Portal Vein In Dogs Research Articles

The effectiveness of intraoperative mesenteric portography for preventing misdiagnosis of congenital absence of the portal vein in dog with extrahepatic portosystemic shunt: a case report

A 5-month-old mixed-breed dog and a 10-month-old Welsh corgi dog were presented for evaluation with signs of congenital portosystemic shunt. In both dogs, computed tomography angiography revealed a single extrahepatic portosystemic shunt with the absence of the portal vein cranial to the shunt origin. Intraoperative mesenteric portography (IOMP) was performed after temporary complete occlusion of the shunt, revealing the portal branches faintly opacified with contrast medium. A cellophane band was applied around the shunt vessel without intraoperative attenuation. Postoperatively, both the dogs showed significant clinical improvement and the portal veins, not observed on preoperative ultrasonography, were visualized on postoperative ultrasonography. This study suggests the efficacy of IOMP, enabling the appropriate surgical procedure to be determined.

Importance of fasting in preparing dogs for abdominal ultrasound examination of specific organs.

To describe the effect of fasting on the technical success of abdominal ultrasonography specifically in respect of examination of the gall bladder, duodenum, pancreas, adrenal glands and portal vein in dogs. Randomised, prospective study of 150 dogs with a variety of physical characteristics. Animals were divided into two groups of 75 dogs each. Dogs in Group 1 were fasted for 8 to 12 hours before ultrasonographic evaluation and those in Group 2 were not but received food anytime between 10 minutes and 2 hours before the procedure. Intraluminal gas can influence the visibility of organs, but intraluminal gas accumulation occurred independently of fasting status. The assessment of abdominal organs was not affected by whether or not an animal was fasted. Routine fasting of dogs before abdominal ultrasonography is not essential.

Histamine responses mediated via H1- and H2-receptors in the isolated portal vein of the dog.

The effects of histamine were studied on the isolated circular muscle strip and longitudinal muscle strip of the dog portal vein. Histamine-induced contractions of the circular muscle were inhibited by H1-receptor antagonist pyrilamine but increased by H2-receptor antagonist ranitidine. When the tissues were contracted with PGF2 alpha in the presence of pyrilamine, histamine produced the relaxation of the circular muscle but not longitudinal muscle. The relaxation of the circular muscle was inhibited by ranitidine in a concentration dependent manner, the pA2 value for ranitidine being 6.97 (6.55-7.39). It is concluded that the response of the circular muscle to histamine is the sum of two components, H1-receptor mediated contraction and H2-receptor mediated relaxation.

Experimental Training Model of Pancreas Transplant

Pancreas transplant (Ptx) is the gold standard for the treatment of type I diabetes, mainly when associated with renal failure. The number of Ptx is increasing worldwide, but in developing countries, such as Brazil, the number of centers is small and transplant surgeons need to practice the technique. Methods For this model, 21 pancreas harvestings were performed in patient corpses after death from extra-abdominal causes, without pancreatic disease and peritoneal or systemic infection. The vessels of the grafts were prepared on the backtable according to the usual practice in humans. The pancreas was implanted in the inferior vena cava and aorta of mixed breed dogs, with 10 exocrine-bladder drainage and 11 duodenum-ileal anastomosis. Results There were anastomotic strictures of the portal vein in dogs 1 and 2. There was no arterial stricture or large bleeding. None of the animals died until the revascularization of the graft. Dogs 2, 5, and 8 died during the exocrine anastomosis. The arterial flow was initially high, but at the end of the procedure there were thromboses of small arteries. Conclusion The experimental surgical technique model is feasible, repeating the stages of clinical pancreatic transplantation and allowing the training of surgeons.

Prognostic Implications of the Degree of Shunt Narrowing and of the Portal Vein Diameter in Dogs with Congenital Portosystemic Shunts

To determine prognostic evaluation and correlation of the degree of narrowing and the diameter of the portal vein in dogs with a congenital portosystemic shunt (CPS). Longitudinal prospective study. Ninety-seven dogs with CPS. Shunt diameter was recorded before and after silk ligation to calculate degree of closure. Portal vein diameter was measured in 74 dogs. Short-term (30 days) and long-term (>1 year) outcome were evaluated. Dogs with clinical signs after 1 year were re-examined to assess the degree of portosystemic shunting and compared with matched operated dogs without clinical signs. Correlations between clinical outcome, degree of closure, and portal vein diameter were statistically analyzed. Short-term and long-term mortality were 27% and 2.9% respectively. Clinical recurrence occurred in 10% of dogs. The degree of closure was significantly associated with mortality, but not with clinical recurrence. A significant correlation was found between degree of closure and the diameter of the cranial part of the portal vein. Portal vein diameter was only significantly associated with mortality in extrahepatic CPS. Subclinical portosystemic shunting was confirmed in 3 of 10 dogs. The degree of shunt closure depended on portal development. Long-term outcome did not depend on the degree of closure or portal development at the time of surgery. This suggested that factors such as hepatic and portal regeneration after surgery may be important. Determination of factors that predict the outcome after surgical treatment of CPS in dogs is important to gain insight in treatment selection or new therapeutic options.

