NATRIURETIC PEPTIDES ELEVATE CYCLIC 3',5'-GUANOSINE MONOPHOSPHATE LEVELS IN CULTURED RAT PINEALOCYTES - EVIDENCE FOR GUANYLATE CYCLASE-LINKED MEMBRANE-RECEPTORS

Cyclic GMP formation in the rat pinealocyte has generally been thought to involve guanylate cyclases (GC) which are activated via GTP-regulatory proteins following beta(1)-adrenergic receptor stimulation. Recent studies have also pointed to a cytosolic GC in these cells whose activity can be elevated by nitric oxide donors. Little attention has been paid to the possibility that pinealocytes might express membrane-bound GC in the form of natriuretic peptide receptors. The present report demonstrates functional membrane GC in rat pinealocytes by (1) cross-linking analyses with radiolabelled atrial natriuretic peptide (ANP); (2) reverse transcriptase polymerase chain reaction (RT-PCR) and DNA blot hybridization with probes for both the GC-A and GC-B forms of the natriuretic receptor; and (3) monolayer cell cultures of pinealocytes, which accumulate cGMP in response to ANP and its related peptides. As the role for cGMP in the rat pineal gland does not appear to be directly coupled to the synthesis of melatonin, the natriuretic peptides may have other regulatory functions in this neuroendocrine tissue.