Thyroidectomy and Thyroxine Replacement Caused Impaired Oral Glucose Tolerance in Rat

Thyroxine influences diverse metabolic pathways important in glucose metabolism and important mediators of glucose homeostasis. Thyroxine replacement therapy is usually given in cases of hypothyroidism thus this study was conducted to assess the effects of thyroxine replacement therapy and thyroidectomy on glucose tolerance. Forty rats were divided into four groups (n=10). Group 1(control) was sham operated, group 2 was thyroidectomised, group 3 was sham operated and treated with 10mcg/100g bdwt for five weeks, Group 4 was thyroidectomised and given 10mcg/100g bdwt T4 for five weeks. The rats were anaesthetized by injecting 0.2ml/100g/bdwt ketamine hydrochloride intraperitonially. The rats were weighed before and weekly after the surgery. Oral glucose tolerance test was performed on the rats after five weeks treatment period and total serum thyroxine was determined by chemi-immunoluminiscence. Results were presented as mean +SEM and P values less than or equal to 0.05 was taken as significant. There was fluctuating weight loss and gain in groups 3 and 4 while group 2 had significant steady weight gain compared with control. Fasting blood sugar at zero minute was significantly higher at groups 2, 3 and 4. At 30 mins, glucose level was significantly reduced in groups 2 and 3 while group 4 was not significantly different from control. At 60 and 90 minutes, glucose level was markedly reduced in the three groups compared with control but at 120 min there was significant difference between glucose level in the groups and control. Based on the results in this study, hypothyroidism and hyperthyroidism cause impairment in glucose tolerance and an elevated fasting blood glucose level while thyroxine replacement did not normalise the disturbances caused by thyroidectomy on glucose tolerance nor did it reduce the fasting blood sugar level as observed when compared to the control.