The comparative effects of small intravenous doses of epinephrine upon arterial pressure and pulse rate in normotensive subjects and in hypertensive patients before and after thoracolumbar sympathectomy

Observations on the responses of rats with spontaneous hypertension and control rats to pressor drugs and to hexamethonium

The establishment, by selective breeding, of a colony of rats with a high incidence of spontaneous hypertension has been confirmed by a kymographic technique with femoral artery cannulation. The reaction of rats to several pressor drugs has been altered by selective breeding. In both control and inherited hypertensive rats, the initial level of the blood pressure prior to administration of the drug influences the magnitude of the responses to several pressor drugs but not to norepinephrine. If hypertensives are compared only with other hypertensives and controls with other controls, it is clear that high preinjection pressures have an inhibiting effect on the pressor responses to biologically and synthetically prepared angiotensin, to vasopressin, and possibly lessen also the responses to s-methyl iso -thiourea. When under experimental conditions the blood pressures of rats with inherited hypertension have fallen into the upper range of control rat blood pressures, the responses to epinephrine, vasopressin, s-methyl iso -thiourea and biological angiotensin are greater in the hypertensives than in the controls. The difference in the case of synthetic angiotensin is not statistically significant. In the case of norepinephrine, the responses are equal. Hexamethoniun reduced the blood pressures of inherited hypertensive and control rats to the same level.

A Vascular Abnormality in Hypertension

Forearm blood flow measurements have been made at rest and after 8 to 10 minutes arterial occlusion in 50 normal and 131 untreated hypertensive subjects. The latter group comprised 91 with essential hypertension; 11 with chronic renal disease (nephritis or pyelonephritis); 21 with renovascular disease; and eight with primary aldosteronism.

The resting blood flow increased with the rising pressure in patients with mild hypertension but there was a significant increase in the resting resistance in the more severe cases. The average minimal resistance obtained during reactive hyperemia was greater in hypertensive (3.1 SE 1.0 units) than in normal subjects (2.0 SE 0.07 units). This abnormality was related to the level of blood pressure but not to the duration of the disease.

Patients with renovascular disease or aldosteronism presented the same vascular fault as the more common causes of hypertension.

Evidence is presented to show that the reactive hyperemia produced maximal dilatation of the forearm vasculature, and acute elevation in pressure in normotensive or acute depression of pressure in hypertensive subjects did not influence the level of resistance achieved by reactive hyperemia.

It is concluded that the blood vessels themselves are abnormal in hypertension and that this abnormality may not be related to the activity of vascular smooth muscle.

Reactivity to pressor agents in hypertension

The pressor responses to intravenous injections of angiotonin and s-methyl iso -thiourea have been studied in 50 hypertensive subjects and 20 normotensive controls. The rises of blood pressure in the two groups were similar, being but slightly greater in the hypertensives. After the blood pressure has been reduced with hexamethonium, however, the pressor responses to angiotonin, s-methyl isothiourea and noradrenaline are much greater in hypertensives than normotensive subjects. The responses under these conditions to all three pressor agents run parallel to each other, suggesting that there is no specific increase in reactivity in hypertensive subjects, either to angiotonin or noradrenaline. It has been concluded that there is evidence of increased reactivity to pressor substances in hypertensive subjects but that this is not demonstrable until the blood pressure control mechanisms have been inactivated by hexamethonium.

Autonomic Drugs and Their Influence on Chorioidal Vessel Caliber

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