| Abstract: | Strain-dependent differences in adrenocortical function were investigated in male White Leghorn domestic fowl. Adrenocortical function of Cornell K strain (K) (genetic control), autosomal dwarf strain (ADW), and sex-linked recessive dwarf strain (SLD) was evaluated in vivo by measuring plasma corticosterone and in vitro by measuring acute (2 hr) corticosterone production by enriched adrenocortical cell populations. Regardless of strain, there was an age-dependent decrease (27-57%) in plasma corticosterone from 1 to 12 weeks of age. However, there was a tendency for plasma corticosterone values of ADW and SLD to be, respectively, greater and less than that of K. In addition, at 12 weeks of age, plasma corticosterone responses of ADW and SLD to transient heat stress (50 degrees C, 30 min) were, respectively, 22.8% greater and 15.9% less than that of K. Strain differences in adrenal weight and relative adrenal weight (mg% body wt) were also apparent. At 12 weeks of age, adrenal weights of ADW and SLD were, respectively, 33 and 42% less than that of K, whereas relative adrenal weights were, respectively, 27.6% greater and 22.4% less than that of K. In addition there were strain-dependent differences in adrenocortical function at the cellular level. Although there were no consistent strain differences in basal and maximal corticosterone production by cells, there were strain differences in cellular sensitivity to ACTH and pregnenolone. On an equal cell concentration basis, the half-maximal steroidogenic concentrations (ED50 values or effective doses for 50% maximal effect) of ACTH for ADW and SLD adrenocortical cells were, respectively, 0.23 and 2.07 times the ED50 value for K cells. In addition, the ED50 value of pregnenolone for ADW cells was 0.46 times that for K and SLD cells. Since ED50 values are a measure of cellular sensitivity (the greater the ED50 value the lesser the cellular sensitivity), the order of sensitivity to ACTH was ADW greater than K greater than SLD and the order of sensitivity to pregnenolone was ADW greater than K = SLD. However, there were no strain differences in ED50 values of 8-bromo-cyclic AMP. These data suggest that strain differences in plasma corticosterone response to stress are, in part, due to differences in relative adrenal weight and differences in adrenocortical cell function. |
