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The metabolism of testosterone was studied in vitro in anterior pituitary, hypothalamic and hyperstriatal tissues taken from male European starlings in the autumn. In all the tissues studied, testosterone was converted into 5α-androstan-17β-ol-3-one (5α-DHT), 5β-androstan-17β-ol-3-one (5β-DHT), 5β-androstane-3α,17β-diol (5β-THT), 5β-androstane-3,-17-dione and androst-4-ene-3,17-dione.
The 5α-DHT was produced in significantly greater amounts by the pituitary gland than by the hypothalamus and hyperstriatum. The amount of 5α-DHT produced, however, was very low in comparison with the amounts of 5β-reduced metabolites. The amount of 5β-reductase was also higher in the pituitary gland than in the two nervous tissues. The ratios between the production of 5β-DHT, 5β-THT and 5β-androstane-3,17-dione were, however, different in the three tissues: 5β-DHT was produced in the greatest quantities by the hyperstriatum, while the production of 5β-THT, 5β-androstane-3,17-dione and androst-4-ene-3,17-dione was greatest in pituitary tissue.
The role of 5α- and 5β-reduced metabolites in the pituitary gland and in the brain of birds is unknown, but some possibilities arising from the present results are discussed.
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The metabolism in vitro of [4-14C]testosterone to reduced derivatives was studied in the pituitary gland, hypothalamus and hyperstriatum dorsale of cockerels from hatch to sexual maturity. The most important metabolites were 5β-dihydrotestosterone (5β-DHT), 5β-androstane-3α,17β-diol (5β-3α-diol) and 5β-androstane-3β,17β-diol. Trace amounts of androstenedione and, in the hypothalamus only, of 5α-DHT were also detected. The amounts of 5β-reduced metabolites produced by all neuroendocrine tissues declined progressively during maturation with the steepest fall occurring during the first 2 weeks after hatch. At all ages studied, 5β-DHT was formed to the greatest extent by the hyperstriatum dorsale, to a lesser extent by the hypothalamus and in the smallest quantities by the pituitary gland. In the three tissues studied, 5β-3α-diol tended to be formed to the greatest extent by the pituitary gland.
No significant change was observed in the metabolism of testosterone to reduced derivatives in any of the neuroendocrine tissues after castration.
It was concluded that in the cockerel, unlike the rat, a change in 5α-reductase activity of the neuroendocrine tissues is unlikely to be involved in the initiation of puberty. The physiological significance of 5β-reductase activity in the neuroendocrine tissues remains to be established.
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In the laying hen, progesterone was shown to be converted in vitro in the pituitary gland and the hypothalamus to 5β-pregnane-3,20-dione (5β-DHP), 5β-pregnan-3α-ol-20-one (5β,3α-ol) and 5α-pregnane-3,20-dione (5α-DHP) and in the hyperstriatum dorsale to 5β-DHP and 5β,3α-ol. The conversion of progesterone to 5β-reduced metabolites was greater in the hyperstriatum dorsale than in the hypothalamus (P<0·001) and greater in the hypothalamus than in the pituitary gland (P <0·01). The conversion of progesterone to 5β-reduced metabolites was greater than its conversion to 5α-DHP in the pituitary gland (P <0·01) and the hypothalamus (P < 0·001).
The possibility was investigated that 5α-DHP and 5β-DHP may act as metabolic intermediaries in the mechanism by which progesterone exerts a positive feedback effect on LH release. Progesterone, 5α-DHP and 5β-DHP were injected into laying hens at doses of 0·05,0·25 and 1·25 mg/kg and the changes in the concentration of plasma LH were followed for 4 h thereafter. Secretion of LH was stimulated after treatment with progesterone or 5α-DHP but not 5β-DHP. Progesterone stimulated LH release more effectively than did 5α-DHP, since an increase in the concentration of plasma LH was observed after 0·25 mg progesterone/kg but not after the same dose of 5α-DHP. It was concluded that in the hen 5α-DHP is unlikely to play a role in the induction of the preovulatory release of LH.
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Testosterone metabolism was studied in vitro in the prostate of intact and castrated golden hamsters maintained either in short days (8 h light: 16 h darkness, 8L : 16D) or in long days (14L : 10D). Testosterone was found to be converted into 17β-hydroxy-5α-androstan-3-one (5α-DHT), 5α-androstane-3α, 17β-diol, 5α-androstane-3, 17-dione and androstenedione. The mean conversion of testosterone to 5α-DHT was higher in prostates from animals maintained in long days than in short days (P < 0·0025) while that to androstenedione was higher in short days (P <0·0005); no significant changes in the formation of the other three metabolites were noted. Castration of animals maintained in short days resulted in a significant (P <0·05) decrease in the mean conversion to all four metabolites. In contrast, castration of animals kept in a long-day regime caused a significant (P <0·01) decrease in the mean formation of 5α-DHT but a significant (P <0·05) increase in the mean formation of 5α-androstane-3α, 17β-diol.
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In the Japanese quail gonadal steroids can depress plasma levels of LH and FSH. Since it is now accepted that testosterone metabolites may be metabolized to the tissue-active forms of the hormone, the in-vitro tissue incubation has been combined with steroid replacement therapy in vivo to investigate the physiological roles of various testosterone metabolites as inhibitory feedback agents on gonadotrophin secretion in quail. After the incubation of quail pituitary glands for 3 h with labelled testosterone four metabolites could be identified; androst-4-ene-3,17-dione, 5β-dihydrotestosterone (5β-DHT), 5β-androstane-3α,17β-diol and 5α-DHT. No 5α-androstane-3α,17β-diol was found. Quantitatively, androstenedione was the major metabolite and conversion of testosterone to 5β-metabolites was significantly greater than to 5α-androgens. Hypothalamic and hyperstriatal tissues converted testosterone to androstenedione, 5β-DHT and 5β-androstane-3α,17β-diol but not to 5α-DHT or 5α-androstane-3α,17β-diol.
