in rats: Drug was administered at three time points (24, 5, and 1 h before testing), and the effects of three doses (2, 5, and 10 mg/kg) was investigated. S-(+)-Niguldipine produced no antidepressant-like effects other than a 14% reduction in immobility time at the highest dose.

(+)-Niguldipine (Ki: 78 nmol/l) and (-)-niguldipine (Ki: 58 nmol/l) bound with approximately equal affinity to the alpha 1-adrenoceptors ('alpha 1B') in liver cell membranes. The (+)-niguldipine alpha 1-adrenoceptor inhibition data for rat brain cortex membranes were better fitted by a two-site model. The high-affinity component ('alpha 1A') had a Ki value of 52 pmol/l in competition experiments with [3H]prazosin. The low-affinity site (alpha 1B) had 200- to 600-fold less affinity. (+)-Niguldipine was the most selective compound for discriminating alpha 1A- from alpha 1B-adrenoceptors and is a novel prototype for 1,4-DHPs which bind with nearly equal affinity to skeletal muscle and brain or heart 1,4-DHP receptors.