Appropriate Blood Flow for Arterio-Portal Shunt in Acute Hypoxic Liver Failure

Hepatic arterial interruption inevitably leads to fatal liver hypoxia when all the collateral arteries to the liver have been eradicated. To prevent such hypoxia, we aimed to determine the appropriate flow of arterial blood in the arterio-portal shunt (APS). After division of all the arteries to the liver, we created three types of APSs between the common hepatic artery (CHA) and the portal vein in dogs, using catheters which were adjusted to pass blood flows of approximately half (group I), equal to (group II) and twice (group III) the CHA blood flow before shunting, except in the control (no-shunt) group. Postoperatively, at 1 and 48 h, we examined the hemodynamics of the liver biochemically and pathologically. After shunting, portal blood flow and oxygen saturation markedly increased, whereas portal venous pressure did not rise significantly. The serum alanine aminotransferase level was significantly higher in the no-shunt group and group I than in group II. Only in group II was the preoperative energy charge maintained, and light- and electron-microscopic examinations revealed no degeneration of the hepatocytes. APS blood flow similar to the original CHA (as in group II) is most appropriate for preventing liver hypoxia.

High-Porosity expanded polytetrafluoroethylene grafts with omentum wrap for portal vein replacement: Intermediate results

The purpose of this study was to examine the intermediate (6-month) patency and healing characteristics of high-porosity expanded polytetrafluoroethylene (ePTFE) grafts with and without omentum wrap in a dog portal vein replacement model, compared with short-term (1-month) results. The grafts, either wrapped by omentum or not, were placed as portal vein replacements in 22 mongrel dogs. After 1 and 6 months, the grafts were retrieved and examined for patency and subjected to pathology study. Although the short-term patency rate in all grafts was 100%, regardless of the presence or absence of omentum wrap, the intermediate patency of high-porosity ePTFE without omentum wrap was very poor (20%). On the other hand, high-porosity ePTFE with omentum wrap had an intermediate patency rate of 100%. At 6 months, the high-porosity ePTFE grafts with omentum wrap were completely healed. The pseudointima was entirely replaced by thin fibrous tissue, with complete endothelial-like cell coverage throughout the graft. This result suggests that high-porosity ePTFE with omentum wrap could be a suitable prosthetic alternative to autogenous vein graft in portal vein reconstruction.

Portal hypertension associated with primary hypoplasia of the hepatic portal vein in dogs.

Portal hypertension caused by primary hypoplasia of the portal vein was diagnosed in 42 dogs. The portal hypertension was manifested by the presence of multiple portosystemic collateral vessels. The main clinical signs were retarded growth or weight loss, apathy, intermittent diarrhoea and vomiting, anorexia, abdominal distension and polydipsia. Major findings at physical examination were ascites in 23 dogs and neurological signs in 16 dogs. The dogs had increased activities of liver enzymes in plasma and increased fasting levels of total bile acids and ammonia; in many of the dogs the packed red cell volume, total serum protein and albumin were low. Gross inspection of the portal vein revealed a patent but underdeveloped extrahepatic vein in 13 of the dogs. Microscopic examination of the liver revealed hypoplasia of the intrahepatic portal veins in all the dogs, and this was associated with minor arteriolar proliferation and absence of fibrosis in 12 of them, with moderate to marked arteriolar proliferation often combined with ductular proliferation in 13, and with marked portal fibrosis (formerly described as hepatoportal fibrosis) with a varying number of arteriolar and bile ductular structures in 17 of the dogs. The disease affected mainly young dogs, and was most likely to have been of congenital origin.

