Regulation of the renal proximal tubule second sodium pump by angiotensins

For several years it was believed that angiotensin II (Ang II) alone mediated the effects of the renin-angiotensin system. However, it has been observed that other peptides of this system, such as angiotensin-(1-7) (Ang-(1-7)), present biological activity. The effect of Ang II and Ang-(1-7) on renal sodium excretion has been associated, at least in part, with modulation of proximal tubule sodium reabsorption. In the present review, we discuss the evidence for the involvement of Na+-ATPase, called the second sodium pump, as a target for the actions of these compounds in the regulation of proximal tubule sodium reabsorption.

Essential regulatory elements for NHE3 gene transcription in renal proximal tubule cells

The objectives of the present study were to identify the cis-elements of the promoter absolutely required for the efficient rat NHE3 gene transcription and to locate positive and negative regulatory elements in the 5’-flanking sequence (5’FS), which might modulate the gene expression in proximal tubules, and to compare this result to those reported for intestinal cell lines. We analyzed the promoter activity of different 5’FS segments of the rat NHE3 gene, in the OKP renal proximal tubule cell line by measuring the activity of the reporter gene luciferase. Because the segment spanning the first 157 bp of 5’FS was the most active it was studied in more detail by sequential deletions, point mutations, and gel shift assays. The essential elements for gene transcription are in the region -85 to -33, where we can identify consensual binding sites for Sp1 and EGR-1, which are relevant to NHE3 gene basal transcription. Although a low level of transcription is still possible when the first 25 bp of the 5’FS are used as promoter, efficient transcription only occurs with 44 bp of 5’FS. There are negative regulatory elements in the segments spanning -1196 to -889 and -467 to -152, and positive enhancers between -889 and -479 bp of 5’FS. Transcription factors in the OKP cell nuclear extract efficiently bound to DNA elements of rat NHE3 promoter as demonstrated by gel shift assays, suggesting a high level of similarity between transcription factors of both species, including Sp1 and EGR-1.

Interactions of ANP and ANG II in tubular nephron acidification

(ANP, 1 µM) on the kinetics of bicarbonate reabsorption in the rat middle proximal tubule, we performed in vivo experiments using a stopped-flow microperfusion technique with the determination of lumen pH by Sb microelectrodes. These studies confirmed that ANG II added to the luminal or peritubular capillary perfusion fluid stimulates proximal bicarbonate reabsorption and showed that ANP alone does not affect this process, but impairs the stimulation caused by ANG II. We also studied the effects and the interaction of these hormones in cortical distal nephron acidification. Bicarbonate reabsorption was evaluated by the acidification kinetic technique in early (ED) and late (LD) distal tubules in rats during in vivo stopped-flow microperfusion experiments. The intratubular pH was measured with a double-barreled microelectrode with H+-sensitive resin. The results indicate that ANG II acted by stimulating Na+/H+ exchange in ED (81%) and LD (54%) segments via activation of AT1 receptors, as well as vacuolar H+-ATPase in LD segments (33%). ANP did not affect bicarbonate reabsorption in either segment and, as opposed to what was seen in the proximal tubule, did not impair the stimulation caused by ANG II. To investigate the mechanism of action of these hormones in more detail, we studied cell pH dependence on ANG II and ANP in MDCK cells using the fluorescent probe BCECF. We showed that the velocity of cell pH recovery was almost abolished in the absence of Na+, indicating that it is dependent on Na+/H+ exchange. ANP (1 µM) alone had no effect on this recovery but reversed both the acceleration of H+ extrusion at low ANG II levels (1 pM and 1 nM), and inhibition of H+ extrusion at higher ANG II levels (100 nM). To obtain more information on the mechanism of interaction of these hormones, we also studied their effects on the regulation of intracellular free calcium concentration, [Ca2+]i, monitored with the fluorescent probe Fura-2 in MDCK cells in suspension. The data indicate that the addition of increasing concentrations of ANG II (1 pM to 1 µM) to the cell suspension led to a progressive increase in [Ca2+]i to 2-3 times the basal level. In contrast, the addition of ANP (1 µM) to the cell suspension led to a very rapid 60% decrease in [Ca2+]i and reduced the increase elicited by ANG II, thus modulating the effect of ANG II on [Ca2+]i. These results may indicate a role of [Ca2+]i in the regulation of the H+ extrusion process mediated by Na+/H+ exchange and stimulated/impaired by ANG II. The data are compatible with stimulation of Na+/H+ exchange by increases of [Ca2+]i in the lower range, and inhibition at high [Ca2+]i levels

