Effect of testosterone and insulin on rat skeletal muscle RNA.

Abstract

Castrated, intact alloxan diabetic and castrated alloxan diabetic rats were utilized to study the effects of testosterone, insulin and a combination of these 2 hormones on the RNA and the RNA :DNA ratio of the rectus femoris and levator ani muscles. Castration decreased the RNA:DNA ratio in the levator ani but not in the rectus femoris. Testosterone in the castrated rat increased the RNArDNA ratio in both muscles. However, the increase in the rectus femoris is of doubtful biologic significance. The μg RNA /mg N in the rectus femoris and levator ani was not influenced by castration, but testosterone increased this parameter in the levator ani. Thus the RNA of the levator ani appears to be more sensitive to the effects of castration and testosterone replacement than the RNA of the rectus femoris. Alloxan diabetes resulted in a reduction of the RNA:DNA ratio in the rectus femoris and levator ani, and insulin replacement elevated the ratio in both muscles. Alloxan diabetes did not influence the μg RNA/mg N in the rectus femoris, but it resulted in an elevation in this parameter in the levator ani. Insulin replacement increased the ;μg RNA/mg N in the rectus femoris and further elevated it in the levator ani. In contrast with the effects of castration, the RNA of the rectus femoris and levator ani responded in a somewhat similar manner in alloxan diabetes and insulin replacement. The induction of alloxan diabetes in the castrated rat reduced the RNA: DNA ratio in the levator ani and rectus femoris. Testosterone was capable of elevating the ratio in the levator ani but not in the rectus femoris. Insulin alone was capable of raising the ratio in both muscles, and the combined administration of insulin and testosterone further elevated the ratio in the levator ani but not in the rectus femoris. Apparently an adequate insulin supply is not necessary for testosterone to exert its effects on the RNA of the levator ani. Conversely, an adequate testosterone supply is not necessary for insulin to exert its effect on the RNA of either muscle. However, a greater response was obtained in the levator ani when insulin was administered with testosterone. Although histologically similar, it is evident that the rectus femoris and levator ani are biochemically different.