Impact of a leptin single nucleotide polymorphism and ractopamine hydrochloride on growth and carcass characteristics in finishing steers.

A total of 2,958 steers (mean initial BW = 549.6 ± 3.88 kg) were used to test for the interactive effects, of leptin R25C genotypes (CC, CT, or TT) and feeding of ractopamine hydrochloride (RH) on growth performance and carcass traits. Before application of the drug, steers were blocked by arrival at the feed yard, genotyped for the leptin SNP, allotted to genotype-specific pens, and assigned randomly within genotype and block to 0 or 28 d of dietary RH. All pens within a block were slaughtered on the same day. Final BW of steers fed RH was 9.1 kg heavier (P < 0.001), and RH-fed steers had greater (P < 0.001) ADG and greater (P = 0.001) HCW than steers not fed RH. Feeding RH did not (P = 0.723) affect DMI but it did increase (P = 0.001) with increased frequency of the T allele (8.62, 8.70, and 8.82 kg/d for CC, CT, and TT, respectively). Consistent with the effect of leptin on DMI, increased frequency of the T allele also positively affected 12th rib fat (P = 0.001) and empty body fat (P = 0.001). Regardless of RH-feeding duration, TT steers produced a greater (P = 0.001) percentage of USDA yield grade (YG) 4 or higher carcasses (6.46 vs. 2.98%) and a lesser (P = 0.023) percentage of YG 1 carcasses (16.0 vs. 21.9%) than CC steers. In addition, RH-fed steers produced a lesser (P = 0.034) percentage of USDA YG 4 or higher carcasses (3.70 vs. 5.31%) and a lesser percentage (P = 0.019) of USDA Choice or higher carcasses (57.5 vs. 62.5%) than steers fed the control diet. Results indicated that leptin R25C genotype impacted most traits associated with fatness, whereas feeding RH for 28 d affected HCW and ADG positively but impacted marbling and USDA quality grades negatively.

Effect of ractopamine HCl supplementation on fecal shedding of Escherichia coli O157:H7 and Salmonella in feedlot cattle.

The effects of the beta-agonist ractopamine, recently approved for use in feedlot cattle to improve carcass quality and performance, on fecal shedding Escherichia coli O157:H7 and Salmonella in feedlot cattle was examined. In the first study, 20 feedlot steers and heifers were randomly assigned to receive ractopamine or no ractopamine (control) by way of oral bolus for 28 days. Fecal samples were collected daily, and shedding of E. coli O157:H7 determined. When examined during the entire 28-day experimental period, ractopamine decreased (P = 0.0006) the percentage of cattle shedding E. coli O157:H7 (58% vs. 42% for control and ractopamine treatments, respectively). A second study was conducted in a commercial feedlot facility in the southwestern United States. Eighteen pens of cross-bred beef heifers (approximately 100 head/pen and 9 pens/treatment) were randomly assigned to receive either 0 (control) or 200 mg ractopamine/head x d(-1). Fresh fecal samples (30/pen) were collected off the pen floor before ractopamine supplementation and again after approximately 28 days of ractopamine supplementation (within a few days of slaughter); the samples were cultured for E. coli O157:H7 and Salmonella. The percentage of animals shedding E. coli O157:H7 was decreased when data were pooled across replicates (P = 0.05) in ractopamine-treated cattle compared with controls. The percentage of animals shedding Salmonella tended to be higher (P = 0.08) with the ractopamine treatment when data were pooled across replicates. Although further research is required to confirm these results, the potential food safety implications of this research are intriguing.

Docosahexaenoic acid restores endothelial function in children with hyperlipidemia: results from the EARLY study.

