AN ULTRASTRUCTURAL AND CYTOCHEMICAL STUDY OF THE MESONEPHROS OF RANA-ESCULENTA DURING ACTIVITY AND HIBERNATION

The biological cycle of most amphibians undergoes seasonal variation. In this study, we investigated the mesonephros of Rana esculenta durin g active life and the natural hibernation period. The ultrastructural morphology of the different tracts constituting the nephron was analys ed. Moreover, to evaluate the effect of seasonal temperature variation s on the mesonephros function, the activity of some enzymes linked to membrane transport and playing regulatory roles in various metabolic p athways was investigated in different tracts of the frog nephron. Duri ng hibernation the glomerular filtration barrier appeared thicker than in the active life, lysosomes and paraplasmatic material, mostly glyc ogen, being accumulated in the proximal and distal tubule cells respec tively. Cytoplasmic organelles, i.e. mitochondria, endoplasmic reticul um were observed in segregated areas. At the same time, changes in som e enzyme activities were noted. The activity of some membrane-transpor t enzymes (5'-nucleotidase and K+-p-nitrophenyl phosphatase) and of en ergetic metabolism (succinic dehydrogenase) was reduced. Nevertheless the alkaline phosphatase activity was not changed significantly and th is suggests that some metabolic activities were preserved in the hiber nating samples. These results indicate morpho-functional adaptations o f the kidney cells that preserve their role in osmoregulation and some metabolic processes, even during unfavourable seasons.