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Biomedical subjects

W K Ramp

Publications and source records attributed to W K Ramp.

At least 55 records · Page 3Linked to original sources
PubMed1979

Effects of calcium and cyclic nucleotides on rat calcitonin and parathyroid hormone secretion.

Recently we developed a system for studying concurrent secretion of calcitonin (CT)and parathyroid hormone(PTH)in vitro from single rat thyroparathyroid gland complexes. In the present study, mechanisms involved in secretion of CT and PTH were explored by altering the medium [Ca ] and by using the Ca antagonist, verapamil. We also re-examined the idea that cyclic nucleotides may help regulate secretion of these hormones and attempted to determine if effects of cyclic nucleotides might be altered by changes in medium [Ca]. Thyroparathyroid glands from 8-day-old rats were incubated in serum-free medium for 8h, and CT and PTH levels in the medium were measured by radioimmunoassays. We show for the first time that: (1) although low [Ca] is well known to promote PTH release, some extracellular Ca is needed for PTH secretion to occur at a maximal rate; (2) inhibition of Ca entry into cells with verapamil mimics the effects of low medium Ca on both CT and PTH release; and (3) cyclic nucleotides may exert their effects on secretion of CT and PTH at least in part via effects on Ca entry into cells.

Animals↗
PubMed1977

Magnesium and the mineral metabolism of chick embryo tibiae in organ culture.

Using bone organ culture techniques, three concentrations of magnesium were evaluated for their effects on the mineral mass of embryonic chick tibiae incubated for 3 days with or without a metabolic inhibitor (1 mM iodoacetic acid) added to the media. Varying the medium Mg level from 0.3 to 3.0 mM had little effect on the net increase in mineral in live bones (without the inhibitor), but in dead tibiae (with the inhibitor) there was a marked net decrease in mineral deposition with increasing Mg concentration. Bone Mg mass varied directly with the level of Mg in the medium regardless of whether or not the tibiae were inhibited. Responsiveness to parathyroid hormone (PTH) with regard to mineral loss and increased lactate production was not affected by Mg even in tibiae incubated in Mg-free media. However, PTH-treated bones cultured in Mg-free media had a significantly elevated Mg mass, suggesting that the hormone may have a Mg-conserving effect on bone during severe Mg deficiency. The findings of this study support the hypothesis that bone cells regulate the level of Mg to which newly forming mineral is exposed and that PTH-responsiveness in embryonic chick tibiae is not dependent on the ambient Mg concentration.

Animals↗
PubMed1977

Influence of dietary vitamin D3 on the circulating concentration of its active metabolites in the chick and rat.

Plasma concentrations of 25-hydroxyvitamin D3 (25-OHD3) and 1 alpha,25-dihydroxyvitamin D3 (1 alpha, 25-(OH)2D3) in growing chicks and weanling rats were measured by a new radioreceptor assay to determine the effects of varying dietary levels of vitamin D3. The plasma concentration of 25-OHD3 fell from 14.1 ng/ml in 1-day-old chicks to undetectable levels after 3 weeks on a rachitogenic diet. Circulating 1 alpha,25-(OH)2D3 hormone also decreased from 8.9 ng/100 ml to undetectable levels at 3 weeks in these chicks. Chicks receiving an optimal supplement of vitamin D3 (1.4 IU/g diet) for three to four weeks had plasma 25-OHD3 and 1 alpha,25-(OH)2D3 levels of 21-35 ng/ml and 5.1-7.5 ng/100 ml, respectively. Nutritional supplementation with a 50-fold excess of vitamin D3 (70 IU/g diet) elicited a substantial increase in plasma 25-OHD3 to 87-130 ng/ml, while plasma 1 alpha,25-(OH)2D3 was not increased. Increasing dietary calcium from 1.4 to 2.8% did not alter the circulating level of vitamin D3 metabolites in chicks fed 1.4 IU of vitamin D3/g diet. Direct measurement of the renal 25-OHD3-1 alpha-hydroxylase in vitro, showed that lowering dietary calcium or exclusion of vitamin D3 stimulated the biosynthesis of 1 alpha,25-(OH)2D3, but raising calcium did not alter the enzyme activity. It is concluded that the circulating concentration of the 1 alpha,25-(OH)2D3 hormone in the chick is unaffected by abnormally high intakes of vitamin D3 or calcium, but the renal production of the hormone increases during vitamin D3 or calcium deprivation. Additional studies in rats fed a diet supplemented with either 2 or 1000 IU of vitamin D3/g verify that the circulating concentration of 25-OHD3 is markedly increased when the dietary intake of vitamin D3 is elevated. Moreover, 1 alpha,25(OH)2D3 is not increased under these conditions, but actually falls significantly when the dietary level of vitamin D3 is raised from 2 to 1000 IU/g. These studies in both the chick and rat indicate that dietary vitamin D3 excess enhances circulating 25-OHD3, probably because the vitamin D3-25-hydroxylase enzyme is not strigently controlled. The fact that the circulating 1 alpha,25-(OH)2D3 is not concomitantly increased may reflect either decreased synthesis or increased utilization of the 1 alpha,25-(OH)2D3 sterol.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1976

