Inhibitory effect of mitragynine, an analgesic alkaloid from Thai herbal medicine, on neurogenic contraction of the vas deferens.

The effect of an indole-alkaloid mitragynine isolated from the Thai medicinal herb kratom (Mitragyna speciosa) on neurogenic contraction of smooth muscle was studied in guinea-pig vas deferens. Mitragynine inhibited the contraction of the vas deferens produced by electrical transmural stimulation. On the other hand, mitragynine failed to affect the responses to norepinephrine and ATP. Mitragynine did not reduce KCl-induced contraction in the presence of tetrodotoxin, prazosin and alpha,beta-methylene ATP. Mitragynine inhibited nicotine- or tyramine-induced contraction. By using the patch-clamp technique, mitragynine was found to block T- and L-type Ca2+ channel currents in N1E-115 neuroblastoma cells. In the Ca2+ measurement by a fluorescent dye method, mitragynine reduced KCl-induced Ca2+ influx in neuroblastoma cells. The present results suggest that mitragynine inhibits the vas deferens contraction elicited by nerve stimulation, probably through its blockade of neuronal Ca2+ channels.

Problems in the use of herbal and natural substances, with a specific example concerning the cardiovascular system.

1. There has been increasing awareness and use of natural preparations for health purposes by consumers. 2. However, recent studies have repeatedly shown that many natural products marketed as nutraceuticals or health food do not deliver the health benefit as claimed and are inconsistent from batch to batch. 3. The present paper describes the scientific rationale of such inconsistency and uses an antihypertensive preparation as an example to demonstrate the significant value of natural products if developed scientifically and properly.

Enhanced survival and regeneration of axotomized retinal ganglion cells by a mixture of herbal extracts.

The aim of this study is to investigate the effects of Panax quinquefolius L. extract (PQE), Ginkgo biloba extract (GBE), and Hypericum perforatum extract (HPE), in combination or alone, on the survival and regeneration of axotomized retinal ganglion cells (RGCs) in an optic nerve transection model in adult hamsters. Unilateral transection of the optic nerve was performed to evaluate the effects of herbal extracts on the survival of axotomized RGCs. Effects of the herbal extracts on axonal regeneration of axotomized RGCs, on the other hand, were studied by attaching a peripheral nerve graft onto the transected ocular stump to induce regeneration. Operated animals received daily oral administration of vehicle or herbal extracts (PQE, GBE, and HPE), alone or in combination, for 7 and 21 days, respectively, in the survival and regeneration experiments. Surviving and regenerating RGCs were retrogradely labeled with Fluoro-Gold. The eyes were then enucleated and the retinas were flat-mounted for the counting of the labeled RGCs. Treatment with PQE, GBE and HPE alone failed to offer neuroprotection to injured RGCs. However, treatment with Menta-FX, a mixture of PQE, GBE, and HPE, significantly augmented RGC survival 7 days postaxotomy. Treatment with Menta-FX also induced a significant (87%) increase in the number of regenerating RGCs 21 days after optic nerve transection. This study demonstrates that herbs can act as a potential neuroprotective agent for damaged RGCs. It also suggests that the therapeutic value of herbal remedies can be maximized by the use of mixtures of appropriate herbs.