Regulation of nephron acidification by corticosteroids

The present paper reviews work from our laboratories evaluating the importance of adrenal cortical hormones in acidification by proximal and cortical distal tubules. Proximal acidification was determined by stationary microperfusion, and measurement of bicarbonate reabsorption using luminal pH determination was performed with H+-ion-sensitive microelectrodes. Rats were adrenalectomized (ADX) 48 h before the experiments, and corticosteroids (aldosterone (A), corticosterone (B), and 18-OH corticosterone (18-OH-B)) were injected intramuscularly 100 and 40 min before the experiments. In ADX rats stationary pH increased significantly to 7.03 as compared to sham-operated rats (6.78). Bicarbonate reabsorption decreased from 2.65 ± 0.18 in sham-operated rats to 0.50 ± 0.07 nmol cm-2 s-1 after ADX. The administration of the three hormones stimulated proximal tubule acidification, reaching, however, only 47.2% of the sham values in aldosterone-treated rats. Distal nephron acidification was studied by measuring urine minus blood pCO2 differences (U-B pCO2) in bicarbonate-loaded rats treated as above. This pCO2 difference is used as a measure of the distal nephron ability to secrete H+ ions into an alkaline urine. U-B pCO2 decreased significantly from 39.9 ± 1.26 to 11.9 ± 1.99 mmHg in ADX rats. When corticosteroids were given to ADX rats before the experiment, U-B pCO2 increased significantly, but reached control levels only when aldosterone (two 3-µg doses per rat) plus corticosterone (220 µg) were given together. In order to control for the effect of aldosterone on distal transepithelial potential difference one group of rats was treated with amiloride, which blocks distal sodium channels. Amiloride-treated rats still showed a significant reduction in U-B pCO2 after ADX. Only corticosterone and 18-OH-B but not aldosterone increased U-B pCO2 back to the levels of sham-operated rats. These results show that corticosteroids stimulate renal tubule acidification both in proximal and distal nephrons and provide some clues about the mechanism of action of these steroids

Effect of intracerebroventricularly injected insulin on urinary sodium excretion by cerebroventricular streptozotocin-treated rats

Recent evidence suggests that insulin may influence many brain functions. It is known that intracerebroventricular (icv) injection of nondiabetogenic doses of streptozotocin (STZ) can damage insulin receptor signal transduction. In the present study, we examined the functional damage to the brain insulin receptors on central mechanisms regulating glomerular filtration rate and urinary sodium excretion, over four periods of 30 min, in response to 3 µl insulin or 0.15 NaCl (vehicle) injected icv in STZ-treated freely moving Wistar-Hannover rats (250-300 g). The icv cannula site was visually confirmed by 2% Evans blue infusion. Centrally administered insulin (42.0 ng/µl) increased the urinary output of sodium (from 855.6 ± 85.1 to 2055 ± 310.6 delta%/min; N = 11) and potassium (from 460.4 ± 100 to 669 ± 60.8 delta%/min; N = 11). The urinary sodium excretion response to icv insulin microinjection was markedly attenuated by previous central STZ (100 µg/3 µl) administration (from 628 ± 45.8 to 617 ± 87.6 delta%/min; N = 5) or by icv injection of a dopamine antagonist, haloperidol (4 µg/3 µl) (from 498 ± 39.4 to 517 ± 73.2 delta%/min; N = 5). Additionally, insulin-induced natriuresis occurred by increased post-proximal tubule sodium rejection, despite an unchanged glomerular filtration rate. Excluding the possibility of a direct action of STZ on central insulin receptor-carrying neurons, the current data suggest that the insulin-sensitive response may be processed through dopaminergic D1 receptors containing neuronal pathways.

