Specific regulation of peptide-induced renal prostaglandin synthesis.

Repeated hourly stimulation of perfused rabbit hydronephrotic kidney (HNK) with a fixed dose of bradykinin resulted in a progressive (to-fold in 6 h) increase in prostaglandin (PG) synthesis. Inhibition of protein synthesis with cycloheximide during perfusion abolished the enhanced time-dependent responsiveness of the HNK to peptide stimulation, whereas pretreatment of rabbits with aspirin, which covalently inactivates cyclooxygenase, only temporarily suppressed the peptide response. Utilization of exogenous arachidonate bypasses the renal peptide receptor and acyl hydrolyase and the PG production by the fatty acid therefore reflects total (peptide-linked and peptide-independent) cyclooxygenase activity of the tissue. Arachidonate metabolism by renal microsomes or intact perfused HNKs was: (a) independent of perfusion time, (b) unchanged by perfusion with cycloheximide, and (c) abolished by aspirin pretreatment of the animal. In addition, cortical (but not medullary) microsomes obtained from HNKs possess more cyclooxygenase activity than microsomes prepared from contralateral (unobstructed) or normal kidneys. The striking quantitative differences between endogenous (ie. peptide-activated) and exogenous arachidonate-induced PG synthesis are further accentuated by major qualitative difference in end product. The primary metabolite of endogenous arachidonate is PGE2, while exogenous arachidonate is converted to prostacyclin. Perfusion of the I-INK apparently results in a selective, time-dependent induction of new protein synthesis (inhibited by cycloheximide) of a highly specific peptide (bradykinin or anglotensin)linked cyclooxygenase. There is another much larger pool of renal cyclooxygenase, in hydronephrotic or normal kidneys, which is irreversibly inhibited by aspirin and therefore does not undergo de nouo synthesis during perfusion and is unaffected by cycloheximide.