Biology
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Intracavernosal Pressure Recording to Evaluate Erectile Function in Rodents
Chapters
Summary June 6th, 2018
Intracavernosal pressure recording (ICP) is an important method to evaluate the erectile function of experimental animals. Here, a detailed protocol is demonstrated for the recording procedure of ICP by catheterizing the crura penis and then electrically stimulating the cavernous nerves in rats.
Transcript
The overall goal of this procedure is to test erectile function of rats by catheterizing the crus corpus cavernosum and recording intracavernous pressure after stimulation of the cavernous nerves. This method can help answer key questions in the male erectile dysfunction field, such as, for evaluating the therapies and medicines for erectile dysfunction. So one advantage of this technique is that it provides a more accurate evaluation of erection function and reflexes, the dynamic change in blood flow associated with erectile response.
Visual demonstration of this method is critical as catheterization is difficult to learn because the small area of the white tunica albuginea of crus corpus cavernosum makes it difficult to insert the needle into the penis crura. To prepare for the surgery, make a pair of bipolar electrodes for intracavernosal pressure recordings. Slightly bend the ends of the electrodes and adjust the distance between them to one to two millimeters.
Then connect the electrodes to the stimulator using two crocodile clamps. Next, assemble the catheter system. First, use tubing to connect a hypodermic 23-gauge needle to a three-way stopcock.
Then connect the stopcock to a pressure transducer. Next attach a 10 milliliter syringe loaded with heparin saline to the third position of the stopcock. Then fill the whole system with heparin saline and check for leaks.
Next lift the needle 20 centimeters and calibrate the recording system to 20 centimeters of water. After the calibration, adjust the height of the needle and check the accuracy of the recording system. As needed, repeat the calibration until the accuracy is confirmed.
Next, transfer the rats from the animal facility to the surgery room and allow them to acclimate to the room for at least 30 minutes. Meanwhile, sterilize the surgical tools with 70%ethanol and prepare the necessary surgical materials. After 30 minutes prepare the first rat for surgery.
Anesthetize it with sodium pentobarbital and wait for five to 10 minutes. Then pinch the rats toes and check for an absence of reflex to confirm a proper anesthetization. Next, shave the fur from the abdomen and neck and place the rat supine on a surgical board.
Now wipe the exposed skin with three alternating scrubs with 10%povidone iodine followed by 70%ethanol. Also, apply ophthalmic ointment to prevent the eyes from drying out. Then proceed with the surgery.
Before isolating the cavernous nerve, catheterize the left carotid artery according to the text protocol. Start the nerve isolation by lifting the skin and muscle of the abdomen with a pair of forceps. Then, with scissors, make a midline incision from the lower abdomen to the penis.
Next, gently move aside the intestines into the upper part of the abdominal cavity. Then grasp the bladder with a pair of forceps and pull it out of the abdominal cavity. Now find the ventral lobes of the prostate which are located on the ventral portion of the urethra.
Next, expose the dorsal lobe of the prostate by pulling out the ventral lobes, seminal vesicle, and vas deferens. Now find the point of adhesion of the vas deferens and prostate. Then separate the space between the prostate and vas deferens.
Proceed by carefully exposing the fibrous capsule located posterior to the junction point of the prostate and vas deferens. Then find the major pelvic ganglion and cavernous nerves located on the surface of the prostate. Now carefully dry the cavernous nerves area with a swab or tissue paper, and then carefully isolate and hook the right cavernous nerve with the bipolar electrodes.
To continue the surgery, cut a small incision in the skin of the penis with dissecting scissors and then carefully denude the skin of the penis shaft. Then expose enough tissue to dissect the striated penile musculature. Now find the upper branch of pubis bone.
Then expose the bulbospongiosus muscle which covers the spongios bulb. Next, using curved forceps, divide the bulbospongiosus muscle from the ischiocavernosus muscle. Proceed by carefully isolating the ischiocavernosus muscle.
Then cut the ischiocavernosus muscle to expose the white tunica albuginea of the crus corpus cavernosum. Now perform the catheterization. Carefully follow the anatomical direction of the crus corpus cavernosum and gently insert the needle through the white tunica albuginea into the cavernosum.
The location of the needle is crucial to the operation's success, so as a test, inject a small amount of heparinized saline. This should result in a slight penile tumescence if the needle has been inserted correctly. Next, without repositioning the needle, or disrupting the connecting tube, carefully release the needle.
Then inspect the area for any leakage. If none is found, proceed with stimulating the nerve and analyzing the data. The described ICP recording test was used to distinguished aged rats with erectile disfunction to help quantify the effect of potential treatment or drugs on erectile function.
A typical ICP response curve of the erectile disfunction group was much lower than the control group's curve. Usually the highest ICP was chosen for statistical analysis. After calculating the ratio of ICP to mean arterial pressure, the pooled data from five rats showed that the ratio in the aged group decreased significantly compared to that of the control groups.
Besides these two key parameters, the peak ICP, the plateau ICP, the detumescence time, the duration of response, and the area under the curve, all significantly decreased in aged rats, thus, data is full of quantitative measurements that reflect erectile function. After watching this video, you should have a good understanding of how to efficiently perform the ICP recording on animals. Don't forget that while attempting this procedure, it's important to remember to use heparin in order to ensure the canula tube remains unobstructed.
Once mastered, this technique can be done in about two hours if it is performed properly.
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