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)     

Characterization of ovine follicles destined to form subfunctional corpora lutea

A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "control" follicles, which would have produced normal corpora lutea. In 15 ewes, the second ovary was removed 63 to 84 h later to collect "treated" follicles before (n = 7) or after (n = 8) the second expected surge of LH. Five ewes (control) were allowed to ovulate from the remaining ovary at first estrus and another five (treated) at the second estrus (3 to 4 d later). Treated ewes had lower serum progesterone than control ewes during the ensuing cycle (P less than .05). Treated follicles contained less estradiol in the theca (4.4 +/- .6 vs 10.0 +/- 2.5 ng; P less than .05), less androstenedione (.1 +/- .1 vs 1.0 +/- .2 ng) and estradiol (.5 +/- .1 vs 2.9 +/- 2.2 ng) in the granulosa (P less than .05) and less progesterone in the follicular fluid (.8 +/- .4 vs 3.3 +/- .8 ng; P less than .05) than control follicles, when removed before the surge of LH. Follicles removed after the surge of LH did not differ. In conclusion, ovulatory follicles with low steroidogenic function became corpora lutea that secreted lower-than-normal quantities of progesterone.     

Age at puberty,total fat and conjugated linoleic acid content of carcass,and circulating metabolic hormones in beef heifers fed a diet high in linoleic acid beginning at four months of age

In the current study, we hypothesized that diets high in linoleic acid would increase conjugated linoleic acid (CLA) tissue content, reduce adiposity and leptin production, and result in an increase in the age at puberty in heifers. Heifers were weaned and blocked by body weight (heavy, n = 10, and light, n = 10) and allocated randomly within block to receive isocaloric and isonitrogenous diets with either added fat (HF, n = 10) or no added fat (C, n = 10) from 4 mo of age until post-pubertal slaughter. Whole sunflower seed (55% oil; 70% linoleic acid) was used as the fat source in HF diets and provided 5% added fat from the start of the study until heifers weighed 250 +/- 8 kg, at which time added fat was increased to 7% of dry matter until slaughter. Body weights were recorded weekly, and blood samples were collected weekly for total cholesterol and hormone analyses. Puberty was confirmed based on serum concentrations of progesterone and ultrasonographic confirmation of corpora lutea. Heifers were slaughtered at 325 +/- 10 d of age, and longissimus muscle between the 9th and 11th rib was collected and analyzed to estimate carcass composition. Subcutaneous and kidney, pelvic, and heart fat were collected at slaughter for fatty acid analyses. The HF heavy group tended (P < 0.10) to reach puberty later than all other groups, and one HF light heifer did not reach puberty during the study. Linoleic acid and cis-9, trans-11 CLA tissue contents were higher (P < 0.03) in HF heifers than controls, but neither total carcass fat nor percentage of dry matter differed by dietary group, although the percentage of protein tended (P < 0.10) to be lower in HF heifers. Mean serum concentrations of leptin did not differ due to diet; however, leptin increased (P < 0.01) linearly as puberty approached. Circulating concentrations of growth hormone and insulin-like growth factor I increased or remained relatively constant between wk 2 to 10 of feeding, and then declined (P < 0.01) until the onset of puberty. Serum IGF-I was lower (P < 0.01) in heifers receiving the HF diet. Mean serum concentrations of insulin and total cholesterol increased (P < 0.01) with time in both groups, but only total cholesterol was increased by the HF diet (P < 0.05). Results indicate that diets high in linoleic acid fed to growing beef heifers beginning early in life have little or no effect on total carcass fat, circulating leptin, or age at puberty despite measurable increases in CLA accumulation.     

Phytoplankton community structure and the drawdown of nutrients and CO2 in the southern ocean

Data from recent oceanographic cruises show that phytoplankton community structure in the Ross Sea is related to mixed layer depth. Diatoms dominate in highly stratified waters, whereas Phaeocystis antarctica assemblages dominate where waters are more deeply mixed. The drawdown of both carbon dioxide (CO2) and nitrate per mole of phosphate and the rate of new production by diatoms are much lower than that measured for P. antarctica. Consequently, the capacity of the biological community to draw down atmospheric CO2 and transport it to the deep ocean could diminish dramatically if predicted increases in upper ocean stratification due to climate warming should occur.     

