In the ewe, estradiol and progesterone inhibit luteinizing hormone (LH) secretion during the breeding season. Endogenous opioid peptides (EOP) are also inhibitory to LH secretion, and both estrogen and progesterone have been reported to enhance EOP inhibition of LH release. Which EOP are involved in this inhibition is unclear. In this study, we concentrated on β-endorphin because evidence for its ability to inhibit LH secretion exists in ewes. We first studied the distribution of β-endorphin-immunoreactive neurons in 4 cycling ewes using immunocytochemistry. Cell bodies were found only within the medial basal hypothalamus (MBH) and were concentrated in arcuate nucleus and mammillary recess of the third ventricle, with a few in the median eminence. Extensive fiber tracts were seen in preoptic area (POA) and median eminence. We next tested the hypothesis that gonadal steroids increase the synthesis of EOP by measuring levels of mRNA for proopiomelanocortin (POMC), the precursor to β-endorphin. Ovariectomized ewes were treated with no steroids (n = 7) or given subcutaneous Silastic implants containing either estradiol (n = 6) or progesterone (n = 6). After 4 days of treatment, EOP inhibition of LH secretion was measured by determining the LH response to WIN 44,441-3 (WIN), an EOP antagonist. LH pulse frequency and pulse amplitude were determined in blood samples collected at 12-min intervals for 3 h before and after intravenous administration of 12.5 mg WIN. WIN injection increased (p < 0.01) the LH pulse frequency only in progesterone-treated and pulse amplitude only in estradiol-treated ewes. After blood sampling, the ewes were killed, and POA, MBH, and pituitary gland were removed. Total RNA was extracted from these tissues and dot blotted onto nitrocellulose membranes for hybridization with a DNA probe complementary to the POMC mRNA. The resulting autoradiographs were quantified densitometrically. Levels of POMC mRNA in the MBH were increased (p < 0.01) by both estradiol and progesterone as compared with the no steroid group. There was no detectable POMC mRNA in the POA. These results suggest that estrogen and progesterone enhance EOP inhibition of LH secretion by increasing POMC mRNA levels and thus synthesis of β-endorphin.

Mastitis or other infectious diseases have been related to reduced fertility in cattle. Inflammatory cytokines such as tumor necrosis factor α (TNFα) are released in response to infection and may have negative effects on embryo development. In the current study the effect of exposure to TNFα on the development of in vitro fertilized bovine embryos was examined. Indomethacin, a prostaglandin synthesis inhibitor, was used to determine if blockade of prostaglandin synthesis would alter the effects of TNFα. Ovaries were obtained from a local abattoir and immature COC were isolated from 2-10 mm follicles, in vitro matured and fertilized. After fertilization, groups of presumptive zygotes were randomly placed into either control development medium, medium containing 25 ng/mL TNFα or medium containing 25 ng/mL TNFα plus 1 μg/mL indomethacin. The proportion of blastocysts formed was assessed at day 7 of culture. Fewer embryos exposed to TNFα alone reached the blastocyst stage (17.5 ± 2.4%, P < 0.01) compared with controls (30.5 ± 2.4%) or embryos developed in TNFα plus indomethacin (25.8 ± 2.8%). There was no difference between control embryos and embryos developed in TNFα plus indomethacin. These results indicate that TNFα is inhibitory to the in vitro development of bovine embryos and that this inhibition may be mediated by prostaglandins because it can be blocked by indomethacin.

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Evidence suggests that endogenous opioid peptides (EOP) inhibit pulsatile luteinizing hormone (LH) secretion during both the luteal and follicular phases of the ovine estrous cycle. Further data from sheep and other species indicate that the hypothalamus is the primary site of action for this EOP inhibition. The purpose of the following experiments was to determine which areas of the hypothalamus are involved in the EOP inhibition of pulsatile LH secretion. Regularly cycling ewes (n = 10) were stereotaxically implanted with guide tubes into the preoptic area (POA) and medial basal hypothalamus (MBH). Implants containing the EOP antagonist WIN 44,441–3 (WIN) were placed into each of these areas. Blood samples were collected at 12-min intervals for 3 h before and during WIN administration in the luteal phase and for 4 h before and during WIN administration in the follicular phase of the estrous cycle. During the luteal phase, WIN implants in either area increased (p < 0.01) LH pulse frequency (POA 1.4 ± 0.3/3 h before vs. 3.1 ± 0.4/3 h during; MBH 1.1 ± 0.2/3 h before vs. 2.8 ± 0.5/3 h during). There was no effect on LH pulse amplitude. In contrast, during the follicular phase, WIN implants selectively increased (p < 0.01) LH pulse frequency when implanted in the POA (3.2 ± 0.4/4 h before vs. 5.2 ± 0.6/4 h during) while increasing (p < 0.05) only LH pulse amplitude when placed in the MBH (0.7 ± 0.2 ng/ml before vs. 1.4 ± 0.3 ng/ml during). These results suggest that although EOP act in both POA and MBH to inhibit LH secretion, different populations of EOP neurons may be activated during different phases of the estrous cycle.

Detrimental physiological effects due to stressors can contribute to the low captive success of primates. The objective of this research was to investigate the potential impact of diet composition on cortisol concentrations in feces and saliva in woolly (n=27) and spider monkeys (n=61). The research was conducted in three studies: the first investigated spider monkeys in the United States, the second investigated spider monkeys within Europe, and the third investigated woolly monkeys within Europe. Fecal cortisol in spider monkeys in US zoos varied (P=.07) from 30 to 66 ng/g. The zoo with the highest fecal cortisol also had the highest salivary cortisol (P≤.05). For European zoos, fecal cortisol differed between zoos for both spider and woolly monkeys (P≤.05). Spider monkeys had higher fecal cortisol than woolly monkeys (P≤.05). Zoos with the highest dietary carbohydrates, sugars, glucose, and fruit had the highest cortisol. Cortisol was highest for zoos that did not meet crude protein requirements and fed the lowest percentage of complete feeds and crude fiber. Differences among zoos in housing and diets may increase animal stress. The lifespan and reproductive success of captive primates could improve if stressors are reduced and dietary nutrients optimized.