Steroid Receptors in Two Types of Rabbit Skeletal Muscle*

T. Saartok

doi:10.1055/s-2008-1025894

International Journal of Sports Medicine, Table of Contents

Int J Sports Med 1984; 05(3): 130-136
DOI: 10.1055/s-2008-1025894

Steroid Receptors in Two Types of Rabbit Skeletal Muscle*

T. Saartok

From the Departments of Surgery, Section of Trauma, Karolinska Hospital, Box 60 500, S-104 01 Stockholm, Sweden, and Department of Medical Nutrition, Karolinska Institutet, Huddinge University-Hospital F 69, S-141 86 Huddinge, Sweden

* The following abbreviations and trivial names are used: methyltrienolone (MT), 17β-hydroxy-17α-methyl-estra-4,9,11-trien-3-one; dexamethasone (DEX), 9α-fluoro-11β,17α,21-tri-hydroxy-16α-methyl-pregna-1,4-diene-3,20-dione; moxestrol (MOX), 17α-ethynyl-11β-methoxy-estradiol-17β; promegestone, 17α,21-dimethyl-19-nor-pregna-4,9-diene-3,20-dione; 5α-dihydrotestosterone (DHT), 17β-hydroxy-5α-androstan-3-one; SA, specific radioactivity; cpm, counts per minute; Ka, the apparent equilibrium association constant; Bmax, the apparent maximum number of binding sites; M-1, l/mol; fmol, femtomol (10-15 mol); DNA, deoxyribonucleic acid; Ci, Curie; FT, fast-twitch (type II) fibers and ST, slow-twitch (type I) fibers; g av, the average gravitation force at ultracentrifugation.

Abstract

PDF Download

Abstract

Radiolabeled synthetic steroid hormones and a charcoal adsorption assay were used to identify cytosolic androgen, glucocorticoid, and estrogen receptors in skeletal muscle from rabbits. The presence of the receptors was verified by saturation analysis showing low-capacity, high-affinity binding for the steroid-receptor complexes, specific for each class of steroids. The concentration of androgen and estrogen receptors were of the same magnitude, whereas the corresponding value for the glucocorticoid receptor was about tenfold higher.

Comparisons of fast-twitch (the gastrocnemius/plantaris complex) and slow-twitch (soleus) muscles revealed that the latter contained higher concentrations (expressed per g of tissue wet weight) of glucocorticoid and estrogen receptors, but not of androgen receptor. Expressed per mg of soluble protein, the slow-twitch muscle contained higher concentrations of all three receptors, but when related to the concentration of DNA, only the concentration of estrogen receptor was higher in the slow-twitch muscle. Different response of the two fiber types to direct action of steroid hormones can hence be expected. The fast-twitch muscle contained a higher concentration of soluble protein, whereas the slow-twitch muscle contained higher concentration of DNA, resulting in lower protein/DNA ratio, i.e., smaller “cell units,” in the latter muscle.

Key words

steroid receptors - protein - DNA - skeletal muscle - rabbit

PDF (147 kb)