Diurnal variations in circulating concentrations of LH, GH, prolactin, corticosterone, oestradiol, progesterone and testosterone were followed in laying and broody White Rock domestic fowl. Throughout the 24 h study prolactin concentrations in serum were consistently (two- to fourfold) higher in broody than in laying birds, in which the prolactin level varied with the light:darkness or ovulatory cycles. Concentrations of GH in serum tended to be lower in broody birds but in both groups were very variable and showed no obvious relationship with either the lighting or ovulatory cycles. Broodiness was also characterized by low LH and gonadal steroid levels and by the absence of preovulatory peaks in the serum concentrations of these hormones. A diurnal rhythm in corticosterone was observed in both the laying and broody birds, with high levels during the period of darkness. Corticosterone concentrations were markedly higher in the broody birds than in laying birds during most of the 24 h study. No diurnal rhythm in the blood haematocrit level was observed in either group, although the level was generally lower in broody birds. This difference, however, was insufficient to account for the lower LH and gonadal steroid levels in the broody birds. The results suggest that prolactin is involved in the initiation or maintenance of broodiness in the fowl and the possibility of an antigonadal role for the hormone is discussed.

SUMMARY The metabolism of 3β-hydroxysteroids, in the presence of NADPH, by testicular homogenates of adult rats acclimatized to a hot environment (33–35 °C, 25–40% relative humidity), was compared with that of control and surgically produced cryptorchid testes. Prolonged exposure to a hot environment stimulated the transformation of 3β-hydroxysteroids to 3-oxo-4-ene metabolites, so that relatively large amounts of the latter accumulated. Pregnenolone was metabolized rapidly to progesterone, 17α-hydroxyprogesterone, androstenedione and testosterone. A similar trend was observed in the metabolism of 17α-hydroxypregnenolone. In-vitro synthesis of testosterone in the rat apparently takes place primarily by the 4-ene pathway. The 5-ene-17,20-lyase reaction appears to be rate-limiting. Heat acclimatization does not seem to affect this step. It does, however, seem to enhance the conversion of dehydroepiandrosterone via 5-androstene-3β,17β-diol to testosterone. Enzymic activity was much lower in cryptorchid than in heat-acclimatized testes, where it actually increased, except for 17β-hydroxysteroid oxidoreductase. Continuous exposure of rats to a high ambient temperature for 4–6 months tended to decrease testosterone concentration in peripheral blood, and retarded growth rate and gonadal size. Histological examination showed atrophied areas in the testes where necrobiosis of the germinal epithelium had occurred. These necrotic foci, unlike those found in cryptorchid testes, were randomly scattered among intact seminiferous tubules in which active spermatogenesis was taking place.

No abstract

The relative activities of enzymes participating in the biosynthesis of testosterone via the 4-ene pathway were determined in testicular homogenates of rats acclimatized to a hot environment (33-35 \ s=deg\ C, 25-40 % relative humidity). Acclimatized animals showed an increase in activity of 17\g=a\-hydroxylase,17,20-lyase and 20\g=a\-hydroxysteroid oxidoreductase, whereas the activity of 17\g=b\-hydroxysteroid oxidoreductase was markedly decreased. Histological examination of the testes disclosed that neither the germinal epithelium nor the Leydig cells were adversely affected by the increased environmental temperature. The results are discussed in relation to the synthesis and release of the gonadotrophins.A similar degree of acclimatization, as determined by the comparable decrease in oxygen uptake, was achieved by either of two methods: daily 4 h exposure to a high ambient temperature for 4 weeks or continuous maintenance at 35 \s=deg\C.The former procedure, however, appeared to be the preferred method for acclimatization of male rats since it did not inhibit growth rate and was free of mortality.