Role for transforming growth factor beta in thromboxane-induced increases in mesangial cell fibronectin synthesis.

Thromboxane A2 (TXA2) has been implicated in the pathogenesis of progressive glomerulosclerosis and stimulates the synthesis of matrix protein by mesangial cells (MCs). This study examined the role of transforming growth factor beta (TGF-beta) in the mediation of the action of the stable TXA2/prostaglandin (PG) endoperoxide analog U-46619 to stimulate fibronectin (Fn) synthesis in cultured rat MC. Exogenous TGF-beta increased Fn synthesis by MC in a concentration- and time-dependent fashion, as reflected by incorporation of [35S]methionine into immunoprecipitable Fn. Submaximal concentrations of TGF-beta (1-2.5 pmol/l) increased Fn synthesis two- to threefold, a response comparable in magnitude to that observed with a maximal stimulatory concentration (1 mumol/l) of U-46619. Anti-TGF-beta antibody, but not isotypic IgG, blocked the increases in Fn synthesis induced by both U-46619 and exogenous TGF-beta. Endogenous TGF-beta bioactivity in MC culture media, assessed by the mink lung epithelial cell system, was significantly increased by 1 mumol/l U-46619 (1.7 +/- 0.3 pmol/l) compared with that of control media (0.6 +/- 0.1 pmol/l, P < 0.05). Total (active plus latent) TGF-beta bioactivity, assayed after heat activation of latent TGF-beta, was also significantly higher in media of MCs cultured with U-46619 (45 +/- 4 pmol/l) compared with control (24 +/- 4 pmol/l). Thus, U-46619 increased endogenous TGF-beta bioactivity to a level sufficient to account for the enhancement of Fn synthesis observed with U-46619, as reflected by the Fn synthetic response to exogenous TGF-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C in diabetic nephropathy.

Protein kinase C is activated in numerous tissues obtained from diabetic animals and in several cultured cell systems exposed to high media glucose in vitro including glomerular mesangial cells. Several activators of protein kinase C, such as high media glucose, angiotensin II, phorbol ester, low density lipoprotein, and the thromboxane analogue U-46619, increase TGF beta bioactivity or mRNA expression and increase the synthesis of extracellular matrix proteins by mesangial cells in culture. The studies described in the present report support the hypothesis that activation of protein kinase C by thromboxane, an eicosanoid whose production is known to be elevated in diabetes, increases TGF beta production by mesangial cells in culture. TGF beta then acts to increase extracellular matrix protein synthesis through a mechanism that does not require active protein kinase C. Thus, activation of protein kinase C in the glomerulus in diabetes could contribute to mesangial expansion by stimulating active TGF beta production.

Individual leaflets of a membrane bilayer can independently regulate permeability.

Water rapidly crosses most membranes, but only slowly crosses apical membranes of barrier epithelia such as bladder and kidney collecting duct, a feature essential to barrier function. How apical membrane structure reduces permeabilities remains unclear. Cell plasma membranes contain two leaflets of distinct lipid composition; the role of this bilayer asymmetry in membrane permeability is unclear. To determine how asymmetry of leaflet composition affects membrane permeability, effects on bilayer permeation of reducing single leaflet permeability were determined using two approaches: formation of asymmetric bilayers in an Ussing chamber, with only one of two leaflets containing cholesterol sulfate, and stabilization of the external leaflet of unilamellar vesicles with praeseodymium (Pr3+). In both systems, permeability measurements showed that each leaflet acts as an independent resistor of water permeation. These results show that a single bilayer leaflet can act as the barrier to permeation and provide direct evidence that segregation of lipids to create a low permeability of barrier epithelial apical membranes.

Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF-beta bioactivity in mesangial cells.

Previous studies have demonstrated that thromboxane (TX) stimulates matrix protein synthesis in mesangial cells (MC), and that this action is signalled by receptor mediated activation of protein kinase C (PKC). In the present study, we examined the hypothesis that activation of PKC by TX signals increases in transforming growth factor beta (TGF-beta) bioactivity, which in turn induces enhanced matrix protein synthesis. In cultured rat MC, the TXA2/prostaglandin endoperoxide analogue U-46619, but not exogenous human platelet TGF-beta 1, activated PKC as reflected by enhanced in situ phosphorylation of MARCKS protein, an endogenous substrate of PKC. U-46619 and TGF-beta 1 stimulated fibronectin (Fn) synthesis in MC, as shown by [35S]methionine incorporation into immunoprecipitable Fn. Pan-specific rabbit anti-TGF-beta antibody blocked the increases in Fn synthesis induced by exogenous TGF-beta and those induced by U-46619 at 24 to 72 hours after addition. Anti-TGF-beta antibody did not block the small increases in FN synthesis observed six hours after addition of U-46619, suggesting that this acute response was not dependent on TGF-beta. Anti-TGF-beta antibody also failed to block activation of PKC by U-46619. U-46619 and 50 nM of the PKC agonist phorbol dibutyrate (PDBu) significantly increased both the active fraction and total (latent plus active) TGF-beta in MC culture media, as assayed with the mink lung epithelial cell bioassay system.(ABSTRACT TRUNCATED AT 250 WORDS)

Permeability properties of the intact mammalian bladder epithelium.

