Gonad steroidogenesis

P and Pg, exist in foUicular fluid. Control of inhibin secretion involves a feedback relationship in which circulating FSH stimulates inhibin secretion, which in turn reduces the secretion of FSH (8). Both the homo- and the heterodimers of the P-subunits of inhibin promote the secretion of FSH and thus have been termed activins. Activin is secreted by the ovary and the testes into the circulation. In addition, both inhibin and activin have intragonadal autocrine and paracrine effects that influence gonadal steroidogenesis (9). 

Lin D, SugawaraT, Strauss JF 3rd, et al. Role of steroidogenic acute regulatory protein in adrenal and gonadal steroidogenesis. Science 267 1821-... 

Catt KH, Harwood JP, Clayton RN, Davies TE, Chan V, Kaiti-neni M, Nozu K, Dufau M (1980) Regulation of peptide hormone receptors and gonadal steroidogenesis. Rec Progr Horm Res 36 557-622... 

Guilette Jr, L.J., Gross, T.S., Gross, D.A., Rooney A.A. and Percival, H.F (1995) Gonadal steroidogenesis in vitro from juvenile alligators obtained from contaminated or control lakes. Environ. Health Perspect., 103 (suppl. 4), 31-36. 

Spironolactone is an antiandrogen which blocks androgen-receptors, alters steroidogenesis by adrenals and gonads and inhibits 5-a reductase. In doses of 100-200 mg daily it reduces sebum production and improves inflammatory acne in women. During treatment, birth control measures are required due to the risk of male fetus feminization. 

Occurrence in molluscs of steroidogenesis along a pathway very similar to that found in vertebrates has been claimed. Testosterone (64) - androstenedione (65) interconversion has been demonstrated in gonads of the male and female bivalve - Mytilus edulis [117] and of the gastropod Crepidula fornicata [118], by using labelled testosterone and androstenedione. Moreover, several steroids have been identified in the gonads and hepatopancreas of the opisthobranch... 

It is rapidly absorbed into the systemic circulation following intranasal delivery. It stimulates the release of LH and FSH from the anterior pituitary resulting in a temporary increase of ovarian steroidogenesis. After 2 to 3 days of daily administration, the pituitary becomes refractory to further stimulation. LH/ FSH release is inhibited within 10 days and is followed by a decrease in secretion of gonadal steroids within 2 to 6 weeks. 

The stimulation of steroid synthesis in gonadal cells is dependent on ongoing protein synthesis. Experiments with protein synthesis inhibitors have shown the presence of one or more proteins with half lives of 5-15 min which are essential for the expression of the stimulating hormone effect on steroidogenesis [42,45-47]. Many attempts to identify the protein(s) have been made but none have been detected that satisfy all the functional and kinetic criteria required. Using two-dimensional gel electrophoresis a 28 kDa protein has been identified recently [48], however its functional properties are unknown. It is also not known if the active protein is synthesised de novo or is derived from a precursor protein by covalent modification [49]. 

Figure 50-9 The regulatory feedback loop of the hypothalamic-pituitary-gonadal axis. Neural and sensory input from the brain elicits the release of Gn-RH. Gn-RH in turn stimulates the synthesis and release of the gonadotropins FSH and LH, which act on the gonads (ovary and testes) to elicit the ripening and ovulation of the ovary and steroidogenesis (estradiol and progesterone) in the female and spermatogenesis and testosterone production in the male. Inhibin formed by the ovaries and testes along with estradiol and testosterone negatively feeds back to the hypothalamic-pituitary axis to modulate Gn-RH, FSH, and LH release.

Conley, A.J. and I.M. Bird. The role of cytochrome P450 17a-hydroxylase and 3/3-hydroxylase and 3(3-hydroxysteroid dehydrogenase in the integration of gonadal and adrenal steroidogenesis via the A5 and A4 pathways of steroidogenesis in mammals. Biol. Reprod. 56 789-799, 1997. 

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