Diabetes mellitus (DM) is a metabolic disease characterised by hyperglycaemia which is associated with absolute and relative deficiencies in insulin secretion or action. Diet plays a major role in the management of DM. Prior to insulin therapy, the main form of treatment was dietary measures, including the use of traditional medicines derived mainly from plants (Platel & Srinivasan, 1997). The fruit juice of one such plant is M. charantia (family: Cucurbitacae) which is widely used in many developing countries as a hypoglycaemic agent to treat DM. In a previous study (Ahmed et al. 1999), we have shown that both the juice and its extract can regulate glucose metabolism and regenerate damaged pancreatic β-cells during DM in vivo. The mechanism of the hypoglycaemic action of M. charantia in vitro is not fully understood. In this study, we have investigated the effect of M. charantia juice and its extract on either ³H-deoxy-D-glucose or N-methyl-amino-α-isobutyric acid (¹⁴C-Me-ATB) uptake in L6 rat muscle cells cultured to the myotube stage (Hundal et al. 1992). The fruit was cut into small pieces and homogenised using a commercial blender. The fresh juice was centrifuged at 5000 r.p.m. and the supernatant lyophilised (fraction A). Fraction B was extracted from fraction A using chloroform and subsequently lyophilised (Day et al. 1990). The uptake of either ³H-deoxy-D-glucose or ¹⁴C-Me-ATB by L6 myotubes was performed by established methods (Hundal et al. 1992) in the absence and presence of different concentrations of insulin, extract A, extract B or a combination of Wortmannin (phosphatidyl inositol 3-kinase inhibitor) and the extracts over a period of 1Ð6 h. Total cell protein content was measured by the method of Bradford (1976). Results are expressed as pmol min^-1 (mg cell protein)^-1; n = 6 for each value.

Basal ³H-deoxy-D-glucose and ¹⁴C-Me-ATB uptakes by L6 myotubes after 1 h of incubation were (means ± S.E.M.) 32.14 ± 1.34 and 13.48 ± 1.86, respectively. Incubation of cells with 100 nM insulin for 1 h resulted in significant (ANOVA, P < 0.05) increases in ³H-deoxy-D-glucose and ¹⁴C-Me-ATB uptakes. Typically, ³H-deoxy-D-glucose and ¹⁴C-Me-ATB uptakes in the presence of insulin were 58.57 ± 4.49 and 29.52 ± 3.41, respectively. Incubation of L6 myotubes with three different concentrations (1, 5 and 10 mg ml^-1) of either extract A or extract B resulted in time-dependent increases in ³H-deoxy-D-glucose and ¹⁴C-Me-ATB uptakes, with maximal uptakes occurring after 6 h using a concentration of 5 mg ml^-1 of each extract. Typically, at a concentration of 5 mg ml^-1, extracts A and B gave uptakes of ³H-deoxy-D-glucose of 57.14 ± 7.85 and 52.14 ± 7.86, respectively; uptakes of ¹⁴C-Me-ATB were 33.02 ± 4.65 and 32.62 ± 2.79, respectively. Incubation of 100 nM Wortmannin with either extract A or extract B resulted in a significant (P < 0.05) reduction in ³H-deoxy-D-glucose uptake. The results suggest that M. charantia fruit juice and its extract are exerting their hypoglycaemic effects by stimulating glucose and amino acid uptake into skeletal muscle.