Surgical anatomy of the pelvis for total pelvic exenteration with distal sacrectomy: a cadaveric study.

PURPOSE: Intraoperative bleeding from the pelvic venous structures is one of the most serious complications of total pelvic exenteration with distal sacrectomy. The purpose of this study was to investigate the topographic anatomy of these veins and the potential source of the bleeding in cadaver dissections. METHODS: We dissected seven cadavers, focusing on the veins in the surgical resection line for total pelvic exenteration with distal sacrectomy. RESULTS: The presacral venous plexus and the dorsal vein complex are thin-walled, plexiform, and situated on the line of resection. The internal iliac vein receives blood from the pelvic viscera and the perineal and the gluteal regions and then crosses the line of resection as a high-flow venous system. It has abundant communications with the presacral venous plexus and the dorsal vein complex. CONCLUSION: The anatomical features of the presacral venous plexus, the dorsal vein complex, and the internal iliac vein make them highly potential sources of bleeding. Surgical management strategies must consider the anatomy and hemodynamics of these veins carefully to perform this procedure safely.

An alternative explanation for the phasic variations in venous flow.

BACKGROUND: Phasic venous flow variation with respiration is surrounded by controversy and not well understood. The current concept assigns a major role to the "abdominal pump." According to this model, inspiratory increases in abdominal pressure compress the vena cava, increasing its internal venous pressure and propelling blood upstream. Some have assigned a secondary role to the "thoracic pump," with the negative intrapleural pressure aiding blood flow toward the heart. The aim of the present study was to examine the phasic changes in flow, pressure, and volume in the central veins and named tributaries. METHODS: Caliber area changes were measured using intravascular ultrasonography in 37 patients undergoing iliac vein stenting. The pressure was measured in 48 patients using transducer tip catheters with electronic zero calibration. Duplex ultrasound flow in the head and neck and truncal and limb veins during inspiration and expiration was measured in 15 normal volunteers. RESULTS: The caliber of the abdominal inferior vena cava had increased by 32% and its lateral pressure had decreased significantly during inspiration. Intravenous pressure in the central veins of the chest and right atrium was positive at 6 to 14 mm Hg. Negative pressures were rarely seen and then only transiently. The internal jugular vein displayed little phasic variation. The upper limb veins displayed weak inspiratory phasicity. Phase polarity was reversed in the lower limbs, with near flow stoppage during inspiration. CONCLUSIONS: These observations conflict with the current notions of venous flow phasicity, which are based on push-pull pressure changes in the abdominal and thoracic veins. The paradoxical inspiratory inferior vena cava caliber increase probably explains the concurrent pressure decrease. Sustained negative pressures in the thoracic central veins and right atrium did not occur. We have proposed an alternate hypothesis for venous flow phasicity based on alternate stretching and relaxation of the mobile section of the great veins with respiratory movement.

Relationship of blood flow in the common iliac vein to lower urinary tract disease.

PURPOSE: The relationship between blood flow and lower urinary tract disease was explored by measuring blood flow in the common iliac vein to examine the influence of pelvic congestion on lower urinary tract symptoms. METHODS: Color Doppler ultrasonography of the right common iliac vein was performed in 113 men and 60 women, who were outpatients of two Japanese hospitals. Average blood flow velocity and cross-sectional area of the vein were measured, and blood flow volume was calculated. The relationship between these parameters and age or urological diseases was then examined. RESULTS: There was no relation between age and average blood flow velocity or blood flow volume of the common iliac vein in either men or women. However, average common iliac vein blood flow velocity was significantly lower in men with chronic prostatitis and in women with overactive bladder than in other male and female patients, respectively. Common iliac vein blood flow volume was also significantly lower in men with chronic prostatitis than in other male patients. CONCLUSIONS: Men with chronic prostatitis and women with overactive bladder have low blood flow in the common iliac vein, suggesting that pelvic congestion may be related to these two conditions.

Unusual spontaneous porto-systemic shunt: The importance of diagnosing non-anatomical porto-systemic shunts to improve portal flow in pediatric living-related liver transplantation. Case report.

