Evaluation of the Antidiabetic Activity of the Seed Extract of Picralima Nitida Stapf (Apocyanaceae)

Abstract

This study investigated the antidiabetic effect of the seed extracts of Picralima nitida in rats treated with alloxan monohydrate at 120 mgkg intraperitoneally. Methanolextract (ME, 5 gkg) caused 20.0 % maximal reduction of mean fasting blood glucose levels in normoglycemic rats while glyburide (5 mgkg) caused 25.9 % maximal reduction. In the alloxanized rats, ME caused 49.7% maximal reduction in the mean fasting blood glucose levels while glyburide caused 71.9% maximal in the mean blood glucose levels after per oral administration. The blood glucose lowering effect of the extract commenced at the first hour and climaxed at twelve hour. The alkaloids extract of Picralima nitida seed given i.p. caused increase in fasting blood glucose levels while the glycosides extract reduced the blood glucose levels in normoglycemic and hyperglycemic rats though not in dose-dependent pattern. Glycosides extract caused significant (p < 0.05) reduction of 38.6 % (250 mgkg) and 22.9% (500 mgkg) of the fasting blood glucose levels in normoglycemic, and 64.4% (250 mgkg) and 39.0 % (500 mgkg) in the hyperglycemic rats. The extract maintained reduced fasting b1~~)d,.glqcosleev els for 24 h which is indicative of long duration of action. On subchronic (10 days) treatment of hyperglycemic rats, glycosides extract (250 mgkg) caused 82.99 % while glyburide (5 mgkg) caused 60.81% reduction of mean blood glucose levels. The n-butanol fractions (F7>F5 >F4>Fs) showed consistent reduction of the fasting blood glucose levels of diabetic rats in the following order, 84.58 %, 80.88 %, 76.83 % and 66.92% while the glyburide caused 86.14 %. These fractions that exhibited significant blood glucose lowering action for 24 hours and F7 has the most persistent hypoglycemic effect. The fraction E of F7 caused 89.17 % maximal reduction of the mean fasting blood glucose levels of treated rats while the standard drug, glyburide caused 79.66% reduction. The peak mean blood glucose concentration achieved after glucagon administration was reduced by the glycosides fractions like glybwide did. They respectively caused reduction in mean blood glucose levels in the following order E>F7>F5. From the fraction E of the seed extract of Picralima nitida, that had the highest hypoglycemic activity, was isolated a hydrophilic triterpenoidal saponin; 2a, 3a 16a, 23- tetrahydroxyloleana-5, 13 (1 8)-dien-28-oic acid which may be the enatiomer of Mimusic acid obtained from the Mimusops elengi. In conclusion, it may be stated that the high hypoglycemic activity of the seed extract of Picralima nitida resides in the hydrophilic saponins which may have achieved this through reduction of hepatic overproduction of glucose or increase in glucagon catabolism, and inhibition of gastric emptying in diabetic conditions.