TOKYO — The Japan Sumo Association began random doping tests of wrestlers Wednesday following a series of drug-related scandals that have damaged the image of the ancient sport.

Several top wrestlers, including grand champion Asashoryu of Mongolia, were given urine tests by Mitsubishi Chemical Medience Corp., Japan's only institution certified by world anti-doping agency WADA. The results will be disclosed at a later date.

In January, second-division wrestler Wakakirin was arrested on suspicion of possessing marijuana, becoming the first Japanese wrestler to be arrested in a marijuana case and the latest to be exiled from the sumo world.

His arrest came after three Russians also were dismissed last year over marijuana charges.

New anti-doping rules were set by the JSA in late February so that all of the association's members could be tested without warning.