It is well known that the gastrointestinal tract undergoes significant changes in enzymatic, secretory, and absorptive function during the neonatal period. The developmental characteristics of gut motility, however, remain less well defined. Recently it has been reported that both the frequency and force of gastric contractions in the newborn are reduced, as compared with the adult. The physiological mechanisms underlying the apparent decrease in motility are not known. Furthermore, it is not known how (or if) the postnatal changes in contractility affect gastric emptying. Therefore, the purpose of this study is to: 1) define the biochemical, contractile, and electrical properties of gastric smooth muscle from the fandus, mid-corpus, and orad antrum of the beagle puppy; 2) determine how these physiological parameters change during the first 5 weeks of postnatal life; and 3) characterize gastric emptying in the immediate newborn period and as a function of postnatal development. Standard in vitro recording techniques will be used to define the contractile response of the tissues to acetylcholine, gastrin, and potassium stimulation. Chemically skinned muscle strip preparations will be used to assess the calcium sensitivity and contractility of the tissues. Electrical field stimulation experiments will be conducted to characterize the development of the intrinsic neural input to the circular muscle layer. Intracellular microelectrodes will be used to quantitate resting membrane potentials, action potential waveform characteristics, and voltage-tension relations of the tissues. SDS polyacrylamide electrophoresis will be used to quantitate the contractile protein content of the tissues. Finally, a non-invasive, radionuclide scintigraphic technique will be used to evaluate gastric emptying of a liquid meal (99m-Tc-sulfur colloid labeled milk). Data will be obtained from animals studied 12 hours after birth, 1, 3 & 5 days after delivery, and 1, 3 & 5 weeks post-delivery. Data will also be obtained from adult animals. The results should provide significant information concerning the postnatal development of the biochemical, contractile, and electrical properties of gastric smooth muscle. In addition, the data will provide a more critical analysis of gastric emptying in the neonate. These data are essential if we are to ultimately understand the factors which affect gastric motility and emptying in premature and low birth weight infants.
