APPARENT LACK OF BETA(3)-ADRENOCEPTORS AND OF INSULIN REGULATION OF GLUCOSE-TRANSPORT IN BROWN ADIPOSE-TISSUE OF GUINEA-PIGS

Norepinephrine-induced thermogenesis was substantial in adipocytes fro m brown adipose tissue (BAT) of cold-acclimated guinea pigs but absent in adipocytes from BAT of warm-acclimated guinea pigs. There was no t hermogenic response to any beta(3)-adrenergic agonist (CL-316,243, ZD- 7114, BRL-28410, CGP-12177). The receptor was characterized as a beta( 1)-adrenoceptor. Adrenergic agonists stimulated adenylate cyclase in m embranes from BAT of both warm- and cold-acclimated guinea pigs also v ia a beta(1)-adrenoceptor; beta(3)-adrenergic agonists had no effect. Glucose transport by brown adipocytes from warm-acclimated guinea pigs was not stimulated by either norepinephrine or insulin. Cold acclimat ion induced the appearance of stimulation of glucose transport by nore pinephrine in association with the appearance of a large capacity for thermogenesis, but there was little improvement in response to insulin . GLUT4 was present in membranes from BAT of both warm- and cold-accli mated guinea pigs. Insulin is known to have an antilipolytic effect on both BAT and white adipose tissue of guinea pigs. Thus there is a sel ective lack of insulin-regulated glucose transport that is not improve d by cold acclimation. Guinea pigs may have ct mutated component of th e translocation mechanism for GLUT4. beta(3)-Adrenoceptors appear to b e absent in brown adipocytes of adult guinea pigs, as in white adipocy tes of guinea pigs, yet are known to be present in the gut. Tissue-spe cific expression of beta(3)-adrenergic receptors in guinea pigs may di ffer from that in rats, in which receptors are expressed in the adipos e tissues and gut.