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Biomedical subjects

R M Garcia

Publications and source records attributed to R M Garcia.

13 recordsLinked to original sources
PubMed2001

Effects of decrease of extracellular sodium in carbachol-evoked catecholamine secretion in isolated adrenal medullae of rats.

The effect of extracellular Na(+) deprivation on the carbachol-evoked catecholamine secretion was evaluated in chromaffin cells. Isolated adrenal medullae of male Wistar rats were incubated in solutions with different sodium concentrations (144,0; 75,0; 25,0 and psi mM). Catecholamine secretions inversely increased as a response to fall of extracellular concentration of sodium. The magnitude of response to cholinergic stimulus (carbachol 100 microM) was decreased in low extracellular sodium concentration. Atropine (100 microM) inhibited secretion of catecholamine induced by carbachol in the presence and in the absence of extracellular sodium. Results suggest that in isolated adrenal medullae of rats (1) decrease in concentration of extracellular sodium increases secretion of catecholamines, perhaps by a greater influx of calcium from the extracellular environment through reversal of Na(+) /Ca(2+) exchanger; (2) intensity of catecholamine secretion induced by cholinergic stimulus seems to depend on extracellular sodium.

Adrenal Medulla↗
PubMed1999

Glucose does not affect catecholamine stimulus-secretion coupling in rat adrenal medulla: relationship to low changes in osmolarity and to insulin.

Glucose levels were analyzed to see whether they directly affect the catecholamine release from chromaffin cells. We incubated isolated adrenal medullae of rats in Krebs-Hepes modified solutions with several glucose concentration, in the presence and absence of carbachol or insulin. Transfer of the medulla from a solution with 11.1 mM of glucose to a 0.56 mM one caused an increase in catecholamine secretion. Relative increase in change of glucose levels from 25 to 0.56 mM and from 50 to 0.56 mM enhanced the effect mentioned above. An inhibitory effect was detected after transfer of the medulla from 0.56 mM to 50 mM glucose. However, correction of solution osmolarity with mannitol or NaCl switched back catecholamine secretion to basal levels in all groups, and correction of solution osmolarity with sucrose indicated an impairment of catecholamine release. No difference was observed in stimulated catecholamine secretion (100 microM of carbachol) at all glucose levels. Further, the presence of insulin did not affect catecholamine secretion in all groups. Our results suggest that in isolated adrenal medullae of rats (1) glucose or variations in glucose levels do not affect catecholamine released; (2) isolated adrenal medulla of rat was highly sensitive to hyperosmolarity and extremely sensitive to hyposmolarity; (3) Insulin had no acute direct effect on catecholamine secretion in isolated adrenal medullae of rats.

Adrenal Medulla↗
PubMed1998

Simulated microgravity conditions enhance differentiation of cultured PC12 cells towards the neuroendocrine phenotype.

We are studying microenvironmental cues which contribute to neuroendocrine organ assembly and tissue-specific differentiation. As our in vitro model, we cultured rat adrenal medullary PC12 pheochromocytoma cells in a novel cell culture system, the NASA rotating wall vessel (RWV) bioreactors. This "simulated microgravity" environment in RWV bioreactors, characterized by randomizing gravitational vectors and minimizing shear stress, has been shown to favor macroscopic tissue assembly and to induce tissue-specific differentiation. We hypothesized that the unique culture conditions in the RWV bioreactors might enhance the in vitro formation of neuroendocrine organoids. To test our hypothesis, we evaluated the expression of several markers of neuroendocrine differentiation in cultures of PC12 cells maintained for up to 20 d in the slow turning lateral vessel (STLV) type RWV. PC12 cell differentiation was assessed by morphological, immunological, biochemical and molecular techniques. PC12 cells, cultured under "simulated microgravity" conditions, formed macroscopic, tissue-like organoids several millimeters in diameter. Concomitantly, the expression of phenylethanolamine-N-methyl transferase (PNMT), but not of other catecholamine synthesizing enzymes, was enhanced. Increased PNMT expression, as verified on both the gene and protein level, was accompanied by an increase in the specific activity of the enzyme. Furthermore, after 20 d in culture in the STLV, we observed altered patterns of protein tyrosine phosphorylation and prolonged activation of c-fos, a member of the AP-1 nuclear transcription factor complex. We conclude that culture conditions in the RWV appear to selectively activate signal transduction pathways leading to enhanced neuroendocrine differentiation of PC12 cells.

Animals↗
PubMed1997

[The effect of massage before venipuncture on the reaction of pre-school and school children].

The objective of this work is to describe the effect of massage done by parents on the reaction to venous puncture of preschooler and school age child hospitalized. Children's reactions were evaluated through the data of vital parameters, non-verbal communication and verbalization. The results obtained indicated that massage had significant effect in non-verbal reactions, especially those related to muscular relaxation. Effects on the reaction of vital parameters showed no difference between the two procedures, with and without massage, realized on the same child.

Anxiety↗
PubMed1995

TPN-induced sympathetic activation is related to diet, bacterial translocation, and an intravenous line.

