INCREASE IN DESACETYL-ALPHA-MSH CELLS IN RAT ANTERIOR-PITUITARY FOLLOWING ADRENAL ENUCLEATION AND ADRENALECTOMY

Radioimmunoassay and immunocytochemistry were used to investigate the cellular localization of the changes in processing of pro-opiomelanoco rtin (POMC) to immunoreactive (IR) alpha-MSH and IR-gamma(3)-MSH in th e anterior pituitary of sham-operated, adrenalectomized and adrenal en ucleated rats. Fourteen days after adrenalectomy, IR-alpha-MSH and IR- gamma(3)-MSH in anterior pituitary increased 2.1 and 1.8 fold respecti vely, relative to sham-operated rats. Similarly, IR-alpha-MSH and IR-g amma(3)-MSH increased 3.1 and 2.1 ford respectively, fourteen days aft er adrenal enucleation. IR-alpha-MSH and IR-gamma(3)-MSH were increase d in approximately equimolar amounts with both surgical operations. Im munocytochemistry using two antisera to alpha-MSH which distinguish au thentic alpha-MSH from the desacetyl form identified the alpha-MSH in anterior pituitary to be in the desacetyl form. Immunoreactive desacet yl alpha-MSH was localized to a subpopulation of corticotrophs which i ncreased in numbers after adrenalectomy or adrenal enucleation. The ra tio of IR-alpha-MSH content/number of alpha-MSH immunopositive cells w as constant between sham-operated, adrenalectomized and adrenal enucle ated animals. We propose that this increase of desacetyl alpha-MSH exp ressing cells is the result of either an induction of the ACTH cleavin g enzyme(s) in a larger number of corticotrophs synthesizing alpha-MSH , or de novo generation of more alpha-MSH expressing cells by cell pro liferation in the anterior pituitary, following adrenal surgery.