Terbutaline tocolytic to treat preterm labor acts by stimulating which receptor to cause uterine relaxation?

• A. Alpha-1 Adrenergic Receptor
• B. Beta-2 Adrenergic Receptor
• C. Dopamine Receptor
• D. GABA Receptor

Answer: (B)

Terbutaline tocolysis works by activating beta-2 adrenergic receptors on uterine smooth muscle. When these receptors are stimulated, they trigger a Gs protein pathway that raises cyclic AMP levels, which activates protein kinase A. This signaling leads to a decrease in intracellular calcium and loosening of the smooth muscle fibers, causing uterine relaxation and suppression of contractions. The other receptors listed don’t produce this effect: alpha-1 stimulation would tend to cause vasoconstriction and contraction of some smooth muscles, dopamine receptor activity isn’t the mechanism for uterine relaxation in this context, and GABA receptors are mainly involved in CNS inhibition rather than directly relaxing uterine muscle.