<PAGE>


                                                                     Exhibit 4.3

                  FIRST AMENDMENT TO SECOND AMENDED AND RESTATED
                            LOAN AND AGENCY AGREEMENT


         THIS FIRST AMENDMENT TO SECOND AMENDED AND RESTATED LOAN AND AGENCY
AGREEMENT (this "Amendment"), dated as of May 15, 1998, is by and among
INTERMAGNETICS GENERAL CORPORATION, a New York corporation, APD CRYOGENICS INC.,
a Pennsylvania corporation, MAGSTREAM CORPORATION, a New York corporation,
MEDICAL ADVANCES, INC., a Wisconsin corporation, and INTERCOOL ENERGY
CORPORATION, a Delaware corporation (each, an "Existing Borrower" and
collectively, the "Existing Borrowers"), POLYCOLD SYSTEMS INTERNATIONAL, INC., a
Delaware corporation (the "New Borrower" and, collectively with the Existing
Borrowers, the "Borrowers"), CORESTATES BANK, N.A., and THE CHASE MANHATTAN BANK
(the "Banks").

                                   BACKGROUND

         WHEREAS, the Existing Borrowers and the Banks are parties to a Second
Amended and Restated Loan and Agency Agreement dated October 23, 1997 (as at any
time amended and/or extended, the "Loan Agreement"), pursuant to which the Banks
agreed to make available to the Existing Borrowers certain credit facilities
upon the terms and conditions specified in the Loan Agreement; and

         WHEREAS, the parties wish to amend the Loan Agreement as set forth
herein to, inter alia, add the New Borrower as a Borrower under the Loan
Agreement;

         NOW, THEREFORE, in consideration of the promises and mutual agreements
herein contained, the parties hereto, intending to be legally bound hereby,
agree to amend the Loan Agreement as herein stated.

         1. Effect of Prior Agreements. This Amendment is intended to amend the
Loan Agreement as it has been in effect to the date hereof and as it shall be
amended on and after the date hereof. All terms used herein as defined terms
shall have the meanings ascribed to them in the Loan Agreement unless herein
provided to the contrary.

         2. Amendments.

                           (a) The introductory paragraph of the Loan Agreement
         is hereby amended and restated in its entirety as follows:

                           THIS SECOND AMENDED AND RESTATED LOAN AND AGENCY
                  AGREEMENT, dated as of October 23, 1997 (this "Agreement"), is
                  entered into by and among INTERMAGNETICS GENERAL CORPORATION,
<PAGE>

                  a New York corporation ("IGC"), APD CRYOGENICS INC., a
                  Pennsylvania corporation ("APD"), MAGSTREAM CORPORATION, a New
                  York corporation ("MC"), MEDICAL ADVANCES, INC., a Wisconsin
                  corporation ("MA"), INTERCOOL ENERGY CORPORATION, a Delaware
                  corporation ("IEC"), and POLYCOLD SYSTEMS INTERNATIONAL, INC.,
                  a Delaware corporation (each, a "Borrower" and collectively,
                  the "Borrowers"), the banking institutions signatories hereto
                  and such other institutions that hereafter become a "Bank"
                  pursuant to Section 10.4 hereof (each, a "Bank" and
                  collectively, the "Banks") and CORESTATES BANK, N.A., a
                  national banking association ("CoreStates"), as agent for the
                  Banks under this Agreement (in such capacity, the "Agent").

                           (b) The following definitions are hereby added to
         Article I of the Loan Agreement, in alphabetical order:

                           "L/C Agreement" shall mean an Agreement for Standby
                  Letter of Credit, substantially in the form of Exhibit D
                  hereto, and in form and substance satisfactory to the Agent.

                           "Letter of Credit Sublimit" shall mean Four Million 
                  Dollars ($4,000,000).

                           (c) The following definitions set forth in Article I
         of the Loan Agreement are hereby amended and restated in their entirety
         as follows:

                           "Loan Documents" shall mean this Agreement, the
                  Notes, the L/C Agreements, and all agreements, amendments,
                  certificates, financing statements, schedules, reports,
                  notices, and exhibits now or hereafter executed or delivered
                  in writing in connection with any of the foregoing, as may be
                  in effect from time to time.

