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Reversible inhibition of sperm under guidance (RISUG), formerly referred to as the synthetic polymer styrene maleic anhydride (SMA), is the development name of a male contraceptive developed at IIT Kharagpur in India by the team of Dr. Sujoy K Guha. Phase III clinical trials are underway in India, slowed by insufficient volunteers. It has been patented in India, China, Bangladesh, and the United States.〔 A method based on RISUG, Vasalgel, is currently under development in the United States. ==Mechanism of action== RISUG works by an injection into the vas deferens, the vessel through which the sperm moves before ejaculation. RISUG is similar to vasectomy in that a local anesthetic is administered, an incision is made in the scrotum, and the vas deferens is tugged out with a small pair of forceps. Rather than being cut and cauterized, as it is in a vasectomy, the vas deferens is injected with a polymer gel and pushed back into the scrotum. In a matter of minutes, the injection coats the walls of the vas with a clear gel made of 60 mg of the copolymer styrene/maleic anhydride (SMA) with 120 µl of the solvent dimethyl sulfoxide. The copolymer is made by irradiation of the two monomers with a dose of 0.2 to 0.24 megarad for every 40 g of copolymer and a dose rate of 30 to 40 rad/s.〔Jha, Pradeep K., Rakhi Jha, B. L. Gupta, and Sujoy K. Guha. "Effect of γ-dose rate and total dose interrelation on the polymeric hydrogel: A novel injectable male contraceptive." Radiation Physics and Chemistry 79, no. 5 (2010): 663-671.〕 The source of irradiation is cobalt-60 gamma radiation. The effect the chemical has on sperm is not completely understood. Originally it was thought that it lowered the pH of the environment enough to kill the sperm.〔()〕 More recent research claims that this is not enough to explain the effect. One explanation is that the polymer is an anhydride, and hydrolizes in the presence of water in the spermatic fluid. Due to the breaking of a cyclic group, the polymer becomes a hydride and has a positive charge. This disturbs the negative charge of the sperm membrane on contact. Professor SK Guha theorizes that the polymer surface has a negative and positive electric charge mosaic. The differential charge from the gel ruptures the sperm's cell membrane as it passes through the vas, deactivating sperm before they initiate their journey to the egg. "Within an hour, the drugs produce an electrical charge that nullifies the electrical charge of the spermatozoa, preventing it from penetrating the ovum," Dr. Guha said. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Reversible inhibition of sperm under guidance」の詳細全文を読む スポンサード リンク
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