Non-linear hepatic first-pass metabolism of salicylamide in dogs after portacaval transposition

The effect of the rate of input of salicylamide into the portal vein of dogs on the clearance and bioavailability of the drug was examined. The four dogs had undergone portacaval transposition so that a hindlimb infusion delivered the drug directly and only into the liver. On separate occasions, salicylamide, 20 mg/kg, was infused into a hindlimb vein at three different rates, the duration of each infusion was 3, 10, and 30 min. Simultaneously, to measure the bioavailability, 14C-salicylamide was infused at the same rate into a forelimb vein. As the duration of the infusion was increased from 3 to 30 min, the clearance of salicylamide increased significantly from 1.05 +/- 0.21 (mean +/- SD) to 1.57 +/- 0.38 L/min and the half-life decreased significantly from 14.66 +/- 3.60 to 9.09 +/- 2.42 min. Bioavailability decreased from 0.84 +/- 0.11 to 0.61 +/- 0.61, but the differences were not statistically significant. As predicted for a drug that has nonlinear clearance and bioavailability, the rate of infusion of salicylamide affects the values of these parameters.

Calcium Channel Blocking Action of Franidipine Hydrochloride (CV-4093-2HCI) In Vitro and In Vivo

The calcium-channel blocking action of franidipine (CV-4093-2HCI) was investigated in vitro and in vivo. CV-4093-2HCI inhibited the 60 mM K+-induced contraction of rabbit aorta and those of coronary, renal, mesenteric and femoral arteries of dog less potently than nifedipine and nicardipine. In dog portal and femoral veins, CV-4093-2HCI inhibited K+-induced contraction as potently as nifedipine and nicardipine did. The inhibitory effect of this drug was fully developed by pretreatment for 60 min, and it lasted long after washout. The drug inhibited both K+-induced 45Ca-influx and K+-induced contraction at a similar concentration range in rabbit aorta and dog portal vein, but had no effect on 45Ca-efflux from either vessel. On the other hand, in the isolated, perfused kidneys and mesenteric vascular beds of SHR, CV-4093-2HCI inhibited K+-induced vasoconstriction more effectively than did nifedipine. Moreover, in pithed rats (i.v.) and ganglion-blocked conscious SHR (p.o.), CV-4093-2HCI inhibited more potently a2-adrenergic pressor responses than did nicardipine. These pharmacological properties of CV-4093-2HCI, especially those seen in the isolated, perfused kidney and mesenteric vascular beds, may be responsible for its potent and long-lasting action as an antihypertensive agent.

Greater in vivo than in vitro pulsatility of insulin secretion with synchronized insulin and somatostatin secretory pulses.

To examine the control of pulsatile insulin secretion by an intrapancreatic pacemaker, samples at minute intervals were taken from the portal vein in dogs in vivo and from an isolated perfused pancreas preparation in vitro. Anesthetized dogs had high amplitude pulsatile insulin secretion which was not consistently regular. Fourier transform analysis showed dominant 20- and 10-min periods of spectral power (P less than 0.01). After vagotomy, the relative oscillatory power was reduced from 83% to 42%, about a lower mean concentration with abolition of the 20-min oscillations. The isolated perfused dog pancreas also had oscillatory insulin secretion with oscillatory power of 12%. Autocorrelation showed regularity of in vitro insulin secretion with a period of 10-11 min (P less than 0.0001). In addition, somatostatin was secreted from the in vitro pancreas in pulses in phase with insulin (cross-correlation P less than 0.0001). These data are in accord with the theory that the pancreas has an internal pacemaker which controls insulin secretion, and that the amplitude of the oscillations is modulated by vagal control. The pacing of the islets may be coordinated by a neural network, whereas coincident pulsatile somatostatin release may temporarily suppress islet secretion and help to synchronize hormonal oscillations.

Stimulation of prostacyclin production in blood vessels by the antithrombotic drug suloctidil

Suloctidil is a calcium antagonist with vascular relaxing activity and an antithrombotic agent: its antiplatelet action has been demonstrated in vivo, but is difficult to reproduce in vitro and the mechanism of this effect remains unknown. We have observed that suloctidil (10 μM) stimulated the release of prostacyclin (PGI 2) from the rabbit aorta, the dog vena cava and the dog portal vein, in vitro. This effect could be explained by an increased mobilization of free arachidonic add. Neither the inactive congener CP894S, nor the two calcium channel antagonists, verapamil and flunarizine, reproduced the stimulatory effect of suloctidil. Suloctidil acted selectively on the vascular endothelium: it stimulated the release of PGI 2 from bovine aortic and human umbilical vein endothelial cells, but neither from the de-endothelialized rabbit aorta nor from the bovine aortic media. The stimulatory effect of suloctidil on the release of the platelet inhibitor PGI 2 from the vascular endothelium might contribute to the known antiplatelet and antithrombotic activity of this drug.

