Search

To determine the effect of metabolic acidosis on expression of L-Gln, L-Glu, and L-Asp metabolizing enzymes and transporters, the relative content of mRNA, protein, or mRNA and protein, of 6 enzymes and 5 transporters was determined by real-time reverse transcription-PCR and immunoblot analyses in homogenates of kidney, skeletal muscle, and liver of growing lambs fed a common diet supplemented with canola meal (control; n = 5) or HCl-treated canola meal (acidosis; n = 5). Acidotic sheep had a 790% greater (P= 0.050) expression of renal Na+-coupled neutral AA transporter 3 mRNA and a decreased expression of renal glutamine synthetase mRNA (47% reduction, P= 0.037) and protein (57% reduction, P= 0.015) than control sheep. No change in renal cytosolic phosphoenolpyruvate carboxykinase (protein and mRNA), glutaminase (mRNA), or L-Glu dehydrogenase (protein) was found. In skeletal muscle, acidotic sheep had 101% more (P= 0.026) aspartate transaminase protein than did control sheep, whereas no change in the content of 3 Na+-coupled neutral AA transporters (mRNA) or 2 high-affinity L-Glu transporter proteins was found. In liver, no change in the content of any assessed enzyme or transporter was found. Collectively, these findings suggest that tissue-level responses of sheep to metabolic acidosis are different than for nonruminants. More specifically, these results indicate the potential capacity for metabolism of L-Asp and L-Glu by skeletal muscle, and L-Gln absorption by kidneys, but no change in hepatic expression of L-Gln metabolism, elaborates previous metabolic studies by revealing molecular-level responses to metabolic acidosis in sheep. The reader is cautioned that the metabolic acidosis model employed in this study differs from the increased plasma lactate-induced metabolic acidosis commonly observed in ruminants fed a highly fermentable grain diet.

Abstract: Total RNA from autotrophic Chlamydomonas reinhardtiicultures grown in constant dim light and 17 °C constant temperature was subjected to Northern blot analyses. The mRNAs for cytochrome c, β‐tubulin, HSP70B (a chloroplastic heat shock protein of the 70 kD family), chloroplastic fructose‐bisphosphate aldolase, and GAS3 (a “gamete‐specific” protein of unknown function with high expression in gametes but low expression in vegetative cells) each exhibit a clear circadian rhythm in abundance. The rhythms differ significantly in phase and amplitude. The findings show that the genes for cytochrome cand β‐tubulin indeed are regulated by the circadian clock, as previously suggested. Experiments with cultures grown at 27 °C instead of 17 °C further revealed that the rhythms in mRNA abundance for HSP70B, chloroplastic aldolase, and GAS3 also occur with a similar period at the higher temperature. Thus, the rhythms conform to the criterion of temperature compensation for the period and therefore represent true circadian rhythms. In contrast, the combined amount of mRNA for ubiquitin 52 amino acid fusion protein and ubiquitin 78 to 81 amino acid fusion protein stays constant under both temperature conditions. Because the combined amount of mRNA for the ubiquitin fusion proteins was previously shown to cycle under diurnal conditions when cell division activity is high, our data suggest a regulation of these genes by the cell division cycle and not the circadian clock. In summary, our data, together with several other reports, suggest that the circadian clock regulates many but not all genes in Chlamydomonas reinhardtii.

Three experiments were conducted to determine the effect of soybean lipid on ruminal proteolysis of soybean meal (SBM) and ground whole soybeans (GSB). Experiment 1 was a 92-d growth experiment using 120 calves (206 kg) allotted to 12 pens of 10 calves each. Three replicate pens were assigned to each of the treatment supplements: low SBM (LSBM), low GSB (LGSB), high SBM (HSBM) and high GSB (HGSB). Calves received ad libitum amounts of corn silage top-dressed with the respective supplement (.81 kg/head). High protein supplements produced greater (P<.05) gains than low protein supplements, with HSBM calves gaining faster (P<.05) than HGSB calves and LSBM and LGSB calves having similar (P>.10) gains. In Exp. 2, 15 ruminally cannulated Angus × Hereford heifers (380 kg) fed corn silage were used to determine ammonia-N release from the treatment supplements: ground corn (control), GSB, SBM and SBM coated with soybean oil (SBMO). Heifers fed the control supplement had lower (P<.05) ruminal NH3-N concentrations than those consuming soybean protein. Ruminal NH3-N concentrations were similar (P>.10) for GSB and SBM; whereas, SBMO had lower (P<.10) concentrations than SBM through 3 h. In Exp. 3, two ruminally cannulated Angus × Jersey steers (250 kg) were used to determine in situ disappearance of SBM, GSB and SBMO. Total and feed N disappearances were greater (P<.001) for GSB than SBM or SBMO. Although SBM and SBMO were resistant to microbial attachment through 4 h, SBMO tended to have lower (P>.10) N disappearance than SBM when corrected for microbial N. Data from these experiments suggest that the endogenous lipid fraction of GSB did not protect soybean protein from ruminal proteolysis; however, physically coating SBM with oil apparently reduced proteolysis.

