Temperature has a major influence on cardiac natriuretic peptide in salmon

1. Natriuretic peptides have a major role in fluid and electrolyte homeosta sis in vertebrates. Ambient temperature has a major influence on physiologi cal processes in ectothermic animals. Here we have studied the mechanisms o f regulation of a natriuretic peptide, sCP (salmon cardiac peptide), in sal mon (Salmo salar) acclimatised and acclimated to varying temperatures. 2. The circulating and cardiac levels of sCP were found to be markedly upre gulated in warm-acclimatised and warm-acclimated salmon. The release of sCP from isolated bi vitro perfused salmon ventricle was, however, not increas ed by acclimation to higher temperatures, either in basal conditions or NN, hen stimulated by mechanical load. 3. Concomitant measurements of circulating sCP and the biologically inert N -terminal fragment of pro-sCP showed that the upregulation of circulating s CP at warm ambient temperature results from decreased elimination rather th an increased secretion of sCP. This is the first direct evidence that chang es in the elimination of a natriuretic peptide are used for important, phys iological regulation. 4. We found a paradoxical increase in cardiac sCP mRNA levels at cold tempe ratures which coincided with hypertrophy of the heart. sCP gene expression may therefore serve as a marker of cardiac hypertrophy in salmon, in analog y to that of atrial and brain natriuretic peptide (ANP and BNP, respectivel y) in mammals. 5. These results show that temperature has a major influence oil the regula tion of natriuretic peptide production and clearance in salmon. Salmon CP o ffers a novel model for the study of the endocrine function of the heart.