GUANETHIDINE AND METHYLDOPA: A HAEMODYNAMIC STUDY

Evaluation and treatment of hypertension in active individuals

Hypertension is a very common vascular disease. It is seen in adolescents, obese persons, postmenopausal women, and the elderly. A nonpharmacologic approach to treatment is a critical first step in management. The modalities include a diet low in salt and saturated fat, exercise, less than 2 ounces of alcohol daily, and abstinence from smoking. Dynamic (aerobic) exercise is effective in lowering blood pressure (BP) only if performed regularly. Weight reduction by diet must be combined with exercise if there is to be a reduction in BP. Strength training is not to be considered as an alternative to aerobic training for reducing BP. Antihypertensive mediation can be added to nonpharmacologic interventions for additional BP reduction. Beta-blockade is not a contraindication to exercise training.

The hypertensive patient with concomitant cardiovascular disease

Many drugs for the treatment of hypertension are available in the United States today. Of the various factors that determine the appropriate treatment for a particular patient, the presence of concomitant heart disease requires specific tailoring of the antihypertensive therapy. Coronary artery disease, aortic insufficiency, congestive heart failure, left ventricular hypertrophy, premature ventricular contractions, supraventricular arrhythmias, mitral valve prolapse, orthostatic hypotension, and aortic dissection are some of the conditions that influence the choice of treatment. Diabetes places hypertensive patients at increased risk of heart disease, and exercise and sexual function are other considerations that govern the selection of treatment for the hypertensive person. For all of these conditions, more than one drug choice is often possible, but usually hypertensive patients can be treated with a beta-blocker or a calcium channel blocker in these special circumstances.

The plasma noradrenaline and growth hormone response to alpha-methyldopa and clonidine in hypertensive subjects

The mechanism of the antihypertensive effect of alpha-methyldopa was compared with clonidine by administering equipotent single doses of clonidine (0.2 mg) and alpha-methyldopa (750 mg) to nine hypertensive patients. Plasma noradrenaline was followed for 8 h thereafter as an index of peripheral sympathetic activity. alpha-Methyldopa and clonidine produced the same hypotensive response at 6 and 8 h after dosing with a similar fall in plasma noradrenaline levels at these times. Linear regression analysis between the systolic blood pressure fall and the corresponding plasma noradrenaline fall, showed that the slopes of the two regression lines were similar for alpha-methyldopa as for clonidine. Equipotent doses of alpha-methyldopa and clonidine produce the same fall in plasma noradrenaline. This supports the current hypothesis that an alpha-methyldopa metabolite acts centrally, like clonidine, to reduce peripheral sympathetic activity.

Minoxidil in severe and moderately severe hypertension, in association with methyldopa and chlortalidone

Minoxidil is a potent antihypertensive drug widely used in severe arterial hypertension and in that refractory to treatment. Its effectiveness in less severe forms of hypertension was evaluated in 15 patients who had either a severe to moderate arterial hypertension not previously treated, or who did not tolerate the side effects of other antihypertensive drugs. The usefulness of methyldopa and chlortalidone to prevent a potential minoxidil-induced tachycardia and fluid retention, respectively, was also tested. The patients were initially treated with chlortalidone 100 mg/day, and methyldopa 500 mg/day. Minoxidil was then given in increasing doses until the diastolic blood pressure was equal to or inferior to 90 mmHg. This occurred consistently at doses which ranged from 5 to 50 mg/day (average, 29 mg). Treatment with minoxidil was continued for four months; tolerance to the drugs was not observed. Low doses of methyldopa and chlortalidone were effective in controlling the tachycardia and the retention of sodium and water induced by minoxidil. The three associated drugs were well tolerated and the life quality improved in most patients. Hypertrichosis was the most consistent side effect. Two patients were withdrawn from the study after the blood pressure was controlled by minoxidil, because of the appearance of angor in one, and edema and heart failure in the other.

