title: Interaction of clonidine and beta-blockers.
abstract: On the hypothesis that non-selective beta-blockers can antagonize or reverse the antihypertensive effect of clonidine (C), 12 hypertensive outpatients were treated with C alone and in combination with propranolol (P), atenolol (A) and prazosin (Pz). C alone (0.11 or 0.22 mg b.i.d.) or in combination with P (80 mg b.i.d.) did not provide normotension. Changing P to A (50 mg b.i.d.) reduced supine systolic and diastolic pressures, which now were significantly lower (p less than 0.01) than during C alone. Changing A to P again resulted in elevated pressures. Pz (1 mg t.i.d.) added to the C+P regimen lowered supine blood pressures to the levels otherwise recorded during C+A. C dose-dependently contracted rabbit aortic spiral in vitro, reaching about 50% of maximum responses to noradrenaline. Pz abolished this response. P (0.1--10 micrograms/ml) but not A somewhat enhanced responses to high doses of C. Sotalol rather antagonized C contractions. We conclude that A but not P enhances the antihypertensive action of C. No hypertensive interaction was observed.
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D000818:Animals; D001262:Atenolol / Q000494:pharmacology / Q000627:therapeutic use; D001794:Blood Pressure / Q000187:drug effects; D002986:Clinical Trials as Topic; D003000:Clonidine / Q000037:antagonists & inhibitors* / Q000627:therapeutic use; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006973:Hypertension / Q000188:drug therapy; D008297:Male; D008875:Middle Aged; D011224:Prazosin / Q000494:pharmacology / Q000627:therapeutic use; D011433:Propranolol / Q000494:pharmacology / Q000627:therapeutic use; D011817:Rabbits; D013015:Sotalol / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D000319:Adrenergic beta-Antagonists; D001262:Atenolol; D011433:Propranolol; D013015:Sotalol; D003000:Clonidine; D011224:Prazosin