Role of ammoniagenesis in the hypocalciuric effect of phosphorus in young men Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xk81jp59n

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  • The present study sought to define a possible role of phosphorus-stimulated ammoniagenesis, previously observed in vitro and in experimental animals, in the hypocalciuric effect of phosphorus in young men. It was hypothesized that titrating some of the hydrogen ions destined for excretion with ammonia would be beneficial to kidney calcium reabsorption because ammonium ion unlike hydrogen ion does not increase urinary calcium loss. To test this hypothesis, seven young men (22 - 31 years old and average weight of 70 kg) were fed a single menu providing 800 mg phosphorus, 1200 mg calcium, 11.7 MJ (~ 2800 kcal) and 14.5 g nitrogen for 10 days. In a subsequent 10-day period, dietary phosphorus was doubled to 1600 mg by the addition of cheddar cheese and milk to the menu. Dietary nitrogen, calcium and vitamin D were equalized for the two periods. Three 24-hour urine samples and a fasting blood sample were collected at the end of each experimental period. Comparison of period 2 with 1 showed urinary phosphorus excretion + 82%, urinary calcium excretion - 38%, serum phosphorus + 6.2%, serum calcium - 3.8%, urinary sulfate and creatinine excretion no change. Urinary ammonia nitrogen excretion increased in all seven subjects with an average increase of 13%. Furthermore each individual increase in ammonia nitrogen excretion was found to be directly correlated with urinary phosphorus excretion (r = 0.76, P < 0.05). Urinary urea nitrogen excretion was found to vary inversely with urinary ammonia nitrogen excretion with an average decrease of 12% and urinary total nitrogen excretion decreased 14% for the entire group. Results obtained therefore offer a mechanism by which phosphorus directly improves the non-parathyroid hormone portion of tubular calcium reabsorption. The magnitude of the effects seen however suggest that phosphorus-stimulated ammoniagenesis only plays a small role in the mechanism of the hypocalciuric effect of phosphorus in young men.
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