Seasonal changes in endocrine organs of the male common frog, Rana temporaria. 3. The gonads and cholesterol cycles.

Abstract

The seasonal histological and histochemical changes in the testes of the common frog, Rana temporaria , have been studied throughout the year. A parallel analysis of the seasonal fluctuations in the free and esterified cholesterol concentration of the gonads and plasma has also been carried out. Whereas the plasma cholesterol levels showed little connection with the gonadal events, the level of total cholesterol in the testis showed a close correlation with the Sertoli cell lipid cycle, and underwent a rapid increase at the time of postnuptial tubule steatogenesis. This was followed by a rapid decline at the time of spermatogenetic recrudescence suggesting a mobilization of this material during this period. The levels of plasma esterified cholesterol were always lower than those of free cholesterol throughout the annual cycle, whereas in the gonad, although the level of esterified cholesterol was consistently lower than that of free cholesterol for 9 months of the year, after the breeding season it rapidly rose to a peak in May and was mainly responsible for the postnuptial rise in total cholesterol concentration. From the changes in nuclear area, lipid and cholesterol content, the functional activity of the interstitial tissue could be closely correlated with the morphological changes in the nuptial thumb-pads. A comparison is made between the seasonal changes in the testes and the corresponding changes in the pars distalis and interrenal tissue of the same animals.