Contribution of the liver to thoracic duct lymph flow in a motionless subject

To ascertain the contribution of the liver to thoracic duct lymph (TDL) flow in a resting subject, afferent hepatic blood flow was temporarily interrupted in dogs by placing an atraumatic clamp across the hepatoduodenal ligament containing the hepatic artery, portal vein and 80% of hepatic lymphatic drainage. To circumvent extrahepatic splanchnic venous sequestration, a side-to-side portacaval shunt (S-S-PCS) was constructed prior to interrupting blood flow. Portal venous pressure, cervical TDL flow, and total protein content were serially monitored. TDL and total protein after S-S-PCS was comparable to that recorded in dogs without celiotomy (0.60 +/- 0.17 ml/min and 3.4 +/- 0.5g/dl, respectively). Interruption of hepatic blood flow was associated with a fall in TDL flow (0.38 +/- 0.8ml; p less than 0.001) and protein content (2.8 +/- 0.7g/dl; p less than 0.01) and TDL/plasma protein ratio (0.58 +/- 0.7 to 0.48 +/- 0.05; p less than 0.01). These data suggest that in the absence of supplemental fluid administration or other exogenous stimulation, hepatic lymph contributes one-third of resting TDL flow.     

Systemic and splanchnic hemodynamics following hemorrhage and volume restitution with Haemaccel in portal hypertensive rats: The effect of propranolol

BACKGROUND AND AIMS: Recently, we found in a portal hypertensive rat model that hemorrhage and volume restitution with Haemaccel, a low viscosity plasma expander, induced an increase in cardiac output and portal venous inflow. The present study was conducted to evaluate whether pretreatment with propranolol will attenuate these hyperdynamic changes. METHODS: Portal hypertension was induced by portal vein constriction. Treatment was initiated 14--21 days later. Propranolol (30 mg/kg per day) or water were administered for 7 days via a gastric gavage. Under ketamine anesthesia, 18 h after the last given dose, blood was withdrawn at a constant rate of 0.3 mL/min for 15 min followed by a 15-min stabilization. Haemaccel was infused at the same rate and volume used for withdrawal. Hemodynamic measurements were performed after volume restitution in both groups by using radioactive microspheres. RESULTS: Eight rats were studied in each group. In the propranolol-treated animals, portal venous inflow was decreased (2.4 +/- 0.8 vs 3.8 +/- 0.7 mL/min per 100 g bodyweight; P < 0.01), while splanchnic arteriolar and porto-collateral resistance were increased (52.8 +/- 21.0 vs 32.8 +/- 13.0 and 6.0 +/- 1.4 vs 4.1 +/- 0.7 mmHg x min x 100 g bodyweight/mL; P < 0.05, respectively). Cardiac output, mean arterial pressure, heart rate, total peripheral resistance and portal pressure were not significantly different between the two groups. CONCLUSION: In this model, pretreatment with propranolol prevented the increase in portal venous inflow, which occurs following hemorrhage and volume restitution with Haemaccel. Although caution should be taken in extrapolating data from animal models to humans, our results suggest that volume replacement during a portal hypertensive-related bleeding episode may be safer in a patient treated with non-selective beta-adrenoreceptor antagonists.     

Relationship of splanchnic blood flow and portal venous resistance to elevated portal pressure in the dog.

To determine the relationship of splanchnic blood flow and portal venous resistance to elevated portal pressure, in situ perfusion of the splanchnic circuit was carried out in 12 freshly killed dogs at varying perfusion rates and degrees of acute and chronic portal vein constriction. In six normal dogs before being killed, portal pressure averaged 8-8 +/- 1-2 mmHg and portal flow 658 +/- 81 ml/min. In the absence of portal vein constriction, increasing splanchnic perfusion to 1800 ml/min, minimally raised portal pressure (12-8 +/- 1-5 mmHg). With progressive acute constriction of the portal vein, however, comparable perfusion rates lead to progressively higher portal pressure levels and with greater than 90% constriction, portal pressure was greater than 30 mmHg with minimal elevation in splanchnic flow rate. In six other dogs before being killed but live to nine weeks after placement of an ameroid constrictor on the portal vein, portal pressure averaged 13-6 +/- 1-4 mmHg or slightly higher than in normal dogs (P greater than 0-02). Mesenteric venography and necropsy findings uniformly demonstrated 90% occlusion of the portal vein with extensive portasystemic collateralization. With increased perfusion of the splanchnic bed, portal pressure rose rapidly to approximately 35 mmHg with a flow rate of 1 800 ml/min.. These data suggest that, in disorders where resistance to transhepatic portal flow is marked, a small increment in splanchnic blood flow, which normally exerts little or no influence on portal pressure, promotes profound portal hypertension and may account for spontaneous 'rupture' of oesophageal varices. On the other hand, where resistance to transhepatic portal flow is mild but splanchnic blood flow is markedly hyperdynamic, reducing inflow may be sufficient to ameliorate extreme portal hypertension and its sequelae.     

