Left-hander Stephen Randolph's contract was purchased by the Astros from Triple-A Round Rock on Thursday, a day after reliever Rick White was injured warming up in the bullpen during a 16-inning game. White, one of the Astros' most reliable relievers this season, strained a muscle in his left side while warming up to pitch the ninth inning of the 4-3 loss to Pittsburgh on Wednesday night. With White unavailable, Astros closer Dan Wheeler ended up pitching the ninth and 10th innings.