Plasma catecholamines in human and experimental hypertension.

Plasma levels of norepinephrine reflect the rate of its release from sympathetic nerves. In patients with hypertension and in spontaneously hypertensive (SHR) rats basal plasma NE levels are normal. SHR rats are abnormally reactive to stress, as are the normotensive (WKY) strain from which they were derived. The amounts of NE released by sympathetic stimulation are similar in pithed SHR and WKY rats, but SHR rats have greater blood pressure responses. This may be due to diminished beta-adrenoceptor-mediated vasodilation in young SHR rats and structural changes in arterioles of older SHR rats. It is concluded that in SHR rats separate abnormalities of centrally-mediated responses to stress and of peripheral sensitivity to catecholamines contribute to the development and maintenance of elevated blood pressure.