Assertion (A) : The person with diabetes insipidus feels thirsty. Reason (R) : A person with diabetes insipidus suffers from excess secretion of vasopressin.

The chief clinical features of diabetes insipidus (DI) include passage of large volumes of dilute urine with compensatory thirst and excessive fluid intake (polydipsia), so the assertion that a person with DI feels thirsty is correct [3]. However, DI is caused by either inadequate production/secretion of vasopressin (central/AVP deficiency) or by renal resistance to vasopressin (nephrogenic/AVP resistance), not by excess vasopressin secretion. Thus the reason given (excess vasopressin) is incorrect; the disorder reflects deficiency or resistance of vasopressin action rather than hormone excess [3]. Therefore A is true and R is false.

Sources

1. [1] https://www.niddk.nih.gov/health-information/kidney-disease/diabetes-insipidus
2. [3] https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2024.1479764/full
3. [2] https://www.ncbi.nlm.nih.gov/books/NBK470458/