Photoperiodic control of testosterone metabolism, plasma gonadotrophins, cloacal gland growth, and reproductive behavior in the Japanese quail

Abstract

The changes in plasma gonadotrophins and testosterone, in cloacal gland area, and in reproductive behavior were observed in male Japanese quails after transfer to long days or testosterone implantation and were correlated with the testosterone metabolism in the hyperstriatum, hypothalamus, pituitary, and cloacal gland. Long days stimulate the growth of the cloacal gland and at the same time enhance its production of androstenedione from testosterone. This increased 17β-hydroxysteroid dehydrogenase activity is correlated at the individual level with cloacal gland area but not with plasma testosterone. Similarly the changes observed in some reproductive activities (aggressive behavior and struts) are correlated with individual differences in the brain metabolism of testosterone (hyperstriatal or hypothalamic production of androstenedione), but not with plasma testosterone. The plasma luteinizing hormone is also related to testosterone metabolism rather than to the circulating level of the hormone (negative correlation with the production of 5α-dihydrotestosterone in the pituitary). The testosterone metabolism in target organs thus appears of critical importance in the control of reproduction and seems largely responsible for the occurrence of individual differences. After exposure to 12 long days the mean testosterone metabolism in the pituitary is also strongly affected (increased 5β-reduction) though not in the same way as after 2 months of photostimulation. It is suggested that these metabolic changes at the pituitary level may play some role in the induction of the increased responsiveness to luteinizing hormone-releasing hormone which can be observed in quails after exposure to 7 long days.