In the following investigation, we have studied the role of polyamines in the regulation of atrial natriuretic peptide (ANP) using ventricular cardiocytes which in culture synthesize and secrete ANP. Polyamines are cellular cations ubiquitous in eukaryotes, and ANP is a hormone synthesized and secreted by the cardiac atria in adult animal. The cardiocytes were isolated from neonatal rat hearts by enzymatic dissociation using trypsin and collagenase. The functional role of polyamines in regulation of ANP was assessed by exposing the cardiocytes to difluoromethylornithine (DFMO) which is an inhibitor of ornithine decarboxylase, an initial rate-limiting enzyme in the biosynthesis of polyamines. The results showed that DFMO reduced the levels of putrescine (diamine) and spermidine (triamine) in cultured cardiocytes, and it decreased the levels of ANP in media and cellular extracts of cardiocytes as a function of its dose. An addition of putrescine (100 microM) restored within 5-15 min the levels of ANP in media of both control and polyamine-depleted cardiocytes. These results suggest that polyamines are one of the cellular factors involved in regulation of ANP secretion in cultured cardiocytes.