Two-thirds of the iron normally present in the body is in hemoglobin. Hemoglobin turnover is generally accepted to be much greater than turnover of iron in storage depots, in which nearly all of the remaining iron is found. For these reasons it was anticipated that hemoglobin synthesis might be measured directly by means of radioactive iron. The pioneering work of Huff and Elmlinger and their associates (1)(2)(3) proposed that hemoglobin synthesis could be determined from the product of the rate of removal of iron from plasma (plasma iron turnover, milligrams per day) and the fraction of radioactive iron incorporated into circulating erythrocytes. Further studies by Huff and others (4-16), however, revealed that hemoglobin synthesis calculated in this way was consistently greater than would be expected from relating circulating hemoglobin to well established data concerning the life span of erythrocytes. Plasma iron turnover data yielded daily hemoglobin synthesis rates of 1.2 to 2.0 per cent of circulating hemoglobin as contrasted with expected rates of 0.75 to 1.00 per cent corresponding to an erythrocyte life span range of 100 to 130 days (17-20).Although plasma iron turnover can be used for relative comparisons of erythropoiesis under certain circumstances, it is apparent that plasma iron turnover must be analyzed into its component parts before it can be used for quantitative determination of hemoglobin synthesis. This study was undertaken in an attempt to quantitate hemoglobin synthesis. For this purpose, mathematical models were developed that are compatible with experimental data obtained from over 400 subjects. Sequential measurements of radioiron were made in plasma, red cells, and at the body surface (21,22). Data obtained from 13 normal subjects and 6 pa-
Crossbred, multiparous beef cows (n = 178 in Year 1; n = 148 in Year 2) were used to evaluate the effects of Cu, Zn, and Mn supplementation and source on reproduction, mineral status, and performance in grazing cattle in eastern Colorado over a 2-yr period. Cows were stratified by expected calving date, age, BW, BCS, and liver mineral status and assigned to the following treatments: 1) control (no supplemental Cu, Zn, or Mn); 2) organic (ORG; 50% organic and 50% inorganic Cu, Zn, and Mn); and 3) inorganic (ING; 100% inorganic CuSO4, ZnSO4, and MnSO4). Free-choice mineral feeders were used to provide current NRC-recommended concentrations of Cu, Zn, and Mn from 82 d (Year 1) and 81 d (Year 2) before the average calving date of the herd through 110 d (Year 1) and 135 d (Year 2) after calving. At the end of Year 1, supplemented cows had greater liver Cu (P < 0.01), Zn (P < 0.05), and Mn (P < 0.01) concentrations compared with controls, whereas liver Cu concentration was greater (P < 0.01) in ORG vs. ING cows. At the end of Year 2, supplemented cows had greater (P < 0.01) liver Cu concentrations relative to controls, whereas control cows had greater (P < 0.02) liver Mn concentration than did supplemented cows. In Year 1, pregnancy rate to AI in control cows did not differ (P = 0.47) from supplemented cows, but there was a trend (P < 0.08) for pregnancy rate to be higher for ORG than ING cows. In Year 2, supplemented cows had a higher (P < 0.02) pregnancy rate to AI than controls. In both years, when cows were inseminated after an observed estrus, supplemented cows had a higher (P < 0.04) pregnancy rate than did controls. Also, for both years, overall 60-d pregnancy rate tended (P = 0.10) to be higher for supplemented cows than for controls. In Year 1, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and kilograms of calf weaned per cow exposed was greater (P < 0.01) in ING than ORG treatments. However, in Year 2, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and tended (P = 0.09) to be greater in ORG than ING treatments. Results indicate that supplementation and source of trace minerals affected mineral status and kilograms of calf weaned per cow exposed in grazing beef cows. Supplementation also improved pregnancy rate to AI compared with cows not supplemented with Cu, Zn, or Mn for more than 1 yr. Furthermore, mineral source may influence pregnancy rate to AI.
The elementary transition state approach has been used to obtain a simple model theory for the Soret effect (thermal diffusion) and the Dufour effect. The flow of heat in the Dufour effect is identified as the transport of the enthalpy change of activation as molecules diffuse. The theory as now formulated applies only to thermodynamically ideal mixtures of substances with molecules of nearly equal size. The results of the theory conform to the Onsager reciprocal relationship. When the results were fit to data on thermal diffusion for two liquid systems, a close fit was obtained and yielded reasonable values of between 2 and 3 kcal mol-I for enthalpy changes of activation and differences between the entropy changes of activation for the two components of between 0 and 1 cal K-1 mol'-.Assume that midway between site a and site b there is a position of high potential energy through which a molecule must pass in jumping from site a to site b or vice versa. The temperature at this position is denoted by Tm, and we can write Xm -Xa = Xb -Xm = X/2.[2]In the elementary transition state theory of isothermal diffusion, the probability per unit time that a molecule of component i makes a transition from one equilibrium site to the next is given by kBT pi= y( -jr exp(-AGi/RT) (i = 1, 2) [3] The Soret effect (thermal diffusion) is the occurrence of a diffusion flux due to a temperature gradient. The Dufour effect is the reciprocal phenomenon, the occurrence of a heat flux due to a chemical potential gradient. Both effects have been extensively studied in gases, and the Soret effect has been studied both theoretically and experimentally in liquids. However, partly because of the smallness of the effect, accurate measurements of the Dufour effect in liquids have only recently been carried out (1). There does not seem to be a model theory of the liquid-state Dufour effect in the literature. This paper presents a simple model theory for both effects in liquids, based on elementary transition state theory. The liquid is represented by a somewhat disordered quasi-lattice model in which a molecule can move from one equilibrium position to another, passing through a transition state of high potential energy. This beginning point has been used in previous theories of the Soret effect (2, 3). The Soret effect Consider a liquid two-component mixture that is uniform in the y and z directions but has a temperature and composition that depend on x and t, the time. Denote two adjacent equilibrium molecular positions by a and b, and assume that the two components are similar enough that these positions can be occupied by molecules of component 1 or component 2. Let xa be the value of the x coordinate at site a and Xb (presumed larger than Xa) be the value of x at site b. Let the jump distance, X, be given by X = Xb -Xa [1] and assume that this distance is equal for all pairs of adjacent sites. The temperature at xa is denoted by Ta, and the concentration of component 1 at xa is denoted by cla, with similar definitions for Tb, C2a, ...
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