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Biomedical subjects

R Silver

Publications and source records attributed to R Silver.

At least 127 records · Page 7Linked to original sources
PubMed1982

Erythropoietin production in response to anemia or hypoxia in the newborn rat.

Erythropoietin production in response to hypoxic-hypoxia is markedly reduced in the newborn when compared to the adult rat. This response improves steadily with age and reaches adult values at about 4 wk. When animals of the same age are stimulated with anemic-hypoxia, considerably higher levels of erythropoietin are found. The erythropoietin level is proportional to the degree of anemia and independent of the age of the animal. Extraction of erythropoietin from tissue homogenates revealed a parallelism between the plasma and kidney erythropoietin content, while no erythropoietin could be extracted from liver tissue at any age. The lack of response to hypoxia in the newborn appears to be related to the high hemoglobin oxygen affinity during the neonatal period, which facilitates oxygen loading. Newborn rats have a very low intraerythrocytic concentration of 2-3 DPG and a marked shift to the left in the oxygen hemoglobin dissociation curve that slowly increases to adult values at 4 wk of age. The response to anemia on the other hand, appears to be normal and not affected by age or by hemoglobin oxygen affinity. These studies suggest that the newborn rat, when properly stimulated, is able to produce normal amounts of erythropoietin, most likely renal in origin.

Anemia↗
PubMed1981

Effects of high glucose and high lard diets on the activities of rat liver glycosyltransferases.

The activities of several enzymes involved in glycoprotein synthesis were measured in the livers of rats (L) fed diets with 67% of calories as lard and compared with those of rats (G) fed 67% glucose diets for 5-9 days. Glucosamine synthetase activity was not influenced by diet, but the activities of UDP-N-acetylglucosaminyl, galactosyl and sialyltransferases were significantly greater in the livers of the rats fed the glucose diet than in L rat livers. The content of UDP-N-acetylglucosamine was also higher in G livers than in the L group. Activities of glycosidases and of sugar nucleotide pyrophosphatases and phosphatases were the same on both diets. Serum total hexosamine was higher in L than in G rats. These findings are discussed in relation to earlier reports that liver plasma membranes from G rats contained more glycoprotein carbohydrate than L membranes.

Animals↗
PubMed1981

Concentrations of prolactin and luteinizing hormone in plasma of doves in relation to incubation and development of the crop gland.

The concentrations of prolactin and LH were measured in the plasma of male and female ring doves (Streptopelia risoria) during the breeding cycle. Prolactin concentrations were low during courtship and early incubation but increased markedly (P less than 0.01 in both sexes) between days 7 and 15 of incubation, during the period of rapid growth of the crop sac. Levels remained raised for 4 days after the young had hatched but then declined as the crop sacs gradually regressed. These observations showed that concentrations of prolactin were high at the time when the crop sacs were proliferating and producing 'milk' for feeding the young, but that there was no increase in prolactin secretion at the onset of incubation as occurs in ducks, hens and other birds. In samples taken from doves at various times of the day and night there was no increase in plasma prolactin during the first few days of incubation. Concentrations of LH in plasma were generally higher in male doves than in females, but in both sexes were significantly higher during courtship than during incubation and brooding the young. Concentrations increased again when the young were independent and the parents began a second round of courtship.

Animals↗
PubMed1981

Erythropoietin production in fasted rats. Effects of thyroid hormones and glucose supplementation.

The effect of T3 replacement and glucose supplementation on erythropoietin production was investigated in fasted hypoxic rats. It was found that 48 hr of fasting significantly reduced the circulating levels of thyroid hormones and the production of renal and extrarenal erythropoietin in response to hypoxia. These effects of fasting were completely abolished when the animals had free access to 25% glucose solution as drinking water, despite their lack of protein intake. Replacement doses of T3 (0.5 micrograms/100 gm per day) restored erythropoietin production in the fasted animals but also increased the response of the fed controls. To avoid the effect of endogenous T3, the experiments were repeated in thyroidectomized rats. Erythropoietin production in athyroid rats was found to be markedly decreased, with values equivalent to those found in normal fasted animals, and were not affected by fasting or glucose supplementation. Replacement doses of T3 increased erythropoietin production in all three groups, but the fasted animals needed five times as much T3 to obtain a response similar to that observed in the fed group. Glucose supplementation enhanced the effect of T3 in the fasted animals but did not completely restore it. These results indicate that caloric deprivation is primarily responsible for the decreased erythropoietin production induced by fasting and that this effect is probably mediated by both a decreased level of T3 and a decreased responsiveness to it.