Serum uric acid and disorders of glucose metabolism: the role of glycosuria

Hyperuricemia has been associated with hypertension, diabetes mellitus, and metabolic syndrome. We studied the association between hyperuricemia and glycemic status in a nonrandomized sample of primary care patients. This was a cross-sectional study of adults ≥20 years old who were members of a community-based health care program. Hyperuricemia was defined as a value >7.0 mg/dL for men and >6.0 mg/dL for women. The sample comprised 720 participants including controls (n=257) and patients who were hypertensive and euglycemic (n=118), prediabetic (n=222), or diabetic (n=123). The mean age was 42.4±12.5 years, 45% were male, and 30% were white. The prevalence of hyperuricemia increased from controls (3.9%) to euglycemic hypertension (7.6%) and prediabetic state (14.0%), with values in prediabetic patients being statistically different from controls. Overall, diabetic patients had an 11.4% prevalence of hyperuricemia, which was also statistically different from controls. Of note, diabetic subjects with glycosuria, who represented 24% of the diabetic participants, had a null prevalence of hyperuricemia, and statistically higher values for fractional excretion of uric acid, Na excretion index, and prevalence of microalbuminuria than those without glycosuria. Participants who were prediabetic or diabetic but without glycosuria had a similarly elevated prevalence of hyperuricemia. In contrast, diabetic patients with glycosuria had a null prevalence of hyperuricemia and excreted more uric acid and Na than diabetic subjects without glycosuria. The findings can be explained by enhanced proximal tubule reabsorption early in the course of dysglycemia that decreases with the ensuing glycosuria at the late stage of the disorder.

Aplicação de medidas de ajuste de risco para a mortalidade após fratura proximal de fêmur

OBJETIVO: Analisar os fatores associados à mortalidade em pacientes para tratamento da fratura proximal do fêmur e as diferentes formas de ajuste de risco. MÉTODOS: Estudo de coorte não-concorrente com 390 pacientes com 50 anos ou mais. Os pacientes foram identificados no Sistema de Informações Hospitalares do Sistema Único de Saúde, internados para correção cirúrgica da fratura proximal do fêmur em um hospital universitário do município do Rio de Janeiro, entre 1995 e 2000. Foram levantados dados complementares nos prontuários desses pacientes e elaborados modelos de regressão logística para a chance de óbito em 90 dias após a data da admissão, segundo perfil dos pacientes e do tratamento. Foram calculados índices de classificação da gravidade do paciente. RESULTADOS: A taxa de mortalidade foi de 7,4% e os fatores que tiveram efeito sobre o óbito foram: idade (OR=1,06; IC 95%: 1,02;1,11), quantidade de comorbidades (OR=1,44; IC 95%: 1,12;1,69), índice de comorbidade de Charlson acima de 2 (OR=6,67; IC 95%: 2,98;22,16) e intervalo de tempo para a realização da cirurgia (OR=1,04; IC 95%:1,02;1,07). CONCLUSÕES: A quantidade de comorbidades e o índice de comorbidade de Charlson auxiliaram na predição da mortalidade.

Percutaneous Stent Implantation for Treating Multivessel Coronary Disease in Patients with and without Involvement of the Proximal Segment of the Anterior Descending Coronary Artery

OBJECTIVE: To assess coronary stent placement in patients with multivessel coronary disease and involvement of the proximal portion of the anterior descending coronary artery. METHODS: We retrospectively analyzed the in-hospital and late evolution of 189 patients with multivessel coronary disease, who underwent percutaneous coronary stent placement. These patients were divided into 2 groups as follows: group I (GI) - 59 patients with involvement of the proximal segment of the anterior descending coronary artery; and group II (GII) - 130 patients without involvement of the proximal segment of the anterior descending coronary artery. RESULTS: No significant difference was observed in the success rate of the procedure (91.5% versus 97.6%, p=0.86), nor in the occurrence of major adverse cardiac events (5.1% versus 1.5%, p=0.38), nor in the occurrence of major vascular complications (1.7% versus 0%, p=0.69) in the in-hospital phase. In the late follow-up, the incidence of major adverse cardiac events (15.4% versus 13.7%, p=0.73) and the need for new revascularization (13.5% versus 10.3%, p=0.71) were similar for both groups. CONCLUSION: The in-hospital and late evolution of patients with multivessel coronary disease with and without involvement of the proximal segment of the anterior descending coronary artery treated with coronary stent placement did not differ. This suggests that this revascularization method is an effective procedure and a valuable option for treating these types of patients.

