Novel cardiac peptide hormone in several teleosts

To find out the significance of the newest member of the natriuretic peptid e family, salmon cardiac peptide (sCP), we have determined the distribution of the peptide and its mRNA as well as the tissue and plasma molecular for ms in several telecosts. Using probes based on the salmon sCP cDNA in North ern biot analysis we found mRNA homologous to that of sCP to be present in the heart of 15 fish species representing nine different genera, We develop ed a specific RIA for the salmon 29 amino acid peptide to be able to study the distribution of the peptide in the heart and plasma of different fish s pecies. Despite the probable interspecies differences in the peptide sequen ce, large quantities of immunoreactive sCP were found ill the atrium, ventr icle and plasma of most of the fish species studied, suggesting that a card iac hormone homologous to sCP has an endocrine function in a large variety of telecost species, The molecular form of the hormone secreted and stored in the tissue was determined by gel filtration high pressure liquid chromat ography. In salmon, as in most of the other fish species studied, the predo minant immunoreactive sCP in plasma corresponded to the low molecular weigh t form, with a size similar to that of the biologically active 29 amino aci d sCP (sCP-29), whereas the form stored in the heart corresponded to the hi gh molecular weight pro-sCP-sized material. The form secreted by isolated p erfused salmon ventricle, in the basal state as well as when mechanically l oaded, was the sCP-29-sized peptide, thus filling out the possibility that the conversion from high to low molecular weight material is caused by plas ma proteases. In conclusion, sCP-like peptides are produced and secreted Fr om the heart of a large number of different fish species. Their post-transl ational processing appears to be remarkably similar to that of mammalian at rial natriuretic peptide.