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Biomedical subjects

R Lindsay

Publications and source records attributed to R Lindsay.

At least 19 recordsLinked to original sources
PubMed1992

Bone mass and body composition in normal women.

The interrelationships between measurements of bone mass and total-body bone mineral were examined in a cross-sectional study of normal healthy women aged 17-82 years. In addition we evaluated the relationship between measures of body composition, estimated by four independent techniques, and bone mass in the same population. Considering the group as a whole, bone mass at all sites correlated with each other and with total-body bone mineral (TBBM). Cancellous and cortical sites could predict TBBM equally well. As expected, all measurements of bone mass were significantly lower in postmenopausal women in comparison to premenopausal women. Declines in bone mass were only seen in premenopausal women in the femoral neck and Ward's triangle, not in lumbar spine, radius, or skeleton as a whole. In postmenopausal women bone mass correlated negatively with age and years from menopause equally at all sites. TBBM was significantly related to height and weight in both premenopausal and postmenopausal women. In premenopausal and postmenopausal women TBBM also correlated with fat mass, but TBBM was much better correlated with percentage body fat in premenopausal than postmenopausal women. TBBM was a constant proportion of lean body mass in premenopausal women, but the fraction of lean mass occupied by the skeleton declined with age in postmenopausal women. Correction of TBBM for lean mass did not change the relationship between TBBM and percentage fat in premenopausal women but eliminated the relationship in postmenopausal women. Regional measurements, which are at least partially corrected for body size by dividing mass by area, correlated less well with height and weight and with any index of obesity, especially in postmenopausal women.

Adolescent↗
PubMed1992

Maintenance of cancellous bone connectivity in primary hyperparathyroidism: trabecular strut analysis.

We previously demonstrated an increase in cancellous bone volume and trabecular number in patients with mild primary hyperparathyroidism (PHPT). To test the hypothesis that this increase is due to preservation of cancellous bone architecture, we conducted a trabecular strut analysis using a new method that measures trabecular connectivity. Iliac crest biopsies from 37 patients with PHPT, 14 men (28-68 years) and 23 women (26-68 years), were examined histomorphometrically and compared to cadaveric samples from 24 age-matched subjects, 17 men and 7 women. Two-dimensional indices of cancellous structure--node number (N.Nd), terminus number (N.Tm), node to node (Nd.Nd), node to terminus (Nd.Tm), and terminus to terminus (Tm.Tm) strut lengths, and total strut length (TSL)--were measured and the ratio of node number to terminus number (N.Nd/N.Tm) calculated. TSL, N.Nd, and Nd.Nd were significantly higher in patients than in controls. TSL and Nd.Nd, but not N.Nd or Nd/Tm, decreased significantly with age in PHPT, indicating that age-related bone loss in PHPT occurs without significant loss of trabecular connectivity. Two-dimensional indices reflecting connectivity or the amount of bone, that is, N.Nd, Nd.Nd, N.Nd/N.Tm, and TSL, correlated positively with cancellous bone volume (BV/TV) and trabecular number (Tb.N) and negatively with trabecular spacing (Tb.Sp) in both PHPT and controls. Trabecular thickness (Tb.Th) correlated positively with Nd.Nd and Tb.N and negatively with Tm.Tm in PHPT but not in controls. The present data show that in PHPT there is not only greater cancellous bone volume and trabecular number but preserved trabecular connectivity as well. The data further support the hypothesis that in PHPT cancellous bone architecture is maintained.

Adult↗
PubMed1992

Effects of combined and separate intermittent administration of low-dose human parathyroid hormone fragment (1-34) and 17 beta-estradiol on bone histomorphometry in ovariectomized rats with established osteopenia.

To evaluate the potential use of a combination of parathyroid hormone (PTH) and estrogen as therapy for osteoporosis, we examined the effects of combined and separate administration of low-dose PTH and estradiol in ovariectomized rats with established osteopenia. Ovariectomized rats were untreated for 5 weeks after surgery and then injected s.c. with vehicle (Ovx + V), 1-34 hPTH (2.5 micrograms/kg/day) (Ovx + P), 17 beta-estradiol (50 micrograms/kg/day) (Ovx + E), or a combination of these (Ovx + P + E), for a further 4 weeks. We found no differences in serum calcium, tubular reabsorption of phosphate, or 25OHD. 1,25(OH)2D levels were significantly higher in Ovx + P and lower in Ovx + E, when compared with Ovx + V. Though there was no change in bone mineral density (BMD) in the diaphysis region of femurs, reduction of BMD in the distal region of the femurs in Ovx + V was reversed in Ovx + E and Ovx + P + E. Compared with Ovx + V, Ovx + P and Ovx + P + E had significantly higher cancellous bone volume (Cn-BV/TV) whereas Ovx + E showed a nonsignificant increase. When indices of bone turnover were examined, PTH alone showed a small but not significant improvement in bone formation rate (BFR). Increased osteoclast surface (OCS), as the result of ovariectomy, was inhibited in Ovx + E and Ovx + P + E. Estrogen alone (Ovx + E) severely inhibited BFR, but co-administration of PTH and estrogen (Ovx + P + E) showed an impressive reversal of such inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Comparative assessment of bone mineral density of the forearm using single photon and dual X-ray absorptiometry.

