Response of hepatic carbohydrate and cyclic AMP metabolism to cadmium treatment in rats

Daily intraperitoneal injection of cadmium chloride (0.25 or 1 mg/kg) for 21 or 45 days into rats significantly stimulated the activities of hepatic pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose 1,6 diphosphate and glucose 6 phosphatase, increased the concentrations of glucose and urea in the blood and decreased the levels of glycogen in the liver. Whereas chronic cadmium treatment failed to alter adenosine 3',5' monophosphate phosphodiesterase (phosphodiesterase) activity, the endogenous levels of cyclic adenosine monophosphate (AMP)(cAMP) and the activity of basal and fluoride stimulated forms of hepatic adenylate cyclase (AC) were markedly increased in cadmium injected animals. Treatment with the higher dose (1.0 mg/kg) of cadmium chloride for 45 days produced greater metabolic alterations in hepatic tissue than those seen with the lower dose (0.25 mg/kg) given for a shorter period of time (21 days). Discontinuation of cadmium administration for 14 days in rats previously injected with cadmium chloride (1 mg/kg per day) for 21 days, failed to reverse the observed changes in hepatic cAMP or carbohydrate metabolism. A similar persistence of metabolic alteration was noted in rats treated with cadmium (1 mg/kg per day) for 45 days and subsequently maintained without additional treatment for 28 days. Administration of an acute dose of cadmium chloride (60 mg/kg) decreased hepatic phosphodiesterase activity and glycogen content 1 hr after the injection. In addition, acute cadmium exposure increased blood glucose, serum urea, and hepatic cAMP levels, and produced an augmentation of basal and fluoride activated AC. However, the activities of various hepatic gluconeogenic enzymes remained unaffected in animals given an acute dose of cadmium chloride (60 mg/kg). Data provide evidence that suggests that the gluconeogenic potential of liver is markedly enhanced following chronic exposure to cadmium and that the cadmium induced changes in carbohydrate metabolism may be associated with an enhanced synthesis of cAMP. In addition, the present study shows that the cadmium induced metabolic alterations persist even after the cessation of cadmium treatment for a period of 28 days.