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J. D. FULTON and J. A. ARMSTRONG

Summary.

In a large percentage of male Schneider mice taken from breeding stock at approximately 1 year of age, the bladder was observed to be grossly distended with urine. The condition was attributable to urethral obstruction by secretory material originating in the vesicular and coagulating glands. The affected animals recovered spontaneously in a period of days, and subsequently proved fertile. Restriction of mating activity while the glands are secreting freely is thought to be the cause of this condition, which did not occur in females and younger males of the same stock nor in other rodents examined.

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D. G. Armstrong and J. W. Wells

The enzyme complex Δ5-3β-hydroxysteroid dehydrogenase (EC 1.1.1.51)–Δ5-3-oxosteroid isomerase (EC 5.3.3.1) catalyses the conversion of pregnenolone to progesterone and dehydroepiandrosterone to androst-4-ene-3,17-dione in tissue producing steroid hormones. A recent study demonstrated that this enzyme complex (3β-HSD) in the ovary of the domestic fowl is distributed predominantly in the microsomal fraction, and there were marked quantitative and qualitative differences in the 3β-HSD obtained from the ovaries of immature pullets compared with that from laying hens (Armstrong & Wells, 1976).

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J. D. Armstrong, J. H. Britt and N. M. Cox

Summary. Primiparous sows were fed to appetite during lactations that occurred during winter or summer, and 11·4 ± 0·4 pigs per litter were weaned at 23·5 ± 0·1 days of age. Sows were slaughtered at 0 or 72 h after weaning or blood samples were collected until 24 h after onset of oestrus. Sows that lactated during summer consumed less food and lost more (P < 0·05) weight, heartgirth and backfat than those that lactated during winter. Weaning-to-oestrus interval was greater (P < 0·05) in summer (224 ± 25 h) than in winter (93 ± 13 h). Content of GnRH in the hypothalamus and concentrations of LH in the anterior pituitary and serum were lower (P < 0·05) after weaning in summer than winter. The numbers of visible ovarian follicles < 5 mm in diameter at weaning were lower (P < 0·05) in summer than in winter. In contrast to LH, FSH concentration in serum was higher (P < 0·10) in summer than winter, but FSH values in the anterior pituitary were lower (P < 0·05) in summer than in winter. Post-weaning patterns of secretion of oestradiol and follicular development differed between winter and summer. For example, in some sows weaned during the summer, transient surges of oestradiol occurred repeatedly during 0 to 280 h after weaning without provoking surges of LH. These results indicate that the period of post-weaning anoestrus in summer is prolonged because of altered activity of the hypothalamic– pituitary axis, possibly because of changes in sensitivity to the feedback of oestradiol. Lower feed intake during lactations that occur during summer may predispose the endocrine system to the aberrations.

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J. D. Armstrong, R. R. Kraeling and J. H. Britt

Summary. Sows (N = 16) were infused intravenously for 8 h with saline or naloxone (200 mg/h) or their litters were transiently weaned for 8 h. Before infusion, 200 mg naloxone were administered to elevate quickly concentrations of naloxone. Blood samples were collected from sows at 15 min intervals for 24 h, beginning 8 h before and continuing until 8 h after imposition of treatments during the middle 8-h segment. Frequency of episodic release of LH and concentrations of prolactin were similar before, during and after infusion of saline. Average concentration of LH was greater during the last than during the middle 8-h segment when sows were given saline. Frequency of episodic release of LH increased and concentrations of prolactin decreased during infusion of naloxone or transient weaning; however, average concentration of LH increased during transient weaning, but not during infusion of naloxone. After transient weaning or infusion of naloxone, frequency of release of LH decreased, returning to pretreatment values in sows infused with naloxone but remaining above pretreatment values in sows subjected to transient weaning. At the resumption of suckling by litters in sows subjected to transient weaning, prolactin increased to levels not different from those observed during the 8-h pretreatment segment. Prolactin did not increase until 4–5 h after cessation of naloxone infusion. We conclude that continuous infusion of naloxone altered secretory patterns of LH and prolactin. Collectively these results provide evidence that the immediate effects of weaning on LH and prolactin in sows are mediated in part through a mechanism involving endogenous opioid peptides.

