SUMMARY

The influence of steroids on the specific activities of glycolytic enzymes was studied in the caput and cauda epididymidis of the rat. In castrated animals, increases in enzyme activities were induced by the administration of androgenic steroids whilst oestradiol and progesterone were without effect. On the other hand, the 'antiandrogenic' steroid, cyproterone acetate (16 mg/kg per day for 2 weeks) did not cause a decrease in enzyme activities when administered to animals with ligated efferent ducts. Not all glycolytic enzymes responded to androgens, but more enzymes responded in the caput than in the cauda epididymidis. Administration of testosterone propionate to castrated animals demonstrated that maximum enzyme activity was produced at a dose of 0·1 mg/kg per day whilst higher doses were required to achieve maximum weight of the epididymis, seminal vesicles and prostate. Following castration of animals with ligated efferent ducts, no changes in enzyme activities were observed for approximately 2 days, but then activities declined over the next 2 weeks. When testosterone propionate was administered to castrated animals, a similar lag of approximately 2 days occurred before enzyme activities began to increase.

SUMMARY

The influence of androgens on the male accessory glands of the rat was assessed in terms of changes in weight and of the specific activity of the mitochondrial enzymes, succinate dehydrogenase, glycerolphosphate dehydrogenase and pyruvate carboxylase, in the epididymis. In some instances, the activity of the cytoplasmic enzymes, hexokinase and phosphofructokinase, was also measured and the influence of androgens on these enzymes was found to be similar to that on the mitochondrial enzymes. After the administration of androgen to castrated rats the specific activity of enzymes reached a new steady state sooner than did epididymal weight. The time taken for the specific activity of the enzymes to reach a new steady state after the removal of androgen was variable, depending on the enzyme and the region of the epididymis. This time was generally longer, however, than the time taken for induction, and in the case of glycerolphosphate dehydrogenase, the decline of activity was slower in the cauda than in the caput. In castrated animals, about 100 times as much androgen was required to attain maximum tissue weight as was required to attain maximum enzyme activity. The epididymis, prostate and seminal vesicles responded similarly to androgen in terms of the dose–response pattern and the time taken for tissue weight to attain a new steady-state value, although the gain in weight of the epididymis relative to its weight in unstimulated control animals was less than the relative gain of the other accessory glands. Enzymes in the cauda epididymidis required lower amounts of androgen to elicit maximum activity than were required by those in the caput. The rate of change in the accessory glands in attaining new steady-state levels of tissue weight and enzyme activity was independent of the dose of androgen except during the first few days of hormone administration. Androgens were the most effective steroids in stimulating an increase of tissue weight and enzyme activity, although some changes were induced by oestradiol-3-benzoate and progesterone.

SUMMARY

Preventing the entry of testicular secretions into the epididymis by ligating the efferent ducts resulted in reduced epididymal weight and an alteration in the distribution of carnitine throughout the segments. The metabolic activity of the distal regions of the duct was unaffected by ligation but some changes were apparent in more proximal regions, particularly in the initial segment. Inhibition of spermatogenesis by the administration of busulphan resulted in a loss of weight of the caput epididymidis similar to that caused by ligation of the efferent ducts, even though testicular fluid was not prevented from entering the epididymis. Treatment with busulphan also led to a reduction in androgen-binding protein (ABP) and to a lower activity of pyruvate carboxylase in the caput. Ligation of the efferent ducts in busulphan-treated animals prevented the entry of testicular fluid into the epididymis as judged by the absence of ABP. Despite the absence of ABP, and hence any androgens normally associated with it, there was no appreciable change in the activity of androgenregulated enzymes, indicating that sufficient androgen was reaching the epididymis by way of the peripheral circulation. However, the results suggest that, in addition to androgens, the testis normally produces some other component(s), possibly associated with spermatozoa, which are required for full maintenance of the weight of the epididymal duct and of metabolic activity in the more proximal regions.

Adult sheep which had been castrated either before or after puberty were treated with a variety of steroids. The administration of testosterone propionate, oestrone, oestradiol-17β or diethylstilboestrol to animals castrated before puberty caused them to mount oestrous ewes. Oestradiol-17α was less effective than these hormones in this regard, whilst oestriol, hexoestrol and 5α-dihydrotestosterone were ineffective. The response to oestradiol-17β was not altered by the concurrent administration of dexamethasone to block the pituitary–adrenal axis which suggests that oestradiol-17β was not exerting its effect indirectly by causing the release of adrenal steroids. When 5α-dihydrotestosterone was administered in conjunction with oestradiol-17β intromission and ejaculation were observed in addition to mounting behaviour.

