcallosa, the lateral septal area, the bed nucleus of stria terminalis (BNST), the preoptic hypothalamic area (POA), the suprachiasmatic nucleus (SCN), the supraoptic nucleus, the paraventricular hypothalamic nucleus parvocellular (PVNp), the paraventricular hypothalamic nucleus magnocellular (PVNm), the arcuate nucleus (ARC), the paraventricular thalamic nucleus, and the stria medullaris in both control and transported goats. The numbers of c-fos immunoreactive cells were increased (P < 0.05) by transportation in the PVNm, the PVNp, the BNST, the POA, the ARC, and the SCN (P < 0.10). In the anterior pituitary gland, the number of c-fos immunoreactive cells in transported goats was 4 to 30 times as much as in control goats; however, there were no differences in the intermediate and posterior lobes between control and transported goats. This study has identified regions in the caprine diencephalon and pituitary gland that show transport-induced increases in c-fos immunoreactive cells. In conclusion, the PVNm, the PVNp, the BNST, the POA, the SCN in the diencephalons, and the anterior lobe of pituitary gland may be involved in the stress responses of goats to transportation.     

Glucoprivation-induced Fos expression in the hypothalamus and medulla oblongata in female rats

Glucoprivation induced by 2-deoxy-D-glucose (2DG) suppresses pulsatile luteinizing hormone (LH) secretion in female rats. The suppression is enhanced in the presence of estrogen. In the present study, 2DG-induced Fos expression was examined in the solitary tract nucleus (NTS), hypothalamic paraventricular nucleus (PVN), raphe obscurus nucleus (ROb) and raphe pallidus nucleus (RPa), which have been previously suggested to be involved in glucoprivation-induced suppression of LH secretion in female rats. Ovariectomized (OVX) or estrogen-primed ovariectomized (OVX+E(2)) rats were injected intravenously with 2DG (400 mg/kg BW). The brain was removed 1 h after the injection. The number of Fos-like-immunoreactive (Fos-li) cells in the PVN and NTS was significantly increased in OVX+E(2) rats compared with control groups, but did not show a significant increase in the OVX group. Few Fos-li cells were observed in the ROb and RPa in all groups. All of the Fos-li cells in the PVN and NTS were neurons because they had immunoreactivities to microtubule-associated protein 2. Some Fos-li cells (8.3%) had tyrosine hydroxylase-like immunoreactivities in the NTS in 2DG-treated OVX+E(2) rats. These results suggest that neurons in the PVN and NTS are involved in the estrogen-dependent neural cascade mediating glucoprivic suppression of LH secretion in female rats.     

促肾上腺皮质激素释放激素结合蛋白功能与调控研究进展

促肾上腺皮质激素释放激素结合蛋白(CRH-BP)是37 ku的分泌糖蛋白,其结构与促肾上腺皮质激素释放激素(CRH)受体不同,但与CRH和尿皮素(UCN)具有很高的亲和力.CRH-BP具有重要的生物调控作用,对CRH诱导的脑垂体促肾上腺皮质激素(adrenocorticotropic hormone,ACTH)的释放具有抑制作用.应激和代谢因素能改变体内CRH-BP的表达与调控,CRH-BP在生产分娩、炎性疾病、阿尔海默症(Alzheiner′s disease)和其他机能障碍等过程中也具有广泛的作用,这说明CRH-BP在大脑和脑垂体中可能还有其他潜在功能,研究CRH-BP在中枢和外周的作用及机理,有利于阐明其在病因学方面的潜在地位,有助于治疗CRH失调引起的机能紊乱.     

Trilostane-induced inhibition of cortisol secretion results in reduced negative feedback at the hypothalamic–pituitary axis

Cushing's disease caused by pituitary corticotroph adenoma in dogs is usually treated by medical treatment, and the efficacy of this treatment has been reported. However, controversy remains as to whether reduced negative feedback through the inhibition of cortisol secretion, similar to Nelson's syndrome, may appear as an adverse effect. The purpose of this study was to investigate the effect of reduced negative feedback through the inhibition of cortisol secretion by daily trilostane administration on the pituitary–adrenal axis in clinically normal dogs. Dogs were administered 5 mg/kg trilostane twice a day every day for 8 weeks (n = 8) or 16 weeks (n = 3). After the initiation of trilostane administration, plasma adrenocorticotropic hormone (ACTH) concentrations were increased remarkably. As assessed by magnetic resonance imaging (MRI) during administration, the pituitary became enlarged. After trilostane administration, the cytoplasmic areas of the pituitary corticotrophs were increased and the ratio of pituitary corticotrophs to all cells in the anterior lobe was greater in the trilostane-treated dogs than that in untreated animals. In addition, histological examinations revealed bilateral adrenal cortical hyperplasia. Using real-time PCR quantification, the expression of proopiomelanocortin (POMC) mRNA in the pituitary and ACTH receptor (ACTH-R) mRNA in the adrenal gland was greater in the dogs treated with trilostane than in untreated dogs. These results indicate that reduced negative feedback induced hyperfunction of the pituitary corticotrophs and pituitary enlargement in healthy dogs. These changes suggest that the inhibition of cortisol secretion by trilostane may increase the risk for accelerating the growth of corticotroph adenomas in dogs with Cushing's disease.     

