Effect of thromboxane synthetase inhibitors on yohimbine-induced norepinephrine release in the circulation.

The role of thromboxane on norepinephrine release mediated by the presynaptic alphareceptor is studied in conscious rabbits. Intravenous administration of yohimbine, a preferential alpha-2 receptor antagonist increases mean arterial pressure (MBP) by 10 to 15%; the plasma norepinephrine concentration by 71 to 125%. OKY-046, a specific thromboxane synthetase inhibitor, fail to affect the baseline levels as well as yohimbine-induced increases in the MBP and plasma norepinephrine. Yohimbine administration increased plasma renin activity by 27 to 41% which are not affected by OKY administration. These results indicate that the thromboxane system does not affect the norepinephrine release from the nerve terminals by the presynaptic receptor-mediated mechanism. The effect of thromboxane on the renin release is minor and the thromboxane system per se may not play an important role for the renal renin regulation.