Adrenal activity in the female lizard Lacerta vivipara jacquin associated with breeding activities

Variations of adrenal activity were studied in captive viviparous females Lacerta vivipara, in relation to breeding activities. The study was restricted to the period of active life which includes both the phase of annual reproduction and a phase of sexual inactivity. Significant seasonal changes in plasma corticosterone levels were measured with a peak during the second half of gestation followed by an abrupt fall at parturition. No significant variations in plasma aldosterone levels were observed. A limited extraovarian production of progesterone was detected which might be of adrenal origin. The half-life of injected tritiated corticosterone was not longer in pregnant than in nonreproductive females, suggesting that the peak of circulating corticosterone in pregnant females corresponds to an increase in the production rate of the hormone. The functional importance of the pituitary-adrenal axis was demonstrated in vivo: plasma corticosteroid levels dropped to the detection limit after adenohypophysectomy. Seasonal variations of adrenal sensitivity to synthetic ACTH 1-39 were examined in vitro, using a perifusion system. No significant variations were observed throughout the period of active life. These results suggest that the peak of plasma corticosterone during gestation can be ascribed to activation of the pituitary-adrenal axis. Experimental modifications of circulating corticosterone level during late gestation altered the timing of parturition, thus indicating that the fall of corticosterone just before term may be involved in the process of parturition in the female L. vivipara.