Hypothalamic control of the thyroidal axis in the chicken: over the boundaries of the classical hormonal axes

The pituitary gland, occupying a central position in the hypothalamo-pituitary thyroidal axis, produces thyrotropin (TSH), which is known to stimulate the thyroid gland to synthetize and release its products, thyroid hormones. TSH is produced by a specific cell population in the pituitary, the so-called thyrotropes. Their secretory activity is controlled by the hypothalamus, releasing both stimulatory and inhibitory factors that reach the pituitary through a portal system of blood vessels. Based on early experiments in mammals, thyrotropin-releasing hormone (TRH) is generally mentioned as the main stimulator of the thyrotropes. During the past few decades, it has become clear that the hypophysiotropic function of the hypothalamus is more complex, with different hormonal axes interacting with each other. In the chicken, it was found that not only TRH, but also corticotropin-releasing hormone (CRH), the main stimulator of corticotropin release, is a potent stimulator of TSH secretion. Somatostatin (SRIH), a hypothalamic factor known for its inhibitory effect on growth hormone secretion, was demonstrated to blunt the TSH response to TRH and CRH. In this review we summarize the latest studies concerning the "interaxial" hypothalamic control of TSH release in the chicken, with a special emphasis on the molecular components of these control mechanisms. It remains to be demonstrated if these findings could also be extrapolated to other species or classes of vertebrates.     

Organotypic slice culture of the hypothalamic paraventricular nucleus of rat

Organotypic slice cultures have been developed as an alternative to acute brain slices because the neuronal viability and synaptic connectivity in these cultures can be preserved well for a prolonged period of time. This study evaluated a stationary organotypic slice culture developed for the hypothalamic paraventricular nucleus (PVN) of rat. The results showed that the slice cultures maintain the typical shape of the nucleus, the immunocytochemical signals for oxytocin, vasopressin, and corticotropin-releasing hormone, and the electrophysiological properties of PVN neurons for up to 3 weeks in vitro. The PVN neurons in the culture expressed the green fluorescent protein gene that had been delivered by the adenoviral vectors. The results indicate that the cultured slices preserve the properties of the PVN neurons, and can be used in longterm studies on these neurons in vitro.     

Effect of spray-dried plasma and lipopolysaccharide exposure on weaned pigs: II. Effects on the hypothalamic-pituitary-adrenal axis of weaned pigs

A study was conducted with 20 weaned barrows (14 d, 4.98 +/- 0.21 kg) to determine the effect of feeding spray-dried plasma (SDP) after weaning on the pig's stress response to a lipopolysaccharide (LPS) challenge. After weaning, pigs were fed a diet containing 0 or 7% SDP for 7 d. On d 6 after weaning, all pigs were nonsurgically fitted with a jugular catheter. On d 7 after weaning, the pigs were given i.p. injections of either saline or LPS (150 microg/kg BW) followed by serial blood collection every 15 min for a 3-h period. Following the 3-h blood collection, all pigs were killed and tissue was collected for mRNA analysis. Pig weight on d 7 after weaning was not affected by dietary treatment (P > 0.21). Pigs fed the diet with SDP had lower (P < 0.05) levels of hypothalamic corticotropin-releasing hormone (CRH) mRNA, pituitary gland CRH receptor mRNA, and adrenal gland adrenocorticotropin-releasing hormone (ACTH) receptor mRNA. Dietary treatment did not affect pituitary gland proopiomelanocortin (POMC) mRNA. No effect of LPS treatment was observed in any of the mRNA levels examined. For both serum ACTH and cortisol, there was a significant diet x LPS treatment interaction (P < 0.01) such that both the ACTH and cortisol responses to the LPS challenge were greater in the pigs fed the diet with SDP than in the pigs fed the diet without SDP. For pigs given the saline injection, diet did not affect basal serum cortisol concentration; however, basal serum ACTH concentration was lower in those pigs fed the diet with SDP (P < 0.0001). A diet x LPS treatment interaction (P < 0.024) was observed for adrenal gland mRNA expression for steroidogenic acute regulatory (StAR) protein such that the LPS-induced increase in StAR mRNA was greater in the pigs fed SDP than in pigs fed the diet without SDP. These results demonstrate that pigs fed a diet with SDP have an increased activation of the pituitary-adrenal axis following an LPS challenge compared to pigs fed a diet without SDP.     

