TISSUE DISTRIBUTION OF BETA-3-ADRENERGIC RECEPTOR MESSENGER-RNA IN MAN

Expression of mRNA for beta1-, beta2-, and beta3-adrenergic receptors (beta1-, beta2-, and beta3-AR) was investigated in human tissues. Beta1- and beta2-AR mRNA distribution correlated with that of the cognate receptors established by pharmacological studies. Beta3-AR transcripts were abundant in infant perirenal brown adipose tissue, characterized by the presence of uncoupling protein (UCP) mRNA. In adult whole adipose tissues, beta3-AR mRNA levels were high in deep deposits such as perirenal and omental, and lower in subcutaneous. In these deposits, UCP mRNA levels paralleled those of beta3-AR. However, isolated omental and subcutaneous adipose cells, enriched in white adipocytes, expressed beta3-AR but no UCP transcripts. Beta3-AR mRNA was highly expressed in gallbladder, and to a much lower extent in colon, independently of UCP mRNA. Quadriceps or abdominal muscles, heart, liver, lung, kidney, thyroid, and lymphocytes did not express intrinsic beta3-AR mRNA. This study demonstrates that substantial amounts of brown adipocytes exist throughout life in adipose deposits, which are generally classified as white. These deposits are the main sites of beta3-AR expression, which also occurs in gallbladder and colon. Beta3-AR may thus be involved in the control of lipid metabolism, possibly from fat assimilation in the digestive tract, to triglyceride storage and mobilization in adipose tissues.