BETA(2)-ADRENOCEPTOR DENSITIES DO NOT CORRELATE WITH GROWTH, CARCASS QUALITY, OR MEAT QUALITY IN CATTLE

Drugs that activate beta(2)-adrenoceptors (beta-agonists) are known to have profound effects on growth, body composition, and meat quality. Physiologically, these adrenoceptors are activated and regulated by th e hormone adrenaline. Because the response to a drug or hormone is dep endent partly on the density of the tissue receptors, the potential fo r predicting growth, carcass quality, or meat quality from knowing bet a(2)-adrenoceptor density in three disparate sample sites in cattle wa s examined. Cell membrane fragments were prepared using samples of lon gissimus muscle, semitendinosus muscle, or ear obtained within 30 min of death from 48 steers. beta(2)-Adrenoceptor density (B-max) was meas ured in these membrane preparations by saturating them with the radiol igand [I-125]iodocyanopindolol. There was no correlation between B-max values measured in ear samples, longissimus muscles, or semitendinosu s muscles. B-max measured in samples of ear did not correlate with any growth or carcass traits, including weight gain, carcass weight, fat depth, or eye muscle area. B-max measured in longissimus muscle only c orrelated weakly with meat color, and B-max measured in semitendinosus muscle only correlated with carcass weight. We conclude that beta(2)- adrenoceptor density is not a useful predictor of growth, carcass qual ity, or meat quality in cattle.