['To explore if the hypoxia/reoxygenation-induced increased activity and expression of PTP-1B in neonatal rat cardiomyocytes are mediated by nitric oxide (NO).', 'Neonatal rat cardiomyocytes were isolated and randomly divided into 4 groups: normal group (N group); hypoxia/reoxygenation group (H/R group); N(omega)-nitro-l-arginine methylester treated group (L-NAME group); hypoxia/reoxygenation plus L-NAME group (L-NA + H/R group). PTP-1B activity in cardiomyocytes was determined spectrophotometrically at 405 nm, PTP-1B expression in cardiomyocytes was detected by Western blot.NO and LDH concentrations in cell medium were also assayed.', 'PTP-1B activity and expression in cardiomyocytes was significantly higher in the H/R group as compared to the N group and this increase could be blocked by cotreatment with L-NAME. As compared to H/R group, nitric oxide and LDH concentrations in cell medium were significantly decreased in the L-NA + H/R group (NO concentration: H/R group, 368% +/- 13% and L-NA + H/R group, 61% +/- 7%, P < 0.005; LDH concentration: H/R group, 41.2 +/- 6.7 and L-NA + H/R group, 23.6 +/- 4.8, P < 0.05).'] Are [ Hypoxia/reoxygenation-induced increased activity and expression of PTP-1B in neonatal rat cardiomyocytes mediated by nitric oxide ]?