Dexamethasone selectively increases sodium‐dependent alanine transport across neonatal piglet intestine.

Abstract

SUMMARY1. Lysine and alanine uptake by pig enterocytes has been measured in piglet mid intestine both during normal development and 3 days after injection of dexamethasone and epidermal growth factor (EGF) into 3-day-old animals.2. Alanine uptake measured in the presence of sodium increased markedly during the first 4 weeks of post-natal life. Similar effects on alanine uptake could be produced through injection of dexamethasone, but not EGF, into 3-day-old piglets. Alanine uptake measured in the absence of sodium and lysine uptake measured in the presence of sodium remained unchanged during development and unaffected by injection of dexamethasone or EGF.3. Enterocytes capable of transporting alanine in the presence of sodium were found, by quantitative autoradiography, to cover the top 400 pum of the villus in 6-day-old and 3-4-week-old control pigs. Alanine concentrations in villus tip enterocytes in 3-4-week-old pigs were four times those found in 6-day-old animals. Qualitative examination of selected villi, however, showed alanine uptake taking place over a considerably greater area of villus surface in 6-day-old compared with 3-4-week-old animals. 4. Injection of dexamethasone and EGF into 3-day-old piglets caused an increase in crypt depth without apparent change in crypt cell proliferation. The rate at which enterocytes migrated out of the crypt and the length of individual villi also remained unchanged by dexamethasone or EGF injection.5. Dexamethasone produces its effect on alanine uptake by acting on older enterocytes present on the upper part of the villus. These enterocytes can be shown, by calculations based on enterocyte migration rate, to have already been present on the villus at the time the pig was born.

Epidermal growth factor selectively increases maltase and sucrase activities in neonatal piglet intestine.

“…The small intestine was then quickly removed and samples taken 25, 50 and 75 % along the length for biochemical and cytochemical determination of disaccharidase and alkaline phosphatase activities. Piglets used in these experiments were identical to those described previously when determining the effect of EGF and dexamethasone on amino acid transport (James et al 1987a). …”

Glucocorticoids differentially regulate Na-bile acid cotransport in normal and chronically inflamed rabbit ileal villus cells

“…MP inhibits many of the major immune pathways (13,51). MP and other glucocorticoids have been shown to reverse the inhibition of nutrient and electrolyte malabsorption in animal models of IBD or Crohn's disease (7,10,16,17,30,32,33,36,43,46). For example, we have demonstrated that SGLT1 (43), ASCT1 (46), and the Na-K-ATPase inhibition (43,46) are reversed by MP in a rabbit model of chronic ileal inflammation.…”

“…Because MP increases the mRNA levels of ASBT as well as the immunoreactive protein levels of ASBT in the BBM of villus cells, the likely mechanism of stimulation of ASBT in villus cells in the normal ileum is secondary to increased number of cotransporters. Indeed, other studies have also concluded that, in the normal intestine, MP may regulate Na-solute cotransport and electrolyte transport pathways directly (16,17,27,32,36). However, glucocorticoids do not indiscriminately stimulate all Na-solute cotransport processes.…”

Administration of 3,5,3'‐triiodothyronine induces a rapid increase in enterocyte lactase‐phlorizin hydrolase activity of young pigs on a low energy intake

“…Methods for estimating crypt depth, villus length and villus area were based on those described previously (James, Smith, Tivey & Wilson, 1987 All pigs received a final meal, corresponding to 2 % of their body weight, 18 h before the start of the infusion protocol and 24 h before the end of the experiment. Littermate pairs of similar body weight had been selected at 3 weeks of age, and since they grew at similar rates throughout the 3 weeks of investigation, mean body weights on the day of experiment were not significantly different between controls and their littermates treated with T3 (7 7 + 0 4 and 7 9 + 0 4 kg respectively).…”