Participation of hepatic α/β-adrenoceptors and AT1 receptors in glucose release and portal hypertensive response induced by adrenaline or angiotensin II

It has been previously demonstrated that the hemodynamic effect induced by angiotensin II (AII) in the liver was completely abolished by losartan while glucose release was partially affected by losartan. Angiotensin II type 1 (AT1) and adrenergic (∝1- and β-) receptors (AR) belong to the G-proteins superfamily, which signaling promote glycogen breakdown and glucose release. Interactive relationship between AR and AT1-R was shown after blockade of these receptors with specific antagonists. The isolated perfused rat liver was used to study hemodynamic and metabolic responses induced by AII and adrenaline (Adr) in the presence of AT1 (losartan) and ∝1-AR and β-AR antagonists (prazosin and propranolol). All antagonists diminished the hemodynamic response induced by Adr. Losartan abolished hemodynamic response induced by AII, and AR antagonists had no effect when used alone. When combined, the antagonists caused a decrease in the hemodynamic response. The metabolic response induced by Adr was mainly mediated by ∝1-AR. A significant decrease in the hemodynamic response induced by Adr caused by losartan confirmed the participation of AT1-R. The metabolic response induced by AII was impaired by propranolol, indicating the participation of β-AR. When both ARs were blocked, the hemodynamic and metabolic responses were impaired in a cumulative effect. These results suggested that both ARs might be responsible for AII effects. This possible cross-talk between β-AR and AT1-R signaling in the hepatocytes has yet to be investigated and should be considered in the design of specific drugs.

The hepatic clearance of recombinant tissue-type plasminogen activator decreases after an inflammatory stimulus

We have shown that tissue-type plasminogen activator (tPA) and plasma kallikrein share a common pathway for liver clearance and that the hepatic clearance rate of plasma kallikrein increases during the acute-phase (AP) response. We now report the clearance of tPA from the circulation and by the isolated, exsanguinated and in situ perfused rat liver during the AP response (48-h ex-turpentine treatment). For the sake of comparison, the hepatic clearance of a tissue kallikrein and thrombin was also studied. We verified that, in vivo, the clearance of 125I-tPA from the circulation of turpentine-treated rats (2.2 + or - 0.2 ml/min, N = 7) decreases significantly (P = 0.016) when compared to normal rats (3.2 + or - 0.3 ml/min, N = 6). The AP response does not modify the tissue distribution of administered 125I-tPA and the liver accounts for most of the 125I-tPA (>80 percent) cleared from the circulation. The clearance rate of tPA by the isolated and perfused liver of turpentine-treated rats (15.5 + or - 1.3 µg/min, N = 4) was slower (P = 0.003) than the clearance rate by the liver of normal rats (22.5 + or - 0.7 µg/min, N = 10). After the inflammatory stimulus and additional Kupffer cell ablation (GdCl3 treatment), tPA was cleared by the perfused liver at 16.2 + or - 2.4 µg/min (N = 5), suggesting that Kupffer cells have a minor influence on the hepatic tPA clearance during the AP response. In contrast, hepatic clearance rates of thrombin and pancreatic kallikrein were not altered during the AP response. These results contribute to explaining why the thrombolytic efficacy of tPA does not correlate with the dose administered

Enzima inativadora de bradicinina liberada de fígado preservado ex-vivo / Bradykinin-inactivating enzyme is released from the ex-vivo stored liver

Objetivo - Ofígado inativa quantidades consideráveis de bradicinina; a principal enzima hepática cinino-inativadora (BIE, bradykinin inativating endopeptidase) hidrolisa especificamente a ligaçao Phe-Ser do nonapeptídio e foi caracterizada como sendo a oligoendopeptidase EC 3.4. 24.15. No transplante ortotópico de fígado existe correlaçao entre aumento da concentraçao de aminoácidos no líquido de preservaçao (conseqUência de proteólise) e falência do enxerto. O objetivo deste trabalho é verificar se ocorre liberaçao da BIE de fígados preservados ex-vivo no líquido Braun-Collins ou em soluçao de Krebs-Henseleit bicarbonato (Krebs). Método. Fígado de ratos Wistar (180-220g) foram exsangüinados e a pós remoçao foram preservados em líquido Braun Collins ou em soluçao Krebs, a 4 graus Celsius. Foram retiradas alíquotas do líquido de preservaçao nos tempos 0, 4, 8 e 24 horas, para dosagem de ALT, AST, DHL e BIE. A atividade fluorimétrica da BIE foi ensaiada com o substrato Abz-RPPGFSPFRQ-EDDnp (análogo sintético da bradicinina) e sua presença confirmada por immunoblotting, revelado com anticorpo específico anti-EC 3.4.24.15. Resultados. A liberaçao de ALT, AST, DHL e BIE é significativa no período 8-24 hs. Nas alíquotas de 24 hs, em relaçao ao tempo zero, a concentraçao das quatro enzimas aumentou, respectivamente, no líquido Braun Collins, 8, 7, 19 e 10 vezes e, na soluçao de Krebs, 21, 17, 27 e 21 vezes; a relaçao ALT/DHL foi sempre inferior a um. Conclusao. Ocorre liberaçao de BIE durante a preservaçao ex-vivo do fígado, o que poderá servir como indicaçao da condiçao de preservaçao do enxerto; diminuiçao da capacidade cinino-inativadora do fígado poderá afetar sua reatividade vascular.

