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Biomedical subjects

W Wu

Publications and source records attributed to W Wu.

At least 487 records · Page 27Linked to original sources
PubMed1985

Effect of maturation and age on lymphocyte proliferation induced by A23187 through an interleukin-independent pathway.

Lymphocyte proliferation induced by lectins declines drastically with age. It has been suggested that the reduction of interleukin production by lymphocytes from old individuals is responsible for the decline in proliferation. In this study, lymphocyte proliferation was stimulated by the calcium ionophore, A23187. A23187 induced the proliferation of spleen lymphocytes from rats through an interleukin-independent pathway; depletion of spleen lymphocytes of macrophages, addition of exogenous interleukin 2 (IL 2), and addition of anti-IL 2 monoclonal antibodies had no effect on the proliferation stimulated by A23187. Spleen lymphocytes from male Fischer F344 male rats of 5, 13, 22, and 30 months of age were stimulated with either concanavalin A (Con A) or A23187. A 50% decrease in Con A- and A23187-induced proliferation was observed between 5 months and 13 months of age. A23187-induced proliferation decreased only slightly between 13 months and 30 months of age (14%), while Con A-induced proliferation decreased by 34%. This is the first report to show that the induction of lymphocyte proliferation through an interleukin-independent pathway decreases with increasing age. In addition, these results suggest that a decrease in the responsiveness of cells to calcium ions might be an important factor in the age-related decline in lymphocyte proliferation.

Aging↗
PubMed1985

Chemical softening and wear of dental composites.

The purpose of this work was to determine the influence of chemical food-simulating liquids on the wear of various commercial dental composite restoratives. In many cases, pre-conditioning the restoratives in these liquids for one week produced swelling of the polymer matrix and considerable surface damage. The resulting degradation reduced the hardness and enhanced the wear as measured by a pin-and-disc apparatus. Four kinds of commercial composites were investigated: a conventional quartz-filled, a strontium-glass-filled, a visible-light-activated, and a microfilled composite. The liquids employed were heptane and several aqueous solutions of ethanol with solubility parameters, delta, ranging from delta = 1.5 to 4.8 X 10(4) J1/2m-3/2. With all restoratives, the decline in hardness during pre-conditioning maximized at about delta = 3 X 10(4), which corresponds to a 75% ethanol solution. The wear behavior was considerably more complicated and variable, as discussed in the text. For the most part, the increase in wear rate from pre-conditioning corresponded to the fall in hardness. A notable exception was for the strontium-glass-filled composite pre-conditioned in pure water. Here the wear was enhanced considerably, with no decrease in hardness. In this case, the degradation mode is assumed to be different from the others in that it is attributed to stress corrosion of the glass filler.

Acrylic Resins↗
PubMed1985

Twenty-four-hour profiles of prolactin and testosterone in ram lambs exposed to skeleton photoperiods consisting of various light pulses.

Individual groups of 6 ram lambs were housed within a controlled environment and exposed to one of 6 photoperiod schedules. Groups I and II received 8 (short day) or 16 (long day) h of continuous light, respectively; Groups III, IV and V were exposed to asymmetrical skeleton photoperiods consisting of a main light period of 7 h followed 9 h later by a light pulse of 1 h, 15 min or 1 min duration, respectively, and Group VI was exposed to a symmetrical skeleton photoperiod consisting of two 1-h light pulses positioned 16 h apart. After 4 weeks of treatment serum concentrations of prolactin and testosterone were measured over 24 h. Long-day responses characteristic of the 16L:8D photoperiod (i.e. elevated prolactin and reduced testosterone) were obtained in each of the asymmetric light-pulse treatment groups, but whereas prolactin was elevated over the full 24 h in lambs exposed to 16L:8D, two prominent nocturnal prolactin releases were largely responsible for the high 24-h mean prolactin values in Groups III, IV and V. Reduced serum testosterone in these same groups could not be attributed to a diurnal pattern of secretion but was associated with an overall decrease in testosterone pulse frequency. Prolactin and testosterone levels in Group IV were intermediate between those observed in lambs exposed to 8 or 16 h of light. In summary, light pulses of short duration (1 min) positioned at 17 h after dawn can produce endocrine changes in lambs similar to those observed in lambs exposed to 16 h of continuous light.

Animals↗
PubMed1984

Vasopressin release from individually superfused neurohypophyses decreases in aged rats.

We studied the effect of aging on vasopressin (VP) release from isolated neurohypophyses (NH) individually superfused with synthetic medium TC 199 with Hanks' salts. The superfusion technique is described in detail. Male Fisher 344 rats 2 months (young, n = 17), 12 months (adult, n = 14) and 30 months (old, n = 17) of age were used. VP was measured by radioimmunoassay (RIA). The age-related VP release was analyzed as follows: initial traumatic release, basal release, VP release evoked by electrical stimulation (10-second trains every 20 s of matched biphasic stimuli, 0.2 ms width, 8 mA, 30 Hz), by chemical stimulation (56 mM K+) and total release for the entire superfusion period. When VP release was expressed per milligram NH, it was significantly lower under all conditions in the old rats than in the young ones. In the adult rats, traumatic, basal and total release values were similar to those of the young rats, whereas their responses to chemical and electrical stimulation were similar to those of old rats. Residual VP content expressed per whole NH was significantly higher in the old and adult rats, reflecting a larger glandular size, but when expressed per milligram NH tissue, it was low in the old rats. The percent of VP released during the entire superfusion period relative to the residual VP content was significantly lower in the old than in the young and adult rats. The magnitude of the maximal VP release exceeding the basal release, in response to electrical and chemical stimulation, was similar in young and old rats. However, in the adult rats it was significantly lower than in both the young and old following chemical stimulation. A significantly larger number of old and adult NHs exhibited a more delayed response to chemical, but not to electrical stimulation, than did the young NHs. These data demonstrate an age-related decrease in VP release in Fisher 344 rats. Since the traumatic and basal VP release in the adult rats is similar to the release in the young rats, while the stimulated release in the adult rats resembles the response of the old animals, the results suggest that an impairment of stimulated VP release occurs at an earlier stage of the aging process than does an impairment of spontaneous (traumatic and basal) release.

