Changes in pituitary LHRH receptor levels in situations of increased or decreased gonadotrophin secretion in the male rat

Anterior pituitary LHRH receptor numbers were studied by measuring binding of ¹²⁵I-labelled (d-Ser-Bu^t)⁶-des-Gly¹⁰ LHRH ethylamide in male rats in which gonadotrophin output is markedly altered. Rats made hyperprolactinaemic by transplantation of 2 pituitary glands under the kidney capsule 98 days previously had significantly lower pituitary contents and serum levels of LH and FSH than controls, although serum concentrations of testosterone remained within the normal range. Pituitary LHRH receptor numbers in these animals were significantly reduced. A condition of further suppression of pituitary contents and serum levels of LH and FSH was achieved by active immunization against LHRH for one year, which also reduced serum concentrations of testosterone to non-detectable levels. This was associated with a marked reduction in LHRH receptor numbers. In contrast, rats castrated 49 days previously demonstrated the expected marked rise in pituitary content and serum levels of LH and FSH and had a marked rise in the number of pituitary LHRH receptors. Castration of animals with pituitary transplants resulted in a similar response. Rats in which testosterone was neutralized by active immunization also showed an increase in pituitary contents and serum levels of LH and FSH, but these changes were lower than in castrated rats, probably owing to the presence of small amounts of non-antibody-bound testosterone. These animals had only a marginal rise in pituitary LHRH receptor numbers.Our results, showing a lowering in LHRH receptors when hypothalamic LHRH stimulation of the pituitary is thought to be reduced (hyperprolactinaemia and LHRH immunization) and an elevation in receptors when LHRH output is thought to be increased (castration and testosterone immunization), add further support to the view that LHRH regulates its own receptors.     

Depression of nocturnal pineal serotonin N-acetyltransferase activity in castrate male rats

Summary Pineal serotonin N-acetyltransferase (NAT) activity was examined in intact rats, castrated rats, and in rats that had been castrated and had received testosterone proprionate. Castration resulted in significantly depressing nocturnal levels of pineal NAT (p<0.05) when compared to enzyme activity in intact rats. Testosterone proprionate administration restored plasma LH levels to normal values in castrate rats but did not induce nocturnal pineal enzyme activity to levels seen in the pineal glands of intact rats. The data substantiate the existence of a feedback control of pineal biosynthetic activity by the hypophyseal-gonadal system, but the identity of the hormone(s) responsible for regulation of pineal NAT activity is not known.     

Effects of neonatal testicular hormones on preference behaviour in the rat

The effects of neonatal testicular hormones on preference behaviour for an oestrous female rat were investigated. A residential maze was used in which the position of the animals was registered continuously without disturbing them. Two experiments are described. In the first experiment adult male rats which had been castrated within 24 h of birth were given testosterone (T), dihydrotestosterone (DHT) or oestradiol (E2) in a subcutaneous silastic implant. The T- and E2-treated males showed preference for an oestrous female rat over an anoestrous female. The DHT-treated animals showed no interest in a female conspecific, irrespective of her hormonal state. In the second experiment females spayed in adulthood were given a T-containing silastic implant. They showed preference for the oestrous female, like intact males. Removal of the T-implant caused this preference to disappear, while locomotor activity was not affected. It is concluded that neonatal testicular hormones have little effect on adult sociosexual preference behaviour.     

Elimination of stored material from the seminal vesicles of the guinea pig following castration

Experiments were carried out to determine what factors are involved in the disappearance of stored secretion from the seminal vesicles of the giunea pig and in the concurrent decline in weight of these glands following castration. Seminal vesicles of sexually mature males were unilaterally ligated, and the males were either castrated or left testes intact for a 14-day period. At necropsy, the seminal vesicles were removed and weighed, and biopsies were collected for histological inspection. The weight of nonligated vesicles from castrated males declined to less than half that of ligated sides. In testes-intact males, the weight of ligated vesicles was nearly double that of nonligated vesicles. Epithelial cell heights remained unchanged during the study. The rapid decline in weight of the guinea pig seminal vesicles following castration was attributed to the elimination of stored secretion by way of the urethra rather than by absorption.     

