Effect of Ca antagonist on prostaglandins and thromboxane B₂ in blood and urine

Abstract

In the present study, the effects of calcium antagonist [Nicardipine hydrochloride (NH)] on the prostaglandin [prostaglandin E₂ (PGE₂), and 6-keto-prostaglandin F_1α (6-keto-PGF_1α)] and thromboxane B₂ levels in the blood and urine were examined in 6 patients with essential hypertension following intravenous infusion of NH for 120 minutes. At the same time, the plasma reamn activity (PRA), plasma aldosterone concentration. (PAC), and plasma and urinary electrolyte levels were also determined. During NH administration, the blood pressure was significantly decreased (p<0.05) with an increased pulse rate (p<0.05). PRA was significantly increased after NH loading (p<0.05) but PAC showed no change. The plasma PGE₂ and 6-keto-PGF_1α levels tended to increase slightly, while the blood thromboxane B₂ level showed a decreasing tendency, The 6-keto-PGF_1α to thromboxane B₂ ratio was significantly increased after NH loading as compared to the preloading ratio (p<0.05), and then returned to the preloading value at about 30 minutes after discontinuation of NH loading. On the other hand, concerning the urinary excretions of PGE₂, 6-keto-PGF_1α and thromboxane B₂, PGE₂ and 6-keto-PGF_1α tended to decrease after NH loading. In particular, the decrease in PGE₂ was statistically significant (p<0.05). No change occurred in the urinary excretion of thromboxane B₂. The above findings indicate that NH increased the plasma 6-keto-PGF_1α to thromboxane B₂ ratio but decreased the urinary excretion of prostaglandins. In addition, the possible involvement of an enhanced 6-keto-PGF_1α/thromboxane B₂ ratio in part of the hypotensive mechanism of NH is suggested.