Cardiac Output in Conscious and Almost Unrestrained Spontaneously Hypertensive Rats

Cardiac output and arterial pressure in the conscious state were measured in spontaneously hypertensive rats and normal control rats with chronically implanted electromagnetic flow probe and arterial indwelling cannula. Cardiac index at rest was greater in hypertensive rats than in controls. However, the mean arterial pressure in probe implanted hypertensive rats was significantly lower than that in those without probe. Even in probe implanted hypertensive rats, those with relatively higher arterial pressures showed elevated total periperal resistance and normal cardiac output. These findings suggest that the hypertensive state is maintained by elevated total peripheral resistance with normal cardiac output and that aortic probe implantation induces a decrease in total peripheral resistance, which, being a decrease in afterload, brings rise to an increase in cardiac output. The increase in cardiac output in transposition response induced by transposing the rat from the home cage to a new cage was greater in hypertensive rats than in controls. The decrease in cardiac output in grasp response induced by grasping the rat by the human hand was insignificant in hypertensive rats.