Some seasonal changes in the thecal gland in the ovaries of hibernators (Citellus citellus L.).

The ovaries of 36 ground squirrels were studied in March, April, July, and December. Morphological and functional seasonal characteristics of theca interna were studied by histological methods, electron microscopy, and quantitative methods for determinating the volume density and histoenzyme activity of NADH2-tetrazolium reductase, glucose-6-phosphate dehydrogenase, and delta 5-3 beta-hydroxysteroid dehydrogenase. Maximal activity of theca interna as a steroid-producing structure was observed during spring awakening. A significant increase in the histoenzyme activity of delta 5-3 beta-hydroxysteroid dehydrogenase in December, versus two other enzymes studied, indicated steroid synthesis in theca terna.