Heterogeneity of alpha1 receptors associated with vascular smooth muscle: Evidence from functional and ligand binding studies

Michael Babich, Norman W. Pedigo, Brent T. Butler, Michael T. Piascik

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


The nature of the alpha1 receptor associated with rabbit aorta has been examined in functional and receptor binding studies. In isolated aortic rings the dose-response curve for (-)metaraminol was not parallel to that of (-)epinephrine, (-)norepinephrine or (-)phenylephrine. Following inactivation of a portion of the alpha receptors with phenoxybenzamine, the occupancy versus response relationship for metaraminol, in contrast to the other test agonists, was biphasic. These results suggest the possibility that metaraminol interacts with different functional groups on the alpha1 receptor than the other test agonists. In microsomes prepared from frozen aorta, metaraminol bound to two classes of sites (KH = 0.41 ± 0.12 μM, KL = 39.1 ± 7.1 μM) labelled by the selective alpha1 antagonist [3H] prazosin. Similar binding characteristics were observed in microsomes prepared from aorta shipped in serum on ice or aorta from animals killed in our laboratory. Norepinephrine also bound to two sites on the alpha receptor in all three preparations tested (KH = 0.06 ± 0.01 μM, KL = 5.09 ± 2.4 μM; estimated from frozen aorta). The Scatchard plot of [3H] prazosin binding to microsomes prepared from frozen aorta was curvilinear. Estimates of the affinities and site densities were 49.6 ± 15.3 pM and 44.8 ± 11.8 pmol/gm protein and 1.0 ± 0.2 nM and 43.8 ± 17.4 pmol/gm for the high and low affinity sites, respectively. These data are consistent with the idea that there are subtypes of the alpha1 receptor.

Original languageEnglish
Pages (from-to)663-673
Number of pages11
JournalLife Sciences
Issue number6
StatePublished - Aug 10 1987

Bibliographical note

Funding Information:
This work was supported by grants from the American Heart Association, Kentucky Affiliate, the University of Kentucky Medical Center, The University of Kentucky Tobacco and Health Research Institute and the NIH (HL-38120). We would like to thank Joyce Anderson and Deborah Turner for supervising the preparation of this manuscript, and Kathy King for assistance in computer fitting of the binding data.

ASJC Scopus subject areas

  • General Pharmacology, Toxicology and Pharmaceutics
  • General Biochemistry, Genetics and Molecular Biology


Dive into the research topics of 'Heterogeneity of alpha1 receptors associated with vascular smooth muscle: Evidence from functional and ligand binding studies'. Together they form a unique fingerprint.

Cite this