PERINATAL DEVELOPMENT OF TUBULAR FUNCTION IN THE PIG

¹ Department of Internal Medicine, Medical School, Hannover, F.R.G.
² Institute of Veterinary Anatomy, State University, Utrecht, The Netherlands
³ Department of Physiology, Middlesex Hospital Medical School, London
⁴ Department of Anatomy, Royal School of Veterinary Studies, Edinburgh

Renal tubular function has been studied in pig fetuses of 105-112 d gestational age in new-born pigs 5-9 d old. The experiments were performed on anaesthetized animals, urines being collected by inserting a catheter into one ureter of the animal under study. The glomerular filtration rate was estimated and plasma concentrations and urinary excretion of the following substances were measured: sodium, potassium, calcium, ammonia, urea, phosphate, glucose, fructose, creatinine, protein and exogenous 4-aminohippuric acid, and inulin. The reabsorption of water was considered in relation to the plasma vasopressin values. New-born pigs were loaded with glucose and fructose in order to determine the maximal tubular transport rate of these substances. Significant changes at birth occur in only a few functions of the tubulus system. Following delivery, major changes are: (1) the increased reabsorption of sodium and water which is probably the most important adaptation to extra-uterine life; (2) an apparent increasing impermeability of the tubular epithelium for creatinine, and (3) the direction of transport of fructose, which is reabsorbed by fetuses whereas neonates demonstrate a net secretion. Glucose and fructose are transported by different mechanisms. The experiments with fructose-loaded piglets demonstrate that there are at least two transport mechanisms for fructose: reabsorption - either passive or active - and secretion. The factors causing a shifting from one mechanism to the other are not yet known.

This article has been cited by other articles:

				J.-P. Guignard and A. Drukker Why Do Newborn Infants Have a High Plasma Creatinine? Pediatrics, April 1, 1999; 103(4): 49e - 49. [Abstract] [Full Text]