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M. J. D'Occhio, D. R. Gifford, R. M. Hoskinson, T. Weatherly and B. P. Setchell

Summary. Groups of heifer calves received a primary immunization against androstenedione (Group A; N = 11) or oestradiol-17β (Group E; N = 10) at 3 months of age and booster injections on 5 occasions at 2- to 3-month intervals. Controls (Group C, N = 11) were immunized against human serum albumin alone using the same protocol. Immunity was achieved against both steroids as judged by the secondary antisteroid antibody titres in Group A (1126 ± 261; reciprocal of titre) and Group E (10 357 ± 4067) heifers. In Groups A and E there was a general decline in the respective peak antibody titres after successive booster injections. From 3 to 9 months of age mean plasma concentrations of LH were higher (P < 0·05) in Group E heifers (0·89 ± 0·08 ng/ml) than in Group C (0·46 ± 0·03 ng/ml) and Group A (0·59 ± 0·05 ng/ml) heifers which did not differ from one another. There were no differences between groups in plasma FSH concentrations. At 10 months of age the LH response to exogenous LHRH was of higher (P < 0·05) amplitude for heifers in Group E (2·59 ± 0·56 ng/ml) than for those in Groups C (0·61 ± 0·07 ng/ml) and A (1·04 ± 0·22 ng/ml). Elevated plasma progesterone concentrations at 5 months of age were shown by 2 heifers in Group C, 10 in Group A, and 6 in Group E. From 8 to 14 months of age a consistently higher proportion of Group A heifers exhibited elevated progesterone compared with Group C and Group E heifers. After ovarian synchronization and booster injection at 15 months of age a corpus luteum was present in 2 heifers in Group C, 7 in Group A and none in Group E. The ovaries of Group A heifers were different from those of Groups C and E and were characterized by greater numbers of 2–4 mm follicles. It is concluded that active immunization against gonadal steroids influences both LH secretion and ovarian function in prepubertal heifers. Early increases in ovarian activity in androstenedione-immunized heifers are maintained after puberty and may therefore confer some lifetime reproductive advantages.

Keywords: heifer; gonadal steroid immunization; gonadotrophins; puberty; ovary

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G. D. Buchanan and E. V. YoungLai

Summary. Monthly collections of hibernating little brown bats contained (1) nulliparous females with small uteri and no antral follicles, (2) nulliparous females with swollen uteri and mature follicles, and (3) parous females, which, despite obvious differences in reproductive status, had equivalent plasma progesterone values. During the principal study season, mean monthly progesterone concentrations (measured by radioimmunoassay) showed recurrent increases with an apparent periodicity of about 60 days, but limited data obtained in the subsequent season did not. However, comparison of activity patterns in the two seasons with monthly progesterone concentrations suggests that ovarian activity during hibernation is affected by variations in metabolic level.

We saw no evidence that nulliparous bats with small uteri developed antral follicles during hibernation. Despite their apparent immaturity, however, they had cornified vaginae and most were demonstrably inseminated. These indications of oestrus and the lack of differences between their plasma progesterone concentrations and those of patently mature females suggest that they were physiologically post-pubertal but failed to complete folliculogenesis before entering hibernation.

Keywords: progesterone; bat; hibernation

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U. W. Huck, N. C. Pratt, J. B. Labov and R. D. Lisk

Summary. Golden hamsters that were mated repeatedly from 55 days of age produced 6–12 litters. Litter size at birth rose between the 1st and 2nd litters, peaked on the 3rd, and declined steadily after the 5th litter. Offspring sex ratio (% male) at birth followed a similar pattern: increasing between the 1st and 2nd litters, remaining high through the 3rd, and becoming increasingly female-biased thereafter. Weaning success decreased sharply after the 6th litter and most dams failed to raise any young to weaning after the 9th litter. These sequential effects on litter size, offspring sex ratio and weaning success were also observed in females mated once at different ages, but they occurred considerably later in life, i.e. increasing parity hastened the effects of advanced age. These ageand parity-related changes in litter composition are consistent with the Trivers–Willard hypothesis that physiologically-stressed females would skew offspring sex ratios to favour daughters. However, since the observed changes in sex ratio were probably due to differential prenatal mortality, their adaptive significance is unclear.