Ncreased 25-hydroxyvitamin D levels in portal blood following cholecystokinin injection in the dog

To establish whether an enterohepatic circulation of the metabolites of vitamin D exists, polyethylene catheters were cannulated into the portal vein of dogs. The dogs were then starved for 24 h and injected with cholecystokinin (CCK) to induce gall bladder contraction. At various time intervals thereafter blood samples were collected from the portal and the saphena veins, and sera prepared and analyzed for the metabolites of vitamin D. The serum levels of 25-hydroxyvitamin D [25(OH)D] were found to be significantly higher in the portal blood when compared with levels in peripheral blood following CCK injection. Since portal blood collects nutrients absorbed from the gut and as the dogs were starved for 24 h prior to blood collection, the only source of the increased concentrations of 25(OH)D in portal blood is likely to be bile. These findings support the notion that an enterohepatic circulation of 25(OH)D does exist under normal physiological conditions.

Evidence for muscarinic cholinergic receptors in dog portal vein: Binding of [ 3H] quinuclidinyl benzilate

Muscarinic cholinergic receptor sites in dog portal veins were analyzed directly using [ 3H] quinuclidinyl benzilate (QNB) as a ligand. Specific [ 3H] QNB binding to crude membrane preparations from the isolated veins was saturable, reversible and of high affinity (K D = 15.5 ± 2.8 pM) with a Bmax of 110 ± 14.7 fmol/mg protein. Scatchard and Hill plot analyses of the data indicated one class of binding sites. From kinetic analysis of the data, association and dissociation rate constants of 1.91 × 10 9 M −1 min −1 and 0.016 min −1, respectively, were calculated. The dissociation constant calculated from the equation K D = K −1/K +1 was 8.3 pM, such being in good agreement with the Scatchard estimate of K D (15.5 pM). Specific binding of [ 3H] QNB was displaced by muscarinic agents. Nicotinic cholinergic agents, α-bungarotoxin, nicotine and hexamethonium, were ineffective in displacing [ 3H] QNB binding at 10 μM. Our findings provide direct evidence for the existence of muscarinic cholinergic receptors in dog portal veins.

A possible hepatic factor in the control of plasma free fatty acid levels

Insulin acts as a regulator of lipid metabolism by inhibiting the rate of lipolysis. Hyperinsulinemia, produced by the peripheral infusion of glucose, therefore, causes a lowering of plasma free fatty acids (FFA) by decreasing the mobilization of fats from peripheral deposits. Based on previous studies, it was postulated that a lowering of plasma FFA could be produced, in the absence of hyperinsulinemia, by the infusion of glucose directly into the liver. This study was undertaken to investigate the existence of endogenous factors other than insulin, which inhibit lipolysis. It was determined that glucose at a dosage of 0.125 gm/kg/hr could be infused into the portal vein of dogs without increasing plasma insulin levels. This dosage significantly lowered plasma FFA levels when injected into the portal vein but had no effect on plasma FFA when infused peripherally. There were significant decreases in FFA turnover following portal glucose administration, with no changes in fractional turnover. This indicated that the lowered plasma FFA concentrations found following portal infusions of glucose, were due to reduced lipid mobilization from adipose tissue, rather than increased tissue uptake of FFA. These results suggested the exitence of an hepatic factor, stimulated by portal glucose infusion, which lowered FFA mobilization from adipose tissue.

New devices and methods for long-term vascular access for blood sampling and insulin infusion.

Studies aimed at quantifying the benefits of infused rather than injected insulin have been impeded by the unavailability of suitable methods for continuous vascular access. We have developed indwelling catheters suitable for the long-term blood sampling as well as insulin infusion. A typical catheter consists of a silicone rubber tube, which terminates with a blunt-point needle. Internal or external reinforcement as well as a removable strain relief fitting protect the area of insertion of the needle. Anchoring of the implanted extravascular portion of the catheter is important and is achieved by special grommets that prevent motion without obstructing the lumen. Methods of catheter assembly as well as implantation in the jugular and portal veins of dogs and jugular veins of humans are described. A total of 34 blood sampling catheters were implanted in 26 beagle dogs: 74% were uncomplicated with a duration of implantation of 18–576 days while 15% and 11%, respectively, failed due to infection or physical damage after an average of 200 days. Thirteen portal infusion catheters were implanted: 62% were functional a mean of 100 days (14–166 days) after implantation while 35% became covered with an endothelial sleeve and had to be removed. Thirty-two peripheral infusion catheters were implanted in dogs: one infection occurred, two catheters were physically damaged, and three were plugged. There were no catheter-related complications in the five adolescent diabetic subjects with such jugular venous catheters studied for an average of 19.5 days and three adult diabetic subjects in whom catheters remained patent for 150–270 days. It is the inherent characteristics of the silicone rubber material as well as the new methods of catheter construction and implantation that virtually eliminate catheter-related problems and that now provide an ideal route of access for long-term intravascular insulin infusion in diabetes mellitus.

