Search PubMed⌕ Search

Biomedical subjects

J H Clark

Publications and source records attributed to J H Clark.

At least 37 records · Page 2Linked to original sources
PubMed1999

Perfusion of kidneys with unformulated "naked" intercellular adhesion molecule-1 antisense oligodeoxynucleotides prevents ischemic/reperfusion injury.

BACKGROUND: We have previously shown that phosphorothioate intercellular adhesion molecule (ICAM)-1 antisense oligodeoxynucleotide (oligo) IP-9125 blocks the expression of rat ICAM-1 mRNA in rat L2 cells. A single ex situ perfusion of grafts with unformulated IP-9125, suspended in Euro-Collins solution, prolonged the survival of kidney allografts in rats. The present experiments examined whether perfusion of kidneys with unformulated IP-9125 prevents ischemic/reperfusion injury. METHODS: Kidneys were perfused ex situ with 2 ml of Euro-Collins solution without or with IP-9125 and exposed to 30-min cold (4 degrees C storage time) and 30-min warm (anastomosis time) ischemia. Kidneys were then transplanted to syngeneic nephrectomized recipients. RESULTS: Within 24 hr after transplantation, the glomerular filtration rate values were reduced by almost 60% to 0.49+/-0.14 ml/min from 1.20+/-0.27 ml/min in normal kidneys (P<0.001). Kidney perfusion with 10 mg of either IP-12140 (0.41+/-0.07 ml/min) or IP-13944 (0.47+/-0.07 ml/min) control oligo was ineffective. In contrast, perfusion with 10 mg of IP-9125 significantly improved kidney function (0.8+/-0.18 ml/min; P<0.005), whereas the lower doses of 2 mg (0.47+/-0.13 ml/min; NS) or 4 mg (0.54+/-0.04 ml/min; NS) had no significant effect. The glomerular filtration rate results were confirmed by measurements of blood creatinine (CR) levels at 24 hr after grafting: untreated recipients had a twofold higher CR value (0.70+/-0.14 mg/dl) compared with normal controls (0.65+/-0.07 mg/dl; P<0.001). Although perfusion with 10 mg of control IP-12140 (0.80+/-0.14 mg/dl) or IP-13944 (0.65+/-0.07 mg/dl) did not affect CR levels, perfusion with 10 mg of IP-9125 (0.45+/-0.07 mg/dl) lowered CR levels. The Western blots or reverse transcription-polymerase chain reaction experiments performed in kidney transplants within 24 hr after grafting showed that 10 mg of IP-9125 (but not control IP-12140) reduced the expression of ICAM-1 protein and ICAM-1 mRNA, respectively. CONCLUSIONS: Perfusion of grafts with unformulated ICAM-1 antisense oligo specifically reduces intragraft ICAM-1 protein expression and prevents ischemic/reperfusion injury.

Animals↗
PubMed1999

Substrate utilization for hepatic gluconeogenesis is altered by increased glucose demand in ruminants.

Hepatocytes isolated from 10 Dorset wethers that were treated with excipient or 1.0 g/d of phlorizin for 72 h were used to determine the effects of increased glucose demand on utilization of [1-(14)C]propionate and [1-(14)C] alanine for oxidative metabolism and gluconeogenesis. Control and phlorizin-treated wethers excreted 0 and 62.8 g/d of glucose into the urine, respectively. Phlorizin treatment tended to increase conversion of propionate and alanine to CO2. A phlorizin x substrate interaction for conversion to glucose indicated that conversion of alanine to glucose was increased more by phlorizin treatment than was conversion of propionate (285 vs 166% of controls). Phlorizin treatment did not affect estimated Ks for conversion of substrates to either CO2 or glucose; however, phlorizin increased estimated Vmax for conversion of substrates to CO2 and tended to increase estimated Vmax for conversion of substrates to glucose. Phlorizin treatment slightly increased the ratio of conversion of propionate to glucose compared with CO2 and slightly decreased the ratio of conversion of alanine to glucose compared with CO2. In vitro addition of 2.5 mM NH4Cl decreased conversion of propionate to CO2 and glucose but had little effect on conversion of alanine to CO2 and glucose. Estimated Ks and Vmax for conversion of substrates to CO2, Ks for conversion of substrates to glucose, and Vmax for conversion of alanine to glucose were not affected by NH4Cl; however, Vmax for conversion of propionate to glucose was decreased by NH4Cl. These data indicate that although utilization of propionate for gluconeogenesis is extensive, amino acids have the potential to increase in importance as gluconeogenic substrates when glucose demand is increased substantially. Furthermore, excess ammonia decreases the capacity of hepatocytes to utilize propionate for oxidation and gluconeogenesis.

