An insurer may invest in loans secured by deposits of collateral consisting of securities in which the insurer may otherwise invest under this article, if the current market value of such collateral is not less than twenty percent in excess of the amount of the loan. The amount so loaned shall be included pro rata in determining the maximum of funds permitted under this article to be invested in the respective categories of securities so pledged. The superintendent may by rule or regulation place reasonable limit upon such loans to a parent corporation, subsidiary or affiliate of the insurer.