Clearance of the alpha2 macroglobulin-tripsin complex and uptake of trypsin by perfused liver

The uptake and degradation of the alpha2macroglobulin-trypsin (alpha2m-trypsin) complex have been studied using isolated liver cells but not in the liver as a whole. We report the clearance of the complex by the isolated and exsanguinated liver of Wistar male rats, weighing 150-280 g, and compare it with that of the free enzyme. The hepatic clearance of the alpha2m-trypsin complex follows a pattern with a distribution phase followed by an elimination phase, which contrasts with that of trypsin where only the distribution phase is observed. The extraction of trypsin from the perfusate is Ca2+ -independent (156 + 14 pmol/g liver in the presence of 2.5 mM Ca2+, N = 9, versus 140 + 8 pmol/g liver in its absence, N = 7) and is not affected by 100 mM NH4Cl (152 + 7 pmol/g liver, N = 6), 100 U/ml heparin (164 + 14 p/mol/g liver, N = 5), 30 mul/ml carbon particle suspension (150 + 13 pmol/g liver, N = 7) or an acute-phase situation induced by turpentine (125 + 10 pmol/g liver, N = 6) (P>0.05, ANOVA). The hepatic clearance of the alpha2m-trypsin complex is Ca2+ -dependent (1.8 + 0.2 ml/min in the presence of Ca2+, N = 8, versus 0.6 + 0.03 ml/min in its absence, N = 4), affected by NH4Cl (<0.1 ml/min, N = 7), heparin (1.1 + 0.2 ml/min, N = 6) and the acute-phase (0.6 + 0.1 ml/min, N = 6) but bot by the carbon particle suspension (1.8 + 0.2 ml/min, N = 7). These results show that trypsin is not internalized by hepatocytes (no NH4Cl effect) or Kupffer cells (no carbon particle effect) and that the alpha2m-trypsin complex is internalized in a Ca2+ -dependent process by hepatocytes, but not by Kupffer cells, and is affected by an acute-phase reaction.

Depuraçäo hepática da calicreína plasmática na cirrose experimental / Plasma kallikrein clearance by the liver in experimental cirrhosis

OBJETIVO. Estudar a depuraçao de glicoproteína, e calicreína plasmática, pelo fígado de ratos com cirrose descompensada. MATERIAL E MÉTODO. Produçao de cirrose pela administraçao de tetracloreto de carbono, 520 mg/kg de peso corporal, uma vez por semana, intragastricamente, durante 16 a 19 semanas. Após o período de tratamento cada fígado foi isolado, exsanguinado e perfundido a 37 graus Celsius com calicreína plasmática de rato (CPR) 10nM. A velocidade de depuraçao da CPR na cirrose foi comparada com a de grupos-controle. RESULTADOS. 58 por cento dos animais morreram durante o tratamento. Os sobreviventes desenvolveram prostraçao, ascite, icterícia e sangramentos; ao final do período de tratamento as aminotransferases séricas eram normais e a albumina sérica diminuída. A histologia hepática (hematoxilina-eosina e coloraçao para reticulina) mostrou cirrose no grupo tratado. A velocidade de depuraçao hepática da CPR no grupo cirrótico (5,4 + 0,9pmol/g fígado/10 min) foi significativamente menor (p < 0,05) do que no grupo controle (13,5 + 2,7pmol/g fígado/10min). CONCLUSAO. O desenvolvimento de cirrose descompensada acompanha-se de diminuiçao da capacidade hepática de depurar glicoproteína, que é internalizada por endocitose mediada por receptor.

Plasma kallikrein clearance by the liver: a review

1. The liver is the main organ clearing both plasma and tissue kallikereins from the circulation. Hepatocytes are responsible for the internalization of rat plasma kallikrein (RPK) and liver cell is located on its heavy chain which is not exposed on prokallikrein. An S-type lectin accounts for the receptor-mediated endocytosis of TPK. 2. These properties of the liver are affected by pathological situations, particularly the acute-phase response to inflammation, in which the kallikrein-kinin system plays a major role. The hepatic clearance of the alfa2-macroglobulin-plasma kallikrein complex is less efficient than the clearance of the free enzyme

Native plasma kallikrein is cleared at similar rates by mammalian and avian livers

Rat plasma kallikrein (RPK) is a serine protease that circulates as an inactive precursor, prokallikrein, and once activated is efficiently cleared by the liver by a carbohydrate-dependent, Ca2+ - independent mecanism. Seven hepatic lectin systems have been described for mammals but not all of these animal lectins are expressed in the avian liver. Using a liver perfusion system we compared the plasmakallikrein clearance of rats (N=10) and pigeons (N+4). Our results show that the lectin responsible for the hepatic clearance of plasma kallikrein is also present in pigeon liver and that this organ clears the enzyme with an efficiency (11.4 ñ 1.3 pmol/g,20 min) similar to that of the rat liver (10.0 ñ 0.7 pmolg, 20 min)_

Plasma kallikrein clearance by the liver in food-restricted rats

We measured the cleaance rate of plasma kallikrein by the liver in three groups of rats: one recently weaned, and two seven weeks old (control and food-restricted groups). The clearance rates were similar in the three groups when expressed as units/g liver. The livers of the recently weaned and food-restricted rats were, however, smaller than those of the controls and consequently their livers cleared plasma kallikrein less efficiently