Lectin Staining of Rat Testis and Epididymis: Effect of Cyproterone Acetate and Testosterone

Control and castrated (C) adult rats were treated with cyproterone acetate (CA), testosterone (T) or their combination (CA + T) for 15 days and the affinity of the testicular and epididymal tissue for seven rhodamine-conjugated lectins was analysed in fluorescence microscopy. In the testis CA caused the appearance of degenerating cells in the basal part of the seminiferous epithelium. These cells (spermatogonia, early spermatocytes) appear to be the most vulnerable germinal cells to anti-androgen treatment and this effect could be prevented by simultaneous administration of T. Castration caused a marked reduction in lectin staining of principal and light cells of distal caput (Dcp) and distal cauda (Dcd) epididymidis accompanied by the disappearance of the intratubular sperm mass. In castrated animals CA caused a moderate and T as well as CA + T a marked increase in the stainability of these cells and the appearance of homogeneous secretory material in the tubules. This material gave moderate or strong affinity for most of the lectins. Some minor differences were found in the staining pattern of the cells and the secretory material in Dcp and Dcd as well as after different treatments. This is consistent with local and qualitative differences in the epididymal secretory and absorptive activity, which can be further modified by the hormonal milieu.     

A STUDY OF THE EFFECTS OF STEROIDS ON α-ADRENOCEPTOR-MEDIATED CONTRACTION OF THE RAT VAS DEFERENS

1. Testosterone propionate (0·5 mg/day) administered for 5 weeks to prepubertal rats increased the weight of sex accessory organs but did not alter the rate of gain of body weight. Methandienone, given in a similar dosage regimen, was without effect on these parameters. The synthetic progestagen, norgestrel, administered orally in a dose of 0·5 mg/day increased the weight of the vas deferens but was without effect on seminal vesicle and testis weights and on the growth rate. Given in combination with testosterone, norgestrel caused a marked decrease in testis weight and reversed the effects of testosterone propionate on seminal vesicle weight. Thus, in the dosage regimen used, this progestagen exhibited an endocrine profile comprising androgenic, synandro-genic and anti-androgenic effects. 2. Rats, which were castrated when they weighed 70–80 g, exhibited rates of gain of body weight which were similar to those of control animals. Testosterone propionate in the doses used reversed castration-induced atrophy of the vas deferens and seminal vesicle. 3. The contractility of the vas deferens of intact rats, determined by direct field electrical stimulation, was unaffected by treatment with the steroids used in this study. However, there was a marked impairment of the contractility of the vas deferens following castration, which was not fully restored by testosterone propionate in the dosage regimen used. 4. The efficacies and potencies of the α-adrenoceptor agonists phenylephrine and 1-metaraminol in causing contraction of the vasa deferentia from intact rats were unaffected by the steroid treatments. In contrast, these agonists did not produce sustained, dose-dependent contractions of the vasa deferentia from castrated rats; however testosterone propionate fully restored the efficacy and potency of both agonists. 5. It is concluded from this study that although adequate testosterone levels are necessary for the maintenance of contractility in the rat vas deferens, the integrity of postjunctional adrenoceptors in not modified by a variety of steroid treatments.     

大豆异黄酮在低雌激素环境下对MMTV-erbB-2转基因小鼠的作用

目的探讨大豆异黄酮在低雌激素环境下对MMTV-erbB-2转基因小鼠乳腺肿瘤发生、发展的影响。方法 MMTV-erbB-2转基因雌性小鼠90只,分为3组,每组30只。60只行卵巢摘除术使MMTV-erbB-2转基因小鼠体内形成低雌激素环境,分别使用含大豆异黄酮饲料(大豆异黄酮组)和普通饲料(普通饲料组)喂养。另30只为对照组,用普通饲料喂养。观察乳腺肿瘤的潜伏期及发生情况,用免疫组织化学法观察各组乳腺组织的雌激素受体、孕激素受体、增殖细胞核抗原的表达情况。结果大豆异黄酮组肿瘤潜伏期较其他2组明显缩短,增殖细胞核抗原表达水平较其他2组高(P<0.05)。3组雌激素受体、孕激素受体表达情况比较差异无统计学意义(P>0.05)。结论在低雌激素环境下,大豆异黄酮对MMTV-erbB-2转基因小鼠乳腺肿瘤的发生、发展起促进作用。