Objective: The use of thiazolidinedione (TZD) derivatives is associated with fluid retention, especially when combined with insulin. Because TZDs improve the metabolic effect of insulin, they may also reverse the blunted vascular response to insulin. We hypothesize that improvement of the action of insulin on vascular tone or permeability is the key mechanism of TZD-related fluid retention.
Research design and methods: In a randomized, double-blind, placebo-controlled, cross-over study in 18 obese, nondiabetic subjects with features of the metabolic syndrome, we investigated the effects of a 12-week treatment with 4 mg rosiglitazone twice a day on glucose disposal, hemodynamics (including forearm vasoconstrictor response to nitric oxide [NO]), synthase inhibition by N-monomethyl-L-arginine-acetate (L-NMMA), vascular permeability (transcapillary escape rate of albumin), and plasma volume during a hyperinsulinemic-euglycemic clamp (120 min, 120 mU/m(2) per min).
Results: As expected, rosiglitazone increased the glucose infusion rate during clamping. However, neither vascular permeability nor forearm blood flow response to hyperinsulinemia or L-NMMA was affected by rosiglitazone. Compared with placebo, rosiglitazone decreased diastolic blood pressure by 5 mmHg (95% CI 2.35-6.87, P = 0.0005) and increased plasma volume by 255 ml/1.73 m(2) (80-430, P = 0.007). Interestingly, the positive effect of rosiglitazone on glucose disposal correlated with change in foot volume (R(2) = 0.53, P = 0.001).
Conclusions: Rosiglitazone improved insulin sensitivity but had no effect on NO-dependent vasodilatation in the forearm or vascular permeability in obese, insulin-resistant, nondiabetic subjects. As such, TZD-related fluid retention was not caused by improvement of the vascular actions of insulin. Nonetheless, rosiglitazone-induced improvement in insulin sensitivity appears to be correlated to edema formation.