Alanine↗
PubMed1998

Metabolic adaptation to experimentally increased glucose demand in ruminants.

Four Dorset wethers were studied in a Latin square design with 72-h periods to determine the metabolic adaptations that occur in support of increased glucose demand in ruminants. Wethers injected at 8-h intervals with excipient or a total of .5, 1.0, or 2.0 g/d of phlorizin excreted an average of 0, 72.7, 97.9, and 98.5 g/d of glucose into the urine, respectively. Both acute (2 to 24 h after the first injection) and chronic (8-h intervals from 8 to 72 h after the first injection) adaptations of plasma variables to phlorizin treatment were assessed. Concentrations of plasma glucose decreased linearly with increasing phlorizin dose during the 1st 24 h of treatment and tended to decrease linearly with phlorizin dose during 8 to 72 h of treatment. Urea N tended to increase linearly during 2 to 24 h and increased linearly during 8 to 72 h. Nonesterified fatty acids increased linearly with phlorizin injection during the entire treatment period. beta-Hydroxybutyrate increased quadratically with phlorizin injection during 2 to 24 h and tended to increase quadratically during 8 to 72 h. The ratio of insulin to glucagon tended to decrease linearly with phlorizin injection during the 1st 24 h but was unaffected from 8 to 72 h. Triiodothyronine, but not thyroxine, tended to decrease linearly with phlorizin injection during 8 to 72 h. Cortisol was not affected by treatment. Digestibilities of energy and N were not affected by treatment. Urinary energy excretion increased with phlorizin injection in proportion to the amounts of glucose excreted into the urine. These data indicate that phlorizin-treated wethers largely adapted to phlorizin treatment by 24 h after the first injection and are a suitable model for further investigations of hepatic adaptation to increased glucose demand in ruminants.

3-Hydroxybutyric Acid↗
PubMed1998

Effects of chain length and unsaturation of fatty acid mixtures infused into the abomasum of lactating dairy cows.

Six cows were utilized in a 6 x 6 Latin square design with 21-d periods to determine effects of the postruminal profile of fatty acids on dry matter (DM) intake, milk yield and composition, nutrient digestibilities, and plasma metabolites. Treatments were abomasal infusions of 1) control [168 g/d of meat solubles (carrier for fatty acids) plus 10.6 g/d of Tween 80 (emulsifier)], 2) control plus 450 g/d of mostly saturated fatty acids, 3) control plus 450 g/d of palm oil fatty acids low in linoleic acid, 4) control plus 450 g/d of palm oil fatty acids, 5) control plus 450 g/d of soybean oil fatty acids, and 6) control plus 450 g/d of soybean oil fatty acids high in palmitic acid. Treatments 2, 3, 4, and 6 contained similar ratios of C16 to C18 fatty acids. Infusion of soybean oil fatty acids or soybean oil fatty acids high in palmitic acid decreased intakes of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, gross energy, and total fatty acids and tended to decrease yields of milk and fat-corrected milk compared with the infusion of mostly saturated fatty acids. Infusion of palm oil fatty acids low in linoleic acid or palm oil fatty acids decreased milk fat percentage compared with other treatments. Ruminal characteristics and apparent digestibilities of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, energy, total fatty acids, and total C18 fatty acids were not different. Infusion of fatty acids increased concentrations of cholesterol in plasma. The amount of unsaturated fatty acids passing into the small intestine may influence responses of dairy cows to supplemental fat.

Abomasum↗
PubMed1998

Supplemental fat and nicotinic acid for Holstein cows during an entire lactation.

