Various studies have shown that a high
protein (HP) diet, compared to a low
protein (LP) diet, leads to
hypercalciuria and alterations in renal and systemic hemodynamics. The authors compared the effects of HP diet to those of normal
protein diet (NP) to determine the possible mechanisms by which changes in systemic hemodynamics and
hypercalciuria occurred. The studies were conducted in awake rats; the effects of
dietary sodium content on the changes induced by HP also were evaluated. The relationship of
prostaglandins (PG),
renin (PRA), and
aldosterone (PA) to changes in blood pressure (BP) was assessed. Two weeks after HP and normal
sodium feeding (40%), glomerular filtration rate (GFR) and urine flow (V) were not different from the same values in a group on an NP diet (23%). When HP was fed with low
sodium, there was a rise in V as a consequence of greater fluid intake. Although plasma
calcium remained constant, the
hypercalciuria correlated with high
protein and
sodium content. Alterations in 1,25(
OH)2
vitamin D3 or PTH (
cyclic AMP excretion) function did not explain the
hypercalciuria induced by HP. This suggests that HP leads to inhibition of tubular
calcium reabsorption by mechanism(s) yet to be elucidated. Although HP did not alter GFR, it led to an increase in BP, a fall in renal vascular resistance, and an increase in RPF, regardless of
sodium intake. PRA and urine
PGE2 excretion were significantly higher in the rats on HP diet, whereas PA remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)