[Effectiveness and mechanisms of the protective action of sidnocarb in experimental weightlessness and cooling]

Twenty-one subjects took part in experiments with acute cooling (maximally allowable time for swimming in ice-cold water and two-day exposure to winter field conditions) or two-day exposure to microgravity (simulated by water immersion). They were divided into a placebo group (5, 5 and 6 man-exposures) and a sydnocarb group (6, 6 and 4 man-exposures) and examined by biochemical, radioimmune and radioligand methods. It was found that physiological responses to cold and microgravity effects as well as sydnocarb were similar. During cold exposures the thermal steady-state was achieved by taking maximum daily doses of the drug. In thermoneutral water immersion body temperature fall was controlled by therapeutic doses of the drug. Body temperature decline beginning with immersion day 2 can be related to the endogenous decline of heat production due to a new functioning level which is well known in gravitational physiology, i. e. this is the effect of microgravity per se. With respect to old and new information about the pharmacological properties of sydnocarb, mechanisms of its high thermoregulatory effects on CNS structures responsible for heat production and heat loss are discussed.