Effect of propionic acid on urea synthesis by sheep liver

Experimental soybean meal intoxication in cattle

BACKGROUND

Cattle are commonly fed soybean meal (SBM) and accidental intoxication sometimes occurs.

OBJECTIVES

To describe the biologic and clinical features of SBM intoxication.

ANIMALS

Four steers with ruminal cannula.

METHODS

Controlled experimental trial. SBM was administered once at 1 and 2% of body weight (BW) via cannula at 2-month intervals.

RESULTS

This study showed a 2-phase pathogenic course for 2% BW SBM intoxication. The 1st phase (until 10 hours post-administration) is restricted to ruminal modification with volatile fatty acid overproduction and moderate ruminal ammonia concentration. In the 2nd phase (12-22 hours post-administration), ruminal pH returned to initial values and marked ammonia accumulation occurred in blood, inducing severe metabolic alkalosis with hyperglycemia, hyperinsulinemia, and delayed aciduria (30-40 hours post-administration). Among the clinical signs, nervous signs were only observed during the period with increased plasma ammonia concentration. At 1% BW, ruminal and blood modifications were less pronounced than at 2% BW, and clinical signs were not observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Ammonia accumulation in blood during the second phase is the consequence of continued ammonia production, decreased carbohydrate fermentation, and overwhelming of hepatic detoxifying capacity. Because ammonia accumulation is associated with the clinical signs, treatment of SBM intoxication could be similar to treatment of urea intoxication, including rumenotomy, oral administration of cold water and vinegar, and measurement of ruminal pH.

Maternal undernutrition during late pregnancy in sheep. Its relationship to maternal condition, gestation length, hepatic physiology and glucose metabolism

There is a paucity of information on the metabolic effects of undernutrition of the ewe carrying multiple fetuses in late pregnancy. In the present study the effects of induction of ketosis from 132 d gestation in ewes carrying twin fetuses were compared with a control group. The ewes were well fed up to 132 d. Ketotic ewes showed a loss of condition score from 3.7 (SE 0.11) at 130 d gestation to 3.0 (SE 0.15) 10 d later after clinical recovery, compared with control twin-pregnant ewes (P < 0.01). The weight loss during the same time period was from 70.6 (SE 2.7) kg at 130 d to 64.2 (SE 2.7) kg at 140.d gestation. As expected, both groups lost weight and condition score in the first 28 d of lactation. Induction of ketosis caused a significant shortening of the gestation period to 142.8 (SE 0.7) d compared with 150 (SE 0.4) d in normal twin-pregnant ewes (P < 0.001). Ewes with induced ketosis recovered clinically and showed a normal feed intake by 3.4 (SE 0.07) d; three required treatment. Induction of ketosis resulted in reduction of hepatic uptake of bromosulphthalein (P < 0.01) and its biliary excretion (P < 0.05), metabolic clearance rate (P < 0.001), fractional clearance (P < 0.001) and 15 and 30 min retention compared with control twin-pregnant ewes. Most values had returned to normal by the first week of lactation. It is thought that in human pregnancy similar changes in bromosulphthalein clearance may be related to reduced binding sites for bromosulphthalein in the liver caused by increased circulating oestrogens. Induction of ketosis resulted in a significant hypoglycaemic (P < 0.01), ketotic (P < 0.001) state compared with well-fed twin-pregnant ewes. These changes could be correlated with the severity of the clinical signs, together with a significant rise in plasma urea (P < 0.001) and NH3 (P < 0.05) concentrations. Again, the return of most of these values to normal by the first week of lactation lends support to the reversibility of hepatic lesions caused by fatty infiltration of the liver. The severity of this condition in naturally occurring cases suggests that factors other than undernutrition may be contributory, such as the general body condition of the ewe and glucose metabolism by the liver, including the conversion of propionate to glucose.