Collateral circulation secondary to liver cirrhosis may cause the development of large PSSs that may steal flow from the main portal circulation. It is important to identify these shunts prior to, or during the transplant surgery because they might cause an insufficient portal flow to the implanted graft. There are few reports of "steal flow syndrome" cases in pediatrics, even in biliary atresia patients that may have portal hypoplasia as an associated malformation. We present a 12-month-old female who received an uneventful LDLT from her mother, and the GRWR was 4.8. During the early post-operative period, she became hemodynamically unstable, developed ascites, and altered LFT. The post-operative ultrasound identified reversed portal flow, finding a non-anatomical PSS. A 3D CT scan confirmed the presence of a mesocaval shunt through the territory of the right gonadal vein, draining into the right iliac vein, with no portal inflow into the liver. The patient was re-operated, and the shunt was ligated. An intraoperative Doppler ultrasound showed adequate portal inflow after the procedure; the patient evolved satisfactorily and was discharged home on day number 49. The aim was to report a case of post-operative steal syndrome in a pediatric recipient due to a mesocaval shunt not diagnosed during the pretransplant evaluation.

A Novel Lymphaticovenular Anastomosis Rat Model.

INTRODUCTION: Lymphaticovenular anastomosis (LVA) has become an important procedure for the surgical treatment of lymphedema. In the past, the anatomy of the lymphatic system of animal models has been reported. However, to our knowledge, there have been few reports of animal models of LVA including training model. In this study, we report on a relatively simple and ideal animal LVA model based on peritoneal lymph ducts and veins. PATIENTS AND METHODS: For 10 rats, diameters of lumbar lymphatic ducts and iliolumbar veins in the peritoneal cavity on both sides were measured, and LVA was performed. In addition, we measured the diameters of 28 lymphatic ducts and veins in 8 patients who had previously undergone LVA and compared the results with those obtained in this rat model. RESULTS: The mean diameter of the lymphatic ducts was 0.61 mm, and the iliolumbar veins were 0.81 mm. On the other hand, the mean diameters of the 28 lymphatic ducts and veins of the 8 patients in whom we performed LVA were 0.58 and 0.76 mm, respectively. The differences in the diameters of the lymph vessels and veins between the rats and patients were not statistically significant. CONCLUSIONS: We report on an LVA model involving the use of the lumbar lymphatic duct and iliolumbar veins of rats. The diameter, nature, and placement of the anastomosis using this model are very similar to that noted during real human surgery. We believe that our rat model will be useful as a practical training model for LVA and in studies on postoperative changes in LVA.

Iliac venous pressure estimates central venous pressure after laparotomy.

BACKGROUND: Central venous pressure (CVP) is traditionally obtained through subclavian or internal jugular central catheters; however, many patients who could benefit from CVP monitoring have only femoral lines. The accuracy of illiac venous pressure (IVP) as a measure of CVP is unknown, particularly following laparotomy. METHODS: This was a prospective, observational study. Patients who had both internal jugular or subclavian lines and femoral lines already in place were eligible for the study. Pressure measurements were taken from both lines in addition to measurement of bladder pressure, mean arterial pressure, and peak airway pressure. Data were evaluated using paired t-test, Bland-Altman analysis, and linear regression. RESULTS: Measurements were obtained from 40 patients, 26 of which had laparotomy. The mean difference between measurements was 2.2 mm Hg. There were no significant differences between patients who had laparotomy and nonsurgical patients (P = 0.93). Bland-Altman analysis revealed a bias of 1.63 ± 2.44 mm Hg. There was no correlation between IVP accuracy and bladder pressure, mean arterial pressure, or peak airway pressure. CONCLUSIONS: IVP is an adequate measure of CVP, even in surgical patients who have had recent laparotomy. Measurement of IVP to guide resuscitation is encouraged in patients who have only femoral venous catheter access.

Proposal for a new classification of variations in the iliac venous system based on internal iliac veins: a case series and a review of double and left inferior vena cava.

There are many reports on variations in the inferior vena cava (IVC), particularly double IVC (DIVC) and left IVC (LIVC). However, no systematic report has recorded iliac vein (IV) flow patterns in the DIVC and LIVC. In this study, we examined IV flow patterns in both DIVC and LIVC observed during gross anatomy courses conducted for medical students and in previously reported cases. During the gross anatomy courses, three cases of DIVC and one case of LIVC were found in 618 cadavers. The IV flow pattern from these four cases and all other previously reported cases can be classified into one of the following three types according to the vein into which the internal iliac vein drained: the ipsilateral external IV; confluence of the ipsilateral external IV and IVC; and the communicating vein, which connects the IVC and the contralateral IVC or its iliac branch. This classification, which is based on the internal IV course, is considered to be useful because IV variations have the potential to cause clinical problems during related retroperitoneal surgery, venous interventional radiology, and diagnostic procedures for pelvic cancer.

