[Seasonal changes in cutaneous blood vessel tone in the frog Rana esculenta]

Experiments have been carried out on frogs immobilized by diplacine. The diameter of arteries and veins in the web was measured before and after sectioning the sciatic nerve. Denervation of the hindlimb resulted in dilatation of web vessels, which was different at various seasons. Changes in the arterial tone were found to be polyphasic. The highest tone was observed in March, April and September, the lowest one-in May, August, October and January. Changes in the venous tone are less pronounced and follow biphasic pattern, the tone being increased in spring and summer and decreased in autumn and winter. Stimulation of the peripheral end of the sectioned nerve leads to the constriction of web vessels, its amplitude being dependent on the level of vascular tone at the given period of year. It is suggested that seasonal changes in the tone of cutaneous arteries are partially based on changes in the reactivity of the blood vessels.