The effect of "Teucrium polium L." extracts on insulin release from in situ isolated perfused rat pancreas in a newly modified isolation method: the role of Ca2+ and K+ channels.

BACKGROUND "Teucrium polium L." (TP) has been long recommended in Iranian folk medicine for its anti-diabetic activities. We attempt here to evaluate the effect of TP extract on insulin secretion in rat pancreas. METHODS Rat pancreas was isolated in situ and perfused with Krebs solution containing low glucose (LG, 2.8 mM) or high glucose (HG, 16.7 mM) as perfusate. The aqueous extract (Aq. E) and methanolic extract (Met. E) of TP aerial parts and two partition fractions of Met. E were added to perfusate to evaluate insulin release. Diazoxide (DZX) and verapamil (VPM) were also used for assessing the probable mechanism of the effects. In each experimental group, the peak and baseline of insulin levels in effluent samples were compared. The GC/MS analysis was carried out to detect active ingredients in the extracts. RESULTS Adding Met. E to the LG caused a significant increase (P<0.05) in insulin release from the basal level of 0.17 ± 0.05 µg/l to a peak value of 3.94 ± 1.29 µg/l. when Met. E was introduced to the HG, there was a further protracted stimulation of insulin release from 2.15 ± 1.35 µg/l to 6.16 ± 0.52 µg/l. Both DZX and VPM when added separately to the LG, led to inhibition of Met. E induced insulin secretion. The Aq. E and fractions had no significant effect on insulin secretion. Only in the Met. E, the component 5-hydroxy-4',7-dimethoxyflavone (apigenin-4',7-dimethylether) was detected. CONCLUSION It can be concluded that the insulinotropic properties of TP extracts can be attributed to the presence of apigenin existing only in Met. E, but not in Aq. E and fractions. Moreover, certain types of K+ and Ca2+ channels take part in this effect.