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

Step 1: Recall the main prostaglandins and their receptors.
Prostaglandins (PGE2, PGI2, PGF2alpha) and thromboxane (TXA2) are eicosanoids derived from arachidonic acid. They act through different G-protein coupled receptors on smooth muscle, platelets and other tissues, so their effects can differ sharply even though they come from the same pathway.

Step 2: Check option 1, vascular smooth muscle.
PGE2 and PGI2 (prostacyclin) act on receptors that raise cyclic AMP in vascular smooth muscle, causing relaxation and vasodilation. TXA2 and PGF2alpha act on a different receptor that raises intracellular calcium, causing vasoconstriction. This statement matches standard pharmacology, so it IS correct.

Step 3: Check option 2, platelet aggregation.
PGI2 (and to a lesser extent PGE1) raises platelet cyclic AMP, which blocks aggregation, giving prostacyclin its anti-thrombotic role. TXA2 does the opposite, lowering cyclic AMP and driving platelets to aggregate and vessels to constrict, which is why aspirin's anti-platelet effect works by blocking TXA2 synthesis. This statement IS correct.

Step 4: Check option 4, bronchial smooth muscle.
PGE2 relaxes bronchial smooth muscle and is a bronchodilator, while PGF2alpha contracts it and is a bronchoconstrictor, which is why PGF2alpha analogues are avoided in asthmatics. This statement IS correct.

Step 5: Check option 3, action on the uterus.
Both PGE2 and PGF2alpha contract uterine smooth muscle and are oxytocic (uterotonic); this is exactly why both are used clinically to induce labour or terminate pregnancy (for example, PGF2alpha analogues like carboprost are used for postpartum hemorrhage and abortion). Neither of them is tocolytic; a tocolytic drug is one that relaxes the uterus, such as ritodrine or nifedipine. So calling PGF2alpha "tocolytic" is wrong; it should be oxytocic like PGE2, not its opposite.

Step 6: Final answer.
The statement that is NOT correct is the one about PGE2 having oxytocic action while PGF2alpha has tocolytic action, because PGF2alpha is oxytocic too, not tocolytic.
\[ \boxed{\text{PGE2 has marked oxytocic action while PGF2alpha has tocolytic action}} \]