Actin and creatine kinase mRNAs in rat levator ani and vastus muscles as a function of androgen status

The plasticity of two selected mRNAs was studied in two typical fast-twitch muscles at different time intervals after orchiectomy (GDX). The levator ani muscle of the rat (LA) is exquisitely sensitive to androgens, whereas the superficial vastus lateralis (SVL) lacks such sensitivity. In vitro translation of RNA isolated from both tissues indicated that actin was among the most repressed proteins of the LA at day 10 postsurgery (GDX-10 days), whereas the template activity of the SVL mRNAs remains virtually unmodified. We used an available actin cDNA and demonstrated that the expression of the LA actin message is reduced by 85% in GDX-10 days and can be recovered after testosterone propionate (TP) injections (GDX + TP). In contrast, the actin expression in SVL remains constant up to day 20 postsurgery. In the LA, the expression of creatine kinase (CK) mRNA was increased 140% in GDX-5 days and decreased 34 and 17% in GDX-10 days and GDX-20 days, respectively, although the measured CK activity, as well as the in vitro translation of the message, remained elevated in those two latter groups. Control level of the CK mRNA expression was recovered in the GDX + TP group. Again, the expression of the message was unchanged in SVL, suggesting that the protein synthesis of this skeletal muscle is far less sensitive to androgen deprivation than that of the LA muscle.