In Vitro Contraction of the Canine Corpus Cavernosum Penis by Direct Perfusion with Prolactin or Growth Hormone

Purpose

It is well established that hyperprolactinemia, most typically seen in prolactinoma patients, causes hypogonadism and impotence. There seem to be a good possibility that hyperprolactinemia causes impotence, at least partially via some intrinsic property of prolactin (PRL), rather than through its suppressive effects on the hypothalamic-pituitary-gonadal testosterone dynamics. In the present investigation, we used an in vitro canine model to attempt to clarify whether direct action of PRL on the corpus cavernosum penis may lead to erectile insufficiency. Growth hormone (GH) and placental lactogen (PL), both having close structural and functional homologies to PRL, were also studied.

Materials and Methods

Isometric tension measurement with cavernous strips was performed in the presence or absence of 10 sup -5 to 10 sup -9 M. PRL, GH, or PL in the perfusion medium. The tension change induced by the test substances was normalized relative to that induced by 120 mEq KCl.

Results

Both PRL and GH produced dose-related elevations (p less than 0.01) of the cavernous tension, whereas PL and thiol-cleaved PRL in comparable doses were without effect (p greater than 0.05). When the tension rise produced by 120 mEq KCl was taken as 100 percent, the maximum contractions produced by PRL and GH were 80 percent and 110 percent. The minimum effective concentration was 10 sup -8 to 10 sup -7 M. for both PRL and GH. Pretreatment with indomethacin (10 sup -5 M.), but not tetrodotoxin (10 sup -5 M.), partially suppressed (p less than 0.05) the effects of PRL.

Conclusion

These results suggest that PRL and GH directly and specifically produced contraction of the corpus cavernosum penis, resulting in erectile insufficiency, and that the effect of PRL is partially mediated by prostaglandin.