Nature and metabolic consequence of hypophosphaturia in spontaneously hypertensive rats

Previous studies suggest abnormalities in PO4 and perhaps vitamin D metabolism in the spontaneously hypertensive rat (SHR) compared with normotensive Wistar-Kyoto (WKY) control rats. The mechanism for the hypophosphaturia obscure, but intestinal malabsorption of P and/or the possibility of linkage to renal Na avidity has not been evaluated. Furthermore, if sustained, the potential effects of the hypophosphaturia on P balance are not known. The present investigation examined these issues. We found that the reduced P excretion occurs as early as age 22 days, the second day after weaning in the SHR, well before the onset of detectable hypertension. This phenomenon is dissociable from renal Na avidity, and sustained through the 12th week of age, the last week of our studies. Since P absorption is normal, external P balance is increased relative to the WKY control rats. The greater cumulative P retention from infancy to adulthood may explain the age-dependent fall in serum 1,25 dihydroxyvitamin D3 [1,25(OH)2D3] reported in the SHR by some investigators.