The recent observation by Schally & co-authors (1971) that the release of both LH and FSH is dependent upon the one`r eleasing' hormone (LH-RH) has made the study of the hypothalamus\p=m-\pituitary\p=m-\testis axis much more complex. Furthermore, the normal maintenance of both spermatogenesis and testosterone secretion depends upon LH and FSH acting synergistically. It may, therefore, be surmised that there is no absolute specificity of gonadal steroids or other substances in the regulation of secretion of gonadotrophins.Nevertheless, FSH and LH secretion appear to be dissociated in certain pathological conditions. When the Leydig cells are normal but the germinal epithelium has been damaged or destroyed, as after irradiation, certain viral infections, the administration of anti-fertility agents or in idiopathic infertility, the LH levels stay within the normal range whilst those for FSH are elevated (Franchimont, 1966(Franchimont, , 1971(Franchimont, , 1972Paulsen et al., 1968;Rosen & Weintraub, 1971;de Kretser et al., 1972;Leonard et al., 1972; van Thiel et al., 1972).It is intended in this paper to examine the basal secretion of the gonado¬ trophins (mainly LH and to a lesser extent FSH) and the response in males to administration of steroids and LH-RH, and also the relationship between spermatogenesis and gonadotrophins. EFFECT OF ANDROGENS ON GONADOTROPHINSIt is well accepted that the administration of testosterone to males is followed by a decrease in plasma LH levels. The effects on FSH, however, are controversial ( Table 1). The reasons for the conflicting results obtained using virtually the same amounts of testosterone propionate (TP) are obscure. They may reflect the differences in the number of subjects studied, the route of administration, the action of sex hormone-binding protein and/or the particular radioimmuno¬ assay used for FSH determination.In general, TP administered in small doses preferentially suppresses serum LH as compared to serum FSH (Dufy-Barbe & Franchimont, 1972;Swerdloff et al., 1972;Demoulin et al., 1973;Stewart-Bentley et al., 1974). For example, when five normal men were treated intramuscularly with 50 mg TP daily for 5 days, plasma LH levels were lowered but FSH was not affected. The release of FSH and LH is unaffected by the administration of TP if 25 µg LH-RH are given intravenously before treatment (see Text- fig. 1). These results are in agreement with those of von zur Mühlen & Kobberling (1973) who have shown that four intramuscular injections of 100 mg TP for 1 week significantly decreas-335

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A simple, short procedure for the isolation of inhibin from bull seminal plasma has been described. Following conversion of the seminal plasma into acetone powder, it was subjected to gel filtration on Sephadex G-100 using 4 m urea\p=m-\0.05 m sodium acetate buffer pH 4.0 as the eluent. Further purification of the active fraction was achieved by 'straight elution analysis' using CM-cellulose. The final preparation (UX) has been shown to reduce the response of immature rat ovaries to human chorionic gonadotrophic hormone (HCG) stimulation in the bioassay system of Chari et al. (1976) and also been shown to suppress the immediate post-castration rise in serum gonadotrophin levels in immature male rats. Homogeneity of the isolated fraction has been assessed electrophoretically at different pH's above and below its isoelectric point. On the basis of gel filtration studies, electrophoresis and amino acid analysis, the molecular weight of UX has been estimated to be 19 000 daltons. The electrophoretic behaviour of UX at an alkaline pH has been discussed as a possible evidence for its existence as isohormones.

A bioassay for inhibin, based on a dose-dependent suppression of HCG-induced ovarian weight increase in intact, immature female rats, is described. The method is specific and has acceptable sensitivity and precision such that it lends itself to statistically valid quantitative assay of inhibin activity. Being a 24-hour assay, it is conveniently and rapidly performed as well as being a multiple bioassay for estimating potencies of various preparations.

As a simplification of the in vitro fertilization (IVF) procedure, repeated sonographic scanning of follicular diameters in stimulated cycles was performed, until the largest visible follicle reached a mean diameter of at least 20 mm, at which time human chorionic gonadotropin (hCG) was administered. Follicle puncture was performed either guided by sonography or by laparoscopy 34-36 hr after the hCG injection, and following insemination oocytes were cultured for 48-60 hr before embryo transfer (ET). Serum levels of luteinizing hormone (LH), prolactin (PRL), and estradiol-17 beta (E2) at the time of hCG injection as well as follicular fluid levels of follicle stimulating hormone (FSH), LH, and PRL as well as progesterone (P), testosterone (T), and E2 at the time of puncture were determined in retrospect using specific radioimmunoassay (RIA). It was found that the knowledge of a single value of LH or E2 in serum should have been of little additional value for the decision to give hCG in all stimulation models used: clomiphene + hCG, human menopausal gonadotropin (hMG) + hCG, and clomiphene + hMG + hCG. The concentrations of the three steroids measured in follicular fluid were, in a high proportion of the follicles, within a normal range in all stimulation models. The group receiving clomiphene + hMG + hCG appeared promising through its higher proportion of estrogenic follicles. It is concluded that sonographic measurement of follicular diameters may be used as the sole index of follicular maturity in an IVF program.(ABSTRACT TRUNCATED AT 250 WORDS)