Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) relax cholecystokinin-induced tension in guinea pig gallbladder strips.

Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) have been shown to relax various types of smooth muscle, e.g. vascular, uterine and gastric. This study demonstrates that PTH and PTHrP both relaxed cholecystokinin octapeptide (CCK)-induced tension in guinea pig gallbladder strips. This relaxation was concentration-dependent. The use of PTHrP (7-34) blocked the relaxant effect of both agents. This suggested PTH and PTHrP were acting through the same receptor. The use of Rp-cAMPs, an inhibitor of cAMP activation of protein kinase A, and H-89, a selective inhibitor of protein kinase A, suggested that cAMP mediated the relaxant action of PTH and PTHrP. The use of iberiotoxin indicated that the high conductance Ca(2+)-activated potassium channels also mediated the actions of PTH/PTHrP. The use of KT5823, a selective blocker of protein kinase G, also decreased the amount of relaxation induced by PTH/PTHrP. This suggested that crosstalk between the two second messenger (cAMP and cGMP) systems occurred.