Etude de la fonction corticosurrenalienne au cours du cycle annuel chez un hibernant: le Lérot ( Eliomys quercinus L.) : I. Activité durant l'été: période de reproduction

Abstract

In a hibernating mammal, the garden dormouse, breeding, which occurs at the beginning of summer, is correlated with both qualitative and quantitative changes in the activity of the adrenal cortex. In this species cortisol and corticosterone appear to be the major products secreted by the adrenals in vitro. Quantitatively, the evolution of the secretion of corticosteroids, as revealed through the values of in vitro secretion and of the plasmatic level of corticosteroids, is characterized by a phase of important activity in June which is followed toward the end of July by a phase of very clear regression of this activity. At this last stage, the response of the adrenal gland, in vitro, to ACTH is much less than at any other period of the annual cycle. Qualitatively, the changes in the secretion of corticosterone are of greater importance than those occurring with cortisol. During the period of important adrenocortical activity the values recorded for both in vitro secretion of corticosterone and plasma concentration were the maxima observed during the annual cycle. During the period of declining adrenal activity, moreover, the ratio of 17-hydroxycorticosteroids/corticosterone was close to 1.0 and significantly lower than the ratio at any other time of the year when the secretion of hydrocortisone is then ever clearly prevailing. Furthermore, during July, 17-hydroxy-11-deoxycorticosterone was found to be secreted in relatively large quantities which suggests an inhibition of 11β-hydroxylation at the adrenal level due to the presence of androgens. Together, these data suggest that the modifications observed in the functioning of the adrenal cortex during summer in the garden dormouse are consequent upon the endocrinological changes associated with reproduction.