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N. C. Rawlings and W. R. Ward

Summary. In 7 ewes during late pregnancy, peripheral plasma concentrations of oestrogens were correlated with uterine activity (P < 0·01; r=+0·47).

In myometrial tissue, the concentration of progesterone was similar to that in plasma; it rose to a plateau from Days 115 to 130 of pregnancy and then fell, but was still detectable during parturition. Myometrial oestrogen concentration was much higher than in plasma; from a peak at Days 100–115 it decreased, but rose sharply just before parturition.

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A. P. Beard and N. C. Rawlings

The mammalian reproductive system is sensitive to exposure to endocrine disrupting chemicals, particularly during sexual maturation. The purpose of this study was to examine reproductive function in second and third generation male and female mink exposed to pesticides from conception to maturity. The mink were fed untreated feed or feed treated with Lindane (1 mg kg−1 day−1), Carbofuran (0.05 mg kg−1 day−1 or Pentachlorophenol (1 mg kg−1 day−1) from the time they were weaned. The second generation mink had also been exposed to the pesticides in utero and from their mother's milk as their mothers were similarly fed pesticides, from 3 weeks before breeding. The third generation mink were the offspring of mink (second generation females) who had themselves undergone long-term exposure to pesticides from conception onwards. Blood samples and endocrine tissues were obtained at necropsy from both generations of mink. No overt signs of toxicity were seen. The pesticides did not affect the percentage of mink mated. Lindane treatment reduced the proportion of mated mink that subsequently whelped (P < 0.1) and the litter size of mink that whelped (P <0.05). Testis size was reduced in the Lindane-treated, third generation males (P < 0.05). Serum concentrations of cortisol, testosterone and oestradiol were not affected by any pesticide treatment; however, thyroxine concentration was reduced by Pentachlorophenol (P < 0.05). In conclusion, exposure of mink to Lindane from conception resulted in a decrease in reproductive efficiency when they were subsequently mated, leading to a 60% reduction in the number of kits born.

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N. C. Rawlings and W. R. Ward

Summary. In 4 Clun Forest ewes maternal peripheral plasma concentrations of progesterone were still elevated at the onset of parturient uterine activity. Fetal and maternal plasma concentrations of oestrogen started to rise before parturition and concentrations in maternal plasma were positively correlated with parturient uterine activity (P < 0·05; r = +0·42). Fetal plasma concentrations of corticosteroids were positively correlated with fetal plasma concentrations of oestrogen (P < 0·01; r = +0·65), but negatively correlated with maternal peripheral plasma progesterone concentrations (P < 0·05; r = −0·50). Before parturition plasma concentrations of PGF rose but stayed high only in maternal peripheral plasma. Maternal peripheral plasma concentrations of PGF were positively correlated with uterine activity (P < 0·05; r = +0·79) and plasma concentrations of oestrogen (P < 0·05; r = +0· 79), but negatively correlated with plasma concentrations of progesterone (P < 0·01; r = −0·54).

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J. P. Ravindra and N. C. Rawlings

Daily transrectal ovarian ultrasonography was performed in ten ewes for 5 consecutive days, once in early July, once in late July (anoestrus) and then continuously until from mid-August until ewes had completed one ovulatory cycle. During anoestrus the size range and numbers of ovarian antral follicles were similar to those seen during the breeding season. However, numbers of small antral follicles (2–3 mm in diameter) decreased during late anoestrus, and maximum follicle diameter increased just before the short period of progesterone secretion preceding the first observed ovulation. The ovarian antral follicles that ovulated first and second in the breeding season grew from 2 mm in diameter to 5.7 ± 0.3 mm and 6.2 ± 0.3 mm diameter over 4.7 ± 0.3 days and 4.6 ± 0.3 days, respectively, and the interovulatory interval was 16.6 ± 0.2 days. During the first ovulatory cycle, follicles emerged to grow from the 2 mm size class on 11 of the 17 days, but peaks of emergence were seen on days 2 and 11. The first observed ovulation was preceded by a transient increase in serum concentrations of progesterone (6 days duration), with a peak concentration of 1.30 ± 0.22 nmol l−1. With ultrasonography, no evidence of ovulation was seen before the increase in progesterone secretion and no luteal structure was detected during the small increase in progesterone secretion; however, luteal structures are normally detected by ultrasonography only from 3 to 5 days after ovulation. An LH surge similar to a preovulatory LH surge preceded the first increase in progesterone secretion in five ewes. Oestrus occurred consistently with ovulation only at the second observed ovulation of the breeding season, after a normal luteal phase. LH pulse frequency and mean and basal serum concentrations of LH all increased in late anoestrus, but no major trends in serum concentrations of FSH and oestradiol were seen during this period. It was concluded that at the end of anoestrus there is no major change in ovarian antral follicle dynamics. At this time, increased LH secretion was seen as was a reduction in numbers of small antral follicles and a greater maximum diameter of follicles. A surge release of LH resulted in a short-lived secretion of progesterone, the source of which was unclear; this was followed by the first observed ovulation and the first ovulatory cycle of the breeding season. Oestrus occurred consistently only at the second observed ovulation of the season and the peak concentration of progesterone at each period of progesterone secretion increased to at least the second ovulatory cycle.