Intestinal microvascular adaptation to chronic portal hypertension in the rat

Microvascular pressures, diameters, and flow velocities were measured in the small intestine of rats with chronic stenosis of the portal vein. Ten days after portal vein stenosis, portal venous pressure increased (13.8 +/- 0.4 mmHg vs, 7.3 +/- 0.5 mmHg; p less than 0.05) whereas systemic arterial pressure decreased (94.2 +/- 2.0 mmHg vs. 106.5 +/- 1.6 mmHg; p less than 0.05). Red blood cell centerline velocity, measured in first-order arterioles, was significantly higher in portal hypertensive rats (24.3 +/- 1.2 mm/s vs. 19.6 +/- 1.3 mm/s), yet there was no significant change in the diameters of these vessels. Microvascular pressures and diameters of first- and second-order arterioles were not different between control and portal hypertensive rats. However, both pressure (34.3 +/- 2.7 mmHg vs. 28.0 +/- 1.8 mmHg) and diameter (30.4 +/- 0.6 microns vs. 21.4 +/- 2.1 microns) were significantly increased in the third-order arterioles of portal hypertensive rats. A consistent elevation in pressure was observed throughout the distal segments (capillaries to first-order venules) of the intestinal microcirculation of portal hypertensive rats. The results of these studies indicate that the increased intestinal vascular pressures associated with chronic portal hypertension result from a combination of reduced arteriolar resistance and venous congestion.     

Effect of interleukin-2 on microvascular liquid and protein transport in the rat small intestine

Interleukin-2 (IL-2), a glycoprotein lymphokine derived from activated T-lymphocytes displays potent anti-cancer properties but its therapeutic use has been limited by generalized tissue swelling. To shed light on the mechanism underlying this potentially life-threatening edematogenic syndrome, recombinant IL-2 or an equal volume of control solution (excipient or 5% dextrose) was administered to 88 adult, male Sprague-Dawley rats. Initially, rats were injected with 50,000 Cetus units (equal to 300,000 I.U.) of IL-2 intraperitoneally, either one-time ("acute" rats) or every eight hours for two or seven days ("chronic" rats). Thereafter, under pentobarbital anesthesia, the main mesenteric lymph duct was isolated, incised, and measurements made of intestinal lymph flow (JV) and the total protein content and protein fractions in lymph (L) and plasma (P) (refractometry and agarose gel electrophoresis, respectively). Final measurements were also carried out after superior mesenteric vein constriction to assess filtration-independent L/P total protein "washdown." After IL-2, JV and protein clearance (JV x L/P) were increased (p less than 0.001) while lymph and plasma total protein content and protein fractionation were unchanged. Protein washdown was also maintained. These data are not only inconsistent with bulk "plasma leak" from damaged capillaries, but in conjunction with previously demonstrated increased cardiac output and reduced systemic vascular resistance after IL-2 administration, the findings favor augmented microvascular surface exchange area from increased capillary perfusion as the primary mechanism underlying increased transcapillary liquid and protein flux. This conclusion conforms to the rapid reversal of edema in patients after cessation of IL-2 therapy.     