Gonadotrophin secretion was studied in castrated quail after chronic s.c. implantation of steroid-containing silicone elastomer capsules or acute injection i.m. of steroid in ethanol: saline. Irrespective of the route of administration seven androgens, listed in descending order of potency, reduced the increased levels of plasma LH: testosterone; 5α-DHT; androstenedione; 5α-androstane-3,17-dione; 5α-androstane-3α,17β-diol; 5α-androstan-3α-ol-17-one; 5α-androstan-3β-ol-17-one. No changes in levels of plasma LH were observed after the administration of 5β-DHT, 5α-androstane-3β,17β-diol, 5βandrostane-3α,17β-diol, 5β-androstane-3,17-dione, androst-5-ene-3β,17β-diol or androst-5-en-3β-ol-17-one.
Testosterone and oestradiol-17β were effective in inhibiting secretion of both LH and FSH in young photostimulated quail and completely blocked testicular growth: 5α-DHT inhibited only the release of LH and testicular growth was unaffected.
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A cloacal gland complex whose growth and development is androgen-dependent exists in the Japanese quail. In-vitro incubation studies of the cloacal gland using 4-14C-labelled testosterone as substrate allowed the positive identification of five metabolites: androstenedione, 5β-dihydrotestosterone (5β-DHT), 5β-androstane-3α,17β-diol, 5α-DHT and 5α-androstane-3α,17β-diol. More polar metabolites, not yet chemically identified, were detected in trace amounts. Androstenedione appeared to be the main testosterone metabolite in immature birds while in mature birds on long daylengths testosterone was preferentially metabolized to 5α-DHT. This change may have been in response to the higher levels of plasma steroids found in mature birds. When various testosterone metabolites, contained in silicone elastomer capsules, were implanted s.c. into castrated birds maintained on a photostimulatory light régime, 5α-DHT, 5α-androstane-3,17-dione, androstenedione and 5α-androstan-3α-ol-17-one were shown to be equipotent with testosterone in stimulating the development of the cloacal gland. 5α-Androstane-3α,17β-diol and 5α-androstan-3β-ol-17-one stimulated some growth while 5β-DHT, 5α-androstane-3β,17β-diol, 5α-androstane-3α,17β-diol, 5β-androstane-3,17-dione, androst-5-en-3β-ol-17-one and androst-5-ene-3β,17β-diol were completely ineffective.
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Department of Endocrinology, University of Milan, Via A. del Sarto 21, 20129 Milan, Italy
(Received 8 May 1978)
It is well established that the rat prostate gland converts testosterone mainly into 5α-androstan-17β-ol-3-one (5α-dihydrotestosterone, 5α-DHT) and to a lesser extent into 5α-androstan-3α,17β-diol (5α-tetrahydrotestosterone, 5α-THT). This occurs, both in vivo and in vitro, through the action of a 5α-reductase and a 3α-hydroxysteroid dehydrogenase system (Baulieu, Lasnitzki & Robel, 1968; Bruchovsky & Wilson, 1968; Gloyna & Wilson, 1969; Kniewald, Massa & Martini, 1971). It has also been recognized that, although the 5α-reduction of testosterone is an irreversible reaction, the reduction of 5α-DHT to 5α-THT is reversible (Becker, Grabosch, Hoffmann & Voigt, 1973; Cresti & Massa, 1977). Consequently, the question has been raised as to whether the biological actions of 5α-THT are attributable to the compound as such or to 5α-DHT. At the anterior pituitary level, 5α-reductase activity is increased by castration and decreased
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The possible relationship between changes in islet cell mass and in islet neogenesis-associated protein (INGAP)-cell mass induced by sucrose administration to normal hamsters was investigated. Normal hamsters were given sucrose (10% in drinking water) for 5 (S8) or 21 (S24) weeks and compared with control (C) fed hamsters. Serum glucose and insulin levels were measured and quantitative immunocytochemistry of the endocrine pancreas was performed. Serum glucose levels were comparable among the groups, while insulin levels were higher in S hamsters. There was a significant increase in beta-cell mass (P<0.02) and in beta-cell 5-bromo-2'-deoxyuridine index (P<0.01), and a significant decrease in islet volume (P<0.01) only in S8 vs C8 hamsters. Cytokeratin (CK)-labelled cells were detected only in S8 hamsters. INGAP-positive cell mass was significantly larger only in S8 vs C8 hamsters. Endocrine INGAP-positive cells were located at the islet periphery ( approximately 96%), spread within the exocrine pancreas ( approximately 3%), and in ductal cells (<1%) in all groups. INGAP positivity and glucagon co-localization varied according to topographic location and type of treatment. In C8 hamsters, 49.1+/-6. 9% cells were INGAP- and glucagon-positive in the islets, while this percentage decreased by almost half in endocrine extra-insular and ductal cells. In S8 animals, co-expression increased in endocrine extra-insular cells to 36.3+/-9.5%, with similar figures in the islets, decreasing to 19.7+/-6.9% in ductal cells. INGAP-positive cells located at the islet periphery also co-expressed CK. In conclusion, a significant increase of INGAP-positive cell mass was only observed at 8 weeks when neogenesis was present, suggesting that this peptide might participate in the control of islet neogenesis. Thus, INGAP could be a potentially useful tool to treat conditions in which there is a decrease in beta-cell mass.
