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Biomedical subjects

H Sheppard

Publications and source records attributed to H Sheppard.

At least 37 records · Page 2Linked to original sources
PubMed1980

Effects of ascorbic acid on 3H-thymidine incorporation by isolated mouse thymocytes.

The 15-min incorporation of 3H-thymidine (Tdr) and 3H-uridine (Ur) into nucleic acids of freshly isolated mouse thymocytes decreased steadily with time of preincubation at 37 degrees C. Sodium ascorbate at 5 mM prevented the decline of 3H-Tdr incorporation by preventing the decrease in its uptake. No such effect was noted on the incorporation of 3H-Ur, suggesting that ascorbate might be more specific for cells in or near the S phase of the cell cycle. The ene-diol group on the ascorbate molecule was required for this function, as ascorbyl-2-sulfate was ineffective and dehydroascorbate (DHA) reduced 3H-Tdr incorporation even further. Ascorbate was also inhibitory at a lower concentration (0.1 mM) or lower cell density. Thiols such as dithiothreitol or reduced glutathione seemed to act like 0.1 mM rather than 5 mM ascorbate. The inhibition by 0.1 mM ascorbate was presented by 0.1% bovine serum albumin (BSA), catalase or anaerobiosis. BSA had its own protective effects on the cells, since at 0.1% it increased the uptake of both 3H-Tdr and 3H-Ur. The combined effects of 5 mM ascorbate and 0.1% BSA on 3H-Tdr uptake were additive, but some synergism was noted at the lower BSA concentrations. These results suggest that with low concentrations of ascorbate (0.1 mM) oxidative reactions occur in vitro, resulting in the accumulation of the toxic hydroxyl radical (. OH). High concentrations apparently override this inhibition by a mechanism possibly involving an increase in critical cellular thiol groups.

Animals↗
PubMed1980

The regulation of nucleotide metabolism of immune cells: papaverine induced nucleotide breakdown.

During a period of prelabeling of mouse thymus cells with any nucleoside at 4 degrees C, nucleoside phosphates accumulated, but no nucleic acid synthesis occurred. Elevating the temperature to 37 degrees C then led to incorporation into the respective nucleic acid reaching a maximum in 5--15 min. Papaverine inhibited this incorporation (IC50:50 muM) and caused an efflux of label into the medium as a nonphosphorylated product. The responses of the different nucleotide phosphate pools showed more dependency on the base then the sugar moeity. The effect of papaverine could not be altered or mimicked by deprivation of oxygen, glucose, or calcium. Mouse spleen cells responded like thymocytes to papaverine, but rat GH3 pituitary cell DNA syntesis was only transiently inhibited with no concomitant efflux of 3H into the medium. As expected, thymus cellular adenosine triphosphate (ATP), determined by the luciferin-luciferase reaction, decreased in the presence of papaverine; suprisingly, extracellular ATP fell as well. The results suggest that decreases in cellular ATP of mouse thymus cells leads to reductions of all nucleoside phosphates and the efflux of the resultant nucleosides. Papaverine may effect a decrease in the ATP levels by activating a phosphohydrolase rather than, or in addition to, the previously suggested inhibition of mitochondrial electron transport.

Animals↗
PubMed1980

The effect of rehabilitation at different stages of development of rats marginally malnourished for ten to twelve generations.

1. Rats which have been maintained for ten to twelve generations on diets of low protein value were rehabilitated in utero (group P), from birth (group F) and from 4 weeks of age (group W). 2. Group W showed little change in physique, behaviour or learning, indicating that for recovery to be effective refeeding must begin earlier. 3. Group F just failed to attain full physical recovery (90%) whereas group P overgrew by 18.6% in weight and 8.5% in length. 4. In a test designed to evaluate learning ability rehabilitated rats of groups P and F were significantly less successful than normal rats, but more successful than rats of group W or rats of the original undernourished colony. 5. Rehabilitation for a further two generations in groups F and P corrected any residual physical and behavioural defects but produced no further improvement on the Lashley (1938) jumping platform.

Acoustic Stimulation↗
PubMed1978

The effect of dihydroxy-2-aminotetraline (DATs) on dopamine and beta type adenylate cyclases.

A number of DATS have been studied for agonist activity with dopamine (DA) and beta (beta) type adenylate cyclases and the most potent ones were found among the 6,7-DATs and the 5,6-DATs, respectively. None of the compounds tested possessed antagonist activity. The observed activities were not expected on the basis of structural analysis of model compounds such as apomorphine and 6,7-dihydroxy-1-benzyltetrahydroisoquinoline. A new view was constructed which suggests that the nitrogens of the DAT compounds were positioned better than those of the model compounds with regard to their binding sites.

Adenylyl Cyclases↗
PubMed1978

Retained inhibition of the beta receptor by propranolol after preincubation and washout.

