Pituitary adenylate cyclase activating polypeptide induces vascular relaxation and inhibits nonvascular smooth muscle activity in the rabbit female genital tract

In vitro effects of two bioactive forms of pituitary adenylate cyclase activating polypeptide (PACAP): PACAP–38 and PACAP–27 were studied on rabbit vascular and non–vascular smooth muscle. Segments of the ovarian artery and muscle strips from the fallopian tube were used. Two series of experiments were performed on vessels: the dose–response relationship of PACAP–38 (10–10–7 M) was established on noradrenaline– (NA, 10–6 M) contracted vessels. In the other set of experiments the contractile effect of 10–8–10–4 M NA added cumulatively, was studied on arterial segments incubated with PACAP–38 (10–7 M), PACAP–27 (10–7 M) or VIP (10–7 M). The effect of PACAP–38, PACAP–27 and VIP (10–10–10–⁶ M) was investigated on spontaneously contracting smooth muscle of the fallopian tube. Longitudinally as well as transversally cut specimens were investigated. PACAP–38 produced a significant dose–related relaxation on the NA–precontracted vessels. However, pre–incubation of the vessels with 10–7 M PACAP–38, PACAP–27 and vaso active intestinal polypeptide (VIP) did not induce a general rightward shift of the NA concentration–response curves, although a tendency to inhibition in the low–dose interval was observed. The peptides caused a significant, dose–dependent inhibition of both frequency and amplitude on the fallopian tube smooth muscle activity. The effects of the three peptides on longitudinally as well as transversally cut specimens were alike.