title: Loss of high affinity cardiac beta adrenergic receptors in dogs with heart failure.
abstract: We studied the alterations in myocardial beta-adrenergic receptor-adenylate cyclase activity and muscarinic receptor density in a canine model of left ventricular (LV) failure. LV failure was characterized by a doubling of LV weight/body weight ratio (3.3 +/- 0.1 to 6.9 +/- 0.4 g/kg) and an elevation of LV end-diastolic pressure, 32 +/- 4.5 mmHg, compared with 7.7 +/- 0.6 mmHg in normal dogs. Despite a 44% increase in receptor density as measured by antagonist binding studies with [3H]dihydroalprenolol, there was a twofold decrease in receptor affinity, i.e., an increase in the dissociation constant (Kd) (5.6 +/- 0.7 to 12 +/- 1.6 nM) in heart failure. Agonist displacement of [3H]dihydroalprenolol binding with isoproterenol in the presence and absence of 5'-guanylylimidodiphosphate [Gpp(NH)p] demonstrated a striking loss of high affinity binding sites in heart failure (51 +/- 16 to 11 +/- 5%). Beta-Adrenergic receptor-mediated stimulation of adenylate cyclase and maximal stimulation with Gpp(NH)p or sodium fluoride was reduced in heart failure. There was a concomitant marked, P less than 0.01, reduction in muscarinic receptor density (242 +/- 19 vs. 111 +/- 20 fmol/mg). Thus, while muscarinic receptor density fell, beta-adrenergic receptor density actually increased in LV failure. However, a larger portion of the beta-adrenergic receptors are not functionally coupled to the GTP-stimulatory protein (Ns), as evidenced by a decrease in the fraction of receptors that bind agonist with high affinity.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism; D006333:Heart Failure / Q000378:metabolism*; D007545:Isoproterenol / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; D006165:Guanylyl Imidodiphosphate; D000262:Adenylyl Cyclases; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D009638:Norepinephrine