[Reactivity of the arterial system during vasodilation induced by sodium nitroprusside]

A stepwise decrease in the blood pressure by means of sodium nitroprusside infusion led to progressing diminishing of mesatone pressor effects in anaesthetised rats. Cardiac output changes due to mesatone administration did not depend on the initial blood pressure. The latter being lower than physiological limits, a direct linear correlation occurred between pressor responses and shifts of general peripheral resistance, on one hand, and the degree of the blood pressure initial drop, on the other hand. The constrictor responses under study are discussed in respect to their dependence on initial tone of arterial vessels.