Role of adrenergic receptors in the caffeine-induced increase in glucose uptake by the canine hindlimb

The present study was designed to investigate the effects of alpha and beta adrenergic receptor blockers on caffeine-induced increase in canine hindlimb glucose uptake. The study was carried out on fasted male anaesthetized dogs divided into five groups (5dogs per group). Each dog was given a bolus injection of normal saline, caffeine (6mg/kg) caffeine after pretreatment with prazosin (0.2mg/kg). Caffeine (6mg/kg), caffeine after pretreatment with prazosin (0.2mg/kg), propranolol (0.5mg/kg) or combination of prazosin (0.2mg/kg) and propranolol (0.5mg/kg). The experiments were carried out under resting and exercising conditions of the hindlimb. Hindlimb glucose uptake (HGU) was calculated as the product of blood flow and arterio-venous glucose difference. Blood glucose was determined by the glucose oxidase method and blood flow to the hindlimb was determined by time-collection method. The results showed that pretreatment of the animal with either prazosin or propranolol significantly reduced caffeine-induced hyperglycemia, glucose extraction and hindlimb glucose uptake at rest. The two blockers also separately reduced caffeine-induced hyperglycemia during contraction of the hindlimb. Prazosin or propranolol did not however influence the effect of caffeine on glucose extraction and hindlimb glucose uptake during contraction of the hindlimb. It was therefore concluded that alpha and beta adrenergic receptors are involved in caffeine induced responses at rest and not during hindlimb contraction.