Mechanisms involved in the spasmolytic effect of extracts from Sabal serrulata fruit on smooth muscle.

1. The effects of two extracts from Sabal serrulata fruits [total lipidic (L) and saponifiable (S)] on smooth muscle contractions have been assayed. 2. Both extracts (0.1-1 mg/ml) relaxed the tonic contraction induced by norepinefrine (30 nM) on rat aorta [EC50, 0.53 +/- 0.05 mg/ml (L) and 0.5 +/- 0.04 mg/ml (S)] and by KCl (60 mM) on rat uterus. The Sabal extracts (0.3-1 mg/ml) also antagonized the dose-response curve of contractions induced by acetylcholine (0.1-100 microM) on urinary bladder. 3. dL-Propranolol (1 microM) but not the inactive (R)-(+)-propranolol(1 microM) potentiated the Sabal extracts relaxant effect by lowering the EC50 (0.35 +/- 0.2 vs 0.20 +/- 0.01 mg/ml for L and 0.43 +/- 0.02 vs 0.19 +/- 0.02 mg/ml, P < 0.01, for S extract). 4. Cycloheximide (10 micrograms/ml) antagonized the effect of extracts from Sabal. However, actinomycin D (5 micrograms/ml) significantly (P < or = 0.01) antagonized the effect of the total lipidic extract without modifying that of the saponifiable extract. 5. The relaxant effect of both extracts was not modified by the tyrosine kinase inhibitor genistein (10 microM) or the ornithine decarboxylase inhibitor alpha-difluoromethyl-ornithine (10 mM).