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Supplementing ruminants with nitrate (NO3-) reduces their enteric methane (CH4 ) emissions; however, the greenhouse gas (GHG) mitigation achieved can be partially offset by small emissions of nitrous oxide (N2 O), a more potent GHG. Sheep were dosed intraruminally with 15 NO3- to investigate whether dietary NO3- is a precursor of N2 O and/or di-nitrogen gas (N2 ), and to quantify the amounts of NO3- recovered as N2 O and N2 in gas emissions from sheep adapted or not adapted to dietary NO3-. Ruminally cannulated sheep were adapted to a hay diet supplemented with NO3- (n = 3; 10 g NO3-/kg DM) or urea (n = 3; 5.3 g urea/kg DM). On the day of the experiment all sheep were dosed intraruminally with 15 NO3- and quickly moved into gas-tight chambers to enable recovery of 15 N in N2 O and N2 to be measured. Measurements of gases accumulating in the chambers were made over 10 successive 50 min periods; this enabled the amount of N2 O produced, and the recovery of 15 NO3--N in N2 O and N2 to be determined over a total of 10 hr. Only 0.04% of labelled NO3--N was recovered as N2 O, and this was not dependent (p > .05) on whether or not the animals had been adapted to dietary NO3-. Approximatively 3% of 15 NO3--N was recovered as 15 N2 , which was also not dependent (p > .05) on whether sheep had been adapted to NO3-. Because the kinetics of rumen ammonia (NH3 ) were uncertain, the recovery of 15 N from NO3- in rumen NH3 could not accurately be quantified, but our results suggest that approximately 76% of dietary NO3- was converted to NH3 in the rumen. We conclude that the small amount of NO3- recovered in N2 was evidence of denitrification, previously thought not to occur in the rumen.

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1. Blood samples were obtained from fallow deer (Dama dama) and red deer (Cervus elaphus). Basic haematology, red cell enzymes, and metabolic intermediates and the glycolytic rate of the red cells incubated with different substrates were measured. 2. The major findings were (i) the activity of glucose phosphate isomerase was notably high in the red blood cells of the red deer; (ii) red deer cells also utilized adenosine more efficiently than those of fallow deer and (iii) red cells of both species utilized galactose more efficiently than other species of ruminants.

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1. Metabolic intermediates, substrate utilization and enzyme activities were determined in the red blood cells of the common bent-wing bat and the red fruit bat. Standard haematological parameters and oxy-haemoglobin dissociation curves were also determined in both species. 2. The glycolytic rate as measured by lactate production was much higher for all substrates in the bent-wing bats. The activities of the glycolytic enzymes were also much higher in this species. 3. The standard haematological parameters were similar for the two species. The levels of 2,3-diphosphoglycerate (DPG) in the red cells of the fruit bat were nearly twice as high as those in the bent-wing bats. 4. The oxy-haemoglobin dissociation curve for the red fruit bat was located to the right of that for the bent-wing bat and both these curves were located to the right of that normally seen for human blood. 5. Both species of bat show blood characteristics well adapted to carrying the increased oxygen demands of flight.

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A study comprising two experiments comparing the effects of the alkyllead compounds triethyllead acetate and tetraethyllead as well as an inorganic lead compound (Pb(NO3)2) on human erythrocytic delta-aminolevulinic acid dehydratase activity was undertaken. In Experiment 1, four human blood samples were pre-incubated for 0 min or 60 min with increasing concentrations (0-1000 microM) of triethyllead acetate, tetraethyllead and Pb(NO3)2, and the delta-aminolevulinic acid dehydratase activity was determined. There was no discernible inhibitory effect of tetraethyllead at any concentration, with or without pre-incubation. Pb(NO3)2 showed a distinct effect at an addition concentration of 1 microM, with a substantial inhibition only following pre-incubation. Triethyllead acetate showed no difference in effect with pre-incubation. In the second experiment, the activating effects of zinc chloride (60 microM) and dithiothreitol (20 mM) on delta-aminolevulinic acid dehydratase activity were examined on four human blood samples in the presence of varying concentrations of Pb(NO3)2 (0-50 microM) and triethyllead acetate (0-1000 microM). The addition of zinc chloride alone showed little effect on enzyme activity, while dithiothreitol alone caused a substantial activation of the enzyme at all lead concentrations. The addition of both zinc chloride and dithiothreitol caused an even greater activation of the enzyme. The data indicate that Pb(NO3)2 is a much more potent inhibitor of delta-aminolevulinic acid dehydratase activity than triethyllead acetate (Ki values of 0.77 microM versus 130.37 microM. respectively). The use of delta-aminolevulinic acid dehydratase activity as an indicator of exposure may be questionable in cases of alkyllead exposure. Possible causes for differences in the inhibition of delta-aminolevulinic acid dehydratase by these compounds is also discussed.

