Catecholamines are the major lipolytic agents in fat cells and are mediated primarily by beta-adrenergic receptors. The present experiment was designed to study p-receptor numbers in growing pigs of various genotypes in relation to their body compositions.

Fat samples from 5 representative pigs of each genotype were removed immediately after slaughter, at about 60 kg body weight, and stored at -80°C prior to analysis. Adipocytes were extracted by incubation with 1 mg/g (w/v) collagenase in a tris/MgCl2/ EDTA/Bovine serum albumin buffer (pH 7.4) for 1 hour at 37°C. Cells were mechanically ruptured and membranes were removed by ultracentrifugatlon (37,000 rpm for 20 minutes). Recovery was estimated by protein assay using the method of Lowry (1951). Approximately 20 μg of adipocyte membrane protein in 300 μl tris/MgCl2/EDTA assay buffer was added to graded concentrations of the 125I-labelled β-antagonist Iodocyanopindolol (100 μl) together with 100 μl of either assay buffer or the non-specific β-antagonist propanolol (to determine non-specific binding). Samples were then incubated for 1 hour at 37°C. Total β-receptor numbers (maximum binding - Bmax) expressed as pmol/g protein, were estimated by Scatchard analysis using the computer programme ‘EBDA’ by Elsevier - BIOSOFT, Cambridge.