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Biomedical subjects

R Gross

Publications and source records attributed to R Gross.

At least 253 records · Page 14Linked to original sources
PubMed1992

Expression of bacterial cytotoxin genes in mammalian target cells.

We have studied the expression of the gene fragments encoding the enzymatically active portion of three bacterial cytotoxins: exotoxin A (ETA) of Pseudomonas aeruginosa, and pertussis toxin (PT) and adenylate cyclase toxin (CYA) of Bordetella pertussis, in sensitive mammalian target cells. Expression of active ETA and CYA was lethal to the producing cells and stable transfectants of Cos-1 cells containing the corresponding genes could not be obtained. The expression of the PTS1 subunit was tolerated by the producing mammalian cells. Since PT is cytotoxic because of ADP-ribosylation of G-proteins, we assume that the endogenously expressed PTS1 may not find the cellular target G proteins or PTS1 alone may not be sufficient for ADP-ribosylation of these proteins in vivo.

ADP Ribose Transferases↗
PubMed1992

Evidence for a glutamate receptor of the AMPA subtype which mediates insulin release from rat perfused pancreas.

1. The effect of L-glutamate has been studied on insulin secretion by the isolated perfused pancreas of the rat. The glutamate receptor subtype involved has been characterized. 2. In the presence of a slightly stimulating glucose concentration (8.3 mM), L-glutamate (5 x 10(-5)-4 x 10(-3) M) induced an immediate, transient and concentration-dependent insulin response. On the other hand, in the presence of a non stimulating glucose concentration (2.8 mM), L-glutamate (10(-3) M) did not modify the basal insulin secretion. 3. The three non-NMDA receptor agonists, kainate (10(-4)-10(-3) M), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA, 5 x 10(-5)-10(-4) M) and quisqualate (5 x 10(-6)-5 x 10(-5) M) all provoked a transient and concentration-dependent insulin response from pancreas perfused with 8.3 mM glucose. Compared with glutamate, kainate exhibited a similar efficacy, whereas AMPA and quisqualate elicited only a 3 fold lower maximal insulin response. In contrast, NMDA (10(-4)-10(-3) M) was ineffective. 4. An antagonist of non-NMDA receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 5 x 10(-5) M) totally prevented the stimulatory effect of L-glutamate (4 x 10(-4) M) and kainate (2 x 10(-4) M). In contrast, the NMDA receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ((+) MK801) was without effect. 5. The insulin secretory effect of glutamate (4 x 10(-4) M) was not affected by atropine (3 x 10(-7) M) or tetrodotoxin (3 x 10(-6) M). 6. Quisqualate at a high maximally effective concentration (4 x 10(-4) M) inhibited glutamate (10(-3) M) or kainate (4 x 10(-4) M)-induced insulin release. 7. This study shows that L-glutamate stimulates insulin secretion in rat pancreas, by acting on an excitatory amino acid receptor of the AMPA subtype.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

P2y purinoceptor responses of beta cells and vascular bed are preserved in diabetic rat pancreas.

1. To investigate the effect of experimental diabetes on the P2y purinoceptor responses of pancreatic beta-cells and vascular bed, we used adenosine-5'-O-(2-thiodiphosphate) (ADP beta S), a potent and stable P2y agonist. This work was performed in the isolated perfused pancreas of the rat. 2. Diabetes was induced by streptozotocin (66 mg kg-1, i.p.). Five weeks after the induction of diabetes, on the day of pancreas isolation, the animals displayed marked hyperglycaemia (37.6 +/- 2.7 mM). Age-matched rats were used as controls. 3. Insulin response to a glucose stimulation from 5 to 10 mM was completely lost and stimulation of insulin release by the sulphonylurea, tolbutamide (185 microM), was drastically impaired in the diabetic pancreas (maximum responses were 1.5 +/- 0.4 and 7.0 +/- 1.4 ng min-1 for diabetic and age-matched rats respectively). 4. In contrast, in the diabetic pancreas ADP beta S (15 microM), infused in the presence of glucose 5 mM, elicited an immediate and significant insulin release similar to that observed in the age-matched pancreas (maximum responses were 7.6 +/- 1.5 and 6.7 +/- 1.3 ng min-1 respectively). This ADP beta S stimulating effect occurred independently of the glucose concentration (5, 8.3 and 28 mM) in the diabetic pancreas. On pancreatic vascular resistance, ADP beta S induced a similar vasodilatation in diabetic and age-matched rats. 5. In conclusion, ADP beta S retains its insulin stimulatory and vasodilator effects in experimental diabetes; P2y purinoceptors could therefore be considered as a new target for the development of antidiabetic drugs.

