Pituitary-adrenal response to ether vapor in the weanling animal: characterization of the inhibitory effect of glucocorticoids on adrenocorticotropin secretion.

The hypothalamic-pituitary-adrenal axis is hyporesponsive to stimuli during early life in the rat. Once the adrenocortical response is established, failure to terminate the corticosterone (B) rise is evident after certain stressors, such as ether. The purpose of this study was 2-fold: 1) to investigate the B and ACTH response to ether vapor in young animals and 2) to test the ability of glucocorticoids to inhibit the ether ACTH-stimulated secretion in weanling animals. Rats aged 14, 18, and 25 d and adult rats were subjected to ether vapor for 3 min. Plasma was collected for B and ACTH determination by RIA at 0, 5, 15, 30, 60, and 120; min after ether exposure. Maximum B levels were observed at different times after exposure: 15 min in the adult and 30 min in the younger animals. In addition, B levels were significantly elevated at 60 min in the d 25 and d 18 rats compared with the adult (d 25 = 672.4 +/- 28.9, d 18 = 744.6 +/- 31.7, adult = 323.2 +/- 8.7 mol/L +/- SEM; d 25 = 23.3 +/- 1.0, d 18 = 25.8 +/- 1.1, adult = 11.2 +/- 0.3 micrograms/dL +/- SEM). The B delay observed in the younger animals was not due to a delayed ACTH response because maximal ACTH values were observed 5 min after ether exposure in all ages (d 14 = 21.9 +/- 4.8, d 18 = 35.8 +/- 21.3, d 25 = 82.01 +/- 16.5, adult = 98.9 +/- 25.2 x 10(-12) mol/L +/- SEM). However, in the d 25 rats the ACTH level remained significantly elevated 30 min after the ether vapor challenge (5 min = 86.9 +/- 25.2, 30 min = 61.8 +/- 4.8, 60 min = 15.3 +/- 4.1 x 10(-12) mol/L +/- SEM). The delay to return to resting ACTH levels was consistent with the time delay observed for the B release from the adrenal.(ABSTRACT TRUNCATED AT 250 WORDS)