Targeting the Rat's Small Bowel: Long-Term Infusion into the Superior Mesenteric Artery

Superior mesenteric artery cannulation in the rat is difficult and it's not often used as an experimental model. This technique make it possible to perform a functional cannulation and opens a field of experimentation with first passage effects of intra-arterial drugs. This method avoids bleeding and thrombosis while consenting the cannulation of the superior mesenteric artery.

And allowing for long term infusion of drugs in a relatively free animal who can eat and move. Pharmacological research on drugs active on intestine may greatly benefit from this technique. There is no alternative to study the effect of a direct single passage of the drug.

Begin by cutting the larger cannula. Then cut the smaller cannula, and insert it one centimeter into the larger cannula. Fix the two cannulas together with cyanoacrylate glue avoiding occlusion of the lumen.

Afterwards, connect the free extremity of the larger cannula to a luer stub adapter mounted on a one milliliter syringe filled with saline solution. Sharpen the free tip of the smaller cannula with scissors to facilitate the insertion of the catheter into the branch of the superior mesenteric artery. Check the patency of the cannula by flushing with saline solution.

Shave the fur from the surgical regions of the anesthetized rat, including the abdomen for the branch of the superior mesenteric artery or SMA cannulation, and the back of the neck for the cannula exit. Clean the surgical regions aseptically. And place the animal in a supine position immobilizing the four limbs.

Use a scalpel blade to open the abdominal wall with a straight three centimeter incision on the midline of the meso gastric region through all the abdominal planes into the peritoneum. Place gauzes soaked with saline solution around the laparotomy incision, using sutures to keep the surgical incision open. Use cotton swabs to identify and expose the small intestine, and extract the mesentery out of the laparotomy cut and lay it downward on the gauzes.

Identify the SMA by feeling pulsation. Using cotton swabs, separate the mesenteric fat and uncover the SMA and two to three of its proximal branches. Choose a proximal branch of the SMA that is sufficiently large to allow the surgical maneuvers of cannulation.

Tie this branch three to four centimeters downstream from its origin to allow its expansion by keeping the suture ends long enough to be manipulated later. Place a rigid support under the branch of the SMA and hold the extremity of the smaller cannula using forceps then pull the suture ends with the other hand to strain the vessel and facilitate the entry of the catheter. Hold the tip of the cannula at a 20 degree angle from the plane of the vessel in the direction opposite to the blood flow.

Then lightly press the tip to penetrate the artery wall and insert the cannula. Continue the insertion of the cannula for one centimeter in the arterial branch close to the origin from the SMA. Fix the cannula to the artery with a surgical knot, and verify its correct functioning by flushing one milliliter of sterile saline solution or by blood sampling.

Make a one centimeter incision in the posterior region of the neck and accommodate a spherical valve. Then pass the cannula from the laparotomy access to the valve placed in the neck through subcutaneous tissues and close the distal extremity of the cannula with a catheter plug to avoid air inflow. Replace the small valve in the abdominal cavity and close the abdominal wall.

Then secure the valve to the next skin with stitches. Dress the rat with a jacket to protect the button valve. Protect the exposed part of the cannula with a steel rod during infusion and secure it to the valve.

Connect the distal extremity of the cannula to an elastomeric pump filled with 50 milliliters of sterile saline solution, and proceed with infusion for 24 hours. After the infusion, disassemble the animal's external infusion system by removing the pump, the jacket, the steel rod and the valve from the rat. Close and cut the cannula as it out of the neck, leaving the extremity under the skin of the neck after wound suture.

In this study, 15 rats were subjected to this procedure and average daily food and water intake increased progressively until normal after three days. The weight gain was also regular and gradually increasing until the end of the observation period. After 24 hours, there was saline residue in just two balloon pumps, while the other 13 were completely empty.

Furthermore, after the infusion period, 12 cannulas were still functional for both blood sampling and saline infusion, while three cannulas were not patent anymore. At necropsy, 100%of the cannulas were located in the SMA branch. And no rats had signs of bowel ischemia or intraabdominal bleeding.

An angiography was obtained in five rats by injecting iodonated contrast medium into the mesenteric cannula. The mesenteric arterial circle, particularly the SMA and its main branches were observed without contrast medium spreading in the abdomen, confirming that the cannula was well placed and fixed to the branch of the SMA. Patent, a meticulous desolation of the branch to cannulate ligature of the vessel downstream passing the suture underneath the vessel and choosing the most appropriate position to puncture and insert the cannula are the most important aspects of this protocol.

Errors are uncorrectable.