Lung morphometry in guinea pigs acclimated to cold during growth.

Weanling male guinea pigs, Cavia porcellus [initial weight (W) = 200-250 g], were chronically acclimated to 5 degrees C for 2-18 wk before they were killed. Controls were raised at 22 degrees C. Food and water were given ad lib., and growth was the same in both groups. Under pentobarbital anesthesia (30 mg/kg), lungs were fixed by tracheal instillation of glutaraldehyde and processed for electron microscopy. Lung volume (VL, ml) was measured by displacement; alveolar and capillary surface areas (SA and Sc, m2) were determined morphometrically. Regressions of lung variables vs. W at 22 degrees C (range of W = 89-1,274 g) were as follows: VL = 0.175 W0.676, SA = 0.0097 W0.759, and Sc = 0.0055 W0.825; for 5 degrees C animals (range of W = 239-1,074 g): VL = 0.384 W0.584, SA = 0.0334 W0.594, and Sc = 0.032 W0.562. The total arithmetic mean thickness of lung tissue did not vary with W, and averaged 1.39 microns at 22 degrees C and 1.41 microns at 5 degrees C. VL, SA, and Sc are significantly greater in 5 degrees C guinea pigs than in 22 degrees C animals when W = 300-600 g, but are indistinguishable between groups when W > 700 g. Chronic increases in oxygen consumption, which occur with prolonged exposure to cold, result in accelerated lung development in immature guinea pigs toward normal adult dimensions.