Effect of hepatic nerves, norepinephrine, angiotensin, and elevated central venous pressure on postsinusoidal resistance sites and intrahepatic pressures in cats

Portal venous pressure was controlled by resistance localized to specific sites in hepatic lobar veins in cats. All of the pressure drop from the portal vein to the vena cava occurred across postsinusoidal vessels; portal pressure, lobar venous pressure, and, therefore, sinusoidal pressure were not significantly different. Norepinephrine and angiotensin infusions (intraportal) caused elevation in portal pressure due to constriction of hepatic venous resistance sites as well as some constriction of presinusoidal (portal or sinusoidal) resistance sites. At low doses of norepinephrine presinusoidal constriction dominated whereas at higher doses the postsinusoidal constriction increased proportionately more. Hepatic nerve stimulation produced a similar response measured at an early time (1 min), but by 3 min the presinusoidal constriction showed complete escape so that elevated portal pressure was entirely due to hepatic venous constriction. The same site that provided basal vascular resistance also provided the increased hepatic venous resistance with nerve stimulation and infusion of angiotensin and norepinephrine. Rapid elevation of central venous pressure (CVP) caused elevated sinusoidal pressure. At high CVP (16 mm Hg), 75% of a rise in CVP was transmitted whereas at normal CVP (less than 4.5 mm Hg) less than 20% transmission occurred. The presence of a high resistance in the hepatic veins protected intrahepatic pressure from the effects of normal fluctuation of CVP.     

Effects of acute volume loading and hemorrhage on intestinal vascular capacitance: a mechanism whereby capacitance modulates cardiac output

BACKGROUND: Changes in intestinal vascular capacitance during acute volume loading and hemorrhage have not been described. OBJECTIVES: To determine the effects of volume loading and hemorrhage on the intestinal vascular pressure-volume relationship and cardiac output. PATIENTS AND METHODS: In 11 alpha-chloralose-anesthetized dogs, a pneumatic portal venous constrictor and catheter were positioned to increase and measure portal venous pressure (Ppv), respectively. Relative changes in intestinal blood volume (IBV) were determined by blood-pool scintigraphy and expressed as the percentage change from control values (taken as 100%). Ppv-IBV relationships were constructed by graded portal vein constriction. RESULTS: IBV and cardiac output increased by 60 6% and 178 48%, respectively, and Ppv increased from 5.8 0.9 mmHg to 13.2 1.8 mmHg after initial volume loading (40 mL/kg of an isotonic glucose-saline solution over 7 min). IBV gradually decreased and reached near-control values after 75 min. In seven dogs, hemorrhage (sufficient to decrease mean aortic pressure by 56 4%) decreased IBV and cardiac output to 88 4% and 52 3% of control values, respectively, and Ppv decreased to 3.2 0.8 mmHg. CONCLUSIONS: A sigmoid function curve defined the relationship between cardiac output and IBV. Cardiac output remained constant over a wide range (between approximately 95% and 135% of control IBV). Outside this range, insufficient dilation or constriction resulted in a marked increase or decrease in venous pressures and cardiac output. These data indicate that vasculature capacitance modulates cardiac output during acute volume loading and hemorrhage, thereby maintaining cardiac output relatively constant over a wide range of total vascular blood volume.     

Measurement of portal vascular resistance in patients with portal hypertension

Portal vascular resistance was measured percutaneously in 60 patients with chronic liver disease and in 5 control subjects. The portal vascular resistance (PVR) was calculated, using the following equation, from the portal blood flow (QPV), portal venous pressure (PPV), and hepatic venous pressure (PHV): PVR = (PPV - PHV)/QPV. The portal blood flow was measured using an ultrasonic Doppler duplex system, and the portal venous and hepatic venous pressures were measured using percutaneous transhepatic catheterization and venous catheterization, respectively. The wedged hepatic venous pressure was measured by occluding the hepatic venous branch using a balloon catheter. The portal vascular resistance was 0.25 +/- 0.13 mmHg X ml-1 X min X kg body weight (mean +/- SD, n = 5) in the control group, 0.64 +/- 0.29 mmHg X ml-1 X min X kg body wt (n = 13) in the chronic active hepatitis group, 1.34 +/- 0.79 mmHg X ml-1 X min X kg body wt (n = 30) in the cirrhosis group, and 0.85 +/- 0.69 mmHg X ml-1 X min X kg body wt (n = 13) in the idiopathic portal hypertension group.     

