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Two experiments were conducted to evaluate factors influencing the release rate of octacosane (C28) and dotriacontane (C32) synthetic alkanes from controlled-release devices (CRD) inserted into the rumen of sheep, and the resultant accuracy of alkane-based estimates of herbage intake. In the first experiment, estimates of the rate of release of alkanes from CRD suspended in the rumen of 7 rumen-fistulated ewes were obtained by directly measuring the rate of CRD plunger travel. In the second experiment, CRD were administered orally to 24 castrate male sheep to evaluate the effects of level of feeding (1200 v. 600 g DM/day), frequency of feeding (continuous v. once-daily), and number of CRD inserted (1 v. 2) on temporal trends in faecal alkane concentrations and ratios and on the accuracy of estimation of intake. In both experiments, animals were also dosed orally, once daily with paper pellets containing 56 mg hexatriacontane (C36). In Expt 1, linear alkane release from the CRD commenced after a lag period of 2-3 days, at mean rates of 40.1 mg/day (C28) and 41.7 mg/day (C32), close to the desired rates of 40 mg/day. There was no evidence of curvilinearity, and differences in release rate between sheep were small (CV 4.1%). Alkanes attributable to the CRD appeared in faeces after 2-3 days and reached plateau concentrations by 6-7 days. Data are presented to indicate that the release rate was not affected by the removal of CRD from the rumen for measurement, and that the release rates in fistulated (Expt 1) and intact sheep (Expt 2) were similar. In Expt 2, there was no effect of level of feeding on CRD release rates and faecal alkane concentrations were consistent with the differences in faecal output caused by feeding level. As a result, the accuracy with which known intakes were estimated was unaffected by level of feeding. Similarly, there were no effects of feeding frequency on the accuracy of estimated intake, implying that in this study, feeding frequency had no effect on CRD release rates. The administration of 2 CRD to half the animals in this experiment increased faecal concentrations of C28 and C32 and the synthetic : herbage alkane ratios associated with these alkanes [e.g. faecal C32 : tritriacontane (C33)] but these changes were not significantly different from those expected from the release rates estimated in Expt 1. As a result, the accuracy with which known intakes were estimated was not influenced by the number of CRD administered. In both experiments, once-daily dosing with C36 alkane resulted in a more rapid rise in faecal C36 concentrations and faecal C36 : pentatriacontane (C35) ratios to maximal levels (3-4 days), compared with alkanes derived from the CRD (6-7 days), but thereafter, faecal C36 concentrations were much more variable, especially in the fistulated sheep. As a result, intake estimates based on the C36 : C35 alkane pair significantly over-estimated known intakes by 13% (Expt 1) and 8% (Expt 2). Data are presented to indicate that C36 alkane functioned satisfactorily as a faecal output marker and, with C32 : C33 estimates of intake, provided accurate estimates of herbage digestibility. The results indicate that intra-ruminal controlled-release devices provide a satisfactory means of delivering an accurate, daily dose of alkanes for the estimation of herbage intake, faecal output, and digestibility in sheep.

There is a paucity of data on the chemical composition of the humanbody during growth. Total body calcium (TBCa) has been reported for only onemale child, aged 41/2 yr. We have obtained TBCa values for 25 children and27 young women using in vivo neutron activation analysis. Our TBCa resultswere lower than those reported for the one male cadaver, as well as the estimatesderived for the “Reference Man” model. We conclude that the referencevalues for TBCa may need to be adjusted to appropriately describe skeletalmineralization of contemporary children.

We have designed a Web site intended to inform the general public aboutexisting nuclear technologies based on the measurement of radioisotopes inthe human body. The presentation is focused on the concept of radioisotopemeasurements for determination of body composition (bone, muscle, water, fat),and the risks, benefits, and clinical applications of these techniques. Procedurescovered are 40K whole body counting, delayed-gamma neutron activation,prompt-gamma neutron activation, and dual-energy X-ray absorptiometry. Theinformation presented is tailored for the nonscientific public, in order topromote familiarity with and understanding of the basic concepts of radioisotopemeasurements in the human body. Further development of the site will includegreater scientific detail, suitable for student instruction or for continuingeducation requirements of various certification programs.

Prompt-gamma neutron activation (PGNA) is used to measure total-bodynitrogen and hydrogen in humans. Background interference in the gamma spectraarises from both subject and shielding. A Monte Carlo simulation program (MCNP4B2)was used to examine the neutron and gamma signals in the PGNA system ( 241AmBe source). N and H peak regions were assessed in the presenceand absence of calibration phantoms. The simulations suggested extracorporealH peak contributions of up to 30%, depending on subject body habitus. MostN background could be attributed to detector pileup events. The MCNP resultsallowed us to improve shielding design and develop background correction algorithmsto improve measurement precision.