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The morphological changes used to confirm a diagnosis of coeliac disease (CD) are precisely those predicted if the surface energy of the interface between duodenal epithelium and the luminal contents were raised to levels comparable to those demonstrated by the hydrophobic nature of the stomach wall. This hypothesis pursues the concept that, in coeliac patients, the gastric mucosal barrier (GMB) is effectively extended from the stomach to coat the duodenum, thus closing the window of absorption in the Gl tract. If studies are correct which indicate that the GMB is a physical reality provided by an adsorbed monolayer of surface-active phospholipid (surfactant) which renders surfaces hydrophobic, then it could also act as a barrier to the absorption of nutrients in the duodenum. Gluten, or its more active polypeptide fragment gliadin, exacerbates the situation in CD by acting as very effective carriers for the insoluble phospholipid which is deposited at the duodenal surface where they are digested by brush-border and pancreatic enzymes.

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1. Sheep were given 800 g low-protein roughage/d at 2 h intervals and infused intraruminally with 0,500, 750, 1000, 1250, 1500 or 2000 mmol sodium chloride/d in 436 ml water. The digestibility of various food fractions and rumen ammonia, volatile fatty acids (VFA) and liquid turnover rate were measured, along with renal haemodynamics and the renal excretory patterns of nitrogen and electrolytes. Ad lib. food intake was determined during the infusion of 0 and 2000 mmol NaCl/d. 2. Infusion of NaCl up to 750 mmol/d had virtually no effect on the indices measured, except water intake and water excretion. Infusion of greater amounts caused a step-wise decrease in the digestibility of organic matter (OM) and N. Rumen liquid turnover rate was increased substantially and rumen NH3 and VFA concentrations were decreased. Ad lib. food intake was not different when either 0 or 2000 mmol NaCl/d were infused into the rumen. 3. The glomerular filtration rate and effective renal plasma flow (ERPF) were substantially increased after the infusion of 1250 mmol or more NaCl/d. Extracellular fluid volume was also increased. The renal excretion of urea and uric acid + allantoin (URAL) were decreased at the higher infusion rates but the fractional excretions of both these substances were enhanced. The excretion of sodium, chloride, calcium and magnesium were markedly increased with increasing salt infusion. 4. The results suggest that high NaCl inputs into the rumen increase the rumen turnover rate, which in turn decreases the digestibility of OM, particularly N. This causes lower rumen NH3 and VFA concentrations. Plasma urea and URAL concentrations are also decreased and this causes lower renal excretion of these substances despite a much higher fractional excretion resulting from the greatly enhanced urine flow rate. 5. When roughages low in N are given, NaCl intake should be kept below 20 mmol/kg body-weight per d to prevent a decline in the digestibility of the food and any consequent reduction in protein available to the sheep.

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Aspects of red blood cell metabolism were compared among three species of small macropodid marsupials from different habitats. Packed cell volume (PCV), erythrocyte reduced glutathione (GSH) concentration and GSH regeneration rates were similar in all three species. The Parma wallaby had very low red cell potassium levels compared to the other species studied. The Tammar wallaby had higher rates of glucose consumption and lactate production in vitro at both pH 7.4 and 8.2 than did the Parma and significantly lower adenosine triphosphate (ATP) levels than the other species. These findings are consistent with preliminary reports published previously. The differences noted cannot be directly related to differences in the habitats of the species.

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Two merino ewes were fed 800 and then 1000 g of lucerne chaff per day and renal responses and extracellular fluid volume (E.C.F.) were determined. Urine urea nitrogen, glomerular filtration rate (G.F.R.), urine volume, effective renal plasma flow (E.R.P.F.) and E.C.F. increased in both animals with the greater nitrogen intake. In a second experiment, five merino wethers and four merino ewes were infused intraruminally with increasing quantities of urea, whilst being fed a mainly roughage ration, and the above parameters were determined. No significant changes in G.F.R., E.R.P.F. or E.C.F. were noted. Urinary excretion maintained a linear response to nitrogen input until 20.6 g of urea nitrogen per day were infused. At this level of infusion, an increased fractional reabsorption of urea resulted in a large increase in plasma urea concentration, but when 500 mmol of NaCl or KCl were added to the infusate, urine urea nitrogen excretion increased from 10.4 to 11.4 and 11.9 g/d respectively and plasma urea concentration decreased from 68.0 to 35.2 and 37.3 mg nitrogen/100 ml. Urea clearance virtually trebled with both electrolyte infusions and E.C.F. and G.F.R. increased by approximately 10 and 25% respectively. It is concluded that urea alone has limited diuretic ability and that the increased electrolyte content of higher protein dry roughage diets aids urine urea excretion by increasing G.F.R., and the urine flow rate by an osmotic diuretic effect.

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