Effects of intraruminal infusion of propionate on the concentrations of ammonia and insulin in peripheral blood of cows receiving an intraruminal infusion of urea

To test the hypothesis that propionate can reduce hepatic capacity to detoxify ammonia, effects of the inclusion of propionate in intraruminal infusions of urea on the concentrations of ammonia, other metabolites and insulin in peripheral blood were investigated in two experiments with non-lactating dairy cows. Both experiments were of a 4 x 4 Latin square design with four animals, four treatments and four experimental periods of 7 d; feed was given in two equal meals each day, all intraruminal infusions were given for 1 h at the time of the morning feed, and propionic acid was partly neutralized with NaOH. In Expt 1, the treatments were a basal diet of pelleted lucerne and chopped hay alone or with the following infusions (g/d): urea 80, propionic acid 350, urea 80 plus propionic acid 350. The inclusion of propionate in the urea infusion markedly increased (P < 0.001) the concentration of ammonia in plasma compared with infusion of urea alone. Moreover, the inclusion of urea with the propionate infusion abolished (P < 0.01) the increase in blood insulin level seen with the infusion of propionate alone. In Expt 2, less severe treatments were imposed, the aim being to reproduce metabolic loads of propionate and ammonia that might be expected from a diet of high-protein grass silage rich in lactic acid. The treatments were a basal diet of grass silage alone or with the following infusions (g/d): NaCl 145, NaCl 145 plus urea 50, propionic acid 200, urea 50 plus propionic acid 200. Effects were less pronounced than in Expt 1 but, in the period immediately after infusion, similar effects were seen. It is concluded that propionate-ammonia interactions may have potentially important effects on milk production especially for diets with high proportions of grass silage containing high levels of protein and lactic acid.

Response of renal orotic acid and creatinine to treatments affecting metabolic protein supply of ruminants

90 urine samples obtained in three lamb trials and one experiment using adult wethers were analyzed for their contents of orotic acid and creatinine. The average daily excretion of orotic acid accounted for 0.5 mg to 1.5 mg (35 micrograms to 130 micrograms/W0.75) with a high individual variation. Correlation coefficients between orotic acid and other urinary constituents were low indicating an entirely different response to metabolic variations. There was only a weak relationship to live weight, protein retention and rumen fluid traits. Defaunation reduced the orotic acid excretion (significant in the adult wethers) whereas the addition of rumen-protected lysine as well as the use of different dietary carbohydrate sources were without effect. The urinary excretion of creatinine increased with live weight and age from 0.4 g/d in the 20 kg lambs to 1.7 g/d in the adult 53 kg wethers. The correlations with live weight were close whereas the apparently negative correlation with protein retention was not real as could be evaluated by calculation of the partial correlations. There was a close correlation of creatinine with total N, urea and allantoin. Neither defaunation nor rumen-protected lysine and the kind of carbohydrate source had significant effects on creatinine. The use of orotic acid and creatinine as indicators of metabolic disorders were discussed. Easy application in practical diagnosis without quantitative urine collection might be possible by the determination of orotic acid in the milk of cows and of the creatinine/N ratio in urine.

Effect of mesenteric vein infusion of propionate on splanchnic metabolism in primiparous Holstein cows

Our objective was to assess the effects of increased propionate supply on gut and liver function in lactating cows. Four multicatheterized, primiparous cows (30.4 +/- .5 kg/d of milk) were fed for ad libitum intake a diet of 50% alfalfa hay and 50% concentrate (20.6 +/- 1.9 kg/d of DM, 226 +/- 21 MJ/d of metabolizable energy, and 611 +/- 56 g/d of N). Each cow received intramesenteric infusions of NaCl (control) or Na-propionate (150 mmol/h of a 2.5 M solution) in a reversal design. After 72 h of infusion, blood flow (by indicator dilution) and net flux (venoarterial differences multiplied by blood flow) were measured across portal-drained viscera and the liver. Energy supply from feed consumed and from infusion was similar between treatments. Energy that was excreted as milk decreased with propionate infusion. Propionate infusion increased arterial concentration of propionate; decreased absorption of acetate, butyrate, and valerate; and decreased hepatic removal of L-lactate, butyrate, valerate, NEFA, and oxygen. Propionate infusion decreased splanchnic release of glucose and increased splanchnic release of acetate and alanine. Net flux of urea, BHBA, insulin, or glucagon was unaffected by treatments. Our data show a link between a greater proportion of energy supplied as propionate and decreased energy excreted as milk. This response was associated with decreased net removal of glucogenic and ketogenic substrates by the liver and increased supply of acetate for use by peripheral tissues.

