Which of the following can reverse one or more smooth muscle effects of circulating histamine in humans?: (A) Granisetron, (B) Adrenaline, (C) Ranitidine, (D) Sumatriptan
Answer is B. Adrenaline is a physiological antagonist of histamine. It reverses bronchoconstriction caused by histamine. Ranitidine is an H2 antagonist that decreases gastric acid secretion but has no effect on smooth muscles.