Neurohypophysial hormones and cardiac activity in the frog, Rana tigrina, and in the snake, Ptyas mucosa.

The cardiac effects of neurohypophysial hormones (NH) in the frog, Rana tigrina, and in the snake, Ptyas mucosa, were studied in isolated atrial preparations. Arginine vasopressin (AVP), vasotocin (AVT), isotocin (ISN), mesotocin (MSN), and oxytocin (OXY) produced dose-related positive chronotropic and inotropic responses in the frog atria. AVT was the most potent. In the snake, AVP, AVT, MSN, and OXY produced dose-related positive inotropic but not chronotropic changes. OXY was the most potent. Data indicate that there is a direct action of NH on the heart in both animals, the atrial rate and tension responses to NH are not coupled, and judging by the efficacy, AVT and OXY might be the natural NH in the frog and snake, respectively, which may account for the high concentrations required of other NH to be cardiac stimulating.