Modes of regional chemotherapy

Injection of Am (2 mg/kg) into the hepatic artery or portal vein of dogs gives higher liver tissue levels (15.1 μg/g) than systemic intravenous administration (6.4 μg/g). This difference is increased by injection of the drug distal to the temporarily occluded hepatic artery or portal vein. Bolus injection of Am (1 mg/kg) into the femoral artery of dogs results in no detectable ipsilateral calf muscle levels and no subsequent macroscopic changes in the extremity. When injected distally to the temporarily occluded femoral artery, muscle drug levels were below the level of sensitivity of the fluorometric assay used, but all animals showed varying degrees of ipsilateral skin ulcerations and melanosis. With a tight tourniquet applied to the extremity proximally and maintained for 15 min after Am injection, 40-fold or higher muscle levels of Am were found, compared to those after simple intraarterial injection. There was fairly uniform drug distribution throughout the infused limb and minimal systemic leak. Severe ulcerations occurred after injection of 1 mg Am/kg with tourniquet application. With reduction of the dose to 0.25 and 0.125 mg/kg, erythema in the first 2 weeks and melanosis of the skin at 2 to 4 weeks occurred and involved the whole extremity. This technique of intraarterial injection of chemotherapeutic drug(s) with a proximal tourniquet has a potential clinical applicability in extremity tumors; high tissue drug levels are obtained and frequent administration is possible via an indwelling catheter. With the present development of the ability to assay microconcentrations of drugs in tissues, a critical reappraisal of the methods of regional infusion chemotherapy should now be possible, in association with the physiochemical characteristics of the drugs used.

Microvibration: capable of inducing spontaneous contractions in smooth muscles.

Spontaneous contractions were elicited by the vibration of small amplitude (microvibration) imposed upon the quiescent strips prepared from the ureter and portal vein of dogs. An acceleration of the existing rhythm in the spontaneously contracting strips was also brought about by microvibration. Frequencies and amplitudes of microvibration ranged from 1 to 90 Hz and from 50 to 150 mum, respectively. Imposed cyclic strains were less than 1% at their maximum. Up to the amplitude of 150 mum, the greater the amplitude, the faster the induced rhythm. Stepwise increase of the frequencies up to 30 Hz brought about a gradual acceleration of rhythmicity. At frequencies of above 30 Hz, no appreciable frequency-dependent differences were observable among the responses induced. Local adrenergic mechanism proved to have nothing to do with these effects.

Concentration and transport of different sugars in the lymph of the thoracic duct and in blood of the portal vein in dogs after enteral and parenteral administration.

The uptake and distribution of glucose, galactose, fructose and inulin in dogs was investigated in the lymph of the thoracic duct and in different blood vessels after enteral and parenteral administration. Whereas inulin could be detected neither in the lymph nor in portal venous blood after enteral administration, all other sugars were found in different concentrations in blood and lymph. Although the concentration of different sugars in the lymph after enteral and parenteral application can be compared to that in serum, the amount of sugars transported via the lymphatics is so small that it can be neglected.

Toxicity of intraperitoneal bisulfite.

Studies were carried out in animals to investigate the toxicity of intraperitoneal bisulfite. The LD50 (dose lethal to 50 per cent of the animals) for a single intraperitoneal injection of NaHSO3 was calculated in the mouse, rat, rabbit, and dog. Studies indicated that the LD50 dose was increased by dilution of the bisulfite. When sodium bisulfite was infused at a rate of 80 mg. of NaHSO3 per kilogram per hour in the portal vein of dogs having bilateral ureteral ligations, bisulfite did not accumulate in the serum. Autoclaving dialysis fluid substantially reduced its bisulfite concentration. These studies suggest that NaHSO3 in amounts usually added to dialysis solutions is unlikely to cause toxicity in patients undergoing peritoneal dialysis.