Modulation of Enzyme-Catalyzed Synthesis of Prostaglandins by Components Contained in Kidney Microsomal Preparations.

In the kidney, prostaglandins formed by cyclooxygenase 1 and 2 (COX-1 and COX-2) play an important role in regulating renal blood flow. In the present study, we report our observations regarding a unique modulatory effect of renal microsomal preparation on COX-1/2-mediated formation of major prostaglandin (PG) products in vitro. We found that microsomes prepared from pig and rat kidneys had a dual stimulatory-inhibitory effect on the formation of certain PG products catalyzed by COX-1 and COX-2. At lower concentrations, kidney microsomes stimulated the formation of certain PG products, whereas at higher concentrations, their presence inhibited the formation. Presence of kidney microsomes consistently increased the K m values of the COX-1/2-mediated reactions, while the V max might be increased or decreased depending on stimulation or inhibition observed. Experimental evidence was presented to show that a protein component present in the pig kidney microsomes was primarily responsible for the activation of the enzyme-catalyzed arachidonic acid metabolism leading to the formation of certain PG products.