Beta-adrenoreceptors in the trout (Oncorhynchus mykiss) heart: characterization, quantification, and effects of repeated catecholamine exposure

Gen Comp Endocrinol. 1994 Aug;95(2):259-72. doi: 10.1006/gcen.1994.1123.


Specific binding of the hydrophilic radioligand [3H]CGP-12177 to cell surface (functional) beta-adrenoreceptors was quantified in ventricular micropunches (2 mm diameter, 350 microns thickness) from seawater-acclimated rainbow trout held at 7-9 degrees. Binding was stereospecific, saturable, of high affinity, and displaceable by appropriate agonists and antagonists. Phentolamine failed to displace [3H]CGP at concentrations up to 10(-4) M, indicating an absence of [3H]CGP binding to alpha-adrenergic receptors. Trout ventricular beta-adrenoreceptors are exclusively of the beta 2 type. This conclusion is based on (1) the IC50 value for the beta 2-antagonist ICI 118551 (2.9 x 10(-6) M); (2) the inability of the beta 1-antagonist atenolol to displace [3H]CGP from beta-adrenoreceptors; and (3) the order of agonist-binding affinity (isoproterenol > epinephrine >> norepinephrine). The Bmax and Kd values for [3H]CGP binding to myocardial tissue were approximately 0.04 fmol micrograms protein-1 and 0.25 nM, respectively. The Bmax value indicates that the density of cell surface (functional) beta-adreno-receptors in the ventricle was 12,000 sites per cell or 3.38 sites per microns 2 of sarcolemma. The Kd and Bmax values for [3H]CGP binding to ventricular beta-adrenoreceptors were unaffected by the in vivo administration of five bolus catecholamine injections (4.0 micrograms kg-1 epinephrine, 2.0 micrograms kg-1 norepinephrine). This suggests that stress-induced increases in plasma catecholamines are unlikely to cause the down-regulation of heart beta-adrenoreceptors in fish. The method described here represents a simple but powerful technique for the quantification and characterization of adrenergic receptors in the fish heart.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic beta-Antagonists / pharmacokinetics
  • Animals
  • Binding, Competitive / drug effects
  • Catecholamines / pharmacology*
  • Down-Regulation / drug effects
  • Freezing
  • Heart / drug effects
  • Heart Ventricles / drug effects
  • Heart Ventricles / metabolism
  • Myocardium / metabolism*
  • Oncorhynchus mykiss / metabolism*
  • Propanolamines / pharmacokinetics
  • Receptors, Adrenergic, beta / analysis
  • Receptors, Adrenergic, beta / drug effects
  • Receptors, Adrenergic, beta / metabolism*
  • Stereoisomerism
  • Stress, Psychological / metabolism
  • Timolol / pharmacokinetics


  • Adrenergic beta-Antagonists
  • Catecholamines
  • Propanolamines
  • Receptors, Adrenergic, beta
  • Timolol
  • CGP 12177