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J. Pudney and D. Lacy

Summary. Distinct differences in the ability of isolated seminiferous tubules and interstitium to utilize steroid precursors for androgen production in vitro were observed during the reproductive cycle of the American grey squirrel, Sciurus carolinensis. In spermatogenically active testes, the seminiferous tubules and the interstitium readily synthesized androgens from labelled C21 steroid precursor; seminiferous tubules also produced significant amounts of 17α,20α-dihydroxyprogesterone. However, during sexual regression androgen synthesis was drastically reduced in both testicular components, while the production of 20α-reduced metabolites of progesterone and 17α-hydroxyprogesterone was increased. Many of the fine-structural changes occurring in Leydig and Sertoli cells during the reproductive cycle could be correlated with the capacity of isolated seminiferous tubules and interstitium to formulate androgens from labelled precursors.

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E. C.-F. TSO and D. LACY

Department of Zoology and Comparative Anatomy, St Bartholomew's Hospital Medical College, Charterhouse Square, London, E.C.1

(Received 13th December 1974)

Prostaglandins have been found to occur in the semen of man (see Samuelsson, 1963a, b) and ram (Bygdeman & Holmberg, 1966), in various male accessory sex organs (Euler, 1936; Bergström & Sjövall, 1960; Jouvenaz et al., 1970) and in the testes of the rat (Carpenter & Wiseman, 1970) and boar (Michael, 1973), and may also be synthesized in the rat testis (Carpenter & Wiseman, 1970; Ellis et al., 1972). Comparatively few studies, however, have been carried out to determine their effects, particularly on the seminiferous tubules. Ericsson (1972) administered very high doses of PGE1 and PGE2 (2·0 mg/kg body weight) subcutaneously to rats and obtained a marked inhibition of spermatogenesis. Since this was also accompanied by severe general body stress resulting in the death of several animals, it was

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W. N. TSANG, P. M. COLLINS and D. LACY

Androgens are capable of maintaining the progressive development of the germ cells in immature male rats which have either been hypophysectomized (Leathem, 1944; Ludwig, 1950; Lostroh, 1969) or treated with compounds which interfere with the release and/or secretion of gonadotrophins (Ludwig, 1950; Kalra & Prasad, 1967; Steinberger & Steinberger, 1969). Similar results have also been obtained in adult male rats (Boccabella, 1963; Clermont & Harvey, 1967; Lacy & his co-authors, 1969). Studies on steroid metabolism in vitro by isolated seminiferous tubules of rats denuded of their germ cells by heat-treatment has led to the view that not only Leydig cells but also Sertoli cells may be a major source of androgens (Collins, Bell & Vinson, 1968; Lacy et al., 1969). Similar conclusions have also been reached by Ellis & van Kampen (1971) from studies on

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W. N. TSANG, D. LACY and P. M. COLLINS

Several workers have studied various parameters as an index of Leydig cell differentiation and attempted to correlate them with the growth of the accessory sex organs. In the prepuberal rat, little correlation seems to have been achieved (see Niemi & Ikonen, 1963; Clegg, 1966). Others have examined testosterone production in vitro by the immature testis and attempted to correlate this with the increase in weight of the seminal vesicles and prostate gland. In this connection, a good deal of attention has been paid to the production of testosterone in vitro and its apparent regulation by 5α-reductase activity. Nayfeh, Barefoot & Baggett (1966) reported an increase in testosterone production per unit weight of tissue at about the time of sexual maturity and suggested that this might be due mainly to reduced metabolism to 5α-androstane-3α,17β-diol (androstanediol). Inano, Hori & Tamaoki (1967) found a remarkable increase in the activity of various enzymes