The effects of testosterone on insulin sensitivity in male rats.
In order to examine the effects of testosterone (T) on insulin sensitivity, male rats were castrated or sham-operated, and exposed to low or high doses of T to substitute normal or to produce high serum T concentrations. Insulin sensitivity was followed by euglycaemic, hyperinsulinaemic glucose clamp measurements. An index of insulin-stimulated glucose transport was obtained in the white gastrocnemius (WG), extensor digitorum longus (EDL), red gastrocnemius (RG) and soleus (SOL) muscles after a bolus dose of [2-3H]deoxyglucose (2-DOG) when steady state was obtained in the clamp measurements. Glycogen synthesis was followed similarly with [U-14C]glucose as a labelled precursor after isolation of glycogen in the muscles mentioned, and in the liver. Castration and high T were followed by a marked insulin resistance in the clamp measurements. This was paralleled by a diminished insulin stimulation of glucose incorporation into glycogen down to about 50% of control values, apparently equally pronounced in all muscles but not found in liver glycogen synthesis. 2-DOG uptake was diminished by castration in the WG and RG muscles but was unaffected by high doses of T. Substitution of castrated rats with a low dose of T, restoring their serum T concentrations to the normal range, completely abolished these perturbations of insulin sensitivity. It is concluded that T is an important regulator of muscular insulin sensitivity, which seems to be highest in a 'window' of normal serum T concentrations.
Holmäng
A
A
Department of Medicine I, Sahlgrenska Sjukhuset, University of Göteborg, Sweden.
Björntorp
P
P
D000818:Animals; D003345:Corticosterone / Q000097:blood; D003847:Deoxyglucose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis; D007333:Insulin Resistance / Q000502:physiology*; D007700:Kinetics; D008297:Male; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D009919:Orchiectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013737:Testis / Q000502:physiology; D013739:Testosterone / Q000097:blood / Q000494:pharmacology*
D013739:Testosterone; D006003:Glycogen; D003847:Deoxyglucose; D005947:Glucose; D003345:Corticosterone