BIOL 472 - Mammalian Physiology - Topic V - Cell Signaling

Penn State - Fall 2026 - Dr. James Strauss

Eicosanoids

“Local hormones” produced from polyunsaturated fat and arachidonic acid present in phospholipids

Prostaglandins, Thromboxanes, Leukotrienes

3 Principal Classes of Eicosanoids

Phospholipase A2

Converts phospholipid to arachidonic acid, inhibited by glucocorticoids

Cyclooxygenase

Converts arachidonic acid to endoperoxides

Aspirin, NSAIDs

What drugs inhibit cyclooxygenase?

Subtype of cyclooxygenase: involved in platelet aggregation pathway that protects stomach

COX1

Subtype of cyclooxygenase: pain and inflammation pathway

COX2

Vasodilator, bronchodilator, decreases platelet aggregation

Function of PGI2 (Prostacyclin)

Vasoconstrictor, bronchoconstrictor, increase platelet aggregation

Function of TxA2 (Thromboxane)

Lipoxygenase

Enzyme responsible for the synthesis of leukotrienes

Stimulate T cells, interleukin, interferon production, bronchoconstriction, increase vascular permeability

Function of SRA-A (Slow reacting substance anaphylaxis, Leukotrienes)

Aspirins

Drug class that uses anticlotting pathways and can lead to ulcers

Ibuprofens and Naproxens

Drug class that inhibits inflammatory reactions in the pathway, especially PGI2

Indomethacin

Drug class that has a more powerful anti-inflammatory pathway, especially for arthritis

Cox2 Inhibitors

Drug class that inhibits pain/inflammatory pathway without altering clotting

Acetaminophens

Drug class that is a good analgesic and antipyretic, but the mode of action is poorly understood, and anti-inflammatory response is not very strong

cAMP (cyclic AMP)

Cyclic second messenger that activates protein kinases

Adenyl Cyclase

Effector enzyme for cAMP

Phosphodiesterase

Enzyme that degrades cAMP into 5” AMP

Phospholipase C

Effector enzyme that cleaves PIP2 into IP3 and DAG

DAG

Second messenger that activates protein kinases

IP3

Second messenger that increases the concentration of calcium (Ca2+) in the cytosol, making ER membranes leaky to Calcium (Ca2+)

Calcium (Ca2+)

Second messenger that can bind to calmodulin, other enzymes, directly to proteins, and mediate neurotransmitter release

Blocks adenosine receptors, inhibits acetylcholinesterase, blocks phosphodiesterase

Mechanism of action for caffeine