Short Communication: PDF OnlySelective Down Regulation of Vascular β1 Adrenergic Receptors After Prolonged Isoproterenol InfusionCohen, Marlene L.; Schenck, Kathryn W.Author Information Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana U.S.A. Journal of Cardiovascular Pharmacology: September 1987 - Volume 10 - Issue 3 - p 365-368 Free Abstract Summary: Prolonged isoproterenol infusion (400 μg/kg/h for 4 days) in rats was previously shown to produce a reduction in the sensitivity of both cardiac and vascular β-adrenergic receptors without affecting responsiveness to α1 agonists or phosphodiesterase inhibitors in either vascular or cardiac muscle. The present study was designed to determine if the loss in β receptor responsiveness was similar for both β1 and β2 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 β1 adrenergic receptors and isoproterenol-induced relaxation being mediated by its interaction with β2 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 β1-adrenergic receptors in blood vessels are considerably more susceptible to down regulation than are β2-adrenergic receptors. This observation may have importance in both the therapy of congestive heart failure, where down regulation of β-adrenergic receptors has been observed, and in our understanding of the mechanism for the inotropic effects of β receptor agonists. © Lippincott-Raven Publishers.