In vitro and in vivo temporal aspects of ACTH secretion: stimulatory actions of corticotropin-releasing hormone and vasopressin in cattle

The objective of the present study was to evaluate the temporal aspects associated with corticotropin-releasing hormone (CRH) and vasopressin (VP) stimulated bovine adrenocorticotropic hormone (ACTH) secretion in vitro and in vivo. For the in vitro studies, bovine anterior pituitary glands were enzymatically dispersed to establish primary cultures. On day 5 of culture, cells were challenged for 3 h with medium alone (Control) or various combinations and concentrations of bovine CRH (bCRH) and VP. Both CRH and VP each increased (P < 0.05) ACTH secretion. Maximal increases in ACTH secretion occurred in response to 0.1 microM CRH (5.5-fold) and 1 microM VP (3.7-fold), relative to Control cells. The in vivo portion of the study examined possible temporal differences in the activation of the pituitary-adrenal axis by CRH and VP. Jersey cows were randomly assigned to one of four groups (n = 8 cows/group): (i) Control (saline); (ii) bCRH (0.3 microg/kg BW); (iii) VP (1 microg/kg BW) and (iv) bCRH (0.3 microg/kg BW) + VP (1 microg/kg BW). Jugular blood samples were collected at 15-min intervals for 4 h pre- and for 6 h post-treatment; samples were also taken at 1, 5 and 10 min post-treatment. Plasma concentration of ACTH did not differ among treatment groups for the 4-h pre-treatment period. At 1 min post-treatment, bCRH + VP, VP and bCRH increased ACTH secretion by 22.4-, 9.6- and 2.2-fold, respectively, relative to Control (32.7 +/- 7.2 pg/ml). Maximal plasma concentration of ACTH occurred at 5, 10 and 15 min post-treatment for the VP (1017.7 +/- 219.9 pg/ml), bCRH + VP (1399.8 +/- 260.1 pg/ml) and bCRH (324.8 +/- 126.2 pg/ml) treatment groups respectively. Both the in vitro and in vivo data demonstrated that while VP acutely activates the bovine pituitary-adrenal axis, CRH-induced ACTH secretion is slower in onset but of longer duration. The present study also provides insight into the dynamics of ACTH and cortisol (CS) responsiveness to CRH and VP in cattle.     

The impact of maternal overnutrition and obesity on hypothalamic-pituitary-adrenal axis response of offspring to stress

We evaluated the effect of maternal obesity before and throughout gestation on offspring hypothalamic-pituitary-adrenal axis function. Multiparous Rambouillet by Columbia crossbred ewes were fed either 100% of National Research Council (NRC) recommendations (control, C) or 150% of NRC recommendations (obese, OB) from 60 d before mating until lambing. Ten lambs born to OB ewes (five males and five females), and eight lambs born to C ewes (three male and five female) were studied. From delivery to weaning lambs were maintained with their mothers, who were all fed 100% NRC recommendations. After weaning, all lambs were group housed and fed the same diet to meet NRC requirements. At 19 mo of age lambs were placed in individual pens and fed a pelletized diet to meet maintenance requirements. Jugular vein catheters were placed and 2 d later lambs received an intravenous (i.v.) adrenocorticotropic hormone (ACTH) challenge followed by an i.v. corticotropin-releasing hormone (CRH)/arginine vasopressin (AVP) challenge 1 d later. Thirty d later offspring were again catheterized and placed into metabolism crates for 2 d before receiving an isolation stress test. ACTH and cortisol responses to the isolation stress test and CRH/AVP challenge and cortisol responses to ACTH challenge were determined. Cortisol was quantified via radioimmunoassay and ACTH was quantified using an Immulite 1000; both were analyzed using repeated measures using the MIXED procedure of SAS. Offspring from OB ewes had elevated basal plasma ACTH and cortisol compared with C offspring before all three challenges (P < 0.05). Offspring from OB mothers tended (P = 0.06) to have a greater ACTH response after an i.v. CRH/AVP injection than offspring from C mothers (12,340 ± 1,430 vs 8,170 ± 1,570 area under the curve, respectively). Cortisol response to the CRH/AVP and ACTH challenges was not influenced by maternal nutrition (P = 0.46) and averaged 4.77 ± 0.2 μg/dL and 1.94 ± 0.01 μg/dL, respectively. The ACTH response following the isolation stress test was also similar (P = 0.82) for OB and C offspring (147 ± 20 pg/mL), and cortisol response during the isolation stress test was similar between C and OB offspring (P = 0.64, 5.25 ± 0.3 μg/dL). These findings suggest that maternal obesity before and during gestation does not affect stress responses by the offspring, but has an impact on hypothalamic-pituitary-adrenal sensitivity. The lack of differences in cortisol release under the influence of difference concentrations of ACTH during the CRH/AVP challenge could indicate adrenal dysfunction in OB offspring.     

