Histopathological change of corpora cavernosa after long-term intracavernous injection

Repeated intracavernous injections in healthy monkeys with 2 kinds of vasoactive agents [papaverine and prostaglandin E1 (PGE1) 3 monkeys each] and normal saline (2 monkeys) were conducted in this study. The purpose was to observe the effect of long-term injection on histopathological changes of the cavernous tissue, as well as the change in drug sensitivity (dosage dependence). Different dosages of the same volume (double, single and half dose) of these 3 agents were injected, twice weekly, 10 times alternatively, with rigidity and maintenance of erection recorded. After long-term injection (papaverine group: 37, 60, 60 times; PGE1 group: 26, 60, 60 times; normal saline group: 60, 60 times), all monkeys were sacrificed and the penises were collected for light-microscopic (LM) and electron-microscopic (EM) examinations. Dose-dependent response with reversed drug sensitivity was found in the papaverine group, but only elongation to tumescence was found in the PGE1 group, even with double dosage (probably because of scarce PGE1 receptors in monkey's penile tissue). Histopathologically, mild to moderate fibrotic changes and distortion of normal architecture were predominant findings in LM while aggregation of mitochondria, irregular shape or atrophy of cells were obvious in EM observation in the papaverine group. On the other hand, limited fibrosis with preservation of corpora cavernosa and hypertrophy of smooth muscle were noted in the PGE1 group. This study indicated that less histopathological change occurred in the PGE1 group after long-term intracavernous injection.