An insurer may loan its funds upon the pledge of securities or evidences of debt eligible for investment under this chapter. As at date made, no such loan shall exceed in amount 90 percent of the market value of such collateral pledged, except that loans upon pledges of United States government bonds may be equal to the market value of the bonds pledged. The amount so loaned shall be included in the maximum percentage of funds permitted to be invested in the kinds of securities or evidences of debt pledged or permitted by section 553 of this title.