The effect of potassium chloride infusion to the rumen or duodenum of sheep upon the absorption of magnesium from the stomach and intestinal regions has been examined. Three Merino ewes, each prepared with a cannula into the rumen and a re-entrant cannula into the duodenum, were offered a basal diet (control) which provided 46.3–51.1 mmoles magnesium and 299–320 mmoles potassium per day. Potassium chloride (500–800 mmoles/day) was infused continuously to either the rumen or duodenum. Digesta fluid flows were estimated from the dilution of a Cr-EDTA solution continuously infused to the rumen. Potassium infusion to either gastrointestinal site led to a comparable increase in the water intake, urine volume and levels of plasma and urinary potassium. Infusion to the rumen caused a marked increase in the potassium levels and a decrease in sodium levels in rumen fluid, as well as an increase in the rumen fluid to blood bioelectrical potential. No effect of treatment on digesta fluid flows was observed. Net magnesium absorption was lowered only when potassium was infused to the rumen, and the reduction was almost entirely due to reduced absorption of magnesium from the stomach. There was no consistent effect on absorption of magnesium from the intestines. Plasma magnesium levels were lowered by both the intraruminal infusion and, to a lesser extent, the duodenal infusion of potassium. The results indicate that although one consequence of potassium ingestion by sheep may be an enhancement of the urinary excretion of magnesium, the major effect on magnesium metabolism is a substantial reduction of absorption of magnesium from the reticulorumen.
I. A low-magnesium diet was fed to four sheep, each of which had been surgically prepared with a rumen fistula, a tube into the cranial one-third of the omasum, a tube to the cranial onethird of the abomasum and a re-entrant duodenal cannula. Mg, as gluconate or acetate, was continuously infused for 12-14 d in turn into ( I ) the caudal duodenal cannuia, (2) the abomasum, (3) the omasum, (4) the rumen. A continuous infusion of the chromium-ethylenediaminetetraacetic acid complex (CrEDTA) was maintained to the rumen. The abomasal effluent which flowed through the cranial duodenal cannula was continually sampled and the flow of Mg calculated from the concentrations of Mg and CrEDTA. Blood and rumen fluid samples were taken and urine and faeces collected during each period of Mg infusion.2. The Mg infused to either the abomasum or omasum was completely recovered at the duodenum, indicating a lack of net absorption of Mg from these stomach compartments. In contrast, 13.7-187 mmol(36-61 yo) of the Mg infused to the rumen was not recovered at the duodenum which suggested that a substantial net absorption of the infused Mg occurred from the reticulo-rumen. Absorption of Mg caudal to the pylorus was not related to the site of Mg infusion and averaged 3 2 8 k 0.56 (SEM) mmol/d. 4. It is concluded that no significant absorption of Mg occurs from either the omasum or abomasum in sheep and that the reticulo-rumen is the principal site of hlg absorption before the pylorus. Absorption of Mg post-ruminally is insufficient to maintain normal Mg status in the animal.
The function of the kidney tubules of sheep which, for periods of 6 months or more, have been confined solely to saline water (1.3% sodium chloride) for drinking, has been compared with that of sheep on identical fodder but receiving drinking water with a low salt content (rain-water). As no consistent difference was observed between the maximal rates of excretion and reabsorption in the kidneys of the two groups, it is probable that prolonged ingestion of sodium chloride by the sheep does not induce an increase in the number of active tubules in its kidneys. The sodium content of the plasma remained unchanged, but slight increases in potassium and chloride were observed in the plasma of those sheep confined to saline water. Urinary excretion of sodium and chloride was greatly increased, and potassium to a lesser extent. Reabsorption of each of these electrolytes, after filtration at the glomerulus, was found to be reduced during transit through the renal tubules. In the sheep which drank saline water, urinary pH was increased and osmolarity reduced. Clearance of total free water, however, was negative, and the osmotic concentration of body fluids was maintained by the production and excretion of urine which was hyperosmotic with blood plasma. The findings illuminate the manner in which renal adjustments assist the sheep to tolerate water relatively high in salt.
The renal function of sheep; after the ingestion of solutions containing 0.89% sodium chloride and 0.5% sodium sulphate, 1.14% sodium chloride and 0.2% sodium sulphate, and 1.3% sodium chloride offered as the only source of drinking water for a period of 6 months, was studied and compared with that of sheep fed on an identical diet and provided with rain-water. The daily fluid intake and the quantity of urine excreted increased in proportion to the concentration of the sodium chloride ingested. The glomerular fi1tration rate and filtration fraction were increased in the sheep drinking the saline water, but the renal plasma flow was only slightly reduced. The observations indicate that the sheep is able to tolerate relatively high salt water by virtue of a renal adjustment which favours increased filtration and so the elimination of the ingested salt.
Intravenous injection of insulin into ruminants leads to reduction of the concentration of hlood sugar without precipitating typical hypoglycaemic symptoms (Bodansky, 1923; Strand, Anderson and AUcroft, 1934; Krzywanek and Hofmann, 1937; Hitchcock and Phillipson, 1946). Cutler (1934), who administered large doses of insulin to goats hy intravenous injection, noted only signs of lassitude after they had heen rendered hypoglycaemic for a period of 8-9 hours, and interpreted this hehaviour as further evidence of a peculiarity in the carbohydrate metabolism of ruminants. Reid (1951) presented further evidenee to show that the response of sheep to intravenous injections of insulin differs from that of non-ruminants; he noted that doses of insulin sufficient to produce hypoglycaemic eonvulsions in non-ruminants often failed to elicit these symptoms in adult sheep.Relatively small doses of insulin given hy subcutaneous injection to diabetic sheep were ohserved to produce bypoglycaemic coma (Jarrett, 1946), and it ia probable that intravenous insulin is rapidly destroyed and its action not merely terminated by the counteraction of hypoglycaemia (Drury and Greeley, 1939).As the carbohydrate metabolism of young lambs during the first few weeks of life is, in some respects at least, very similar to that of non-ruminants (McCandless and Dye, 1950;Jarrett and Potter, 1952) the young lamb might be expected to behave like non-ruminant animals in its response to injected insulin.The following study was undertaken to throw further light on these phenomena. METHODS.A group of adult merino ewes (age 3-5 years) and a group of male and female lambs (age 1 day to 3 months) were uaed in these experiments. The adrenal glands of three iambs, aged 4 weeks, and of two ewos, aged 4 years, were denervated by severing the splanchnic nerve and any detectable branches of it on each side. The response of these animals to injected insulin was observed daring the post operative period. Six rabbits were treated pither with intravenous or subcutaneous injections of various amounts of insulin to allow a comparison to be made between their reactions and those of the sheep. Regular insulin (Burroughs Wellcome) was administered in all eases.
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