To begin, place the anesthetized mouse supine on the surgical field. Apply i-gel and secure the nose cone with surgical tape. Then secure the mouse's front and hind paws with surgical tape.
Examine the mouse's lower abdomen for the bladder. To help create space within the abdomen during surgery, induce voiding by gently applying external pressure to the bladder between the thumb, index, and middle fingers. Use a piece of gauze to wick away the urine.
Disinfect the abdomen with iodine or a chlorhexidine-based scrub, starting from the center and working outward in a circular motion. Then repeat three times with 70%alcohol. Perform a toe pinch to confirm the depth of the anesthesia.
Then place a surgical drape over the mouse with the opening directly over the surgically prepped abdomen. Exchange gloves for sterile gloves. Use a scalpel to make a midline abdominal incision approximately 2-3 centimeters in length.
Lift the rectus muscles with forceps to identify the translucent linea alba. Use scissors to enter the abdominal cavity through the linea alba. Then extend along the linea alba proximally and distally.
Dampen a strip of gauze and two cotton tipped swabs with warm saline. Create an abdominal roll by tightly rolling one end of the gauze halfway, leaving a generous tail. Using a skin retractor, retract the right abdominal wall.
With the help of dampened cotton tipped swabs, perform a right medial visceral rotation by gently sweeping the small and large intestines to the left upper quadrant to visualize the aorta and inferior vena cava. After retracting the bowel out of view, tuck the rolled end of the gauze underneath the bowel. Then bring the tail and around and out of the body to gently swaddle the bowel.
Apply gentle tension to the tail of the gauze to hold the bowel out of the field of view. Adjust the abdominal roll and skin retractor to gain an optimal view of the retroperitoneal organs. After confirming that the inferior vena cava and infrarenal aorta are in full view, expose the aorta by entering and dividing the retroperitoneal fascia.
Identify the gonadal arteries that run parallel along the anterior infrarenal aorta. Using forceps, bluntly divide the fascia between the gonadal arteries and continue longitudinally to expose the aorta anteriorly. Now, with tips of forceps, gently spread apart the connective tissue fibers between the aorta and inferior vena cava and continue working circumferentially around the aorta at this level.
Continue bluntly dissecting the plane between the aorta and inferior vena cava, working caudally toward the aortic bifurcation. Once the right edge of the aorta is separated from the inferior vena cava, return proximally to the level of the left renal vein. Dissect the retroperitoneal fascia off the lateral left edge of the aorta, working circumferentially around until the aorta is fully isolated.
After examining the isolated aorta, place a strip of gloves along the right and left edges of the aorta. Using sterile handheld calipers, measure the widest aortic diameter. Dab any extra blood or fluid from the aorta with a cotton tipped swab.
Place a 10 x 2 millimeter piece of dry gauze on top of the aorta. Using a pipette, add 5 microliters of elastase to saturate the gauze and aorta. Gently fold the pieces of the glove around the aorta for 5 minutes.
After 5 minutes, reset bowel retractions and unfold the pieces of the glove. Irrigate the abdominal cavity with 1 milliliter of warm 0.9%sterile saline while carefully removing the gauze and pieces of gloves from the aorta. Absorb the saline in the abdomen with gauze.
Using handheld calipers, remeasure the widest aortic diameter post elastase application. Carefully remove the abdominal roll from underneath the bowel and out of the body. Observe to make sure the bowel appears pink and adequately perfused.
Re-approximate the abdominal fascia using a running 5-0 non-absorbable monofilament suture. Close the skin with 3-4 skin staples. Elastase-treated male mice demonstrated a 43.4%increase in aortic diameter after 5 minutes of exposure compared to untreated baseline aortic diameters, while treated female aortas increased by 33.6%Sham mice exhibited relatively no change in aortic diameter.
Of the female-treated mice, three of six died from AAA rupture, while no AAA ruptures were observed among treated males. At 28 days, the average AAA diameter of treated males was approximately 2.86 millimeters, with an average percent change of 257. While AAA diameters of surviving treated female mice were 3.6 millimeters, with an average percent change of 417.
Sham mice exhibited relatively no change in aortic diameters.
