CARCIA, Rocco V.; JOHN-ALDER, Henry B.: Season-Specific Alterations in Adrenocortical Cell Function of the Eastern Fence Lizard (Sceloporus undulatus)

We previously reported that S. undulatus adrenocortical cells are well suited to investigate adrenal steroidogenic function at the cellular level. We conducted the present study to determine whether seasonal changes in circulating corticosterone could, in part, be explained by adrenocortical cell function per se. Dispersed adrenocortical cells were prepared from male and female lizards collected in April, August, and October. We evaluated corticosteroid responses of cells to adrenocorticotropin (ACTH), angiotensin II (ANG II), and 25-hydroxycholesterol [25(OH)Chol]. Plasma corticosterone in both sexes was highest in April, lowest in August, and intermediate in October. Basal and net maximal rates of corticosterone production in response to ACTH and 25(OH)Chol were highest in October and lowest in August (60-80% reduction), whereas net maximal corticosterone rates in response to ANG II were highest in August (about 60% greater than those in October and April). Seasonal changes in rates of corticosterone production were generally similar between sexes. Seasonal changes in cellular corticosterone production are consistent with but not entirely parallel to seasonal differences in plasma corticosterone. By contrast, seasonal changes in cellular aldosterone and progesterone production rates differed between sexes, thus precluding a pattern similar to that shown for corticosterone. Nevertheless, our data indicate a role of alterations in adrenocortical cell function in determining the season-specific differences in circulating corticosterone in S. undulatus. Supported by USDA 00-35206-9330 to R.V.C. and NSF IBN95-05729 to H. J.-A.