Forearm bone mineral density (BMD) was measured at proximal and distal sites by 125I single photon absorptiometry (SPA) and by dual energy X-ray absorptiometry (DXA) in 67 consecutive subjects, aged 18-75 years. Correlations and regression equations between these two techniques were determined. All forearm measurements were significantly correlated with each other (r = 0.599-0.926; P < or = 0.0001). Although SPA and DXA correct for fat in different ways, we found similar correlation and regression equations in women with body mass index measurements above and below the mean. In addition, forearm measurements by both techniques were moderately correlated with vertebral spine and hip BMD. We conclude that overall, SPA forearm measurements in a population can be calibrated to DXA measurements if necessary, and that DXA forearm measurements are as predictive of the remainder of the skeleton as SPA measurements.

Absorptiometry, Photon↗
PubMed1992

The effect of sex steroids on the skeleton in premenopausal women.

Whereas peak bone mass is genetically determined, the skeletal growth, maturation, and maintenance required to reach this peak may be influenced by physical activity, ovarian function, and nutrition. Estrogen deficiency at menopause leads to increased skeletal remodeling and loss of bone mass, which can result in osteoporotic fractures. Entering menopause with low bone mass is a risk factor itself, because bone mass predicts future risk of fracture. The administration of exogenous steroids can reverse the setting of the "mechanostat" to lower levels after ovarian dysfunction, although it is unclear whether oral contraceptives can modify bone mass in the ovulatory premenopausal woman. Our recent data suggest that the use of steroidal hormones to treat menstrual irregularity (presumably relative to ovarian dysfunction), as opposed to fertility control, is more likely to positively affect bone mass. It is even less clear whether hyperestrogenic states (e.g., pregnancy) affect the skeleton. Recent evidence from bone mass changes that occur in women with ovulatory cycles and inadequate luteal phase function suggests that progestins may also influence skeletal metabolism.

Bone Density↗
PubMed1992

Lack of changes in histomorphometric, bone mass, and biochemical parameters in ovariohysterectomized dogs.

A predictable animal model with skeletal remodeling characteristics similar to those of humans is needed to facilitate the understanding of the mechanism of postmenopausal osteoporosis. We have utilized the ovariohysterectomized (Ovh) dog to examine cellular and biochemical responses to estrogen depletion and PTH stimulation. Histomorphometric measurements of bone biopsies taken prior to (first biopsy) and five months after the operation (second biopsy) showed no significant differences in static and dynamic parameters. Bone mineral density of the excised vertebrae displayed the same values between the two groups six months after surgery. Between the second biopsy and sacrifice, two infusion studies were performed. A two-hour infusion of EDTA followed by a two-hour recovery period elicited a rapid response in PTH production, highly correlated to the changes in ionized calcium, but no significant difference in response was observed between Sham and Ovh groups. A short-term (24-h) infusion of 1-34 hPTH increased circulating ionized calcium and 1,25-(OH)2-D levels to a similar extent in both groups. The levels of alkaline phosphatase were constant and both groups showed a small but nonsignificant increase in osteocalcin. The lack of sizable responses in histomorphometric, bone mass, and biochemical parameters may limit the utility of dogs for the study of cancellous bone loss in ovarian-dysfunction osteoporosis.

Animals↗
PubMed1992

Relationships between quantitative histological measurements and noninvasive assessments of bone mass.

We performed a comprehensive analysis of the relationships between histologic indices in the iliac crest (cancellous bone volume, trabecular structural indices, cortical width, and core width) and bone density in the spine, hip, and wrist in 81 patients with various metabolic bone diseases including osteoporosis, osteomalacia, hyperparathyroidism, and Paget's disease. In the whole group, all of the histologic indices correlated significantly with bone mineral density (BMD) of the spine and the three regions of the hip (r = 0.28-0.73), with the exception of cortical width which correlated with the hip but not the spine (r = 0.21). There was no relationship between the histologic variables and either the distal or proximal radius. When the osteoporotic subgroup was considered separately, the relationships between BMD and both cancellous bone volume and the structural indices (trabecular number, separation, and thickness) were lost. In contrast, cortical width correlated more strongly with both spine and hip BMD. The relationship between core width and the spine was lost but persisted in the hip region. In female osteoporotic patients alone, only cortical width remained significantly correlated with spine or hip BMD. We conclude that the relationships between bone densities in the axial and peripheral regions and histomorphometric variables in iliac crest are not constant. In addition, cancellous bone volume and the trabecular structural indices relate well to noninvasive axial BMD measurements only in a heterogenous group with a large variance in both parameters. In the more homogeneous group with osteoporosis, cortical width appears to be a more powerful predictor of BMD at the important sites of osteoporotic fracture.

