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
