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Biomedical subjects

S Kaufman

Publications and source records attributed to S Kaufman.

At least 91 records · Page 5Linked to original sources
PubMed1996

Influence of atrial natriuretic factor on fluid efflux from the splenic circulation of the rat.

1. Atrial natriuretic factor (ANF) causes a reduction in plasma volume that is abolished by splenectomy. Experiments were conceived to investigate whether ANF acts within the spleen to increase efflux of fluid from the intravascular to the extravascular space. 2. ANF, infused into the splenic artery of anaesthetized rats at rates of 1, 5 and 20 ng min -1, caused a dose-dependent increase in the arteriovenous difference in haematocrit as blood flowed through the spleen (basal difference, 0.18 +/- 0.10%; difference after 10 min at 20 ng min -1 ANF, 1.5 +/- 0.18%; n = 6). There was no such change in plasma protein concentration. 3. ANF (20 ng min -1) did not alter splenic arterial blood flow. However, splenic venous blood flow fell so that the arteriovenous difference increased significantly (basal difference, 0.34 +/- 0.19 ml min -1; difference at 60 min, 1.1 +/- 0.20 ml min-1, n = 7). There was no change in mean arterial pressure. 4. These data confirm our hypothesis that ANF acts within the spleen to increase fluid efflux from the intravascular to the extravascular space. Since there is no change in total splenic blood flow, we propose that the effects of ANF are mediated by dilatation of the splenic afferent arterioles and constriction of the efferent venules, thus increasing filtration pressure.

Animals↗
PubMed1996

Structure-function relationships of phenylalanine hydroxylase revealed by radiation target analysis.

Phenylalanine hydroxylase (PAH) purified from rat liver is an oligomeric protein (predominantly tetramers) composed of 52-kDa subunits that are identical in primary structure. We have used radiation target analysis to probe the subunit organization of the enzyme. When 6-methyltetrahydropterin was used as the cofactor, the loss of hydroxylase activity as a function of radiation dose was defined by a single exponential decay, yielding a target size of about 120 kDa. However, when the enzyme was assayed with the natural cofactor tetrahydrobiopterin (BH4), the inactivation curves were much more complex. In these cases, the activity first increased, then decreased, as a function of radiation dose. The inactivation profile at higher radiation doses implied a target size of approximately 100 kDa. Kinetic analysis of the enzyme was significantly activated relative to the nonirradiated sample. In addition, the irradiated enzyme was desensitized to substrate-level activation by phenylalanine. The initial increase in activity at low radiation doses is due to the destruction of a large inhibitor. Analysis of the irradiated samples by high-performance size-exclusion chromatography indicated that the hydroxylase tetramer was lost with a target size of 110 kDa. Our data indicate that the tetrameric form of purified PAH consists of two enzymatically active dimers and that BH4 interacts with a tetramer to inhibit or deactivate the enzymatic activity.

Animals↗
PubMed1996

Splenic blood flow and fluid efflux from the intravascular space in the rat.

1. Previous evidence has suggested that fluid is extracted from the blood during its passage through the splenic circulation. In order to further investigate this phenomenon, flow probes were placed around the splenic artery and vein of rats. Splenic blood flow and mean arterial blood pressure were measured immediately after surgery, while the rats were still anaesthetized. Five days later, the measurements were repeated first in conscious rats, and then after administering sodium pentobarbitone. Final measurements were made in the conscious animals at day 10 post surgery. 2. Splenic arterial blood flow was lowest at the time of surgery. It had doubled by day 5, and remained stable thereafter at about 8 ml min-1. Splenic venous blood flow also increased after surgery, but less so than the arterial flow, so that the arteriovenous difference had increased to 2.0 +/- 0.4 ml min-1 by day 5. 3. In response to sodium pentobarbitone (20 mg I.V.), there was a transient fall in splenic arterial blood flow from 6.7 +/- 0.9 to 4.9 +/- 0.7 ml min-1. There was no significant change in the arteriovenous difference of blood flow. 4. In conclusion, we have shown that splenic blood flow is considerably higher than previously reported. We have also revealed a significant new path for fluid efflux from the intravascular space; at least 25% of fluid volume flowing into the splen is removed from the circulating blood. 5. Although anaesthesia modulates splenic blood flow, the changes are not as pronounced as those observed in the acute surgically prepared animal.