Animals↗
PubMed1992

Organ- and age-specific replication of polyomavirus in mice.

A novel organ- and age-specific pattern of polyomavirus DNA replication in mice is described. Two broadly defined classes of response to polyomavirus infection were observed: class I organs (mammary gland, bone, and skin) responded with high levels of replication in neonate mice and moderate levels in adults; class II organs (kidney, liver, and lung) responded with high levels in neonates and very low levels in adults. Thus, aging affected replication in all organs, and organ specificity was superimposed on this age-related decrease. We argue that the organ- and age-specific pattern likely reflects in part the activities of a multiplicity of general or tissue-specific, age-dependent transcription factors, which modulate viral replication or viral transcription or both. Interestingly, the majority of tumors in mice infected as neonates or as immunoincompetent adults originate in class I organs, suggesting that the ability to replicate in adult tissues is an important factor controlling polyomavirus oncogenesis. From the analysis of the infection process in adult mammary glands, a novel mode of polyomavirus infection emerged which contrasts with that derived from observations of tissue culture systems. A nonproductive infection was seen, characterized by very low levels of live virus (in the range of 10(-4) PFU per cell) and maintenance of the viral genome in an unintegrated, moderately replicating state. Maintenance of the viral genome was accomplished without integration into host cell DNA in all three tumor-prone organs, both prior to as well as beyond oncogenesis.

Aging↗
PubMed1992

The output and outcome of two types of formal health structures--health post and creche--for nutritional interventions for preschool children in two urban, low-income communities of Belo Horizonte, Brazil (1986).

In order to observe the nutritional and health status of pre-school children, the output and outcome of two formal health services -health post and creche- for this vulnerable group in two urban slum areas of Belo Horizonte, Brazil were studied in 1986. A total of 420 children were surveyed, 254 children randomly selected from the communities and 156 from three creches. Growth monitoring was not undertaken systematically, and mothers did not have growth control charts. When a child had diarrhea, mothers preferred to apply home remedies or to buy proprietary drugs rather than to consult medical personnel. 72% of mothers reported using ORT, and 11% suspending feeding completely. After three month of life, 50% of infants were receiving some breast milk. 75% of children were immunized completely. The prevalence of health and nutrition indicators such as anemia (50% vs. 30%), parasitosis (87% vs. 70%), and stunting (28% vs. 20%) was worse in the creches than in the communities.

Anemia↗
PubMed1992

The group work of the workshop.