The body composition of 23 infants was examined at postmortem. All infants were live births and lived from 1 to 192 days. Their body weights at birth ranged from 480 to 3280 g; gestational ages ranged from 24 to 42 weeks. Total body composition was determined using the nondestructive in-situ procedures of 40K counting and neutron activation analysis. The absolute amounts of K, Ca, P, Na, and Cl were measured. Although body Cl was in general agreement with estimates for the reference fetus model, body K and Na values were lower. Body Ca content was higher than the reference fetus at body weights above 2 kg, yet body P levels agreed with the reference fetus. Furthermore, those infants whose survival was brief had reduced body K, an index of body cell mass. All elements except body Cl were linearly related to fat-free mass (FFM). The correlations with gestational age were non-significant when the variation in elemental content was accounted for by FFM or body weight. The two preterm infants who survived for more than 10 weeks had significantly reduced bone growth as shown by their Ca and P deficiences.

In many problems of data analysis it is necessary to fit the data to a mathematical equation. Random errors of measurement will be responsible for deviations between the data and the equation, but superimposed on this there may be deviations that result from the equation being an inadequate description of the system from which the data were obtained. Plots of the residual (i.e. the difference between the experimental and calculated values of the dependent variable) against each of the experimental variables have been previously used to detect a misfit between the data and the equation. In the present paper, we show that the shape of the residual plots may be used as a guide in choosing a more appropriate equation. In addition, residual plots give useful information on the error structure of the data, and hence the weighting factors that should be used in the analysis.

The carboxylic acid ionization constants of mercaptoacetic acid (MAA), 2-mercaptopropionic acid (2-MPA), 2-mercaptoisobutyric acid (2-MIBA) and 2-mercaptosuccinic acid (2-MSA) have been measured in perchlorate media at an ionic strength of 1.0M and over the temperature range 273–309°K. Appropriate thermodynamic quantities have been derived. The variation in the temperature T? at which the constants exhibit a maximum has been interpreted in terms of the effect of hydrophobic substituents on the extent of solvation of the participating species.

1. Young, sub-totally nephrectomized rats were used to study the altered mineral metabolism of renal failure and its effects on bone growth and mineral maturation. 2. Rats killed at 4 weeks after sub-total nephrectomy demonstrated less bone growth than the age-matched control animals. These differences diminished in successive 4 week periods and were not significant at 12 weeks after operation. 3. The major differences in bone mineral composition between the uraemic rats and the control rats were: (i) lower CO23;- concentrations, and (ii) higher PO34;- and HPO24;- concentrations. 4. These differences are consistent with the view that bone mineral matures by the conversion of an acidic calcium phosphate precursor into a carbonate-containing apatite, an essential feature of this conversion being the replacement of PO34;- or HPO24;- by CO23;-. By this definition, uraemic rats at 4 weeks after operation contained more immature bone mineral than the control rats. These differences corresponded to the changes in bone weight, and were similarly unaffected at 12 weeks after operation. 5. The effects observed were transient and were reversed as renal function recovered. If renal failure is sustained, however, as in patients with end-stage renal disease, the maturation defect could become a feature of renal bone disease. Specific aetiological factors are discussed, but not identified.

Twenty-six 3-week-old genetically obese pigs were fed in two experiments to determine the serum chemistry profile during severe protein malnutrition and repletion. Severe protein deficiency was produced in pigs fed the high-fat, low-protein diet (growth failure, rough hair, low serum total protein and albumin). In Experiment 1, blood was sampled from the anterior vena cava of each pig five times during depletion and three times during repletion to determine serum total cholesterol, high density lipoprotein (HDL)-cholesterol, triglycerides, total protein, albumin, glucose, Ca, inorganic P, Mg, Na, K, CI, total bilirubin, urea N, creatinine, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, and γ-glutamyltransferase. In Experiment 2, blood was sampled weekly for 8 weeks for serum total cholesterol, HDL-cholesterol, triglycerides, albumin, glucose, Ca, P, Mg and alkaline phosphatase. HDL-cholesterol was increased (P< 0.01) and albumin was decreased (P< 0.01) in protein-deficient pigs in both experiments. Creatinine, total bilirubin, γ-glutamyltransferase, alanine aminotransferase, and aspartate aminotransferase were elevated in protein-deficient pigs compared with controls after 7 weeks of depletion. Inorganic P (P< 0.01), Ca (P< 0.01), and Mg (P< 0.05) concentrations were depressed in protein-depleted pigs compared with controls in both experiments. After 8 weeks of repletion in Experiment 1, all elements except inorganic P were similar in the two groups. Short-term, severe, protein malnutrition affected lipid, electrolyte, and structural mineral metabolism and indices of liver function in the absence of parasites, diarrhea, and infection. The effects were reversed after 8 weeks of repletion. We conclude that the elevated serum cholesterol in protein deficiency is related primarily to an increase in the HDL fraction.