Castro was recalled from Triple-A Albuquerque on Friday, Thomas Harding of MLB.com reports.
The Rockies optioned Castro upon activation from the DL earlier in the week, but he has been summoned back to Colorado ahead of Friday's series opener against the Pirates. Castro, 21, has an electric arm and there has been talk that he could see some save chances late in the year, but he will help bridge the cap to current closer Jake McGee for the time being.