Recent evidence from animal research and in vitro experiments indicates that changes in dietary calcium intake could cause changes in lipolysis through alterations of the intracellular calcium concentration in adipocytes. The objective of the study was to examine whether the calcium antagonist hydralazine affects blood flow and lipolysis in subcutaneous abdominal adipose tissue in vivo in humans. Three different concentrations of hydralazine (12.2, 24.4, and 48.8 mumol/L) were locally administered in adipose tissue using the microdialysis technique to assess effects on lipolysis and blood flow in subcutaneous adipose tissue in the abdominal region. Subjects from the general community were studied ambulatorily at a university hospital. Eight healthy men (age, 33.1 +/- 3.3 years; body mass index, 24.2 +/- 0.2 kg/m(2)) were recruited by local announcement. Subcutaneous adipose tissue in the abdominal region was perfused with increasing concentrations of hydralazine. The main outcome measures were adipose tissue lipolysis and blood flow. Hydralazine had no effect on ethanol outflow-inflow ratios, but significantly increased interstitial glycerol concentration at the highest concentration (P < .05). The present results indicate that hydralazine increases lipolysis in abdominal subcutaneous adipose tissue in healthy lean subjects, but hydralazine had no significant effects on local blood flow in adipose tissue. AD - Nutrition and Toxicology Research Institute Maastricht, University of Maastricht, PO Box 616, Maastricht, The Netherlands.