Pharmacology and Toxicology

Holarrhena pubescens belongs to the family Apocynacea, commonly known as kurchi is highly reputed in traditional medicine as a remedy for Amoebic dysentery and other Intestinal ailment. Bioassay-directed fractionation by chromatographic methods the ethanolic extract of Holarrhena pubescens resulted in the isolation of steroidal alkaloids i.e. Holamide and Pubscinine. Holamide showed a three proton doublet at 1.45 (J=6.56 Hz) and two AB doubles at 3.17 and 3.00 each for on proton (J=12.06 Hz) in the 1H NMR spectrum suggested that it belongs to conanine series of alkaloid (A class of compound with the steroid nucleus and a five members heterocyclic ring with nitrogen). In contrast pubscinine showed one methyl at 1.28 while the doublet is missing a three proton singlet was observed at 2.28 due to a vinylic methyl indicated a double bond in the 18, 20-epimino ring of the conanine series of alkaloids. In anaesthetized rats, the Holamide and Pubscinine caused a fall in blood pressure in a Dose-Dependent Manner. Pretreatment of animals’ atropine completely abolished the hypotensive response of acetylcholine; whereas hypotensive effect of holamide and pubscinine were not modified by Atropine. Similarly Acetylcholine produced contractile effect in guinea-pig ileum, which was antagonized by atropine; however both (Holamide and Pubscinine) failed to produce any stimulant response on guinea-pig ileum. These data indicate that the steroidal alkaloids i.e. Holamide and Pubscinine from Holarrhena pubescens mediated hypotensive response through a mechanism different to that of acetylcholine.