Cardiac activity of some peptide hormones in the frog, Rana tigrina

Abstract

1. The cardiac responses of isolated frog ( Rana tigrina) atria to peptide hormones were studied. 2. Calcitonin gene-related peptide (CGRP), arginine vasotocin (AVT), bovine parathyroid hormone fragment (bPTH-(1–34)) and oxytocin (OXY) produced dose-related positive chronotropic and inotropic responses; atrial natriuretic peptide (ANP) was negative chronotropic and inotropic; cholecystokinin (CCK), vasoactive intestinal peptide (VIP) were without effects. 3. The dose-related responses under bPTH-(1–34) stimulation but not CGRP or AVT were attenuated in the presence of ANP (300 ng/ml, ≈0.98 × 10 −7 M). As expected ANP decreased the basal AR and AT responses of the isolated atria and the inhibitory effects were dose-dependent. 4. As shown previously, propranolol blocked the atrial tension stimulated by bPTH (1–34) but did not alter the cardiac responses to CGRP and AVT. 5. In the presence of β-adrenergic blocker (propranolol 10 −7M) or ANP (10 −7M), the AR and AT changes under ISO stimulation in the frog were also decreased. 6. These cardiac changes suggest the cardiac inhibitory effects of ANP are related to β-adrenoceptor activity and ANP might be a β antagonist.