I suppose you want your plant extract to be assessed with regards to potential insulin sensitizing properties (inhibition of insulin resistance [sic]), then simply treat two groups of insulin resistant mice (they may be insulin resistant due to high fat feeding or genetically induced hyperphagia/obesity: ob/ob, db/db, NZO mice... etc.) with your plant extract/compound in their food/drinking water for a reasonable amount of time. To assess insulin sensitivity, perform an oral glucose tolerance test and measure blood glucose and blood insulin during the test.