Mammary blood flow and metabolic activity are linked by a feedback mechanism involving nitric oxide synthesis

To test which, if any, of the major milk precursors can elicit a rapid change in the rate of mammary blood flow (MBF) and to define the time course and magnitude of such changes, 4 lactating cows were infused with glucose, amino acids, or triacylglycerol into the external iliac artery feeding one udder half while iliac plasma flow (IPF) was monitored continuously by dye dilution. Adenosine and saline were infused as positive and negative controls, respectively, and insulin was infused to characterize the response to a centrally produced anabolic hormone. To test the roles of cyclooxygenase, NO synthase and ATP-sensitive K (K) channels in nutrient-mediated changes in blood flow, their respective inhibitors-indomethacin, N-nitro-L-arginine methyl ester hydrochloride (L-NAME), and glibenclamide-were infused simultaneously with glucose. Each day, 1 infusate was given twice to each cow, over a 20-min period each time, separated by a 20-min washout period. In addition, each treatment protocol was administered on 2 separate days. A 73% increase in IPF during adenosine infusion showed that the mammary vasodilatory response was quadratic in time, with most changes occurring in the first 5min. Glucose infusion decreased IPF by 9% in a quadratic manner, most rapidly in the first 5min, indicating that a feedback mechanism of local blood flow control, likely through adenosine release, was operative in the mammary vasculature. Amino acid infusion increased IPF 9% in a linear manner, suggesting that mammary ATP utilization was stimulated more than ATP production. This could reflect a stimulation of protein synthesis. Triacylglycerol only tended to decrease IPF and insulin did not affect IPF. A lack of IPF response to glibenclamide indicates that K channels are not involved in MBF regulation. Indomethacin and L-NAME both depressed IPF. In the presence of indomethacin, glucose infusion caused a quadratic 9% increase in IPF. Indomethacin is an inhibitor of mitochondrial function, so the glucose-induced increase in IPF was interpreted as feedback on mammary adenosine release from an anabolic response to glucose. Because NO synthase was not inhibited during indomethacin infusion, the feedback system is postulated to act through endothelial NO synthase. In the presence of L-NAME, glucose infusion had no effect on IPF, indicating that endothelial cyclooxygenase is not involved in glucose-induced changes in MBF

Composition and structure of the RuO2(110) surface in an O2 and CO environment: implications for the catalytic formation of CO2

The phase diagram of surface structures for the model catalyst RuO2(110) in contact with a gas environment of O2 and CO is calculated by density-functional theory and atomistic thermodynamics. Adsorption of the reactants is found to depend crucially on temperature and partial pressures in the gas phase. Assuming that a catalyst surface under steady-state operation conditions is close to a constrained thermodynamic equilibrium, we are able to rationalize a number of experimental findings on the CO oxidation over RuO2(110). We also calculated reaction pathways and energy barriers. Based on the various results the importance of phase coexistence conditions is emphasized as these will lead to an enhanced dynamics at the catalyst surface. Such conditions may actuate an additional, kinetically controlled reaction mechanism on RuO2(110).Comment: 12 pages including 8 figure files. Submitted to Phys. Rev. B. Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Behavioral and physiological responses to an inspired-air supplemental cooling system for dairy cows in free-stall housing

During heat stress, dairy cows spend less time lying down to dissipate heat. Heat stress abatement strategies generally target cows outside of their resting areas. However, cooling cows while in their stalls could help alleviate heat stress without compromising lying behavior. The objective of this study was to assess the effects of an inspired-air supplemental cooling system (SCS) on respiration rate, rectal temperatures, lying behavior, rumination time, and milk production (energy-corrected milk, ECM) of lactating dairy cows. A free-stall pen was retrofitted with custom stall partitions to deliver cooled air and mist. The pen, including the stall platform, was divided into two separate sides. Twenty-eight lactating Holstein cows were randomly sorted into two groups, each housed on one side of the experimental pen. Cows experienced four treatments (control, CTRL; cooled air, AIR; mist, MIST; cooled air and mist, AIR + MIST) in a four-treatment, four-period, two-sequence crossover design, with each period lasting seven days. Cooled air was provided continuously, and mist was cycled 3 min on, 12 min off from 0900 to 2100 h. Respiration rates were observed hourly between 0900 and 1500 h, and only measurements recorded while cows were lying down were used in the analysis. Rectal temperatures of 16 focal cows were recorded at 1545 h once per day. Lying behavior and rumination were recorded continuously, and milk yields recorded twice daily were used to calculate ECM. Throughout the experimental period, the average temperature-humidity index was 66.4 ± 6.07. During the MIST treatment, the respiration rate was lower than the CTRL (45.7 vs 49.0 ± 1.92 breaths/min) and AIR (45.7 vs 48.7 ± 1.92 breaths/min). CTRL and AIR did not differ (48.7 vs 49.0 ± 1.92 breaths/min), and MIST and AIR + MIST (45.7 vs 47.1 ± 1.92 breaths/min) did not differ. All other variables were not significantly different between treatments. In conclusion, the SCS appeared to be tolerated by cows and shows the potential to assist in alleviating heat stress. The cooling capacity needs to be evaluated under more extreme environmental conditions causing heat stress than those experienced during this study. Further testing is required to determine the cooled air temperature specifications and mist delivery frequency

Milk Synthetic Response of the Bovine Mammary Gland to an increase in the Local Concentratioin of Amino Acids and Acetate

Rates of secretion of components into milk are a function of precursor concentrations and parameters that describe expression of the milk synthetic enzymes and their sensitivity to precursor concentrations. To establish the enzymatic sensitivities of milk fat yield and mammary acetate utilization to circulating acetate concentration, lactating cows were infused for 10 h with 0 or 40 g of acetate/h in an external iliac artery supplying one udder half. In addition, to investigate the possibility that energy supply influences the milk protein response to an elevated amino acid (AA) concentration, 2 different AA profiles were infused with and without acetate. Six cows, fed a total mixed ration of 21% crude protein ad libitum, were infused with AA at 0 g/h, 30 g/h in the profile of rumen microbes, or 30 g/h in the profile of milk proteins, in a 3 × 2 factorial arrangement with the 2 acetate treatments of 0 and 40 g/h, all in a 6 × 6 Latin square. Amino acid infusion caused a 60% increase, on average, in plasma concentration of AA entering the infused udder half. From the microbial AA profile, 49% of infused AA were taken up by the udder half, 42% of which occurred during the first pass. From the milk AA profile, 44% of infused AA were taken up by the udder half, 50% of which occurred during the first pass. There was an 8% increase in yield of milk protein with AA infusion, representing 7% capture, but no effect of the infused profile. Acetate infusion caused a decrease in the yields of milk protein and lactose when AA were infused, but not when AA were absent. Milk fat yields were not affected, although acetate concentrations in plasma entering the infused udder half increased by 123% and mammary uptakes increased by 128%. Mammary uptakes of long-chain fatty acids and β-hydroxybutyrate were not affected by acetate infusion, whereas glucose uptakes tended to increase. It was suggested that excess acetate may have been sequestered in adipose tissue in the udder. Yields of both protein and fat in milk showed a low sensitivity to the concentration of their precursors in circulation. It was concluded that the Km in Michaelis-Menten-type equations describing milk synthesis should be assigned a low value, and that the Vmax is regulated to bring about changes in milk yield and composition