Influence of age on plasma adrenocorticosteroids in rats, rabbits, and guinea pigs

¹ Department of Pediatrics, University of Utah College of Medicine, Salt Lake City, Utah

Circulating concentrations of free 17-hydroxycorticosteroids (17-OHCS) and "cortisol" and "corticosterone" were determined in rats, guinea pigs, and rabbits. (Quotation marks indicate that fluorescence present in plasma of these species has identical column chromatographic mobility of cortisol and corticosterone in human plasma.) In rats, "corticosterone" was present in greater amounts in adult than in young rats. Fluorescent material was also found in the "cortisol" fraction in both age groups but the 17-OHCS values were very low. In baby guinea pigs the fluorescent values for "cortisol" and "corticosterone" were about equal and were very high, as were the 17-OHCS values. During maturation all three values declined. In the younger age groups 17-OHCS values were two to three times greater than the "cortisol" values. In the two age groups of rabbits observed no 17-OHCS and only low "corticosterone" values were obtained. Instead, an unidentified, presumably steroidal, fluorescent material was found in the cortisol fraction.