Biomedical subjects
Publications and source records attributed to A Rubinacci.
To evaluate the effects of freezing and thawing on Ca2+ transport and permeability, inside-out red cell membrane vesicles (IORCMV) are examined. Exposure to the cryoprotectant Me2SO as well as different cooling regimes on unprotected and cryoprotected vesicles do not affect the membrane Ca2+ transport. However, freezing and thawing increase the membrane permeability to sucrose.
The measurement of diastasis of the spinous processes and of muscular action potentials by means of bio-feedback equipment is a clinically valid means to evaluate the extent of reflex muscular contracture. The methods were used to study the relaxant effect of pridinol mesylate on the lumbar extensor muscles in subjects with acute low back pain. It was found that pridinol mesylate significantly reduced the contracture of the extensor lumbar muscles in low back pain when given per os or parenterally.
A high coefficient of variation is characteristic of the bioelectric potentials recorded from living long bones. As a consequence, the data collected from animal and human experiments are difficult to use in practical ways. A distribution curve for bone bioelectric potentials has been calculated using polynomial regression analysis to process the voltage values recorded on the whole length of rabbit tibiae, with reference electrodes positioned in three different points of the bone. The distribution curve so obtained is presented to fulfill the need for a reference curve for the bioelectric potentials recorded from rabbit tibial surfaces.
According to results of experimental study on 70 women, either normal or osteoporotic, the authors come to a critical valuation of known radio-morphometric index concerning the measure of amount of bone and propose the cortical planimetric percent area of the second right hand metacarpal as original radio-morphometric index, greatly correlated (r = 0,879) to gamma-absorptsiometric mineralometry.
The origin of the bioelectric potentials in unstressed living bones is still an open question. Blood-flow in vessels, stationary potentials on peripheral nerves, muscle injury potentials, and viability of bone cells are claimed to be possible sites of origin of the electric potentials recorded on bone surface. The present data show that the topographic quantitative distribution of tetracycline labeling at sequential levels of rabbit tibia and the distribution pattern of the bioelectric potentials in this bone are significantly superimposable. This coincidence of bone formation rates and bioelectric potentials seems to support the view that the latter are in some way linked with the laying down of new bone.
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Controversies surround the view that the blood-bone ionic equilibrium is controlled by ionic changes at a so called "bone membrane" that display a pump-leak mechanism able to maintain a concentration gradient for chloride in addition to that for calcium, sodium and potassium. On the other hand it is known that a chloride-bicarbonate transport is active at bone cells membrane to control cytosolic pH. We tested the hypothesis that a modification of the chloride concentration of the culture medium, as well as a block of the chloride-bicarbonate transport by an anionic channels blocker, in an experimental model that keeps intact the bone membrane, may influence the bone cells activity and that the influence may be quantitatively different to that previously observed in isolated bone cells. The experimental model is the intact fetal rat limb bone, cultured for 24 hours in a simplified medium at different chloride concentrations obtained by substituting chloride with isethionate. Alkaline phosphatase activity released in the medium was measured as a marker of osteoblasts activity. By progressively reducing the chloride concentration from 117 mM to 29 mM, alkaline phosphatase activity was found unchanged. By dramatically reducing the medium chloride concentration to the range 14-0 mM, alkaline phosphatase activity was significantly (p = 0.0002) inhibited by 31.58%.(ABSTRACT TRUNCATED AT 250 WORDS)
The oral calcium load test, originally proposed for evaluating the intestinal calcium absorption and the renal calcium leak triggers some endocrine and metabolic responses addressed to correct the "calcemic error" induced by the load. Besides the increased plasma calcium there are: plasma PTH drop, increment in the urinary calcium excretion and in the threshold of tubular phosphate reabsorption. These responses have been measured and reciprocally correlated in 9 young adults at different times after the oral calcium load. The responses can be assessed with high precision in clinical practice and are in agreement with the known physiological models. The oral calcium load test is proposed as a tool for studying in the osteopenic population in the individual's capacity of correcting the calcemic error induced by the load.
The purpose of this study was to verify if a decreased inhibition of PTH secretion (abnormal suppressibility) in response to physiological increment of plasma calcium is present in patients with osteoporosis. The plasma concentration curve of intact PTH 1-84 following an oral calcium load (Pak) has been calculated in a selected population of 38 osteopenic patients (16 males and 22 females) and in a control group of 9 young healthy adults. All the patients included in this study a) had no past or present diseases and medications of potential influence on calcium homeostasis, b) showed a maximal calcemic response to the oral calcium load equal to that of the control group. PTH suppressibility was significantly smaller in the osteoporotic patients (-42% in males and -32% in females) than in the control group (-76%). This abnormal suppressibility of PTH is independent on sex and, in the females, also on postmenopausal estrogen deficiency. These results support the hypothesis that osteoporosis is associated to an altered secretory response of parathyroid glands maybe due to reduced sensitivity of the parathyroid cells to extracellular calcium.
Bone mineral content measurement is not as widely used in experimental conditions as in clinical practice because of the lack of adequate experimental methods. An in vivo measurement method of bone mineral content in the rat is here presented. Measurements were made at the proximal tibio-peroneal segment, which has a mainly trabecular structure, by means of single photon absorptiometry. The presence of the fibula, having cortical structure, has been shown not to affect the read values, which can be therefore attributed to the tibial metaphysis, having a mainly trabecular structure. Expressing mineral content values as a function of the measured bone diameter has proven useless. Limb repositioning on the instrument holding device is critical for the reproducibility of the measurement, but the latter is not affected by the repositioning method. Method reproducibility (depending on either the intrinsic instrumental error or the repositioning error) is 5-6%. This relatively low reproducibility of the suggested method does not prevent its use in the study of physiological and pathological variations of bone mineral content in rats, and of the means to influence it.
This study was aimed at verifying whether accuracy and reproducibility of mineral content measurements of bone phantoms by single-photon absorptiometry change as a function of source strength, and whether these changes depend on the phantom's width. To these purposes, the Norland 2780 bone mineralometer was used. With this unit, the mineral contents of two cylindrical phantoms of different diameter and of known mineral content were measured every week, 5 times on the whole, up to exhaustion of the source. Both accuracy and reproducibility decreased as source strength decreased. The lowest reproducibility was observed for the measurement of the smaller phantom with low source strength. It was therefore concluded that when source strength reaches the threshold value of 2000 cps, the measurement is so much affected as to jeopardize the reliability of short-term longitudinal studies of bone mineral content in patients.
Diabetes and osteoporosis are linked. The question remains, however, as to whether insulin has any direct effect on bone formation. To test this hypothesis we have measured, as a marker of osteoblast activity, alkaline phosphatase (ALP) released by rat limb intact bones incubated in the presence and in the absence of physiological concentration of insulin. The results indicate that insulin significantly (p less than 0.012) increases ALP by a mean value of 48% (from 5.4% to 215%) over matched controls. We conclude that insulin has a direct stimulatory effect on osteoblast activity, and that in the absence of this effect, as in diabetes, bone loss might occur.
A study was carried out to characterize in the growing skeleton the absorptiometric measurement of the ultradistal radial epiphysis where the trabecular bone is higher than at proximal scanning planes. The study showed that a radius scan, 1 to 1.4 cm proximal to the ulnar tip, and consequently 4 to 6 mm proximal to the growing plate, gives reproducible informations in infants aged 6 years or more when the BMC, and not the BMC/BW, is considered, as the measurement error is 3.5% and 5.7%, respectively.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.