When rams were castrated as adults their mating behaviour slowly declined over the course of 2 years. After this time, mounting behaviour was rapidly restored by the administration of oestradiol-17β but not by 5a-dihydrotestosterone. These results are consistent with the hypothesis that oestrogens are the ultimate agents responsible for promoting mating behaviour in male animals and hence aromatizable androgens, such as testosterone, are effective whereas non-aromatizable androgens, such as 5α-dihydrotestosterone, are not.

ABSTRACT

Castrated sheep were used to study the effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. In the first experiment serum LH and FSH concentrations were determined in intact rams, recently castrated (2 days and 3 weeks) and long-term castrated animals (> 2 years, wethers) during intravenous testosterone infusion at physiological and supraphysiological levels. In intact rams, testosterone infusions effectively suppressed serum LH whilst FSH levels were suppressed only after prolonged infusion at the supraphysiological dose. Recently castrated sheep, which had higher gonadotrophin levels than intact rams, were less sensitive to testosterone feedback. Neither rate of testosterone infusion had any effect on the raised gonadotrophin levels in wethers. In a second experiment gonadotrophin concentrations and mating behaviour were determined in wethers bearing subdermal polydimethylsiloxane implants of testosterone, dihydrotestosterone and oestradiol. Testosterone implants stimulated mating behaviour in all wethers but suppressed gonadotrophins in only a proportion (three out of seven) of the animals. Both oestradiol and dihydrotestosterone suppressed LH and FSH in all wethers, whilst oestradiol, but not dihydrotestosterone, also stimulated mating behaviour. The present findings indicate that testosterone imposes continuing negative feedback on gonadotrophin secretion and that changes in the gonadotrophin regulatory system, which lead eventually to a loss in sensitivity to testosterone feedback, develop soon after gonadectomy. The results also provide the first direct evidence that long-term gonadectomy in male sheep has differential effects on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. A loss in sensitivity to testosterone feedback in castrated animals may involve a lesion in 5α-reductase, the enzyme required for conversion of testosterone to dihydrotestosterone.

J. Endocr. (1985) 104, 69–75

Abstract

In order to investigate the ontogeny of gonadal inhibin production in the male fetal sheep, testes were collected from male fetuses at days 70, 100, 130 and 140 of gestation (term=145 days). The expression and localization of inhibin α- and inhibin β_A-subunit mRNA and protein were evaluated using in situ hybridization and immunocytochemistry. The expression of inhibin α-subunit mRNA was localized within the seminiferous cords of the developing fetal testis and progressively increased with gestational age. Immunostaining corresponding to immunoreactive inhibin α-subunit was detected in Sertoli cells within the seminiferous cords at days 100, 130 and 140 of gestation. In addition, immunostaining was detectable in a small proportion of Leydig cells. No expression of inhibin β_A-subunit mRNA or immunoreactivity was detected in any testicular tissue at any stage of gestation. These data show that the Sertoli cells of the developing fetal sheep testis have the capacity to produce inhibin α-subunit by day 100 of gestation and that production increases during late gestation.

Journal of Endocrinology (1995) 145, 35–42

The liver is a major metabolic and endocrine organ of critical importance in the regulation of growth and metabolism. Its function is determined by a complex interaction of nutritionally regulated counter-regulatory hormones. The extent to which hepatic endocrine sensitivity can be programed in utero and whether the resultant adaptations persist into adulthood is unknown and was therefore the subject of this study. Young adult male sheep born to mothers that were fed either a control diet (i.e.100% of total live weight-maintenance requirements) throughout gestation or 50% of that intake (i.e. nutrient restricted (NR)) from 0 to 95 days gestation and thereafter 100% of requirements (taking into account increasing fetal mass) were entered into the study. All mothers gave birth normally at term, the singleton offspring were weaned at 16 weeks, and then reared at pasture until 3 years of age when their livers were sampled. NR offspring were of similar birth and body weights at 3 years of age when they had disproportionately smaller livers than controls. The abundance of mRNA for GH, prolactin, and IGF-II receptors, plus hepatocyte growth factor and suppressor of cytokine signaling-3 were all lower in livers of NR offspring. In contrast, the abundance of the mitochondrial protein voltage-dependent anion channel and the pro-apoptotic factor Bax were up regulated relative to controls. In conclusion, maternal nutrient restriction in early gestation results in adult offspring with smaller livers. This may be mediated by alterations in both hepatic mitogenic and apoptotic factors.