[Potentiative effects of noradrenaline on the neurogenic vasoreactivity diminished by cooling].

The effect of 0.03--1.0 μM noradrenaline on the response to electrical field stimulation of the juvenile rat tail artery segment at 36 degrees C and after cooling to 25 degrees C was studied. At 25 degrees C, the neurogenic vasoconstriction was inhibited, but low dose noradrenaline potentiate the constriction. This potentiation was greater at 25 degrees C than at 36 degrees C, following spontaneous decline in the constriction counteracted by noradrenaline. At low temperature, the potentiative effects of noradrenaline were greater at high frequency of electrical field stimulation. The phenomenon of increase in the noradrenaline-evoked potentiation of neurogenic vasoconstriction inhibited by cold may be of importance for thermoregulation. It could provide restoration of diminished effectiveness of the neurogenic contractile signal thus leading to low heat emission at low temperature.