cAMP response of vascular smooth muscle cells to bovine parathyroid hormone

Parathyroid hormone (PTH) is a vasodilator of vascular smooth muscle tissue. It has been shown to produce this vasodilation in normotensive and hypertensive laboratory rats. The effect is log dose dependent, maximal at 1 min and persists for 3-5 min. The cellular mechanisms involved in PTH-mediated vasodilation are unknown. In this study, we sought to determine the cellular changes of cAMP after administration of bovine (b)PTH (1-34). cAMP content of vascular smooth muscle cells was measured at 30 s, 1, 3, and 5 min after incubation with synthetic bPTH (1-34). Tissue cAMP content was decreased by 55% at 1 min (4.1 +/- 0.5 pmol/mg protein at time 0 vs. 1.9 +/- 0.2 pmol/mg protein at 1 min, P less than 0.001). After 5 min, cAMP levels returned to base-line values and increased over the next 5-10 min to levels above base line (P less than 0.01). In conclusion, our data suggest that the initial response of vascular smooth muscle cells to short-term incubation with bPTH (1-34) is an acute decrease in cAMP content.