Antidiabetic and antihypertensive effect of a polyphenol-rich fraction of Thymelaea hirsuta L. in a model of neonatal streptozotocin-diabetic and NG-nitro-l-arginine methyl ester-hypertensive rats

Background: The present study examined the effect of the polyphenol-rich fraction from Thymelaea hirsuta (PRF-Th) in a rat model of streptozotocin (STZ)-diabetes and nitric oxide (NO)-deficient hypertension. Methods: Diabetes was induced by a single dose of STZ (90 mg/kg, i.p.). To induce NO-deficient hypertension, rats were treated with the NO synthase inhibitor NG-nitro-l-arginine methyl ester; l-NAME; 30 mg/kg per day, p.o. for 3 weeks. The effects of 21 days treatment with 80 mg/kg per day PRF-Th in the drinking water were evaluated in diabetichypertensive (DH) rats. In all groups (n = 6 in each), glycemia and systolic blood pressure were determined weekly. At the end of the experiment, hepatic glycogen was determined. Results: Blood glucose levels decreased gradually from baseline until the end of the experiment in untreated DH rats (from 1.92 +/- 0.09 to 1.3 +/- 0.1 g/L; P < 0.05). Administration of PRF-Th concomitantly with l-NAME prevented the blood pressure increase in rats. After 21 days, blood pressure in PRF-Th + l-NAME- and l-NAME-treated rats was 132 +/- 1 and 157 +/- 1 mmHg, respectively (P < 0.001). Administration of 2 mL/kg per day PRF-Th to DH rats significantly increased hepatic glycogen levels compared with levels in untreated DH rats (13.65 +/- 1.84 vs 6.34 +/- 0.75 mg/g tissue, respectively; P < 0.01). Moreover, PRF-Th significantly reduced the amount of glucose absorbed in in situ perfused jejunum segments compared with control (by 33.6%; P < 0.001). This effect of PRF-Th was comparable with that of acarbose, an a-glucosidase inhibitor. Conclusions: The findings of the present study indicate that T.similar to hirsuta has antidiabetic and antihypertensive activity in STZ-diabetic, NO-deficient hypertensive rats. This effect seems to be due to its rich polyphenol content. Therefore, T.similar to hirsuta may be useful as a food supplement for the prevention of type 2 diabetes and hypertension.