Assessment of an intraprostatic injection technique through a perineal approach in macaques

We developed a surgical procedure for accessing the prostate gland of the cynomolgus monkey (Macaca fascicularis) through the perineal cavity. The procedure can be used for direct injection of compounds into the prostate gland and (or) for the collection of biopsies. The rationale for developing this technique at our site was the need for precise injection into the gland with a low probability of error, as the compound tested in a subsequent study required prostate-specific antigen for activation. A perianal incision was made approximately 1 cm ventral to the anus, and the muscle and subcutaneous tissue were bluntly dissected between the urethra and the rectum. The prostate gland was easily visualized after dissection, and could be grasped gently by the capsule and exteriorized through the incision, thus allowing easy access to the prostate for study purposes. On the basis of mock injections with methylene blue dye and gross observation of prostate tissue at necropsies immediately after injection, we recommend that 2 injections be given per lobe of prostate, and injections should be to a depth of 2 to 3 mm to provide uniform distribution of injected compounds. To minimize back pressure and leakage from the injection site, a smallgauge needle (23-27 gauge) should be used and the needle held in place for approximately 30 s before withdrawal. Injection volumes 64 mul per g prostate or less did not cause the back flow of methylene blue dye into the seminal vesicles.