                           (d) A new Section 2.1(g) is hereby added to the Loan
         Agreement, to read as follows:

                           (g) Letters of Credit.

                                    (1) Generally. In addition to making
                  Revolving Credit Loans to the Borrowers as provided in this
                  Section 2.1, the Agent, on behalf of the Banks, shall, upon
                  the request of the Borrowers and subject to the terms of this
                  Agreement, also issue one or more letters of credit and/or
                  bank guarantees ("Letters of Credit") for the account of the
                  Borrowers, provided that in connection with each issuance of a
<PAGE>

                  Letter of Credit the Borrowers shall execute and deliver to
                  the Agent an L/C Agreement substantially in the form of
                  Exhibit D hereto; and provided further, that in the event of
                  any conflict between the terms of any L/C Agreement and the
                  terms of this Agreement, the terms of this Agreement shall be
                  controlling. All amounts drawn under Letters of Credit shall
                  be deemed to be Revolving Credit Loans evidenced by the
                  Revolving Credit Notes, and the amount available to be
                  borrowed under the Revolving Credit facility, and the Letter
                  of Credit Sublimit, shall be reduced by the aggregate amounts
                  drawn and available to be drawn at any time under all
                  outstanding Letters of Credit. In no event shall the aggregate
                  amount available to be drawn on all outstanding Letters of
                  Credit plus the outstanding principal balance of Revolving
                  Credit Loans exceed the Aggregate Revolving Loan Commitment.
                  In no event shall the aggregate amount available to be drawn
                  on all outstanding Letters of Credit exceed the lesser of (i)
                  the Aggregate Revolving Loan Commitment, or (ii) the Letter of
                  Credit Sublimit. The duration of any Letter of Credit shall
                  not extend beyond the Revolver Termination Date. Not more than
                  three (3) Letters of Credit with a face amount of less than
                  $25,000 shall be outstanding hereunder at any one time. No
                  Letter of Credit in excess of $4,000,000 shall be issued by
                  the Agent on behalf of the Banks except upon the approval of
                  the Required Banks, in their sole discretion. Each Bank hereby
                  absolutely and unconditionally agrees to pay to the Agent such
                  Bank's Commitment Percentage of each disbursement made by the
                  Agent pursuant to a Letter of Credit and not reimbursed by the
                  Borrowers pursuant to Section 2.1(g)(3), or of any
                  reimbursement payment required to be refunded to the Borrowers
                  for any reason ("LC Disbursements").

                                    (2) Issuance of Letters of Credit. Subject
                  to the provisions of Section 2.1(g)(1), the Agent, on behalf
                  of the Banks, shall issue Letters of Credit for the account of
                  the Borrowers, provided that the Borrowers (i) provide a
                  written request for each such Letter of Credit specifying the
                  terms thereof, including, without limitation, the amount and
                  the name and address of the beneficiary of such Letter of
                  Credit; (ii) execute and deliver to the Agent an application
                  for each such Letter of Credit pursuant to the form provided
                  for such purpose by the Agent; and (iii) execute and deliver
                  to the Agent such other documents and instruments which the
                  Agent, in its sole and absolute discretion, deems reasonable
                  and necessary. In connection with each Letter of Credit, the
                  Borrowers shall pay to the Agent, for the benefit of the
                  Banks, a non-refundable fee equal to: (A) for bank guarantees,
                  the Applicable Margin in effect on each day during the
                  calendar quarter, and (B) for letters of credit, such rate as
                  the Agent and the Borrowers may agree upon, in either case
                  multiplied by the amount of such Letter of Credit outstanding
                  each day during such calendar quarter (after giving effect to
                  any drawings thereunder); which fee shall be payable quarterly
                  in arrears. The Borrowers shall also pay to the Agent, for the
                  benefit of the Agent, and not for the benefit of the other
<PAGE>

                  Banks, all transactional and customary fees required by the
                  Agent in connection with the issuance of each Letter of Credit
                  hereunder, including, without limitation, the Agent's standard
                  remittance, transfer and issuance fees, which fees may be
                  deducted by the Agent from the Borrowers' account as such fees
                  are incurred.

