EXPRESSION OF C-TYPE NATRIURETIC PEPTIDE IN THE BOVINE PINEAL-GLAND

Recent studies have pointed to membrane-bound guanylyl cyclases (GCs) type A and type B in the rat pineal gland, which augment levels of cyc lic GMP (cGMP) in response to atrial natriuretic peptide (ANP), brain- type natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). The present report demonstrates for the first time the expression of C NP in the bovine pineal gland, The CNP prohormone transcript (unlike p repro-ANP) was found by reverse transcriptase (RT)-PCR in bovine pinea l extracts, CNP immunoreactivity (ir) was revealed in a subpopulation of pinealocytes in situ and in nearly all pinealocytes in culture. Ele ctron microscopic immunohistochemical investigations showed the presen ce of CNP-ir in cytoplasmic vesicles, providing evidence for the poten tial secretion of this peptide by pineal cells. Furthermore, the CNP r eceptor (GC-B) and GC-A (receptor for ANP and BNP) were identified by RT-PCR. Although melatonin secretion was unaffected, natriuretic pepti des were able to elevate markedly cGMP production in cultured bovine p inealocytes with a rank order of potency of CNP > BNP = ANP, These fin dings describe a tissue CNP system in the bovine pineal gland and sugg est that CNP may be a local auto- or paracrine modulator of pineal fun ction.