A pharmacology researcher is studying a new cardiovascular drug intended to manage hypertension and tachycardia. In a series of isolated cardiac tissue experiments, the researcher observes that the new drug binds reversibly to the same receptor site as a known agonist — specifically a catecholamine — without activating the receptor or producing any intrinsic sympathomimetic activity. When increasing concentrations of the agonist are applied to the tissue preparation, the original maximal contractile response is fully restored, though a significantly higher agonist concentration is required to achieve the same effect. The dose-response curve shifts to the right in a parallel fashion with no change in the maximum response. Which of the following best describes this second drug?

1. A)Irreversible antagonist
2. B)Competitive antagonistGABARITO
3. C)Noncompetitive antagonist
4. D)Inverse agonist
5. E)Partial agonist