The effects of guanethidine and of alpha-methyldopa on the digital circulation in hypertension

Cardiovascular counterregulation during sympathetic inhibition in normal subjects and patients with mild hypertension

The influence of agents that inhibit sympathetic nerve activity on cardiovascular responsiveness as related to major pressor factors has been unclear. Therefore, these components were evaluated in 11 normal subjects and 13 patients with mild essential hypertension before and after 4 weeks of sympathetic neuron blockade with the agent debrisoquine. In these normal and mildly hypertensive subjects, sympathetic neuron blockade caused approximately similar decreases in urinary and supine or upright plasma norepinephrine (NE) levels (average changes in the two groups, -41% and -45%, respectively; p less than 0.05 to less than 0.005), the chronotropic dose of isoproterenol (-45% and -38%), and the NE pressor dose (-47% and -51%, p less than 0.01), while the relationship between NE-induced changes in blood pressure and concomitant plasma NE concentrations was displaced to the left (p less than 0.01). Supine heart rate was also lowered (-10% and -8%, p less than 0.05). Compared to the orthostatic variations during placebo conditions, mild postural decreases in blood pressure were apparent in both the normal and hypertensive groups (-8% and -7.5%). However, supine blood pressure was unchanged following debrisoquine treatment. Other parameters were also not consistently changed, such as total blood volume, exchangeable body sodium, urinary electrolytes, plasma epinephrine, renin, and angiotensin II (AII) levels, the pressor dose of infused AII, and the relationship between AII-induced changes in blood pressure and plasma AII measured before and during AII infusion. These findings demonstrate that the reduction in sympathetic outflow during sympathetic neuron blockade may elicit a hyperresponsiveness of alpha- and beta-adrenergic receptors that is equal in normal subjects and patients with mild essential hypertension.

Some theories of hypertension: fact and fancy

1. Various theories on the origin and development of hypertension offered over the years have been assessed critically. 2. It is concluded that no one theory is adequate at the present time to encompass all the known facts. 3. Continuously expanded understanding of hypertensive mechanisms, however, help in the individualization and therefore the improvement of various modalities of therapy, including treatment with presently available agents, as well as with those which may be developed in the future.

Changes in plasma and extracellular fluid volume during long-term treatment with alpha-methyldopa in 11 thiazide-treated patients with essential hypertension

In eleven patients with essential hypertension, plasma volume (T-1824) (PV), extracellular fluid volume (82Br-distribution space) (ECFV), blood pressure (BP) and the ratio plasma to interstitial fluid volume (PV/IF) have been determined three times before treatment, after more than two months of thiazide treatment and after three and six months of combined thiazide-alpha-methyldopa (AMD) therapy. During combined treatment, PV/IF showed a significant increase, whereas PV and ECFV did not change significantly. Compared to values during thiazide therapy, PV and PV/IF increased, whereas ECFV was unchanged. BP was reduced significantly after thiazide treatment and showed a further significant fall when AMD was added. Based on the results and a review of the literature, it is concluded that AMD acts by interfering with the normal sympathetic activity, thereby producing a reduced venomotor tone and increased venous capacity. The concomitant reduced venous return of blood to the heart is suggested to contribute to the antihypertensive effect of AMD by means of a decreased cardiac output.