Prudential Insurance Co. of America reported sharply...

Prudential Insurance Co. of America reported sharply improved 1991 results, bolstered by strong gains on investments and a dramatic turnaround at its brokerage unit, Prudential Securities Inc.

The nation’s largest insurer said its capital base, an important measure of an insurer’s financial health, rose $1.7 billion to $9.7 billion, an increase of 21%. Chairman and Chief Executive Robert C. Winters called the gain “an impressive accomplishment, considering the weak economy and the tough challenges for financial services firms” last year.

Prudential, based in Newark, N.J., is a mutual insurer, owned by policyholders rather than shareholders. It is not required to calculate financial results using generally accepted accounting principles that show revenue and earnings.

Prudential Securities earned $201 million last year, contrasted with a $259-million loss in 1990.

Revenue from all businesses grew to $42.8 billion, up from $40.8 billion in 1990. Prudential now has consolidated assets of $189 billion, up from $169 billion in 1990.

Earnings, D8