Keywords: age; parity; sex ratio; weaning success; golden hamsters; litter size

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M. A. de las Heras, M. O. Suescun and R. S. Calandra

Summary. After castration, there was a marked decrease in serum androgen concentration at 6 h, and a dramatic inhibition of ornithine decarboxylase (ODC) at 12 h. Administration of testosterone propionate to castrated rats at a dose of 0·05 mg/animal restored ODC activity to the normal value. However, no change was observed when intact rats were treated with testosterone even at a 40-fold higher dose, indicating that endogenous androgens present in intact rats are far in excess for maintenance of maximal levels of activity. Administration of the antiandrogen flutamide to intact rats caused a moderate decrease in epididymal weight, whereas this effect was more pronounced in castrated, androgen-treated rats. In the latter, the effect of flutamide was significant at the lowest dose used (0·5 mg/day). ODC activity was significantly decreased by flutamide treatment of intact rats, but even at the highest dose used (10 mg/day) only a 39% inhibition was observed. In flutamide-treated rats, LH concentrations were markedly increased, as were serum and epididymal androgens. In androgen-treated castrated rats, flutamide caused epididymal ODC to fall to undetectable values. These results show that: (1) androgens are essential for the maintenance of ODC activity in the epididymis; (2) epididymal ODC activity is maximally stimulated by endogenous androgens, at least in the pubertal rat; (3) the apparent potency of flutamide is substantially lowered by an increase in epididymal androgens. We suggest that ODC is a sensitive marker of the action of androgens and antiandrogens in the epididymis.

Keywords: androgen; antiandrogen; epididymis; ornithine decarboxylase; rat

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H. Badawi and M. Wilkinson

Summary. Daily subcutaneous injections of 100 μg melatonin given to prepubertal female rats housed in 14L:10D or 12L:12D failed to delay puberty as evidenced by the age at which vaginal opening occurred; neither the Sprague–Dawley nor the Wistar strain rats were responsive to melatonin treatment. Reproductive organ weights (ovaries and uteri) at vaginal opening were unaffected by such treatment. Administration of melatonin through the drinking water in doses of 100, 500 or 1000 μg/day did not alter the timing of puberty or the reproductive organ weights in rats of the Sprague–Dawley or Long–Evans strains (housed in 12L:12D). Our experimental methods are identical to a previous report and we have no explanation for our failure to reproduce the earlier results.

Keywords: melatonin; puberty; vaginal opening; rat

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P. S. Campbell and P. M. Satterfield

Summary. Neonatal Sprague–Dawley rats were injected with the antioestrogens nafoxidine or CI-628 on Day 3 of life alone or in combination with oestradiol benzoate 24 h later. Oestrogen-stimulated glucose oxidation and cytoplasmic oestrogen binding sites of the uteri were assessed at 21–23 days of age. Neither antioestrogen antagonized the prepubertal uterine impairments produced by neonatal oestradiol treatment. Both antioestrogens administered alone produced deficits which mimicked those produced by neonatal oestrogenization. However, the agonist property of each antioestrogen was differentially expressed: treatment with CI-628 reduced prepubertal oestrogen binding sites in the uterus, but nafoxidine exposure decreased the sensitivity of the uterus to oestradiol stimulation of glucose oxidation. It is postulated that CI-628 directly affects the uterus to reduce production of oestrogen receptor protein, while nafoxidine affects the development of the uterine phosphogluconate oxidative pathway indirectly through impaired ovarian function. However, antioestrogens blocked the neonatal oestradiol-induced reduction in the oestrogen-stimulated production of actomyosin in the adult uterus. Therefore, while both CI-628 and nafoxidine are clearly agonists in the neonatal rat, each appears to exhibit cell-specific agonist and antagonist properties.

Keywords: uterus; antioestrogen; oestrogen receptor; glucose metabolism; neonate; rat

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T. P. Fletcher, A. E. Jetton and M. B. Renfree

Summary. Forty tammar wallabies, presumed to be carrying quiescent blastocysts, were injected with progesterone and oestradiol alone, or in combination, during seasonal quiescence when the corpus luteum is inactive. Plasma progesterone concentrations were increased to values equivalent to those of late pregnancy for the duration of the treatment in progesterone-treated groups but otherwise remained at values equivalent to seasonal quiescence. Tammars treated with low doses of oestradiol showed no measurable increase in plasma oestradiol concentrations but in those treated with high doses plasma concentrations were increased to oestrous levels. At autopsy on Day 18 after the start of treatment the embryos and reproductive tracts were assessed. While progesterone alone caused reactivation of about 50% of the embryos, blastocysts in tammars treated with oestradiol alone remained in diapause (low dose) or disappeared from the uterus (high dose): 2 blastocysts collapsed after some slight expansion. No synergistic effect on pregnancy was noted in tammars receiving both oestradiol and progesterone. We conclude that oestrogen alone is not capable of stimulating normal growth of blastocysts, and its role during early pregnancy in tammars remains unclear.