Keywords: LH; endogenous opioid peptides; naloxone; lactation; prolactin

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L. A. Johnston, D. L. Armstrong and J. L. Brown

The annual reproductive cycle of the male snow leopard (Panthera uncia) was characterized by evaluating seminal and endocrine traits monthly. Testicular volume was greatest (P < 0.05) during the winter months when the quality of ejaculate was optimal. Ejaculate volume, total sperm concentration ml−1, motile sperm concentration per ejaculate, sperm morphology and sperm motility index were lowest during the summer and autumn months compared with the winter and spring. Peripheral LH, FSH and testosterone concentrations were also lowest during the summer months, increasing during the autumn just before the increase in semen quality, and were maximal during the winter months. There was a direct relationship (P < 0.01) between: (1) testosterone and testicular volume, total sperm concentration ml−1, motile sperm concentration per ejaculate and ejaculate volume, and (2) LH and testicular volume and motile sperm concentration per ejaculate. In summary, although spermatozoa were recovered throughout the year, optimal gamete quality was observed during the winter and spring. Although previous studies in felids have demonstrated seasonal effects on either seminal or endocrine traits, this is the first study to demonstrate a distinct effect of season on both pituitary and testicular function.

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D. J. Kiehm, D. L. Walters, S. A. J. Daniel and D. T. Armstrong

Summary. Oestrous cycles of goats were synchronized hormonally. Immunoreactive oxytocin was undetectable (< 0·1 ng/mg protein) in media from granulosa cells isolated before the LH surge for small (1–2 mm), medium (3–5 mm) and large >5 mm diameter) follicles when cultured for 24 h without or with added hormones. Granulosa cells from large and medium, but not small, follicles isolated 6–12 h after spontaneous preovulatory LH surges secreted high concentrations of oxytocin (4–12 ng/mg protein). Addition of PGE-2 (1 μg/ml) caused a further significant (P < 0·05) increase in oxytocin secretion by cultured granulosa cells, whereas PGF-2α, FSH and LH were ineffective when added to culture media.

Ovarian venous blood and granulosa cells were collected at 0, 6, 12 or 18 h after GnRH injection in hormonally synchronized goats. Peripheral serum LH values were increased significantly in all but 2 of 22 goats within 2 h of GnRH injection. At the earliest sampling time after GnRH (6 h), ovarian venous levels of oxytocin were increased significantly from basal levels of 0·4 pg/ml to 2·4 pg/ml. Oxytocin concentrations in follicular fluid increased from a basal value of 67 pg/ml to 155 pg/ml by 6 h and to 372 pg/ml by 18 h after GnRH injection. Oxytocin secretion by cultured granulosa cells was not increased significantly by 6 h (0·1 ng/mg protein) but rose to 1·4 and 3·5 ng/mg protein at 12 and 18 h, respectively. Approximately parallel increases occurred in progesterone in ovarian venous blood and granulosa cell culture media over the same time period. Oestradiol secretion by granulosa cells cultured with androstenedione as an aromatizable substrate was essentially unchanged when obtained from 0 to 12 h after GnRH injection (31–37 ng/mg protein), but fell significantly to 7·4 ng/mg in cells obtained 18 h after GnRH injection, indicative of decreasing aromatase activity as luteinization progresses during the preovulatory period. It is concluded that granulosa cells, in response to the preovulatory LH surge, acquire the ability to synthesize and secrete oxytocin in parallel with the increased progesterone and decreased oestradiol secretion which occurs during luteinization.

