Engineering topics

Navidi, M.

Publications and source records attributed to Navidi, M..

7 records

NASA NTRS1999

Bone Density and High Salt Diets in a Space Flight Model

High salt diets accelerate bone loss with aging in patients with postmenopausal osteoporosis except when calcium supplementation is provided. We have observed that the decrease in mineral content of growing femurs in juvenile rats, exposed to a space flight model which unloads the hind limbs , is substantially less in animals fed excess salt. To determine whether excess dietary salt has the same effect on the skeleton of the mature animal whose response to unloading is increased resorption and bone loss rather than impaired growth, we carried out a metabolic study in mature rats with hindlimbs unloaded by tailsuspension.

Arnaud, S. B.↗

NASA NTRS1997

Deoxypyridinoline in the Urine of Rats with Unloaded Hindlimbs

The urinary excretion of deoxypyridinoline (U-Dpd), a nonreducible collagen crosslink in bone released by osteoclastic activity, is thought to be an accurate marker of bone resorption. The role of increased resorption in the osteopenia of a space flight model which unloads the hindlimbs by suspending the tail is controversial. To assess skeletal resorption in the model we measured U-Dpd (Pyrilinks-D, Metro Biosystems, Inc.) in serial 24 hour urine specimens collected from 250 a (Y) and 450 a (M) male rats with unloaded hindlimbs for four weeks. Both groups of rats were fed AIN76 diets with calcium restricted to 0.2% in Y and to 0.1 % in M. Blood was obtained after 28 days for parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25-D) and alkaline phosphatase (Alkptase). Basal U-Dpd was higher and more variable in Y than M (475+/-200 vs 67+/-9, nM/mM creatinine, p<.001). Repeated measures ANOVA in Y revealed decreases in U-Dpd, 36% in control (C) and 24% in unloaded (S) rats (p<.005). There was a nadir in YS on the 14th day not observed in YC (p<.05). U-Dpd in MC showed no change, but increased in MS by the 14th day and remained elevated. At the end of the experiment, body weights in both Y and M were less in S than C (337+/-16 vs 306+/-12g and 485+/-10 vs 461+/-6g, p=.002). Bill was inversely related to U-Dpd only in M (r=0.699, p=.024). PTH, similar in C and S in Y (52+/-15 vs 42+/-7pg/ml, NS) and M (68+/-13 vs 61+/-12, NS), was unrelated to U-Dpd. 1,25-D tended toward higher values in YC than YS (197+/-103 vs 119+/-30, NS) and correlated with U-Dpd (0.773, p=.015). Alkptase, 1.3 times higher in Y than M, was similar in C and S at the end of unloading. These findings indicate that bone resorption, as reflected by U-Dpd, is suppressed in young and stimulated in mature rats exposed to a space flight model. U-Dpd reflects reduced growth from the diet change in young control and experimental rats and loss of Bill in mature animals exposed to the space flight model, 2 situations with opposite effects on bone resorption.

Arnaud, Sara B.↗

NASA NTRS1997

Calcium Balance in A Rat Space Flight Model

One of the main characteristics of calcium (Ca) metabolism during space flight and the human bed rest model for microgravity is negative Ca balance, attributed, to an increase in urinary Ca excretion and depressed intestinal Ca absorption. No differences or less positive Ca balances are reported after skeletal unloading in similar studies in weaning or juvenile rats. To determine Ca balances and evaluate the Ca endocrine system in mature rats exposed to a space flight model which unloaded the hind limbs by tail suspension, we modified the cage to quantify dietary, fecal and urinary Ca. Five 2-5 d balance periods in 8 loaded (C) and 8 unloaded (S) rats were compared during a 4 week study in 6 month old 490 g male rats. The first period revealed negative balances of -16+/-3 and -14+/-5 mg/d which reflected adaptation to the cages, the change in diet from Purina to AIN 76 and weight loss in both C and S. Average Ca balances in rats fed 0.1% Ca and 0.3% phosphorus (Pi) diets, remained negative in S and were less than C after 6 -10 d (-2.9 vs 0.12 mg/d, p<.05) but not thereafter. In spite of eating 10% more food than C, initial weight loss, restored in C, was never recovered in S. Fecal excretion exceeded dietary intake by -3.7% in S and reflected absorption and retention of 8.4% dietary Ca in C. Urinary Ca was the same fraction of dietary intake in S and C (9.0 vs 8.6%, NS). Serum Ca, Pi, parathyroid hormone and 1,25-dihydroxyvitamin D were the same in both groups after 28 days. In contrast to the human, a major determinant of negative Ca balance in the mature rat exposed to a space flight model appears to be losses from gastrointestinal Ca secretion, rather than urinary Ca excretion.

Arnaud, Sara B.↗

NASA NTRS1994

A metabolic cage for the hindlimb suspended rat

Hindlimb suspension has been successfully used to simulate the effects of microgravity in rats. The cage and suspension system developed by E. R. Holton is designed to produce a headward shift of fluid and unload the hindlimbs in rodents, causing changes in bone and muscle similar to those in animals and humans exposed to spaceflight. While the Holton suspension system simulates many of the conditions observed in the spaceflight animal, it does not provide for the collection of urine and feces needed to monitor some metabolic activities. As a result, only limited information has been gathered on the nutritional status, and the gastrointestinal and renal function of animals using that model. Although commercial metabolic cages are available, they are usually cylindrical and require a centrally located suspension system and thus, do not readily permit movement of the rats. The limited floor space of commercial cages may affect comparisons with studies using the Holton model which has more than twice the living space of most commercially available cages. To take advantage of the extra living space and extensive data base that has been developed with the Holton model, Holton's cage was modified to make urine and fecal collections possible.

