Thirst and plasma levels of vasopressin, angiotensin II and atrial natriuretic peptide in patients with non-insulin-dependent diabetes mellitus.

To clarify a possible mechanism whereby the perception of thirst may be associated with diabetes mellitus, we measured plasma levels of vasopressin (AVP), angiotensin II (ANG II), atrial natriuretic peptide (ANP) and plasma renin activity (PRA) in non-insulin-dependent (NIDDM) diabetic patients with or without thirst. Thirteen male NIDDM patients complaining of thirst had a significantly high blood hematocrit, plasma urea nitrogen and creatinine concentrations and plasma osmolality, indicating a reduction in plasma volume. In addition, the patients had a significantly high mean plasma concentrations of AVP (3.20 +/- 1.27 pmol/l) ANG II (33.8 +/- 31.4 pmol/l) and PRA, but a low mean plasma ANP concentration (8.9 +/- 4.5 pmol/l). After treatment with diet and/or sulfonylurea, plasma levels of AVP, ANG II and PRA decreased with a concomitant increase in plasma volume and disappearance of thirst. In contrast, 13 NIDDM patients (9 females and 4 males) without thirst had normal plasma urea nitrogen and creatinine concentrations, and the hematocrit did not change significantly after treatment. Plasma AVP (0.95 +/- 0.34 pmol/l), ANG II (14.7 +/- 8.8 pmol/l) and ANP (10.7 +/- 4.9 pmol/l) concentrations, and PRA were normal in this group of patients. There was no significant difference between the two groups of patients, however, in fasting glucose concentration and HbA1c. We conclude from these results that a reduction in plasma volume may be the major factor responsible for the induction of thirst sensation and for increased AVP secretion in NIDDM patients. The mechanism underlying a reduction in plasma volume remains unclear.