Department of Basic Medical Sciences (Biochemistry), University of the West Indies, Mona, Kingston 7, Jamaica

Capsicum frutescens has been used to treat diabetes mellitus by traditional healers in Jamaica. This study was designed to identify any hypoglycaemic principle(s) and to determine the mechanism of action. Purification experiments employing thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) led to the extraction of the active principle, capsaicin. Capsaicin caused a decrease in blood glucose levels of 4.91 +/- 0.52 (n = 6) mmol/dL versus 6.40 +/- 0.13 mmol/dL (n = 6) for the control (p < 0.05) at the 2.5 h time interval when the oral glucose tolerance test (OGTT) was performed on dogs treated with capsaicin and compared with the control. Plasma insulin levels measured at the 2.5 h time interval showed that there was an increase in plasma insulin levels of 5.78 +/- 0.76 microIU/mL (n = 6) for the capsaicin treated dogs versus 3.70 +/- 0.43 microIU/mL (n = 10) for the control (p < 0.05). Insulin receptor studies, using a modification of the method of Gambhir et al. done on monocytes obtained from blood at the 2.5 h time interval showed that there was a decrease in the percentage receptor binding for the capsaicin treated dogs when compared with the control. Insulin affinity results showed that there was a decrease of 2.4 x 10(-4) in monocytes for the capsaicin treated dogs versus 8.77 x 10(-4) for the control (p < 0.05). Also, insulin receptor calculations showed a decrease in number, 2.63 x 10(8) +/- 5.73 x 10(7), compared with 8.77 x 10(8) +/- 1.47 x 10(8) for the control. In conclusion it can be stated that capsaicin is responsible for the hypoglycaemic episodes seen in the dogs and that it also causes an increase in insulin secretion which leads to a reduction of insulin binding on the insulin receptors.