                                    (3) Reimbursement. If the Agent shall make
                  any LC Disbursement in respect of a Letter of Credit, then
                  either (i) the Borrowers shall reimburse such LC Disbursement
                  by paying to the Agent an amount equal to such LC Disbursement
                  not later than 12:00 noon, Philadelphia time, on the date that
                  such LC Disbursement is made, if the Borrowers shall have
                  received notice of such LC Disbursement prior to 10:00 a.m.
                  Philadelphia time on such date, or, if such notice is received
                  by the Borrowers after 10:00 a.m. Philadelphia time on such
                  date, then not later than 10:00 a.m. Philadelphia time on the
                  Business Day immediately following the day on which the
                  Borrowers receive such notice; or (ii) such LC Disbursement
                  shall become and be deemed a Revolving Credit Loan, bearing
                  interest at the Adjusted Base Rate in effect at such time. The
                  Agent shall notify each Bank of any LC Disbursement, the
                  payment then due from the Borrowers in respect thereof, and
                  such Bank's Commitment Percentage thereof. Promptly following
                  receipt of such notice, each Bank shall pay to the Agent its
                  Commitment Percentage of the payment then due from the
                  Borrowers, in the same manner as provided in Section 2.3, with
                  respect to Loans. Promptly following receipt by the Agent of
                  any payment from the Borrowers pursuant to this Section
                  2.1(g)(3), the Agent shall distribute such payment to the
                  Banks, to the extent that such Banks have made payments
                  pursuant to this Section to reimburse the Agent. Any payment
                  made by a Bank pursuant to this Section to reimburse the Agent
                  for any LC Disbursement shall not relieve the Borrowers of
                  their obligations to reimburse such LC Disbursement.

                                    (4) Obligations Absolute. The Borrowers'
                  obligations to reimburse LC Disbursements as provided in
                  Section 2.1(g)(3) shall be absolute, unconditional and
                  irrevocable, and shall be performed strictly in accordance
                  with the terms of this Agreement under any and all
                  circumstances whatsoever and irrespective of (i) any lack of
                  validity or enforceability of any Letter of Credit or this
                  Agreement or any term or provision thereof; (ii) any draft or
                  other document presented under a Letter of Credit proving to
                  be forged, fraudulent or invalid in any respect or any
                  statement therein being untrue or inaccurate in any respect;
                  (iii) payment by the Agent under a Letter of Credit against
                  presentation of a draft or other document that does not comply
                  with the terms of such Letter of Credit; or (iv) any other
                  event or circumstance whatsoever, whether or not similar to
                  any of the foregoing, that might, but for the provisions of
<PAGE>

