If an industrial loan company has investment or thrift certificates outstanding, then such company shall not borrow, except by the sale of investment or thrift certificates, in an amount in excess of 300 percent of the amount represented by its outstanding capital stock, surplus and undivided profits, without the written consent of the commissioner. All sums so borrowed in excess of 150 percent of outstanding capital stock, surplus and undivided profits shall be unsecured borrowings or, if secured, approved in writing by the commissioner in advance of the borrowings, and be included as investment or thrift certificates for

purposes of computing the ratio allowed under Sections 18319 and 18320.