Background Iodine is a nonpareil constituent of thyroid hormones (THs) and a prime regulator of thyroid gland functioning. Although essential at recommended levels for the prevention of iodine deficiency disorders (IDDs), exposure to excess iodine reportedly causes hypothyroidism, hyperthyroidism, and several other emerging deleterious impacts. The objective of the present study is to explore the influence of excess iodide exposure on carbohydrate and lipid metabolism along with the histoarchitecture of certain associated organs such as the pancreas, liver, kidney, and skeletal and cardiac muscle because information on those aspects was found to be scanty. Methods Twelve rats were taken, six were fed with iodine through gavage at a dose of 3.5 mg potassium iodide (KI)/100-g body weight, which corresponded to 500 times of the physiological daily dosage of iodide for a period of 60 days, while the other six formed the control group. Results KI-treated rats presented high body weight and urinary iodine with low TH levels, suggesting a primary thyroid dysfunction. There was an increase in blood glucose, cholesterol, triglycerides, low density lipoprotein (LDL), and very low density lipoprotein (VLDL), while high density lipoprotein (HDL) levels decreased. Tissue glycogen content in the liver and skeletal muscle was decreased and was increased in the heart and kidney. Histological sections of the pancreas showed a complete disruption with hardly recognizable histoarchistructure. Treated liver sections displayed the broadened central vein with degenerated hepatocytes, while skeletal muscle sections showed dissolution of muscle fibre cells linked with loss of glycogen from these organs. Histological changes in the heart include features similar to those of a fatty heart with cardiac muscles mutilation, while that of the kidney shows an increase in glomerular tuft size and Bowman's space expansion with general deterioration. Conclusions It may thus be concluded that excess iodine exposure for a long duration causes the development of a biochemical state of hypothyroidism. The developed hypothyroidism was found responsible for the hyperglycaemic and hypercholestromic status evident by high blood glucose and cholesterol levels and the depletion of glycogen at its storage sites in the liver and skeletal muscle but the extra deposition in the cardiac muscle and kidney; histomicrophotographs showed severe destruction of the pancreatic structure. All these alterations are conducive for the pathogenesis of cardiovascular and kidney diseases.
Keywords: excess iodine; glucose metabolism; heart; kidney; lipid profile; pancreas.