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D. L. Kingsbury and N. C. Rawlings

Serum concentrations of LH, FSH, oestradiol and cortisol were measured in control gilts not exposed to a boar and in gilts with fence-line exposure to a boar that allowed full muzzle contact. All gilts were between 134 and 200 days of age. Control gilts showed first oestrus at 193 ± 7 days of age (n = 5). Twelve of the gilts exposed to the boar showed first oestrus at 169 ± 5 days of age and five had not shown oestrus by 200 days of age. Introduction of a boar produced a transient increase in LH pulse frequency lasting no longer than 20 days (P < 0.001) in gilts responding to the boar with oestrus. Basal and mean serum LH concentrations were also increased (P < 0.05) in the gilts that responded to a boar with oestrus, but only in the 6 h after introducing the boar. Mean serum concentrations of FSH were lower in gilts exposed to a boar compared with the controls at 10 days after introduction of the boar, but by 20 days only gilts responding to the boar with oestrus had lower FSH concentrations (P < 0.05). Serum concentrations of cortisol decreased over the day the boar was introduced in all groups of gilts (P < 0.05) and were always highest in gilts exposed to a boar but not showing oestrus by 200 days of age (P < 0.05). There were no significant trends in serum concentrations of oestradiol but oestradiol concentrations varied over a wide range in gilts that did not respond to the boar with oestrus. These data suggest that the presence of an intact male stimulates an increase in LH pulse frequency over 10 days in prepubertal gilts, and that this increase may stimulate some gilts to become cyclic before 200 days of age. It was of interest that high cortisol concentrations were measured in the gilts that did not respond to the boar with oestrus. An increase in cortisol secretion would not appear to mediate the ability of a boar to induce oestrus in gilts.

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W. D. Currie and N. C. Rawlings

Summary. In ewes in the mid-luteal phase, LH pulse frequency (P < 0·01) and amplitude (P < 0·05) increased during a 24 h infusion of naloxone (0·5 mg/kg/h) compared to a 24 h infusion of vehicle (mean ± s.e.m.; 0·25 ± 0·03 vs 0·14 ± 0·01 pulses/h and 0·84 ± 0·08 vs 0·55 ± 0·08 ng/ml serum, respectively). The increase in pulse amplitude was immediate, but was less (P < 0·05) during the second 12h, compared to the first 12 h, of naloxone infusion (0·52 ± 0·14 vs 0·98 ± 0·08 ng/ml serum). Oestradiol concentrations were higher (P < 0·01) during naloxone than during control infusion (5·63 ± 0·26 vs 4·13 ± 0·15 pg/ml serum). In ovariectomized ewes in the breeding season, LH pulse frequency was lower (P < 0·01) during a 24 h infusion of morphine (0·5 mg/kg/h) than during a 24 h infusion of vehicle (mean ± s.e.m.; 1·17 ± 0·08 vs 1·71 ± 0·06 pulses/h). We conclude that long-term infusion of naloxone results in a sustained increase in LH pulse frequency but only a transient elevation in pulse amplitude. No effects on FSH secretion were noted. LH secretion was sensitive to morphine in the absence of ovarian steroids, suggesting that ovarian steroids are not required for the presence of functional opioid receptors capable of modulating LH release.

Keywords: LH; FSH; ewe; morphine; naloxone

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N. C. Rawlings and I. J. Churchill

Summary. Spring-born crossbred ewe lambs were raised in a natural photoperiod and saline (N = 6) or naloxone (1 mg/kg) in saline (N = 6) was injected (i.m.) every 2 h for 6 h at 5, 10 and 15 weeks of age and for 8 h at 20,25 and 30 weeks of age. Blood samples were taken every 12 min during treatment periods.

Naloxone had no effect on time to first oestrus (controls 235 ± 6 days, naloxone 242 ± 7 days). Mean serum LH concentrations and LH pulse frequency were elevated by naloxone in ewe lambs at 20, 25, and 30 weeks of age (P < 0·05). The only FSH response to naloxone was a depression of mean serum concentrations at 30 weeks of age (P < 0·05). LH pulse amplitude was elevated at 5 weeks of age in all ewe lambs and declined thereafter to a nadir at 30 weeks of age in control, but not in naloxone-treated animals (P < 0·05). LH pulse frequency was elevated at 10 weeks of age in control ewe lambs and in all animals at 30 weeks of age (P < 0·05). FSH pulse frequency declined from 5 weeks of age in control ewe lambs (P < 0·05), with very few pulses noted in 25- and 30-week-old animals. We conclude that (1) opioidergic suppression of LH, but not FSH, secretion developed at 20 weeks of age in the growing ewe lambs used in the present study, with no obvious change in suppression before the onset of first oestrus: (2) pulsatile FSH secretion occurred in the young ewe lamb but was lost as the lamb matured: (3) attainment of sexual maturity was preceded by an elevation in LH pulse frequency.