The project aims at determining how aging influences nutritional status (as determined by measurements and indicators from clinical evaluation, anthropometric, laboratory, and biophysical tests) in a Chronic degenerative disease burden; 5) Use of drugs and medications (both Western and traditional) and 6) physical activity as the direct mediators of nutritional status of the elderly. A chain of causal determinants of each of the six mediators was developed. The primary target population is composed of persons from 60 to 75 years of age who are migrants to the metropolis from the same rural province. They share the same religious practices and ethic heritage in common and are free living (non-institutionalized) in the community. We shall enroll, in a stratified randomized manner (stratified for danger, urban community, and existence of participating second generation relative), 400 elderly persons in two groups: Group 1A: 100 males and 100 females who migrated more than 40 years earlier from the province to the metropolis; Group 1B: 100 males and 100 females who migrated less than 20 years earlier from the province to the metropolis. In a "controlled cross-sectional survey" format these represent two exposure groups: long-residency and short residency. A secondary contrast group will be gender specific, second generation relatives (sons or nephews for older men; daughters or nieces for older women), 400 in all, ie, one for each first generation (elderly) subject. They will range from 25 to 42 years of age and will also be living in low-income peri-urban communities of the metropolis. The tests from the overall battery of measurement indicators, appropriate to young adults, will be applied. The primary contrast is G1A vs G1B, aggregated or deseggregated by gender, using 1) relative risk based on long vs short urban exposure and 2) conventional parametric and non-parametric intergroup comparisons. The secondary contrast is within individual generation pairs (father-son, uncle-nephew; mother-daughter, aunt-nice) using conventional parametric or non-parametric tests for dependent variables.

Adult↗
PubMed1991

Diabetes alters the responses of glucagon secreting cells and vascular bed to isoprenaline and forskolin in vitro in rat pancreas.

Diabetes is known to disturb pancreatic glucagon secreting alpha cell function and blood flow control. In a previous study we could show that streptozotocin-induced diabetes suppressed adenosine stimulating effect on glucagon secretion and reduced its vasodilatory properties; since the nucleotide exerts these effects by activation of A2 purinergic receptors known to be positively coupled to adenylate cyclase, we investigated the effect of streptozotocin diabetes on the responses of alpha cells and vascular bed to stimulation of adenylate cyclase through 2 different ways: 1) with isoprenaline by activation of beta adrenergic receptor positively coupled to the enzyme; 2) with forskolin by direct activation of the catalytic unit of adenylate cyclase. In the isolated perfused pancreas of normal rats, isoprenaline (0.01 microM) or forskolin (1 microM) induced a +200 to +300% increase of glucagon secretion and a 20 to 30% increase of pancreatic vascular flow rate. In pancreas of 5-week diabetic rats, alpha cell responses to isoprenaline and forskolin were completely suppressed and the vasodilatory effects of both drugs were significantly reduced (-35 to -50%). Long term in vivo insulin treatment with glycaemia normalization was able to correct both defects. We can conclude that streptozotocin diabetes suppresses glucagon secretion and reduces pancreatic vasodilatation not only in response to activation of receptors positively coupled to adenylate cyclase but also to a direct activation of this enzyme.

Adenylyl Cyclases↗
PubMed1991

Endogenous atrial natriuretic factor is involved in the natriuresis following sodium loading in rats with chronic heart failure.

STUDY OBJECTIVE: Plasma levels of atrial natriuretic factor are increased in chronic heart failure; however, it is still controversial whether these raised levels contribute to the diuresis and natriuresis in this setting. To address this issue the potential contribution of endogenous atrial natriuretic factor in the renal excretion of a moderate oral sodium load in a rat model of chronic heart failure was studied. DESIGN: A monoclonal antibody against atrial natriuretic factor was used for specific antagonisation of its in vivo effects. Animals were subjected to oral sodium loading (30 ml.kg-1 0.9% NaCl, 2.5% dextrose) at baseline, immediately after, and 5 d after injection of monoclonal antibody or control solvent. EXPERIMENTAL MATERIAL: Sham operated rats and rats with chronic heart failure due to myocardial infarction (infarct size 35(SEM 4)% of left ventricle) were studied 4-5 weeks after surgery. MEASUREMENTS AND MAIN RESULTS: The renal excretion of cyclic guanosine monophosphate (cGMP), which represents a specific marker for the activation of the atrial natriuretic factor system, was markedly increased in infarcted rats, at 17.9(SEM 3.4) vs 5.8(1.2) nmol.kg-1, p less than 0.01. Atrial natriuretic factor antibody given immediately before sodium loading reduced the natriuretic response (0-4 h period) in infarcted rats from 1270(171) to 805(76) mumol.kg-1 (p less than 0.01) but not in sham operated animals. Similarly, the excretion of cGMP was only decreased by atrial natriuretic factor antibody in infarcted rats, from 29.8(6.3) to 20.7(3.7) nmol.kg-1. The reduction in sodium and cGMP excretion in infarcted rats was confirmed with a purified antibody preparation. CONCLUSIONS: Endogenous atrial natriuretic factor appears to be involved in the natriuresis following a moderate oral volume load in chronic heart failure. Thus the raised concentrations found in chronic heart failure may contribute to the regulation of urinary sodium excretion under these conditions despite the fact that the diuretic effects of exogenous atrial natriuretic factor are attenuated in chronic heart failure.

