The pharmacological actitvity of Rhoicissus tridentata subsp cuneifolia in relation to parturition
Katsoulis, Lynn Coleen
Decoctions and infusions of Rhoicissus tridentata subsp. cuneifolia (Vitaceae) roots and Hgnotubers are widely used as traditional medicine by South African women during pregnancy and childbirth. Pharmacological studies using isolated rat uterus and ileum were done to determine whether there is any pharmacological grounding for the use of the remedies to induce labour. Initial studies showed a large variation in the contractile activity of the extracts, so investigations were done to determine whether the contractile activity varied according to the season in which plant material was harvested, the location in which the plant grew, or the length of storage of harvested plant material. Plant material harvested from Umlazi (KwaZulu-Natal) and the Suikerbos Nature Reserve (Gauteng) was used for studies on the mechanism of contractile activity. Seasonal variation was investigated by harvested three plants from Suikerbosrand for two years at approximately three monthly intervals. The distributional effect was done using material harvested from around South Africa. Material from Suikerbosrand was stored for either three months or a year to determine whether storage altered the contractile activity. After each harvesting, the different parts of the plants were separated, dried, milled and boiled for approximately an hour. The solutions were allowed to settle overnight at 4°C, after which the supernatant was siphoned off, then frozen and lyophilised. All lyophilised end products were kept frozen until use. Oestrogenized virgin Sprague-Dawley rats euthanazed with CO2. Uterine and ileal tissue was dissected out and mounted in 50 ml organ baths containing Tyrode solution, aerated with 5% CO2 in O2. After a resting period the organs were challenged with cumulative doses of reference agonist or herbal extract, or pretreated with the herbal extract before adding the reference drugs. The pharmacological action of an aqueous extract of R. tridentata subsp. cuneifolia was investigated using isolated rat uterus and ileum. The results showed that the extract directly stimulates concentration dependent contractions of uterus and ileum. Preincubation of the organs with the plant extract had no effect on the maximal uterine response to the cumulative addition of acetylcholine or oxytocin, and slightly depressed the response to serotonin and noradrenaline. The maximal ileal response to acetylcholine was depressed where the response to maximal concentrations of serotonin was unchanged. Pretreatment with atropine and indomethacin both blocked the initial response to the Rhoicissus extract which indicates that the muscarinic receptors and prostaglandin synthesis could be involved in the contractile response to the extract. Methysergide and prazosin had no effect on the direct action of the extract which infers that serotonin receptors and a-adrenoceptors do not play a role in mediating the smooth muscle response to the plant extract. Cellular toxicity of R. tridentata extracts from Umlazi and Suikerbosrand was determined using M Tf assays, and enzyme immunoassays were used to determine the effect of the extracts on cellular prostaglandin E2 production. Results from the pharmacological studies indicate that the contractions of isolated rat uterus and ileum seem to be mediated by muscarinic receptors and the synthesis of cyclooxygenase products. The contractility of the plant extract appears to be mediated predominantly by muscarinic M4 receptors. The other muscarinic receptor subtypes play less of a role. The contractions seem to be devoid of serotonergic, adrenergic, histaminergic or nicotinic activity. Studies on the variation in contractile activity suggest that the activity of the extract does vary according to the season or location of material harvesting. The extracts form material harvested during summer or autumn was more active than material harvested during winter or spring. The lignotubers yielded the most active extracts. Extracts of plants from most geographic areas stimulated contractions although the response varied in magnitude, however, the extract of a plant from Mondeor, acted in an opposite manner, inhibiting acetylcholine induced contractions. Storing dried plant material did not alter the activity of the extracts. The plant extracts, up tv a concentration of 1 mg/ml, appear not to be toxic to human kidney epithelial ns>H, human hepatoma cells, human histiocytoma cells or mouse leydig cells. The production of PGE2 by human histiocytoma cells was stimulated by 1 mg/ml R. tridentata extract confirming that contractions are possible mediated by the synthesis of cyclooxygenase products.