The objectives of this experiment were to determine long-term responses to supplemental fat (from whole soybeans and liquid animal fat) and to determine whether the supplementation of nicotinic acid would enhance milk protein content or yield. From wk 4 through 43 postpartum, 44 multiparous Holstein cows (10 to 12 per treatment) were assigned to one of four dietary treatments: 1) control, 2) control plus 12 g/d of nicotinic acid, 3) supplemental fat, and 4) supplemental fat plus 12 g/d of nicotinic acid. The dry matter intake of cows did not differ among dietary treatments. Yields of milk, solids-corrected milk, and 3.5% fat-corrected milk were increased by nicotinic acid; the yield of fat-corrected milk during wk 4 to 25 was increased by supplemental fat. Contents of crude protein (CP) and true protein in milk were less for cows fed diets supplemented with fat or nicotinic acid; casein content was decreased by nicotinic acid. Intake of net energy for lactation was greater for cows fed supplemental fat; energy balance was greater during wk 4 to 25 for cows fed diets supplemented with fat. Body condition score and body weight were less when nicotinic acid was added to the control diet than when it was added to the diet supplemented with fat. Supplemental fat increased the concentration of nonesterified fatty acids (NEFA) in plasma; nicotinic acid increased NEFA when it was added to the control diet but decreased NEFA when it was added to the diet supplemented with fat. Nicotinic acid did not prevent the decrease in milk CP content that was induced by dietary fat, but it did increase milk yield and tended to increase the yield of milk CP.

3-Hydroxybutyric Acid↗
PubMed1998

Effects of source of carbohydrate and protein and rumen-protected methionine on performance of cows.

Multiparous Holstein cows were fed diets consisting of alfalfa silage, corn silage, and a concentrate mixture containing primarily ground shelled corn or corn gluten feed; the diets were supplemented with 0 or 20 g/d of rumen-protected Met. The 183-d experimental period followed a 21-d covariate period beginning at calving. Data from early lactation (d 22 to 105) and the entire experiment were analyzed. Yields of milk and milk crude protein were not affected by treatment. Corn gluten feed increased the percentages of milk fat and total solids. The rumen-protected Met tended to increase both the crude protein and casein N content of milk. Body weight, milk fat percentage, and yields of milk fat, 3.5% fat-corrected milk, and total solids were greater when ground shelled corn and 20 g/d of rumen-protected Met or corn gluten feed and 0 g/d of rumen-protected Met were fed than when ground shelled corn and 0 g/d of rumen-protected Met or corn gluten feed and 20 g/d of rumen-protected Met were fed. A similar interaction for dry matter intake was significant only during d 22 to 204. Corn gluten feed increased plasma concentrations of His, Ile, Leu, and Val. Rumen-protected Met increased plasma concentrations of Met, decreased His, and tended to decrease Arg, Lys, and Orn. These data suggest that the dietary source of carbohydrate and protein can modulate the response of cows to rumen-protected Met.

Amino Acids↗
PubMed1998

Effects of Yucca shidigera extract and soluble protein on performance of cows and concentrations of urea nitrogen in plasma and milk.

Twelve multiparous Holstein cows averaging 122 d postpartum were used in a replicated Latin square design with 21-d periods. Cows were fed diets containing either low or high soluble protein supplemented with 0 or 9 g/d of Yucca shidigera extract per cow. Dry matter intake and yields of milk, fat, 3.5% fat-corrected milk, and total solids were not affected by treatment. High soluble protein increased percentages of fat and total solids in milk but decreased percentages of crude protein and true protein in milk. Yucca shidigera extract did not affect percentages or yields of milk components, ruminal NH3 N, or urea N in milk or plasma. High soluble protein tended to increase both ruminal pH and concentrations of ruminal NH3 N. Yucca shidigera extract did not affect ruminal pH or NH3 N. High soluble protein increased concentrations of urea N in plasma and milk when both were measured by enzymatic assay, but differences in milk urea N measured by mid infrared reflectance spectroscopy were not significant. Neither Yucca shidigera extract nor increased ruminally undegradable protein was beneficial in this trial when fed to cows milking 30 to 35 kg/d. Concentrations of urea N in milk as measured by mid infrared reflectance spectroscopy were higher than those measured by enzymatic assay, but measurements by mid infrared reflectance spectroscopy were not as sensitive to treatment differences as were measurements by enzymatic assay.

Ammonia↗
PubMed1998

Fatty acid flow to the duodenum and in milk from cows fed diets that contained fat and nicotinic acid.

