[Effect of premature birth on retinal vascular development in the neonatal rat]

To study the effects of premature birth on the development of rat retinal vasculature.

Experimental study. Sixty pregnant Sprague-Dawley rats were divided into four groups: bacterial lipopolysaccharide-induced preterm group (LPS group), RU-486 induced preterm group (RP group), cesarean section induced preterm group (CP group), and the normal delivery rats as the control group. The weight of rats from each group was recorded until postnatal day 21. On postnatal day 4, 7, 10 and 14 (P4, P7, P10 and P14), the retina of right eye was dissected and whole-mounted. Each premature group was divided into two subgroups based on the number of rats in each litter, the small subgroup (6-8 rats per litter, group 1) and the large subgroup (14-18 rats per litter, group 2). The development of retinal vascularization process was observed on P4, P7 and P10 (n = 6).Independent t test, one-way ANOVA and LSD-t test were used to analyzed the results.

The weight of premature rats in LPS, CP and RP groups was significantly lower than that in the normal group within postnatal 21 days (LSD-t test: all P < 0.05). On the P4 and P7 in LPS group, the proportions of retinal superficial vascularized area of newborn rats [(0.47 ± 0.02) % ,(0.63 ± 0.04)%] were less than that in the normal group [(0.57 ± 0.04) % , (0.74 ± 0.05)%] (t4 d = 6.427, P 4 d = 0.000;t7 d = 5.111, P 7 d = 0.000). On the P4 and P7 in RP group, this proportions [(0.49 ± 0.04) %,(0.65 ± 0.04)%] were less than that in the normal group [(0.57 ± 0.04) %, (0.74 ± 0.05)%] (t4 d = 4.469, P 4 d = 0.000;t7 d = 2.491, P 7 d = 0.022). On P4, P7 and P10 in CP group, this proportions [(0.49 ± 0.05) %, (0.61 ± 0.05) %, (0.94 ± 0.03)%] were also less than that in the normal group[ (0.57 ± 0.04) %, (0.74 ± 0.05) %, (0.97 ± 0.02)%] (t4 d = 4.044, P 4 d = 0.001;t7 d = 6.011, P 7 d = 0.000; t 10 d = 2.331, P 10 d = 0.030). Retinal superficial vascularization completed on P14 in all groups. On the P4 and P7 in LPS group, the proportion of retinal vascularized area of group 2 [(0.44 ± 0.02)%, (0.60 ± 0.03)%] were less than that of group 1 [(0.53 ± 0.04)%, (0.74 ± 0.03)%] (t4 d = 3.852, P 4 d = 0.008; t7 d = 5.630, P 7 d = 0.001). On the P4 and P7 in CP group, this proportion in group 2 [(0.43 ± 0.02)%, (0.64 ± 0.03)%] were less than that of group 1 [ (0.54 ± 0.03)%, (0.76 ± 0.02)%] (t4 d = 4.695, P 4 d = 0.003; t7 d = 6.025, P 7 d = 0.001). On P4 in RP group, the proportions of group 2 [ (0.44 ± 0.01)%] was less than that of group 1 [ (0.54 ± 0.04)%] (t4 d = 5.000, P 4 d = 0.002).

The premature rats have lower weight and much slower rate of early retinal vascularization, as compared with the normal rats. Furthermore, in the premature rats, the proportion of retinal vascularization in larger litters is less than that in smaller litters. These results indicate that premature birth and larger litter size have effects on the development of rat retinal vasculature.