OBJECTIVE: The primary objective of this study was to determine whether the National Cholesterol Education Program Step II (NCEP-II) diet or supplementation with docosahexaenoic acid (DHA) with the diet, affects endothelial function in children with familial hypercholesterolemia (FH) or the phenotype of familial combined hyperlipidemia (FCH). As secondary endpoints, the influence of diet and DHA supplementation on lipid profiles as well as biomarkers for oxidative stress and inflammation, and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, were all evaluated. METHODS: In a double-blind, placebo-controlled, randomized, crossover study design, 20 children (ages 9-19 years) with FH (n = 12) and FCH (n = 8) received nutritional counseling based on the National Cholesterol Education Program Step II (NCEP-II) and food guide pyramid dietary guidelines for 6 weeks. They were then randomly assigned to supplementation with docosahexaenoic acid (DHA 1.2 g/d) or placebo for 6 weeks, followed by a washout phase of 6 weeks and crossover phase of 6 weeks while continuing the NCEP-II diet. Endothelium-dependent flow-mediated dilation (FMD) of the brachial artery was determined by high-resolution ultrasound. Plasma levels of total cholesterol, triglycerides and lipoprotein classes (LDL, HDL, VLDL) were measured by ultracentrifugation and enzymatic methods, plasma F2 isoprostanes by gas chromatography/mass spectrometry, urinary 8-OH-2' deoxyguanosine by liquid chromatography, high sensitivity C-reactive protein by immunonephelometry and ADMA by liquid chromatography. RESULTS: FMD increased significantly after DHA supplementation compared to baseline (p < 0.001), diet alone (p < 0.002), placebo (p < 0.012) and washout (p < 0.001) phases of the study without affecting biomarkers for oxidative stress, inflammation or ADMA. DHA supplementation was associated with increased levels of total cholesterol (p < 0.01), LDL- and HDL cholesterol concentrations (p < 0.001) compared to the NCEP-II diet. CONCLUSION: This study demonstrates that DHA supplementation restores endothelial-dependent FMD in hyperlipidemic children. The endothelium may thus be a therapeutic target for DHA. This is consistent with a hypothesis of increasing NO bioavailability, with the potential for preventing the progression of early coronary heart disease in high-risk children.

Docosahexaenoic acid is an antihypertensive nutrient that affects aldosterone production in SHR.

The effects of dietary docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, on blood pressure and some pressure-regulating systems were measured in young spontaneously hypertensive rats (SHR). Plasma aldosterone and corticosterone levels, adrenal aldosterone production in vitro, and characteristics of adrenal angiotensin receptors were measured after 6 weeks of diet. Renal cytochrome P450 (CYP) 4A gene expression and arachidonic acid metabolism by renal microsomes were also investigated. Plasma cholesterol, triglycerides, and high-density lipoprotein cholesterol were measured. Diets contained either corn/soybean oil alone (CSO), or oil enriched with DHA. After 6 weeks, rats fed DHA had systolic blood pressures averaging 34 mmHg less than controls (P < 0.001). Plasma aldosterone levels were 33% lower in the DHA-fed animals than in controls (22 +/- 3 vs. 33 +/- 3.7 ng/dl, P < 0.05). Plasma levels of corticosterone were 18% lower in animals fed DHA than in controls, but this difference was not statistically significant. Adrenal glomerulosa cells from DHA-fed rats produced less aldosterone in vitro in response to angiotensin II, ACTH, or potassium. The difference was less marked when aldosterone production was stimulated by supplying exogenous corticosterone, suggesting an effect of DHA on postreceptor steps in signal transduction or the early pathway of aldosteronogenesis. We found no significant differences in angiotensin receptor subtype, number, or affinity. Production of arachidonic epoxides by renal microsomes was 17% lower in DHA-fed animals than in controls (P < 0.05). Renal cortical mRNA levels of CYP4A genes and formation of 19- and 20-hydroxyeicosatetraenoic acid (HETE) did not differ between dietary groups. Plasma total cholesterol and high-density-lipoprotein (HDL) levels were significantly reduced in SHR fed the DHA supplement, but triglyceride levels were not significantly different. The effects of DHA on steroid and eicosanoid metabolism may be part of the mechanism by which this fatty acid prevents some of the hypertension in growing SHR.

