An enzyme-histochemical, ultrastructural and morphometric study on fetal and neonatal rat diaphragms.

The organogenesis of the rat diaphragm was studied with enzyme-histochemical, ultrastructural and morphometrical methods. 18 to 20 and 22 day in utero diaphragms were examined as well as 2-8-14 and 25 day old ones, in order to determine the age related changes in the diameter and the percentage of muscle fibers and mitochondria. In all examined ages, morphometric data showed type II fiber predominance. Type I and II fibers were equivalent in diameter. During fetal life, mitochondrial size increases appreciably with age while the mitochondrial percentage does not. Instead in postnatal life, the mitochondrial diameter is almost constant both for the small type I fibers and for the large ones (type II fibers). The mitochondrial percentage gradually increases particularly in the small fibers.