EFFECTS OF AGE AND ENDURANCE TRAINING ON BETA-ADRENERGIC-RECEPTOR CHARACTERISTICS IN FISCHER-344 RATS

The purpose of this investigation was to examine changes in beta-adren ergic receptor characteristics in various tissues with age and enduran ce training. Forty-eight young (6 months), middle-aged (15 months), an d old (25 months) male Fischer 344 rats were assigned to either a trai ned or sedentary running group. Animals were endurance trained by 10 w eeks of treadmill running at 75% maximal capacity, 1 h/day, 5 days/wee k. Animals were sacrificed at rest and the heart, liver: and soleus we re removed for analysis. Percent of high and low affinity binding site s were determined by competitive binding experiments. Competition curv es were generated using 12 concentrations of ICI-89406 (beta(1) antago nist) and ICI-118551 (beta(2) antagonist) to inhibit the total binding of (-) [I-125] pindolol (IPIN). Maximal binding site number (B-max) a nd affinity (K-D) were determined by Scatchard analysis. Heart B-max d id not differ with age or training. An aging effect was observed in li ver such that middle-aged and old animals had greater B-max compared t o young animals. In soleus, B-max was not altered with training but de creased with age. While training had no affect on affinity in the live r and soleus, heart affinity increased with training in both the middl e-aged (21%) and old (27%) animals. In soleus, affinity increased but remained unaltered in heart and liver with age. The ratio of beta(1):b eta(2) receptors in the heart and liver did not differ with age or tra ining. The influence of age and training on beta-adrenergic receptor c haracteristics appear to be tissue specific.