[Cyclic activity of adrenal function and seasonal variations of cortisol peripheral metabolism in a hibernating mammal, the hedgehog (Erinaceus europaeus L.) (author's transl)].
In the male hedgehog we have studied the nycthemeral and seasonal variations of plasma corticosteroids (cortisol and corticosterone) and different parameters (Half-life: t 1/2; apparent volume of distribution: VAD; Metabolic clearance rate: TCM; Production rate: TP) which characterize the metabolism of cortisol, the main corticosteroid in the hedgehog, and give and accurate representation of the cortico-adrenal gland activity. This study was done on unanesthetized animals, kept under natural climatic conditions and equipped with an arterial catheter which allowed blood to be sampled without visible disturbance. Plasma corticosteroids levels were measured at 4 h intervals over a period of 24 h, each month for one year. Monthly evolution of cortisol peripheral metabolism was studied on animals treated with dexamethasone, using a single injection of 3H-cortisol as a tracer after previous comparison with the continuous infusion technique. Plasma glucocorticosteroid levels show a marked nycthemeral rhythm from February to October : maximums are before sunset or during the first hours of the night and minimums are near sunrise. This nycthemeral cycle was not evident during November, December and January when the animals present many periods of torpor. The nycthemeral mean level of plasma corticosteroids (mean of 7 plasma sample concentrations determined over a period of 24 h) fluctuates during the year : corticosteroid levels are maximum in December, then decrease rapidly at the beginning of winter, stay at relatively low levels in spring and the increase which starts in summer becomes more pronounced in autumn. Cortisol peripheral metabolism shows large seasonal variations characterized by a strong reduction in autumn during hibernation, a large increase at the end of winter when the seasonal rhythm of locomotor activity is being restored, and then a gradual decrease in spring and summer which is interrupted by a brief increase in July. The seasonal change in corticoadrenal gland cortisol production rate is polyphasic and shows a maximum rise in autumn (December) and two other peaks which occur at the end of winter and in summer. In light of this it appears that in autumn and winter, the cortisol production rate and cortisol metabolic clearance rate are in opposite phase. The important changes observed during July (increases of t 1/2, VAD, TCM and TP) are probably connected to the metabolic preparation for the autumnal and winter rest.