Sympathetic nervous function and renin activity in hypertensives on long term drug treatment with propranolol, methyldopa or bendrofluazide

Advantages and disadvantages of alpha 2-adrenoceptor agonists for systemic hypertension

Alpha 2-receptor agonists are effective antihypertensive drugs that reduce sympathetic activity by both central and peripheral mechanisms. Plasma noradrenaline and renin concentrations are reduced. Hemodynamic disturbances are minor with a near-normal cardiovascular response to standing, exercise and volume depletion. The main problems are due to central adverse effects, particularly sedation, and a syndrome of sympathetic overactivity on sudden withdrawal. These problems can be minimized by using lower doses, while therapy with a useful antihypertensive drug is maintained. Clonidine and its analogs have a low toxicity and very few contraindications. They remain a useful part of the therapeutic armamentarium in hypertension.

Effects of pindolol and methyldopa on blood pressure and plasma norepinephrine

Thirty patients with essential hypertension (supine diastolic blood pressure 100 to 115 mm Hg) were treated in a randomized, double-blind study with either pindolol (mean dose 28 +/- 5 mg twice a day) or methyldopa (673 +/- 158 mg three times a day) for 12 weeks after a 3-week, single-blind placebo period. In 17 pindolol-treated patients mean supine blood pressure was 163 +/- 3/106 +/- 1 during the placebo period and 155 +/- 3/99 +/- 2 mm Hg (p less than 0.01) during the high-dose period. In 13 patients treated with methyldopa mean supine blood pressure fell from 160 +/- 4/104 +/- 1 to 156 +/- 5/97 +/- 2 mm Hg. Mean standing heart rate was reduced during pindolol therapy from 84 +/- 2 to 79 +/- 2 bpm (p less than 0.05) but was unchanged during methyldopa treatment. Mean supine pretreatment plasma norepinephrine fell from 379 +/- 40 to 337 +/- 33 pg/ml in patients on pindolol therapy and from 448 +/- 76 to 223 +/- 39 pg/ml (p less than 0.02) in the methyldopa-treated group. Although norepinephrine generally decreased in pindolol responders and not in nonresponders, changes in supine diastolic blood pressure and supine plasma norepinephrine did not correlate. In contrast, norepinephrine declined consistently in methyldopa-treated patients regardless of the blood pressure response; changes in diastolic blood pressure and norepinephrine correlated (r = 0.59; p less than 0.05). The results suggest that suppression of sympathetic nervous system activity may play a role in the hypotensive effect of both pindolol and methyldopa.

Plasma noradrenaline concentration in essential hypertension during long-term beta-adrenoceptor blockade with oxprenolol

1. Chronic beta-adrenoceptor blockade with oxprenolol causes elevation of plasma noradrenaline levels, as compared with placebo, despite a significant fall in blood pressure and pulse rate. 2. The plasma noradrenaline concentration is not influenced by the frequency of administration or the formulation of the drug. 3. Plasma noradrenaline levels are not correlated with the plasma concentration of the drug. 4. The changes in plasma noradrenaline concentrations support a peripheral rather than central mechanism of action of beta-adrenoceptor blockers in man.

The effects of desmethylimipramine on the pharmacological actions of alpha methyldopa in man

The effect of pretreatment with the tricyclic antidepressant desmethylimipramine (DMI) 75 mg daily for 3 days on the action of oral methyldopa 750 mg was investigated in a double blind crossover design in volunteers. DMI pretreatment caused a small but not significant increase in supine systolic and diastolic blood pressure and heart rate. However, the effects of methyldopa on lying and standing blood pressure and heart rate were not markedly altered by pretreatment. In particular, the fall in standing blood pressure after methyldopa was present with and without DMI and the sedative action of methyldopa was similar. DMI alone reduced saliva production. No evidence was found that tricyclic antidepressant drugs significantly modify the hypotensive effect of methyldopa in man.