Question

Prostaglandins (PGs) have effects on a variety of tissues. Different prostaglandins may have different effects. Which one of the following is NOT a correct statement?

• A. The human arteriolar smooth muscle is relaxed by PGE2 and PGI2, whereas TXA2 and PGF2alpha cause vasoconstriction.
• B. PGE1 and PGI2 inhibit platelet aggregation, whereas TXA2 facilitates aggregation.
• C. PGE2 has marked oxytocic action while PGF2alpha has tocolytic action.
• D. PGE2 is a bronchodilator whereas PGF2alpha is a bronchoconstrictor.

Hint:

Both PGE2 and PGF2alpha contract the uterus (oxytocic); neither is tocolytic. That makes the third statement the false one.

Answer 1

The Correct Option is C

Prostaglandins act on many different tissues, and each one has its own typical action. The question asks us to find the one statement that does not match real pharmacology. Let's check each claim against known prostaglandin actions.

1. Vascular smooth muscle: PGE2 and PGI2 relax arterioles (vasodilators), while TXA2 and PGF2alpha constrict them. This is standard textbook fact, so the statement is correct.
2. Platelets: PGE1 and PGI2 raise cyclic AMP inside platelets and stop them from clumping, while TXA2 does the opposite and drives aggregation. This matches known physiology, so the statement is correct.
3. Uterus: the claim says PGE2 contracts the uterus (oxytocic) but PGF2alpha relaxes it (tocolytic). In reality, PGF2alpha also contracts the uterus, it is oxytocic just like PGE2, and is used in obstetrics to control bleeding or end a pregnancy. Nothing about it is tocolytic. This statement is false.
4. Bronchial smooth muscle: PGE2 relaxes airway muscle (bronchodilator) and PGF2alpha contracts it (bronchoconstrictor), which fits how these drugs are used and avoided clinically. This statement is correct.

Since three of the four claims check out against known prostaglandin pharmacology and only the uterus claim gets PGF2alpha's action backwards, the incorrect statement is the one about PGE2 being oxytocic and PGF2alpha being tocolytic.

Let's summarize:

• PGE2, PGI2: vasodilators, block platelet aggregation.
• TXA2, PGF2alpha: vasoconstrictors.
• PGE2 and PGF2alpha: both oxytocic on the uterus, neither is tocolytic.

The false statement is that PGE2 is oxytocic while PGF2alpha is tocolytic.