The function of oestradiol and its receptor in the rat testis

The testis consists of 2 different tissues i.e. the interstitial tissue, which is the site of steroidogenesis, and seminiferous tubules where spermatogenesis occurs. Testosterone production takes place in the Leydig cells of the interstitial tissue and is under the influence of the tropic hormone LH. The action of LH is initiated by interaction with specific receptors located on the cell membrane of the interstitial cells. Binding to the receptor leads to a stimulation of cAMP production and this in turn leads to an activation of cAMP dependent protein kinases. The obligatory function of cAMP in the stimulation of testosterone production can be questioned since cAMP production is undetectable with doses of LH which result in maximum steroidogenesis. The role of protein kinase seems more clear since a correlation exists between protein kinase activation and stimulation of testosterone production. The involvement of protein synthesis in the mechanism of action of LH was confirmed by the discovery of the synthesis of a specific protein after LH stimulation and the inhibition of testosterone production by protein synthesis inhibitors

Effects of Oestrogens and FSH on LH Stimulation of Steroid Production by Testis Leydig Cells from Immature Rats

Hypophysectomy of immature male rats results after 5 days in a decreased production of testosterone by isolated testis Leydig cells in response to LH. The LH responsiveness of the Leydig cells can be partly restored by treatment of the hypophysectomized rats with FSH. In continuation of previous reports on this subject (Steroids 28 (1976) 847; and 30 (1978) the following conclusions were derived from the results in the present paper: 1. After hypophysectomy of immature male rats the production of testosterone (T) as well as of 5‐pregnenolone (Δ5P) by isolated Leydig cells in response to LH is reduced. 2. Daily administration of FSH after hypophysectomy restores the Δ5P production in response to LH almost completely, but has a much smaller effect on the restoration of T production. 3. Administration of oestradiol benzoate (E2B) together with FSH has no effect on the restoration of LH‐stimulated Δ5P production, but causes a reduction of T production, when compared with Leydig cells from animals treated with FSH only. 4. Treatment of intact immature rats with E2B results in a decreased production of T and an increased production of Δ5P in isolated Leydig cells. 5. From experiments with labelled pregnenolone it appears that E2B and diethylstilboestrol (DES) inhibit the 17α‐hydroxylase activity of Leydig cells from intact as well as from hypophysectomized rats. This results in a reduced conversion of pregnenolone to C1:)‐steroids and in increased production of 3α‐hydroxy‐5α‐pregnan‐20‐one from δ5P. 6. The observed effects of FSH and E, were similar within a dose range of 100–10000 ng LH per 106 Leydig cells. Copyrigh

Follicle-stimulating hormone-stimulated secretion of an immunoreactive 29 kDa inhibin α-subunit complex, but not of 32 kDa bioactive inhibin, from cultured immature rat Sertoli cells

The medium of cultured Sertoli cells from immature rat testes contains 29 and 32 kDa proteins, which are recognized by an antiserum against the 22 N-terminal amino acids of the inhibin α-subunit. These proteins were detected by immunoprecipitation of labelled proteins after incubation of Sertoli cells with [35S]methionine, and by Western blotting. The amount of the 32 kDa protein was not affected by the addition of follicle-stimulating hormone (FSH) to the culture medium of the Sertoli cells, whereas FSH induced a large increase of the amount of the 29 kDa protein. Finally, the 29 and 32 kDa proteins in the medium from control and FSH-stimulated Sertoli cells were separated by sodium dodecyl sulfate-polyacrylamide electrophoresis, and inhibin bio- and immunoactivity were determined in eluates of the slices of the gel. Equal amounts of bioactivity were found in control and FSH-stimulated samples at 32 kDa, while the amount of immunoactivity at 29 kDa was increased; no bioactivity was detected in the eluates of these slices. It is concluded that FSH stimulates the secretion of a 29 kDa inhibin-like protein, which does not contain inhibin bioactivity. This indicates that results of experiments, in which antibodies against N-terminal peptides of the inhibin α-subunit are used to detect inhibin, do not necessarily reflect the amount of bioactive inhibin produced