Effect of Cortisol on Plasma Lactate Levels following Cortisolinduced Hyperglycaemia in Common African Toad, Bufo regularis

摘要

Summary: Previous studies in man have shown that cortisol induces hyperglycemia through gluconeogenesis. However, the metabolic substrates involved in cortisol-induced hyperglycemia and the role of adrenergic receptors in lactate production in toads have not been well studied. This study investigated the effects of adrenergic receptor blockers in cortisol-induced hyperglycemia and blood lactate levels in the common African toad (Bufo regularis). Each toad was fasted and anaesthetized with sodium thiopentone given intraperitoneally (50mg/kg/i.p). The animals (control) received 0.7% amphibian saline while animals (untreated) received cortisol intravenously (50μg/kg/i.v). In pre-treatment groups, animals received propanolol (0.5 mg/kg/i.v), prazosin (0.2 mg/kg/i.v) and combination of propanolol (0.5mg/kg/i.v) and prazosin (0.2 mg/kg/i.v) respectively followed by administration of cortisol 50μg/kg/i.v. Thereafter, blood samples were collected for estimation of glucose and lactate using the modified glucose oxidase method and colorimetric method respectively. Cortisol caused significant increase in blood glucose level ((p<0.05) and reduction in blood lactate levels. Pre-treatment with Prazosin (0.2 mg/kg/i.v) caused significant (p<0.05) increase in blood glucose level and significant reduction in blood lactate levels while pre-treatment with Propanolol (0.5mg/kg/i.v) abolished cortisol-induced hyperglycemia and caused increase in blood lactate levels compared with the untreated group. The combination of both blockers abolished the hyperglycemic effect of cortisol and caused increase in the blood lactate levels. The results of this study show that cortisol-induced hyperglycemia is a consequent of gluconeogenesis and mediated through the beta-adrenergic receptors. The results also show that lactate is produced and used as a gluconeogenic substrate to induce cortisol hyperglycemia in the Common African toad bufo regularis. The beta adrenergic receptors are involved in the use of lactate to induce cortisol hyperglycemia in the Common African toad Bufo-regularis.