Milk and calcium prevent gastrointestinal absorption and urinary excretion of oxalate in rats

Abstract

Dietary oxalate plays a very important role in the formation of calcium oxalate stones, and dietary intake of calcium may decrease oxalate absorption and its subsequent urinary excretion. The purpose of the present study was to determine the effect on urinary oxalate excretion of an acute oral calcium load, standard milk, or high-calcium low-fat milk followed by a dose of oxalic acid. Male Wistar rats weighing 180-200 g were divided into 7 groups of 6 rats each. All animals were fasted for about 24 hours, anesthetized, and hydrated with normal saline at 3-4 mL/hour. Then the animals were given 1 mL of normal saline [Control], 10 mg (111.1 micromol) of oxalic acid [Ox alone], 2 mL of standard milk (calcium: 1.16 mg or 29 micromol/mL) [NCa milk], 2 mL of high-calcium low-fat milk (calcium: 2.05 mg or 51.3 micromol/mL) [HCa milk], equimolar calcium (4.44 mg or 111 micromol) followed by 10 mg of oxalic acid [Ca + Ox], 2 mL of high-calcium low-fat milk followed by 10 mg of oxalic acid [HCa milk + Ox], or 2 mL of standard milk followed by 10 mg of oxalic acid [NCa milk + Ox]. All treatments were administered via a gastrostomy. Urine samples were collected by bladder puncture just before administration and at hourly intervals up to 5 hours afterwards. Urinary oxalate was measured by capillary electrophoresis, while urinary calcium, magnesium and phosphorus were measured by inductively coupled plasma spectrometry. Urinary oxalate excretion peaked at 1 hour in the Ox alone group, while it peaked at 2 or 3 hours in the Ca + Ox, HCa milk + Ox, and NCa milk + Ox groups. Urinary oxalate excretion decreased significantly when 10 mg of oxalate was administered immediately after the administration of equimolar calcium, high-calcium low-fat milk, or standard milk. The cumulative urinary oxalate excretion over 5 hours was approximately 13.6%, 3.5%, 1.6%, and 2.4% in the Ox alone, Ca + Ox, HCa milk + Ox, and NCa milk + Ox groups, respectively. In conclusions, this study demonstrated that calcium salt, or dairy products containing calcium (especially high-calcium low-fat milk) could decrease the gastrointestinal absorption and subsequent urinary excretion of oxalate.

Medicinal Potential of Acalypha wilkesiana Leaves

“…An estimated 80% of kidney stones are formed from calcium oxalate [40]. Those with kidney disorders, gout, rheumatoid arthritis, or certain forms of chronic vulvar pain (vulvodynia) are typically advised to avoid foods high in oxalic acid [41,42]. The high amount of oxalate in Acalypha wilkesiana leaves may pose problem for those with gout, rheumatoid arthritis or kidney disorders, taking the plant (leaves) for either hypertensive condition or cardiovascular diseases.…”

Influence of a low- and a high-oxalate vegetarian diet on intestinal oxalate absorption and urinary excretion

“…Consequently, the oxalate (249 mg ¼ 2.7 mmol) in the spinach of the tortellini in the lunch meal of the high-oxalate vegetarian diet could have been bound to the calcium (211 mg ¼ 5.2 mmol) in the cream sauce and withdrawn from absorption. Studies have shown that ingestion of milk products together with a Vegetarian diet: influence on oxalate absorption and urinary oxalate excretion E Thomas et al spinach meal significantly reduces the oxalate bioavailability in the gastrointestinal tract (Hesse et al, 1984;Brogren and Savage, 2003;Savage et al, 2003;Hossain et al, 2003Hossain et al, , 2005. Probably, this effect caused the significant difference in the mean calcium excretion between the mixed diet and the high-oxalate vegetarian diet, as less calcium was absorbed (shown in Table 3).…”

Regulation of bone mineral density in the grey squirrel, Sciurus carolinensis: Bioavailability of calcium oxalate, and implications for bark stripping

“…The pack rat, Neotoma albigula , and the fat sand rat, Psammomys obesus , for instance can achieve this feat (Shirley & Schmidt‐Nielsen, 1967), and it is possible that grey squirrels could also. The CaOx complex is practically inert (Hossain et al., 2003), and so if grey squirrels lack the ability to break it down, it will likely pass through the body and be excreted unchanged, with no calcium absorbed.…”

“…If, as the calcium hypothesis suggests, grey squirrels are damaging trees to ingest calcium, it would be expected that grey squirrels can utilise CaOx. However, not all mammals can utilise CaOx because it is poorly absorbed unless it is broken down into its constituent parts (Hossain, Ogawa, Morozumi, Hokama, & Sugaya, 2003). The resultant oxalate proves problematic as it is a dietary deterrent for grey squirrels (Schmidt, Brown, & Morgan, 1998), and oxalic acid can be poisonous to mammals (Blackwell, 1990), unless it is degraded.…”

“…The CaOx complex is practically inert (Hossain et al, 2003), and so if grey squirrels lack the ability to break it down, it will likely pass through the body and be excreted unchanged, with no calcium absorbed.…”