Castro was optioned to Triple-A Nashville on Tuesday. With Eric O'Flaherty (shoulder) returning from the disabled list, Castro's second stint in the majors only lasted three days and didn't include any appearances. Castro could return to Oakland next time the team loses a bullpen arm to injury, as he's having a nice year for Triple-A Nashville.

Castro was recalled from Triple-A Nashville on Saturday. Ongoing shoulder issues have forced Sean Doolittle back to the DL and created another opportunity for Castro. Castro made four appearances in a little under three weeks during his first stint with the big club, allowing one run on six hits and three walks with three strikeouts in three innings.

Castro was optioned to Triple-A on Tuesday, Jane Lee of MLB.com reports. The move comes as a response to Oakland activating Sean Doolittle from the DL on Tuesday. Castro appeared in four games for the A's, allowing six hits, three walks and one earned run over 3.0 total innings.

Castro was called up by the A's Friday, the San Francisco Chronicle's Susan Slusser reports. The 32-year-old righty had a 3.79 ERA in 19 innings at Triple-A and will likely serve in low-leverage situations for the A's while he is up in the majors.

The Cardinals traded Castro to the A's on Friday in exchange for cash consideration. In 26 appearances (14 starts) with the Cards' Triple-A Memphis affiliate, Castro posted a 4.01 ERA, 1.29 WHIP and 6.0 K/9, and he'll now join the A's to provide organizational depth. Castro, who's never appeared in the majors, faces an uphill battle to crack the team's 40-man roster.

Cardinals optioned RHP Angel Castro to Triple-A Memphis. Castro will serve as organizational depth this season for St. Louis after posting a decent 3.48 ERA with 91 strikeouts in 116 1/3 innings last summer for the Dodgers' Triple-A club. The right-hander turned 31 years old this winter.