Studies on the cardiovascular actions of hydralazine.

Resumo

In conscious normotensive rabbits, the intravenous administration of hydralazine (0.3 mg/Kg) induced a significant decrease of mean arterial blood pressure (MBP) (p<0.001) and a significant increase of heart rate (HR) (p< 0.01). Pretreatrnent ot the animals with two prostaglandins (PGS) synthesis inhibitors, indomethacin (1  mg/Kg) and acetyisalicylic acid (10 mg/Kg) abolished the hypotensive effect (p> 0.05) and did not modify the tachycardia. In the same model, the continuous infusion of a PGS precursor, arachidonic acid (7.5-10 μg/Kg/min), modified the blood pressure lowering effect of hydralazine which began sooner and was considerably prolonged. In spontaneously beating guinea-pig isolated atria, hydralazine (X10^-5M) had no direct chronotropic effect and did not rnoclify the responses to noradrenaline (2 to 8X10^—7M) and isoprenaline (1 to 4X10^-8M), but markedly enhanced the tachycardia provoked by tyramine (1.5 and 3.0x10^-5M). These results suggest that the hypotensive effect of hydralazine in normotensive conscious rabbits are related to the endogenous PGS system and that hydralazine has a stimulating effect on the heart probably mediated by a modification of the adrenergic neurotransmission to the heart.