Effects of dopamine and sodium nitroprusside on myocytes of regional arteries and veins during whole-body hypothermia and hypoxia.

In experiments on cats, dopamine induced constriction, while sodium nitroprusside dilation of arteries and veins perfused with a constant volume of autoblood in the decentralized gastrocnemius muscle and small intestine. Vascular responses to both test substances were reduced under the effect of hypothermia and especially under the effect of hypoxia alone. During combined exposure to hypoxia and hypothermia the decrease in the amplitude of vascular responses to dopamine and sodium nitroprusside was similar to that observed during hypoxia alone.

Dilatory humoral adrenergic reactions of regional veins and arteries during systemic hypoxia and hypothermia.

In experiments on anesthetized cats, perfusion of neurally decentralized vessels in the gastrocnemius muscle and small intestine with constant flow of autoblood containing isoproterenol induced dilator reactions in arteries and veins. Against the background of hypoxic hypoxia, the reactions of arteries and veins in the gastrocnemius muscles and veins in small intestine attenuated, although the arterial reactions in the latter region did not change. Total hypothermia (30 degrees C) attenuated the dilator reactions in regional vessels. Under the combined action of hypoxia and hypothermia, the amplitudes of dilator reactions of muscle vessels and intestine veins were equal to the baseline values, although the responses of intestinal arteries were pronouncedly weakened. It is concluded that blood vessels in the gastrocnemius muscle and veins in the small intestine possess positive resistance to whole-body hypoxia and hypothermia.

[Adrenergic responses of arterial and venous vessels in the cat skeletal muscle in hypoxia and hypothermia]. / Adrenergicheskie reaktsii arterial'nykh i venoznykh sosudov skeletnoi myshtsy koshki pri gipoksii i gipotermii organizma.

In 12 anesthetized cats both hypoxia and hypothermia enhanced the shifts in arterial resistance against blood flow in response to noradrenaline and diminished the shifts in response to isoproterenol. Combination of both stress factors considerably weakened the adrenergic vasoconstriction and rather little affected the adrenergic vasodilatation. The findings suggest that protective effect of hypothermia against the background of a hypoxic stress might be a mechanism preventing disorders in the tissue metabolism.

Adrenergic reactivity of visceral veins in hypoxia and hypothermia.

Adrenoreactivity of veins in skeletal muscle to norepinephrine decreased, while reactivity of intestinal veins remained virtually unchanged during combined exposure to hypoxia and hypothermia. In skeletal muscles cooling enhanced the direct effect of hypoxia on vascular smooth muscle cells, while in the intestine hypothermia prevented hypoxia-induced endothelial dysfunction, as it did under normothermic conditions. The results of experiments on the intestine indicated possible protective effect of hypothermia with respect to hypoxia-induced damage, and experimental findings on muscles showed potentiation of the direct effect of oxygen deficiency on venous smooth muscles.