654 EFFECT OF PERORAL ADMINISTRATION OF ACTH ON PLASMA CORTICOSTERONE LEVELS IN SUCKLING RATS: TIME AND DOSE DEPENDENCY

Abstract

The presence of ACTH in rats' milk prompted us to explore whether ACTH given perorally (p.o.) to suckling rats has an effect on plasma corticosterone (C). After this was demonstrated in preliminary experiments, we studied the time dependency of the ACTH effect. In suckling Sprague-Dawley rats (11-14 days old), starved for 2 hours and then fed ACTH1-39 (Armour, 0.50 U/g BW in water), plasma C peaked at 30 minutes and remained significantly higher until 180′ when compared with water-fed controls.To determine the lowest effective dose, varying amounts of ACTH were given p.o. (0.06; 0.13; 0.25; 0.50 and 1.00 U/g BW) and plasma C measured 2 hours later. The two lower doses evoked an insignificant change; a significant increase was seen using the 0.25 U dose. Its effect was the same as that of the higher doses used.These studies thus demonstrate the acute effect of p.o. ACTH in suckling rats. Further studies are needed to evaluate the physiologic role of ACTH normally present in rats' milk.