Pharmacological studies on siculine syrup. II: effects on smooth, skeletal and cardiovascular muscle preparations

Earlier pharmacological screening showed that siculine syrup (a traditional herbal remedy purported to be useful in the prevention and treatment of sickle cell pain - crises, due to sickle cell anaemia - SCA) had antisickling and analgesic activities as well as antimicrobial and diuretic effects. SCA is an important haemoglobinopathy in Africa and many other communities/countries worldwide, with relatively high morbidity and mortality. The present study was to determine the effects of the extract on various isolated muscle preparations - smooth, skeletal and cardiovascular. Siculine (4-20 microg/mL), like acetylcholine (40-400 microg/mL), contracted the isolated rat uterus concentration dependently. Similar effects were observed with the guinea-pig ileum and rabbit jejunum (2-20 microg/mL). In contrast to these effects, the direct (muscle) and indirect (nerve) stimulations of rat phrenic nerve-diaphragm were relaxed by siculine (4 and 8 microg/mL) and d-tubocurarine (0.8 microg/mL). Siculine also concentration-dependently decreased both the rate and force of contraction of guinea-pig atria and rabbit heart and also resulted in a fall in cat blood pressure in a manner similar to those of acetylcholine. The possible therapeutic and/or toxicological consequences of these effects including the hypotensive activity is noteworthy since siculine syrup is used by the local population for the prevention and treatment of sickle cell pain crises.