Elevated urinary excretion of orotic acid in sheep caused by intraruminal infusion of sodium propionate

1. The effect of sodium propionate on urinary excretion of orotic acid was investigated. 2. Solutions containing sodium propionate or NaCl, 750 mM/day each, were continuously infused into the rumen for 10 days. 3. During NaCl infusion, an urinary orotic acid excretion of 290 +/- 80 micrograms/day was noted. The intraruminal infusion of sodium propionate raised the concentration of propionic acid in the rumen fluid from 14.0 +/- 0.9 to 26.9 +/- 1.9 mM. 4. During this experimental period the excretion of orotic acid via urine significantly increased to 492 +/- 30 micrograms/day. Parameters of nitrogen balance were not altered by propionate. 5. It is suggested that the site of propionate action in intact sheep is in the pyrimidine synthesis pathway.

Interactions between propionate and amino acid metabolism in isolated sheep hepatocytes

The purpose of the present study was to evaluate the contribution of various substrates to glucose synthesis in isolated sheep hepatocytes, and more specifically to quantify the contribution of propionate to gluconeogenesis. Liver cells from fed sheep have a very high capacity for propionate utilization and conversion into glucose. The gluogenicity of lactate or amino acids was very low in hepatocytes from fed sheep, but was significantly increased in hepatocytes from starved animals. Amino acids such as alanine or glutamine were characterized by a substantial utilization towards ureogenesis; whereas their conversion to glucose was very low. Propionate utilization and conversion into glucose was inhibited by butyrate, ammonia and especially ethanol (by up to 80%). Ethanol promoted a striking accumulation of intracellular malate in hepatocytes incubated with propionate (reaching 14.9 mumol/g cell) and led to a depletion of phosphoenolpyruvate; ethanol inhibition could be counteracted by pyruvate. Propionate and butyrate enhanced ureogenesis from ammonia in ruminant liver cells but their effects were not additive. Propionate also elicited a marked increase in cellular concentrations of phosphoserine and serine, particularly in the presence of ammonia; such effects could influence phospholipid metabolism in the liver. These findings emphasize the contribution of propionate, compared with the other glucogenic substrates, to glucose synthesis in ruminants and point to the possibilities of modulation of the glucogenicity of propionate by various substrates which may be present in portal blood.

Effect of propionate on the utilization of nitrogen from 15NH4Cl for urea synthesis in hepatocytes isolated from sheep liver

1. The effect of ornithine (2.0 mM) and propionate (5.0 mM) on the utilization of N from 15NH4Cl (5.0 mM) for urea synthesis in hepatocytes isolated from sheep liver was investigated. 2. The capacity of sheep hepatocytes to utilize [15N]ammonia in the absence of the other exogenous substrates was very low and amounted 132 +/- 37.3 mumol/hr per 1 g dry wt. 3. Ornithine failed to affect the total [15N]ammonia uptake and total urea synthesis, but at the same time it markedly increased the utilization of [15N]ammonia for ureagenesis and diminished the rate of urea synthesis from endogenous sources. 4. Propionate markedly increased total [15N]ammonia utilization and total urea formation; this increase resulted from the rise of ammonia utilization for urea synthesis and it was similar in the presence or absence of ornithine. 5. The capacity of sheep liver cells to utilize ammonia in the presence of propionate (in the presence or absence of ornithine) amounted to 256 mumol/hr per 1 g dry wt, thus being similar to the values in vivo. 6. It is concluded that in sheep hepatocytes both ornithine and propionate stimulate the utilization of ammonia for urea synthesis and these effects take place independently and occur by different mechanisms.

Propionate and butyrate metabolism in rat or sheep hepatocytes

The capacities of isolated hepatocytes to metabolize volatile fatty acids have been compared in rat and sheep hepatocytes. In both species, acetate utilization in vitro was quite limited. Significant species differences for propionate and butyrate consumption were found: propionate utilization by rat hepatocytes was relatively limited and plateaued at about 0.8-1.0 mM, whereas butyrate utilization was approx. 2-times higher. In contrast, ruminant hepatocytes exhibited a lower rate of butyrate utilization, but propionate metabolism was much more active than in rat liver cells. With relatively low concentrations of substrates (max. 2 mM), only propionate, compared to lactate or alanine, had a significant glucogenicity with hepatocytes from fed sheep. In both species, butyrate inhibited propionate consumption, although to a larger extent in sheep. The conversion of [2-14C]propionate to glucose by sheep hepatocytes was inhibited by 2 mM butyrate (60%) or ammonia (30%); 1 mM oleate or 10 mM glucose were ineffective. The basal rate of ammonia utilization by sheep hepatocytes was much lower than in rat and was unaffected upon addition of ornithine. Ammonia metabolism was markedly enhanced by butyrate and, in contrast to rat liver cells, also by propionate.