Ontogeny of Na+ transport in rat colon

To obtain information about whether nutrient and hormonal factors are critical for the developmental pattern of electrogenic amiloride-sensitive Na+ transport (NaSCC) in rat distal colon, we studied the effect of adrenalectomy, high dietary Na+ intake, and hypothyroidism on colonic NaSCC in weanling rats. Adrenalectomy and high dietary Na+ intake inhibited NaSCC, decreased plasma level of aldosterone, and did not influence plasma level of thyroxine. Hypothyroidism inhibited NaSCC without significant changes of plasma aldosterone. These results suggest that the high activity of NaSCC during weaning period reflects the relatively low Na+ intake, and that thyroid hormones have an important permissive role in the developmental changes of NaSCC.