Adjuvants, Anesthesia↗
PubMed1996

Effects of depletion of intracellular tetrahydrobiopterin in murine erythroleukemia cells.

The biosynthesis of 6(R)-5,6,7,8-tetrahydrobiopterin (BH4) in murine erythroleukemia (MEL) cells is almost completely inhibited by 10 mM, 2,4-diamino-6-hydroxypyrimidine (DAHP), which targets GTP cyclohydrolase. The inhibition results in dephosphorylation of the retinoblastoma gene product, prolongation of the G1-phase in the cell cycle, and subsequent commitment to terminal differentiation of MEL cells. Reversal of the processes by repletion of cellular BH4 with biopterin-related compounds including BH4, 7,8-dihydrobiopterin (7,8-BH2), sepiapterin, and 7,8-dihydroneopterin has generated complicated results. Low micromolar exogenous pterin compounds had little or no effect. At 300 microM or higher, the synthesis of hemoglobin by DAHP-induced MEL cells is significantly inhibited by 7,8-dihydrobiopterin and sepiapterin. However, further cell cycle analysis shows that the inhibition of cell differentiation by 7,8-BH2 and sepiapterin may not be due to the reversal of cell proliferation. Inhibition of BH4 biosynthesis in MEL cells by inhibitors of sepiapterin reductase has also been studied. None of the inhibitors that were tested, including N-chloroacetyl-dopamine and N-acetylserotonin, which are specific for sepiapterin reductase, can block MEL cells in G1-phase or induce the cells to commit to terminal differentiation. Furthermore, inhibitors of sepiapterin reductase are found to reduce or to abolish hemoglobin synthesis in differentiating MEL cells induced by hexamethylene bisacetamide. The mechanism for this is not clear. Not all of the effects caused by the depletion of BH4 synthesis can be rescued by repletion of BH4. These results suggest that BH4 may not regulate proliferation or differentiation of MEL cells as previously thought. Its function in MEL cells is still not clear.

Acetamides↗
PubMed1996

Transjugular intrahepatic portosystemic shunt for the management of severe venoocclusive disease following bone marrow transplantation.

Hepatic venoocclusive disease (VOD) is a common, life-threatening complication of bone marrow transplantation (BMT). Portal hypertension is usually present and accounts for many of the clinical manifestations of this syndrome. We describe the results of transjugular intrahepatic portosystemic shunt (TIPS) for the management of VOD after BMT TIPS was performed in six patients with histologically confirmed VOD who had progressive jaundice and ascites. Portal hypertension was improved by TIPS in all patients (mean portal pressure gradient before TIPS, 20.2 +/- 4.6 vs. 6.7 +/- 1.9 mm Hg post-TIPS, P < .004). Three patients who underwent TIPS late in the course of VOD did not demonstrate any clinical improvement after TIPS and expired within 2 weeks of the procedure. The remaining three patients had less advanced disease and demonstrated decreases in serum bilirubin, improvement in coagulopathy, and decreased ascites after TIPS. Two patients subsequently expired, one with persistent histological changes of VOD. The lone survivor continues to do well with resolution of ascites, jaundice, and coagulopathy as of her last outpatient visit. TIPS was an effective method for portal decompression in patients with VOD after BMT, and was associated with clinical improvement in some patients. However, these effects may be transient and may not improve overall survival.

Adult↗
PubMed1996

E2F-1 blocks terminal differentiation and causes proliferation in transgenic megakaryocytes.

