Metabolic and cardiovascular changes during physical restrains in rats.

When conscious rats were physically restrained, their body temperature, heart rate and heat production increased within minutes. The rate of increase in heat production was less than that in heart rate, particularly in warm environments. Reduction of oxygen pulse, consequently either stroke volume or (A-V) O2 difference, was suggested. Stroke volume cardiac output and its fractional distribution to most of the calorigenic organs measured by the reference sample method using 85Sr-labelled microspheres decreased significantly by restraint. However, fractional distribution of cardiac output increased greatly to the skeletal muscles. The restraint-hypermetabolism may be attributed to the increased metabolism of the skeletal muscles supported with an increased availability of oxygen. With a slight increase in mean aortic pressure, total peripheral resistance increased greatly as observed during Valsalva-like maneuver. The decrease in cardiac output and stroke volume during restraint may be caused by obstruction to the systemic venous return.