Search PubMed⌕ Search

Biomedical subjects

S H Doppelt

Publications and source records attributed to S H Doppelt.

29 records · Page 2Linked to original sources
PubMed1982

Gut-mediated hypercalcemia in rabbits bearing VX2 carcinoma: new mechanism for tumor-induced hypercalcemia.

The VX2 carcinoma-bearing rabbit is an animal model for tumor-induced hypercalcemia, thought to be due to increased bone destruction effected by prostaglandin E2. The present experiments suggest that the pathophysiology of the hypercalcemia differs from that previously proposed. Tumor was transplanted intramuscularly into 2.5- to 3-kg male New Zealand White rabbits, which were conditioned to a 1.5% calcium diet and treated with daily subcutaneous injections of dichloromethane diphosphonate (10 mg . kg-1 . day-1), a potent inhibitor of bone resorption, or 0.9% NaCl (2 ml . kg-1 . day -1). The diphosphonate had no significant effect on plasma Ca2+ in either group. After day 31, half the animals of each group were fed a calcium-free diet. This normalized the plasma Ca2+ in each VX2-bearing rabbit within 3 to 4 days but had little effect in control rabbits. In a second series of experiments, VX2-bearing rabbits maintained on standard rabbit chow were treated for 11 days with parenteral indomethacin (30--60 mg/day) or 0.9% NaCl. Although indomethacin normalized the markedly elevated urinary excretion of prostaglandin E2, both treatment groups became severely hypercalcemic. Dietary calcium restriction promptly restored to normal the plasma Ca2+ concentration. In a third series of experiments, rabbits were fed standard rabbit chow and treated with oral indomethacin (40 mg/day) while control-rabbits were pair fed in identical chow. Transplantation of VX2 tumor into both groups caused hypercalcemia. We conclude that the hypercalcemia produced by this tumor strain is indomethacin resistant and dependent on an increase in gastrointestinal calcium absorption, not on skeletal calcium mobilization.

Animals↗
PubMed1981

Regulation of cutaneous previtamin D3 photosynthesis in man: skin pigment is not an essential regulator.

When human skin was exposed to simulated solar ultraviolet radiation, epidermal 7-dehydrocholesterol was converted to previtamin D3. During prolonged exposure to simulated solar ultraviolet radiation, the synthesis of previtamin D3 reached a plateau at about 10 to 15 percent of the original 7-dehydrocholesterol content, and previtamin D3 was photoisomerized to two biologically inert isomers, lumisterol3 and tachysterol3. Increases either in skin melanin concentration or in latitude necessitated increases in the exposure time to simulated solar ultraviolet radiation required to maximize the formation, but not the total content, of previtamin D3. In order of importance, the significant determinants limiting the cutaneous production of previtamin D3 are (i) photochemical regulation, (ii) pigmentation, and (iii) latitude.

Animals↗
PubMed1981

Operational and financial aspects of a hospital bone bank.

Although bone banks have existed for many years, the elements of organizing and maintaining a hospital bone bank have not been well documented. The experience with a bone bank at the Massachusetts General Hospital between 1971 and 1980 provides a model on which to base an explanation and discussion of methods of procurement, storage, and retrieval, and the costs associated with such a facility. In 1979, the procurement rate averaged one donor per month; during that year a total of ninety-one bones were stored and six different surgeons utilized more than twenty allografts from the bank. During the same year, the approximate cost of maintaining the bank was more than $50,000. On the basis of the number of bones used, the cost averaged more than $2000 per implant. Such a hospital facility offers the benefits of quality control of the banked bone but is expensive and may not be feasible for many hospitals.

Adolescent↗
PubMed1976

An interpretation of acute changes in plasma 45Ca following parathyroid hormone administration to thyroparathyroidectomized rats.

Acute changes in plasma calcium and 45Ca were studies in young adult male thyroparathyroidectomized (TPTX) rats injected with moderate doses of parathyroid hormone (PTH). For plasma calcium changes, comparison was made between rats fasted or fed prior to PTH injection. For plasma 45Ca changes, the effect of the time of administration of the radionuclide was also studied; this included rats injected with PTH 1 h after radionuclide ("1 h 45Ca"), 18 h later ("18 h 45Ca") and more than 6 days later ("6 day 45Ca"). The results can be summarized as follows: (1) Plasma calcium changes were greater when PTH was injected into "fed" rather than into "fasted" rats. (2) PTH always produced a relative increase (compared to controls tested concurrently) in plasma 45Ca concentrations. This increase was the same in the "1 h 45Ca" and the "18 h 45Ca" group. (3) Plasma 45Ca rose at least temporarily following PTH injection in the "18 h 45Ca" group. (4) The 45Ca rise following PTH was always greater in "fed" than in "fasted" groups. (5) Plasma 45Ca specific activities (S.A.) tended to rise in the "6 day 45Ca" group and to fall in the "18 h 45Ca" group, following PTH injection. However, the 45Ca S.A. was always higher in fed than fasted groups. (6) In a few experiments in which 32P was injected with 45Ca, specific activity changes in plasma 45Ca following PTH injection were not accompanied by similar changes in 32P specific activity. These results could not be adequately explained by PTH effects on bone resorption, but the data supported the postulate that PTH controls plasma calcium concentrations by increasing transport of calcium through the osteocyte-lining cell (osteoblast) bone cell complex from the bone fluid compartment to the ECF.

Animals↗
PubMed1975

Relationship of blood concentrations of calcium, phosphate, gastrin and calcitonin to the onset of feeding in the rat.

Daily fluctuations in plasma calcium concentrations in rats trained to a closely regulated feeding pattern have been compared to corresponding plasma gastrin and calcitonin concentrations. The time period studied was that extending from 4 hr prior to the start of the feeding. Both plasma calcium and phosphate levels fedd prior to the start of the feeding period and remained low at least for the first 2 hr of feeding. This pattern was also observed in rats in which food was withheld for 2 hr past the regular feeding time. Plasma 45Ca and 32P concentrations (radionuclide injected at least one week prior to sampling) did not follow the pattern of their stable counterparts. Instead, these values rose or remained constant until after feeding had commenced, after which they fell precipitously. Both plasma calcitonin and gastrin levels rose rapidly after the start of the feeding period. The primary point of emphasis is that calcitonin secretion was produced in these rats by an intestinal related stimulus and not by a rise in plasma calcium concentration.

Animals↗
PubMedDate not supplied

Quantitative computed tomography for spinal density measurement. Factors affecting precision.

Quantitative computed tomography (QCT) was performed in duplicate on 84 patients to test the short-term precision of the technique. Statistical analysis of the data revealed that precision was not a function of spinal density. It appeared to be worse in osteopenic individuals only when expressed as a percentage. Precision was slightly better in male than in female patients. There is a 90% likelihood that a duplicate measurement will fall within 20 CT units of the first determination in female patients and within ten units in male patients.

Adult↗