VASOACTIVE INTESTINAL POLYPEPTIDE (VIP) - EFFECT ON RABBIT UTERINE SMOOTH-MUSCLE INVIVO AND INVITRO

The effect of vasoactive intestinal polypeptide (VIP) on uterine smooth muscle electrical and mechanical activity in non-pregnant estradiol-treated rabbits was investigated using in vivo and in vitro methods. The studies were performed on spontaneous and oxytocin-, carbachol- and prostaglandin F2.alpha.-induced activity. VIP had a dose-related inhibitory effect on both myoelectrical and mechanical activity. The concentration needed for 50% inhibition (ID50) was 2 .times. 10-10 mol VIP.cntdot.1-1 (in vivo), and 6 .times. 10-8 mol VIP.cntdot.1-1 (in vitro). This inhibition was unaffected by the presence of atropine (10-5 mol.cntdot.1-1), propranolol (10-5) phentolamine (10-5), naloxone (10-5), apamin (10-4), and tetrodotoxin (10-5). These findings indicate that VIP may act via a specific receptor on the smooth muscle and support the hypothesis that VIP may be a neurotransmitter involved in the local nervous control of uterine smooth muscle activity.