Activity of sap from Croton lechleri on rat vascular and gastric smooth muscles.

The effects of red sap from Croton lechleri (SdD), Euphorbiaceae, on vascular and gastric smooth muscles were investigated. SdD, from 10 to 1000 microg/ml, induced concentration-dependent vasoconstriction in rat caudal arteries, which was endothelium-independent. In arterial preparations pre-constricted by phenylephrine (0.1 microM) or KCl (30 mM), SdD also produced concentration-dependent vasoconstriction. To study the mechanisms implicated in this effect we used selective inhibitors such as prazosin (0.1 microM), an antagonist of alpha(1)-adrenoceptors, atropine (0.1 microM), an antagonist of muscarinic receptors, and ritanserin (50 nM), a 5-HT(2A) antagonist; none of these influenced vasoconstriction caused by SdD. Likewise, nifedipine (50 nM), an inhibitor of L-type calcium channels, did not modify the action of SdD. Capsaicin (100 nM), an agonist of vanilloid receptors, also did not affect vasoconstriction by SdD. We also investigated the action of SdD (10-1000 microg/ml) on rat gastric fundus; per se the sap slightly increased contractile tension. When the gastric fundus was pre-treated with SdD (100 microg/ml) the contraction induced by carbachol (1 microM) was increased, whereas that by KCl (60mM) or capsaicin (100 nM) were unchanged. The data shows that SdD increased contractile tension in a concentration-dependent way, both on vascular and gastric smooth muscles. The vasoconstriction is unrelated to alpha(1), M, 5-HT(2A) and vanilloid receptors as well as L-type calcium channels. SdD increased also contraction by carbachol on rat gastric fundus. Thus for the first time, experimental data provides evidence that sap from C. lechleri owns constricting activity on smooth muscles.