Interrelationship between splenic and superior mesenteric venous circulation manifested by transient splenic arterial occlusion using a balloon catheter

We examined the hemodynamic changes induced by transient splenic arterial occlusion using a balloon catheter to investigate the hemodynamic effect of transcatheter splenic arterial embolization--a procedure that has been used since its introduction in 1973 as therapy for hypersplenism and more recently for portal hypertension. The blood flow volume was measured in 20 patients with liver disease using an ultrasonic duplex system (Toshiba SAL50A/SDL-01A). The portal venous pressure was also measured via a 3F catheter using a transducer. The catheter was placed in position by substituting it for a 25-gauge needle that had been inserted into the portal vein under ultrasonic guidance percutaneously and transhepatically. Splenic arterial occlusion caused a drop in splenic venous blood flow from 708 +/- 487 to 241 +/- 155 ml per min, in portal venous blood flow from 993 +/- 439 to 807 +/- 419 ml per min and in portal venous pressure from 17.4 +/- 7.2 to 14.4 +/- 6.1 mm Hg. The latter two reductions were less than expected from the decrease in the splenic venous blood flow volume. This phenomenon was caused by an increase in the mesenteric venous blood flow from 475 +/- 126 to 630 +/- 270 mm per min. This increase may be due to a compensatory mechanism under the control of a regulatory loop in the liver or portal vein, and there seems to be a relationship between splenic and intestinal circulation in portal hypertension that maintains hepatic circulation.     

Comparison between portal vein pressure and wedged hepatic vein pressure in hepatitis B-related cirrhosis

Portal vein pressure and wedged hepatic vein pressure were measured simultaneously in 21 patients with hepatitis B-related cirrhosis of the liver and were compared to pressure measured in six patients with idiopathic portal hypertension. No significant difference in the portal venous pressure gradient was found between patients with cirrhosis and those with idiopathic portal hypertension (17.3 +/- 4.3 mmHg (mean +/- S.D.) vs. 19.7 +/- 3.1 mmHg, P greater than 0.05). However, the difference between the portal and the hepatic venous pressure gradient was significantly smaller in patients with cirrhosis than in idiopathic portal hypertension patients (1.3 +/- 1.7 vs. 10.8 +/- 2.1 mmHg, P less than 0.001). An excellent correlation was found between portal vein pressure and wedged hepatic vein pressure in hepatitis B-related cirrhosis (r = 0.94, P less than 0.001). There was no linear relationship between the portal venous pressure gradient and varix size or bleeding episodes. We concluded that a close agreement existed between portal vein pressure and wedged hepatic vein pressure in hepatitis B-related liver cirrhosis. Therefore, measurement of wedged hepatic vein pressure reliably reflects portal vein pressure in these patients.     

Flow in lymphatic networks: interaction between hepatic and intestinal lymph vessels

OBJECTIVE: Lymph from both the liver and intestine flows into the cisterna chyli. We hypothesized that increasing liver lymph flow would increase cisterna chyli pressure and, thereby, decrease intestinal lymph flow, potentiating intestinal edema formation. METHODS: Anesthetized dogs were instrumented to measure and manipulate portal vein pressure and cisterna chyli pressure. The effects of directly increasing portal pressure with and without directly increasing cisterna chyli pressure on intestinal wet-to-dry ratio and intestinal ascites formation rate were determined. Target values for portal and cisterna chyli pressures were determined following elevation of inferior vena caval pressure to levels seen in patients with obstructive caval disease. RESULTS: Direct elevation of portal pressure (P(port)) alone to 17.5 mm Hg caused a significant increase in intestinal wet-to-dry ratio (3.98 +/- 0.24 vs. 3.40 +/- 0.43) and the rate of ascites formation (0.36 +/- 0.12 vs. 0.05 +/- 0.03 mL/g dry wt/h). Simultaneous direct elevation of cisterna chyli pressure to 6.0 mm Hg and P(port) to 17.5 mm Hg caused further increases in intestinal wet-to-dry ratio (5.52 +/- 1.20) and ascites formation (0.57 +/- 0.11 mL/g dry wt./h). CONCLUSIONS: Inferior vena caval hypertension increases liver lymph flow that elevates cisterna chyli pressure, which inhibits intestinal lymph flow and augments intestinal edema formation.     

Late hemodynamic changes following controlled hemorrhage and volume restitution with blood or Haemaccel in anesthetized portal hypertensive rats