Relationship between arginine vasopressin and high signal intensity in the pituitary posterior lobe on T1-weighted MR images in dogs

The posterior lobe of the pituitary gland (PL) normally shows characteristic high signal intensity (SI) on T1-weighted MR images (T1WI) in humans. The high SI is thought to represent storage of arginine vasopressin (AVP) in the PL. Normal dogs also show a high SI on T1WIs, but the origin is unclear. In the present study, we investigated whether the high SI in the PL on T1WIs in normal dogs is caused by AVP. We examined the SI in the PL on T1WIs, plasma AVP concentrations and plasma osmolality in normal dogs after excessive AVP secretion was induced by hypertonic saline overload. In addition, functional changes in the supraoptic nucleus and paraventricular nucleus of the hypothalamus under AVP secretion-stimulated conditions were examined immunohistologically. Under hypertonic saline overload, plasma osmolality and plasma AVP concentrations gradually increased, while the SI of the PL gradually decreased. This suggests that AVP secretion was stimulated by elevated osmolality. Moreover, there was a significant negative correlation between plasma AVP concentrations and the SI ratio of the PL. An immunohistochemical study of the hypothalamus nucleus revealed that AVP-immunopositive cells significantly increased in the hypertonic saline loaded dogs. We concluded that the high SI in the PL in T1WIs in normal dogs was caused by AVP stored at the site, and examination of the SI in the PL using MRI is useful for diagnosis of abnormal pituitary glands.     

Decreased ACTH secretion during prolonged transportation stress is associated with reduced pituitary responsiveness to tropic hormone stimulation in cattle

The present study examined the effect of transportation stress on hypothalamic–pituitary–adrenal axis responsiveness to tropic hormone stimulation and on abundance of corticotropin releasing factor (CRF) receptor R1 (CRFR1) and arginine vasopressin (AVP) receptor V3 (V3) mRNAs in the anterior pituitary (AP) of cattle. Holstein steers were transported for 10 h or used as non-transported controls (NTC). Blood samples were collected at start of transportation and every 1–2 h thereafter. To test AP responsiveness to tropic hormones, animals were challenged (i.v.) with CRF (0.5 μg/kg), AVP (1 μg/kg) or CRF plus AVP immediately after end of transportation and blood samples collected every 30 min for 3 h. The AP of animals transported for 0, 4 or 10 h were harvested for mRNA analyses. Plasma ACTH in transported animals increased within 1 h and remained elevated for 6 and 8 h versus NTC and 0 h values, respectively. Plasma concentrations of cortisol increased in response to transportation and remained elevated throughout the transport period. Injection of CRF or AVP to NTC animals increased plasma ACTH, but ACTH secretion in response to CRF or AVP was dramatically reduced in transported animals. ACTH secretion following co-injection of CRF and AVP tended to be less in transported animals, but was almost 100% greater than when secretagogues were administered separately. Despite decreased AP responsiveness to CRF and AVP, AP CRFR1 and V3 mRNAs were increased after 10 h transportation. Results indicate decreased AP responsiveness to CRF and AVP may regulate duration of ACTH secretion in response to transportation stress in cattle.     

