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Biomedical subjects

R Neer

Publications and source records attributed to R Neer.

11 recordsLinked to original sources
PubMed2001

Body mass index in mid-life women: relative influence of menopause, hormone use, and ethnicity.

OBJECTIVE: To assess the relative influence of menopausal status and hormone use on body mass index (BMI) among a multiethnic sample of mid-life women. DESIGN: Cross-sectional telephone survey conducted at seven sites where each site targeted an ethnic minority group and Caucasians as part of Study of Women's Health Across the Nation (SWAN). SUBJECTS: A total of 7181 Caucasians, 3949 African-Americans, 1660 Hispanics, 562 Chinese Americans, and 803 Japanese Americans between ages of 40 and 55 y residing in or near Boston, Chicago, Detroit, Los Angeles, Newark, NJ, Oakland, CA, and Pittsburgh, PA. MEASUREMENTS: Self-reported BMI based on weight in kg divided by height in m(2) menopausal status, physical inactivity, postmenopausal hormone use, ethnicity, and age in years. RESULTS: Compared to premenopausal women (covariate adjusted M=27.3), women reporting a surgical menopause (M=28.2) or being in the perimenopausal transition (M=27.7 for early and 27.9 for late perimenopause) had higher BMI. Women reporting a natural menopause (M=27.4) did not have a higher BMI than premenopausal women, after adjusting for chronological age and other covariates. Hormone use was associated with lower BMI (M=26.5 vs 27.3). A comparison of effect sizes showed that menopausal status (F=13.1), followed by chronological age (F=24.0), were the least powerful predictors of BMI, whereas the more powerful predictors were physical activity level (F=1377.1) and ethnicity (F=400.5). CONCLUSIONS: The menopausal transition affects body mass index in mid-life, but the effect is small relative to other influences. Interventions to increase physical activity are highly recommended to prevent increases in adiposity common in mid-life.

Adult↗
PubMed1984

Protamine: a powerful in vivo inhibitor of bone resorption.

Protamine is shown to be a powerful disrupter of calcium homeostasis, acutely inducing a severe hypocalcemia in both rabbits and rats. The magnitude of its effect correlates with bone turnover. Protamine does not significantly alter the renal excretion of calcium, and is effective whether or not there is calcium present in the gut. Protamine causes a significant fall in the specific activity of 45Ca in the blood in animals whose bone has been prelabeled with 45Ca. These data suggest that protamine induces hypocalcemia by blocking calcium efflux from bone. Further work seems indicated to define the biochemical mechanism of this action.

Animals↗
PubMed1982

Vitamin D and bone health in the elderly.

The state of vitamin D nutrition depends on synthesis in the skin under the influence of sunlight as well as on dietary intake. In European countries that do not fortify milk with vitamin D, reduced sun exposure is the major factor leading to a fall in body stores of vitamin D with age and to a high frequency of hypovitaminosis D in the elderly sick. In the US, because vitamin D is added to milk and the use of vitamin D supplements is more common, the dietary intake of vitamin D is relatively more important than in Europe, and the total vitamin D intake and body stores of vitamin D are generally higher. Nevertheless, body stores of vitamin D probably fall with age in the US as they do in Europe, and it is likely that some sick elderly persons in the US, especially among those confined to institutions, become vitamin D deficient. For several reasons, the vitamin D requirement increases with age, and a total supply of 15 to 20 micrograms/day (600 to 800 IU) from all sources is recommended. Special attention should be paid to persons most likely to need supplementation, such as the housebound, persons with malabsorption, and persons with interruption of the enterohepatic circulation. Osteomalacia, the bone disease produced by severe vitamin D deficiency, is less common in the US than in Europe, but subclinical vitamin D deficiency may contribute to the pathogenesis of hip fractures, both through increased liability to fall and through PTH-mediated bone loss. The extent to which vitamin D deficiency contributes to hip fractures in the US is unknown, and is an important area for future research. Excess intake of vitamin D or of its metabolites may result in hypercalcemia and extra-osseous calcification, particularly in arterial walls and in the kidney, leading to chronic renal failure. The dose of vitamin D that causes significant hypercalcemia is highly variable between individuals but is rarely less than 1000 micrograms/day. Smaller doses can cause hypercalciuria and nephrolithiasis and possibly impaired renal function. Vitamin D administration may raise plasma cholesterol but there is no convincing evidence that the risk of myocardial infarction is increased. The recommended total supply for the elderly of 20 micrograms/day is most unlikely to be harmful, except in patients with sarcoidosis or renal calculi.

Adult↗
PubMed1982

Calcium nutrition and bone health in the elderly.

