Studies were done to determine the role of endogenous prostaglandins (PGs) for norepinephrine (NE) clearance in 10 male borderline hypertensives (BHT) (age: 20-28) and six age-matched male normotensives (NT). Two experimental protocols were followed in these subjects: 10 min orthostasis with blood sampling (protocol I), and 100 ng/kg/min of L-NE infusion for 60 min at supine position. Blood was collected from indwelling catheter at every min for 10 min after stopping the NE infusion (protocol II). Plasma NE was measured by THI method using HPLC. Disappearance curve of plasma NE was analyzed following the two compartment open model. The orthostasis and the steady state NE infusion were repeated after 150 mg/day of indomethacin (Ind) for three days. There were significant increases in plasma NE after orthostasis in both groups: from 180.8 +/- 28.0 pg/ml to 346.2 +/- 78.0 pg/ml (p less than 0.05) in NT and from 120.1 +/- 12.8 pg/ml to 289.6 +/- 20.3 pg/ml (p less than 0.001) in BHT, but there were no significant differences between the two groups. Ind pretreatment did not alter these responses. The calculated half-time of the first exponential phase (T 1/2) was 1.50 +/- 0.07 min in NT which decreased to 0.98 +/- 0.10 min (p less than 0.05) after Ind pretreatment. In BHT, T 1/2 was 1.03 +/- 0.08 min (p less than 0.01 vs NT), which was not significantly changed after Ind. These results may suggest that endogenous PGs have some role(s) in NT for NE clearance, probably exerting inhibitory action on neuronal uptake. In BHT, neuronal uptake of NE is increased, probably due to an adaptation mechanism to elevated blood pressure.