Updated from 12:23 p.m. EDT

Shares of

Select Medical

(SEM) - Get Report

plunged on heavy volume after the company warned of Medicare changes that could torpedo its acute-care operations.

Late Tuesday, the company said, the Centers for Medicare and Medicaid Services outlined proposals that if adopted could lower the rate at which Select's long-term acute-care centers receive government reimbursement. The rules apply to centers that are run inside of hospitals and would cut payments to facilities that receive more than 25% of their admissions from their host.

"Most of Select's long-term acute-care hospitals currently would not meet this proposed requirement, and therefore would be subject to lower levels of reimbursement," the company said in a press release. Analysts at Thomas Weisel Partners, Legg Mason and Merrill Lynch downgraded Select on Wednesday.

The shares traded down $2.66, or 19.2%, to $11.20, on volume of 21.3 million shares.

Shares of

Cisco

(CSCO) - Get Report

fell after the company reported earnings after the bell on Tuesday. The networking giant announced

pro forma earnings of 19 cents a share on revenue of $5.6 billion. Analysts were expecting Cisco to do pro forma earnings of 18 cents a share on revenue of $5.55 billion.

More than 114 million shares traded hands on Wednesday, as investors digested the earnings news. Shares of Cisco traded down 29 cents, or 1.3%, to $21.96.

Shares of

Con Edison

(ED) - Get Report

joined the list of heavily traded stocks after the company announced the pricing of a public offering. The company priced 14 million shares at $37.74 each to raise about $528 million. Proceeds will be used for investing in its Con Edison of New York subsidiary. Shares of Con Edison traded up 11 cents, or 0.3%, to $37.85, on volume of 9.5 million shares.

In addition to Cisco,

Nasdaq

companies on the high-volume list included

Intel

(INTC) - Get Report

,

Microsoft

(MSFT) - Get Report

and

Sirius Satellite Radio

(SIRI) - Get Report

.

NYSE

high-volume leaders included

Lucent

( LU),

Altria Group

(MO) - Get Report

,

General Electric

(GE) - Get Report

and

Nortel

( NT).

Looking at Nasdaq price movers, shares of

Maxim Pharmaceuticals

( MAXM) rose after the company announced

positive phase 3 data for its leukemia drug. The company said that its Ceplene drug in combination with Interlukin 2 extended the cancer-free survival of patients with acute myeloid leukemia. Maxim said that it would present further information at upcoming hematology meetings. Shares of Maxim traded up 70 cents, or 8.8%, to $8.70.

Shares of

Park-Ohio Holdings

(PKOH) - Get Report

rose after the company announced strong first-quarter results. The Cleveland company earned 52 cents a share on revenue of $192.4 million, adding that "although we are not prepared to issue additional guidance at this time, the strength in our core customer base and improved operating efficiency appear likely to produce better 2004 results than previously forecast." Shares of Park-Ohio traded up $1.81, or 16.5%, to $12.75.

Vital Signs Lifeless

Vital Signs

( VITL) fell after the medical products maker delivered weaker-than-expected second-quarter earnings. The company earned 42 cents a share on revenue of $46.6 million. Analysts were looking for 46 cents a share on revenue of $45 million.

Vital Signs also announced that Fred Schiff, the company's CFO, resigned effective May 10. Schiff said that he "did not resign because of any concerns with or lack of faith in the company." Shares of the company traded down $3.79, or 12%, to $27.89.

Shares of

RedEnvelope

( REDE) fell after it announced fourth-quarter earnings results and weaker-than-expected 2005 earnings guidance. The online gift company reported a loss of 27 cents a share on revenue of $17.3 million. Analysts were looking for the company to lose 32 cents a share on revenue of $16.8 million.

Looking ahead, the company said it would deliver 2005 sales of $93 million to $96 million and a loss of $2.5 million to $3.5 million. Analysts were expecting the company to turn a profit of 2 cents in 2005 on revenue of $93.8 million. Shares of RedEnvelope traded down 96 cents, or 9.9%, to $8.78.

Over on the Big Board,

Principal Financial Group

(PFG) - Get Report

jumped after it agreed to sell its mortgage banking business to Citigroup for about $1.26 billion. The deal is expected to close in the third quarter of 2004. Principal said the sale of its mortgage business would allow it to focus on growth in the rest of its core businesses. Shares of Principal traded up $2.40, or 7.4%, to $34.73.

Jack in the Box

( JBX) sprang after the fast-food chain announced second-quarter earnings and

better-than-expected third-quarter earnings guidance. During the second quarter, Jack in the Box earned 53 cents a share on revenue of $517.3 million.

Analysts polled by Thomson First Call were looking for the company to earn 43 cents a share on revenue of $507.2 million. Looking ahead, the company said that it expects to deliver third-quarter earnings of 53 cents a share and full-year earnings of $1.99. Analysts were expecting the company to earn 45 cents a share during the third quarter and $1.93 for the entire year. Shares of Jack in the Box traded up 24 cents, or 0.9%, to $27.22.

Meridian Gold

( MDG) rose after it reported strong first-quarter results. The Toronto-based company earned 10 cents a share on revenue of $29.9 million vs. net income of 8 cents a share on revenue of $35.9 million a year ago. Shares of Meridian traded up 42 cents, or 4.2%, to $10.55.

Shares of

CarMax

(KMX) - Get Report

crashed after the company lowered first-quarter earnings guidance. The company now says that it will earn 30 cents to 32 cents a share during the first quarter. Analysts had expected CarMax to deliver 34 cents a share. The used-car company also said that same-stores sales would come in 2% to 4% below last year's numbers. It had previously guided for same-store sales growth of 1% to 3%. Shares of CarMax traded down $3.30, or 13.2%, to $21.70.

Weight Watchers

(WTW) - Get Report

reduced after the company delivered first-quarter earnings results and disappointing 2004 earnings guidance. On a pro forma basis, the company earned 47 cents a share on revenue of $281.4 million. Earnings and revenue were in line with analysts' forecasts.

Looking ahead, however, the company said that it expects to deliver full-year earnings of $1.70 to $1.80. Analysts were expecting the company to earn $1.93 during 2004. Shares of Weight Watchers traded down $4.61, or 12.2%, to $33.13.