EFFECTS OF ACTH AND AMINOGLUTETHIMIDE ON THE CATECHOLAMINE CONTENT AND CHROMAFFIN CELL MORPHOLOGY OF THE ADRENAL-MEDULLA OF THE NEONATAL RAT

The rat adrenal medulla is immature at birth, composed of phaeochromob lasts and undifferentiated chromaffin cells, but by 7 d postnatally mo rphologically distinct adrenaline-storing (A) and noradrenaline-storin g (NA) cells can be distinguished in the adult proportions of approxim ately 80-85 % A and 15-20 % NA cells. Glucocorticoid hormones are know n to play an important role in the initial expression and maintenance of phenylethanolamine N-methyl transferase (PNMT), the enzyme characte ristic of A cells. The purpose of the study was to investigate the eff ects of glucocorticoids on the establishment of the A and NA cell phen otype in vivo during the first postnatal week. Neonatal rats were trea ted from postnatal d 1 to 7 either with ACTH to increase circulating l evels of glucocorticoids or with aminoglutethimide to reduce blood glu cocorticoids. On postnatal d 7 the volume fractions of A and NA cells in the adrenal medulla were estimated and the amounts of stored adrena line and noradrenaline determined by HPLC and compared with untreated controls. Adrenaline levels were increased following ACTH treatment an d there was an apparent decrease after aminoglutethimide which was not statistically significant. There was cytological evidence of the effe cts of ACTH and aminoglutethimide on the adrenal cortex but no resulta nt effect on medullary cell morphology. A cells remained predominant w ith NA cells making up approximately 15 % of chromaffin cells, suggest ing that any effects of altered glucocorticoid levels were confined to a modulation of adrenaline synthesis by a morphologically unchanged c hromaffin cell population. Plasticity of the A cell/NA cell phenotype was not demonstrated and it was concluded that although the rat chroma tin cell is immature at birth differentiation potential has already be come restricted.