title: Selective down regulation of vascular beta 1 adrenergic receptors after prolonged isoproterenol infusion.
abstract: Prolonged isoproterenol infusion (400 micrograms/kg/h for 4 days) in rats was previously shown to produce a reduction in the sensitivity of both cardiac and vascular beta-adrenergic receptors without affecting responsiveness to alpha 1 agonists or phosphodiesterase inhibitors in either vascular or cardiac muscle. The present study was designed to determine if the loss in beta receptor responsiveness was similar for both beta 1 and beta 2 vascular receptors. The rat jugular vein was previously shown to relax in response to both norepinephrine and isoproterenol with norepinephrine-induced relaxation being mediated by interaction with beta 1 adrenergic receptors and isoproterenol-induced relaxation being mediated by its interaction with beta 2 vascular receptors. Using this preparation, tissues from isoproterenol-infused rats were approximately threefold less responsive to isoproterenol when compared to responses in tissues from saline-treated rats. Relaxation to norepinephrine in jugular veins from isoproterenol-infused rats was virtually abolished relative to the response in saline-treated animals. These data suggest that beta 1-adrenergic receptors in blood vessels are considerably more susceptible to down regulation than are beta 2-adrenergic receptors. This observation may have importance in both the therapy of congestive heart failure, where down regulation of beta-adrenergic receptors has been observed, and in our understanding of the mechanism for the inotropic effects of beta receptor agonists.
mesh_terms: D000818:Animals; D001808:Blood Vessels / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D011943:Receptors, Adrenergic, beta / Q000032:analysis / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects
chemical_list: D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D007545:Isoproterenol; D009638:Norepinephrine; D011224:Prazosin