Radioreceptor binding studies were carried out in broiler chickens in order to characterize adrenergic receptors on their abdominal fat adipocytes. The radioligands ($ sp3$H) DHA and ($ sp3$H) YOH were used to identify $ beta$- and $ alpha sb2$-adrenoceptors respectively. The determination of receptor criteria indicated that the optimal protein concentration for the simultaneous binding of both receptor types was between 0.35 and 1.0 mg/ml. Pharmacological specificity for both $ beta$- and $ alpha sb2$-adrenoceptors was demonstrated using receptor specific antagonists and an agonist. Saturation isotherms indicated that ($ sp3$H) DHA and ($ sp3$H) YOH labelled with high affinity, a homogenous population of non interacting $ beta$- and $ alpha sb2$-binding sites respectively. Scatchard analysis of the saturation data for ($ sp3$H) DHA revealed a Kd value of 8.1 nM and a Bmax value of 420 fmol/mg protein, while ($ sp3$H) YOH binding had a Kd value of 7.0 nM and a Bmax value of 68 fmol/mg protein. The variation in $ beta$- and $ alpha sb2$-adrenoceptor binding parameters was then investigated on the abdominal fat pad adipocytes of male and female broiler chickens at 4, 6 and 9 weeks of age. Scatchard analysis of the binding data for $ beta$-adrenoceptors indicated that Bmax values were greater in male and female broilers at 9 weeks of age (p $<$ 0.05) and that overall Bmax values were greater in females than in males (p $<$ 0.05). Scatchard analysis of $ alpha sb2$-adrenoceptor binding revealed that in females Bmax values remained constant but differed at all ages in males. The $ beta$-adrenoceptor Bmax values were always significantly greater (p $<$ 0.05) than the corresponding $ alpha sb2$-adrenoceptor Bmax values. / These results established for the first time the existence of adrenergic receptors on broiler chicken adipocytes using a radioreceptor binding assay. Although the physiological implication of these receptors is not known, it is a critical step toward the understanding of the influence of the adrenergic system on adipose tissue metabolism in avian species.

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