Keywords: progesterone; oestradiol-17β blastocyst; seasonal diapause; marsupial

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B. L. Penzhorn and N. J. van der Merwe

Summary. Testis mass of adult Cape mountain zebra stallions (mean 70·0 g) was appreciably less than that of other zebra species and domestic horses. The histological appearance of the testes of 11-, 24- and 29-month-old colts was typically prepubertal. Spermatogenic activity of a 4-year-old stallion obtained at the end of summer was at a very low level, while a 4·5-year-old stallion obtained 6 weeks after the winter solstice showed a marked increase in spermatogenesis compared with the 4-year-old. Stallions 6·5–19 years of age collected in different seasons all showed active spermatogenesis.

Keywords: mountain zebra; testis size; spermatogenesis

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T. P. Fletcher and M. B. Renfree

Summary. The quiescent corpus luteum of female tammars was reactivated by removal of the pouch young (RPY). The reactivated corpus luteum was ablated 3 days after RPY. Plasma progesterone and oestradiol concentrations were measured by radioimmunoassay in these and in sham-operated controls. Excision of the CL abolished the rise in progesterone seen at Day 5–6 in the sham-operated animals (130·7 ± 56·6 vs 452·4 ± 176·0 pg/ml, mean ± s.d.). By contrast, oestradiol-17β values increased within 6–16 h of CL excision to 16·3 ± 6·9 pg/ml and remained high for 1–3 days while in the sham-operated animals there were less sustained and more variable peaks of 10–20 pg/ml between Days 3 and 5 (mean 12·0 ± 3·6 pg/ml at Day 4–5). We conclude that the early transient increase in peripheral plasma of progesterone is of luteal origin but the source of the oestradiol remains unknown.

Keywords: corpus luteum; progesterone; oestradiol-17β; early pregnancy; marsupial

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K. K. Schillo, M. A. Green and S. H. Hayes

Summary. Finnish Landrace × Southdown ewes were ovariectomized (OVX) and subjected to daily photoperiods of 16L:8D (Group I) or 8L:16D (Group II) for 84 days. Ewes were then either adrenalectomized (ADX) (N = 5 for Group I; N = 4 for Group II) or sham ADX (N = 6 for Groups I + II). After surgery, ewes in Group I were subjected to 8L:16D for 91 days and 16L:8D for 91 days whereas ewes in Group II were exposed to 16L:8D for 91 days and 8L:16D for 91 days. Oestradiol implants were inserted into all ewes on Day 148. Sequential blood samples were taken at 28, 56, 91, 119, 147 and 168 days after surgery to determine secretory profiles of LH and prolactin. Photoperiod did not influence LH release in Group I in the absence of oestradiol. Although photoperiod influenced frequency and amplitude of LH pulses in Group II before oestradiol treatment, adrenalectomy did not prevent these changes in patterns of LH release. However, in Group II the increase in LH pulse amplitude during exposure to long days was greater (P < 0·01) in adrenalectomized ewes than in sham-operated ewes. Mean concentrations of LH increased in ADX ewes on Days 91 (P = 0·07) and 119 (P < 0·05). Adrenalectomy failed to influence photoperiod-induced changes in mean concentrations of LH, amplitude of LH pulses and frequency of LH pulses in the presence of oestradiol. Concentrations of prolactin were influenced by photoperiod. In Groups I and II concentrations of prolactin increased (P < 0·01) after adrenalectomy, but the magnitude of this effect decreased over time. These results suggest that the effects of photoperiod on patterns of LH release are mediated in part by a mechanism that is not dependent on sex steroids and that the adrenal may influence release of prolactin.

Keywords: photoperiod; LH; prolactin; adrenalectomy; sheep