The Sertoli cells of the androgen insensitive (tfm) rat are capable of producing androgen binding protein (ABP) both in vivo and in vitro. ABP levels in the tfm testis are significantly higher (P < 0.01) than that in normal littermates (NL); 2.9 ± 0.5 (SD) pmoles/mg protein and 63.7 ± 15 (SD) pmoles/testis in the tfm compared to 0.41 ± 0.07 pmoles/mg protein and 34.3 ± 6.7 pmoles/testis in the NL. However, ABP secretion rate in vitro is significantly lower in the tfm testis than that in the NL testis; 0.12 ± 0.02 (SD) pmol/testis per h and 0.31 ± 0.06 pmol/testis per h respectively. Thus, the increased levels of ABP in the tfm testis does not reflect increased ABP secretion, but is due to the atresia of the excurrent ducts and accumulation of seminiterous tubular secretion. The tfm testes show a higher concentration of FSH receptors than that in NL (171 fmoles/mg protein and 57 fmoles/mg protein respectively). However, when FSH binding is calculated per testis, binding capacities in tfm and NL testis are very similar (632 fmoles/testis and 798 fmoles/testis respectively). The present study shows that normal induction of FSH receptors is not dependent on the presence of an androgen receptor and that production and secretion of ABP is taking place in a situation where the target cells are insensitive to physiological doses of androgen. The reduction in ABP secretion rate in vitro in the tfm rat testis supports previous studies showing that both FSH and androgens are important for normal Sertoli cell function.

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The testis homogenate from Red bull (3-17 months of age) show specific binding of hLH and hFSH with Kd of 1.3 2 0.1 x 10-"'M and 1.5 ? 0.1 x 10-yM, respectively. Prepubertal bulls (3-5 ' /4 months) exhibit the highest binding capacity of both L H and FSH. revealing the fact that L H and FSH receptors are present in high concentrations prior to the first rise in plasma T. The testicular T concentration was significantly higher in the four prepubertal bulls than in the four older animals in spite of the fact that circulating T is lower before puberty. Thus, local androgen effects within the testis may occur before peripheral androgenization. The prepubertal bull Leydig cell also displayed steroidogenic capacity. The ratio of biologically active (testosterone, dihydrotestosterone) to inactive androgens (androstenedione) increased as the animals approached puberty. Such qualitative changes in steroid production may be one of the factors responsible for peripheral androgenization.

Oestradiol-enriched food (25 mg kg 1 oestradiol) fed for 91 days to small eels (2 or 7 g) with undifferentiated gonads (UD) significantly favoured development of gonads with the macroscopic appearance of ovaries (8-gonads) during the next 8 months. Fifty-four and 51% of control eels and 75 and 78% of oestradiol-treated eels developed 8-gonads. Minced porcine testicular tissue fed to 2-g eels for up to 371 days had effects similar to oestradiol-enriched food (68% with 8-gonads), whereas feeding for only 91 days had no effect during the next 8 months. Oestradiol-enriched food was also fed to larger eels with already macroscopically differentiated gonads (30-70 g; 95% with 7-gonads, 5% with 8-gonads). After 27 days significantly more eels with a 8-gonad or with a mixture of ovary-like and testis-like regions in the gonads (7+8-gonads) were found. After 96 days there were 44% with 8-gonads, 40% with 7+8-gonads and 16% with 7-gonads. Oestradiol thus had a feminizing effect, not only on morphologically undifferentiated gonads but also on morphologically differentiated 7-gonads. The presence of sex steroid hormones or their precursors in porcine testicular tissue may also exert a feminizing influence. In all experiments the hormone-fed groups showed a tendency (not significant) towards increased growth rate. In small eels early rapid growth and differentiation of 8-gonads were clearly correlated, both in hormone treated and in control eels. Otherwise no correlation was found between growth rate and gonadal sex. 1996 The Fisheries Society of the British Isles