Mouse thymus cells possess a B2-adrenergic receptor and, when centrifuged through a solution of propanolol at 5 degrees and washed three times, will produce reduced amounts of cyclic AMP during a 5 minute challenge with isoproterenol at room temperature. Depending on the concentration and nature of the antagonist, the retained inhibition may be greater or less than that seen when it is added with the agonist. This retained inhibition is readily reversed at 37 degrees even in the absence of the agonist. These effects can also be demonstrated with rat erythrocytes and with their subsequently prepared ghosts making it most likely that they result from the specific and tight binding of the antagonist to the beta receptor.

Adrenergic beta-Antagonists↗
PubMed1977

Effect of hydroxy-vitamin D3 derivatives on 45Ca release from rat fetal bones in vitro.

Several hydroxy vitamin D3 (OH-D3) derivatives were tested for biological activity by measuring 45Ca release from prelabeled rat fetal bones, in vitro. In a 72 h continuous culture, 1 alpha,25-(OH)2-D3 produced a significant effect at 10 pg/ml. A similar effect was produced by 50 ng/ml of either 25-OH-D3 or 5,6-trans-25-OH-D3, and by 500 pg of 3 deoxy-1 alpha,25-(OH)2-D3. 24R,25-(OH)2-D3 was more active than 24S,25-(OH)2-D3, and the R isomer had activity that more closely resembled the biosynthetic compound. 3-deoxy-1 alpha-OH-D3 was inactive at a concentration of up to 1 microgram/ml. Using a 24 h preincubation period with no added vitamin D3 derivative, a steep dose-response curve could be obtained with 1 alpha,25-(OH)2-D3 over a range of 2-10 pg/ml during a subsequent 96 h incubation period, and 1 alpha,25-(OH)2-D3 was found to have about 5000 times the activity of 25-OH-D3.

Animals↗
PubMed1977

A structure-activity analysis of the preferred conformation of the benzyl substituent of tetrahydropapaveroline at the beta receptor.

The effect of restricting the motion of the 3,4-dihydroxybenzyl substituent of tetrahydropapaveroline (THI) on its ability to stimulate the beta adenylate cyclase of the rat erythrocyte was investigated. A number of protoberberines and aporphines were tested as models of two classes of compounds where the benzyl substituent is rigidly but differently fixed. Unexpectedly, the beta agonist activity was associated with both structural types. This could be explained by the assumption that a phenylalanyl or tyrosyl residue of the receptor protein is free to rotate and bind with either position of the benzyl moiety as fixed in the protoberberine and aporphine structures.

Adenylyl Cyclases↗
PubMed1976

Increase of cyclic GMP induced in murine thymocytes by thymosin fraction 5.

Using a radioimmunoassay (RIA) for the determination of adenosine 3'5' cyclic monophosphate (cAMP) and an acetylation-RIA procedure to measure guanosine 3'5' cyclic monophosphate (cGMP), we observed that cGMP levels, but not cAMP levels, were significantly elevated in murine thymocytes which had been incubated with preparations containing the thymic hormone, thymosin. Stimulation of intracellular cGMP levels was seen as early as 1 minute after incubation with thymosin fraction 5 and was maximal at approximately 10 minutes. Dose response studies indicated an optimum stimulation of cGMP with a thymosin concentration of 100 microg/ml. A control spleen fraction prepared by an identical procedure as fraction 5 did not affect the levels of either cyclic nucleotide.

Animals↗
PubMed1975

Calcium balance in children treated with diphosphonates.

Serial mineral balances have been obtained in 3 children undergoing therapy with EHDP (ethane-1-hydroxy-1, 1-diphosphonate) for diseases involving ectopic calcification. Although clinical outcome was not uniformly satisfactory, all cases showed an overall reduction in calcium balance. This was due to increased faecal excretion of calcium and was most marked after a long duration of therapy. Although these results conflict with reported experience in adults, they are in agreement with published observations of the effects of EHDP on calcium absorption in experimental animals.

Adenosine Monophosphate↗
PubMed1975

Alterations in the hydrolytic activity, inhibitor sensitivity and molecular size of the rat erythrocyte cyclic AMP phosphodiesterase by calcium and hypertonic sodium chloride.

Hypertonic NaCl irreversibly reduced the sensitivity of the rat erythrocyte cyclic AMP phosphodiesterase to inhibition by Ro 20-1724 but not by papavarine. This effect could be prevented by 1 mM EDTA and mimicked by by CaCl2. The reduction in inhibitor sensitivity was associated with an increase in hydrolytic activity and a four-fold reduction in molecular weight as estimated by Sephadex G-200 chromatography. The response to CaCl2, like that to NaCl, was time and concentration dependent and proceeded more slowly in 2 M NaCl. This concentration of NaCl contained sufficient Ca++ as an impurity to account for its effects on inhibitor sensitivity and molecular size. However, the initial and reversible increase in inhibitor sensitivity and hydrolytic activity obtained in the presence of EDTA, probably resulted from the high salt concentration, per se.

3',5'-Cyclic-AMP Phosphodiesterases↗