Effects of rapid and slow cooling on thermoregulatory reactions in hypertensive rats after administration of calcium.

Iontophoretic administration of calcium ions into the skin close to the application site of a cold stimulus decreased the threshold of thermoregulatory reactions in hypertensive rats to a greater extent than in normotensive control animals, which may be evidence that the tissues involved in thermoregulatory reactions to cold have a greater sensitivity to calcium in hypertensive rats. The initially earlier onset of vascular and metabolic reactions and the increase in the vascular reaction seen in hypertensive rats became more marked after administration of calcium. Treatment with calcium, increasing the vascular reaction to cooling, facilitates a more marked discrimination between hyper-and normotensive animals in terms of the appearance of the vasoconstrictor reactions of skin blood vessels in response to cold. The effects of the added calcium on cold-dependent reactions depended on the rate of cooling.

[Cold-induced changes in blood lipoproteins in normotensive and hypertensive rats].

It is shown that in thermoneutral conditions ISIAH (Inherited Stress-Induced Arterial Hypertension) hypertensive rats had a lower level of high-density lipoproteins (HDLP) in plasma and a higher atherogenic coefficient compared to normotensive Wistar rats. After cooling there were different changes in fractional composition of plasma lipoproteins both in normo- and hypertensive rats. These changes depended on the cooling rate and were more pronounced after slow cooling. Slow cooling resulted in a more significant increase of plasma HDLP and in a greater decrease in LDLP and atherogenic coefficient in hypertensive rats compared to normotensive ones.

[Effect of rapid and slow cooling on thermoregulatory responses in hypertensive and normotensive rats after calcium administration].

The effect of iontophoretic administration of calcium ions to skin in the area of cold stimulus application on the thermal thresholds and the magnitude of cold defense responses in normotensive Wistar and hypertensive ISIAH rats was studied. In thermoneutral conditions, administration of calciumions wos without effect on the measured thermoregulatory parameters. Under the effect of calcium, the thresholds of all the thermoregulatory responses to cooling (such as heat loss, oxygen consumption, shivering) are lowered and the values of heat loss and shivering thermogenesis are considerably increased. The effects of calcium on thermoregulatory responses depend on the rate of cooling. All changes are more expressive in hypertensive rats. The increased sensitivity of hypertensives to calcium suggests that change in their calcium metabolism may be a cause of the observed shifts in the thermoregulatory response to cold.

Slow cooling improved blood lipoprotein composition in hypertensive rats.

Under normal thermal conditions, hypertensive NISAG rats are characterized by lower plasma levels of high-density lipoproteins and increased coefficient of atherogenicity compared to normotensive Wistar rats. Slow cooling significantly modified fractional composition of plasma lipoproteins in hypertensive rats: decreased the content of low-density lipoproteins, markedly increased the content of high-density lipoproteins, and normalized coefficient of atherogenicity. Our results demonstrated the possibility of correcting disturbances in lipoprotein spectrum in essential hypertension by using thermal exposures.

Thermoregulatory reactions to cooling in rats with hereditary arterial hypertension.

Experiments on rats with hereditary stress-induced arterial hypertension showed that hypertension shortened the latency and increased the amplitude of constrictive reaction of skin blood vessels to rapid cooling characterized by more rapid and considerable increase in blood norepinephrine content compared to slow cooling. Decreased thermal threshold of metabolic reaction suggests that arterial hypertension is accompanied by changes in both the vascular walls and tissues involved in metabolic reaction to cooling.