An experimental male contraceptive that prevents pregnancy by blocking sperm flow using a special gel showed promise in a trial involving rhesus monkeys.

The new method has already been proven effective when tested in rabbits and now in rhesus monkeys, which are more closely related and more anatomically similar to humans.

In the study published in Basic and Clinical Andrology on Feb. 7, researchers squirted the male contraceptive gel called Vasalgel into the sperm ducts of monkeys and found it was effective at preventing pregnancy.

Injectable Polymer Gel

Vasalgel is a polymer gel injected directly into the vas deferens, the tiny muscular tube that carries sperm from the testes to the penis. The gel becomes a sort of blockade for the sperm in the tube.

For the new study, Angela Colagross-Schouten, from the California National Primate Research, and colleagues tested the contraceptive effect of Vasalgel in 16 adult male monkeys that were housed with females. The animals were tracked for two years, which covered at least one breeding season per monkey.

No Pregnancy During The Course Of The Study

The typical pregnancy rate among female rhesus monkeys housed with males is about 80 percent but while mating did occur during the study period, none of the female monkeys became pregnant during the course of the study.

Minimal Complications

Researchers likewise reported that use of Vasalgel appeared well-tolerated among monkeys and resulted in minimal complications. Although one of the 16 monkeys showed symptoms of sperm granuloma, a buildup in the vas deferens, the researchers said that this is a common complication in about 60 percent of human males who undergo vasectomy.

"Intravas injection of Vasalgel in sexually mature adult male rhesus monkeys was effective in preventing conception in a free-living, group environment," the researchers wrote in their study. "Complications were few and similar to those associated with traditional vasectomy."

Contraceptive Effect Of Vasalgel Is Reversible

The contraceptive is likewise reversible. In an earlier trial involving rabbits, researchers were able to reverse the contraceptive effect of Vasalgel by flushing the material out using a simple sodium bicarbonate solution to resume the flow of the sperm.

New Contraceptive Option For Males

The findings offer hope for men who are currently limited to using condoms, which many men claim to interfere during sexual contact; withdrawal, which come with high pregnancy risks; or vasectomy, which is meant to permanently prevent a man from impregnating a woman. Although vasectomy can be reversed in some cases, the procedure is technically challenging and may result in low fertility rates.

Long-acting and reversible contraceptives are not currently available for men but Vasalgel may finally offer a new option. Researchers likewise said Vasalgel may also have important implications for nonhuman primates.

"Vasectomies are a routine procedure for nonhuman primate veterinarians, so to have similar or even slightly better outcomes trying a brand-new procedure is very encouraging," Colagross-Schouten said. "Hopefully, Vasalgel placement can be an option for other captive colonies, including zoos, that want to manage reproductive rates while allowing for social housing."

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