Inhibition of stress-induced adrenocorticotropin and prolactin secretion mediating hypophysiotropic factors by antagonist of AMPA type glutamate receptor

Glutamate is the dominant excitatory neurotransmitter in a large number of physiological processes including neuroendocrine regulation. Some pharmacological studies have shown that different subtypes of glutamate receptor, such as the N-methyl-D-aspartic acid (NMDA) and alpha-amino-3-hydroxy-5-methy-4-isoxazolepropionic acid (AMPA) receptors, are involved in stress-induced adrenocorticotropin (ACTH) and prolactin secretion. However, the roles of the respective glutamate receptors and the mechanism of ACTH and prolactin secretion during stress via these receptors have not been investigated in detail. In the present study, we evaluated the role of AMPA-type glutamate receptor in ACTH and prolactin regulation under restraint stress in adult male rats. Male rats pretreated with a selective AMPA receptor antagonist, 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX; 50 microg), through a lateral ventricle cannula were stressed by immobilization. Administration of NBQX inhibited ACTH and prolactin secretion in response to restraint stress. However, NBQX had no significant effects on the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis, as measured by the accumulation of 3, 4-dihydroxyphenylalanine (DOPA). In addition, administration of NBQX suppressed stress-induced prolactin secretion in the male rats pretreated with alpha-MT, an inhibitor of dopamine synthesis, and infused with dopamine solution (2.5 microg/200 microl/10 min). These results indicated that the effects of NBQX on prolactin secretion might be mediated by non-dopamine mechanisms. The contents of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the median eminence (ME) of the male rats decreased during restraint stress; however, the fluctuations in CRH and AVP were eliminated by NBQX administration. These results suggest that stress-induced ACTH and prolactin release mediated by neurotransmission via AMPA receptors might be partly attributable to hypophysiotropic regulatory factors in the hypothalamus.     

ER免疫反应产物在幼龄公山羊下丘脑-垂体-性腺轴的表达

应用免疫组化SP法时雌激素受体(ER)免疫反应产物在幼龄公山羊下丘脑、垂体、性腺中的分布特点进行了研究。结果显示，下丘脑中ER免疫反应阳性神经元主要分布在视上核、室旁核、室周核等9个核团，在视前区、下丘脑外侧区等核团也有一定数量的阳性神经元；阳性细胞呈圆形、卵圆形、三角形不等，阳性物质大多位于细胞质和胞核，阳性纤维散布于各阳性核团中；在正中隆起和第三脑室室管膜可见大量小而密集排列的深染的阳性神经元。神经垂体中可见大小不等、排列较均匀且染色较深的纤维，腺垂体中腺细胞呈强阳性着色。睾丸曲细精管中的初级精母细胞和支持细胞以及睾丸间质细胞中的ER阳性产物均为微弱表达。由此表明，幼龄公山羊雌激素除作用于性腺外，还主要作用于中枢神经系统的广泛区域，推测其参与了脑中生殖、内分泌、认知等多种功能的调控。     

Adrenocorticotropic hormone and cortisol in calves after corticotropin-releasing hormone.

The aim for this study was to analyze responsiveness of the hypothalamo-pituitary-adrenocortical axis to exogenous bovine corticotropin-releasing hormone (bCRH) in calves. Two dose-response studies were carried out, using either bCRH alone (dose rates of 0, .01, .03, and .1 microg bCRH/kg live weight) or in combination with arginine-vasopressin (bCRH:AVP, 0:0, .1:.05, .5:.25, and 1:.5 microg kg live weight). The bCRH was administered i.v. to calves (n = 5 to 7 per dose) housed individually or in groups. Serial blood samples were obtained from before to 300 min after injection and analyzed for plasma ACTH and cortisol concentrations. The lowest bCRH dose that produced a response in all calves was .1 microg/kg. In the experiment using bCRH with AVP, increasing the bCRH dose from .1 to 1 microg/kg resulted in an increase in peak ACTH concentration (321 vs. 2,003 pg/mL) but did not significantly affect the peak cortisol concentration (37 vs. 40 ng/mL). The time to reach the peak cortisol concentration increased with the dose of bCRH with AVP (from 38 to 111 min). The ACTH and cortisol concentrations determined at any time between 20 and 90 min after bCRH injection were correlated to the integrated responses calculated as areas under the ACTH and the cortisol curves (r between .61 and .99, P<.05). In comparison with results from studies in humans, pigs, and sheep, our data showed that the pituitary of calves seems less sensitive to CRH than that of other mammals, despite a greater capacity to produce ACTH. Moreover, the calf's adrenals seem to have a lower capacity to produce cortisol than adrenals of other mammals. As in other species, it seems that AVP enhances the release of ACTH and cortisol. For CRH challenge to be used in calves, we suggest injecting at least .1 microg of bCRH/kg live weight either with or without AVP and taking several blood samples before injection and between 20 and 90 min after injection.