Four cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design; treatments were arranged in a 2 x 2 factorial. Treatments were 1) low fat diet, no nicotinic acid; 2) low fat diet, 12 g/d of nicotinic acid; 3) high fat diet, no nicotinic acid; and 4) high fat diet, 12 g/d of nicotinic acid. Cows were fed for ad libitum intake diets consisting of 35% alfalfa silage, 15% corn silage, and either 50% low fat concentrate or 40% high fat concentrate (tallow supplied 6.25% of concentrate) and 10% whole raw soybeans (dry matter basis). Intake of gross energy (104 Mcal/d) was not different among treatments. Ruminal and postruminal digestibility of energy was not altered by fat or nicotinic acid. Fatty acid intake and flow to the duodenum were increased by fat but were not affected by nicotinic acid. For all diets, flows to the duodenum of C16:0, C18:0, total C18, and total fatty acids increased, and flows of C16:1, C18:1, C18:2, and C18:3 decreased, compared with their intakes. Biohydrogenation of unsaturated C18 was decreased by fat but was not affected by nicotinic acid. Digestibilities of C18:0, C18:1, C18:2, C18:3, and total fatty acids that flowed to the duodenum were decreased by fat but were not affected by nicotinic acid. The yield of C18:0 in milk was increased, and yields of C6:0 to C16:0 fatty acids were decreased, by fat, but yields were not affected by nicotinic acid.

Animals↗
PubMed1997

Effects of amount and ruminal degradability of protein on nutrient digestibility and production by cows fed tallow.

Five cows with ruminal cannulas were used in a 5 x 5 Latin square design to determine the effects of fat and amount and ruminal degradability of dietary crude protein (CP) on nutrient digestibility and production of milk and milk components. Treatments were 1) control; 2) 15% CP, soybean meal; 3) 15% CP, by-product proteins; 4) 18% CP, soybean meal; and 5) 18% CP, soybean meal and by-product proteins. Diets 2 through 5 contained 3.5% tallow. Diets consisted of 28% alfalfa haylage, 22% corn silage, and 50% concentrate on a dry matter (DM) basis. Fat did not affect dry matter intake or percentages and yields of fat and CP in milk but increased milk yield 2.5 kg/d. Fat did not affect N fractions in milk but decreased the percentages of short- and medium-chain fatty acids (C6:0 to C16:0) and increased the percentages of long-chain fatty acids (C18:0 and C18:1) in milk fat. Fat did not affect ruminal fermentation characteristics or the percentages of dietary DM, organic matter, CP, acid detergent fiber, neutral detergent fiber, starch, ether extract, and energy that were digested. An increase in dietary CP from 15 to 18% increased dry matter intake 1.7 kg/d; increased intake of gross energy 8 Mcal/d; increased the percentages and quantities of DM, organic matter, CP, and energy digested; increased the quantities of acid detergent fiber and neutral detergent fiber digested; decreased ruminal pH; increased concentrations of total volatile fatty acids; and increased NH3 N in ruminal fluid. However, the difference in dietary CP did not affect milk yield or composition. Replacement of soybean meal in the diet with a mixture of by-product proteins decreased NH3 N in ruminal fluid, tended to decrease concentrations of total volatile fatty acids and increase pH of ruminal fluid, but did not affect milk yield or percentages and yields of milk components.

Analysis of Variance↗
PubMed1997

Production and composition of milk from Jersey cows administered bovine somatotropin and fed ruminally protected amino acids.

Eight multiparous and 4 primiparous Jersey cows averaging 92 d of lactation were utilized in a replicated 4 x 4 Latin square design with 28-d periods to determine responses to bovine somatotropin (bST) and ruminally protected Met and Lys when diets were fed that contained supplemental fat. Treatments were 1) control [no bST or ruminally protected amino acids (AA)], 2) control plus bST, 3) control plus ruminally protected AA, and 4) control plus bST plus ruminally protected AA. Dry matter intake was increased by bST but was unaffected by ruminally protected AA. Milk yield was increased by bST but was not altered by ruminally protected AA compared with the control diet. The bST tended to increase percentages of fat and total solids in milk and increased yields of fat, protein, 3.5% fat-corrected milk, and total solids. Ruminally protected AA increased percentages of fat, protein, and total solids in milk; however, yields of milk components were unaffected by ruminally protected AA. Body weight and body condition scores were unaffected by treatment. Concentrations of essential AA in plasma were unaffected by bST administration. Ruminally protected Met and Lys increased the concentration of Met and tended to increase the concentration of Lys in plasma. The lack of an increase in yields of milk and milk protein when ruminally protected AA were fed suggests that adequate amounts of Met and Lys were supplied by the control diet and protein reserves of the cows to meet the AA requirements for synthesis of milk and milk components.

