A two-way scanning method for total body in vivo neutron activation analysis

When determining the total body content of many elements by neutron activation analysis, irradiation and whole body counting by scanning along the length of the body has significant advantages. A neutron source of lower output and a whole body counter using smaller detectors and shielding (than otherwise needed) can provide a high, uniform response for many elements throughout the body. This was previously achieved by making the speed and direction of scanning identical in irradiation and counting (one-way scanning). A simple theoretical model for scanned irradiation and counting is described. The model is used to show that a scanning regime in which both scanning directions are used (two-way scanning) can provide acceptably uniform response for elements having induced activities of a wide range of half-life. This is supported by measurements made using an existing scanning facility for total body in vivo neutron activation analysis. The two-way scanning regime offers the advantages of increased patient comfort, simpler operation and more efficient use of the time available for counting induced activity.

The relationship between uric acid and potassium in normal subjects

The serum uric acid concentration in normal healthy subjects has been studied in relation to sex, height, weight, lean body mass measured from total body potassium and predicted from the Hume-Weyers formula (1971), total body potassium, plasma potassium and urea, and packed cell volume. The strongest correlation was found with sex, but height, weight, total body potassium, lean body mass (measured and predicted) also correlated significantly with serum uric acid concentration. However, when the sex variable was removed, the other factors lost their significant correlation. Finally, total red blood cell and plasma volumes were predicted (Hume and Goldberg, 1964) and from these an estimate of total plasma uric acid, total plasma potassium, and total red blood cell potassium obtained. Measured total body potassium was found to correlate well with total plasma potassium and total red blood cell potassium independent of sex. Total plasma uric acid correlated well with measured total body potassium when both sexes were considered and when separated into male and female groups the males retained a significant correlation as did the female group.

Calibration and evaluation of a system of total body in vivo activation analysis using 14 MeV neutrons

A system has been established for determining the total body contents of calcium, phosphorus, sodium, chlorine and nitrogen by neutron activation analysis using sealed-tube neutron generators and a shadow-shield whole-body counter. The system was calibrated using three anthropomorphic phantoms of different sizes, filled with various mixtures of the activatable elements in amounts similar to those in man. The reproducibility determined from replicate measurements, was on average +/- 2.9% (SD). The average uncertainty in absolute measurements was estimated to be +/- 4.2% (68% confidence interval).

Magnesium metabolism in patients with coronary heart disease

1. The oral absorption of magnesium, its myocardial uptake and exchangeable magnesium have been studied in patients with coronary heart disease and controls using the radioactive isotope magnesium-28. 2. No significant difference in oral absorption or myocardial uptake was found between patients and controls. 3. The exchangeable magnesium per kg body weight was significantly lower in the patients than in the controls.

Neutron uniformity studies related to clinical total body in vivo neutron activation analysis

Methods of assessing the uniformity of thermal and fast neutron fluence in relation to total body in vivo neutron activation analysis are described. Results are presented for 14 MeV neutrons emitted by sealed tube generators housed in a massive concrete shield, representing a substantial source of neutrons degraded in energy. Optimisation of conditions for patient irradiations is discussed and it is shown that acceptable uniformity of fluence can be achieved with little or no premoderation of the incident neutrons.

Concurrent estimation of total body and exchangeable body sodium in hypertension

1. Total-body neutron-activation analysis in vivo was carried out in 11 hypertensive subjects to measure simultaneously the total body content of sodium, chlorine, calcium, phosphorus and nitrogen. 2. There was a highly significant correlation between total body sodium measured by activation analysis and total exchangeable sodium measured by a standard isotope-dilution technique (r = 0.92, P less than 0.001). Exchangeable sodium averaged 80.3% of total body sodium. 3. The measured values of chlorine, calcium, phosphorus and nitrogen were similar to those for healthy subjects reported by others. 4. Activation analysis in vivo appears promising as an additional tool for investigating sodium metabolism in hypertension, as it is the only method available for determining the total body content of this element. The radiation dose (1 rem) is sufficiently low to permit repeated measurements in the same subject.

Total body and exchangeable potassium in chronic airways obstruction: a controversial area?

Potassium deficiency is an important complication in the treatment of heart disease. However, there is a serious dichotomy in the literature. Severe potassium depletion has been reported in this condition when exchangeable potassium was measured whereas normal levels or marginal depletion were found in measurements of total body potassium. To clarify this situation, simultaneous measurements of total body potassium by whole-body counting, and of exchangeable potassium by isotope dilution using 43K, were made in 10 male subjects with established airways obstruction. Sequential determinations showed that exchangeable potassium increased up to 68 hours after administration, and values obtained at only 24 hours would have been a substantial underestimate. In this group of subjects neither total body nor exchangeable potassium at 48 hours was significantly different from the expected normal value.

