Augmented vasoconstrictor response to head-up tilt in peripheral tissues during beta-receptor blockade.
Subcutaneous and skeletal muscle blood flow in the forearm during 30 degrees head-up tilt was studied in 15 healthy subjects before and during treatment with propranolol. Relative blood flow was estimated by the local 133Xe washout technique. Head-up tilt elicited greater vasoconstriction in both tissues during beta-receptor blockade as compared to the pretreatment period. Proximal nerve blockade with lidocaine prevented the vasoconstrictor response in subcutaneous tissue to the tilt. In skeletal muscle injection of a low dose of propranolol had no effect on the vasoconstrictor response to tilt. Therefore, the augmented vasoconstrictor response to head-up tilt during beta-receptor blockade is most probably due to centrally elicited (baroreceptor) and neurogenically mediated impulses to resistance vessels in peripheral tissues and not to "unmasking" of peripheral alpha-receptors.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D009132:Muscles / Q000098:blood supply; D011187:Posture; D011433:Propranolol / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*
D000319:Adrenergic beta-Antagonists; D011433:Propranolol