Sildenafil Swimming Shrinkage Study

July 26, 2000

Background

Since its introduction in 1998, sildenafil citrate (Viagra), has been used successfully to treat erectile dysfunction (ED). Sildenafil is a selective inhibitor of cyclic guanosine monophosphate specific phosphodiesterase type 5 (PDE5). When sexual arousal occurs, nitrous oxide is released locally, blocking PDE5, which causes an increased level of cGMP in the corpus cavernosum, resulting in relaxation and increased blood flow.

Shrinkage, a temporary ED condition, is a condition caused by immersion of the external male genitalia into a cold body of water, such as the North Atlantic or an unheated pool. Sildenafil's use as a part of a strategy to combat shrinkage has not previously been assessed.

Methods

This open-labeled 4-winged study was completed during the summer months of 1999. 12 migrating male mallard ducks with 2 wings each were assigned to each wing, for a total of 96 wings. Mallards were chosen as the subject of study due to the ease with which adult males can be separated from females, as adult male mallards have green heads and females do not. Additionally, mallards were chosen over humans because no male human volunteers could be located for this study (all human males meeting entry criteria had already enrolled in a "Sildenafil Erectile eXperiment"). One group of mallards received sildafenil; the other received placebo. Blinding was not used in this study as the IRB deems ducks to be illiterate, making the added expense of blinding unnecessary. All ducks were measured before and after immersion into 40 degree Fahrenheit water using precision Victorinox "Original" Swiss Army calipers.

Results

Of the 24 male mallards entered into the study, 4 declined to take the medication (2 sildenafil, 2 placebo). Of the remaining 20 mallards, 10 escaped and flew away immediately upon entering the water (9 sildenafil, 1 placebo p<0.0001). That left one sildafenil-ingesting mallard to compare to the nine who took placebo. There was no difference in before, after, or change in "size" of all remaining mallards regardless of whether or not sildafenil was taken.

Conclusions

Sildenafil appears to have no effect on shrinkage in mallard ducks. Note that the results of this study may skewed as the 9 escapee ducks from the sildenafil wing of the study all returned 2 weeks later with an average of 5 ducklings. On the other hand, the one mallard which received placebo prior to escaping, was seen identified alone in the public pond early last fall.

Further studies are required to investigate sildenafil's utility in preventing shrinkage in human males. Congress has recently approved funding for additional study, shifting 12 million dollars away from female oral contraceptive research.

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