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Arotinolol is a weak partial agonist on beta 3-adrenergic receptors in brown adipocytes

J Zhao1, V Golozoubova, B Cannon

  • 1The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, Sweden.

Canadian Journal of Physiology and Pharmacology
|August 2, 2001
PubMed

Insights

Arotinolol, an alpha/beta-blocker, may aid weight loss by activating brown fat thermogenesis. However, its weak agonist and antagonist effects on beta3-adrenergic receptors suggest other mechanisms are involved in its anti-obesity action.

Area of Science:

  • Pharmacology
  • Adrenergic Receptor Research
  • Obesity Studies

Background:

  • Arotinolol is an alpha/beta-adrenergic blocker with demonstrated anti-obesity properties.
  • Its anti-obesity effect is hypothesized to stem from direct activation of thermogenesis in brown adipose tissue.

Purpose of the Study:

  • To investigate arotinolol's ability to stimulate thermogenesis in brown fat cells and intact animals.
  • To elucidate the specific adrenergic receptor interactions involved in arotinolol's thermogenic effects.

Main Methods:

  • Assessed thermogenesis (oxygen consumption) in isolated brown fat cells from mice and hamsters.
  • Utilized propranolol to determine the adrenergic receptor subtype involved.
  • Evaluated arotinolol's agonist and antagonist properties on the beta3-adrenergic receptor.
  • Observed arotinolol's effects in intact animal models.

Main Results:

  • Arotinolol stimulated thermogenesis in isolated brown fat cells.
  • Evidence suggested interaction with the beta3-adrenergic receptor, with low sensitivity to propranolol.
  • Arotinolol acted as a weak partial agonist (EC50 ~20 microM, ~50% maximal effect) and antagonist (pKB ~5.7) at the beta3-receptor.
  • Only the antagonistic action of arotinolol was observed in intact animals.

Conclusions:

  • Direct stimulation of brown adipose tissue thermogenesis by arotinolol is unlikely to be the sole mechanism for significant weight loss.
  • The anti-obesity effects of chronic arotinolol treatment may involve additional, yet unidentified, pathways.
  • Further research is needed to fully understand the complex mechanisms underlying arotinolol's anti-obesity effects.

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