Animals↗
PubMed1991

Measurement of regional myocardial blood flow with multiple colored microspheres.

BACKGROUND: The use of radioactive microspheres (RM) for the measurement of regional myocardial blood flow (RMBF) is limited and inaccessible to many investigators due to radiation safety concerns and radioactive waste disposal problems. Therefore, a new method for the measurement of RMBF using colored microspheres (CM) was developed. METHODS AND RESULTS: Polystyrene spheres (diameter, 15 +/- 0.1 [SD] micron; density, 1.09 g/ml) were dyed with one of five colors. With the injection of CM into the left atrium or into a coronary perfusion line, RMBF and its distribution can be determined. CM are extracted from the myocardium and blood by digestion with potassium hydroxide and subsequent microfiltration. The dyes are then recovered from the CM within a defined volume of a solvent, and their concentrations are determined by spectrophotometry. The separation of composite absorbance spectra by spectrophotometry with the CM technique was as good as the separation of energy spectra by a gamma-counter using the RM technique. Leaching of dye from the CM was less than 0.1% during a 2-month period in vitro. Significant leaching of dye from the microspheres also did not occur during 8 hours in the blood and myocardium of four anesthetized dogs in vivo. For further validation of this method, pairs of CM and RM (15.5 +/- 0.1 [SD] microns) were simultaneously injected under five different RMBF conditions (range, 0-10 ml/[min.g]) into the left anterior descending coronary artery of four anesthetized pigs, with coronary inflow as a flow reference, or into the left atrium of four anesthetized dogs using aortic blood withdrawal as a reference. The relation between RMBF determined by CM and RM was CM = 0.01 + 1.00.RM (r = 0.98, n = 1,080 data points) in the pigs, and CM = -0.19 + 0.92.RM (r = 0.97, n = 1,813 data points) in the dogs. CONCLUSIONS: Measurement of RMBF with CM yields values very similar to those of RM. Their use is less expensive and avoids all the disadvantages related to radioactivity, thus offering an alternative method for as many as five RMBF measurements in a single experiment.

Animals↗
PubMed1990

P2 purinoceptor agonists stimulate somatostatin secretion from dog pancreas.

The effects of ATP and ADP structural analogues (2-methylthio ATP; alpha,beta-methylene ADP) on somatostatin secretion were tested in dogs. Insulin and glucagon secretion was also evaluated. Our experiments were performed in vivo and in vitro. In vivo, 2-methylthio ATP was infused directly into the pancreaticoduodenal artery of anesthetized dogs and blood was sampled from the pancreaticoduodenal vein. This ATP analogue (approximately 15 microM) immediately induced stimulation of both somatostatin and insulin secretion, which was accompanied by a slight reduction of glycemia. A delayed increase in glucagon output was observed. In vitro, using the isolated perfused dog pancreas uncinate process, alpha,beta-methylene ADP, a stable ADP analogue (16.5 microM), was infused in the presence of a substimulating glucose concentration (4.2 mM). Under these conditions, alpha,beta-methylene ADP immediately induced the stimulation of somatostatin secretion without affecting basal insulin and glucagon secretion. In conclusion our results suggest the presence of P2 purinoceptors on pancreatic somatostatin secreting cells.

Adenosine Diphosphate↗