Microvascular pressure responses of second-generation rats chronically exposed to 2 G centrifugation

The purpose of thses studies was to compare systemic arterial and microvascular pressures in the second generation of rats reared in a 2-G centrifuge with pressure data from animals subjected to 1 G centrifugation. Systemic arterial pressures were measured in anesthetized animals via carotid catheters and microvascular pressures were measured in mesenteric arterioles by a micropipette servo-null system. Systemic arterial pressures in the 1-G and 2-G groups were not significantly different from each other, but both were considerably higher than those reported for normal rats. In the microcirculation, pressures in the terminal arterioles (20 to 35 micron) were significantly higher in the 2-G animals, but pressures at the level of the smaller (10 to 15 micron) precapillary arterioles were not significantly different between the two groups. The pressure responses to intravenous infusion of norepinephrine were also compared in the two groups and found to be significantly less in the 2-G animals. It is concluded that both 1 G and 2 G chronic centrifugation will elevate arterial blood pressure, and that 2 G, of itself, will affect the pressure distribution in the microcirculation as well as attenuate the pressor effects of norepinephrine.