BACKGROUND AND AIM: In portal hypertensive rats, hemorrhage and acute volume restitution with Haemaccel induced increased cardiac output and portal venous inflow. In the present study, the late hemodynamic effects of this procedure were explored. METHODS: Portal hypertension was induced by portal vein constriction. Blood was withdrawn 11.2 +/- 3.2 days later, at a rate of 0.3 mL/min, for 15 min, followed by 15 min of stabilization. Haemaccel or blood were infused at the same rate and volume used for withdrawal. Hemodynamic measurements were performed after 24 h, using radioactive microspheres. Viscosity was measured with an Ostwald viscometer. Vascular hindrance was calculated as resistance/viscosity ratio. RESULTS: Blood viscosity of the Haemaccel group (n = 11), was lower than in the blood group (n = 11): 2.7 +/- 0.2 versus 4.0 +/- 0.4 (P < 0.01). Arterial pressure, cardiac output, peripheral resistance, portal pressure, portal venous inflow and splanchnic arteriolar resistance were not significantly different. Splanchnic arteriolar and portocollateral hindrance were higher in the Haemaccel group (11.7 +/- 5.3 and 1.5 +/- 0.6 vs 7.7 +/- 3.0 and 0.9 +/- 0.4 mmHg x min x 100 gram body weight/mL, respectively, P < 0.05). CONCLUSION: In portal hypertensive rats, vital organs perfusion, 24 h after hemorrhage and isovolemic volume restitution with Haemaccel and blood, was similar. However, in Haemaccel-transfused animals, a reduction in vascular hindrance, indicating vasoconstriction, was observed in the splanchnic organs, which drain into the portal circulation. Vasoconstriction of the portocollateral vascular bed was observed as well. We suggest that slow-rate volume replacement during a portal-hypertensive-related bleeding episode enables hemodynamic adaptation to occur. Thus, undesirable hyperdynamic changes, which may aggravate secondary bleeding, are attenuated.     

The Effects of Endoscopic Sclerotherapy Combined with Transhepatic Variceal Obliteration on Portal Hemodynamics

We studied the effects of endoscopic sclerotherapy with transhepatic variceal obliteration on portal hemodynamics in 20 patients with cirrhosis (six with a spontaneous splenorenal shunt and 14 without it). Portal venous flow 1 month after combined therapy (measured by pulsed Doppler flowmeter) was significantly increased compared with that before therapy (n = 20, 843 +/- 339 vs. 669 +/- 253 ml/min, p less than 0.001). Portal vein catheterization and portal venous flow measurement were repeated 18 months after therapy in eight patients without a splenorenal shunt before therapy and in two patients with a splenorenal shunt before therapy. Two of the former developed a splenorenal shunt. In these 10 patients, portal venous flow before, one month, and 18 months after therapy was 617 +/- 219, 784 +/- 227, and 720 +/- 224 ml/min, respectively, and in 8 of 10 patients the portal venous flow at 18 months remained similar to the values at one month. Portal vein pressures were not significantly elevated 18 months after therapy (35.4 +/- 6.4 vs. 33.6 +/- 5.1 cm H2O) and the mean portal vein pressure change was 2.75 cm H2O (range -6 to +7.5 cm H2O). To summarize, portal venous flow was significantly increased one month after combined sclerotherapy in cirrhotics, the portal venous flow at 18 months remained similar to the values at 1 month in most patients, and the change in portal vein pressure after therapy was small.     

Effects of Esophageal Transection Combined with Splenectomy on Portal Hemodynamics

Portal hemodynamics were studied in 69 patients with cirrhosis and 29 patients with idiopathic portal hypertension to investigate the effects of an operative procedure for varices that consists of transabdominal esophageal mucosal transection, paraesophagogastric devascularization, pyloroplasty, and splenectomy. Portal venous flow measured by the pulsed Doppler flowmeter in 14 patients with cirrhosis and nine patients with idiopathic portal hypertension, who underwent operation 2-5 yr earlier, was significantly reduced compared with that in unoperated 49 patients with cirrhosis and 17 patients with idiopathic portal hypertension who had esophageal varices (410 +/- 158 versus 660 +/- 263 ml/min in cirrhosis; 443 +/- 185 versus 912 +/- 189 ml/min in idiopathic portal hypertension). In nine patients (six cirrhosis, three idiopathic portal hypertension), portal venous flow and portal vein pressure were measured before and after operation. In patients with cirrhosis, portal vein pressure did not change significantly postoperatively even though portal venous flow was reduced. In contrast, portal vein pressure decreased in two patients with idiopathic portal hypertension in whom portal venous flow was reduced. Portal vein pressure was elevated in one patient with idiopathic portal hypertension in whom portal venous flow was increased postoperatively as a result of resection of a large gastro- and splenorenal shunt conducted additionally.     

