The heart as an endocrine gland.

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Abstract
The sequence of atrial natriuretic factor (ANF) has been determined, as well as the complete structure of the rat and human complementary DNA and gene. ANF and ANF messenger RNA are present not only in atria but also in ventricles. The circulating form of ANF has been identified as the C-terminal of the molecule, ANF (Ser 99-Tyr 126). The isolated secretory granules of rat atrial cardiocytes contain only pro-ANF (Asn 1-Tyr 126). An enzyme (IRCM-SP1) has been isolated from heart atria and ventricles. This enzyme is highly specific in cleaving ANF (Asn 1-Tyr 126), to yield ANF (103-126), (102-126), and (99-126). In target cells, ANF produces a rise in cyclic guanosine 3',5'-monophosphate (cGMP) due to activation of particulate guanylate cyclase, and inhibition of adenylate cyclase leading in some cases to a decrease in cyclic adenosine 3',5'-monophosphate (cAMP). ANF produces relaxation of rabbit and rat aortic strips, inhibits steroidogenesis in both zona glomerulosa and zona fasciculata cells, and inhibits the release of arginine vasopressin from the isolated rat hypothalamohypophysial preparation in vitro but decreases AVP release in vivo only at pharmacological doses. In all forms of experimental hypertension, plasma levels of ANF are increased and, at some time periods, atrial levels are also decreased. The ventricular levels of immunoreactive ANF are also increased in renal hypertension. Infusion of ANF by minipumps decreases the blood pressure near control levels in several models of experimental hypertension. In cardiomyopathic hamsters with heart failure, the atrial levels of immunoreactive ANF are decreased while the plasma and ventricular levels are increased.(ABSTRACT TRUNCATED AT 250 WORDS)