Goldman Sachs Group said Wednesday that two high-ranking leaders of its trading business have left the firm as Wall Street executives come under more pressure to cut costs and put less of their money at risk in trades.

David B. Heller and Edward K. Eisler, two of four co-heads of securities trading at Goldman Sachs Group , decided to retire, according to internal memos sent. Heller, based in New York, has been with Goldman for 22 years and Eisler, based in London, for 18 years.

While financial companies worldwide have announced plans to lay off more than 100,000 people in recent months, the Goldman departures still came as a surprise. Goldman has given notice to about 1,000 people, including some of its partners.

Both men will continue with the firm as non-employee advisers, according to spokesman Michael DuVally.

Investment banks are facing near-term and long-term trading issues that have dispirited many professionals. Profits in recent quarters have been trimmed by volatile world markets while impending regulations known as the Volcker Rule are forcing banks to close their proprietary trading units that have long fueled strong profits.

Wall Street firms also are cutting jobs and compensation for top executives who oversee units where revenues are falling.

Goldman last year closed two proprietary trading desks that were part of the securities division in anticipation of the new regulations.

Heller, who was based in New York, is a long-time equities trader while London-based Eisler specialized in global interest rate products.

Goldman's earnings per share for 2011 are estimated to be down 62 percent from 2010, according to analysts surveyed by Thomson Reuters I/B/E/S.

Goldman is scheduled to report financial results next week.

Equities volume across the securities industry fell 10 percent in the fourth quarter of 2011 from the previous year, and was down 18 percent from this year's third quarter, according to estimates by analyst Brad Hintz of Bernstein Research.

At the same time, firms are under pressure to automate to lower costs for themselves and clients, said analyst Richard Bove of Rochdale Securities.

It is becoming a machine-driven business, and traders around Wall Street are vulnerable, said Bove. It is a battle of who has the best technology and who has scale.

Heller and Eisler shared oversight of fixed income, currency, commodity and stock trading with credit markets veteran Pablo Salame and fixed-income sales expert Harvey Schwartz, who are staying in their roles.

Goldman promoted Isabelle Ealet, its global head of commodities and a rising star at the firm, to work alongside Salame and Schwartz as a third co-head of the securities division.

Goldman annually goes through two rounds of routine cutting. Early in the year, a so-called 5 percent cull occurs in which the company weeds out the bottom tier of performers. Late in the year, the investment bank asks some of its partners to leave, almost always with lucrative retirement packages, in order to make room for an up-and-coming round of talent who compete fiercely for the title.

Goldman does not say how many partners it has, but the culling in 2011 was exceptionally high and took the number down below 400, people close to the firm said.

Goldman Chief Executive Lloyd Blankfein said in November that the average tenure of a partner at the firm was 15.5 years.

In December, Edward Forst, 50, a co-head of investment banking retired after 16 years with Goldman.

About the same time, Milton Berlinski, a partner who oversaw Goldman's relationships with private-equity firms, retired as global head of the financial sponsor group. Berlinski who had been with the firm for 26 years, became a partner in 1996 before the company went public, and at one time was head of firmwide strategy.

(Reporting by David Henry and Jed Horowitz in New York. Additional reporting by Carrick Mollenkamp in New York; Editing by Bernard Orr and Matthew Lewis)