Permeability of intestinal microvessels in chronic arterial hypertension

We studied changes in intestinal microvascular permeability resulting from chronic arterial hypertension. Normotensive dogs and dogs made chronically hypertensive utilizing the one-kidney, one clip Goldblatt technique were used to obtain values for: arterial pressure, portal pressure, intestinal lymph flow, and the lymph-to-plasma protein concentration ratio (CL/Cp). Values for the normotensive dogs were 111 mm Hg, 7.1 mm Hg, 6.2 ml/hr, and 0.64, respectively, while values for the chronically hypertensive dogs were 165 mm Hg, 7.3 mm Hg, 12.5 ml/hr, and 0.66, respectively. Control lymph flow in the hypertensives was 100% greater than in the normotensives, while there was no significant difference in control CL/Cp between the two groups. When portal venous pressure was acutely increased to 30 mm Hg, lymph flow increased to approximately the same maximum value in both groups. This represents an eightfold increase in normotensive and a fourfold increase in hypertensive lymph flows. The reflection coefficient determined as 1 - (CL/Cp) for total proteins at maximum lymph flow was 0.78 for the normotensives and 0.56 for the hypertensives. An electrophoretic analysis indicated sieving of large molecular weight protein fractions was considerably reduced in the hypertensives when compared to the normotensives. Our results indicate a significant increase in intestinal microvascular permeability to macromolecules resulting from the one-kidney, one clip Goldblatt model of chronic arterial hypertension.     

Effect of heparin on increased pulmonary microvascular permeability after bone marrow embolism in awake sheep

We examined the alterations in pulmonary transvascular fluid and protein exchange after intravenous infusion of fat emboli, i.e., bone marrow suspension (BMS) in awake sheep prepared with chronic lung lymph fistulas and compared these changes with those observed in sheep pretreated with heparin. The BMS injection (0.2 ml/kg) over 15 min caused rapid, but transient, increases (p less than 0.05) in mean pulmonary artery pressure and pulmonary vascular resistance. These increases were accompanied by significant increases in the lymph concentrations of thromboxane B2 and 6-keto-PGF1 alpha. Pulmonary lymph flow increased by 3.9-fold (+/- 0.8) over baseline by 120 min after BMS with no change in the lymph-to-plasma protein concentration ratio (L/P ratio). Heparin pretreatment (700 U/kg) enhanced the BMS-induced increases in pulmonary artery pressure and pulmonary vascular resistance. Thromboxane B2 concentrations in the lymph increased, whereas there was no change in the concentration of 6-keto-PGF1 alpha. Lung lymph flow increased 4-fold (+/- 1.0) over baseline by 120 min after BMS without a change in L/P ratio. Changes in lung vascular permeability were evaluated by elevating pulmonary microvascular pressure (left atrial balloon catheter inflation) at 120 min after BMS. Lung lymph flow increased 7-fold (+/- 1.1) from baseline, whereas the L/P ratio decreased to a mean value of 0.48 +/- 0.03. The protein reflection coefficient (sigma = 1 - L/P ratio) decreased from a control mean of 0.69 +/- 0.02 to 0.52 +/- 0.03 after the BMS challenge.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of augmenting portal venous inflow on intrahepatic pressure and resistance in the isolated perfused porcine liver

BACKGROUND/AIMS: The literature regarding the relationship between portal venous flow and pressure is controversial. The aim of this study was to examine the effects of doubling portal venous inflow on hepatic hemodynamics. METHODOLOGY: Portal venous pressure, intrahepatic portal venous resistance, hepatic arterial pressure and intrahepatic arterial resistance were assessed during basal portal venous inflow (756 +/- 142 mL/min; mean +/- SD) and enhanced portal venous inflow (1512 +/- 284 mL/min) in an isolated perfused normal porcine liver model (n = 6). Hepatic arterial flow was maintained constant throughout the experiments. RESULTS: During the period of enhanced portal venous flow there was an increase in: portal venous pressure (from 9 +/- 2 to 22 +/- 7 mm Hg, P = 0.0076); the difference between portal venous and hepatic venous pressures (from 2 +/- 2 to 10 +/- 5 mm Hg; P = 0.0289); hepatic arterial pressure (from 84 +/- 9 to 151 +/- 33 mm Hg, P = 0.0019); and intrahepatic arterial resistance (from 0.3488 +/- 0.0637 to 0.6387 +/- 0.2020, P = 0.0046). CONCLUSIONS: The increases in hepatic artery pressure and intrahepatic arterial resistance are a result of the hepatic arterial 'buffer response', a phenomenon not previously demonstrated in vitro. The magnitude of the observed changes in portal venous and hepatic venous pressure leads to the conclusion that, in the porcine liver, the intrahepatic venous resistance sites react by constricting to increases in portal venous inflow.     

