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P. M. Collins and W. N. Tsang

Summary. The ability of testicular steroids to maintain the quantitative aspects of spermatogenesis was compared with reference to their androgenic properties. Hypophysectomized rats were injected daily with 0·2 mg progesterone, 20α-dihydroprogesterone, 3β-hydroxy-5α-pregnan-20-one, testosterone or testosterone propionate for 30 days beginning 2 days after the operation. Testosterone propionate was the most potent steroid tested both in terms of its peripheral androgenic effects and its ability to prevent the post-operative decline in the weight of the testis and seminiferous tubules and the numbers of germ cells throughout their differentiation. The natural androgen, testosterone, exhibited weak gametogenic properties and only partly maintained the normal measures of spermatogenesis. Progesterone exhibited low intrinsic androgenic potency yet was significantly more effective than testosterone in maintaining spermatogenesis; it prevented the degeneration of spermatocytes during the later stages of meiotic prophase and the reduction divisions resulting in an increased yield of step 7 spermatids. Low androgenic and gametogenic properties were exhibited by 20α-dihydroprogesterone and 3β-hydroxy-5α-pregnan-20-one. These results may indicate that testosterone produced locally in the seminiferous tubules from progesterone is more effective in maintaining spermatogenesis than androgens entering from the circulation. Alternatively, progesterone may act more directly on the germ cells than previously envisaged.

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P. M. Collins, W. P. Collins, A. S. McNeilly and W. N. Tsang

Summary. Rats were treated by exposure of the scrotum to a temperature of 43°C for 30 min or bilateral ligation of the vasa efferentia and bled at 0, 3, 7, 14 and 21 days after treatment. In heat-treated rats FSH levels rose linearly from pretreatment levels while those in efferentiectomized animals remained unchanged for 3 days before increasing. In both groups FSH concentrations reached similar maximum values after 7 days and were significantly higher than those of intact controls at 7, 14 and 21 days. LH levels, although not generally different from those in the controls, rose from pretreatment levels in parallel with FSH. No differences were found in testosterone concentrations in any of the groups. Histological examination at 3 weeks after treatment confirmed that the germinal epithelium consisted mainly of spermatogonia and Sertoli cells. The cytological appearance and lipid content of the Leydig cells of the aspermatogenic testes were indistinguishable from those of the controls and the weight and histological appearance of the accessory sex organs and the fructose content of the coagulating glands were also normal. It is concluded that the sterilizing effects of heat treatment and efferentiectomy are independent of changes in Leydig cell function and that the increase in gonadotrophin levels is related to the germ cell degeneration.

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W. N. TSANG, P. M. COLLINS and D. LACY

Androgens are capable of maintaining the progressive development of the germ cells in immature male rats which have either been hypophysectomized (Leathem, 1944; Ludwig, 1950; Lostroh, 1969) or treated with compounds which interfere with the release and/or secretion of gonadotrophins (Ludwig, 1950; Kalra & Prasad, 1967; Steinberger & Steinberger, 1969). Similar results have also been obtained in adult male rats (Boccabella, 1963; Clermont & Harvey, 1967; Lacy & his co-authors, 1969). Studies on steroid metabolism in vitro by isolated seminiferous tubules of rats denuded of their germ cells by heat-treatment has led to the view that not only Leydig cells but also Sertoli cells may be a major source of androgens (Collins, Bell & Vinson, 1968; Lacy et al., 1969). Similar conclusions have also been reached by Ellis & van Kampen (1971) from studies on

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W. N. TSANG, D. LACY and P. M. COLLINS

Several workers have studied various parameters as an index of Leydig cell differentiation and attempted to correlate them with the growth of the accessory sex organs. In the prepuberal rat, little correlation seems to have been achieved (see Niemi & Ikonen, 1963; Clegg, 1966). Others have examined testosterone production in vitro by the immature testis and attempted to correlate this with the increase in weight of the seminal vesicles and prostate gland. In this connection, a good deal of attention has been paid to the production of testosterone in vitro and its apparent regulation by 5α-reductase activity. Nayfeh, Barefoot & Baggett (1966) reported an increase in testosterone production per unit weight of tissue at about the time of sexual maturity and suggested that this might be due mainly to reduced metabolism to 5α-androstane-3α,17β-diol (androstanediol). Inano, Hori & Tamaoki (1967) found a remarkable increase in the activity of various enzymes

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M. J. Kilpatrick, J. R. Newton and W. P. Collins

Summary. Isolated pituitary glands from adult male rats were maintained in a continuous flow system. Gn-RH (1000 pmol/ml) caused a characteristic release of cyclic AMP, LH and FSH. Cyclic AMP (1000 nmol/ml) liberated a similar amount of both gonadotrophins. Theophylline (1 mmol/ml) enhanced the effect of cyclic AMP by 21% for LH and 41% for FSH. The infusion of oestradiol (184 pmol/ml) alone or before Gn-RH infusion did not produce a significant effect on the secretion of either gonadotrophin or cyclic AMP. In contrast, there was a significant reduction in the amount of LH (P < 0·025) and FSH (P < 0·05) released by pituitaries infused with oestradiol and cyclic AMP.

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M. J. Kilpatrick, W. P. Collins and J. R. Newton

Summary.

