Prostaglandin endoperoxide and thromboxane generating systems and their selective inhibition

Area of Science:

• Biochemistry
• Pharmacology

Background:

• Ram seminal vesicles (RSV) microsomes metabolize arachidonic acid.
• This metabolism produces endoperoxides, precursors to potent biologically active substances.

Purpose of the Study:

• To characterize the enzyme systems involved in producing rabbit aorta contracting substances.
• To investigate the selective inhibition of these enzyme systems by indomethacin and benzydamine.

Main Methods:

• Incubation of ram seminal vesicles (RSV) microsomes with arachidonic acid.
• Incubation of endoperoxides and RSV products with horse platelet microsomes (HPM).
• Assay of rabbit aorta contracting substance (RCS) generation and characterization.
• Determination of inhibitor IC50 values for enzyme systems.

Main Results:

• RSV microsomes produced endoperoxide-like substances from arachidonic acid.
• Horse platelet microsomes converted endoperoxides to thromboxane A2 (TXA2), a potent RCS with a short half-life.
• Benzydamine selectively inhibited thromboxane synthetase (IC50 = 100 µg/ml) over RSV cyclo-oxygenase (IC50 = 250 µg/ml).
• Indomethacin selectively inhibited RSV cyclo-oxygenase (IC50 = 5 µg/ml) over thromboxane synthetase (IC50 = 100 µg/ml).

Conclusions:

• Two distinct enzyme systems are involved in the biosynthesis of potent vasoconstrictors.
• Indomethacin and benzydamine exhibit selective inhibition profiles against these enzymes, offering potential for targeted therapeutic intervention.