Cardiac effects of relaxin in rats.

Relaxin is usually considered to be a hormone of pregnancy, but porcine relaxin has been shown to increase heart rate in rats. We investigated the cardiac effects of synthetic human gene-2 relaxin (hRlx-2) in vitro in isolated rat atria. Synthetic hRlx-2 produced concentration-dependent positive chronotropic effects in spontaneously beating right atria (EC50 [concentration required to produce 50% of the maximal response] = 0.09 [SE 0.03] nmol/l) and concentration-dependent positive inotropic effects in electrically driven left atria (EC50 = 0.31 [0.02] nmol/l). The potency of hRlx-2 is greater than that of endothelin, angiotensin II, and (-)-isoprenaline in isolated rat atria. Relaxin has powerful chronotropic and inotropic effects on the heart that are probably mediated through a direct action on relaxin receptors.