Stretch-induced release of atrial natriuretic factor from the heart of rainbow trout (Oncorhynchus mykiss)

We investigated the effect of both cardiac filling and after-load pressures on the release of atrial natriuretic factor (ANF) from rainbow trout hearts (Oncorhynchus mykiss). Our experimental approach was to perfuse hearts in situ and collect perfusate ejected from the heart in 1-min fractions and assay for immunoreactive ANF-(99-126) (human and canine). Increases in cardiac filling pressure produced repeatable and sustained increases in cardiac output. At the same time, there was an immediate and sustained increase in ANF secretion. ANF secretion increased sixfold from the control level of 30.68 ± 4.76 pg∙min −1 ∙g −1 wet heart mass for a fourfold increase in cardiac output from 15.24 ± 0.73 mL∙min −1 ∙kg −1 body mass. ANF secretion was unaffected by increases in after-load pressure. Measurement of immunoreactive ANF content in trout myocardial tissues revealed ANF in both the atrium and ventricle, but 92% of the total ANF store was contained within the atrium. This suggests that in rainbow trout, the atrium serves as the primary cardiac tissue for ANF release. These data are consistent with the mechanism of ANF release for mammalian hearts, and provide additional evidence that ANF secretion in vertebrates is mediated by atrial stretch and not ventricular stretch.