Comparison of vein valve function following pharmacomechanical thrombolysis versus simple catheter-directed thrombolysis for iliofemoral deep vein thrombosis.

BACKGROUND: Successful catheter-directed thrombolysis (CDT) for iliofemoral deep vein thrombosis (IFDVT) reduces post-thrombotic morbidity and is a suggested treatment option by the American College of Chest Physicians for patients with IFDVT. Pharmacomechanical thrombolysis (PMT) is also suggested to shorten treatment time and reduce the dose of plasminogen activator. However, concern remains that mechanical devices might damage vein valves. The purpose of this study is to examine whether PMT adversely affects venous valve function compared to CDT alone in IFDVT patients treated with catheter-based techniques. METHODS: Sixty-nine limbs in 54 patients (39 unilateral, 15 bilateral) who underwent catheter-based treatment for IFDVT form the basis of this study. Lytic success and degree of residual obstruction were analyzed by reviewing postprocedural phlebograms. All patients underwent bilateral postprocedure duplex to evaluate patency and valve function. Phlebograms and venous duplex examinations were interpreted in a blinded fashion. Limbs were analyzed based on the method of treatment: CDT alone (n = 20), PMT using rheolytic thrombolysis (n = 14), and isolated pharmacomechanical thrombolysis (n = 35). The validated outcome measures were compared between the treatment groups. RESULTS: Sixty-nine limbs underwent CDT with or without PMT. The average patient age was 47 years (range, 16-78). Venous duplex was performed 44.4 months (mean) post-treatment. Of the limbs treated with CDT with drip technique, 65% demonstrated reflux vs 53% treated with PMT (P = .42). There was no difference in long-term valve function between patients treated with rheolytic and isolated pharmacomechanical thrombolysis. In the bilateral group, 87% (13/15) demonstrated reflux in at least one limb. In the unilateral group, 64% (25/39) had reflux in their treated limb and 36% (14/39) in their contralateral limb. There was no correlation effect of residual venous obstruction on valve function, although few patients had >50% residual obstruction. CONCLUSIONS: In patients undergoing catheter-based intervention for IFDVT, PMT does not adversely affect valve function compared with CDT alone. A higher than expected number of patients had reflux in their uninvolved limb.

Individual propensity for thrombosis: comparison of venous and arterial circulations.

INTRODUCTION: The pathogenesis of venous thrombosis has been attributed to complex interaction between environmental and inherited variables. A basal predisposition for venous thrombophilia independent of environmental variables has not been previously defined experimentally. Both to address the existence of an individual propensity to venous thrombosis and to establish an animal model in which variables governing this propensity could be tested, we provoked venous thrombi in a cohort of pigs of uniform size and age. We furthermore sought to determine whether the thrombotic propensity in the venous circulation is associated with similar propensity for arterial thrombosis. MATERIALS AND METHODS: Bilateral iliac venous stents were deployed and 2 h later, thrombi were harvested and weighed. The thrombotic response was compared to carotid arterial thrombi generated by crush injury within the same pig. Venous and arterial thrombus platelet deposition were measured by scintillation detection of autologous (111)In-platelet content. RESULTS: In a cohort of 27 pigs, venous thrombus weights and platelet content varied over greater trrhan 10-fold range from least to greatest responders. There was strong intra-individual correlation of thrombus platelet deposition (r=0.86; p=0.008) and thrombus weights (r=0.68; p=0.015) between stented iliac vein pairs. Venous thrombosis correlated with whole blood platelet counts but not carotid platelet-rich thrombus formation. CONCLUSIONS: The wide variation in venous thrombotic response to a standardized injury appears to represent an intrinsic propensity of the individual. The poor correlation with arterial thrombosis implies unique mechanisms responsible for this propensity in arteries and veins.

The venous reflux.