The transcription factor E2F-1 plays a central role in the cell cycle through its ability to activate genes involved in cell division. E2F-1 activity is regulated by a number of proteins, including the retinoblastoma susceptibility gene product, cyclin-dependent kinases, and their inhibitors, proteins that have been implicated in the control of certain developmental processes. To investigate a potential role of E2F-1 in differentiation, we assayed the ability of megakaryocytes to form platelets in an in vivo transgenic model. E2F-1 expression in megakaryocytes blocked differentiation during maturation, resulting in severe thrombocytopenia. Ultrastructural analysis of megakaryocytes revealed abnormal development characterized by hyperdemarcation of cytoplasmic membranes and reduced numbers of alpha granules. Administration of megakaryocyte growth and development factor or interleukin 6 could not overcome the differentiation block. Additionally, E2F-1 caused massive megakaryocyte accumulation in both normal and ectopic sites, first evident in E15 embryonic liver. Furthermore, significant apoptosis was observed in transgenic megakaryocytes. These data indicate that E2F-1 can prevent terminal differentiation, probably through its cell cycle-stimulatory activity.

Animals↗
PubMed1996

Effect of age on stretch-induced secretion of atrial natriuretic factor.

Plasma atrial natriuretic factor (ANF) levels are known to be higher in aged rats and humans. Although this may be partially explained by a reduction in clearance from the circulation, it was not known whether the secretory nature of the atrial tissue also changes with age. We measured ANF release in response to atrial distention in young adult (2-3 months) and older retired breeder (4-6 months) male rats both in vivo (conscious instrumented animals) and in vitro (isolated perfused atria). Whereas increased intraluminal pressure caused a rise in ANF secretion when using atria derived from the younger rats, there was no such response when using atria derived from the older rats, i.e., stretch induced secretion was impaired. This appeared to be secondary to a reduction in atrial compliance in the older animals. Unlike previous studies, basal plasma ANF levels were lower in our retired breeders, although the response to volume loading was preserved. These results suggest that, already by about 6 months of age, the atrial tissue is less responsive to changes in atrial pressure. The increased plasma levels previously reported in senescent rats are therefore probably a result of reduced clearance rather than increased secretion.

Aging↗
PubMed1996

Postoperative nausea and vomiting after strabismus surgery: mechanisms, treatment, and implications for practice.

The occurrence of postoperative nausea and vomiting in children after strabismus surgery has historically been a challenging aspect of anesthetic management. This article provides an overview of the cause, physiology, and mechanisms of post surgical vomiting in this patient population. Current pharmacological treatment modalities and implications for future practice are examined.

Child↗
PubMed1996

[Diarrhea and AIDS: more complex diagnostic techniques; better therapeutic results].

During 17 months, 73 HIV-positive patients with diarrhea lasting at least for 14 days, were studied prospectively. The patients had stool specimen examinations negative for enteric pathogens, or positive for one of them, but with no response to specific treatment. All patients were subcomitted to digestive endoscopy and biopsies were taken for microbiological and histological studies. The etiology of the diarrhea could be established in 48 patients (66%). In 45, the cause was an enteric infection. There was association of 2 pathogens in 11 patients, and of 3 in 1 patient. The agents found were: Cryptosporidium (24%), MAI (16%), Giardia lambila (12%), isospora belli (5%), Shigella (5%), Salmonella (5%); Entamoeba histolytica (3%), HSV (3%), tuberculosis (2%), adherent bacteria (2%) and spirochetes (2%). In 3 patients the etiology was not infection, their diagnoses were coeliac disease, lymphoma and idiophatic colonic ulcers, respectively. In 51% of the cases only the examination of endoscopic biopsy specimens could identify the cause of the diarrhea. These results justify the use of these methods to improve diagnosis and therapeutic attempts in these patients.

AIDS-Related Opportunistic Infections↗
PubMed1995

Characterization of the wild-type form of 4a-carbinolamine dehydratase and two naturally occurring mutants associated with hyperphenylalaninemia.

