The Effects of Potassium Supplements Upon the Absorption of Potassium and Sodium From the Sheep Rumen

Abstract

The infusion of potassium salts into the rumen of sheep led to an increase in both the concentration and amount of potassium in the fluid in the rumen and to a decrease in the concentration and amount of sodium. The amount of potassium absorbed from the rumen increased as the intake of potassium was increased and was related to the concentration of potassium in the rumen fluid. The amount of potassium flowing out of the rumen increased and the amount of sodium flowing out decreased with increase in potassium intake but neither the volume of fluid in the rumen nor the rate at which it flowed on to the omasum was affected. There was no evidence that potassium supplements reduced the amount of sodium entering the rumen in the saliva. These results indicate that the amount of sodium absorbed from the rumen is increased when potassium supplements are given.IN experiments designed to study the absorption of sodium and chloride from the rumen of the sheep, Dobson and Phillipson [1958] demonstrated that the contents of the rumen were 30 to 40 mV electrically negative with respect to the blood. It is well known that large amounts of sodium move from the rumen to the blood [Danielli et al., 1945; Sperber and Hyden, 1952; Parthasarathy and Phillipson, 1953] and Dobson [1959] showed that the process is an 'active' one since absorption occurred against the electrochemical gradient for this ion.On the other hand, rather meagre evidence suggests that potassium may be absorbed from the rumen by passive diffusion. Sperber and Hyden [1952] found that potassium accumulated in a rumen pouch in a conscious goat to a level of about 5 times higher than that in the plasma, but this would only necessitate active transport if the potential difference between the rumen contents and the blood were less than 40 mV. Parthasarathy and Phillipson [1953] studied absorption from the isolated rumen of the sheep and suggested that potassium may be absorbed by passive diffusion.Large amounts of potassium are normally ingested by the ruminant and the purpose of the present experiments was to examine the quantitative aspects of absorption and outflow of potassium from the rumen in conscious sheep receiving a varied potassium intake. METHODSAnimals and Diets. -Two adult Scottish Blackface ewes (Sheep 1 and 2) weighing 38 and 40 kg. were used in the absorption studies. Both sheep were fitted with permanent ebonite cannulas into the rumen several months before observations were begun. During the experiments the sheep were kept in metabolism cages. Four 382

Transport of cations and anions across forestomach epithelia: conclusions from in vitro studies

“…As mentioned, the K (Figure 2). This mechanism might in part be responsible for the increased Na 1 absorption seen at high ruminal K 1 concentrations (Scott, 1967;Warner and Stacy, 1972). The increase in the active, electrogenic transport of Na 1 across the tissue under high K 1 conditions also has implications for the transport of K 1 : as the transepithelial potential across the rumen increases, the gradient driving the efflux of K 1 decreases.…”

“…However, when the luminal K 1 concentration was increased from 4 to 100 mmol/l, net K 1 absorption across rumen epithelia increased by 2.5 meq/cm 2 h (Kronshage and Leonhard-Marek, 2009), corresponding to an amount of 0.7 mol/day (or 27 g/day) across the estimated 1.2 m 2 of ruminal surface in sheep (Ferreira et al, 1972). This equals the amount of K 1 absorption observed in vivo by Scott (1967), but exceeds that observed by Warner and Stacy (1972) at the same ruminal potassium concentration of 100 mmol/l. Although the efflux of K 1 from the rumen is passive, in that it follows the electrochemical gradient, the permeability of the rumen to the K 1 ion is thus clearly regulated in a complex fashion that is yet poorly understood.…”

“…When animals are Na 1 -depleted (Scott, 1966) and under stimulation by aldosterone (Blair-West et al, 1963), both the salivary and the ruminal concentration of K 1 may rise to 100 mmol/l (Kay, 1960;Blair-West et al, 1963;Scott, 1966 and1967) Under these conditions, K 1 replaces (scarce) Na 1 in saliva, and not surprisingly, perhaps, a sizable reabsorption of K 1 from the rumen can be observed. Provided that ruminal K 1 is sufficiently high, a number of in vivo and in vitro studies have shown that preintestinal regions can contribute substantially to total recirculation of K 1 in the gastrointestinal tract of ruminants.…”

“…When the potassium level in the diet was increased from 0.6% to 2.4% and 4.8% in steers or lambs and from 1.5% to 2.6% in lactating cows, the animals absorbed between 40% and 72% of the additional K 1 intake in preintestinal regions (Greene et al, 1983a and1983b;Khorasani et al, 1997), thus recirculating not only the entire amount of K 1 secreted with saliva, but also absorbing a certain proportion of dietary K 1 . Scott (1967) calculated ruminal K 1 absorption with the aid of marker infusions, and found a linear increase in absorption with ruminal K 1 concentrations through the range of 35 to 100 mmol/l. Conversely, Warner and Stacy (1972) calculated positive K 1 absorption rates only when ruminal concentration exceeded 100 mmol/l, suggesting that the absorption of K 1 may be regulated in a complex manner.…”

“…The release of high amounts of potassium from plant material after an increase of dietary K intake results in an increased Na 1 absorption from the rumen (Scott, 1967;Warner and Stacy, 1972) and keeps the sum of Na 1 and K 1 concentrations within the rumen almost constant. As ruminal K 1 concentration rises, the potential across the ruminal tissue in toto increases (Dobson, 1959;Scott, 1966;Martens et al, 1987), while the apical membrane of the ruminal epithelium depolarizes (Leonhard-Marek and Martens, 1996).…”