Thermogenic effects of dihydrocodeine in the rat

Area of Science:

• Pharmacology
• Physiology
• Metabolism

Background:

• Thermogenesis is crucial for maintaining body temperature and energy balance.
• Brown adipose tissue (BAT) plays a significant role in non-shivering thermogenesis.
• Understanding the regulation of thermogenesis is vital for metabolic research.

Purpose of the Study:

• To investigate the impact of dihydrocodeine on thermogenesis and BAT activity.
• To elucidate the physiological pathways involved in dihydrocodeine-induced thermogenesis.
• To assess the dose-dependent effects and regulatory mechanisms of dihydrocodeine.

Main Methods:

• Measurement of oxygen consumption (VO2) and tissue blood flow using radiolabelled microspheres in Sprague-Dawley and Zucker rats.
• Administration of dihydrocodeine tartrate via subcutaneous injection or gastric intubation.
• Utilizing pharmacological antagonists (propranolol, WIN44441-1), hormonal treatments (ACTH, corticosterone), and surgical interventions (adrenalectomy, hypophysectomy, sympathectomy).

Main Results:

• Dihydrocodeine dose-dependently increased resting VO2 in rats, with peak effects at 10-25 mg/kg.
• The thermogenic response was reduced by beta-adrenergic and opiate antagonists, and significantly diminished by adrenalectomy or hypophysectomy.
• Dihydrocodeine markedly increased blood flow to BAT (9-10 fold) but not other tissues, an effect abolished by sympathectomy.
• Both lean and obese Zucker rats exhibited increased VO2, with responses modulated by hypophysectomy and corticosterone treatment.

Conclusions:

• Dihydrocodeine stimulates thermogenesis and BAT activity in rats.
• The effect is mediated through complex interactions involving the pituitary-adrenal axis, adrenergic system, and potentially opioid pathways.
• BAT blood flow augmentation is a key component of dihydrocodeine's thermogenic action, regulated by sympathetic innervation.