Venous reflux is the most common cause of venous hemodynamic disorders. In this paper 2 issues are discussed: how and where does reflux arise and what are the hemodynamic consequences of retrograde flow. Pressure gradient and incompetent vein connecting both poles of the gradient are the prerequisite for venous reflux to arise. Ambulatory pressure gradient occurs during the activity of the calf muscle venous pump between deep veins of the thigh and the lower leg. Thus the incompetent reflux-carrying vein must connect the popliteal, femoral, profunda femoris, or iliac vein with 1 of the deep veins of the lower leg. Reflux can be considered as shunting of blood from thigh veins into the lower leg veins. The most frequently found incompetent veins are the long and short saphenous veins and perforators communicating with deep veins of the thigh. On the other hand, calf perforators emptying into the deep veins of the lower leg, where the lower pole of the pressure gradient is located, cannot be the feeding source of reflux. A physiological bidirectional flow takes place in calf perforators connecting superficial and deep veins of the lower leg and making them conjoined vessels. Venous reflux produces ambulatory venous hypertension. The quantity of reflux volume and not the localization of retrograde flow in superficial or deep veins is the most important hemodynamic factor. Reflux in superficial veins, when large enough, can cause the most serious symptoms of chronic venous insufficiency including leg ulcers. Plethysmographic findings have shown that incompetence of the femoral and calf perforating veins is hemodynamically unimportant. Large incompetent calf perforators are not the cause of venous abnormality but are the consequence of saphenous retrograde flow.

Neurotropism revisited.

The purpose of this study is to re-examine the probable directive effect of the distal stump of a severed peripheral nerve on regenerating axons. Forssman postulated the existence of such a directive influence and Cajal interpreted it as chemotactic in nature. This view was subsequently refuted by Weiss and Taylor. In our study the proximal stumps of transected rodent sciatic nerve were inserted into the single inlet end of a Y-shaped autogenous inferior vena cava graft. Into one limb of the double outlet end, namely the common iliac nerve bifurcation, the distal stump of the same sciatic nerve was inserted, while the counter limb was ligated in one group, left open in the second group, inserted with a segment of autogenous tendon in the third, and grafted with a segment of autogenous nerve in the fourth group. Both outlets were left unoccupied in yet another group as the control. The vena cava conduit was prepared so that a 1.5 cm gap existed between the proximal stumps of the sciatic nerve and the distal sciatic nerve stumps and the tendon grafts respectively. The grafted sciatic nerves were explored and biopsied after 12 weeks. The direction of nerve tissue regeneration in each group was analyzed histologically. Predilection of the regenerating nerve fibers toward the distal stumps was observed in each of the test groups. These results indicate the existence of a guiding influence at the distal stump toward the regeneration nerve fibers.

Anastomotic vessels in the retropubic region: corona mortis.

Anastomosis between the pubic rami of the inferior epigastric and the obturator arteries has been referred to as the corona mortis. Because anomalous vessels in the retropubic region are at risk in groin or pelvic surgeries, they have an importance not only for general surgery but also for orthopaedics. Because it is hard to distinguish these vessels, they can be injured during ilioinguinal incision, which can lead to massive uncontrolled bleeding. For this purpose, 54 cadaver halves were dissected to determine the occurrence and location of the corona mortis anastomosis. We found venous corona mortis in 11 halves (20.37%). Additionally, in 8 halves (14.81%), the obturator artery originated from the inferior epigastric artery.

Influence of pneumoperitoneum and patient positioning on preload and splanchnic blood volume in laparoscopic surgery of the lower abdomen.

STUDY OBJECTIVE: To determine the hemodynamic effects of pneumoperitoneum and patient positioning during laparoscopic surgery of the lower abdomen. DESIGN: Prospective study. SETTING: University-affiliated medical center. PATIENTS: 10 ASA physical I and II female patients scheduled for laparoscopic surgery of the lower abdomen. INTERVENTIONS: Patients were anesthetized with propofol and an alfentanil infusion, then intubated, and normoventilated. MEASUREMENTS: After intubation, a transesophageal multiplane probe for measurements of right (RVESA) and left (LVESA) ventricular end-systolic and end-diastolic areas (RVEDA and LVEDA) and ejection fraction area (RVEFa, LVEFa) was introduced; heart rate (HR) and noninvasive blood pressure (BP) were recorded every minute. Ventilation was not changed during the measurements. A transvaginal ultrasound probe was inserted to measure the diameter of the common iliac vein. Measurements were performed 15 minutes after induction of anesthesia and while patients were in the supine position (P 0), 10 minutes after CO(2) insufflation to 10 mmHg IA pressure (P 10), 10 minutes after a further increase to 15 mmHg (P 15), 10 minutes after 20 degrees Trendelenburg (P 15 T), and 20 degrees reverse Trendelenburg positions (P 15 RT). Data are shown as medians, 25th to 75th percentiles, and comparisons between P 0, P 10, P 15, and P15 T were made with the Friedman test, followed by Wilcoxon test, when significant. Data at P 15 T, P 15 RT, and P 15 were compared using the Wilcoxon test, with a p-value < 0.05 regarded as significant. MAIN RESULTS: Pneumoperitoneum at 10 mmHg abdominal pressure caused a significant increase of LVESA by 78% (RVESA: 61%) and LVEDA by 48.5% (RVEDA: 45%). The diameter of the common iliac vein was decreased by 6%. A further increase of abdominal pressure to 15 mmHg led to an additional increase of 20% (LVESA) and 17% (LVEDA). Mean arterial pressure increased by a significant 7% at P 10, decreasing subsequently by 5% at P 15. The Trendelenburg position did not alter any hemodynamic findings. Reverse Trendelenburg position, however, caused a significant LVEDA-and RVEDA-decrease by 18% and 27%, respectively, and an increase in the diameter of the common iliac vein by 22%. The LVEFa and RVEFa decreased significantly after abdominal CO(2) insufflation by 18% each (P 10) without further change. CONCLUSIONS: The lithotomy position and subsequent pneumoperitoneum increased preload, probably as a result of blood shifting from the abdomen to the thorax by compression of splanchnic vessels caused by the pneumoperitoneum. Careful fluid management, maintaining low abdominal pressure, and use of the reverse Trendelenburg position are favored to prevent adverse hemodynamic effects in laparoscopic surgery.

