<prompt> In a patient if administration of exogeneus vasopressin does not increase the osmolality of urine the likely cause isSIADHPsychogenic polydipsiaRenal Hyposensitivity to ADHADH Deficiency  <response>: Answer is C Renal Hyposensitivity to ADH: Failure of urine osmolality to rise even after administration of exogenous ADHvasopressin suggests a diagnosis of Nephrogenic Diabetes Insipidus due resistance to action of vasopressin on the Renal tubule Renal Hyposensitivity to ADH. 