Keywords: oxytocin; granulosa cells; goat; LH; luteinization

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G. Evans, D. Claire Wathes, G. J. King, D. T. Armstrong and D. G. Porter

Summary. Theca and granulosa layers were isolated from the preovulatory follicles of prepubertal gilts which were untreated (Group A), killed 72 h after 1000 i.u. PMSG (Group B), killed 84 h after PMSG (Group C), or killed 84 h after PMSG + 500 i.u. hCG given at 72 h (Group D). The tissues from individual follicles were cultured for 24 h alone (C), with FSH (F) or with LH (L), and the content of immunoreactive relaxin in the culture media was measured by RIA. Concentrations of relaxin-like material were close to the limit of detection of the assay in all granulosa cell cultures, and in the thecal cultures from the untreated gilts. However, thecal cultures from all 19 treated gilts produced relaxin. The mean ± s.e.m. concentrations (pg/follicle) in Groups AC, BC, CC and DC were 26·5 ± 3·04, 93·1 ± 4·6, 138 ± 16·4 and 285·6 ± 54·1 respectively. Therefore relaxin production was stimulated by PMSG (P < 0·05), with hCG treatment in vivo leading to a further significant increase (P < 0·05). In-vitro treatment with gonadotrophins had no effect in Groups A, C and D, but in Group-B gilts LH produced a significant (P < 0·05) rise in relaxin levels. These studies indicate that the theca is the principal source of relaxin in the porcine preovulatory follicle. The increased production before ovulation suggests that relaxin may be involved in follicular growth or rupture.

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J. L. Brown, K. L. Goodrowe, L. G. Simmons, D. L. Armstrong and D. E. Wildt

Summary. Frequent blood samples were collected to study hormonal responses to GnRH in male and female leopards and tigers. Animals were anaesthetized with ketamine–HCl and blood samples were collected every 5 min for 15 min before and 160 min after i.v. administration of GnRH (1 μg/kg body weight) or saline. No differences in serum cortisol concentrations were observed between sexes within species, but mean cortisol was 2-fold greater in leopards than tigers. GnRH induced a rapid rise in LH in all animals (18·3 ± 0·9 min to peak). Net LH peak height above pretreatment levels was 3-fold greater in males than conspecific females and was also greater in tigers than leopards. Serum FSH increased after GnRH, although the magnitude of response was less than that observed for LH. Basal LH and FSH and GnRH-stimulated FSH concentrations were not influenced by sex or species. Serum testosterone increased within 30–40 min after GnRH in 3/3 leopard and 1/3 tiger males. Basal testosterone was 3-fold greater in tiger than leopard males. LH pulses (1–2 pulses/3 h) were detected in 60% of saline-treated animals, suggesting pulsatile gonadotrophin secretion; however, in males concomitant testosterone pulses were not observed. These results indicate that there are marked sex and species differences in basal and GnRH-stimulated hormonal responses between felids of the genus Panthera which may be related to differences in adrenal activity.

Keywords: GnRH, leopard, tiger, LH, cortisol, testosterone

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D. G. Armstrong, Maida F. Davidson, A. B. Gilbert and J. W. Wells

Summary. The activity of Δ5-3β-hydroxysteroid dehydrogenase (3β-HSD) in the postovulatory follicle (POF) of the domestic hen was studied; it declined rapidly during the first 15 h after ovulation and then fell gradually until 50 h when there was no detectable activity. Comparison of 3β-HSD and glucose 6-phosphate dehydrogenase activities in the theca and granulosa cells indicated that the changes in enzymatic activity can be attributed to the thecal component; the enzyme activity in granulosa cells was stable up to 35 h after ovulation.

The results appear consistent with the hypothesis that the POF is a source of steroid hormones.

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X. Zhang, G. M. Kidder, A. J. Watson, G. A. Schultz and D. T. Armstrong

The sensitive mRNA phenotyping technique of reverse transcription–polymerase chain reaction was used to demonstrate that insulin receptor mRNA is present in rat embryos during the preimplantation period. In addition, mRNA encoding insulin-like growth factor (IGF) type I and type II receptors have also been detected in rat preimplantation embryos. IGF-I mRNA was not detected in preimplantation embryos but was found in oviducts and uteri of prepubertal and early pregnant rats. IGF-II mRNA was present in both embryos and in oviducts and uteri during the preimplantation period. These findings suggest that insulin and IGF-I could influence early embryo development in endocrine or in paracrine fashions, whereas IGF-II may have an additional autocrine mode of action in affecting preimplantation embryos in rats.