In vivo inhibition of nitric oxide synthase impairs upregulation of contractile protein mRNA in overloaded plantaris muscle.
Inhibition of nitric oxide synthase (NOS) activity in vivo impedes hypertrophy in the overloaded rat plantaris. We investigated the mechanism for this effect by examining early events leading to muscle growth following 5 or 12 days of functional overload. Male Sprague-Dawley rats (approximately 350 g) were randomly divided into three treatment groups: control, N(G)-nitro-L-arginine methyl ester (L-NAME; 90 mg.kg(-1).day(-1)), and 1-(2-trifluoromethyl-phenyl)-imidazole (TRIM; 10 mg.kg(-1).day(-1)). Unilateral removal of synergists induced chronic overload (OL) of the right plantaris. Sham surgery performed on the left hindlimb served as a normally loaded control. L-NAME and TRIM treatments prevented OL-induced skeletal alpha-actin and type I (slow) myosin heavy chain mRNA expression at 5 days. Conversely, neither L-NAME nor TRIM affected hepatocyte growth factor or VEGF mRNA responses to OL at 5 days. However, OL induction of IGF-I and mechanogrowth factor mRNA was greater (P < 0.05) in the TRIM group compared with the controls. Furthermore, the phosphorylated-to-total p70 S6 kinase ratio was higher in OL muscle from NOS-inhibited groups, compared with control OL. At 12 days of OL, the cumulative proliferation of plantaris satellite cells was assessed by subcutaneous implantation of time release 5'-bromo-2'-deoxyuridine pellets during the OL-inducing surgeries. Although OL caused a fivefold increase in the number of mitotically active (5'-bromo-2'-deoxyuridine positive) sublaminar nuclei, this was unaffected by concurrent NOS inhibition. Therefore, NOS activity may provide negative feedback control of IGF-I/p70 S6 kinase signaling during muscle growth. Moreover, NOS activity may be involved in transcriptional regulation of skeletal alpha-actin and type I (slow) myosin heavy chain during functional overload.
Sellman
Jeff E
JE
P. O. Box 118206, Center for Exercise Science, University of Florida, Gainesville, Florida 32611, USA.
DeRuisseau
Keith C
KC
Betters
Jenna L
JL
Lira
Vitor A
VA
Soltow
Quinlyn A
QA
Selsby
Joshua T
JT
Criswell
David S
DS
D000818:Animals; D000843:Ankle Joint / Q000503:physiopathology; D003285:Contractile Proteins / Q000235:genetics / Q000378:metabolism*; D012090:Cumulative Trauma Disorders; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000293:injuries* / Q000503:physiopathology*; D009133:Muscular Atrophy; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D003285:Contractile Proteins; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester