Alpha-adrenergic receptors in orthostatic hypotension syndromes.

Alpha-adrenergic receptor function was measured in platelets from patients with orthostatic hypotension and normotensive controls. Patients with idiopathic orthostatic hypotension (IOH) or multiple system atrophy (MSA) had more alpha-receptors than controls. Patients with IOH, but not MSA, produced less prostaglandin E1 (PGE1)-stimulated cyclic AMP (cAMP) than controls. Patients with sympathotonic orthostatic hypotension (SOH) were similar to controls in receptor number and cAMP production. The percent norepinephrine (NE) inhibition of PGE1-stimulated cAMP production was similar in patients and controls. An increase in alpha-receptor number may result from decreased peripheral NE secretion in IOH and MSA. Increased alpha-receptor number and decreased cAMP production, which accompany essential hypertension, may contribute to the supine hypertension of IOH, and an increase in alpha-receptor number may contribute to the supine hypertension of MSA. SOH patients appear to have no abnormalities of alpha-receptor function.