Changes in lymphocyte beta-adrenoceptor density after dilevalol oral treatment.

Dilevalol (R,R'-isomer of labetalol) is an antihypertensive agent combining non-specific beta blockade with peripheral vasodilatation due to beta 2-receptor agonism. The aim of this study was to determine the effects of chronic dilevalol administration on lymphocyte beta 2-adrenoceptor density. The investigation was conducted as a double-blind, placebo-controlled comparison. Ten days of chronic dilevalol (400 mg) or placebo treatment was administered to 12 healthy normotensive volunteers. Clinical and biochemical parameters: heart rate (HR) systolic and diastolic blood pressure (SBP, DBP), electrocardiogram, norepinephrine (NE), epinephrine (E), MHPG (3-methoxy-4-hydroxyphenylethylene glycol; one of the major brain metabolites of NE) were analysed on the first day (D1) before (H0) and 3 h after oral treatment (H3) and on the tenth day (D10). Clinical results showed no significant changes in HR, DBP, SBP in the two groups (placebo, n = 6; dilevalol, n = 6). NE increased 3 h after the first oral dilevalol intake (p less than 0.05). This increase is greater than that due to the circadian variation observed in the placebo group. Acute dilevalol treatment seems to increase the plasma circulating NE level, which returns to normal values after 10 days of chronic treatment. Binding assays were performed before and after 10 days of treatment. In the placebo group, no change in beta-adrenoceptor density was observed (36.6 +/- 8.3 versus 38.3 +/- 9.4 femtomol/mg of protein). Lymphocyte beta-adrenoceptor density (Bmax) significantly decreased after 10 days of dilevalol treatment without any changes in affinity (KD). Results were 40.3 +/- 11.6 (D1) and 30 +/- 7.6 (D10) (p less than 0.05). It was concluded that dilevalol down-regulated lymphocyte beta 2-adrenoceptor density, suggesting that beta 2 agonism of dilevalol is predominant.