In the present study, the effects of calcium antagonist [Nicardipine hydrochloride (NH)] on the prostaglandin [prostaglandin E
2 (PGE
2), and 6-keto-prostaglandin F
1α (6-keto-PGF
1α)] and thromboxane B
2 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 PGE
2 and 6-keto-PGF
1α levels tended to increase slightly, while the blood thromboxane B
2 level showed a decreasing tendency, The 6-keto-PGF
1α to thromboxane B
2 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 PGE
2, 6-keto-PGF
1α and thromboxane B
2, PGE
2 and 6-keto-PGF
1α tended to decrease after NH loading. In particular, the decrease in PGE
2 was statistically significant (p<0.05). No change occurred in the urinary excretion of thromboxane B
2. The above findings indicate that NH increased the plasma 6-keto-PGF
1α to thromboxane B
2 ratio but decreased the urinary excretion of prostaglandins. In addition, the possible involvement of an enhanced 6-keto-PGF
1α/thromboxane B
2 ratio in part of the hypotensive mechanism of NH is suggested.
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