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  • Author: W. G. E. J. Schoonen x
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W. G. E. J. Schoonen, J. G. D. Lambert, J. W. Resink, W. J. A. R. Viveen and P. G. W. J. Van Oordt

ABSTRACT

Quantitative aspects of bioconversions in the testes of the African catfish (Clarias gariepinus) were studied in vitro by incubation of tissue with [3H]pregnenolone or [3H]androstenedione. During the breeding period, spawning and non-spawning animals were collected from their natural habitat, the Hula nature reserve, in northern Israel. In the same period, non-spawning animals were collected from a fish pond in the same region. It was shown that spawning was accompanied by significant changes in steroid bioconversions, i.e. a reduction in androgen synthesis, especially of 11β-hydroxyandrostenedione and 11β-hydroxytestosterone and an increase in the production of C21-steroids, especially progesterone, 17α-hydroxyprogesterone and a pregnenolone ester. These changes resulted from a decreased contribution of the cytochrome P-450 enzymes 17α-hydroxylase, C17–20-lyase and 11β-hydroxylase. A rise in plasma gonadotrophin concentration was observed only in spawning catfish. In the absence of such an increase in plasma gonadotrophin, steroid synthesis in the testes of non-spawning feral and pond catfish was primarily directed towards the production of 11-oxygenated androgens and 5β-pregnane-3α,17α,20α-triol. It is suggested that spawning is induced by gonadotrophin and the ensuing change in steroidogenesis. It is possible that husbandry conditions inhibit the necessary increase in gonadotrophin release.

J. Endocr. (1987) 112, 323–332

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M.C. Slootweg, A.G.H. Ederveen, L.P.C. Schot, W.G.E.J. Schoonen and H.J. Kloosterboer

ABSTRACT

Oestrogens play an important role in bone metabolism; they preserve bone mass after the menopause. Their action in bone has recently been shown to be, partly, a direct one, as oestrogen receptors and their effects have been demonstrated in bone cells. The role of progestogens in bone metabolism is less clear. In this study it has been shown that 17β-oestradiol exerts only a small, although not significant, stimulatory action with regard to SaOS-2 human osteosarcoma cell proliferation. A pure progestogen (Org 2058) has no effect when added alone. In combination with 17β-oestradiol, however, it has a highly synergistic action on SaOS-2 cell proliferation. The same effect was observed in primary rat osteoblasts, showing that this synergism is a general phenomenon in osteoblastic cells. High numbers of oestrogen and progestogen receptors have been demonstrated in SaOS-2 cells, indicating that the effects of these steroids are mediated via the normal route of steroid receptors. These data provide a cellular basis for the clinically recognized positive effect of oestrogen/progestogen combinations on bone formation.