                  this Section, constitute a legal or equitable discharge of, or
                  provide a right of setoff against, the Borrowers' obligations
                  hereunder. Neither the Agent nor the Banks, nor any of their
                  Affiliates, shall have any liability or responsibility by
                  reason of or in connection with the issuance or transfer of
                  any Letter of Credit or any payment or failure to make any
                  payment thereunder (irrespective of any of the circumstances
                  referred to in the preceding sentence), or any error,
                  omission, interruption, loss or delay in transmission or
                  delivery of any draft, notice or other communication under or
                  relating to any Letter of Credit (including any documents
                  required to make a drawing thereunder), any error in
                  interpretation of technical terms or any consequence arising
                  from causes beyond the control of the Agent; provided, that
                  the foregoing shall not be construed to excuse the Agent from
                  liability to the Borrowers to the extent of any direct damages
                  (as opposed to consequential damages, claims in respect of
                  which are hereby waived by the Borrowers to the extent
                  permitted by applicable law) suffered by the Borrowers that
                  are caused by the Agent's failure to exercise care when
                  determining whether drafts and other documents presented under
                  a Letter of Credit comply with the terms thereof. The parties
                  hereto expressly agree that, in the absence of gross
                  negligence or willful misconduct on the part of the Agent (as
                  finally determined by a court of competent jurisdiction), the
                  Agent shall be deemed to have exercised care in each such
                  determination. In furtherance of the foregoing and without
                  limiting the generality thereof, the parties agree that, with
                  respect to documents presented which appear on their face to
                  be in substantial compliance with the terms of a Letter of
                  Credit, the Agent may, in its sole discretion, either accept
                  and make payment upon such documents without responsibility
                  for further investigation, regardless of any notice or
                  information to the contrary, or refuse to accept and make
                  payment upon such documents if such documents are not in
                  strict compliance with the terms of such Letter of Credit.
                  Each Bank acknowledges and agrees that its obligations to make
                  payments to the Agent pursuant to this Section 2.1(g) are
                  absolute and unconditional and shall not be affected by any
                  circumstance whatsoever, including any amendment, renewal or
                  extension of any Letter of Credit or the occurrence and
                  continuance of an Event of Default or reduction or termination
                  of the Revolving Loan Commitments, and that each such payment
                  shall be made without any offset, abatement, withholding or
                  reduction whatsoever.

                           (e) Section 2.5(a) of the Loan Agreement is hereby 
         amended and restated in its entirety as follows:

                           (a) The Borrowers shall pay to the Agent for the
                  ratable benefit of the Banks, and as compensation for the
                  Banks' Revolving Loan Commitments, a fee (the "Commitment
                  Fee") computed at the rate per annum equal to 12.5 basis
<PAGE>

                  points (0.125%) on the average daily amount of the unused
                  portion of the Aggregate Revolving Loan Commitment (reduced by
                  the amount of Letters of Credit outstanding from time to time)
                  accrued from and after the date hereof. The Commitment Fee
                  shall be payable in arrears on the first day of each January,
                  April, July and October, commencing October 1, 1997 (for the
                  three month period or portion thereof ended on the preceding
                  day), and on the Revolver Termination Date. Payment shall be
                  made to the Agent on behalf of the Banks and the Agent shall
                  promptly forward to each Bank the portion of the Commitment
                  Fee amount due such Bank. The Commitment Fee shall be
                  calculated on the basis of a 360 day year.

                           (f) Section 2.6(a) of the Loan Agreement is hereby
         amended and restated in its entirety as follows:

                           (a) Voluntary. The Borrowers may at any time, on not
                  less than three (3) Business Days' written notice, terminate
                  or permanently reduce the Aggregate Revolving Loan Commitment
                  pro rata among the Banks, provided that (i) any reduction
                  shall be in the amount of $1,000,000 or a multiple thereof,
                  (ii) no such termination or reduction shall cause the sum of
                  the aggregate principal amount of Loans outstanding and the
                  aggregate face amount of any Letters of Credit then
                  outstanding to exceed the Aggregate Revolving Loan Commitment,
                  as reduced, and (iii) no termination of the Aggregate
                  Revolving Loan Commitment shall reduce the Aggregate Revolving
                  Loan Commitment to an amount which is less than the aggregate
                  face amount of any Letters of Credit then outstanding.

         3. Joinder of New Borrower The New Borrower hereby joins in the Loan
Agreement, the Obligations thereunder, the Notes and all other Loan Documents as
a joint and several obligor thereunder and party thereto, subject to all the
terms and provisions thereof. Without limiting the foregoing, the New Borrower
expressly agrees to be jointly and severally liable for all fees under the Loan
Agreement and all other amounts of principal and charges which may be due
thereunder, and hereby ratifies all actions heretofore taken, and all
obligations incurred by the Existing Borrowers under the Loan Agreement and the
other Loan Documents executed in connection therewith.

