Effects of prenatal undernutrition on developing rat diaphragm.

The effects of maternal nutritional deprivation (ND) on the proportions and cross-sectional areas (CSAs) of type I and II fibers in the developing rat diaphragm (Dia) were examined. In addition, the effects of ND on in vitro contractile and fatigue properties were also studied. Compared with in the control (CTL) group (from pups of well-nourished mothers), proportions of type II fibers were significantly lower in the ND group during the first 3 postnatal wk. However, this difference did not persist into adulthood. CSAs of type I and II fibers were larger in ND Dia than in CTL Dia during early postnatal development, but in adults type I and II fiber CSAs were larger in CTL than in ND Dia. Interstitial space comprised a smaller fraction of total muscle area in ND Dia throughout postnatal development and persisted in adults. Estimated fiber density (no. of fibers/CSA muscle) was lower in ND groups at all ages. In addition, the total number of fibers was significantly lower in ND Dia at all ages. Optimal muscle fiber length for peak twitch and maximum isometric force generation was shorter in ND Dia at all ages. At postnatal days 7 and 14, specific force (maximum tetanic force in N/cm2) of ND Dia was significantly lower than that of CTL Dia. At day 21, Dia specific force was comparable between the two groups but was significantly lower in adult ND compared with adult CTL Dia. Except for days 0 and 14, ND Dia was more fatigue resistant than CTL Dia.(ABSTRACT TRUNCATED AT 250 WORDS)