Electron microscopic localization of lactate dehydrogenase in osteoclasts of chick embryo tibia.

Lactate dehydrogenase (LDH) was localized in osteoclasts of fixed and unfixed 19-day chick embryo tibias using a copper ferrocyanide capture reaction and osmiophilic polymer generation. This study revealed that: (I) LDH activity in fixed, briefly rinsed osteoclasts was associated principally with limiting membranes of cytoplasmic vacuoles and vesicles and with the plasma membrane; (2) LDH activity in unfixed osteoclasts was associated only with mitochondria; and (3) some mitochondria were stained in fixed tissue given a long rinse. These results indicate that: cytoplasmic LDH diffused out of unfixed tissue; mitochondrial LDH was inactivated by formaldehyde in fixed tissue; and formaldehyde-inhibited mitochondrial LDH can be reactivated by a long rinse. Although the vesicles that stained for LDH activity were found in all parts of the cell, they were concentrated near the ruffled border, and there is evidence that they contained material from the bone surface. These results suggest that the LDH associated with cytoplasmic vesicles of the osteoclasts may be important in processing of material resorbed from the bone surface and that osteoclasts mitochondria may utilize lactate from the bone fluid for energy production.

Animals↗
PubMed1976

Effects of dietary vitamin D and calcium on lysyl oxidase activity in chick bone metaphyses.

Activity of lysyl oxidase, an enzyme responsible for production of aldehydic precursors for lysine-derived collagen crosslinks, was measured in tibial metaphyses from chicks receiving different dietary levels of vitamin D and Ca for 2 weeks after hatching. Enzyme activities were increased twofold in D-deficient chicks compared to activities from chicks receiving control levels of vitamin D. Addition of Ca to the D-deficient diet had no effect on lysyl oxidase activity. It is suggested that vitamin D may play a role in the age-related decrease in lysyl oxidase activity that normally occurs in chick bone.

Age Factors↗
PubMed1975

The effect of vitamin D on the structural crosslinks and maturation of chick bone collagen.

The quantitative relationships were determined between the structural crosslinks, dihydroxylysinonorleucine (Lys(OH)2-Nle) and hydroxylysinonorleucine (Lys (OH) -Nle) in NaB 3H4-reduced diaphyseal bone collagen from 1-, 2-, 3- and 4-week-old chicks fed either a vitamin D-deficient diet, a normal-vitamin D diet or a high-, but non toxic, vitamin D diet from time of hatching. Chicks fed the normal diet showed a progressive decrease in the ratio of Lys(OH)2-Nle/Lys(OH)-Nle with age. This decrease was accelerated in chicks receiving the High-vitamin D diet. In the vitamin D-deficient group, the ratio was higher than controls at 1 and 2 weeks and increased further at 3 and 4 weeks. Similar changes in Lys(OH)2-Nle/Lys(OH)-Nle ratio did not occur in skin collagen. Compared to Control-vitamin D animals, the increased crosslink ratios in the vitamin D-deficient bone collagen occurred prior to changes in growth rate and could not be correlated with lysine hydroxylation or the hypocalcemia seen in this group. These results suggest that the type of crosslink analysis used in this study provides one of the earliest and most sensitive indications of a bone disturbance due to vitamin D deficiency and that vitamin D specifically acts to increase the rate of maturation of bone collagen.