Impact of unilateral common iliac vein occlusion on trapping efficacy of the Greenfield filter: an in vitro study.

RATIONALE AND OBJECTIVES: The purpose of this study was to assess the effect of unilateral common iliac vein occlusion on the capturing efficacy of the Greenfield filter in vitro. MATERIALS AND METHODS: A stainless steel over-the-wire Greenfield filter was placed in the Silastic inferior vena cava module of a pulsatile circuit. Three 30-mm blood clots in sets of five were injected through the module's right iliac limb with the circuit in four experimental conditions: vertical position, both iliac limbs patent (VP); vertical position, left iliac limb occluded (VOC); horizontal position, both iliac limbs patent (HP); and horizontal position, left iliac limb occluded (HOC). Each experiment was repeated 15 times, resulting in 75 clots per condition and a total of 300 clot introductions. RESULTS: Clot trapping efficacy was 36 of 75 (48%) for VP, 41 of 75 (55%) for VOC, 32 of 75 (43%) for HP, and 26 of 75 (35%) for HOC. Cross comparisons of the four conditions revealed a marginally significant difference (P = .0138 with a corrected test-wise alpha = .0125) only between horizontal and vertical positions with unilateral common iliac limb occlusion. CONCLUSION: Unilateral common iliac vein occlusion decreases the capturing efficacy of the Greenfield filter in the horizontal position in vitro. In patients with unilateral common iliac vein occlusion, use of inferior vena cava filters with higher capturing efficacy may be considered.

Central venous pressure from common iliac vein reflects right atrial pressure.

PURPOSE: To determine whether central venous pressure at the common iliac vein reflects right atrial pressure in adult patients. METHODS: In this prospective, non-blinded study 26 mechanically-ventilated adult patients were studied. Simultaneous pressure readings were obtained from the right atrium (TCVP) and the common iliac vein (ACVP). RESULTS: There was a correlation between TCVP and ACVP (r = 0.987; P < 0.0001). The mean difference between TCVP and ACVP was 0.93 mm Hg. And the limits of agreement were: -1.93 to 1.77 mm Hg. CONCLUSION: Venous pressure recorded from the common iliac vein reflects that in the right atrium. Adopting a femoral route for central venous pressure measurement may avoid some of the complications associated with the subclavian route.

A negative arterial-portal venous glucose gradient decreases skeletal muscle glucose uptake.