The average elderly person is in negative calcium balance and accordingly is losing bone mass. While factors such as decreased mechanical loading of the skeleton undoubtedly figure in this age-related loss, a growing body of evidence suggests that inadequate calcium intake may contribute to this loss. On any given day men and women in the US 65 yr or older ingest about 600 and 480 mg calcium, respectively. Calcium intake in the elderly is less than in the young, and reduced absorption efficiency further lowers effective intake. Additionally, other nutrients such as protein and fiber, taken in excess, effectively increase the calcium requirement. Estrogen withdrawal at menopause leads to a decrease in intestinal calcium absorption efficiency and in renal calcium conservation, both effects equivalent to an effective increase in calcium intake requirement. Thus it is not surprising that all studies of mean requirements for zero balance performed in elderly subjects have yielded values above the current RDA for the US. The available evidence thus suggests that the RDA for adults should surely not be lowered below its current level (800 mg), but that, instead, it ought to be raised. It is not possible to say with certainty to exactly what level, but available evidence is compatible with allowances of at least 1200 to 1500 mg/day. Further, the evidence indicates that the mean requirement ought to be thought of as a complex function of age, sex, absorption efficiency, intake of protein, fiber, and probably other nutrients, estrogen status, and mechanical loading. Extensive experience with calcium supplements indicates that daily intakes up to at least 2.5 g of elemental calcium are quite safe in all persons except for certain subsets of the population uncommon among the elderly (eg, those with sarcoidosis, active tuberculosis, or other absorptive hypercalciuric syndromes). At the same time it must be said that osteoporosis is a complex, multifactorial disorder, and that factors unrelated to calcium nutrition undoubtedly play important, even dominant roles in many--perhaps most--osteoporotics. The available evidence, taken together, does not indicate that raising calcium intake will abolish the problem of osteoporosis. It does indicate, however, that calcium nutrition is considerably more important in the genesis of osteoporosis than has been commonly thought for the past 35 yr. As our listing of "important issues" indicates, the full extent of that importance, in both pathogenesis and prophylaxis, remains to be elucidated.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption↗
PubMed1982

Model for parathyroid hormone secretion and metabolism in calves.

A model for parathyroid gland response to differing calcium and magnesium concentrations is proposed based on direct determinations of parathyroid hormone (PTH) secretion rate. A proportional control seems adequate for physiological variations of calcium and magnesium levels. At extreme hypocalcemia, nonlinearities are observed: a model involving the depletion of a storage compartment is proposed, the size of which is calculated. PTH distribution was studied in another group of animals; sampling was made from the saphenous artery and the thoracic duct. Concentrations of plasma and lymph-intact PTH and carboxy-terminal fragments were determined by means of two different radioimmunoassays. The analysis of the results leads to the formulation of a five-compartment model, which shows that the metabolism of intact PTH is only partly due to the formation of carboxy-terminal fragments, most being directly secreted or catabolized. Linking these models for secretion and distribution of PTH, simulation studies were undertaken and compared with published data. This model is then discussed in comparison with previous work concerning other polypeptide hormones.

Animals↗
PubMed1982

Parathyroid gland response to epinephrine: a rate-sensitivity mechanism.

A model for parathyroid gland response to an epinephrine infusion is proposed. It is based on direct measurements of the parathyroid hormone (PTH) secretion rate as measured directly after cannulation of the venous drainage of single superior parathyroid glands of calves. When epinephrine was infused into a jugular vein, a large increase of PTH secretion rate was observed at the beginning of the infusion. The PTH secretion rate thereafter fell, but it was still significantly above the control rate. At the end of the epinephrine infusion a sharp decrease was observed when the infusion was terminated. These observations are consistent with a rate-sensitive control mechanism. Calculation of the parameters yielded a model, which was then linked with a kinetic model for PTH distribution. Simulation studies were undertaken to predict plasma PTH concentration in response to an epinephrine infusion. Good agreement was found between predicted results and previously published work. The role of this rate-sensitive mechanism in the parathyroid gland is discussed.

Animals↗
PubMed1981

Pseudohypoparathyroidism: inheritance of deficient receptor-cyclase coupling activity.

Pseudohypoparathyroidism, type I (PHP-I) is an inherited disorder of primary resistance to multiple hormones that work by stimulating adenylate cyclase. In an attempt to clarify the mode of inheritance of PHP-I, we measured the activity of the N protein, a receptor-cyclase coupling component, in erythrocyte membranes. Erythrocyte N-protein activity was reduced by approximately 50% in erythrocytes of 15 PHP-I patients and was normal in 19 of their clinically normal first degree relatives. Reduced N-protein activity and the PHP-I phenotype in these families exhibited both dominant and recessive patterns of inheritance. This suggests that at least two distinct genetic loci are involved in inheritance of N-protein deficiency. In two additional families, dominant inheritance of the PHP-I phenotype was associated with normal activities of erythrocyte N protein. Thus, it appears that mutation of at least one additional genetic locus, not involving the N protein, can produce PHP-I.

Adenylyl Cyclases↗
PubMed1978

Use of stable 48Ca in the clinical measurement of intestinal calcium absorption.

Measurements of intestinal-calcium-absorption efficiency are fundamental for understanding calcium homeostasis in health and disease. Stable calcium isotopes are attractive tracers for such measurements, to avoid excessive radiation exposure to the subject and permit serial studies at short intervals. To realize this, we found it necessary to improve the sensitivity and precision of existing thermal neutron activation analyses for 48Ca. This report describes the details, sensitivity, precision, and accuracy of the improved method, and gives the results of studies in which intravenous 48Ca was used in conjunction with oral 47Ca to measure intestinal-calcium-absorption efficiency in patients.

Calcium↗
PubMed1967

Multicompartmental analysis of calcium kinetics in normal adult males.

This report describes studies of calcium kinetics in ten normal young men. Serum, urinary, and fecal radioactivity was measured from 1 minute to 20 days after intravenous tracer (47)Ca injection, and these results were analyzed jointly with data obtained from a simultaneous metabolic balance study, using digital computer techniques. Surface radioactivity measurements were also obtained to gain further insight into the anatomic correlates of the tracer distribution. The data were satisfied by a model with four exchanging compartments. Series, branching, and mammillary models were analyzed. Several parameters of physiologic interest were independent of the model, but two were dependent on the duration of the study. Individual and mean values for these kinetic analyses are presented with their statistical uncertainties. These studies present detailed analyses in a healthy, normal population and provide a reference for future studies of skeletal metabolism and serum calcium homeostasis.

Journal Article↗