A homeostatic adaptive response to alpha-methyl-dopa in conscious dogs.

Repeated daily administration of an oral dose of 1000 mg of alpha-methyl-dopa (methyl dopa) to conscious dogs produced a conditioned adaptive hypertensive systolic and diastolic arterial pressure response along with the direct hypotensive pharmacological effect. The lower dose of 500 mg/day appeared to be devoid of direct or adaptive response effects, while the higher dose of 2000 mg/day only produced a blood pressure lowering response. The abrupt drug withdrawal unmasking the homeostatic state resulted in a marked systolic and diastolic pressor response which endured for about 10-days with peak effect reached at 17-days after termination of drug treatment. Comparable results were obtained whether the dogs were evaluated while in their normal horizontal body position or in a repositional upright condition.