On the inotropic actions of arginine vasopressin in ventricular muscle of the guinea pig heart

Arginine vasopressin (AVP) (0.03-3 mu M) produced transient negative responses that were followed by slowly developing positive inotropic responses in guinea pig papillary muscles. The inotropic responses were antagonized by OPC-21268 (10 mu M), but not by OPC-31260, and suppressed by neomycin (3 mM). The negative inotropic response was hardly affected by staurosporine (10 nM) and H-7 (10 mu M). AVP (1 mu M) elicited a transient decrease followed by a slowly developing increase in I-Ca. The latter increase in I-Ca was not elicited in the presence of staurosporine (1 nM). These results indicate that AVP stimulates V1 receptors that couple to phosphoinositide hydrolysis and thereby increases intracellular Ca2+ and activates protein kinase C.