Effects of insulin and exercise on rat hindlimb muscles after simulated microgravity.
This study was designed to examine insulin- and exercise-stimulated glucose uptake and metabolism in the hindlimb muscles of rats after conditions of simulated microgravity. To simulate microgravity, male Sprague-Dawley rats were suspended in a head-down (45 degrees) position with their hindlimbs non-weight bearing (SUS) for 14 days. In addition, rats were assigned to suspension followed by exercise (SUS-E), to cage control (CC), or to exercising control (CC-E) groups. Exercise consisted of five 10-min bouts of treadmill running at the same relative intensity for the CC-E and SUS-E rats (80-90% of maximum O2 consumption). Hindlimb perfusion results indicated that glucose uptake for the entire hindquarter at 24,000 microU/ml insulin (maximum stimulation) was significantly higher in the SUS (8.9 +/- 0.5 mumol.g-1.h-1) than in the CC (7.6 +/- 0.4 mumol.g-1.h-1) rats, signifying an increased insulin responsiveness. Glucose uptake at 90 microU/ml insulin was also significantly higher in the SUS (48 +/- 4; % of maximum stimulation over basal) than in the CC (21 +/- 4%) rats. In addition, exercise-induced increases in glucose uptake for the hindlimbs (133%) and glucose incorporation into glycogen for the plantaris (8.4-fold), extensor digitorum longus (5.4-fold), and white gastrocnemius (4.8-fold) muscles were greater for the SUS-E rats than for the CC-E rats (39% and 1.9-, 1.9-, and 3.0-fold, respectively). Therefore, suspension of the rat with hindlimbs non-weight bearing leads to enhanced muscle responses to insulin and exercise when they were applied separately. However, insulin action appeared to be impaired after exercise for the SUS-E rats, especially for the soleus muscle.
Stump
C S
CS
Department of Exercise and Sport Sciences, School of Health Related Professions, University of Arizona, Tucson 85721.
Balon
T W
TW
Tipton
C M
CM
D000818:Animals; D001835:Body Weight / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D004326:Drinking / Q000502:physiology; D004435:Eating / Q000502:physiology; D005947:Glucose / Q000378:metabolism; D005958:Glucosephosphates / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006614:Hindlimb / Q000098:blood supply / Q000502:physiology*; D007328:Insulin / Q000494:pharmacology*; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008297:Male; D009132:Muscles / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000502:physiology; D014893:Weightlessness / Q000009:adverse effects*
D005958:Glucosephosphates; D007328:Insulin; D007773:Lactates; D011773:Pyruvates; D002245:Carbon Dioxide; D019344:Lactic Acid; D019289:Pyruvic Acid; D006003:Glycogen; D005947:Glucose