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

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 productionin toads have not been well studied. This study investigated the effects of adrenergic receptor blockers in cortisol-inducedhyperglycemia and blood lactate levels in the common African toad (Bufo regularis). Each toad was fasted and anaesthetizedwith sodium thiopentone given intraperitoneally (50mg/kg/i.p). The animals (control) received 0.7% amphibian saline whileanimals (untreated) received cortisol intravenously (50µg/kg/i.v). In pre-treatment groups, animals received propanolol (0.5mg/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) respectivelyfollowed by administration of cortisol 50µg/kg/i.v. Thereafter, blood samples were collected for estimation of glucose andlactate 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) causedsignificant (p<0.05) increase in blood glucose level and significant reduction in blood lactate levels while pre-treatment withPropanolol (0.5mg/kg/i.v) abolished cortisol-induced hyperglycemia and caused increase in blood lactate levels comparedwith the untreated group. The combination of both blockers abolished the hyperglycemic effect of cortisol and causedincrease in the blood lactate levels. The results of this study show that cortisol-induced hyperglycemia is a consequent ofgluconeogenesis and mediated through the beta-adrenergic receptors. The results also show that lactate is produced andused as a gluconeogenic substrate to induce cortisol hyperglycemia in the Common African toad bufo regularis. The betaadrenergic receptors are involved in the use of lactate to induce cortisol hyperglycemia in the Common African toad Buforegularis.