Journal of Applied Physiology AJP: Endocrinology and Metabolism
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J Appl Physiol 90: 850-856, 2001;
8750-7587/01 $5.00
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Vol. 90, Issue 3, 850-856, March 2001

Exogenous testosterone treatment decreases diaphragm neuromuscular transmission failure in male rats

Cesar E. Blanco1, Wen-Zhi Zhan2, Yun-Hua Fang2, and Gary C. Sieck2,3

1 Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California 90033; and Departments of 2 Anesthesiology and 3 Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, Minnesota 55905

The effect of chronic exogenous testosterone (T) treatment on neuromuscular transmission in the diaphragm (Dia) muscle of adult male rats was determined. The contribution of neuromuscular transmission failure (NTF) to Dia fatigue was evaluated by superimposing intermittent direct muscle stimulation on repetitive nerve stimulation of isometric contraction in vitro. T treatment significantly reduced the contribution of NTF to Dia fatigue by ~20% (P < 0.001). Fiber type-specific effects on NTF were determined by measuring Dia fiber glycogen levels subsequent to repetitive nerve or muscle stimulation. T treatment had no effect on glycogen depletion in Dia type I and IIa fibers regardless of stimulation route. In the control group, type IIx fibers demonstrated significantly less glycogen depletion after nerve stimulation compared with direct muscle stimulation (P < 0.05), suggesting the presence of NTF. In contrast, T treatment increased glycogen depletion of type IIx fibers during nerve stimulation to levels similar to those after direct muscle stimulation. These data indicate that testosterone treatment substantially improves neuromuscular transmission in the Dia.

fatigue; contractile properties; anabolic-androgenic steroids


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