The effect of a negative arterial-portal venous (a-pv) glucose gradient on skeletal muscle and whole body nonhepatic glucose uptake was studied in 12 42-h-fasted conscious dogs. Each study consisted of a 110-min equilibration period, a 30-min baseline period, and two 120-min hyperglycemic (2-fold basal) periods (either peripheral or intraportal glucose infusion). Somatostatin was infused along with insulin (3 x basal) and glucagon (basal). Catheters were inserted 17 days before studies in the external iliac artery and hepatic, portal and common iliac veins. Blood flow was measured in liver and hindlimb using Doppler flow probes. The arterial blood glucose, arterial plasma insulin, arterial plasma glucagon, and hindlimb glucose loads were similar during peripheral and intraportal glucose infusions. The a-pv glucose gradient (in mg/dl) was 5 +/- 1 during peripheral and -18 +/- 3 during intraportal glucose infusion. The net hindlimb glucose uptakes (in mg/min) were 5.0 +/- 1.2, 20.4 +/- 4.5, and 14.8 +/- 3.2 during baseline, peripheral, and intraportal glucose infusion periods, respectively (P < 0.01, peripheral vs. intraportal); the hindlimb glucose fractional extractions (in %) were 2.8 +/- 0.4, 4.7 +/- 0.8, and 3.9 +/- 0.5 during baseline, peripheral, and intraportal glucose infusions, respectively (P < 0. 05, peripheral vs. intraportal). The net whole body nonhepatic glucose uptakes (in mg . kg-1 . min-1) were 1.6 +/- 0.1, 7.9 +/- 1.3, and 5.4 +/- 1.1 during baseline, peripheral, and intraportal glucose infusion, respectively (P < 0.05, peripheral vs. intraportal). In the liver, net glucose uptake was 70% greater during intraportal than during peripheral glucose infusion (5.8 +/- 0.7 vs. 3.4 +/- 0.4 mg . kg-1 . min-1). In conclusion, despite comparable glucose loads and insulin levels, hindlimb and whole body net nonhepatic glucose uptake decreased significantly during portal venous glucose infusion, suggesting that a negative a-pv glucose gradient leads to an inhibitory signal in nonhepatic tissues, among which skeletal muscle appears to be the most important.

Resistance to venous outflow during laparoscopic cholecystectomy and laparoscopic herniorrhaphy.

The effects of pneumoperitoneum on peak venous flow velocity in the common femoral vein and the vena cava have already been studied. The results suggested that venous stasis occurs during surgical pneumoperitoneum. This study determines the effects of pneumoperitoneum on the overall venous outflow resistance of the lower limbs. Venous outflow resistance was measured during surgical procedures by impedance plethysmography in 12 patients undergoing laparoscopic cholecystectomy, 4 patients undergoing laparoscopic herniorrhaphy, 4 patients undergoing conventional cholecystectomy, and 2 patients undergoing conventional herniorrhaphy. Venous outflow resistance did not change significantly during laparoscopic cholecystectomy or herniorrhaphy. No difference in venous outflow resistance between laparoscopic cholecystectomy and herniorrhaphy was found. During pneumoperitoneum, no obstruction to total lower limb venous outflow could be demonstrated, indicating that venous stasis in the limbs did not occur, and consequently, flow in the iliac and inferior caval veins was not compromised. Hypothetically, active vasodilatation resulting from mild compression may explain this. In our view, no special measures to prevent deep venous thrombosis have to be taken during laparoscopic procedures.

Anatomical differences in responsiveness to vasoconstrictors in the mesenteric veins from normal and portal hypertensive rats.

The present study evaluates the effects of pre-hepatic portal hypertension, induced in rats by partial portal vein ligation, on the responsiveness of rostral (proximal) and caudal (distal) rings from the mesenteric vein. The anatomical origin of the sample influenced the response to vasoconstrictors in sham-operated animals, and this pattern of reactivity was specifically modified in portal-ligated rats. In veins from sham-operated rats, contraction induced by a submaximal concentration of KCl (60 mM) was greater in proximal than in distal rings. Vasopressin and 5-hydroxytryptamine contracted mainly distal rings, methoxamine showed a greater effect on proximal rings, and endothelin-1 and angiotensin-II contracted vein rings independently of their anatomical origin. In veins from portal hypertensive rats, response to KCl (60 mM) were increased in distal rings, and all rings exhibited enhanced reactivity to vasopressin and 5-hydroxyptyptamine as well as attenuation of the response to methoxamine. Responses to endothelin-1 were decreased in proximal vein rings from portal hypertensive rats whereas responses to angiotensin-II were not influenced by the anatomical origin. Incubation with atropine, propranolol or indomethacin, did not modify the responses to vasopressin and 5-hydroxytryptamine in tissues from either sham-operated or portal hypertensive animals. Likewise, the hyporeactivity to methoxamine and endothelin-1 in rings from portal hypertensive rats persisted in the presence of the nitric oxide inhibitor NG-nitro-L-arginine methyl ester. These results suggest the physiological existence of anatomical differences in the responsiveness to vasoconstrictors throughout the mesenteric vein and that changes in the responsiveness of the mesenteric vein induced by portal hypertension are specific for each agonist and possibly result from individual variations at a receptor or post-receptor level.