Changes in the renal handling of urea in sheep on a low protein diet exposed to saline drinking water

Abstract

<span>Previous trials have demonstrated that sheep on a low protein diet and free access to water, and sheep dosed with boluses of NaCl intraruminally also with free access to water, showed decreases in urea loss via the urine compared to control animals. <br />We monitored urea excretion in sheep on a relatively poor protein diet when they were exposed to saline drinking water, i.e. they were unable to vary their intake of NaCl:water. <br />Sheep on isotonic saline drinking water (phase 3) excreted significantly more urea via the urine (284 mM/day) compared to phase 1 when they were on non-saline drinking water (urea excretion = 230 mM/day) and phase 2 when they were on half isotonic saline drinking water (urea excretion = 244 mM/day).This finding was explained by the high glomerular filtration rate (GFR) 91.9 <em>ℓ</em>/day, compared to 82.4 <em>ℓ</em>/day (phase 1) and 77.9 <em>ℓ</em>/day (phase 2), together with a significantly raised fractional excretion of urea (FE<sub>urea</sub>) (51.1 %) during this phase, and was in spite of the significantly lower plasma concentrations of urea in phase 3 compared to phase 1. The FE<sub>urea</sub> probably results from the osmotic diuresis caused by the salt. There were indications of a raised plasma antidiuretic hormone (ADH) concentration and this would have opposed urea loss, as ADH promotes urea reabsorption. However, this ADH effect was probably counteracted to some extent by a low plasma angiotensin II concentration, for which again there were indications, inhibiting urea reabsorption during the phases of salt loading. <br />As atrial natriuretic peptide both increases GFR and decrease sodium reabsorption from the tubule, it was probably instrumental in causing the increase in GFR and the increase in the fractional excretion of sodium (FE<sub>Na</sub>).</span&gt

Impact of drinking of saline water on hemato-biochemical parameters of Black Bengal goats in the selected areas of Bangladesh

“…Changes in the glomerular filtration rate (GFR) may explain this finding. GFR was found to be significantly higher in goats given higher salt concentrations, indicating that waste products such as urea, uric acid, and creatinine were filtered more thoroughly in the kidneys ( Meintjes and Engelbrecht, 2004 ).…”

Blood biochemical parameters of Murrah buffalo (Bubalus bubalis) reared in the high salinity area of Bangladesh

“…Excess dietary salt consumption causes hypertension in animals [ 2 , 3 ], as well as increased pulse and respiration rates, water retention, muscle cramps, and neurological problems [ 4 , 5 ]. In sheep, increased water salinity reduced blood and plasma volume, extracellular and interstitial fluids, and urea concentrations, while milk production was decreased in cows [ 6 , 7 , 8 ]. When lambs were exposed to 1.5% saline water for 3 weeks, Yousfi and Ben Salem [ 9 ] observed increased plasma glucose, creatinine, urea, and gamma-glutamyl-transferase.…”

“…Serum creatinine after saline water ingestion was highest in the freshwater phase (up to 2% salt) [ 17 ]. Higher salt concentrations were observed to considerably increase glomerular filtration rate (GFR) in the goats, indicating that the kidneys more effectively filter wastes such as urea, uric acid, and creatinine [ 7 ].…”

Effect of protein supplementation on tropical grass hay utilization by beef steers drinking saline water1

“…But kidney N reabsorption capacity may be affected by high consumption of salt. Godwin and Williams (1984) and Meintjes and Engelbrecht (2004) observed greater urinary N excretion and lower plasma urea N (PUN) in sheep consuming high levels of sodium chloride. Therefore, drinking of saline water, in addition to the depression in feed and water intake, could modify the ability of ruminants to handle situations with N deficient forages.…”