V.N. Yartsev - Ph.D. (Biol.), Senior Research Scientist, Pavlov Institute of Physiology, RAS (St. Petersburg). E-mail: yartsev@infran.ru

Cold-induced constriction of the skin vessels is known to result from the stimulation of the cold-sensitive afferents and sympathetic nerves, increased sensitivity of the smooth muscle cells to noradrenaline, and inhibition of the NO system [1]. Reduced blood flow to the skin layers may result in local pH decrease capable to change blood vessels reactivity [2], but the data concerning effect of cooling on the neurogenic tone of the isolated blood vessels depending on the pH value and noradrenaline concentration are lacking. In order to get them we have performed this study on the segments of the rat tail artery. Neurogenic tone of the vessel segment was simulated by periodic electrical field stimulation. The segment contraction at the stimulation parameters used resulted from perivascular nerves stimulation, as we have shown previously [3]. In four series of experiments, the combination of temperature and pH in the organ bath was as follows: 36 °С and 7.4, 36 °С and 6.6, 25 °С and 7.4, 25 °С and 6.6. In the absence of noradrenaline, neurogenic tone decreased after cooling at all frequencies of electrical stimulation. In the presence of 0.03-0.10 μM noradrenaline, neurogenic tone decreased (at 5 Hz and 10 Hz) or did not changed (at 3 Hz and 40 Hz) after cooling at pH 7.4, but at pH 6.6 it increased at all frequencies of stimulation. In the presence of 0.03-0.10 μM noradrenaline, neurogenic tone observed after cooling at pH 6.6 was much higher in comparison to the tone observed in the normal temperature and pH solution, at 40 Hz stimulation only. We believe that cold-induced vasoconstriction is mainly caused by augmented neurogenic tone decreased by cold, but counteracted by noradrenaline in concentration of 0.03 μM which is close to its concentration in blood during cold stress. This tone can rise considerably at high frequency of electrical field stimulation at acidosis which can develop in the skin as a result of the initial reflex skin vessels contraction in response to the cold-induced augmentation of the sympathetic activity.

 

1. Johnson J.M., Kellogg D.L. Jr. Local thermal control of the human cutaneous circulation //J. Appl. Physiol.2010.V. 109 (4). P. 12291238.
2. Yartsev V.N., Karachentseva O.V., Dvoretsky D.P. EffectofpHchangesonreactivityofratmesentericarterysegmentsatdifferent magnitude of stretch // Acta Physiol. Scand. 2002.V. 174 (1). P. 17.
3. Dvoretsky D.P., Yartsev V.N., Karachentseva O.V., Granstrem M.P.Changes in reactivity of rat arteries subjected to dynamic stretch // Acta Physiol. Scand. 2000.V. 169 (1). P. 1320.