Keywords: ewe lamb; naloxone; LH; FSH; sexual maturation

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N. C. Rawlings and W. R. Ward

Summary. Fetal hypophysectomy performed between 97 and 130 days of gestation caused a significant (P < 0·005) prolongation of pregnancy in 5 goats in which every fetus was treated. Three of these goats gave birth spontaneously. Sham surgery or hypophysectomy of one fetus of twins had no effect on gestation length. Hypophysectomized kids, delivered after prolonged pregnancy, were significantly heavier than normal term kids (P < 0·005) and had lighter adrenals (P < 0·025). Measurements of maternal peripheral plasma concentrations of progesterone and total unconjugated oestrogens showed that the changes in goats carrying hypophysectomized fetuses were similar to those of normal pregnancy except that the prepartum oestrogen peak was absent, whether or not parturition occurred spontaneously.

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A. C. O. Evans, W. D. Currie and N. C. Rawlings

Summary. The pattern and opioidergic control of the secretion of gonadotrophins in prepubertal heifer calves were examined. Ten age-matched Hereford heifer calves were weighed and a blood sample was taken every 2 weeks from 2 to 25 weeks of age and then weekly until 60 weeks of age. At 60 weeks, a fertile bull was introduced and at 75 weeks of age pregnancy diagnosis was performed by transrectal ultrasonography. At 4, 12, 18, 24 and 32 weeks of age, the opioid antagonist naloxone was injected (i.v., n = 5; 1 mg kg−1 body weight) each hour for 12 h. Control heifers received sterile saline at the same ages. Blood samples were collected every 12 min for the 12 h treatment and serum samples were analysed for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Samples taken once every 2 weeks from 2 to 60 weeks were analysed for LH, FSH and oestradiol, and weekly samples were taken for progesterone determination. There was no effect of naloxone on the age at puberty, which was 56·2 ± 0·7 weeks at a body weight of 388·5 ± 8·0 kg. The mean age at conception was 63·4 ± 0·5 weeks. On the basis of samples taken every other week, serum concentrations of LH were high at 10 weeks and between 40 and 60 weeks of age. From the periods of intensive blood collection, the early rise in mean serum concentrations of LH appeared later at 12 and 18 weeks of age and was caused by a rise in LH pulse amplitude. Serum FSH concentrations were increased between 20 and 22 weeks and oestradiol concentrations at 22, 56 and 58 weeks of age. At 4 weeks, naloxone increased mean LH concentrations, pulse amplitude and pulse frequency (P < 0·01) and thereafter only decreased LH pulse amplitude at 18 weeks (P < 0·05) and increased LH pulse frequency at 24 weeks (P < 0·05). The FSH secretion was pulsatile at all ages and naloxone only increased FSH pulse amplitude at 4 weeks.

From these data we conclude that (i) there is an early transient increase in gonadotrophin secretion in prepubertal heifers, (ii) significant opioidergic inhibition of gonadotrophin secretion occurs only in very young heifers and (iii) a decrease in endogenous opioid inhibition of LH secretion, particularly LH pulse amplitude, allows for the early rise in LH secretion.

Keywords: puberty; gonadotrophins; naloxone; heifer

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A. P. Beard, A. C. McRae and N. C. Rawlings

Mink are carnivores of agroforestry fringe habitats and are exposed to pesticides that biomagnify within the food chain. Some pesticides are thought to disrupt reproductive and endocrine functions. In Expt 1, four groups of mink (n = 10) were fed either a control diet, or diets treated with lindane (1 mg kg−1 day−1), carbofuran (0.05 mg kg−1 day−1) or pentachlorophenol (1 mg kg−1 day−1) from before breeding until weaning. Mink were mated twice, at 7–8 day intervals. The treatments had no effect on the proportion of mink accepting the first mating; however, lindane and pentachlorophenol caused a decrease in the percentage of females accepting the second mating. Lindane and pentachlorophenol caused a decrease in whelping rate, although litter size was not affected. Carbofuran had no effect on fertility. Mink that mated only once had a lower whelping rate than mink that mated twice; therefore, it could not be determined whether the decreased whelping rates were due to the lack of a second mating or to increased embryo loss. In Expt 2, two groups of mink (n = 15) were fed a control diet or a diet treated with lindane (1 mg kg−1 day−1) from before mating until weaning. Mink were mated twice on two consecutive days. Lindane did not affect mating response at either mating. Whelping rate, but not implantation rate, was decreased by the lindane treatment. The proportion of embryos lost after implantation (implantation scars not represented by kits at whelping) was increased by the lindane treatment. In conclusion, both lindane and pentachlorophenol decreased fertility in mink, and the lindane effect was primarily a result of embryo mortality after implantation.