Acid-Base Equilibrium↗
PubMed1980

Renal and extrarenal erythropoietin production in anaemic rats.

Rats were rendered anaemic by a single bleeding or by a single injection of phenylhydrazine. At various times after the onset of anaemia they were nephrectomized and challenged with a 6 h exposure to hypoxia. The erythropoietin titre observed at the end of this hypoxic period was corrected for renal erythropoietin induced by the anaemia alone, and the resulting extrarenal component was compared to total erythropoietin production of nephric rats in response to anaemia plus 6 h hypoxia. Extrarenal erythropoietin production was found to increase from 10.3% in normal rats to 12.5% in moderately anaemic rats to 15.1% in rats with severe bleeding anaemia. In phenylhydrazine-treated rats this extrarenal component was found to be 18.3% possibly due to stimulation of extrarenal erythropoietin by haemolysed red cells. Chronic phenylhydrazine administration resulted in splenomegaly and Kupffer cell hyperactivity but not in any further stimulation of extrarenal erythropoietin production.

Anemia↗
PubMed1980

The biogenesis of erythropoietin.

Aerobic living demands a constant supply of oxygen at the cellular mitochondrial level. Numerous interlocking feedback mechanisms insure the constancy of this supply by adapting the supply lines to changes in the intra and extracellular milieu. Among these mechanisms is the feedback circuit which, triggered by an intracellular decrease in oxygen supply, initiates the production of a polypeptide hormone, erythropoietin, which in turn augments the production of an oxygen carrier, the hemoglobin-containing red cell. The biogenesis of this hormone is an important biologic process which is being studied intensively and slowly unravelled.

Animals↗
PubMed1979

Effects of an observer on eating behavior: the induction of "sensible" eating.

An experiment was conducted to investigate the extent of caloric compensation to differential preloading among normally restrained and unrestrained female subjects. Subjects' eating was either explicitly observed or unobserved by the experimenter. Unrestrained eaters compensated appropriately for the preload, whether or not they were observed. Restrained eaters failed to compensate when unobserved , but compensated strongly when observed. A subsequent unobserved eating task revealed that restrained eaters failed to compensate for prior consumption when the observer was withdrawn. Implications for research and therapy are discussed.

Awareness↗
PubMed1977

Visual acuity and contrast sensitivity in multiple sclerosis--hidden visual loss: an auxiliary diagnostic test.

In 48 patients with multiple sclerosis sine-wave gratings were used to test visual sensitivity for coarse, medium, and fine detail rather than measuring visual acuity for fine detail only, as in conventional clinical tests. In 20/48 patients the test revealed a visual defect of neural origin, qualitatively different from that caused by refractive error. In 11 of these 20 patients, visual sensitivity to detail of medium coarseness was markedly degraded, even though sensitivity to both coarse and fine detail was unimpaired. In 3 of these 20 patients visual sensitivity to coarse detail was selectively degraded. These visual defects could not be detected by the Snellen test, yet the patient might experience visual problems in everyday life and also experience distorted visual perception. Possible neural bases for these visual impairments are discussed. Since 8 of the 14 patients with selective loss showed no clinical evidence of visual involvement, the test can aid the earlier diagnosis of multiple sclerosis.

Adolescent↗
PubMed1977

Effect of body temperature on visual evoked potential delay and visual perception in multiple sclerosis.

Seven multiple sclerosis patients were cooled and four heated, but evoked potential delay changed in only five out 11 experiments. Control limits were set by cooling eight and heating four control subjects. One patient gave anomalous results in that although heating degraded perceptual delay and visual acuity, and depressed the sine wave grating MTF, double-flash resolution was improved. An explanation is proposed in terms of the pattern of axonal demyelination. The medium frequency flicker evoked potential test seems to be a less reliable means of monitoring the progress of demyelination in multiple sclerosis patients than is double-flash campimetry or perceptual delay campimetry, although in some situations the objectivity of the evoked potential test would be advantageous.

Body Temperature↗