Vasorelaxant effect of parathyroid hormone on isolated segments of porcine coronary artery.

Parathyroid hormone and it's aminoterminal 1-34 fragment, PTH-(1-34), are potent vasodilators of the coronary circulation in vivo. In order to fully characterize the mechanism of this effect on coronary vascular resistance, it was necessary to determine whether isolated coronary arteries would respond to the action of PTH-(1-34) in vitro. Porcine coronary arteries were cut into cylindrical segments, mounted in a muscle bath containing physiological salt solution, and precontracted with prostaglandin F2. After obtaining stable contractions, PTH-(1-34) was added over the dose range of 10(-10)-10(-7) M. The results showed that PTH-(1-34) produced a dose-dependent vasorelaxation of the coronary segments. A statistically significant relaxation was obtained at a concentration of 10(-10) M. The near-maximal relaxation was 77% with respect to control values. Thus, it has been shown for the first time that PTH-(1-34) relaxes precontracted coronary arteries in vitro, a finding which was consistent with the potent vasodilator action of the polypeptide hormone in vivo.