Effects of Cold on the Adrenoreactivity of the Rat Superior Mesenteric Artery

In experiments on segments of the rat superior mesenteric artery (SMA) under isometric conditions, the effect of cold on the reactivity of this artery, estimated by the magnitude of the contractile reaction of its segments to noradrenaline (NA) at a concentration of 0.01–10.0 µM, as well as to electrical field stimulation (EFS) of perivascular nerves with a frequency of 3, 10 and 40 Hz in the absence and presence of NA in the medium and at a temperature of 37 oC or 25 oC was studied. Cooling was found not to change the tone of the SMA caused by NA at all the concentrations used. In the absence and presence of NA at a low concentration (0.01–0.10 µM), cooling leads to a significant decrease in the neurogenic response of the SMA at all frequencies of EFS, while in the presence of NA at a high concentration (1–10 µM), cooling has no statistically significant effect on this response. In the presence of NA at a low concentration, cooling at low EFS frequencies insignificantly, and at high frequency significantly reduces the potentiating effect of NA on neurogenic contraction of SMA. NA at a high concentration under normal temperature conditions, reduces the neurogenic contraction at all EFS frequencies, while under cooling conditions at low frequencies it has a potentiating effect, and at high EFS frequency it has a depressing effect. The results obtained show that the depressing effect of cold on the neurogenic constriction of the rat SMA, observed at low and disappearing at high concentrations of NA, as well as on the NA-evoked potentiation of the neurogenic vasoconstriction, is not associated with a decrease in the contractile effect of NA, which is the main neurotransmitter in this artery. These effects can contribute to the redistribution of blood from the surface deep into the body, thus reducing heat loss and improve thermoregulation.