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

Arginine vasopressin (AVP) (0.03-3 microM) 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 microM), 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 microM). AVP (1 microM) 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.