Quench the thirst: lessons from clinical thirst trials

Thirst, as a symptom, has long been considered the most prevalent clinical complaint patients voice in healthcare settings. Yet, rarely have researchers examined thirst by its correlation with physiologic factors. This review was undertaken to examine the relationships between thirst ratings and factors mediating its primary physiologic correlates: plasma osmolality (pOsm) and arginine vasopressin peptide (AVP). A literature search was undertaken to identify clinical studies in human subjects that investigated the relationship of thirst to specific physiologic thirst-related correlates and associated thirst mediators. Thirst was induced in 17 selected clinical studies by hyperosmolar infusion, through water deprivation or exercise weight-loss regimens. Positive linear relationships between the subjects' thirst ratings and rising serum pOsm levels confirmed the presence of intact osmotic thirst drives. However, there were significant variations in normal compensatory rises in AVP levels that followed the rises in plasma osmolality after the subjects were exposed to cold, physical pre-conditioning and water immersion tests. Notably, older adults in the studies reported diminished thirst ratings. Weak correlations suggest that angiotensin II may play only a minor role in thirst mediation. Atrial natriuretic hormone's inhibitory effect on thirst was inconsistent. Findings indicated that older adults are at higher risk for profound dehydration due to sensory deficits along with failure to correct volume losses. The thirst trials results support the close correlation between serum pOsm values and patients' thirst ratings, with the exception of the older adult.