Aging↗
PubMed1984

Subsurface damage layer of in vivo worn dental composite restorations.

Dental composite restorations have been examined using a silver staining method to elucidate in vivo wear mechanisms. Emphasis was placed on examination of material immediately beneath the wearing surfaces. Several in vitro tests were also investigated for their ability to generate in vivo-like surface defects. For all the clinically worn composite restorations, a porous layer has been observed beneath those surfaces exposed to the oral environment. A laboratory test using certain substances to simulate the oral environmental effects can reproduce this porous layer. These results suggest that the in vivo wear process of dental composites is one accelerated by environmental softening of the composites.

Acrylic Resins↗
PubMed1983

The effect of microwave irradiation on vasopressin in plasma and hypothalamo-neurohypophyseal system.

Radioimmunoreactive vasopressin was measured in plasma, neurohypophysis and hypothalamus of the rats after different procedures of killing: a) microwave irradiation; b) decapitation; c) decapitation following a stress induced by immobilization in a restrainer. Vasopressin content in the neurohypophysis and hypothalamus was much lower in microwave irradiated than in both decapitated and stressed decapitated rats. In addition, the data from microwave technique were inconsistent with a large scatter. Plasma vasopressin concentration was elevated in both the microwave irradiated and stressed decapitated rats, demonstrating that restraining of the animals induced an excessive stress. Microwave irradiation technique including the necessary manipulation of the animal proved to be less suitable than decapitation technique for the measurement of vasopressin. It is likely that vasopressin in the hypothalamus and neurohypophysis is relatively resistant against post-mortem proteolysis.

Animals↗
PubMed1983

Detecting margin leakage of dental composite restorations.

The degree of microleakage between a restoration and the cavity wall is difficult to quantify objectively. A silver-staining method is used and compared to the radioisotope method with results that indicate a superior definition and more accurate evaluation of microleakage. In addition to the accuracy, two advantages are presented: (1) scoring of the leakage can be refined and divided into more precise numbers, and (2) teeth can be observed directly in a microscope without resorting to the indirect interpretation of film or photograph.

Calcium Radioisotopes↗
PubMed1983

The effect of aging on vasopressin system in Fisher 344 rats.

Vasopressin (VP) was measured by RIA in the plasma, neurohypophysis (NH) and hypothalamus (HT) of young (2 months), adult (12 months) and old (30 months) male Fisher 344 rats, ten of each age. Plasma VP concentration was significantly lower in old compared to adult and to young rats. VP content in the NH expressed per mg weight was similar in all three groups, while the hypothalamic VP content was decreased in the aged rats. This suggests that reduced synthesis and release and/or increased degradation of VP occurs in aged rats. These data are in an agreement with our previous results obtained with Sprague-Dawley rats indicating that these differences are not strain-related. In a pilot experiment, we further studied VP release from isolated perifused NH of young and old rats. Two glands of each age were simultaneously perifused in individual microchambers with medium TC 199 and subsequently stimulated by Locke's medium containing 56 mM K+. Both, the initial and the basal VP release from the NH of the old rats, as well as the response to high K+, were about a half that of the young rats. Thus, a decreased VP release may contribute to the findings of lower plasma VP concentration in aged rats.

Aging↗
PubMed1982

Relationship between subsurface damage and wear of dental restorative composites.

Pin and disc wear measurements were made on a commercial dental composite over a stress range from 2.5 to 20 MPa. The wear rates were found to increase suddenly during wear at times which tended to decrease with increasing stress. The results are interpreted in terms of wear mode conversion which results from the build-up of subsurface damage during wear. Micrographs showing damaged layers are compared with those from restorations worn in vivo.

Adhesiveness↗
PubMed1981

A silver staining technique for investigating wear of restorative dental composites.

A silver staining technique was developed to demonstrate microdefects in dental restorative composites. Fine silver particles were preferentially introduced into the damaged region to provide optical contrast between the damaged and the undamaged regions. The amount of silver deposition determined with an electron probe microanalyzer, provided an indication of the extent of damage within the dental composites. Examples to demonstrate this technique were given with one clinically worn dental composite restoration and one in vitro worn composite sample.

Dental Materials↗
PubMed1980

Purification of Torpedo californica post-synaptic membranes and fractionation of their constituent proteins.

A rapid methof for preparation of membrane fractions highly enriched in nicotinic acetylcholine receptor from Torpedo californica electroplax is described. The major step in this purification involves sucrose-density-gradient centrifugation in a reorienting rotor. Further purification of these membranes can be achieved by selective extraction of proteins by use of alkaline pH or by treatment with solutions of lithium di-idosalicylate. The alkali-treated membranes retain functional characteristics of the untreated membranes and in addition contain essentially only the four polypeptides (mol.wts. 40000, 50000, 60000 and 65000) characteristic of the receptor purified by affinity chromatography. Dissolution of the purified membranes or of the alkali-treated purified membranes in sodium cholate solution followed by sucrose-density-gradient centrifugation in the same detergent solution yields solubilized receptor preparations comparable with the most highly purified protein obtained by affinity-chromatographic procedures.

Alkalies↗