Central hemodynamic effects of recombinant human relaxin in the isolated, perfused rat heart model

Objective: To determine the cardiac effects of relaxin in the isolated, perfused rat heart model, and to see if pregnancy modifies the hormone's actions. Methods: Hearts were excised from 18 female Sprague-Dawley rats (ten pregnant, eight nonpregnant) and attached to a Langendorff apparatus. Left ventricular systolic pressure, heart rate, and contractility were measured. Hearts were exposed serially to 0.5, 1.0, 2.0, 4.0, 8.0, and 16.0 ng/mL concentrations of recombinant human relaxin. Results: Hearts from pregnant rats had lower heart rates than those from nonpregnant animals. Relaxin increased heart rate, left ventricular systolic pressure, and contractility in a dose-dependent fashion. Pregnancy did not modify this response. Conclusion: Recombinant human relaxin is a potent inotropic and chronotropic agent. The effects coupled with the physiologic increase of relaxin during human pregnancy indicate that relaxin may be involved in the cardiovascular changes of pregnancy.