Cold exposure of the pregnant rat and neonatal respiration.

Pregnant rats were exposed to a cold environment (4 degrees C for almost the whole pregnancy) and the effects on the newborn rats' ventilation, metabolic rate and morphological lung appearance were examined. In cold-exposed rats oxygen consumption (VO2) increased during pregnancy and was 23% more than in control rats 1 day after delivery. All pups were born at term in litters of similar size. At 2-4 days after birth, in the pups born from cold-exposed mothers ("cold" pups), body weight (BW) and lung weight (LW) were reduced, with respect to control newborns, in a similar proportion. In "cold" pups the mean chord of subpleural alveoli was larger and lung volume smaller than in control pups. Both specific minute ventilation (VE/kg), measured by flow plethysmography, and specific oxygen consumption (VO2/kg), measured manometrically, were similar between the two groups. However, tidal volume/BW was smaller and breathing frequency higher in "cold" pups, a breathing pattern which appears necessary to fulfil normal metabolic requirements despite lung immaturity. These results suggest that cold exposure during pregnancy represents a maternal stress which results in somatic and pulmonary underdevelopment of the neonate.