Amiloride in the treatment of primary hyperaldosteronism and essential hypertension

Amiloride (40 mg/day) was given to nineteen patients with primary hyperaldosteronism. There were significant falls in systolic and diastolic blood pressure, in total exchangeable sodium, and in serum sodium sodium and bicarbonate; while total exchangeable potassium, total body potassium, serum potassium, chloride and urea, and plasma renin, angiotensin II and aldosterone all increased significantly. Amiloride was effective in reducing blood pressure in patients with and without adrenocortical adenoma. No carry-over effect was seen on withdrawing amiloride. Similar changes were associated with amiloride treatment in five patients with essential hypertension; hyperkalaemia was not observed. Only negligible side-effects were encountered in the entire series of twenty-four patients.

Changes in the concentration of adrenocorticotrophin and corticosteroid in the plasma of foetal sheep in the latter half of pregnancy and during labour

The changes in plasma ACTH concentration of pregnant sheep and their foetuses during the latter half of pregnancy and during labour were studied. Before 140 days of gestation the mean concentration in foetal arterial plasma was 117+/-19 (S.E.M.) pg/ml which rose to a mean of 286+/-63 pg/ml. The rise in ACTH occurred at about the same time as, but not before, the rise in corticosteroid concentration in foetal plasma. The maternal plasma ACTH concentration did not change during the latter half of pregnancy and had a mean concentration of 64+/-9 pg/ml. During labour there was a progressive rise in the ACTH concentration in foetal plasma which was not associated with any corticosteroid changes. Ethanol did not suppress labour but reduced the ACTH concentration in foetal plasma.

Developmental changes in the responses of the adrenal glands of foetal sheep to endogenous adrenocorticotrophin, as indicated by hormone responses to hypoxaemia

The change in plasma ACTH and corticosteroid concentrations in response to a 60 min period of hypoxaemia were studied in foetal and adult sheep during the latter half of pregnancy. Hypoxaemia consistently caused large rises in the concentration of ACTH in foetal plasma, the magnitude of which did not change with gestational age but was related to the physiological state of the foetus. Before 139 days small and slow rises in corticosteroid (predominantly cortisol) concentration in foetal plasma were observed during hypoxaemia, and these may have been of maternal origin. After 139 days, hypoxaemia caused a rapid and large rise in the concentration of cortisol and corticosterone in foetal plasma, which was largely of foetal origin. Hypoxaemia caused no consistent change in maternal plasma ACTH concentration but was associated with progressive increases in plasma cortisol concentrations. The cortisol: corticosterone ratio in foetal plasma was 1-5 before 139 days and increased to 4-1 several days before term which was lower than the value of 9 in maternal plasma. Small concentrations of 11-deoxycortisol and cortisone were detected in maternal and foetal plasma, the changes of which were small during hypoxaemia. The results indicate that a maturational change in the sensitivity of the foetal adrenal to endogenous ACTH occurs several days before term.

Total body potassium in cor pulmonale

Total body potassium was measured in 12 patients with cor pulmonale, by determination of potassium-40, a naturally occurring radioisotope. In all subjects the observed value of total body potassium showed no significant depletion when compared with that predicted from height and age. All previous studies in similar groups of patients have been confined to the estimation of exchangeable potassium by the technique of isotope dilution. Results using the latter technique have shown gross potassium depletion. It is suggested that the apparent disparity between total body potassium and exchangeable potassium could be explained by the requirement for a longer equilibration period when using isotope dilution techniques in patients who are in chronic hypoxaemic state.

A study of changes in whole-body calcium, phosphorus, sodium and nitrogen by neutron activation analysis in vivo in rats on a calcium-deficient diet

1. A method of measuring changes in the total body content of calcium, phosphorus, nitrogen and sodium in rats by activation analysis in vivo is described. 2. The change in the body content of the elements has been measured in rats on a calcium-deficient diet and in control animals, the body nitrogen being used to represent lean body mass for normalization. 3. There were siginificant differences in Ca/N and P/N but not in Ca/P ratios between the animals on a deficient diet and control animals at the end of the dietary period.

Influence of muscular development, obesity, and age on the fat-free mass of adults

Body fat and the fat-free mass (FFM) were estimated in 36 men and 43 women deliberately chosen to represent a variety of physical types; these were 1) young sedentary, 2) "muscular," 3) younger obese, 4) older obese, and 5) older nonobese individuals of both sexes. The body fat and the FFM were estimated from measurements of body density (by total immersion in water, measurement being made of the residual volume of air present in the lungs at immersion) and from measurements of total body potassium (using a whole-body monitor to assess the natural 40K isotope present in the body). The muscular men and women and the younger obese men and women had a considerably greater FFM and thus had greater quantities of potassium than the corresponding sedentary groups. There were significantly different estimates of the FFM calculated from density and from total body K in three groups, the sedentary young men, the muscular, and the younger obese women. The density and the potassium content of the FFM appear to decline with obesity and aging. Muscular development is associated with a decrease in the density but an increase in the potassium content of the FFM.