A continuous flow system has been developed to study the endocrine functions of isolated organs. The procedure has been used to investigate the effect of a synthetic gonadotrophin-releasing hormone (Gn-RH) upon the anterior pituitary gland of the adult male rat. A Radiometer blood gas/pH analyser was used to monitor the pH and partial pressures of oxygen and carbon dioxide in the perfusion medium. A series of six experiments with four pituitaries per flask established that the rate of gonadotrophin release under basal conditions was 646±301 (S.D.) ng LH/ml and 404±124 (S.D.) ng FSH/ml. The duration and intensity of the response to Gn-RH was assessed by measuring the areas under the curves according to the trapezoidal rule. A significant increase in the release of FSH and LH was obtained by the administration of 250 ng Gn-RH/ml medium, and dose-response curves were produced for up to 10 μg/ml.

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J. P. P. Tyler, P. L. Matson, W. P. Collins and M. Dukes

Summary. Treatment of mice with a dihydropyridazinone derivative (6-(4′-aminophenyl)-4,5-dihydro-5-methylpyridazin-3-one; ICI 109,081) inhibited the maturation of oocytes in the presence of gonadotrophins without affecting ovulation. The spontaneous resumption of meiosis in oocytes cultured in vitro was reversibly inhibited. ICI 109,081 may therefore be useful for evaluating the relationship between follicular development and the resumption of meiosis.

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M. E. Wilson, T. P. Gordon, M. S. Blank and D. C. Collins

Summary. A comparison of the age and season at first parturition was made for spring-born female rhesus monkeys and for females born in the fall to mothers who had been laboratory-housed before being transferred outdoors. Females (N = 9) born during the fall had first parturition during the spring and summer, as did all spring-born females (N = 68), and not during the fall as would be predicted if age were the determining factor. A separate analysis of post-menarchial, spring-born females (N = 5) beginning in September at 29 months of age revealed that the ensuing 12 months were characterized by low serum levels of oestradiol (< 50 pg/ml), progesterone (< 1·0 ng/ml), LH (< 7·0 ng/ml), and FSH (< 5·50 μg/ml). First ovulation subsequently occurred in the fall in all subjects at a mean age of 41 ·9 ± 0·1 months, and was preceded by significant elevations in basal LH and FSH, coincident in time with the transition of summer to fall (September). Female copulatory behaviour was restricted to the period surrounding first ovulation, beginning some 2 weeks before and ceasing within 3 days after the oestradiol peak. The most rapid gain in weight occurred during the summer months before first ovulation, and was associated with significant elevations in serum GH and prolactin. These data suggest that season may influence the timing of sexual maturation in rhesus monkeys kept outside in such a way that the occurrence of first ovulation is restricted to the fall and winter months.

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K. P. McNatty, N. L. Hudson, F. Collins, M. Fisher, D. A. Heath and K. M. Henderson

Summary. The plasma concentrations of FSH and LH were measured in ovariectomized Booroola FF and ++ ewes before and after treatment with subcutaneous implants of oestradiol-17β (0, 2 or 8 cm Silastic capsules; 5 ewes/genotype per dose) or progesterone (0, 1 or 3 Silastic envelopes; 5 ewes/genotype per dose) or subcutaneous injections of steroid-free bovine follicular fluid (bFF; 0, 0·5, 1·0, 2·5 or 5 ml; 4 ewes/genotype per dose). During the first 50 h after implantation of oestradiol or progesterone, or the first 24 h after bFF treatment, the FSH and LH concentrations in plasma were not different between the genotypes although there were significant effects of the steroids and bFF with respect to dose (P < 0·05). At 6 days after steroid implantation, no gene-specific effects were noted for the plasma concentrations of FSH although significant effects of dose of oestradiol (P < 0·01) but not progesterone were noted. Also at 6 days after steroid implantation, no gene-specific differences in the pulsatile patterns (i.e. peak frequency or amplitude) of plasma LH concentrations were noted although there were significant effects of steroid dose (P < 0·05) on frequency and/or amplitude.

It is concluded that the higher ovulation-rate in FF than ++ Booroola ewes is unlikely to be due to gene-specific differences in the sensitivity of the hypothalamic– pituitary axis to ovarian hormones.

Keywords: Booroola ewes; oestradiol-17β; progesterone; bovine follicular fluid; FSH; LH; ovariectomy

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K. P. McNatty, N. L. Hudson, M. Gibb and F. L. Collins

Summary. A significant increase in the plasma concentrations of FSH (P < 0·05) and LH (P < 0·001) was observed during the luteal (Days 9–11) phase but not during the subsequent cloprostenol-induced follicular phase in androstenedione-immunized ewes compared to those in control ewes. Over the same time period the geometric mean (and 95% confidence limits) androstenedione antibody titres in the immunized ewes was 1/305 (1/158, 1/590) whereas they were not detectable in the controls. In the subsequent cycle, the ovulation rates were 1·6 ± 0·2 for the immunized ewes and 1·1 ± 0·1 for the control ewes (P < 0·05) and the luteal progesterone concentrations were significantly higher in the immunized ewes compared to the controls (P < 0·01). Collectively, these results suggest that active immunization against androstenedione leads to an increase in the plasma concentrations of both FSH and LH. The results are consistent with the hypothesis that FSH plays a central role in determining the ovulation rate in sheep.

Keywords: FSH; androstenedione immunization; sheep; ovulation rate