Blood pressure lowering effects of Ranunculus scleratus Linn. in normal and fructose induced hypertensive rats and estimation of underlying mechanisms

Ranunculus scleratus Linn. is used in folk medicine to treat hypertension. This study was aimed at providing validation to its traditional use and to explore underlying mechanisms of action. Effects of hydro-ethanolic crude extract of the plant and its fractions on blood pressure was evaluated using direct surgical method in normotensive and in fructose induced hypertensive rats. Various doses of crude extract, RSC, (5, 10, 20, 30mg/kg) and all fractions (3, 5, 10, 20mg/kg) were studied. Results suggested that aqueous fraction of R. scleratus (RSA) produced most pronounced effects at 10mg/kg in normotensive and at 20mg/kg in hypertensive animals. Underlying mechanisms, using various pharmacological antagonists were also elucidated. Results suggested the involvement of muscarinic receptor, angiotensin converting enzyme (ACE) inhibition, ganglionic block and nitric oxide (NO) release in presenting hypotensive response.

Isolation of a polypeptide from the venom of Bungarus multicinctus that binds to ganglia and blocks the ganglionic transmission in mammals

A 15,000 dalton polypeptide purified from Bungarus multicinctus venom (which normally copurifies with alpha-bungarotoxin) was characterized biochemically and its biological effects were studied. This polypeptide, P15, had an aminoacid composition and molecular weight different from those of both alpha- and beta-bungarotoxin. It inhibited the ganglionic transmission in the guinea-pig hypogastric nerve-vas deferens preparation and did not block, even at very high concentrations, the neuromuscular transmission in the rat phrenic nerve-diaphragm preparation. In the same preparations alpha-bungarotoxin was unable to block the response at the ganglionic synapse while it was fully active in blocking the neuromuscular transmission. However, a pretreatment of the vas deferens preparation with alpha-bungarotoxin prevented the inhibitory effect of P15. 125I-Labeled P15 showed a specific and saturable binding to rat superior cervical ganglia homogenate and to a Torpedo postsynaptic membrane fraction. The binding of P15 to ganglia was inhibited by curare. The binding was Ca2+ dependent. The density of binding sites was of 300 fmol/mg of protein in the ganglion and 500 fmol/mg of protein in Torpedo membranes. The amount of P15-binding sites in ganglia was not modified by denervation, indicating that P15 binds to postsynaptic receptors. The binding of 125I-labeled P15, both in ganglia and Torpedo membranes, was inhibited by alpha-bungarotoxin. P15 had a Ca2+-dependent phospholipase A2 activity. Lowering Ca2+ concentration in incubation media affected the phospholipase A2 activity more than binding properties and inhibition of phospholipase activity with p-bromophenacyl bromide did not affect the activity of P15 on vas deferens preparation, suggesting that the phospholipase activity is not necessary for the activity of P15 on nicotinic receptors. Our results suggest that P15 toxin may be a specific and valuable probe for studying the ganglionic nicotinic receptor.