The characterization of a bio-assay of erectile function in a rat model.

The investigation of biological phenomena in impotence using an animal system requires a determination of the erectile capabilities of the animal. Rats respond reliably to apomorphine by the exhibition of a phenomenon of erections and yawns. This property has been used to form the basis of a bio-assay of erectile integrity in the rat. We compared rats treated with placebo alone, sham operated rats, rats rendered surgically impotent and castrated rats with and without testosterone. Rats did not respond to placebo. The sham operated rats remained normal in all measured respects (2.66 erections/rat/30 minutes). Surgically impotent rats yawned normally but had no erections. Castrated rats did not have erections and had diminished yawning (3.21 yawns/rat/30 minutes vs. 7.7 for controls p less than .001) but responded normally after testosterone administration. The bio-assay is useful as a standard test of erectile function in the rat.