The purpose of this study was to examine the effect of blocking nitric oxide synthase (NOS) activity via NG-nitro-L-arginine methyl ester (L-NAME) on myonuclear addition in skeletal muscle under basal and overloaded conditions. Female Sprague-Dawley rats (approx. 220 g) were placed into 1 of the following 4 groups (n = 7-9/group): 7-day skeletal muscle overload (O), sham operation (S), skeletal muscle overload with L-NAME treatment (OLN), and sham operation with L-NAME treatment (SLN). Plantaris muscles were overloaded via bilateral surgical ablation of the gastrocnemius muscles and L-NAME (0.75 mg/mL) was administered in the animals' daily drinking water starting 2 days prior to surgery and continued until sacrifice. Myonuclear addition was assessed as subsarcolemmal incorporation of nuclei labeled with 5-bromo-2'-deoxyuridine (approx. 25 mg.(kg body mass)-1.day-1) delivered via osmotic pump during the overload period. As expected, muscle wet mass, total protein content, fiber cross-sectional area, and myonuclear addition were significantly higher (p <or= 0.05) in O vs. S; however, only the increase in wet mass and total protein content (per body mass) were attenuated by L-NAME administration. Interestingly, L-NAME significantly reduced myonuclear addition by 75% in non overloaded muscles (SLN vs. S). Muscle hepatocyte growth factor protein content increased with overload, but was unaffected by L-NAME in either loading state. These data indicate that NOS inhibition in rat plantaris muscle attenuates myonuclear addition under basal, but not overloaded, conditions.

Skeletal muscle capillary proliferation is known to occur in response to an overload hypertrophy stimulus. Nitric oxide is necessary for muscle capillary proliferation in an aerobic exercise model; however, nitric oxide's role in capillary proliferation in overloaded skeletal muscle is unknown. Thus, the aim of this investigation was to determine to effect of N□-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) administration on capillary angiogenesis in overloaded, hypertrophying rat skeletal muscle. Adult female Sprague Dawley rats (200–225g) were weight matched into either a control group (n=8) or L-NAME group (n=10). Twenty-one days of functional overload of the plantaris muscle in the left leg was produced by unilateral surgical ablation of the synergistic gastrocnemius muscle, while the right leg of each animal underwent a sham operation. A dosage of 20.9±0.3 mg/kg BW/day of L-NAME (in the daily drinking water) was administered to the L-NAME group two days prior to surgery and continuing throughout the loading period. After the loading period, plantaris muscles were harvested and subjected to histochemical staining for capillarity and fiber size in l0μm cross-sections. Although plantaris mass, fiber cross-sectional area, and fiber perimeter were all significantly (p<0.05) lower in the L-NAME group vs. the control group regardless of loading condition, all of these variables increased to an equal relative extent with overload in both groups. In contrast, significant increases in capillary contacts per fiber and capillaries per fiber due to overload were observed only in the control group. This L-NAME-induced prevention of the increase in capillarity during an overloading stimulus in rat plantaris muscles indicates that nitric oxide is important for the angiogenic response observed in overloaded, hypertrophying skeletal muscle. Supported by a grant from Experimental and Applied Sciences.