Effect of sodium nitroprusside on blood pressure responses to histamine

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Abstract
Effects of decrease in tone produced by sodium nitroprusside on blood pressure responses to histamine were studied in dogs anesthetized with sodium pentobarbital. A series of graded doses of l-histamine acid phosphate was given before and during infusion of sodium nitroprusside (three levels: 2,5 and 8 µg/kg/min.) and blood pressure responses to each dose of the administered histamine were recorded. Blood pressure records were analyzed in terms of minimum blood pressure attained, actual fall in blood pressure and duration of fall in blood pressure before and during the infusion. There was a significant reduction in the fall in blood pressure, but no significant change in the duration of the depressor response. The amount of reduction in minimum attained blood pressure decreased as the size of the dose of histamine increased. This together with the decrease in fall in blood pressure seems to indicate that decrease in blood vessel tone by the prior administration of sodium nitroprusside antagonizes the depressor response of histamine. The extent of this antagonism is such that the minimum obtainable blood pressure with maximum doses of histamine is unchanged by the infusion of sodium nitroprusside.

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