Because the mammalian bladder must store urine of composition which differs markedly from that of plasma for prolonged periods, the bladder permeability barrier must maintain extremely low permeabilities to substances which normally cross membranes relatively rapidly, such as water, protons, and small nonelectrolytes like urea and ammonia. In the present studies, permeabilities of the apical membrane of dissected rabbit bladder epithelium to water, urea, ammonia, and protons were measured in Ussing chambers and averaged (in cm/s) for water, 5.15 +/- 0.43 x 10(-5); for urea, 4.51 +/- 0.67 x 10(-6); for ammonia, 5.14 +/- 0.62 x 10(-4); and for protons, 2.98 +/- 1.87 x 10(-3), respectively. These permeability values are exceptionally low and are expected to result in minimal to no leakage of these normally permeable substances across the epithelium. Water permeabilities in intact whole rabbit bladders were indistinguishable from those obtained in the dissected epithelial preparation. Moreover, addition of nystatin to the apical solution of dissected epithelia rapidly increased water permeability in conjunction with loss of epithelial resistance. These results confirm that the apical membrane of the bladder epithelial cells represents the bladder permeability barrier. In addition, they establish a model system that will permit examination of how membrane structure reduces permeability and how epithelial injury compromises barrier function.

[Massive pneumoperitoneum secondary to barotrauma in a newborn infant]. / Neumoperitoneo masivo secundario a barotrauma en un recién nacido.

A case of a newborn infant that develops a pneumoperitoneum secondary to barotrauma is reported. Alternatives about the decision to operate or not, are presented. It is concluded that in pneumoperitoneum subsequent to a pneumothorax and/or pneumomediastinum, in association to mechanical ventilation or possible barotrauma during resuscitation, a non-surgical attitude should be taken and the indication for surgery will be given by the deteriorating condition of the patient.

[Usefulness of clobazam in the treatment of refractory epilepsy in children]. / Utilidad del clobazam en el tratamiento de la epilepsia refractaria en niños.

Below is report on our experience using a relatively new benzodiazepine as treatment for refractory epilepsy in 30 children. All of the patients had a severely fixed encephalopathy; 17 presented mixed epilepsy, 9 had Lennox-Gastaut syndrome and 4 others, West Syndrome. The seizures were totally controlled in 20% of the children; in a proportion superior to 75%, seizures were decreased in 46% of the patients. There were positive results in 6% of the cases and side-effects were seen in 13%. The usefulness of the clobazam as a co-adjuvant medication in the control of refractory epileptic seizures was demonstrated since the number of seizures decreased from 15 to 3 per day.

Low permeabilities of MDCK cell monolayers: a model barrier epithelium.

Barrier epithelia such as the renal collecting duct (in the absence of antidiuretic hormone) and thick ascending limb, as well as the stomach and mammalian bladder, exhibit extremely low permeabilities to water and small nonelectrolytes. A cell culture model of such epithelia is needed to determine how the structure of barrier apical membranes reduce permeability and how such membranes may be generated and maintained. In the present studies, the transepithelial electrical resistance and isotopic water and urea fluxes were measured for Madin-Darby canine kidney (MDCK) type I and type II cells, as well as type I cells expressing the mucin protein, MUC1, in their apical membranes. Although earlier studies had found the unstirred layer effects too great to permit measurement of transepithelial permeabilities, use of ultrathin semipermeable supports in this study overcame this difficulty. Apical membrane diffusive water permeabilities were 1.8 +/- 0.4 x 10(-4) cm/s and 3.5 +/- 0.5 x 10(-4) cm/s in MDCK type I and type II cells, respectively, at 20 degrees C. Urea permeability in type I cells at the same temperature was 6.0 +/- 0.9 x 10(-6) cm/s. These values resemble those of other barrier epithelial apical membranes, either isolated or in intact epithelia, and the water permeability values are far below those of other epithelial cells in culture. Transfection of MDCK type I cells with the major human urinary epithelial mucin, MUC1, led to abundant expression of the fully glycosylated form of the protein on immunoblots, and flow cytometry revealed that virtually all the cells expressed the protein. However, MUC1 had no effect on water or urea permeabilities. In conclusion, MDCK cells grown on semipermeable supports form a model barrier epithelium. Abundant expression of mucins does not alter the permeability properties of these cells.

[Brain tumors in nursing infants]. / Tumores cerebrales en lactantes.

The purpose of this study was to determine the anatomical-pathological distribution of brain tumors in children under two years of age and their clinical characteristics (age, sex, time span from the start of symptoms or signs to the time the tumor was diagnosed, main clinical manifestations, evolution and prognosis). From 1981 to 1989, 16 children with brain tumors, under two years of age, were studied. The tumors arose in 13 patients during first year of life and during the second, in the remaining three. In 50% of the patients, the tumors were supratentorial. The histological diagnosis was made in all cases, finding the ependymoma the most frequent tumor, followed by the astrocytoma and other tumors: teratoma, choroid plexi papilloma. The increase in size was within the cephalic perimeter, with a risen fontanelle, irritability, vomiting and convulsive episodes, as main clinical manifestations. In 15 of the patients a partial or total resection of the tumor was performed, 6 were given radiotherapy and 2 chemotherapy. The prognosis correlated with the greatest surgical risk, the anatomical-pathological characteristics and the lateness in its diagnosis. We emphasize the greater morbi-mortality rate with respect to other pediatric ages.

Neumoperitoneo masivo secundario a barotrauma en un recien nacido. / Massive pneumoperitoneum secondary to barotraum in a newborn infant

Se describe el caso de un recien nacido que desarrolla neumoperitoneo secundariamente a barotrauma. Se plantean las alternativas que se presentan ante la decision de intervenir o no quirurgicamente en presencia de un neumoperitoneo. Se concluye que en el neumoperitoneo precedido por neumotorax y/o neumomediastino en asociacion a ventilacion mecanica o posibilidad de barotrauma a la reanimacion, la conducta puede ser conservadora y se adoptara el criterio quirurgico en caso de deterioro del paciente