Intestinal phosphate transport in spontaneously hypertensive rats and genetically matched controls.
Hypophosphatemia has been documented in patients with hypertension and in spontaneously hypertensive rats compared with genetically matched control Wistar-Kyoto rats. However, renal tubular reabsorption is increased in spontaneously hypertensive rats. Therefore, it was hypothesized that decreased serum phosphate levels in spontaneously hypertensive rats may be related to a decrease in the intestinal transport of phosphate. To test this hypothesis, sodium-dependent phosphate uptake by jejunal brush-border membrane vesicles of spontaneously hypertensive rats and genetically matched Wistar-Kyoto rats was determined. Phosphate uptake consisted of two components: sodium-independent passive diffusion across the brush border and sodium-dependent, carrier-mediated uptake. The initial rate of uptake in spontaneously hypertensive and Wistar-Kyoto rats was linear up to 20 seconds. The initial rate and time course of jejunal sodium-dependent phosphate uptake was decreased in adult spontaneously hypertensive rats compared with corresponding mean values in Wistar-Kyoto rats. This decrease was secondary to a decrease in Vmax rather than Km, suggesting tha the number and/or the activity of the sodium-phosphate transporters is decreased. Sodium-dependent phosphate uptake was pH dependent, with greater uptake at pH 6.0 than at pH 7.4. However, uptake values were lower in spontaneously hypertensive rats than in Wistar-Kyoto rats at all pH levels tested. In contrast, sodium-dependent phosphate uptake in weanling rats (prehypertensive state) was not significantly different between spontaneously hypertensive and Wistar-Kyoto rats. Vitamin D deficiency in both spontaneously hypertensive and Wistar-Kyoto rats decreased Vmax and Km of sodium-dependent phosphate uptake, whereas 1,25(OH)2 vitamin D3 administration increased Vmax and Km in both spontaneously hypertensive and Wistar-Kyoto rats. These results suggest that the hypophosphatemia seen in adult spontaneously hypertensive rats is secondary to a decrease in sodium-dependent phosphate uptake compared with controls. The sodium phosphate transporter in spontaneously hypertensive rats is responsive to vitamin D administration.
Ghishan
F K
FK
Department of Pediatric Gastroenterology, Vanderbilt University, Nashville, Tennessee.
Arab
N
N
Shibata
H
H
D000818:Animals; D001692:Biological Transport; D001794:Blood Pressure; D002112:Calcifediol / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology / Q000378:metabolism; D010710:Phosphates / Q000493:pharmacokinetics*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012964:Sodium / Q000494:pharmacology; D014808:Vitamin D Deficiency / Q000378:metabolism
D010710:Phosphates; D012964:Sodium; D002112:Calcifediol