Twenty-four Hampshire × Suffolk wether lambs (40 kg) were used in a 2 × 2 factorial arrangement of treatments to study the influence of water restriction and high levels of dietary K on nutrient utilization. Lambs were offered either a normal K diet (1.86% K) or a high K diet (3.66% K). Additionally, the lambs were offered either a normal quantity of water (previously determined voluntary intake of lambs fed normal K levels) or were restricted to a water intake 80% of normal. Each lamb received 800 g/d of a fescue hay-corn diet (77.5% fescue hay) with an additional 20 g of KCl offered to lambs on high K treatments. The experiment consisted of 14 d of adjustment and 7 d of total collection with blood and ruminal parameters measured on the last day of collection. Both acid detergent fiber digestibility and N balance were reduced (P<.05) by high K intake. Urinary Mg excretion tended (P>.05) to be decreased by water restriction. Plasma Mg concentrations at 2 h post-feeding (PF) tended (P>.05) to be reduced by a high K intake at a normal level of water consumption but increased at high K intake when water intake was restricted. A similar pattern was observed for plasma K concentrations. Although high K intake resulted in elevated (P<.05) ruminal K concentrations both at 2 and 6 h PF, ruminal concentrations of ammonia-N and volatile fatty acids were not affected (P>.05) by treatment. These data suggest that nutrient utilization in both the digestive tract and tissues is altered by level of K and modest water restriction.

Thirty pregnant beef cows were utilized to determine the effects of winter Mg supplementation regimen on blood minerals after cows were turned to a spring tetanigenic tall fescue pasture. The winter Mg treatments were (1) tall fescue hay with free access to a Mg-deficient salt-mineral mix, (2) 6.4 kg of corn silage dry matter plus 114 g Mg0/d and (3) tall fescue hay with free access to a salt-mineral mix containing 40% Mg0 from January 1 to February 15. All cows were then placed on the same tetanigenic pasture from February 15 to April 17 with free access to a Mg-deficient salt-mineral supplement. Forage Mg remained below .2% during the experiment. Forage Ca, P and Al changed throughout the spring, attaining maximum values of .35%, .46% and 415 ppm, respectively. Forage N and K also increased throughout the spring, reaching values of 3.5 and 3.8%, respectively, at the April 3 sampling. The forage K:(Ca + Mg) ratio approached 2.2 by March 26, which coincided closely with the average tetany date (March 29). Serum Mg averaged 1.97, 3.58 and 2.06 mg/dl for treatments 1, 2 and 3, respectively, on February 15 before turning cows to pasture. There were no treatment differences for serum Ca, P and K during the experiment. Eight cows exhibited symptoms of grass tetany (collapse) on an average date of March 29. Winter Mg supplementation provided little long-term protection against Hypomagnesemia after turning cows to tetanigenic pasture, indicating that cows must have a supplemental source of Mg during this critical period.

Twenty-one wether lambs averaging 30.0 kg were utilized in a study to determine the influence of level of muscular activity (via electrical stimulation) on metabolism of amino acids and glucose of isolated-perfused hind limbs. Treatments consisted of: (1) control, (2) low electrical stimulation and (3) high electrical stimulation. Mean perfusion flow rate was unaffected by treatment or time of perfusion. Perfusion pressure and hematocrit were increased (P<.05) by stimulation. Glucose levels decreased from a pretreatment average of 44.7 to 41.3, 26.8 and 20.0 mg/dl for treatments 1 to 3, respectively. Lactic acid levels increased from the pretreatment mean of 37.7 to 46.7, 63.8 and 69.4 mg/dl, respectively. Plasma-free fatty acids were utilized from the perfusate at .84, .76 and .68 meq•liter−1·min−1, respectively. Perfusate urea N levels were unaffected by treatment or time of sampling, but perfusate ammonia levels increased in all treatments (ammonia levels for treatments 1 to 3 increased by .50, 1.09 and 1.47 mg/dl, respectively). Perfusate amino acid changes suggested a flux of some amino acids from muscle to perfusate due to electrical stimulation, but perfusate branched chain amino acid concentrations decreased in all treatment groups. Fifty microcuries of 14C-lysine were included in the initial perfusate. Total perfusate radioactivity in all treatments declined with time, reflective of lysine uptake by the muscle. Total perfusate lysine concentration changed less markedly, suggesting that muscle is contributing to maintenance of plasma amino acid levels. Muscle lysine uptake was highest for the control group and lowest at the high level of stimulation, indicating that cellular uptake and incorporation into muscle protein was impeded by muscular stimulation.