The role of alpha and beta adrenergic receptors in cortisol-induced hyperglycaemia in the common African toad (Bufo regularis)

摘要

The role of adrenergic receptors in cortisol-induced hyperglycaemia is not well known. The present study investigated the effects of adrenergic receptor blockers in cortisol-induced hyperglycaemia in the common African toad (Bufo regularis). Each toad was fasted and anesthetized with sodium pentobarbitone (3 mg/100 g i.p). The animals (control) received intravenous (i.v) injection of 0.7% amphibian saline while animals (untreated) were given cortisol (20 μg/kg). In pre-treatment groups, animals received prazosin (0.2 mg/kg i.v), propranolol 0.5 mg/kg or combination of prazosin (0.2 mg/kg i.v) and propranolol (0.5 mg/kg i.v) before i.v injection of cortisol (20 μg/kg). Thereafter, blood samples were collected for estimation of blood glucose level using the modified glucose oxidase method. Cortisol caused significant increase in blood glucose level from 44.4±3.8 to 71.7±9.7 mg/dl. Pre-treatment of the toads with propranolol (0.5 mg/kg i.v) caused significant reduction (p≤ 0.01) in cortisol-induced hyperglycaemia while pre-treatment with prazosin (0.2 mg/kg i.v) produced no significant effect on hyperglycaemia induced by cortisol. The combination of both prazosin and propranolol completely abolished the effects of cortisol on blood glucose level. The results suggest that cortisol-induced hyperglycaemia in the toad (B. regularis) is mediated probably by both the α- and β-adrenergic receptors with the beta adrenergic receptors playing dominant role.