The effects of a diet rich in docosahexaenoic acid on organ and vascular fatty acid composition in spontaneously hypertensive rats.

Previous research has shown that dietary docosahexaenoic acid (DHA) attenuates the development of high blood pressure in young spontaneously hypertensive rats (SHR). The purpose of this study was to investigate the effects of dietary DHA on organ and vascular fatty acid composition in SHR. Given the important structural and functional role of fatty acids in cell membranes, alterations in fatty acid composition may contribute to the antihypertensive effect of DHA. SHR were fed a purified diet containing either a corn/soybean oil mixture (CSO, control) or a DHA-enriched oil for 6 weeks. The DHA diet markedly increased the levels of DHA in the aorta, renal artery, plasma, liver, heart, kidney, and lung by 5-, 15-, 7-, 6-, 3.8-, 3.5-, and 8.8-fold (P<0.001), respectively. The levels of eicosapentaenoic acid were also increased while there was a concomitant reduction in arachidonic and adrenic acids. Therefore, dietary DHA increases the incorporation of omega-3 polyunsaturated fatty acids in specific organs and vascular tissue in SHR at the expense of omega-6 polyunsaturated fatty acids.

Dietary borage oil alters plasma, hepatic and vascular tissue fatty acid composition in spontaneously hypertensive rats.

Dietary borage oil rich in gamma-linolenic acid (GLA) has been shown to lower blood pressure in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). A potential mechanism for this effect may be attributed to changes in metabolism of GLA to dihomogamma-linolenic (DGLA) and arachidonic acids (AA). We investigated the effects of dietary borage oil on fatty acid composition in the plasma, liver and vascular tissue in WKY and SHR. The diet significantly increased the levels of omega-6 polyunsaturated fatty acids. GLA and DGLA levels in the plasma, liver, aorta and renal artery tissues increased in SHR (P < 0.001) and WKY (P < 0.001). AA levels were also increased in both plasma and liver of SHR (P < 0.05) and WKY (P < 0.05) fed the borage oil enriched diet. The results demonstrate that dietary borage oil produces marked changes in the metabolism of GLA which may contribute to its blood pressure lowering effect in WKY and SHR.

Vasorelaxant properties of n-3 polyunsaturated fatty acids in aortas from spontaneously hypertensive and normotensive rats.

BACKGROUND: Dietary consumption of fish, rich in n-3 polyunsaturated fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), has been shown to reduce blood pressure in both animal studies and clinical trials. Although the antihypertensive mechanisms are not known, the blood-pressure-lowering effect of n-3 polyunsaturated fatty acids may be partially attributed to their vasorelaxant properties. METHODS: Aortic rings with and without endothelium, from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR), 16-17 weeks old, were suspended in tissue baths and isometric tension was measured. Concentration-response curves were generated for DHA and EPA (1-100 mu mol/l) in norepinephrine-contracted rings. Blood pressure was measured using the tail-cuff method and aortic media thickness was determined. RESULTS: Blood pressure was significantly increased in SHR (n=10; 194 +/- 4.4 mmHg) compared with WKY (n=10; 124 +/- 1.2 mmHg, P < or = 0.0001). DHA (1-100 mu mol/l) relaxed aortic rings f rom WKY (-3.3 +/- 0.7 to -13 +/- 2.3%, P < or = 0.001) and from SHR (-6.5 +/- 1.8 to -22.9 +/- 4%, P < or = 0.01) in a concentration-dependent manner. EPA (1-100 mu mol/l) evoked greater relaxation in SHR (-10.1 +/- 2.0 to -33 +/- 3.9%, P < 0.01) than in WKY (-2.9 +/- 1.1 to -18.3 +/- 2.1%, P < 0.01) aortic rings. The relaxant effect of DHA in both WKY and SHR and of EPA in WKY were not dependent on an intact endothelium. However, EPA (1-10 mu mol/l) induced greater responses in intact SHR rings (-10.1 +/- 2.0 to -14.5 +/- 3.1%) than in de-endothelialized SHR rings (0 to -2.1 +/- 1.7%, P = 0.001). CONCLUSION: The direct relaxant effects of n-3 fatty acids as seen in WKY and SHR may contribute, in part, toward the blood-pressure-lowering effect of dietary fish and fish-oil supplementation.

