This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'Tolvaptan is approved for use in- \nSelect and explain. \nA. High Na, B. High K, C. High Ca, D. Low Na', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Tolvaptan is a vasopressor receptor antagonist used to correct hyponatremia in the treatment of syndrome of inappropriate water excretion or SIADH :-\nSyndrome of inappropriate secretion of ADH is caused due to excesive secretion of antiduretic hormone.\nAntidiuertic hormone (ADH) or arginine vasopressin is synthesized by the hypothalamus.\nIts major effect is to prevent diuresis by promoting reabsorption of water in the kidneys.\n\n- ADH is the primary physiological determinant of the rate of free water excretion.\n- Its major renal affect is to augument the water permeability of the leminal membranes of the cortical and\xa0medullary collecting tubules thereby promoting water reabsorption.\n\nThe antidiuretic effect of ADH is mediated by "V2\xa0 receptors".\nTolvaptan is V2 receptor antagonist\n\n- It can be used to correct hyponatremia due to excesive water retnetion caused by increased ADH secretion.\n\nRandomized double blind trials have shown that oral or intravenous vasopressin antagonists are more effective than placebo in raising the serum sodium of hyponatremic patients.\n"Tolvaptan" and "conivaptan" but not lixivaptan are approved for use in the united states.\n\n\u200bVasopressor receptor antagonist \n\nThere are three receptor for vasopressin (ADH).\n\t- The V1 a, Vlb and V2 receptors.\nThe V2 receptors primarily mediate the antidiuretic response while V1 a and Vlb primarily cause vasoconstriction and adrenocorticotropic hormone (ACTH) release.\n\n\nV2\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0→\xa0 \xa0 \xa0 \xa0 Mediate antidiuretic response\nVlaVlb\xa0 \xa0 \xa0 \xa0 \xa0→\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Cause vasoconstriction and adrenocorticotropic hormone (ACTH) release.\n\n\u200b\n\nThe vasopressin receptor antagonist tolavaptan produces a selective water diuresis (aquaresis) without affecting sodium and potassium excretion.\n\n- The ensuing loss of electrolyte free water will tend to raise the serum sodium in patients with SIADH and may improve mental status in patients with serum sodium under 130 meq/L.\n\u200b', 'role': 'assistant'}]