A bone calcium index based on partial-body calcium measurements by in vivo activation analysis.
(1/35)
Measurements of partial-body calcium by in vivo neutron activation analysis have been carried out on normal and osteoporotic subjects. Based on measurements on 16 normal subjects (volunteers less than 55 years of age), a calcium index has been established that takes into account variation in skeletal frame size. On the basis of this index, all osteoporotic patients have bone mineral content less than any of the normal subjects. The normal calcium indices range from 0.9 to 1.2, and the osteoporotic indices ranged from 0.41 to 0.83. Thirteen of 22 volunteers over 55 years of age had calcium indices less than 0.9 in agreement with the expected loss of calcium with age. Measurements of total-body potassium were also made on these same subjects and the calcium/potassium ratios calculated. Although as groups the older volunteers and older osteoporotic subjects had mean calcium/potassium ratios similar to the mean for the normal subjects, the osteoporotic subjects under 55 years of age had a mean calcium/potassium ratio significantly lower, indicationg that for this latter group the loss in bone mineral was not associated with a corresponding loss in muscle mass. (+info)
Phonton absorptiometry and skeletal mass in the treatment of osteoporosis.
(2/35)
Thirty-six osteoporotic patients who underwent several therapeutic regimes were studied on two occasions by photon absorptiometry and total-body neutron activation analysis (TBNAA). These determinations were made at a mean interval of 8.9 plus or minus 0.8 months. The 8-cm radial site was chosen for the photon absorptiometry which was performed with the Norland-Instruments Densitometer. Mean initial bone mineral content (BMC) was 0.724 plus or minus 0.069 gm/cm and mean bone width was 1.235 plus or minus 0.072 cm. The mean percent change in BMC (%deltaBMC) was 1.02 plus or minus 4.2. The initial total-body calcium (TBCa) as determined by TBNAA was reduced when compared with values that would be expected from empirically derived formulas. The mean percent change in TB-Ca (%deltaTB-Ca) was -3.2 plus or minus 4.7. Most patients displayed a change in BMC and TB-Ca that was at least 2 s.d. greater than the precision of the methods used (%deltaTB-Ca greater than 2). No relationship was found between the deltaBMC and the deltaTB-Ca (r = 0.17). These findings suggest that changes in the radical BMC at the 8-cm site cannot be extrapolated to indicate changes in skeletal mass in response to treatment of osteoporosis. Whether photon absorptiometry at other sites or at multiple sites provides a closer relationship to changes in skeletal mass (TB-Ba) remains to be determined. (+info)
Preliminary observations on excretion of 37Ar from man following whole-body neutron activation--an indicator of total-body calcium.
(3/35)
Measurements of exhaled 37-Ar produced by total-body neutron irradiation of 40-Ca were used to determine total-body calcium in 16 human subjects. There was a good correlation between body calcium using the 30-min postirradiation breath sample of 37-Ar and body calcium determined by measurement of 49-Ca. (+info)
Effects of activation sequence on the local recovery of ventricular excitability in the dog.
(4/35)
We measured refractory periods at ventricular sites in the dog heart during drive from ventricular test sites and during combined drive from the test sites and other ventricular sites or the atrium. We found that ventricular activation sequence caused significant alterations on refractory period. Combined drive from two sites which resulted in fusion complexes was associated with shorter refractory periods at the test sites than those observed during drive at the test sites only. Our findings are explicable because earlier excitation and consequent earlier recovery of surrounding areas during fusion beats exerts an electrotonic influence on test sites. (+info)
Length-induced changes in activation during contraction. A study of mechanical oscillations in strontium-mediated contractions of cat and frog heart muscle.
(5/35)
The plateau phase of prolonged Sr-mediated contractions of preparations of cat and frog heart muscle was used to study the transient response to abrupt changes in load or length. An oscillatory response (total amplitude equal to or less than 5% Lmax) was obtained. Isotonic oscillations were less damped than their isometric counterparts, implying positive feedback and thus a causal role of the perturbation in length. Oscillation frequency was 2-3 HZ at 29 degrees C (Q 10, 2-3); it could be increased by epinephrine or caffeine, independently of their effects on extent of shortening; it otherwise changed as a generally constant function of the length at which the oscillation occurred, whether this was altered by changes in extracellular [Sr], frequency of contraction, or load (independent of the direction and magnitude of the preceding load step). Similar oscillatory responses were induced during Sr- or Ca-mediated contractures. Cat muscles showed an additional slower component to the oscillatory response. Transient augmentation of the velocity-length relationship after abrupt reduction in load, previously described for twitch contractions under certain conditions, appears to be analogous to the first phase of the oscillatory response studied here. Our findings indicate that the oscillation is not attributable to any mechanism intrinsic to myofilament interaction, but rather that it involves length-induced changes in the level of activation, probably mediated by Ca2+ or Sr2+. We conclude that length influences the level of activation during contraction of heart muscle. (+info)
MICROSCOPIC DETERMINATION OF BONE PHOSPHORUS BY QUANTITATIVE AUTORADIOGRAPHY OF NEUTRON-ACTIVATED SECTIONS.
(6/35)
Longitudinal sections of human cortical bone were submitted to thermal neutrons. gamma-ray spectra were recorded repeatedly during 15 days following irradiation. They showed that Na(24) is predominant as early as 3 hours after activation and that all the gamma-emitters have decayed on the 15th day. When the gamma-rays have disappeared, beta-rays are still produced by the sections. It was proved by the absorption curve in aluminium that all these beta-rays are issued from the P(32) induced in the sections by activation of P(31). Therefore autoradiograms registered 15 days after activation reveal the distribution of P(32) in the sections. gamma-ray spectra and beta-ray absorption curves of neutron activated sections of ivory demonstrated a mineral composition similar to that of bone. Autoradiograms of ivory sections activated for various times were used to establish the relation between the optical density of the autoradiograms and the radioactivity in P(32). When the bone autoradiograms are compared with the ivory standards of known radioactivity, the optical densities of single osteons (Haversian systems), can be related to their phosphorus contents. Autoradiograms and microradiograms of the same sections were examined side by side. The least calcified osteons, that contain 80 per cent of the calcium of the fully calcified osteons, also contain about 80 per cent of the phosphorus of the fully mineralized osteons. It is concluded that the Ca:P ratio remains constant while mineralization of bone tissue is being completed. (+info)
Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma.
(7/35)
Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied. (+info)
Post-separation detection of nucleic acids and proteins by neutron activation.
(8/35)
We describe approaches to neutron activation analysis and their application to post-separation autoradiographic detection of biological compounds. Specifically, we have extended the use of a "direct-labeling" method to the post-separation detection of DNA after gel electrophoresis and to the detection of nucleotides separated by TLC. In addition, we describe a more generally applicable "indirect-labeling" method in which separated compounds of interest are selectively bound to ligands containing highly neutron-activatable elements, such as manganese (55Mn), europium (151Eu), or dysprosium (164Dy), and then irradiated with thermal neutrons. This method is illustrated with nucleotides separated by TLC and with proteins separated by polyacrylamide gel electrophoresis. In contrast to the direct-labeling approach, the indirect-labeling method can be adapted to detect any class of substances for which a highly neutron-activatable, selectively binding ligand is available. The theoretically achievable sensitivity of the indirect-labeling method is in the attomole (10(-18) mol) range. (+info)