Amino Acids↗
PubMed1996

Dopaminergic regulation of progesterone receptors: brain D5 dopamine receptors mediate induction of lordosis by D1-like agonists in rats.

To characterize the signaling pathway by which the neurotransmitter dopamine modulates progesterone receptor (PR) activation, the steroid-dependent behavior lordosis was used in estrogen-primed ovariectomized Sprague-Dawley rats with stereotaxic implanted third ventricle cannulas. Lordosis was observed in response to solicitous males in females after central administration of the D1-like agonist SKF38393 and three of its analogs (SKF77434, SKF75640, and SKF85174). In contrast, D1-like antagonist SCH23390 and D1-like/D2 repopulation inhibitor EEDQ blocked behavior inducible by the D1-like agonists. Further, antisense oligonucleotides to D5, but not D1, dopamine receptor mRNA suppressed reproductive behavior associated with D1-like stimulation. This finding provides strong evidence that dopaminergic modulation of lordosis is mediated by the novel D5 dopamine receptor. Although D1, but not D5, dopamine receptor mRNAs were detected in the ventromedial nucleus (VMN) by in situ hybridization, agonists microinjected into the VMN, but not into the arcuate nucleus or preoptic area, induced lordosis, suggesting the functional presence of D5 dopamine receptors in the VMN. Also in support, D5 receptor mRNA antisense microinjected into the VMN blocked the subsequent induction of lordosis by D1-like agonists. Finally, facilitation of sex behavior by D1-like agonists was blocked by the antiprogestin RU38486 and PR antisense oligonucleotide. Collectively, the data provide strong evidence for dopaminergic modulation of reproductive behavior through D5 dopamine receptor-mediated modulation of PR-dependent behavior in rat CNS.

Animals↗
PubMed1996

In vivo regulation of central nervous system progesterone receptors: cocaine induces steroid-dependent behavior through dopamine transporter modulation of D5 receptors in rats.

To characterize the membrane pathway by which the cocaine-sensitive dopamine transporter (DAT) modulates progesterone receptor activation, steroid-dependent behavior lordosis was used in estrogen-primed ovariectomized Sprague-Dawley rats with stereotaxic implanted third ventricle cannulas. Lordosis in response to solicitous males was observed in females after intercerebral ventricular administration of DAT antagonists WIN35,428 (80 ng) and cocaine (0.016-1.6 micrograms). Significantly, antisense oligonucleotides (AS) to DAT mRNA also induced reproductive behavior. In contrast, the D1-D2 receptor membrane-repopulation inhibitor N-ethoxycarbonyl-2 ethoxy-1,2-dihydroquinoline and the D1-like antagonist SCH23390 blocked cocaine-inducible behavior. Further, facilitation of behavior by AS to the DAT was suppressed by N-ethoxycarbonyl-2 ethoxy-1,2-dihydroquinoline. Behavior was not dependent on D2 receptors, since animals pretreated with the D2 antagonist sulpride displayed lordosis after cocaine challenge. Antisense oligonucleotides to D5 but not D1 dopamine receptor mRNA suppressed reproductive behavior associated with cocaine. Microinjections of cocaine to the ventromedial nucleus (VMN) but not arcuate nucleus or preoptic area potentiated lordosis, suggesting the functional presence of DAT in the VMN. Finally, cocaine facilitation of behavior was blocked by both antiprogestin RU486 and progesterone receptor AS microinjected into either the third ventricle or the VMN. Collectively, the data provide strong evidence for cocaine modulation of reproductive behavior through presynaptic cocaine-sensitive dopamine transporters and postsynaptic D5 dopamine receptor mediation of progesterone receptor-dependent behavior in rat central nervous system.

