EFFECTS OF PERINATAL UNDERNUTRITION ON ELIMINATION OF IMMATURE MYOSIN ISOFORMS IN THE RAT DIAPHRAGM

The effect of perinatal undernutrition on the postnatal elimination of immature myosin isoforms in rat diaphragm muscle was examined using electrophoretic and immunocytochemical techniques. Electrophoresis of native myosin showed that neonatal bands were present in diaphragm muscles of both control and undernourished rats on day 4. By day 21, the neonatal bands were diminished in the control diaphragm compared with the diaphragm of the undernourished rats. Neonatal bands persisted on postnatal day 30 in the diaphragm of the undernourished rats but not in the diaphragm of control rats. No significant difference in the time course of elimination of embryonic myosin light chain (LC(emb)) was observed between the diaphragm muscles of control and undernourished rats with two-dimensional gel electrophoresis. Immunocytochemical analysis demonstrated embryonic myosin heavy chain (MHC(emb)) in all myofibers of the diaphragm muscle of both groups at day 4, but this isoform was not detected in either group by day 14. Reactivity with anti-neonatal myosin heavy chain (MHC(neo)) indicated that rate of elimination of the MHC(neo) was delayed in the undernourished state as compared with the normal rats (P < 0.001). Serum triiodothyronine levels were measured at 14, 21, and 30 days and were significantly lower in the undernourished rats compared with age-matched controls. These data demonstrate that the normal postnatal decrease in MHC(neo), but not MHC(emb) or LC(emb), is affected by the nutritional state of the animal. We speculate that these alterations in myosin isoform transitions are induced by hypothyroidism associated with undernutrition.