Dogs of different ages without testicular diseases were evaluated to study possible age-related changes in hormone concentrations in serum. Dogs with testicular tumours were also investigated to study the relation between tumour type and hormone concentrations; in this study, dogs with Sertoli cell tumours, Leydig cell tumours and seminomas were included. We measured testosterone, oestradiol, LH, FSH and inhibin-like immunoreactivity concentrations in peripheral venous and testicular venous blood of these animals. In normal dogs there appeared to be no age-related changes in the concentrations of the investigated hormones, except for a significant age-related decrease in oestradiol concentrations in testicular venous blood (P<0.02). Dogs with a Sertoli cell tumour had greater oestradiol concentrations and inhibin-like immunoreactivity in both peripheral and testicular venous blood than did dogs without a neoplasm (P<0. 05). Testosterone concentrations were reduced in dogs with Sertoli cell tumours, as were FSH and LH. Feminisation occurred in eight of 13 dogs with a Sertoli cell tumour and in two of 14 dogs with a Leydig cell tumour; it was accompanied by a significantly greater oestradiol concentration than in normal dogs and in dogs with Sertoli cell tumours without signs of feminisation. Dogs with a Leydig cell tumour had greater concentrations of oestradiol and inhibin-like immunoreactivity in both peripheral venous and testicular venous blood than did dogs without a neoplasm (P<0.05). The testosterone concentration in testicular venous blood of these dogs was lower than that in dogs with normal testes. The concentration of LH in peripheral venous blood was also reduced (P<0. 05). Hormone concentrations in dogs with a seminoma were not different from those in normal dogs. It was concluded that seminomas are not endocrinologically active. In contrast, both Sertoli cell tumours and Leydig cell tumours can cause increased oestrogen production leading to signs of feminisation. These tumours also have considerable amounts of inhibin-like immunoreactivity, but only in Sertoli cell tumours does this result in a reduction in FSH concentrations, suggesting that Sertoli cell tumours secrete dimeric inhibin, whereas Leydig cell tumours presumably produce loose alpha-subunits that cross-react in the inhibin assay but are not biologically active.

This study aimed to investigate the time course of disappearance of the mRNAs of the various subunits of inhibin in follicles which become atretic. An animal model was used in which atresia of preovulatory follicles could be studied in a chronological order. Injection of gonadotrophin-releasing hormone (GnRH) antagonist (20 microg) at the morning of pro-oestrus (P) blocked ovulation and the 10-12 preovulatory follicles became gradually atretic. A second injection was given the next day to prevent delayed ovulation. The rate of atresia could be delayed by simultaneous administration of a subovulatory dose of human chorionic gonadotrophin (hCG) (0.5 IU) and could be advanced by administration of a fivefold larger amount of GnRH antagonist. Functional activity of follicles becoming atretic was studied by measuring oestradiol production after incubation of individual follicles for 4 h. Follicles isolated 24 h after the first injection of GnRH antagonist (P+24) already secreted significantly less oestradiol in vitro than follicles isolated at pro-oestrus, although they were morphologically not different from pro-oestrous follicles. Follicles isolated at P+24 from hCG-treated rats secreted more oestradiol compared with follicles from rats not treated with hCG. In contrast, follicles isolated at P+24 from rats that were given a fivefold larger amount of GnRH antagonist secreted less oestradiol. Once this model was validated, temporal changes in inhibin subunit mRNAs in follicles undergoing atresia were measured by in situ hybridization and RNase protection assay. In situ hybridization showed abundant alpha- and betaA-subunit mRNA in the whole granulosa layer of preovulatory follicles at P and P+24, while betaB-subunit mRNA was restricted to the antral layer and cumulus. At P+48 the amount of alpha- and betaA-subunit mRNA had declined and was restricted to the cumulus, whereas betaB-subunit mRNA was absent. In the atretic follicles present at P+72 and P+96, mRNAs of all three inhibin subunits were absent. Administration of 0.5 IU hCG delayed the decline in the amount of alpha, betaA and betaB mRNA in preovulatory follicles at P+48. RNase protection assay of inhibin subunits in isolated follicles revealed no changes between P and P+24. However, at P+48, the mRNAs of alpha- and betaA-subunits were decreased. Expression of the mRNA of betaB-subunit declined gradually from P to P+48. The present study demonstrates that in follicles which are becoming atretic, mRNAs of alpha- and betaA-subunits decline simultaneously with the appearance of pycnotic cells in the granulosa layer, while betaB-subunit mRNA declines earlier, simultaneously with the decrease in the ability to secrete oestradiol in vitro.

Recent studies have revealed that TRH-like immunoreactivity (TRH-LI) in human serum is predominantly pGlu-Glu-ProNH2 (< EEP-NH2), a peptide previously found in, among others tissues, the pituitary gland of various mammalian species. In the rat pituitary, < EEP-NH2 is present in gonadotrophs and its pituitary content is regulated by gonadal steroids and gonadotrophin-releasing hormone (GnRH). Hence, we reasoned that < EEP-NH2 in human serum may also arise, at least in part, from the pituitary, and that its secretion may correlate with that of gonadotrophins. Therefore, blood was simultaneously sampled from both inferior petrosal sinuses, which are major sites of the venous drainage of the pituitary gland, and a peripheral vein from seven patients with suspected adrenocorticotrophin-secreting pituitary tumours. In addition, in six postmenopausal and six cyclic women, peripheral vein blood was collected at 10-min intervals for 6 h, then a standard 100 micrograms GnRH test was performed. In the sera, TRH-LI was estimated by RIA with antiserum 4319, which binds most tripeptides that share the N- and C-terminal amino acids with TRH (pGlu-His-ProNH2). In addition, LH and FSH were measured in these sera by RIA. In the blood samples taken at 10-min intervals, an episodic variation in serum TRH-LI was noted and pulses of TRH-LI were detected at irregular intervals (from one to six pulses per 6 h) in five postmenopausal and six cyclic women. In general, these pulses did not coincide with those of LH and FSH, suggesting that TRH-LI is not co-secreted with gonadotrophins. Moreover, unlike LH and FSH, serum TRH-LI did not increase during the menopause or after exogenous administration of GnRH. Whereas gonadotrophin concentrations were significantly greater in the inferior petrosal sinus than in peripheral serum, there were no differences in TRH-LI concentrations between these serum samples. In conclusion, serum TRH-LI in humans seems not to be regulated by gonadal steroids or GnRH. Moreover, serum derived directly from the pituitary contained no more TRH-LI than did peripheral serum, which suggests that the human pituitary gland does not secrete significant amounts of < EEP-NH2, and therefore does not contribute significantly to serum TRH-LI concentrations. Further research is required to identify the site of origin of < EEP-NH2 in human serum.