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The postnatal development of sodium transport in the proximal small intestine of the rabbit
Insights
Newly born rabbits show limited intestinal sodium (Na+) transport and fluid absorption due to immature, leaky gut cells. This capacity improves with age, reaching adult levels later in development.
Area of Science:
- Physiology
- Gastroenterology
- Developmental Biology
Background:
- Intestinal sodium (Na+) transport is crucial for fluid absorption.
- Postnatal development significantly impacts intestinal function.
Purpose of the Study:
- To investigate the developmental changes in intestinal Na+ transport after birth.
- To understand the capacity for spontaneous and glucose-coupled Na+ transport in developing rabbit jejunum.
Main Methods:
- Measurement of Na+ transport in short-circuited epithelium and isolated villus enterocytes.
- Analysis of tissue conductance and unidirectional fluxes.
- Assay of (Na+-K+)ATPase activity and thymidine kinase in enterocytes.
Main Results:
- Villus cells from suckling rabbits showed active Na+ transport and glucose response, but at lower capacity than older animals.
- Short-circuited jejunal epithelium from suckling rabbits failed to respond to glucose, with negligible Na+ fluxes.
- Immature intestinal tissue exhibited significant paracellular shunting and reduced (Na+-K+)ATPase activity.
Conclusions:
- Proximal intestinal epithelium in suckling rabbits has limited active Na+ transport capacity.
- The developing intestine is incompletely differentiated and exhibits increased ion permeability (leakiness).
- Maturation of intestinal Na+ transport and barrier function occurs postnatally.
Abstract:
To investigate the postnatal development of intestinal Na+ transport, a major determinant of fluid absorption, we measured spontaneous and glucose-coupled Na+ transport across short-circuited epithelium and in isolated villus enterocytes from rabbit jejunum at age intervals after birth. Villus cells from suckling animals actively transported Na+ and responded to glucose, but their capacity to do so was less than that of villus cells from older animals. Net Na+ fluxes across short-circuited epithelium from suckling animals failed to respond to glucose, remaining negligible and less than adult values. This lack of response to glucose in tissue from younger animals was associated with marked paracellular shunting as evidenced by greater unidirectional fluxes and greater tissue conductance. Villus enterocytes from suckling animals compared to those from adults had reduced (Na+-K+)ATPase activity, but were rich in thymidine kinase. We conclude that proximal intestinal epithelium in suckling animals has a limited capacity for active Na+ transport, is incompletely differentiated, and is leaky, with a greater permeability for ions compared with adult intestine.