Antiadrenergic therapy: special aspects in hypertension in the elderly

The effect of antiadrenergic treatment with methyldopa was studied in 17 patients with established essential hypertension who were subdivided with respect to age in a group younger (n = 10; mean age, 47 +/- 2.4 (SEM) years; and a group older than 60 years of age (n = 7, mean age, 67 +/- 2.8 SEM). The fall in arterial pressure was associated with a significant (p less than 0.05) decrease in cardiac output and heart rate in patients over 60 years of age and no change in total peripheral resistance, whereas a (nonsignificant) fall in resistance occurred in younger patients. In both age groups, a significant (p less than 0.05 and less than 0.01, respectively) decrease in plasma norepinephrine levels was observed, whereas epinephrine and dopamine showed no changes. Pre- and posttreatment values of mean arterial pressure correlated directly with plasma norepinephrine values (r = 0.35 p less than 0.05). Regardless of whether cardiac output was reduced or remained unchanged, renal blood flow, plasma and total blood volume did not change in either group with antiadrenergic treatment. Further, reflexive cardiac changes (responses to isometric exercise and upright tilt) remained qualitatively unchanged. It is concluded that antiadrenergic treatment with methyldopa lowers arterial pressure additionally by decreasing circulating norepinephrine levels. The antihypertensive effect is associated with a fall in peripheral resistance in the younger and a decrease in cardiac output in the older patients, and does not compromise renal blood flow or cardiac reflexive responses.

Comparison of the acute and chronic hemodynamic effects of captopril and guanethidine in spontaneously hypertensive rats

The present study compared the hemodynamic effects of captopril with those of guanethidine as well as with a combination of these two drugs in conscious male spontaneously hypertensive rats. Acutely, captopril or guanethidine or a combination of the two lowered arterial pressure to similar levels. The reduction in pressure with captopril alone or in combination with guanethidine, was due to a lowering of all organ vascular resistances. Guanethidine alone lowered pressure by reducing cardiac output. Chronically, captopril or guanethidine lowered arterial pressure to similar levels by reducing organ vascular resistances to comparable levels, particularly skeletal muscle, skin and splanchnic organs. Combination of these two drugs had an additive effect on the reduction of arterial pressure and organ vascular resistances. Since, chronically, the addition of guanethidine to captopril therapy enhanced rather than attenuated the hemodynamic changes induced by captopril, these drugs are probably acting by different mechanisms and the mechanisms of action of captopril does not require an intact sympathetic nervous system.

Effects of reserpine, guanethidine and methyldopa on cardiac output and its distribution

In anaesthetized rats with a renal model of hypertension, effects of reserpine, guanethidine and methyldopa on cardiac output (the dye-dilution method) and its distribution among the heart, the lung, the kidney, the large and small intestine, the stomach, the liver, the spleen, skeletal muscle and skin (the rubidium method) were studied. Several hours administration of all three drugs under study, a definite decrease in cardiac output was observed. Cardiac output then escaped from the influence of the drugs despite a reduction in heart rate. Fall of arterial pressure 24 hr after administration of the drugs was only due to the decrease in total peripheral resistance. Effects of the drugs on distribution of cardiac output were studied at the time when cardiac output was not changed to any significant extent. Under this condition the features common to all the drugs were an increase of the cardiac output fractions to the gastro-intestinal tract and a decrease to the heart and the spleen. This fact indicates that decrease in resistance of gastro-intestinal vascular region plays a basic role in the hypotensive effect of reserpine, guanethidine and methyldopa.

The use of radioactive microspheres to compare the effects of hydralazine, guanethidine and SK & F 24260 on the redistribution of cardiac output in anaesthetized rabbits

1 The use of radioactive microspheres is described for the measurement of cardiac output in anaesthetized rabbits and its redistribution after the administration of drugs which lower blood pressure. 2 Hydralazine increased peripheral vascular conductance by 123%. The vascular beds in which it had most effect were those of the carcass (mainly muscle) and the kidneys. 3 SK&F 24260, (1,4 dihydro-2, 6-dimethyl-4(2-trifluoremethylpheny)-3,5,-pyridinedicarboxylic acid diethyl ester), had similar vasocilator actions. Its effect in the carcass contributed relatively more to the increase of total peripheral conductance. It also caused a remarkable degree of cerebral vasodilatation. 4 Guanethidine had a relatively small effect on total peripheral conductance and lowered blood pressure mainly by reducing stroke volume and cardiac output.