Evans, J.↗

NASA NTRS1994

Vitamin D Status in Monkey Candidates for Space Flight

In preparation for the Cosmos 2229 Biosatellite space flight experiments in Rhesus monkeys, we evaluated the status of vitamin D in animals of different origins: candidates for space flight raised in Moscow (IMBP) and animals housed at Ames Research Ctr. (ARC) for pilot studies. Diets at IMBP were natural foods found by analysis to contain 1.4% Ca, 2.8% P and<240 IU D3/kg and at ARC standard monkey chow with 0.9% Ca, 0.5% P and 6600 IU D3/kg. We measured body weights (BW), serum calcium (TCa), total protein (TP), phosphorus (Pi), alkaline phosphatase (AP), 25-hydroxyvitamin D (25D) and 1,25-dihydroxyvitamin D (1,25D) in 16 IMBP and 15 ARC male animals and indices of bone formation in cancellous bone obtained from iliac crest biopsy of 6 IMBP and 13 ARC animals. BW were the same in juveniles at IMBP as ARC although ARC monkeys were born a year later. Mean(1SD) TCa and TP were higher and 25D lower (1819 vs. 93+18 ng/ml,p<.001) in IMBP than ARC animals. 1,25D (174156 vs. 212+77 pg/ml), Pi and AP were similar. In bone, osteoid and osteoblast surfaces averaged 38114% and 33+15% in all, with %vol. of osteoid higher in IMBP than ARC monkeys of the same BW (p<.05) Indices of bone formation were inversely related to 25D, not 1,25D. Of interest are similar 1,25D levels associated with a wide range of substrate and extensive osteoid in bone of D replete animals.

Arnaud, S. B.↗

NASA NTRS1994

Space Flight Effects on Intracellular Ions in Sublingual Cells of Non-Human Primates

We have used a novel technique that quantifies minerals and electrolytes from smears of sublingual cells by x-ray microanalysis to monitor metabolic changes in bed rest subjects. Increases in intracellular calcium (Ca), phosphorus (P), and potassium (K) were characteristic of subjects whose exercise regimen was inadequate to maintain calcium metabolism. To test the effects of space flight on intracellular ions, we analyzed cells from 2-4 kg Rhesus monkeys before and after 2 weeks in space or chair restraint (CR). There were increases in sublingual cell Ca, P and K after space flight which paralleled the clinical estimates of metabolic status of the animals and exceeded the levels found during CR on R+11. Increases after 2 weeks CR were 26% in Ca, 6% in P and 29% in K. Species similarity ill responses of intracellular ions to inactivity imposed by bed rest, restraint or microgravity suggest that this innovative non-invasive technique would be a useful in-flight monitor of exercise countermeasures directed toward maintaining calcium balance.

Arnaud, Sara B.↗

NASA NTRS1994

Role of Growth Hormone, Exercise and Serum Phosphorus in Unloaded Bone of Young Rats

Growth hormone, known to be stimulated by exercise, is suppressed in rats after space flight and in a ground-based model in which the hind-limbs are unloaded (S). To determine the role of GH in the osteopenia of unloaded bones of S rats, young males were treated with GH combined with insulin-like growth factor-1 (IGF-1), a peptide that mediates the local actions of the hormone. 200 g rats, hypophysectomized (hypox) 17 d earlier, were treated with 1 mg/kg/d GH/IGF-1 (H) or saline (C) in 3 divided daily doses x10 d. Hind-limb bones were unloaded (S), ambulated (A) or exercised (X) by climbing a ladder while carrying a weight. Growth was monitored daily. Tibial growth plate (Tepi) was measured with a micrometer, and femoral (F) area, length, and mineral content (BMC) by DEXA. Parameters of calcium metabolism were measured by autoanalyzer and calciotropic hormones by radioimmunoassay. F bone density, g/square cm, (BMD) or BW were not affected by S in Hypox. However, FBMD was lower in S+H than A+H (p is less than 0.002) and H stimulated whole body growth in S (5.2 g/d) and SX (5.6 g/d) to a lesser extent than in A (6.6 g/d) (p is less than 0.05). Adjusted for BW, Tepi showed the greatest increase in S+H+X (64%), the next highest increase in S+H (50%) and no change in S+X. F area, length and BMC/100 g BW were lower in all H groups than respective C's. By multiple regression analysis, serum phosphorus (Pi) which correlated with Tepi (r = 0.88, p is less than 0.001) and was inversely related to FBMC (r = -0.68, p is less than 0.001) proved to be the most significant determinant of BMC. This illustrates the dependence of osteopenia in S on GH, the maximizing effect of X for epiphyseal growth and the major role of Pi metabolism on BMC in weight bearing bone during growth.

Arnnaud, Sara B.↗