The testicular cycle and androgen biosynthesis in the tree sparrow Passer montanus saturatus

Abstract

The annual testicular cycle of the tree sparrow (Passer montanus saturatus) has been studied by histochemical and biochemical techniques.The spermatogenetic cycle has two clearly defined peaks of activity. Throughout the winter the gonads are sexually regressed, but a recrudescence of spermatogenetic activity begins in the spring and the gonads rapidly develop into full breeding condition by April. In late April and early May a rapid testicular regression takes place as spermatogenetic activity terminates. Then, in July, a second seasonal spermatogenetic wave begins and gonads once again develop into a breeding condition. By August the testes have become fully regressed into their sexually quiescent post‐nuptial phase and remain this way until the following spring. The seasonal rehabilitation of the interstitial tissue, which is a characteristic part of many avian cycles, does not occur until this latter regressive phase.The seasonal fluctuations in the in vitro production of testosterone from A5‐pregnenolone‐16T shows the same annual bimodal pattern as the spermatogenetic cycle, being high at times when the seminiferous tubules are spermatogenetically active, and low during times of sexual quiescence. There is a close correlation between the level of testicular androgen synthesis and the seasonal fluctuations in the interstitial cell lipid cycle. Thus, testosterone synthesis builds up in the spring at a time when small sudanophilic lipid droplets are present in the interstitial Leydig cells, and reaches a peak at a time when this material is becoming rapidly depleted from the cell cytoplasm. During the first period of testicular regression, the Leydig cells become markedly sudanophilic, possibly as a result of the accumulation of precursor material at a time of low testosterone synthesis, then again become depleted of this material as secretory activity builds up once again.The possible interrelationship between the histochemical and biochemical cycles, and also the spermatogenetic cycle and the daily photoperiods, are discussed.