Effect of PTH on blood pressure and response to vasoconstrictor agonists.

Parathyroid hormone (PTH) is known to be a vasodilator and to exert a hypotensive action. The present study examined the possible mechanisms involved, with special emphasis on the role of vasodilatory prostaglandins. The effects of the intact 1-84 PTH and that of its amino-terminal 1-34 fragment on mean arterial pressure (MAP) and on the vascular response to norepinephrine (NE) or angiotensin II (ANG II) were examined in rats before and after pretreatment with indomethacin. Bolus injections of 30 U of both 1-84 and 1-34 PTH produced a significant (P less than 0.01) decrease in MAP; however, the hypotensive response to 1-34 PTH (-28 +/- 4.6 mmHg) was more marked (P less than 0.01) than to 1-84 PTH (-9 +/- 1.8 mmHg). The infusion of 1-84 PTH (30 U/h) did not alter MAP, whereas the infusion of 1-34 PTH (30 U/h) led to a decrease in MAP from 124 +/- 2 to 103 +/- 4.0 mmHg (P less than 0.01) and to a rise in heart rate from 359 +/- 30 to 437 +/- 13 beats/min (P less than 0.02). Both 1-84 and 1-34 PTH antagonized the pressor effects produced by bolus injections of NE and ANG II. Pretreatment with indomethacin (5 mg/kg body wt) abolished the inhibitory effect of 1-84 and 1-34 PTH on the response of MAP to NE and ANG II and the hypotensive action of 1-34 PTH. Infusion of 1-84 and 1-34 PTH produced a significant rise in urinary excretion of 6-keto-PGF1 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)