Subject to the provisions of subsection (b), in the case of a guarantee of any loan to a nonprofit private agency under this part with respect to a hospital or other medical facility, the Secretary shall pay, to the holder of such loan and for and on behalf of such hospital or other medical facility amounts sufficient to reduce by 3 per centum per annum the net effective interest rate otherwise payable on such loan. Each holder of a loan, to a nonprofit private agency, which is guaranteed under this part shall have a contractual right to receive from the United States interest payments required by the preceding sentence.