Prolonged treatment with the beta3-adrenergic agonist CL 316243 induces adipose tissue remodeling in rat but not in guinea pig: 1) fat store depletion and desensitization of beta-adrenergic responses.

Beta3-adrenergic agonists have been considered as potent antiobesity and antidiabetic agents mainly on the basis of their beneficial actions discovered twenty years ago in obese and diabetic rodents. The aim of this work was to verify whether prolonged treatment with a beta3-adrenergic agonist known to stimulate lipid mobilisation, could promote desensitization of beta-adrenergic responses. Wistar rats and guinea pigs were treated during one week with CL 316243 (CL, 1 mg/kg/d) by implanted osmotic minipumps. In control animals, beta3-adrenergic agonists were lipolytic in rat but not in guinea pig adipocytes. CL-treatment did not alter body weight gain in both species, but reduced fat stores in rats. Lipolysis stimulation by forskolin was unmodified but responses to beta1-, beta2- and beta3-agonists were reduced in visceral or subcutaneous white adipose tissues of CL-treated rats. Similarly, the beta3-adrenergic-dependent impairment of insulin action on glucose transport and lipogenesis in rat adipocytes was diminished after CL-treatment. In rat adipocytes, [125I]ICYP binding and beta3-adrenoceptor mRNA levels were reduced after sustained CL administration. These findings show that CL 316243 exerts (beta3-adrenergic lipolytic and antilipogenic effects in rat adipocytes. These actions, which are likely involved in the fat depletion observed in rat, also lead to the desensitization of all beta-adrenergic responses. Therefore this desensitization, together with the lack of slimming action in guinea pig, seriously attenuates the usefulness of beta3-agonists as antiobesity agents, and may explain why such agonists have not been conducted to a widespread clinical use.