Novel salmon cardiac peptide hormone is released from the ventricle by regulated secretory pathway

We used the secretion of the novel salmon cardiac peptide (sCP) as a model to examine the mechanisms of ventricular hormone release. Mechanical load i ncreased dose dependently the secretion of immunoreactive sCP from isolated perfused salmon ventricle, with 3.3-fold increase when a load of 13 cmH(2) O was applied. Endothelin-1 (5 nmol/l) was also able to rapidly increase th e secretion of sCP. The released peptide corresponded to the biologically a ctive sCP-29, whereas the large ventricular storage consisted of pro-sCP-si zed material. With the use of immunoelectron microscopy, a large number of granules containing immunoreactive sCP could be detected in salmon ventricl e. As judged by RNA blot analysis, there was very active basal expression o f the sCP gene in the ventricle, which was not increased by mechanical load of up to 2-h duration. Our results show that the ventricle actively expres ses the gene of sCP, stores the prohormone in secretory granules, and relea ses the peptide in response to mechanical load and endothelin-1. Thus the s almon ventricle uses the regulated pathway to produce and release a hormone structurally related to the mammalian natriuretic peptides.