METABOLIC CLEARANCE AND PRODUCTION RATES OF CORTICOSTERONE IN MALE AND FEMALE VIRGIN AND BREEDER RATS

Abstract

Repeatedly bred male and female rats spontaneously develop arteriosclerosis. In order to evaluate the endocrine aspects of this condition volumes of distribution, metabolic clearance (MCR) and production rates (PR) of corticosterone (B) were measured in ether-stressed virgin male and female rats initially and after a significant gain in weight for comparison with heavier breeders. After the iv injection of [1,2-³H]B values were calculated from the disappearance of total radioactivity and [1,2-³H]B from plasma employing a single- and double compartment model. The latter was used for final comparisons. There was a significant difference in the half-lives of the initial and slower disappearance curves between males (3.7 and 14 min) and females (2.4 and 10 min), respectively. For both sexes with an increase in size there was a corresponding increase in the volumes of distribution, MCR and PR of B. In female breeders there was a significant decrease in these same parameters: MCR dropped from 8.5 to 5.7 1/day, PR from 6.4 to 3.5 mg/day. Circulating plasma levels decreased from 76.4 to 61.3 μg/100 ml. The results indicate that physiological factors in addition to the adrenal are responsible for the decreased PR in arteriosclerotic breeder female rats.