Maturation of Jejunum and Ileum in Rats

Abstract

A B S T R A C T During osmotic diarrhea, loss of water and electrolytes appears to be greater in infants than in adults. In 2-, 3-, and 7-wk-old rats, we studied net transport of H20, Na, and Cl, during in vivo perfusion of segments of the jejunum and ileum, from solutions with osmolalities of 300, 375, 500, or 700 mosmol/kg. In the jejunal segments, from the hypertonic solutions net transport of H20, Na, and Cl was into the lumen and greater in the 2-than 7-wk-old rats. In the ileal segments, transport of water was into the lumen, transport of Na was minimal and variable, whereas transport of Cl was usually out of the lumen. In 3-wk-old rats, transport rates were intermediate between those in 2-and 7-wk-old rats. The calculated filtration coefficient (microliters of H20 transported per hour per unit osmolality gradient-lumen-serum -per gram dry weight) of water suggested that the resistance to water flow did not increase with rise in luminal hypertonicity in the jejunum of the 2-and 3-wk-old rats, whereas in jejunum of the 7-wk-old rats and in ileum of rats in all three ages, the resistance to water flow increased with the rise in luminal osmolality. The differences in the transport rates and the resistance to water flow, between segments of the 2-, 3-, and 7-wk-old rats, suggested a maturational phenomenon that appears to continue beyond the 3rd wk of life and could have been due to differences in some physical property of the mucosal membrane.

In Vivo Transport of Water and Electrolytes in the Infant Rat Small Intestine

“…Because net absorption and net secretion rates are the sum of the unidirectional fluxes, lumen-to-plasma and plasma-to-lumen, it is possible that an alteration in the magnitude of one or both of these fluxes were responsible for the observed developmental changes. The results of the present study are in agreement with those of our previous studies which showed that when the intestinal lumen was perfused with hypertonic solutions the permeability of the small intestinal mucosa to water decreased with increasing age (7).…”

Concerted action of dopamine on renal and intestinal Na+-K+-ATPase in the rat remnant kidney

“…At the intestinal level, previous studies have shown that the inhibitory effects of dopamine on jejunal sodium absorption and Na ϩ -K ϩ -ATPase activity in rat jejunal epithelial cells are limited to animals under 20 days of age, adult animals being insensitive to the inhibitory effects of dopamine (12,44,46). Intestinal function has a great impact during early postnatal life, not only on the uptake of nutrients but also on the maintenance of electrolytes and water metabolism (19,50). In fact, although nephrogenesis is completed at birth, renal tubular function continues to develop postnatally, and the kidney has a limited capacity to regulate fluids and electrolyte homeostasis (34).…”

Ontogenic aspects of D1 receptor coupling to G proteins and regulation of rat jejunal Na+, K+ ATPase activity and electrolyte transport

“…Intestinal function is determined by a developmental process that has a great impact in maintaining electrolyte and water metabolism (Younoszai et al ., 1978). At this stage of maturation, the possible occurrence of complementary functions between the intestine and the kidney may be essential to achieve adequate electrolyte and water homeostasis.…”