[Reactions of the microcirculatory bed of cat mesentery during exposure to heat].

The TV-microscopy in cats revealed that, by the 30th minute of 2-hr overheating, the arterioles are dilated and venules constricted. In the course of raise of body temperature from 36 degrees to 40 degrees C, the number of dilatory and constrictory responses of venules remains the same while the number of arteriole dilatory responses diminishes and of constrictory responses increases. At 40 degrees C of body temperature, the number of dilatory responses of the mesenteric arterioles and venules makes about 20--30% while the number of constrictory responses--70--80%. The extent of dilation of arterioles and venules increases with the heating while the extent of constriction, having achieved a certain level, starts to diminish. The greatest responses occurred in the microvessels with initial diameter 60 and more microns. The responses of microvessels with a lesser diameter could be different. The data obtained using hexonium, dihydroergotoxin, inderal, atropin, dezeril, methyamide, and tavegil, suggest participation of adrenergic and histamingergic substances in vasomotor responses of the microvessels to the hyperthermia.