The drug, called Adjudin, is a long way from human use. But lab tests on rats showed no signs of side effects, and the drug's effects wore off in 20 weeks.
The researchers included Chuen-yan Cheng, PhD, of the Population Council's Center for Biomedical Research. The Population Council is a New York-based international nonprofit organization that conducts biomedical, social science, and public health research.
Basically, Adjudin nips wannabe sperm cells in the bud. Those cells, called germ cells, ordinarily develop into sperm. But they need the help of other cells, called Sertoli cells, to reach that destiny.
Adjudin interferes with the process.
Cheng's team previously reported from other animal tests that Adjudin, given orally by itself, was too toxic to be a suitable contraceptive because it caused liver inflammation and muscle shrinkage (atrophy).
So the scientists bundled Adjudin with a synthetic version of the sex hormone FSH (follicle-stimulating hormone) and injected it into the bellies of four male rats.
The researchers played matchmaker four, six, 12, and 20 weeks later, putting the treated rats in cages with virgin female rats for two to four days.
For comparison, they put male rats that hadn't gotten the contraceptive in other cages with female rats.
The male and female rats mated, as expected.
All the male rats that had gotten the contraceptive shots were infertile four and six weeks after treatment. Their fertility resumed 20 weeks after getting the shots. That shows the contraceptive is "reversible," the researchers write.
In comparison, all the female rats that mated with the untreated male rats gave birth to baby rats.
No side effects were reported in the treated rats.
SOURCES: Mruk, D. Nature Medicine, Oct. 29, 2006; advance online publication. WebMD Medical News: "Gene Therapy Offers Hope to Infertile Men." News release, Nature and the Nature research journals.
By Miranda Hitti
Reviewed by Louise Chang