Vascular effects of omega-3 fatty acids: possible therapeutic mechanisms in cardiovascular disease.

Dietary consumption of omega-3 polyunsaturated fatty acids (PUFAs) found in seafood and fish oils is associated with a decrease in coronary heart disease and overall cardiovascular mortality. Omega-3 PUFAs exert a number of physiologic effects, including relaxation of vascular smooth muscle, lowering of blood pressure, interference in phosphatidylinositol signaling, a reduction in platelet aggregation and growth factors, a decrease in atherogenic lipoproteins, a reduction in thrombotic factors, alterations in eicosanoid metabolism, a decrease in platelet and macrophage activating factors, and an increase in thrombolytic substances. These factors may provide a therapeutic means of reducing cardiovascular disease. This article reviews the vascular effects of omega-3 PUFAs and discusses the hypolipidemic, antihypertensive, antiatherosclerotic, antiinflammatory, and antithrombotic actions of the omega-3 PUFAs. Specific nursing implications are addressed.

Comparative study of diets enriched with evening primrose, black currant, borage or fungal oils on blood pressure and pressor responses in spontaneously hypertensive rats.

The effects of oils enriched with gamma-linolenic acid (GLA) on blood pressure and pressor responses were examined in spontaneously hypertensive rats (SHR). Rats were fed purified diets containing evening primrose (EPO), black currant (BCO), borage (BOR) or fungal (FGO) oils for 7 weeks. Significant reductions in blood pressure were obtained in SHR rats maintained on diets enriched with GLA oils. The antihypertensive effect was not associated with enhanced pressor responsiveness to norepinephrine or angiotensin II. Moreover, no differences were found in blood pressure responses to the calcium channel blocker, verapamil. The results suggest that GLA-enriched oils inhibit the development of hypertension in the SHR rat. The blood pressure lowering effect is not mediated by altered pressor responses to vasoconstrictor hormones or intracellular calcium mechanisms.

Dietary gamma-linolenic acid lowers blood pressure and alters aortic reactivity and cholesterol metabolism in hypertension.

OBJECTIVE: To determine the effects of dietary gamma-linolenic acid upon blood pressure, aortic reactivity and cholesterol metabolism in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. DESIGN: Randomized parallel-group study. METHODS: SHR and WKY rats were fed a purified diet containing either sesame or borage oil rich in gamma-linolenic acid for 7 weeks. Blood pressure measured by the tail-cuff method and weight were monitored weekly. At the end of the study, intra-arterial pressor responses to norepinephrine and angiotensin II, and reactivity of isolated aortic rings to norepinephrine, angiotensin II, KCl and acetylcholine were determined. Serum cholesterol and triglycerides were measured. Hepatic and intestinal enzymes and receptors of cholesterol metabolism were also measured. RESULTS: Dietary borage oil significantly decreased blood pressure in SHR and WKY rats compared with sesame oil-fed rats. Pressor responses to norepinephrine and angiotensin II, and aortic reactivity to norepinephrine, angiotensin II, KCl and acetylcholine were not significantly different. The borage oil diet increased serum cholesterol levels in WKY rats and hepatic B-hydroxy-3-methylglutaryl coenzyme A reductase in SHR. CONCLUSION: These data indicate that dietary borage oil has a blood pressure lowering effect in hypertensive and normotensive rats. However, the effect cannot be explained by altered sensitivity to humoral and neural vasoconstrictors or changes in cholesterol metabolism. Other mechanisms should be investigated.

