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Biomedical subjects

J C Howe

Publications and source records attributed to J C Howe.

6 recordsLinked to original sources
PubMed1990

Postprandial response of calcium metabolism in postmenopausal women to meals varying in protein level/source.

The postprandial response of calcium metabolism to single meals varying in protein source and level was determined in eight postmenopausal women, age 51 to 65 years. Following an overnight fast, subjects consumed a liquid meal containing either 15 g or 45 g of protein from beef (B), cottage cheese (C), or soy isolate (S; 45 g only); one meal provided 0 g protein (basal). Blood was collected before the meal and at 30, 60, 120, and 180 minutes post-meal. Urine was collected every 30 minutes post-meal. Urinary Ca excretion significantly increased following 45-g protein meals when compared with basal meals, but not when compared with 15 g protein meals. Although glomerular filtration rate (GFR) was unaffected by diet, percent renal tubular Ca reabsorption was significantly reduced following C45 or S45 meals. No consistent changes in serum levels of parathyroid hormone (PTH) and calcitonin (Ct) were observed in response to diet. Serum phosphorus levels were significantly reduced following high-protein meals when compared with no-protein meals. Insulin response varied with protein level and source (C45 greater than S45 greater than C15 greater than B45 greater than B15 greater than basal). Significant associations found between insulin and calcium metabolism indicate a possible role of insulin in the mechanism of protein-induced calciuria.

Absorption↗
PubMed1988

Bone status of senescent male rats: chemical, morphometric, and mechanical analysis.

The bone status of male rats 6, 12, and 24 months of age (n = 10) was examined. Femur calcium (Ca), phosphorus (P), and osteocalcin contents; serum chemistry; and mechanical properties of the bone were measured and correlated. Diaphyseal Ca, P, and osteocalcin contents were not different in animals 6 and 12 months of age but decreased significantly at 24 months: -7.4% for Ca, -4.2% for P, and -24% for osteocalcin compared to 12 months. Femurs from 24-month-old (senescent) rats were characterized by a scalloped appearance of the midfemoral endosteal surface and by cortical porosities. These age-associated changes coincided with nearly two-fold increases in serum immunoreactive parathyroid hormone (PTH) and osteocalcin. Serum Ca did not change with age, whereas serum P decreased (-14.8%) from 6 to 24 months. Maximum breaking force required to fracture femurs at midshaft did not change with age. Hence, the strength of the femur as an intact organ was not compromised with age despite the loss of diaphyseal Ca and P in the senescent animal. However, ultimate stress, a parameter that normalizes for differences in bone geometry and size, decreased 35% in femurs from 12- compared with 24-month-old animals. These mechanical results might be explained by the morphometric finding that, in contrast to the small but progressive age-associated increases in femur weight and length, the cortical and medullary areas increased at least two-fold. Therefore, the strength of the intact femur was maintained by architectural compensations, even though normalized tissue strength decreased with age. These findings suggest that bone status was compromised in the aged male rat.

Aging↗
PubMed1988

Bone mineral content in the senescent rat femur: an assessment using single photon absorptiometry.

The single photon absorptiometry technique was evaluated for measuring bone mineral content (BMC) of the excised femurs of the rat, and the system was used to examine the changes in cortical and trabecular bone from young adult (6 mo), mature adult (12 mo), and senescent (24 mo) male and female animals. BMC of the femur midshaft, representing cortical bone, apparently increased progressively with advancing age. The width of the femur at the scan site also increased with age. Normalizing the midshaft BMC by width partially compensated for the age-associated increase. However, when bone mineral values were normalized by the cortical area at the scan site, to take into account the geometric differences in the femurs of different aged animals, maximum bone densities were found in the mature adult and these values decreased slightly in the femurs from senescent rats. In contrast, the BMC of the femur distal metaphysis, representing trabecular bone, decreased markedly in the aged rat. The loss of trabecular bone was also evident from morphological examination of the distal metaphysis. These findings indicated that bone mineral loss with age was site specific in the rat femur. These studies provided additional evidence that the rat might serve as a useful animal model for specific experiments related to the pathogenesis of age-associated osteopenia.

Aging↗
PubMed1988

Bone status of senescent female rats: chemical, morphometric, and biomechanical analyses.

The bone status of female rats, 6, 12, and 24 months of age was examined. Femur Ca, Pi, and osteocalcin contents, as well as biomechanical properties, were measured and correlated to physical indices and serum chemistry. Diaphyseal Ca, Pi, and osteocalcin did not change significantly with increasing age. Serum Ca and Pi concentrations were not altered in the aged rat. Immunoreactive parathyroid hormone (PTH) levels increased significantly with age, when analyzed by linear regression. Serum osteocalcin decreased progressively from 6 to 12 months (-21%) and from 12 to 24 months (-23%). Maximum breaking force required to fracture femurs at midshaft did not change with senescence. Hence, the strength of the femurs as an intact organ was not compromised in aging. However, ultimate stress, a parameter that normalizes for differences in bone geometry and size, decreased 14% from 12 to 24 months. Changes in other biomechanical parameters, including yield and ultimate deformation, strain, and modulus of elasticity, were relatively small, but statistically significant, or were negligible. Morphometric measurements indicated a progressive age-related increase in second moment of area and cortical area. Medullary area did not change with age. Therefore, strength of the intact femur was maintained by architectural compensations, although normalized tissue strength decreased in senescence. The bone status and Ca/Pi homeostasis of the female rat were compared to similar findings, reported previously, for the male animal. The results suggest that bone status and mineral metabolism were compromised in the aged female rat, but the magnitude of change was less than that found for the senescent male rat.

Aging↗
PubMed1985

Amobarbital interactions with 25-hydroxycholecalciferol: effects on the extraction, quantification, and competitive protein binding in vitro.

Amobarbital has been found to coelute with 25-hydroxycholecalciferol (25OHD3) on a normal phase high performance liquid chromatographic system and cause subsequent interference in the UV detection and plasma transport competitive protein binding assay for this vitamin D metabolite. Concentrations of 25OHD3 were overestimated by 95% in the presence of 0.4 mg amobarbital in the competitive protein binding assay; as little as 0.1 mg amobarbital caused a 22% overestimation in the concentration of 25OHD3 in the assay. Separation of 25OHD3 from amobarbital on a reverse phase high performance liquid chromatographic system allowed for proper quantification without interference. Because of the similarity of chemical structures, other barbital-based compounds may cause similar interactions with 25OHD3 or other vitamin D metabolites as well.

Amobarbital↗