Effects of phototherapy on the growth plate in newborn rats

The aim of the present study was to evaluate the effect of phototherapy and oxidative stress on the growth plate of newborn rats. Forty newborn Sprague-Dawley rats were randomized into a phototherapy group and a control group. Twenty of the rats received phototherapy for 7 days. All zones of the growth plate were assessed with quantitative histomorphometric analysis. Individual zonal lengths were measured for the reserve zone (RZ), the proliferative zone (PZ), the hypertrophic zone (HZ), ossifying cartilage (OC), and total zone (TZ) of the growth plate. Levels of plasma malondialdehyde (MDA), an index of oxidative stress, were also evaluated. Compared with zonal lengths on day 7 after phototherapy between the two groups, the phototherapy group had significantly lower values than those of controls for RZ (5.13 +/- 0.36 vs. 6.4 +/- 0.85 mm x 10(-2); P < 0.001), PZ (20.6 +/- 3.0 vs. 29.25 +/- 1.68 mm x 10(-2); P < 0.001), HZ (15.4 +/- 1.44 vs. 20.87 +/- 1.12 mm x 10(-2); P < 0.001), OC (47.08 +/- 4.25 vs. 62.06 +/- 3.7 mm x 10(-2); P < 0.001), and TZ (88.15 +/- 6.56 vs. 118.48 +/- 4.50 mm x 10(-2); P < 0.001). Plasma MDA levels were correlated with the size of the PZ in the phototherapy group (r = -0.53, P = 0.01). In a multivariate regression model for all rats, being in the phototherapy group was the best predictor of the size of the TZ (beta = -0.94, P < 0.001), with the total variance explained being 88%. These results suggest that in newborn rats, receiving phototherapy is associated with early impairment of growth plate structure, and oxidative stress may be the main risk factor for growth plate injury.