title: Effect of age on the responsiveness of vascular alpha-adrenoceptors in man.
abstract: Aging has been reported to alter the responsiveness of beta-receptors, but there have been few comparable studies of alpha-receptors. This study compares in six young and six healthy elderly subjects the haemodynamic effects of the alpha 1 -antagonist prazosin and the pressor responses to the alpha 1-agonist phenylephrine. Prazosin orally lowered erect (but not supine) blood pressure in both groups by a similar amount between 2 and 6 h after dosing. Maximal falls in systolic pressure were 19.5 +/- 15.7 and 29.3 +/- 11.4 mm Hg (mean +/- SD) in young and old, respectively. There was a significant difference in the associated heart rate response: in the young group mean heart rate increased to 103 beats/min, but there was no corresponding increase in the elderly group, which has a mean heart rate of 80 beats/min. Following the intravenous infusion of increasing doses of phenylephrine, log dose-response curves were deprived, and the dose required to raise mean arterial pressure by 20 mm Hg (PD20) was compared. The mean PD20 was significantly different in the two groups: 2.5 +/- 1.6 in the young, compared to 4.6 +/- 2.3 micrograms/kg/min in the elderly. However, no significant difference was apparent when pressor responsiveness was determined following the administration of prazosin. Thus, while there is no evidence of an age-related increase in the sensitivity of alpha-adrenoceptor-mediated vasoconstriction, the data are not inconsistent with an age-related reduction in responsiveness to alpha-adrenoceptor activation.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000328:Adult; D000368:Aged; D000375:Aging; D001794:Blood Pressure / Q000187:drug effects; D001808:Blood Vessels / Q000378:metabolism*; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*
chemical_list: D000317:Adrenergic alpha-Antagonists; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D011224:Prazosin