Myocardial high energy phosphates in experimental thyrotoxicosis in guinea pigs

Abstract

Experimental thyrotoxicosis was produced in guinea pigs by daily intraperitoneal injection of 0.7 mg/kg thyroxine (T4) or 0.15 mg/kg triiodothyronine (T3), as shown by an increase of PBI over 50 gamma percent, weight reduction of 20--30 percent, and increase in heart rate of 30--50 percent. Control animals received solvent only. Metabolites were determined in heart muscle on the 1st, 3rd, and 7th day using freeze-stop technique and enzymatic methods: creatine phosphate (CP), ATP, ADP, AMP, glucose 6-phosphate (G-6-P), fructose diphosphate (FDP), pyruvate, lactate, and inorganic phosphate (Pi). In thyrotoxic animals there was a decrease in CP which became significant after 3 days and more pronounced after 7 days. The ratio of CP to Pi decreased. G-6-P and FDP levels increased. The results were identical after administration of T4 and T3. ATP decreased slightly and ADP increased slightly after T4. Propranolol up to a dose of 3 mg/kg or practolol up to 10 mg/kg given daily i.p. on the 4th to 7th day did not prevent either the T4-induced decrease in high energy phosphates or the increase in G-6-P.