Potassium supplements in patients receiving long-term diuretics for oedema

Plasma, blood cell, and total body potassium levels were measured serially in 21 patients receiving long-term diuretics for the treatment of cardiac oedema and the results compared with similar measurements in 10 control subjects. Initially, all diuretic recipients received potassium chloride supplements. However, in 17 of the 21 subjects these were discontinued and measurements of potassium status were repeated regularly thereafter. No significant fall in the measured indicators of potassium status were observed in the patients in whom potassium was withdrawn; however, in one subject with persistent cardiac failure who presented with hypokalaemia this was not corrected even after intensive potassium supplementation. It is concluded that for those taking a normal diet who are free of any major gastro-intestinal disorder, routine potassium supplementation is unnecessary, and might indeed occasionally prove harmful.

The relation between potassium in body fluids and total body potassium in healthy and diabetic subjects

1. The concentration of potassium in the erythrocytes and the plasma of forty-one normal subjects and twenty-five diabetic patients was measured and the results were used to calculate the total amount of potassium in the erythrocyte mass and the total amount of potassium in the plasma. The total body potassium was measured in a whole-body monitor. 2. In normal subjects a close correlation was found between total erythrocyte potassium and total body potassium and also between total plasma potassium and total body potassium. 3. The regression relation between total body potassium and total erythrocyte potassium in normal subjects was used to predict the total body potassium in diabetic patients. There was reasonable agreement between the measured and predicted total body potassium but there was poor agreement between the measured total body potassium and that predicted from the patient's height and age or height and age or height, weight and age.

The effects of pentobarbitone and pethidine on foetal breathing movements in sheep

1 Small doses of pentobarbitone (4 mg/kg i.v.) administered to sheep in the last third of pregancy had little overt effect on the mothers. In the foetus they caused arrest of breathing movements, an alteration in the character of the electrocorticogram and cardiovascular changes which varied with gestational age. 2 In contrast, relatively large doses of pethidine (100-200 mg) admininstered to the mother had no consistent effect on normal foetal breathing movements, though they abolished the foetal response to hypercapnia. 3 The results are discussed in relation to feotal sleep state.

Total thyroidal content of iodine in thyrotoxic patients measured by in vivo neutron activation analysis

This paper describes an in vivo method for measuring total thyroidal iodine stores by activation analysis, its evaluation and measurements in thyrotoxic patients. There was good correlation between measurements of solutions of iodine and post-mortem thyroids by activation analysis and chemical analysis. Measurements in thyrotoxic patients showed low levels in untreated and treated (antithyroid drugs) patients and a marked increase in patients studied whilst in clinical remission. The practical importance of this method of measurement of thyroidal iodine stores is that it is a reliable in vivo measurement obtained at a single visit and should enable the definition of the relationship of thyroidal iodine stores to pathophysiology and prognosis.

Total body potassium content in males with X and Y chromosome abnormalities

Total body potassium has been measured in chromatin positive males (Klinefelter's syndrome) and males with a 47,XYY karyotype. In patients with an extra X chromosome the level of potassium was very significantly less than in normal males. Its concentration referred to lean body mass, estimated from the patient's height and weight, was also greatly reduced and not significantly different from values found in normal women. In 47,XYY males individual values were low but there was no reduction in the mean value for the group if allowance was made for the obesity of some XYY subjects. The significance of these findings, however, is difficult to assess as their height frequently exceeded that of the controls on which the predicted potassium values were based. From these findings it would seem that when characteristics which are normally associated with the female sex occur in males, as in Klinefelter's syndrome, there is also a reduction in body potassium either in the total content or the lean tissue concentration, or in both. By comparison, 47,XYY males appear to be more normal in these respects but further normal data is required in order to interpret the results. The possibility that abnormal androgen production in the chromatin positive men may be influencing the potassium levels is the subject of further investigation.

Potassium metabolism in patients with rheumatoid arthritis. Effects of treatment with depot tetracosactrin, spironolactone, and oral supplements of potassium chloride

(1) Plasma and urine electrolytes and whole body potassium have measured before and after a 2-week administration of depot tetracosactrin 0.5 mg on alternate days to eight patients with rheumatoid arthritis (RA.) The effects of adding supplements of potassium chloride (48 mmol/d) and spironolactone 200 mg daily have been investigated. (2) Acute changes in red blood cell water and potassium content, plasma electrolyte concentration, and plasma 11-hydroxycorticosteroid levels were measured for 48 hours after a single intramuscular injection of 0.5 mg depot tetracosactrin in six patients with RA. (3) The measured total body potassium was significantly less than that predicted from the height, weight, and age formula in patients with RA. (4) Treatment with depot tetracosactrin resulted in an acute fall in plasma and red cell potassium independent of external potassium loss. (5) Two weeks of treatment with depot tetracosactrin resulted in hypokalaemia and a rise in plasma sodium and bicarbonate. There was no associated electrocardiogram changes or a rise in blood pressure. (6) Neither oral potassium supplements nor spironolactone altered total body potassium. (7) The significance of the findings and the physiological mechanisms underlying them are discussed.