The characterization of 4a-carbinolamine dehydratase with the enzymatically synthesized natural substrate revealed non-Michaelis-Menten kinetics. A Hill coefficient of 1.8 indicates that the dehydratase exists as a multisubunit enzyme that shows cooperativity. A mild form of hyperphenylalaninemia with high 7-biopterin levels has been linked to mutations in the human 4a-carbinolamine dehydratase gene. We have now cloned and expressed two mutant forms of the protein based on a patient's DNA sequences. The kinetic parameters of the mutant C82R reveal a 60% decrease in Vmax but no change in Km (approximately 5 microM), suggesting that the cysteine residue is not involved in substrate binding. Its replacement by arginine possibly causes a conformational change in the active center. Like the wild-type enzyme, this mutant is heat stable and forms a tetramer. The susceptibility to proteolysis of C82R, however, is markedly increased in vitro compared with the wild-type protein. We have also observed a decrease in the expression levels of C82R protein in transfected mammalian cells, which could be due to proteolytic instability. The 18-amino acid-truncated mutant GLu-87--> termination could not be completely purified and characterized due to minute levels of expression and its extremely low solubility as a fusion protein. No dehydratase activity was detected in crude extracts from transformed bacteria or transfected mammalian cells. Considering the decrease in specific activity and stability of the mutants, we conclude that the patient probably has less than 10% residual dehydratase activity, which could be responsible for the mild hyperphenylalaninemia and the high 7-biopterin levels.

Amino Acid Metabolism, Inborn Errors↗
PubMed1995

Pegylated megakaryocyte growth and development factor abrogates the lethal thrombocytopenia associated with carboplatin and irradiation in mice.

Megakaryocyte growth and development factor (MGDF) is a potent inducer of megakaryopoiesis in vitro and thrombopoiesis in vivo. The effects of MGDF appear to be lineage-selective, making this cytokine an ideal candidate for use in alleviating clinically relevant thrombocytopenias. This report describes a murine model of life-threatening thrombocytopenia that results from the combination treatment of carboplatin and sublethal irradiation. Mortality of this regimen is 94% and is associated with widespread internal bleeding. The daily administration of pegylated recombinant human MGDF (PEG-rMGDF) significantly reduced mortality (to < 15%) and ameliorated the depth and duration of thrombocytopenia. The severity of leucopenia and anemia was also reduced, although it was not clear whether these effects were direct. Platelets generated in response to PEG-rMGDF were morphologically indistinguishable from normal platelets. PEG-rMGDF administered in combination with murine granulocyte colony-stimulating factor completely prevented mortality and further reduced leukopenia and thrombocytopenia. These data support the concept that PEG-rMGDF may be useful to treat iatrogenic thrombocytopenias.

Animals↗
PubMed1995

Atrial natriuretic factor release during pregnancy in rats.

1. We investigated the control of atrial natriuretic factor (ANF) secretion during pregnancy. 2. Plasma ANF levels were measured in conscious virgin female rats under basal conditions, and after atrial distension with an indwelling balloon catheter. The rats were then mated, and the measurements repeated at 7, 14 and 21 days of pregnancy, and at 1 week postpartum. Plasma ANF levels were also measured in ovariectomized rats injected with progesterone, oestradiol, or oestradiol plus progesterone. 3. Basal plasma ANF levels were elevated at 7 and 14 days of pregnancy, but returned to prepregnant levels by 21 days. At 1 week postpartum, they were again elevated. 4. In response to atrial stretch, plasma ANF increased significantly in virgin rats (from 100 +/- 10 to 148 +/- 13 pg ml-1, P < 0.001, n = 20). In contrast, there was no such secretory response observed in the pregnant and postpartum animals i.e. stretch-induced secretion of ANF was markedly attenuated. 5. Treatment with exogenous oestradiol caused a significant increase in plasma ANF levels in acyclic rats. However, neither progesterone nor a combination of oestradiol plus progesterone had any effect. 6. It is concluded that basal and stretch-induced ANF secretion are differentially influenced by pregnancy; oestradiol is identified as a potential stimulatory factor.

Animals↗