Smooth muscle alpha1D-adrenoceptors mediate phenylephrine-induced vasoconstriction and increases in endothelial cell Ca2+ in hamster cremaster arterioles

Br J Pharmacol. 2008 Oct;155(4):514-24. doi: 10.1038/bjp.2008.276. Epub 2008 Jul 7.


Background and purpose: alpha(1)-Adrenoceptor agonists induce Ca(2+)-transients in endothelial cells (ECs) of arterioles. However, the presence of alpha(1)-adrenoceptors on arteriolar ECs has not been excluded, and the identity of alpha(1)-adrenoceptor subtypes in arterioles only has been inferred from pharmacology. Therefore, we determined which subtypes were expressed by vascular smooth muscle cells (VSMCs) and ECs, and which subtype mediated alpha(1)-adrenoceptor-induced constriction.

Experimental approach: EC Ca(2+)-transients in isolated, cannulated hamster cremasteric arterioles or freshly isolated ECs were studied using Fura 2. Arteriolar diameter was measured by video microscopy. alpha(1)-Adrenoceptor expression was assessed by western blot of whole-arteriolar homogenates and real-time RT-PCR on enzymatically isolated VSMCs and ECs.

Key results: Phenylephrine-induced constriction and EC Ca(2+)-transients were abolished by the alpha(1)-adrenoceptor antagonist prazosin (30 nM) in arterioles. Phenylephrine-induced constriction was inhibited by the alpha(1D)-adrenoceptor antagonist BMY 7378 (K(B)=2.96 nM) and the alpha(1A)-adrenoceptor antagonist 5-methylurapidil (K(B)=4.08 nM), suggesting a significant role for alpha(1D)-adrenoceptors. Western blots confirmed alpha(1D)-adrenoceptor expression, but did not detect alpha(1A)-adrenoceptors. VSMCs expressed alpha(1D)- and alpha(1A)-, but not alpha(1B)-, adrenoceptor transcripts. No alpha(1)-adrenoceptor transcripts were detected in ECs. Neither phenylephrine (10 microM) nor noradrenaline (0.1-1 microM) elicited Ca(2+)-transients in freshly isolated ECs, whereas the endothelium-dependent vasodilators methacholine (1 microM) and substance P (100 nM) consistently increased Ca(2+).

Conclusions and implications: We reject the hypothesis that hamster cremasteric arteriolar ECs express alpha(1)-adrenoceptors and conclude that alpha(1)-adrenoceptor agonists predominantly act on VSMC alpha(1D)-adrenoceptors to cause vasoconstriction and a subsequent rise in EC Ca(2+).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic alpha-1 Receptor Agonists*
  • Adrenergic alpha-Agonists / pharmacology*
  • Animals
  • Arterioles / drug effects
  • Arterioles / metabolism
  • Blotting, Western
  • Calcium / metabolism
  • Cricetinae
  • Endothelial Cells / drug effects
  • Endothelial Cells / metabolism
  • Gene Expression
  • Male
  • Muscle, Smooth, Vascular / drug effects
  • Muscle, Smooth, Vascular / metabolism
  • Phenylephrine / pharmacology*
  • Receptors, Adrenergic, alpha-1 / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Vasoconstriction / drug effects
  • Vasoconstrictor Agents / pharmacology*


  • Adrenergic alpha-1 Receptor Agonists
  • Adrenergic alpha-Agonists
  • Receptors, Adrenergic, alpha-1
  • Vasoconstrictor Agents
  • Phenylephrine
  • Calcium