         4. Representations, Warranties and Covenants. Each Borrower hereby
affirms and reaffirms to the Banks all representations and warranties made and
to be made under the Loan Agreement, and confirms that all are true and correct
as of the date hereof and that no Default has occurred and is continuing. Each
Borrower further represents and warrants that it has the authority and legal
right to execute, deliver and carry out the terms of this Amendment, that such
actions were duly authorized by its Board of Directors and that the officers
executing this Amendment on its behalf were similarly authorized and empowered,
and that this Amendment does not contravene any provision of its Certificate or
Articles of Incorporation or Bylaws, or of any contract or agreement to which it
<PAGE>

is a party or by which it or any of its properties is bound. Each Borrower
hereby affirms and reaffirms to the Banks all of the covenants contained in the
Loan Agreement including, without limitation, those contained in Articles V and
VI of the Loan Agreement and agrees to abide thereby until all of the
Obligations to the Banks are satisfied and/or discharged in their entirety.

         5. Conditions. To induce the Banks to enter into this Amendment, the
Borrowers agree as follows:

                  (a) The Borrowers shall execute and deliver to the Agent, on
behalf of the Banks, this Amendment, an Allonge to Revolving Credit Note in form
and substance satisfactory to the Agent, and all other documents as the Agent
may require;

                  (b) The Borrowers shall deliver to the Agent, on behalf of the
Banks, certified resolutions of the Board of Directors of each Borrower
authorizing the execution and delivery of the Amendment and all other documents
executed in connection herewith and therewith, all in form and substance
satisfactory to the Agent; and

                  (c) Each Borrower shall deliver to the Bank an Officer's
Certificate in form and substance satisfactory to the Agent.

         6. Further Assurances. Each Borrower hereby agrees to execute and
deliver to the Agent, on behalf of the Banks, such further agreements, and other
documentation as may be requested by the Agent at any time to assure the
protection and enforcement of the Banks' rights under the Loan Agreement as
amended hereby.

         7. Reservation of Rights. To the extent any Event of Default exists on
the date hereof, any and all undertakings of any Bank under or pursuant to this
Amendment shall not be deemed a waiver by such Bank of any such Event of Default
or any of such Bank's rights and remedies under the Loan Agreement and/or
applicable law; and the Banks hereby reserve any and all such rights and
remedies.

         8. Payment of Expenses. The Borrowers shall pay or reimburse the Agent,
on behalf of the Banks, for their respective reasonable attorneys' fees and
expenses in connection with the preparation and execution of this Amendment and
all other related documents.

         9. Reaffirmation and Extension of Agreement. Except as modified by the
terms hereof, all of the terms and conditions of the Loan Agreement and all
other Loan Documents, including, without limitation, the Notes, are hereby
affirmed and shall continue in full force and effect.

         10. Counterparts. This Amendment may be executed in two or more
counterparts, and by different parties on different counterparts, each of which
shall be

<PAGE>

deemed an original and all of which, taken together, shall constitute
one and the same instrument.

         11. Governing Law. This Amendment and the rights and obligations of the
parties hereunder shall be construed in accordance with and shall be governed by
the laws of the Commonwealth of Pennsylvania.
<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed and delivered by their proper and duly authorized officers, as of the
date first above written.


                               INTERMAGNETICS GENERAL CORPORATION


                               By: /s/ Carl H. Rosner
                                   ---------------------------------------
                               Name: Carl H. Rosner
                               Title: Chairman and Chief Executive Officer


                               APD CRYOGENICS INC.

                               By: /s/ Michael C. Zeigler
                                   ---------------------------------------
                               Name: Michael C. Zeigler
                               Title: Treasurer


                               MAGSTREAM CORPORATION

                               By: /s/ Michael C. Zeigler
                                   ---------------------------------------
                               Name: Michael C. Zeigler
                               Title: Treasurer


                               MEDICAL ADVANCES, INC.

                               By: /s/ Carl H. Rosner
                                     ---------------------------------------
                               Name: Carl H. Rosner
                               Title: Chief Executive Officer


                               INTERCOOL ENERGY CORPORATION

                               By: /s/ Michael C. Zeigler
                                   ---------------------------------------
                               Name: Michael C. Zeigler
                               Title: Treasurer

                               POLYCOLD SYSTEMS
                               INTERNATIONAL, INC.