Ethanol inhalation and dietary n-6, n-3, and n-9 fatty acids in the rat: effect on platelet and aortic fatty acid composition.

The effects of 18-carbon n-6, n-3, and n-9 fatty acid diets and ethanol exposure on the fatty acyl composition of platelets and vascular tissue were examined. An experimental design was devised to control the dietary content of 18-carbon fatty acids. The levels of 18:3n6, 18:3n3 and 18:1n9 were varied by a formulation of dietary oils which contained similar proportions of 18:2n6. Male Sprague-Dawley rats were fed a purified diet containing 11% by weight of either borage oil (BOR) rich in 18:3n6, linseed/safflower oil (LSO) rich in 18:3n3, or sesame oil (SES) rich in 18:1n9 for 7 weeks and exposed to ethanol vapors by means of inhalation for the final 6 days of the dietary regimen. Moderate blood ethanol levels of 118 +/- 6.6 mg/dl were obtained. Total lipids were extracted from platelets and aortae, and the fatty acid distributions were analyzed by gas chromatography. BOR feeding resulted in increases in the proportion of n-6 fatty acids (18:3n6, 20:3n6, 20:4n6) in platelets and aorta. Animals fed the LSO diet had increased levels of n-3 fatty acids (18:3n3, 20:5n3, 22:6n3). The SES-based diet resulted in an increase in 18:1n9 in both aorta and platelets. Following ethanol exposure alone, the most marked change in the fatty acid profile was a decrease in 20:4n6 in the platelet. This effect was not observed in rats supplemented with BOR. No significant changes were observed in the aortic fatty acid content at this level of ethanol exposure. The results suggested that, in the rat, a diet enriched with BOR effectively prevented ethanol-induced alterations in platelet fatty acid composition.

Docosahexaenoic acid (22:6n3)-induced relaxation of the rat aorta.

Dietary consumption of fish and fish oil supplements, containing eicosapentaenoic acid and docosahexaenoic acid, has been associated with favorable alterations in the cardiovascular system, such as, a reduction in blood pressure. Therefore, the effects of docosahexaenoic acid (22:6n3) on isometric tension of rat aortic smooth muscle were investigated. A concentration-dependent (1-127 microM) relaxation (6-30%) was induced by 22:6n3 in non-precontracted vessels. Docosaehexaenoic acid, concentration dependently (1-44 microM) reversed contractions of rat aortic rings induced by phenylephrine (7-43%) and by U44069 (8-52%). These results indicate that the relaxant effects produced by 22:6n3 in the rat aorta are concentration-dependent and not specific to the contractile agonist.

Automated temperature scanning for hyperthermia treatment monitoring.

Ideal descriptors of hyperthermia treatments will most likely depend on complete target temperature distributions. Although these distributions can be modeled numerically, the accuracy of models is limited by the sparseness of temperatures measured in vivo. Thus, the strategy of monitoring temperatures may play a key role in improving hyperthermia therapy. Scanning temperatures by manual translations of thermometers was found to be excessively time consuming. Consequently an automated system was developed consisting of linear actuators, outriggers, guide tubes, thermometry catheters, personal computer, and dedicated hardware and software. During treatments, scan patterns were created with algorithms using temperatures measured preceding each thermometer translation. Measurement position had a noteworthy influence on thermal dose estimated by current models. Relative to manual scanning, automated scanning increased measurement efficiency, reduced probe position uncertainty, reduced operator time, and provided improved data for modeling bioheat transfer and thermal dose.

Clinical application of thermal isoeffect dose.

Clinically, there is strong rationale for developing a method which will provide a scientific basis for comparing the efficacy of one hyperthermia treatment with another. In order to accomplish this goal, methods must first be developed which will allow the clinician to know the three-dimensional temperature distribution in heated tissue. In this paper, examples of how this goal can be achieved are presented. Techniques for compensating for various modifiers of hyperthermia effectiveness are proposed. The limitations and advantages of these approaches are described and directions for future research are discussed.