Glucagon hinders the effects of somatostatin on portal hypertension. A study in rats with partial portal vein ligation.

Whether the decrease of portal venous inflow and portal pressure induced by somatostatin is related to the effects of somatostatin in inhibiting the secretion of glucagon and other vasodilatory peptides that are increased in portal hypertension was investigated in the current study. Splanchnic vascular resistance and splanchnic blood flow were determined using radioactive microspheres in rats with portal hypertension caused by partial portal vein ligation. Somatostatin infusion significantly decreased portal pressure (from 13.1 +/- 1.9 to 12.1 +/- 2.2 mm Hg; P less than 0.05). This was associated with a significant decrease in portal venous inflow caused by splanchnic vasoconstriction, as evidenced by increased splanchnic vascular resistance, and with a marked suppression of glucagon secretion. The simultaneous infusion of somatostatin and glucagon (2.8 ng/min, a dose that prevented any decrease in circulating glucagon levels) abolished all the hemodynamic effects of somatostatin. This effect seems to be specific because no hemodynamic changes were noted in portal hypertensive rats receiving only the glucagon infusion.     

Blockade of ATP-sensitive K+ channels by glibenclamide reduces portal pressure and hyperkinetic circulation in portal hypertensive rats.

Certain results of in vitro studies raise the possibility that blockade of ATP-sensitive K+ channels by glibenclamide may induce vasoconstriction. Therefore, this substance might decrease portal pressure and hyperkinetic circulation in animals with portal hypertension. Thus, systemic and regional hemodynamics (radioactive microspheres) were measured before and 20 min after a bolus intravenous injection of glibenclamide (20 mg/kg) in conscious rats with portal vein stenosis. Blood pressure decreased significantly from 14.5 +/- 1.5 to 12.2 +/- 1.2 (mean +/- SE). Cardiac index significantly decreased by 24%, portal tributary blood flow by 31%, and hepatic artery blood flow by 35%. Systemic vascular resistance significantly increased by 38%, portal territory vascular resistance and hepatic artery vascular resistance by 61%, each, and renal vascular resistance by 17%. Arterial pressure, heart rate, and renal blood flow were unchanged. Moreover, glibenclamide blunted the vasodilating action of diazoxide (an ATP-sensitive K+ channel opener). These results show that in rats with extrahepatic portal hypertension the blockade of ATP-sensitive K+ channels by glibenclamide reduces portal pressure and hyperkinetic circulation.     

Radioimmunoassay study of hepatic clearance and disappearance half-time of somatostatin and vasoactive intestinal peptide in dogs.

The effects of hepatic transit on concentrations of synthetic cyclic (ovine) somatostatin and of highly purified (porcine) vasoactive intestinal peptide were studied in five conscious dogs prepared with indwelling portal catheters. The peptides were infused via peripheral vein catheters or the portal catheters for 40 minutes at actual integrated doses of 2.8 pmol/kg/min for vasoactive intestinal peptide an 8.2 pmol/kg/min for somatostatin. Specific radioimmunoassays were used for the measurement of the circulating peptides. As estimated from the plateau peptide concentrations achieved a hindleg vein during the portal and the peripheral infusions, the transhepatic loss of immunoreactive vasoactive intestinal peptide was 72.9 +/- 2.1%, against 27.5 +/- 12.5% for somatostatin. For the given doses of peptides infused systematically, the half-life, metabolic clearance rate, and distribution volume were, respectively, 1.80 +/- 0.1 minutes, 39.3 +/- 5.2 ml/kg/min, and 103.7 +/- 14.8 ml/kg for vasoactive intestinal peptide, and 1.0 +/- 0.2 minutes, 95.2 +/- 12.5 ml/kg/min, and 114.7 +/- 6.0 ml/kg for somatostatin. These results indicate that (ovine) somatostatin and (porcine) vasoactive intestinal peptide are both readily cleared from plasma in dogs. In the present experimental conditions, vasoactive intestinal peptide, but not somatostatin, was rapidly altered through hepatic transit so that it escaped recognition by the assay system.