Gonadectomy and reduced physical activity: effects on skeletal muscle.
OBJECTIVE
To examine the effects of testosterone (TST) loss on skeletal muscle contractile function and the potential interactive effects of TST loss and physical inactivity.


METHODS
Randomized control trial.


METHODS
Forty-eight male rats (age, 6mo) were placed into control (Con) or gonadectomized (Orx) groups.


METHODS
Two weeks after Orx or sham surgery, half the Con and Orx rats were hind-limb unloaded (HLU) to reduce muscle activity for 2 weeks. Subsequently, in situ contractile function tests were performed on the soleus (SOL), plantaris (PLAN), peroneus longus (PER), and extensor digitorum longus (EDL). These 4 muscles and gastrocnemius (GAST) then were removed, weighed, sectioned, and stained with adenosine triphosphatase for fiber typing and fiber area measures.


METHODS
Peak tetanic tension (P(0)), time to peak twitch contraction (TPT), half relaxation time (RT(1/2)), muscle mass, fiber area, and specific tension (ratio of P(0)/muscle mass).


RESULTS
Body weight and muscle mass were similar in the Con and Orx groups. The ratio of P(0) to muscle mass was significantly (p <.05) reduced with Orx in SOL (20%), PLAN (18%), PER (28%), and EDL (20%). TPT and RT(1/2) were significantly faster after Orx in PLAN, PER, and EDL. HLU significantly reduced muscle mass in SOL, PLAN, and GAST in Orx and intact groups. HLU also caused a significant decline in SOL and PLAN P(0). The loss in P(0) in the Orx-HLU rats was no greater than the decline in P(0) with HLU alone.


CONCLUSIONS
Gonadectomy results in a loss of P(0) regardless of muscle fiber type or function, it is likely to speed up TPT and RT(1/2), and it does not exacerbate HLU-related atrophy and P(0) loss. Findings may have implications for men with reduced TST levels, as in aging, for instance.
Program in Physical Therapy, Washington University School of Medicine, St Louis, MO, USA. brownmar@msnotes.wustl.edu
M
M
Brown
J S
JS
Fisher
E M
EM
Hasser
D000704:Analysis of Variance; D000818:Animals; D001284:Atrophy; D002369:Castration; D007103:Immobilization; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013739:Testosterone / Q000494:pharmacology*; D015431:Weight Loss
D013739:Testosterone