Animals↗
PubMed1996

Evaluation of a ruminally protected methionine product for lactating dairy cows.

In Experiment 1, three ruminally and duodenally cannulated cows were used to assess the extent of ruminal protection and postruminal release of Met from ruminally protected Met using a polyester bag technique. The ruminally protected Met contained 85.1% DL-Met (wt/wt). Ruminal disappearance of Met averaged 5.8, 8.1, 21.8, 37.5, and 87.5% after 3, 6, 12, 24, and 96 h of incubation, respectively. Postruminal disappearance of Met from bags inserted in the duodenum after treatment with pepsin-HCl averaged 63.4, 62.6, 51.6, 43.6, and 8.8% for bags incubated in the rumen for 3, 6, 12, 24, and 96 h, respectively. In Experiment 2, 12 cows were fed either 0 or 20 g/d of ruminally protected Met from 7 to 10 d prepartum until 18 wk postcalving. Cows were fed the same total mixed diet. The DMI; yields of milk, CP, and SNF; and percentages of fat, CP, and SNF in milk were not affected by treatment. However, yields of fat and 3.5% FCM increased when ruminally protected Met was fed. Milk N components were not affected by treatment. Concentrations of Met increased in plasma when ruminally protected Met was fed. The mechanism for the increased production of milk fat and 3.5% FCM when ruminally protected Met was fed is unknown.

Amino Acids↗
PubMed1996

Effects of dietary fat with or without nicotinic acid on nutrient flow to the duodenum of dairy cows.

Four Holstein cows, fitted with ruminal and duodenal cannulas, were utilized in a 4 x 4 Latin square design to investigate the effects of supplementing nicotinic acid to diets that contained 35% alfalfa haylage, 15% corn silage, and either 50% of a low fat concentrate or 10% whole raw soybeans and 40% of a high fat concentrate containing tallow. Treatments in a 2 x 2 arrangement were 1) low fat, no supplemental nicotinic acid; 2) low fat, 12 g/d of nicotinic acid; 3) high fat, no supplemental nicotinic acid; and 4) high fat, 12 g/d of nicotinic acid. The DMI and OM apparently and truly digested in the rumen and apparently digested postruminally were not different among treatments. Addition of fat to the diet decreased the concentration of total VFA in ruminal fluid but did not alter the molar proportions of any of the VFA; supplementation of nicotinic acid tended to decrease the molar proportion of acetate. Amounts of NAN, microbial N, nonammonia nonmicrobial N, and AA that flowed to the duodenum were similar among diets. The concentration of urea N in plasma decreased, and concentrations of cholesterol and triglycerides increased, when cows were fed supplemental fat. Milk composition and production of milk, 4% FCM, and milk components were not altered by addition of fat or nicotinic acid to the diet. Supplementation of fat or nicotinic acid to diets of dairy cows was not beneficial in this experiment.

Animal Nutritional Physiological Phenomena↗
PubMed1996

Response of cows fed a low crude protein diet to ruminally protected methionine and lysine.

Ten cows (mean = 128 DIM) were utilized in a replicated 5 x 5 Latin square design and fed diets formulated to supply adequate (18% CP) or inadequate (14% CP) Met and Lys. A prototype supplement of ruminally protected Met and Lys was added to the 14% CP diet to provide 0, 50, 100, and 150% of the predicted deficiency of Met and Lys. The DMI; yields of milk, 3.5% FCM, total N, protein N, and whey N; plasma concentrations of Arg, Cit, His, Ile, Leu, Orn, Phe, Pro, Tyr, Val, and urea N were greater for cows fed the 18% CP diet. Supplementing ruminally protected Met and Lys to the 14% CP diet did not affect DMI or yields of milk, 3.5% FCM, milk CP, and milk SNF. Milk fat yield was affected quadratically because it was greater when 0 or 150% of the deficiency of Met and Lys was supplied. Percentages of CP and casein N in milk increased linearly as cows were fed increasing amounts of ruminally protected Met and Lys. Plasma concentrations of urea N, Met, and Lys increased when ruminally protected Met and Lys were fed; however, other nutrients probably were limiting for synthesis of milk and milk protein when cows were fed a 14% CP diet because yields of each were not increased by ruminally protected Met and Lys.

Amino Acids↗