A 75 year old man was

moderately dehydrated following an abdominal operation. His mean arterial blood

pressure was at the lower limit of normal. The anaesthetist estimated that his

total peripheral resistance was increased in order to compensate for the hypovolaemia.  The junior doctor on the team prescribed a

non-steroidal anti-inflammatory (NSAID) drug (PGE 2 inhibitor) for pain relief.

Two days later, the patient’s creatinine clearance was found to be markedly

decreased.

Which is the most likely

mechanism responsible for the drop in creatinine clearance?