HOUSTON -- Astros general manager Ed Wade was quick to remind everyone within earshot that rookie catcher Jason Castro, rookie third baseman Chris Johnson and outfielder Jason Bourgeois weren't to be considered the saviors for his struggling team.

But after losing for the eighth time in nine games in getting swept at Minute Maid Park by the Texas Rangers on Sunday afternoon, the Astros' decision to purchase the contracts of Castro and Bourgeois from Triple-A Round Rock and recall Johnson served notice Wade isn't afraid to shake up the roster.

"They are not coming up here to save this ballclub," Wade said. "They are coming up as young players to bring enthusiasm and coming up here to show us what they are capable of doing."

Wade revealed the moves following Sunday's 5-4 loss to the Rangers, announcing veteran outfielder Cory Sullivan, right-handed reliever Casey Daigle and catcher Kevin Cash had been designated for assignment. The Astros have 10 days to trade them, release them or outright them to the Minor Leagues.

"We're 70 games into the season and there are some moves we can make, and some moves are more difficult to make, and in all honesty, in some measure, all three of these players are victims of circumstances," Wade said. "The circumstances we find ourselves in with the way we've been playing over the 70 games."

The debut of Castro, the club's No. 1 prospect, will be one of the most anticipated arrivals in recent years for the Astros. He was the No. 10 overall Draft pick in 2008 and came to Spring Training battling for the starting catching job, which went to J.R. Towles.

Astros manager Brad Mills said Castro will be the starter at the position over Humberto Quintero.

"Obviously, it's something I've been working toward my whole career, and it's finally happening," said Castro, who entered Sunday hitting .265 in 57 games at Round Rock with four home runs, 26 RBIs and 32 walks in his first season in Triple-A. "I couldn't be more excited. I'm just anxious to get out there and get started."

Castro, who turned 23 on Friday, hit just .226 in April, but was hitting .278 since May 1 with four homers and 20 RBIs, including a two-run home run Saturday against Omaha.

"We think the world of Jason Castro," Wade said. "He was on a timeline to get here at some point. We accelerated the timetable. He's allowed us to do that with his performance over the last two months, particularly of late, when he's made some adjustments in Triple-A with his mechanics at the plate. The feedback we've gotten all along from a defensive standpoint is that he's ready. We're excited to have him."

Johnson, 25, made his Major League debut last year, but played sparingly. He opened the season on the 25-man roster and appeared in eight games, going 5-for-22, before being placed on the 15-day disabled list with a strained right intercostal muscle. He was activated from the DL on May 8 and hit .329 with eight home runs and 33 RBIs in Round Rock.

When asked how much playing time Johnson would get at third base with veteran Pedro Feliz already there, Mills said Johnson "will get a big part."

"C.J. has been victimized by some health issues," Wade said. "We had him earmarked to be our third baseman at some point last season, but he had the hand issue at Triple-A and that slowed him down. He kind of swung the bat well there and played good defense. We brought him up here to show him what he's capable of."

Bourgeois, 28, is a Houston native who entered Sunday ranked fifth in the Pacific Coast League with a .345 batting average in 65 games. He was also tied for fourth in the league with 18 stolen bases and tied for eighth with a .405 on-base percentage.

He will take Sullivan's spot as a backup outfielder, leaving Mills with one less left-handed bat off the bench. Bourgeois, who was claimed off waivers by Houston from Milwaukee on Oct. 26, 2009, hit .321 in 13 Spring Training games for the Astros with two triples and a .412 on-base percentage. He has appeared in 30 Major League games in his career, six for the White Sox in 2008 and 24 for the Brewers last season.

"He's very athletic," Wade said. "He's a speed outfielder. He had a hamstring issue, but that is resolved. The only negative I can bring to the equation at this point is that Cory Sullivan's a left-handed hitter and he's a right-handed hitter. He's got energy and enthusiasm."

Cash had been with the Astros since May 5 and was hitting .204 in 20 games, but was lauded for his game-calling abilities. Daigle posted a 7.50 ERA in eight games with the Astros and took the loss in Sunday's game.

Sullivan, who was signed by the Astros as a Minor League free agent in January and made the club out of Spring Training, hit .188 in 64 at-bats. Wade admitted he got emotional informing all three they were being taken off the 40-man roster.

"They're all good guys," Wade said. "They're professionals. They're exactly how they were portrayed when they entered the organization. We've asked them all to stay in the organization."