Pituitary adenylate cyclase activating polypeptide (PACAP): occurrence and vasodilatory effect in the human...

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide which was originally isolated from ovine hypothalamus. PACAP exists in at least two biologically active forms, PACAP-38 and PACAP-27. The aim of this study was to establish the distribution, localization and smooth muscle effects of PACAP-38 and PACAP-27 in the human uteroplacental unit. For this purpose we used radioimmunoassay, immunocytochemistry and in vitro studies of the effect of the peptides on smooth muscle activity.

By radioimmunoassay both peptides were detected throughout the uteroplacental unit. The concentrations of PACAP-27 were in general low, ranging from 1/6-1/25 of the corresponding PACAP-38 concentrations. PACAP-immunoreactivity was localized in nerve fibres of the lower segment of the pregnant uterus, but the number of PACAP-immunoreactive nerves was very clearly reduced compared to the corresponding isthmic region of non-pregnant myometrial tissue. PACAP-immunoreactive fibres were not observed in placenta or in the umbilical cord. Both PACAP-38 and PACAP-27 caused a concentration-dependent relaxation on stem villous arteries and on the intramyometrial arteries. Neither of the peptides displayed any effect on non-vascular smooth muscle specimens from the term pregnant myometrium. In conclusion the findings suggest a vasoregulator role of PACAP in the human uteroplacental unit.