Effect of acute food restriction on pulmonary growth and protein turnover in preterm guinea pigs.

The effects of food restriction on the growth and protein turnover of the immature lung were investigated. Preterm guinea pigs, delivered by cesarean section at 65 days gestation (term = 68 days), were given free access to a lactating dam or restricted from feeding for 48 h. Food restriction resulted in significantly reduced body and lung (P less than 0.05) weight compared with fed controls. The rate of pulmonary protein synthesis determined in vivo was reduced by 33% in the food-restricted pups (28.9 +/- 10.2 vs. 19.4 +/- 4.5%, P less than 0.05 for control and food-restricted pups, respectively), whereas the calculated rate of protein breakdown remained unchanged. The inhibition of protein synthesis was accounted for by a 36% decrease in ribosomal efficiency (11.03 +/- 2.61 vs. 7.04 +/- 1.26%, P less than 0.01 for control and food-restricted pups, respectively), whereas ribosomal capacity was unaltered. Polyribosomal analysis indicated an increase in the proportion of RNA present in polysomes and a fall in the free monomer pool (26%), suggesting that food restriction blocked translation by reducing the rate of peptide chain elongation. This finding was confirmed by the analysis of ribosome transit times, which indicated a significant increase in the elongation rate in the lungs from food-restricted pups (0.51 +/- 0.11 vs. 0.94 +/- 0.19 min, P less than 0.05 for control and food-restricted pups, respectively). These results imply that nutrient supply plays an important role in protein deposition and hence growth and repair capacity of the immature lung.

Biochemical maturation of the guinea pig lung and survival following premature delivery.

1. Viable preterm guinea pigs were delivered by Caesarean section from 62 day gestation (term = 68 days). 2. Survival rates (24 hr) were greater than 90%, greater than 55% and greater than 35% respectively at 65, 63 and 62 days gestation. Guinea pig pups experienced increasing respiratory difficulty with progressive prematurity. 3. Lung phosphatidylcholine concentration increased steadily from 0.52 +/- 0.09 mumol/mg DNA at day 50 to 3.9 +/- 0.5 mumol/mg DNA at term. The relative contribution of the disaturated dipalmitoyl species increased over this time from 24.5 to 42.9%. 4. Pulmonary antioxidant capacity increased markedly over the final eight days of gestation, individual increases being manganese superoxide dismutase 68%, copper/zinc superoxide dismutase 48%, glutathione peroxide 37% and catalase 198%.