Bone Density↗
PubMed1991

A new manual method for assessing two-dimensional cancellous bone structure: comparison between iliac crest and lumbar vertebra.

We have developed a simple method for the direct analysis of two-dimensional trabecular structure. Using this method, we have compared the structure of the left and right iliac crest and the second lumbar vertebra and studied the relationship between two-dimensional trabecular structure and the ultimate compressive stress of bone samples from the second lumbar vertebra. Transverse cores were taken from the left and right iliac crests and second lumbar vertebrae of 35 subjects (12 females) who died suddenly. The trabecular structure was subdivided into nodes (node count) and free ends (free end count), which were expressed per square millimeter of cancellous space. A node was defined as the point of junction between two or more trabeculae; a free end was defined as the end of a trabecula that was unconnected in the plane of the section to any other trabecular element. The following struts were defined by drawing a line between the nodes and the free ends: node to node, node to free end, free end to free end, and cortex-derived struts. Strut lengths were measured and expressed as a percentage of the total strut length and per square millimeter of cancellous space. Intraobserver variation was generally low, with coefficients of variation for repeat measurements in the range 3.9-17.8%. There was no statistically significant difference between left and right iliac crests for any of the variables measured. With the exception of cortex-derived struts, there was no statistically significant correlation between crests for any variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Radiographic absorptiometry: a simple method for determination of bone mass.

Bone mass measurements have been shown to be useful determinants of the risk of development of osteoporotic fractures and may help identify individuals who are most likely to benefit from both primary and secondary prevention of osteoporosis. As standard bone density measurements are not available to all physicians, there is a need for a fast, inexpensive, and widely available technique to measure bone mass. Radiographic absorptiometry of the phalanges requires only routine radiography with processing of the films done at a special off-site laboratory. We performed a preliminary investigation to see whether this simple technique could be used to predict a low bone mass as defined by dual- and single-photon absorptiometry. Correlations between radiographic absorptiometry. Correlations between radiographic absorptiometry and the standard techniques were as good as those among the standard techniques themselves (r = 0.58-0.9). Radiographic absorptiometry measurements predicted low bone mass of the lumbar spine and femoral neck with 90% and 82% sensitivity respectively. If further evaluation supports these initial conclusions, radiographic absorptiometry may be useful as a screening technique for primary care physicians and in research settings where dual-photon or dual-energy X-ray absorptiometry are impossible.

Absorptiometry, Photon↗
PubMed1991

Response of the parathyroid gland to infusion of human parathyroid hormone-(1-34) [PTH-(1-34)]: demonstration of suppression of endogenous secretion using immunoradiometric intact PTH-(1-84) assay.

Alterations in the sensitivity of the parathyroid gland to both stimulative and suppressive stimuli may be partially responsible for skeletal changes that occur with age, estrogen deficiency, osteoporosis, and estrogen treatment of osteoporosis. We sought to define the changes in intact PTH-(1-84) secretion in normal premenopausal and postmenopausal, osteoporotic and estrogen-treated osteoporotic women during the infusion of human (h) PTH-(1-34). hPTH-(1-34) was infused at 0.55 U/kg.h for 24 h, with serum sampling every 4 h. Serum was analyzed for calcium (ionized and total), hPTH-(1-34), and PTH-(1-84). Basal chemistries were no different among groups, except for serum phosphorus, which was highest in osteoporotic women (1.31 vs. 1.07 mmol/L in premenopausal; P less than 0.02), and hPTH-(1-34), which was slightly higher in normal postmenopausal women (19.31 vs. 13.24 ng/L in estrogen treated; P less than 0.02). No differences in PTH-(1-84) were found among groups. hPTH-(1-34) rose similarly in all patient groups, while the calcemic response was somewhat more sluggish in estrogen-treated women, although statistically significant differences were not found. PTH-(1-84) declined rapidly in all patient groups, although estrogen-treated women had a smaller maximal decrease in PTH-(1-84), and the slope of the decremental change in PTH-(1-84) was lower in estrogen-treated women than in osteoporotic or normal postmenopausal women. Untreated osteoporotic women had less suppression of PTH-(1-84) than normal postmenopausal women at every calcium level. Estrogen treatment decreases the calcemic effects of infused hPTH-(1-34) and at the same time reduces calcium-induced suppression of parathyroid secretion. It is possible that such changes in the set-point of the gland contribute to the alterations in bone turnover that result in osteoporosis and the mechanisms by which estrogen prevents bone loss.

Calcium↗
PubMed1990

Body composition studies in premenopausal healthy women.

Body composition studies of healthy premenopausal women were performed using dual photon absorptiometry and the results compared with fat estimates obtained from skinfold measurements, body mass index, and bioelectrical impedance. Total body bone mineral did not decline with age nor did the fraction of lean body mass occupied by the skeleton, which ranged from 4-10%. DPA values for fat were significantly higher than those obtained by other techniques, in part because of calibration but also because of apparent inadequate correction for the fraction of lean body mass occupied by bone in the assumptions made for the other techniques.

Absorptiometry, Photon↗