Presence of pituitary adenylate cyclase activating polypeptide and its type I receptor in the rat kidney.

Pituitary adenylate cyclase activating polypeptide (PACAP), a multifunctional neuropeptide, has 2 active forms, PACAP38 and PACAP27. It is now well-established that PACAP has several actions also in peripheral organs, including renoprotective effects. The peptide itself has not been previously identified in the rat kidney. The first aim of our study was to identify PACAP in the rat kidney using mass spectrometry and radioimmunoassay (RIA). Receptor mRNA and binding studies revealed the existence of all 3 PACAP receptors (PAC1, VPAC1, and VPAC2) in the kidney, but their exact localization in histologic sections was not evident. Because most of the cytoprotective effects of PACAP relate to its specific PAC1 receptor, our second aim was to identify the cell types wherein the PAC1 receptor is expressed in the rat kidney. Mass spectrometry revealed the presence of PACAP38 in the kidney. RIA measurements showed both PACAP38- and PACAP27-like immunoreactivities in kidney homogenates, with PACAP38 being dominant. Immunohistochemistry revealed PAC1 receptor-like immunoreactivity in kidney sections, mainly expressed in cortical tubular epithelial cells. These results showed PACAP to be endogenously present in the kidney. The tubular localization of the PAC1 receptor provides the basis for the renal effects of the peptide under physiologic and pathologic conditions.