RENOVASCULAR PARATHYROID HORMONE-RELATED PROTEIN IN SPONTANEOUSLY HYPERTENSIVE RATS - DILATOR OR TROPHIC FACTOR

Parathyroid hormone-related protein (PTHrP) is expressed throughout th e renovascular system, and it dilates renal vessels, increases renal b lood flow and glomerular filtration rate, and stimulates renin release . Mechanical forces and experimental hypertension have been shown to s timulate PTHrP expression in smooth muscles, suggesting a negative fee dback control of vascular tone by PTHrP in hypertension. In this study , we compared the impact of a PTHrP receptor antagonist, PTHrP (7-34), and a PTHrP receptor agonist, PTHrP (1-36). on the vascular resistanc e of perfused kidneys isolated from spontaneously hypertensive rats (S HR) and Wistar Kyoto rats (WKY). Endogenous PTHrP appears not to act a s a renal vasodilator in either WKY or SHR. However, the vasodilation following infused PTHrP (1-36) is blunted markedly in SHR, possibly du e to desensitization or down-regulation of PTH/PTHrP receptors. Negati ve feedback control of vascular tone by PTHrP in SHR thus appears unli kely. The results raise the question of whether endogenous renovascula r PTHrP behaves rather as a growth factor than as a vasodilator.