EFFECT OF TRIIODOTHYRONINE ON MUSCLE-CELL DIFFERENTIATION AND BLOOD-GLUCOSE LEVEL IN HYPERGLYCEMIC KK MICE

KK mice are genetically diabetic animals, showing glucose intolerance and insulin resistance,We examined the effects of 3,3',5-triiodo-L-thy ronine (T-3) on the blood glucose level and on mRNA levels of muscle c ell. differentiation markers in hyperglycemic KK mice. T-3 treatment ( T1, 1 mg; T3, 3 mg; TID, 10 mg/kg/day) of KK mice for 4 days caused a decrease in blood glucose level by 11%, 25%, and 24%, respectively, wi thout affecting body weight, Skeletal muscle of mice treated with T-3 (T10) showed a 98% increase in the mRNA level of the glucose transport er isotype 4 (Glut4). In contrast, T-3 treatment did not affect the mR NA level of the isotype 1 (Glut1) transporter, The mRNA level of a mus cle cell specific differentiation marker, MyoD, showed a significant i ncrease in the T-3 treatment group with an accompanying enhancement of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA level, These re sults suggest that T-3 stimulates muscle cell differentiation in vivo, concomitant with a stimulation of cellular glucose metabolism, thus d ecreasing the blood glucose level in hyperglycemic KK mice. (C) Academ ic Press.