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 the hormone adrenaline. Because the response to a drug or hormone is dependent partly on the density of the tissue receptors, the potential for predicting growth, carcass quality, or meat quality from knowing beta 2-adrenoceptor density in three disparate sample sites in cattle was examined. Cell membrane fragments were prepared using samples of longissimus muscle, semitendinosus muscle, or ear obtained within 30 min of death from 48 steers. Beta 2-Adrenoceptor density (Bmax) was measured in these membrane preparations by saturating them with the radioligand [125I]iodocyanopindolol. There was no correlation between Bmax values measured in ear samples, longissimus muscles, or semitendinosus muscles. Bmax 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. Bmax measured in longissimus muscle only correlated weakly with meat color, and Bmax measured in semitendinosus muscle only correlated with carcass weight. We conclude that beta 2-adrenoceptor density is not a useful predictor of growth, carcass quality, or meat quality in cattle.