Age Factors↗
PubMed1975

Effects of ethanol on chicks in vivo and on chick embryo tibiae in organ culture.

Hypocalcemia previously reported in rats and dogs following oral administration of ethanol may have been caused by a movement of calcium from blood to bone. This present study was undertaken to determine whether ethanol also causes hypocalcemia in chicks and to investigate the direct effects of ethanol on mineral accretion, glucose metabolism and growth of embryonic chick tibiae in an organ culture system. A high dose of ethanol (6 g/kg body wt) produced hypocalcemia, hypermagnesemia and an elevated hematocrit in chicks. Results in vitro were as follows: 1) 5 to 30 mul ethanol/ml medium produced dose-related increases in bone mineral from 58-440%; 2) lactate production was inhibited at all ethanol levels; 3) increased mineral accretion did not occur in ethanol-treated tibiae when iodoacetate was in the medium, but did occur in mechanically disrupted bones exposed to ethanol; and 4) the ethanol response in bone was directly related to the medium phosphate concentration. The results lead to the following conclusions: 1) ethanol has a direct stimulatory effect on bone mineral accretion and an inhibitory effect on bone glucose metabolism in vitro; 2) viable bone cells and an adequate phosphate supply are necessary for the ethanol response, but tissue integrity is not; and 3) the hypocalcemic effect of ethanol in vivo may at least partially result from ethanol-stimulated bone mineral deposition.

Animals↗
PubMed1975

The effects of fluoride on the mineralization of embryonic chick tibiae in organ culture.

The effects of various concentrations of fluoride on the mineralization of embryonic chich tibiae were studied in vitro. After 4 days incubation in medium with a physiological Ca x PO4 product (1.8 mM2), fluoride promoted a highly significant dose-related enhancement of bone mineralization. In experiments where the medium Ca x PO4 product was varied by changing either Ca or PO4 while keeping the other constant at 1.8 mM, fluoried at 7.5 muM or at 100 muM affected bone mineralization differbntly at low and high products. At medium Ca x PO4 products below 3 mM2, fluoride significantly enhanced bone mineral deposition compared to paired control bones, while at products above 5 mM2, fluoride significantly inhibited bone mineralization. This dual effect of fluoride was observed in both live bones and bones metabolically inhibited by 1 mM iodoacetic acid. Comparison of the effects of fluoride on the mineralization of live and dead bones suggested that the effects are dependent on the cellular control of Ca x PO4 product in the bone extracellular fluid. These findings support the hypothesis that fluoride may play an important role in governing the rate of mineralization in growing bones.

Animals↗
PubMed1975

Vitamin D, dietary calcium and parathyroid hormone interactions in chicks.

The effect of dietary vitamin D levels on the response to iv injected parathyroid hormone (PTH) was studies in chicks fed one of three diets: D-deficient, Control-D (1.4IU cholecalciferol/g diet), or High-D (70 IU cholecalciferol/g diet) during the first 4 weeks post-hatching. Compared to chicks on Control-D diet, chicks on the D-deficient diet had significantly decreased plasma Ca levels at 2 and 4 weeks and increased plasma P levels at 17 and 21 days. The plasma Ca response to a low dose of PTH (15 USP U/100 g body wt) 1 hr postinjection was normal at 1 week, reduced at 2 weeks and absent at 4 weeks in D-deficient chicks. However, a 4-16-fold higher dose of PTH did elicit a significant, though subnormal, response in this group at 3 and 4 weeks. Chicks fed the D-deficient diet with 2.8% Ca, compared to 1.4% Ca, showed a near normal plasma Ca level and bone ash content and only a small increase in plasma P at 17 and 21 days. However, the plasma Ca response to 15 U PTH/100 g body wt in this group was significantly increased only at 17 days and not at 21 days. In contrast, the hyperphosphatemic response to PTH was not markedly diminished in the D-deficient group, and it was restored to Control-D levels in the D-deficienyt High Ca group. These data suggest that different mechanisms may be involved in the Ca and P responses.

Animals↗