CHANGES IN TESTOSTERONE MUSCLE RECEPTORS - EFFECTS OF AN ANDROGEN TREATMENT ON PHYSICALLY TRAINED RATS

From results obtained in physiological investigations carried out on v arious tissues sensitive to androgens, it seems that the hormonal rece ptivity can reflect changes in the endocrine status and specific respo nse of a tissue. The purpose of the present investigation was to test whether an androgen treatment could modify the receptivity to testoste rone of the skeletal muscle and myocardium of endurance trained rats. The experiment extended over 8 weeks, and animals received injections of delayed testosterone heptylate every seven days. The myocardium and two skeletal muscles with opposed functions and typology were examine d : the extensorum digitorum longus (EDL), and the soleus (SOL). Resul ts obtained using techniques based upon the radio-competition principl es provided information on the testosterone-receptor binding. The bind ing curves were plotted up to the saturating concentration of tritiate d mibolerone, a synthetic androgen specific of androgen receptors. The quantity of receptors, calculated at the specific saturation plateau is expressed in fmol/mg protein. Results show that contractile muscula r activity always increased the quantity of receptors whereas the ster oid treatment decreased it. Thus for EDL and SOL of control trained ra ts the quantity of receptors was 0.78 and 0.82 fmol/mg protein, respec tively, compared to 0.23 and 0.43 fmol/mg protein for sedentary testos terone-treated rats. The same ''contractile activity'' effect was obse rved on the myocardium but enhanced with values of 1.63 fmol/mg protei n for control trained rats versus 0.30 fmol/mg protein for sedentary t estosterone-treated rats. The receptivity to testosterone of the skele tal muscle and myocardium changes under the effect of an androgen trea tment. The negative effect of the treatment is more patent on the hear t and EDL, only or mostly consisting of fast twitch fibers, than on th e SOL mostly consisting of slow twitch fibers.