                               By: /s/ Carl H. Rosner
                                   ---------------------------------------
                               Name: Carl H. Rosner
                               Title: Chairman and Chief Executive Officer
<PAGE>


                                     CORESTATES BANK, N.A.,
                                     individually and as Agent


                                     By: /s/ Kaj E. Karch
                                         ------------------------------
                                     Name: Kaj E. Karch
                                     Title: Vice President

                                     THE CHASE MANHATTAN BANK


                                     By: /s/ Stephen P. Malinowski
                                         ------------------------------
                                     Name: Stephen P. Malinowski
                                     Title: Vice President



<PAGE>



STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this 20th day of May, 1998, before me personally came Carl H.
Rosner, to me known, who, being by me duly sworn, did depose and say that he is
the Chairman and Chief Executive Officer of Intermagnetics General Corporation,
the corporation described in and which executed the foregoing instrument and
that he signed his name thereto by order of the board of directors of said
corporation.


                                                            /s/ Karen A. Greene
                                                            NOTARY PUBLIC


STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this 20th day of May, 1998, before me personally came Michael C.
Zeigler, to me known, who, being by me duly sworn, did depose and say that he is
the Treasurer of APD Cryogenics Inc., the corporation described in and which
executed the foregoing instrument and that he signed his name thereto by order
of the board of directors of said corporation.



                                                            /s/ Karen A. Greene
                                                            NOTARY PUBLIC


STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this 20th day of May, 1998, before me personally came Michael C.
Zeigler, to me known, who, being by me duly sworn, did depose and say that he is
the Treasurer of Magstream Corporation, the corporation described in and which
executed the foregoing instrument and that he signed his name thereto by order
of the board of directors of said corporation.


                                                            /s/ Karen A. Greene
                                                            NOTARY PUBLIC
<PAGE>


STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this 20th day of May, 1998, before me personally came Carl H.
Rosner, to me known, who, being by me duly sworn, did depose and say that he is
the Chief Executive Officer of Medical Advances, Inc., the corporation described
in and which executed the foregoing instrument and that he signed his name
thereto by order of the board of directors of said corporation.



                                                            /s/ Karen A. Greene
                                                            NOTARY PUBLIC


STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this 20th day of May, 1998, before me personally came Michael C.
Zeigler, to me known, who, being by me duly sworn, did depose and say that he is
the Treasurer of InterCool Energy Corporation, the corporation described in and
which executed the foregoing instrument and that he signed his name thereto by
order of the board of directors of said corporation.



 
                                                            /s/ Karen A. Greene
                                                            NOTARY PUBLIC


STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this 20th day of May, 1998, before me personally came Carl H.
Rosner, to me known, who, being by me duly sworn, did depose and say that he is
the Chairman & Chief Executive Officer of Polycold Systems International, Inc.,
the corporation described in and which executed the foregoing instrument and
that he signed his name thereto by order of the board of directors of said
corporation.




                                                            /s/ Karen A. Greene
                                                            NOTARY PUBLIC

<PAGE>


COMMONWEALTH OF PENNSYLVANIA  )
                              ) ss.
COUNTY OF LEHIGH              )

         On this 15th day of May, 1998, before me personally came Kaj E. Karch,
to me known, who, being by me duly sworn, did depose and say that he is the Vice
President of CoreStates Bank, N.A., the corporation described in and which
executed the foregoing instrument and that he signed his name thereto by order
of the board of directors of said corporation.


                                                    /s/ Wanda A. Beahm
                                                    NOTARY PUBLIC



STATE OF NEW YORK    )
                     ) ss.
COUNTY OF ALBANY     )

         On this day 5th of May, 1998, before me personally came Stephen P.
Malinowski, to me known, who, being by me duly sworn, did depose and say that he
is the Vice President of The Chase Manhattan Bank, the corporation described in
and which executed the foregoing instrument and that he signed his name thereto
by order of the board of directors of said corporation.



                                                    /s/ Katherine M. Vermilyea
                                                    NOTARY PUBLIC