Revascularização da descendente anterior proximal com stents revestidos por fármacos

OBJETIVO: Avaliar o prognóstico clínico dos doentes coronários submetidos a revascularização percutânea com implantação de stents revestidos com fármacos na descendente anterior proximal. MÉTODOS: Cento e setenta doentes consecutivos, com idade média de 65 anos, 49 (29%) mulheres, receberam implante de pelo menos um stent revestido com fármaco, no nosso centro. O número total de stents revestidos com fármaco implantados foi 189, dos quais 115 (61%) de sirolimus (CYPHER®) e 74 (39%) de paclitaxel (TAXUS®). Em 100 (60%) dos casos, estava presente doença coronário multivaso. Em 61 (36%) dos doentes tratou-se outro segmento coronário para além da descendente anterior proximal. Efetuou-se um seguimento clínico durante um tempo médio de 11 ± 5 meses e controle angiográfico entre os seis e os nove meses. Obteve-se um endpoint final composto por morte, infarto agudo do miocárdio e pela necessidade de reintervenção sobre a descendente anterior. Analisou-se secundariamente a ocorrência de reestenose, a necessidade de reintervenção sobre o segmento proximal da descendente anterior e a trombose de stent. RESULTADOS: O procedimento teve êxito angiográfico imediato em todos os doentes. Registraram-se duas mortes, dois infartos agudos do miocárdio, e duas reintervenções coronárias percutâneas por trombose de stent no período intra-hospitalar. Aos seis meses de seguimento, observou-se mais uma morte cardíaca e identificaram-se três infartos do miocárdio; houve necessidade de três novos procedimentos de revascularização. Até ao final do seguimento, verificaram-se mais três mortes, três infartos do miocárdio e oito revascularizações da descendente anterior, duas delas por cirurgia. A sobrevivência livre de eventos cardíacos adversos maior foi de 91%. A mortalidade cardíaca foi de 3%. A reestenose binária no segmento proximal da descendente anterior foi de 4,1%. A sobrevivência livre de revascularização do vaso alvo foi de 94%. Não se observaram casos de trombose tardia de stent. CONCLUSÃO: A revascularização percutânea da descendente anterior proximal com a implantação de stents revestidos com fármacos constitui uma estratégia terapêutica segura e muito eficaz em curto e longo prazos.

Correlação da espessura médio-intimal das carótidas primitivas proximal e distal

FUNDAMENTO: O aumento da espessura do IMT (do inglês intima-media thickness) das carótidas é utlizado como marcador precoce de aterosclerose e para avaliação do risco de eventos cardiovasculares. O ultrassom é utilizado na sua avaliação pela acessibilidade e baixo custo. São descritas medidas realizadas em diferentes regiões das carótidas. OBJETIVOS: Correlacionar o IMT nas regiões proximal e distal da carótida primitiva bilateral no intuito de orientar a sua utilização na prática clínica. MÉTODOS: O IMT foi medido nas porções proximais e distais da artéria carótida primitiva de 798 indivíduos (35-74 anos) de ambos os sexos usando ultrassom de alta resolução. O coeficiente de correlação de Pearson foi usado para se estabelecer as associações. As análises foram feitas inicialmente para toda a amostra e nos subgrupos com IMT < 0,90 mm (49% da amostra) e > 0,90 mm em pelo menos um sítio de medida. A significância estatística foi considerada para p <0 ,05. RESULTADOS: Ocorreu correlação significativa entre todas as correlações testadas. No grupo com IMT < 0,90 mm, o resultado situou-se entre 0,44 e 0,62. No subgrupo com IMT > 0,90 mm, houve expressiva queda de correlações, que se situaram entre 0,20 e 0,40. CONCLUSÃO: Os dados sugerem que o espessamento médio-intimal é mais uniforme ao longo das carótidas em fases mais precoces do desenvolvimento e tende a adquirir desenvolvimento focal à medida que progride. Portanto, na avaliação clínica de pacientes, toda a extensão das carótidas comuns deve ser investigada bilateralmente para melhor utilizar os softwares disponíveis e concluir sobre a presença ou não de espessamento do complexo médio-intimal.

