Placental exchange area in guinea pigs following long-term maternal exercise: a stereological analysis.

We have used stereological techniques to measure the peripheral labyrinth exchange area of the guinea pig placenta in groups of animals which were exercised 0, 15, 30, 45, or 60 min daily throughout pregnancy. The surface area of the maternal lacunae in the peripheral labyrinth decreased linearly as a function of exercise duration, and the maternal volumes of each exercised group were consistently lower, but not linearly. Placental diffusing capacity for carbon monoxide decreased as a function of exercise duration (r = - 0.88, P less than 0.05). Placental CO diffusing capacity was directly proportional to both maternal surface area of a given volume of peripheral labyrinth (mm2/mm3) (r = 0.43, P less than 0.01), and to the total surface area of the placenta (mm2 . g/mm3) (r = 0.53, P less than 0.001). In addition, diffusing capacity correlated to the total fetal surface area (mm2 . g/mm3), (r = 0.53, P less than 0.001). Average fetal and placental weights did not change significantly in the different exercise groups. Individual fetal weights were proportional to placental diffusing capacity and to both the total maternal and fetal placental exchange area. These results demonstrate for the first time that diffusing capacity of the guinea pig placenta is a function of the surface area of the placenta.