OBJECTIVE: To investigate the effects of an intravenous line and the administration of a total parenteral nutrition (TPN) formula by the parenteral and oral routes on bacterial translocation and urinary catecholamine excretion in rodents. METHODS: Rats were fed chow with or without an intravenous line and a fat-free TPN solution either orally or intravenously for 5 consecutive days. Urine was collected on the first, third, and fifth days of feeding and quantitatively analyzed for norepinephrine and epinephrine excretion. Mesenteric lymph nodes were cultured for bacteria at the end of the study (day 5). RESULTS: Oral and intravenous TPN diets significantly increased norepinephrine excretion over time (P < .0001) compared with excretion in rats fed chow. Oral TPN diets increased epinephrine secretion after 5 days of feeding. The route of feeding TPN solution had no effect on norepinephrine or epinephrine excretion. Chow-fed rats with intravenous lines tended to have increased norepinephrine excretion over 5 days of feeding compared with chow-fed rats without intravenous lines (55% vs 13%, P = .08). Rats with bacterial translocation had greater norepinephrine excretion (mean +/- SEM, 136 +/- 23 pmol/mumol of creatinine) than rats without bacterial translocation (64 +/- 14 pmol/mumol of creatinine) (P < .05). CONCLUSIONS: Intravenous and oral fat-free, hypertonic glucose diets increase sympathetic nervous activity. This diet-induced sympathetic activity may be related to the presence of an intravenous line, bacterial translocation, the thermic effects of hypertonic glucose, and/or the absence of orally ingested food substances in rodent chow. In this model of rodent feeding, increased sympathetic activity may account for alterations in intestinal and immunologic defenses.

Administration, Oral↗
PubMed1995

Polymyxin B prevents increased sympathetic activity and alveolar macrophage tumor necrosis factor release in parenterally fed rats.

OBJECTIVE: To determine the effects of polymyxin B sulfate in rats fed by total parenteral nutrition on norepinephrine excretion, macrophage tumor necrosis factor production, and bacterial translocation. DESIGN: Randomized animal study. SETTING: A university teaching hospital in Seattle, Wash. MATERIALS AND METHODS: Three groups of rats were studied: chow plus intravenous saline, total parenteral nutrition, or total parenteral nutrition supplemented with polymyxin B sulfate. After 5 days, urinary excretion of norepinephrine and epinephrine was calculated, peritoneal and alveolar macrophages were cultured, and their spontaneous and lipopolysaccharide-stimulated tumor necrosis factor production was measured. Mesenteric lymph nodes were cultured for bacteria. RESULTS: Rats fed by total parenteral nutrition had increased urine norepinephrine excretion (33%) and alveolar macrophage tumor necrosis factor production (80%) and trends for increased epinephrine excretion and bacterial translocation compared with rats fed chow. Alveolar but not peritoneal macrophage tumor necrosis factor production was significantly related to norepinephrine excretion (r = .5, P < .01). The addition of polymyxin B to total parenteral nutrition decreased weight gain (P < .05), urinary norepinephrine excretion (P < .01), and alveolar macrophage tumor necrosis factor production (P < .05) compared with rats fed by total parenteral nutrition. Polymyxin B also tended to decrease the magnitude of bacterial translocation. CONCLUSIONS: Alveolar macrophage tumor necrosis factor production appears to be influenced by sympathetic nervous activity. Total parenteral nutrition-induced endotoxemia may indirectly alter macrophage function by stimulating sympathetic nervous activity.

Animals↗
PubMed1995

Control of myocardial reperfusion injury with hypertonic-hyperosmotic solution in isolated rabbit heart.

The effects of postischemic reperfusion were investigated in 14 isolated rabbit hearts in Langendorff preparation. Seven were controls and the others were reperfused with a sodium 7.5% and dextran 60 (60,000 MW) solution diluted with Krebs-Henseleit buffer to a sodium concentration of 150 mEq/l. The incidence of arrhythmias was lower in this group (p = 0.034). Coronary flow was higher than in controls (p = 0.035), the levels of isoenzyme MB of creatine kinase were lower than in controls (p = 0.035), myocardial water content was also lower (p = 0.047), and histological damage was reduced (p = 0.018). It was concluded that early reperfusion with 7.5% sodium chloride, 6% dextran 60 solution has a protective effect in the treatment of cardiac reperfusion injury.

Animals↗
PubMedDate not supplied

Functional heterogeneity of colonic adenocarcinoma mucins for inhibition of Entamoeba histolytica adherence to target cells.

Mucins secreted from the gastrointestinal epithelium from the basis of the adherent mucus layer which is the host's first line of defense against invasion by Entamoeba histolytica. Galactose and N-acetyl-D-galactosamine residues of mucins specifically inhibit binding of the amebic 170 kDa heavy subunit Gal-lectin to target cells, an absolute prerequisite for pathogenesis. Herein we characterized the secretory mucins isolated from the human colon and from three human colonic adenocarcinoma cell lines: two with goblet cell-like (LS174T and T84) and one with absorptive cell-like morphology (Caco-2). By Northern blot analysis the intestinal mucin genes MUC2 and MUC3 were constitutively expressed by confluent LS174T and Caco-2 cells, whereas T84 cells only transcribed MUC2 and not MUC3 mRNA. 3H-glucosamine and 3H-threonine metabolically labeled proteins separated as high M, mucins in the void (Vo > 10(6) Da) of Sepharose-4B column chromatography and remained in the stacking gel of SDS-PAGE as depicted by fluorography. All mucin preparations contained high amounts of N-acetyl-glucosamine, galactose, N-acetyl-galactosamine, fucose and sialic acid, saccharides typical of the O-linked carbohydrate side chains. Mucin samples from the human colon and from LS174T and Caco-2 cells inhibited E. histolytica adherence to chinese hamster ovary cells, whereas mucins from T84 cells did not. These results suggest that genetic heterogeneity and/or posttranslational modification in glycosylation of colonic mucins can affect specific epithelial barrier function against intestinal pathogens.

Adenocarcinoma, Mucinous↗