PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE STIMULATES BOTH ADRENOCORTICAL-CELLS AND CHROMAFFIN CELLS IN THE FROG ADRENAL-GLAND

In a previous report, we have shown that frog pituitary adenylate cycl ase-activating polypeptide (fPACAP38) is a potent stimulator of cortic osteroid secretion by frog adrenal slices in. vitro. The aim of the pr esent study was to determine the mode of action of PACAP on the frog a drenal gland. Immunoelectron microscopic labeling revealed that PACAP- like immunoreactivity is present in electron-dense vesicles within ner ve endings located in the vicinity of both adrenocortical and chromaff in cells. Exposure of dispersed adrenal cells to fPACAP38 caused stimu lation of corticosteroid secretion. Labeling of cultured adrenal cells with [I-125]PACAP27 revealed the existence of PACAP-binding sites on both adrenocortical and chromaffin cells. Saturation and competition e xperiments showed the occurrence of high affinity and selective recept ors for fPACAP38 on cultured adrenal cells. fPACAP38 (10(-8)-10(-5) M) provoked a dose-dependent stimulation of cAMP production by frog adre nal slices. Microfluorimetric studies demonstrated that fPACAP38 induc ed a substantial elevation of the intracellular calcium concentration in both adrenocortical and chromaffin cells. The present results indic ate that in the frog adrenal gland, PACAP fibers innervate both adreno cortical and chromaffin cells. The data show the presence of PACAP rec eptors on the two cell types. PACAP exerts a direct stimulatory effect on corticosteroid-producing cells. This effect is probably mediated t hrough stimulation of adenylyl cyclase activity and/or augmentation of intracellular Ca2+. PACAP also increases intracellular Ca2+ in chroma ffin cells. These data suggest that PACAP, released locally in the adr enal gland, acts as a neuroendocrine factor, regulating the activity o f adrenocortical and chromaffin cells.