PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE (PACAP)-38 AND PACAP27 DIFFERENTIALLY STIMULATE GROWTH-HORMONE RELEASE AND MESSENGER-RNAACCUMULATION IN PORCINE SOMATOTROPES

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been su ggested to regulate growth hormone (GH) secretion in several species. Here, we analyzed the in vitro effects of PACAP38 and PACAP27 on the s ecretory activity of porcine somatotropes. Cultures of porcine pituita ry cells were treated with PACAP38 and PACAP27, and GH release, intrac ellular GH content, and GH mRNA levels were evaluated. Also, the time course of changes in the somatotrope content of GH and its mRNA in res ponse to PACAPs were measured. Both PACAPs stimulated GH release from porcine somatotropes in a broad range of doses (10(-10)-10(-6) M), yet only PACAP27 elicited a dose-dependent response. GH cell content rema ined essentially unchanged after PACAP treatment. In contrast, both PA CAPs induced significant and sustained increases in GH mRNA cell conte nt, although the response to PACAP27 appeared faster (8 h) than to PAC AP38 (16 h). These results demonstrate that PACAP stimulates GH produc tion in porcine somatotropes. Furthermore, the differential responses induced by PACAP38 and PACAP27 suggest that distinct mechanisms mediat e their effects on this cell type.