Circulating Metabolic Hormones During the Peripubertal Period and Their Association with Testicular Development in Bulls

The objective of the present study was to characterize changes in serum metabolic hormones concentrations from 20 weeks before to 20 weeks post-puberty in bulls and to investigate the associations of metabolic hormones concentrations with testicular development. Leptin concentrations increased from 16 weeks before puberty to 8 weeks post-puberty and insulin concentrations increased from puberty to 8 weeks post-puberty. Growth hormone concentrations decreased after 4 weeks post-puberty, whereas IGF-I concentrations increased from 8 weeks before puberty to 8 weeks post-puberty. During this period, testicular growth was accelerated and testosterone secretion increased substantially, without any significant changes in gonadotropin secretion. Monthly circulating concentrations of leptin, IGF-I and insulin accounted for 63% of the variation in scrotal circumference and 59% of the variation in paired testes volume. In conclusion, the secretion of metabolic hormones was not associated with changes in gonadotropins concentrations. Furthermore, the associations of leptin, IGF-I and insulin concentrations with testes size indicated that these hormones might be involved in a gonadotropin-independent mechanism regulating the testicular development in peripubertal bulls.     

Peripheral leptin effect on food intake in young chickens is influenced by age and strain

The acute effect of leptin on the regulation of food intake was investigated in layer and broiler chickens. In an initial study, we observed that a single intraperitoneal injection of recombinant chicken leptin (1 mg/kg BW) dramatically reduced (38%) food intake in 56-day-old layer chickens, more moderately reduced (15%) food intake in 9-day-old layer chicks, and had no significant effect in 9-day-old broiler chicks. In a subsequent study, body weight and plasma concentrations of leptin were measured weekly in layer and broiler chicks from day 1 to 35 of age and brain leptin receptor and neuropeptide Y (NPY) mRNA expression were analyzed at 1, 9, and 35 days of age. At day 1 of age, peripheral concentrations of leptin were significantly greater in layer than broiler chicks. Subsequently, despite increases in body weight and differences in growth rates between layer and broiler chicks from day 8 to day 35 of age, peripheral concentrations of leptin were constant and similar in both genotypes. Leptin receptor and NPY mRNA were expressed in brain from day 1 in chicks of both genotypes and increased significantly to day 35 of age. These observations provide evidence that the inhibitory effect of leptin on the regulation of food intake in growing chicks is an age dependent process. Furthermore, acquisition of the anorectic effect of leptin is likely to be associated with greater expression of the leptin receptor and NPY mRNAs than to changes in blood levels of leptin. Finally, this study provides evidence that chickens selected for high growth rates may be less sensitive or responsive to peripheral concentrations of leptin than chickens with low growth rates (layers), suggesting that the faster growth of broiler chicks may be related to a lessened responsiveness to anorexigenic factors.     

Subclinical mastitis in ewes and its effect on lamb performance.

Two studies were conducted to 1) assess the effectiveness of the California mastitis test (CMT) relative to direct microscopic somatic cell count (DMSCC) and(or) somatic cell count (SCC) procedures for detecting subclinical mastitis in ewes, 2) determine the incidence of subclinical mastitis based on repeated or single sample measures and organisms associated with the inflammation, and 3) assess the relationship between milk quality measures and lamb performance. The relationship between DMSCC and SCC scores was significant (P less than .01); 90% of the variation in DMSCC scores was accounted for by SCC scores. In contrast, CMT scores accounted for only 26% of the variation in DMSCC and 30 to 34% of the variation in SCC scores. Incidence of inflammation varied from 17 to 50% of ewes tested, depending on the study and the method of assessment. Staphylococcus species were cultured from 14/41 samples tested, with cultures of Streptococcus species (3/41) and Micrococcus species (1/41) also present. The effect of subclinical mastitis in ewes on lamb performance was minimal when assessed by regressing lamb weights on subclinical mastitis and milk quality scores. In conclusion, growth performance of lambs in a management system where they had access to supplemental feed was not influenced by the quality of milk produced by ewes, or by the degree of subclinical mastitic inflammation present when they suckled.     

Synthesis and secretion of ovine placental lactogen and its biochemical properties.

The biochemical properties of ovine placental lactogen (oPL) have been previously determined following purification, which has yielded various results. To clarify the properties of oPL prior to purification, oPL was examined in solubilized fetal cotyledonary tissue (d 100 of gestation) or conditioned culture medium by electrophoretic, immunoblotting and immunoprecipitation techniques. In cotyledonary tissue or conditioned culture medium, oPL has an apparent molecular weight (Mr) of 22,000 with an isoelectric point (pI) of 9.2. Incorporation of [3H]-glucosamine or [3H]-mannose into immunoreactive oPL could not be detected, nor did the presence of tunicamycin in explant culture medium alter the apparent Mr of oPL. In vitro translation of d 100 fetal cotyledonary mRNA, followed by immunoprecipitation, provided evidence that pre-oPL has an apparent Mr of 25,000. The size of oPL mRNA was determined to be approximately 1,350 base pairs by Northern hybridization procedures using an oligonucleotide probe which was generated from oPL amino acid sequence data. These experiments suggest that the only intracellular processing oPL undergoes is removal of a amino-terminal signal sequence. We conclude that oPL is synthesized and secreted as a single nonglycosylated-basic protein, at a time during gestation when circulating oPL is elevated.