Pharmacology Vasopressin decreases the volume of urine primarily by causing: A Decrease in glomerular filtration rate B Decrease in renal blood flow C Decrease in water permeability of descending limb of loop of Henle D Increase in water permeability of collecting duct cells 💡 Explanation Vasopressin decreases the volume of urine primarily by causing: ✓ Correct Answer: D. Increase in water permeability of collecting duct cells