Malpighian tubule polytene chromosomes of Culex quinquefasciatus (Diptera, Culicinae)

Dipteran polytene chromosomes provide an excellent model for understanding in species complexes, as well as for structural and functional cytogenetics. The status of species in the Culex pipiens complex is controversial and the use of polytene chromosomes for cytogenetic analysis in the subfamily Culicinae has been difficult because of methodological problems. In this study, Malpighian tubule polytene chromosomes were obtained from young (0 to 12 h, 20ºC) and old (20 to 42 h, 28ºC) laboratory-bred C. pipiens quinquefasciatus pupae. The chromosome maps for this species were constructed and compared with published data for C. pipiens pipiens and C. p. quinquefasciatus. Although the banding patterns were conserved between subspecies, analysis of the structural variations in the bands and interbands revealed differences apparently related to the physiological stage and ecogeographical strain. The organization of the centromeric regions in larval and pupal chromosomes showed greater similarity to each other than did those of pupal and adult chromosomes. The use of pupal polytene chromosomes for in situ hybridization with vector competence probes is discussed.

Influência do volume vesical na avaliação ultra-sonográfica da junção uretrovesical e uretra proximal

OBJETIVO: Investigar a influência do volume vesical na avaliação ultra-sonográfica da mobilidade da junção uretrovesical (JUV) e do comprimento da uretra proximal (UP) em mulheres com incontinência urinária de esforço (IUE). MATERIAIS E MÉTODOS: Mulheres com IUE submetidas à avaliação ultra-sonográfica da JUV e da UP com bexiga praticamente vazia (< 50 ml de urina) e com a bexiga cheia. RESULTADOS: As médias, em milímetros, dos parâmetros medidos com bexiga vazia e bexiga cheia foram, respectivamente: em repouso: distância vertical da JUV (DVJUV) de 15 e 13,5 (p = 0,3347), distância horizontal da JUV (DHJUV) de 14 e 15 (p = 0,3767), distância pubouretral (DPU) de 13 e 13 (p = 0,8065), UP de 15 e 14 (p = 0,8011); em esforço: DVJUV de 0 e 4 (p = 0,0281), DHJUV de 21 e 19,5 (p = 0,7501), DPU de 18,5 e 15 (p = 0,1592), UP de 0 e 4 (p = 0,0479); deslocamento: DVJUV de 16 e 15 (p = 0,0047), DHJUV de 6 e 5 (p = 0,3542), DPU de 7 e 5,5 (p = 0,1789), UP de 12 e 8 (p = 0,0496). CONCLUSÃO: Comparando bexiga quase vazia com bexiga cheia, há diferença significativa na avaliação ultra-sonográfica perineal da JUV e da UP apenas no esforço e sentido vertical, sendo que as pacientes com a bexiga quase vazia deslocam mais a JUV e a UP em relação à bexiga cheia.

Mudanças na vascularização arterial da curvatura menor do estômago após gastrectomia segmentar associada à vagotomia gástrica proximal em cães

Para avaliar os efeitos da gastrectomia segmentar do corpo associada à vagotomia gástrica proximal (GS + VGP), sobre a vascularização arterial da curvatura menor do estômago, foram utilizados 24 cães distribuídos em dois grupos de 12 animais, com as seguintes denominações: Grupo I, animais submetidos à laparotomia e manipulação gástrica; Grupo II, animais submetidos à GS + VGP. Em cada grupo, metade dos animais foi sacrificada no terceiro, metade no oitavo dia pós- operatório. No dia do sacrifício, procedeu-se à injeção de mistura de bário-gelatina, na vascularização arterial do estômago. A seguir, o estômago foi removido do animal, fixado em solução de formol, aberto pela curvatura maior e radiografado com técnica padronizada. A intensidade da vascularização da curvatura menor do estômago foi determinada por microdensitometria e morfometria. Pela microdensitometria, foram determinados os valores de densidade óptica, convertidos em equivalentes de milímetros de alumínio, da imagem radiográfica da curvatura menor do estômago. Com base nesses resultados, verificou-se que os valores médios de densidade óptica do grupo II foram significativamente maiores do que o grupo I (p<0,001). Pelo estudo morfométrico de fragmento histológico da curvatura menor, observou-se que os valores médios de volume relativo das arteríolas, em relação ao volume total da camada submucosa, foram significativamente maiores no grupo II em comparação ao grupo I (p<0,001). Os valores médios dos diâmetros das arteríolas da camada submucosa foram significativamente mais elevados no grupo II que no grupo I (p<0,001). O número de arteríolas por mm2 da camada submucosa não diferiu significativamente entre os dois grupos (p>0,05). Embora a execução da GS + VGP implique desvascularização da curvatura menor do estômago, observou-se aumento da intensidade da vascularização arterial desta curvatura nos animais do grupo II, conseqüente à dilatação das arteríolas da camada submucosa.