Mediation of β-Endorphin by the Isoflavone Puerarin to Lower Plasma Glucose in Streptozotocin-Induced Diabetic Rats

We investigate the mechanism(s) ofplasma glucose lowering action of puerarin in streptozotocin-induced diabetic rats (STZ-diabetic rats). Puerarin at the effective dosage to lower higher plasma glucose increased plasma β-endorphin-like immunoreactivity (BER) in STZ-diabetic rats. Both effects of puerarin were abolished by the pretreatment with prazosin. Also, puerarin enhanced BER release from isolated rat adrenal medulla in a concentration-dependent manner that can be abolished by prazosin. Moreover, bilateral adrenalectomy in STZ-diabetic rats eliminated the actions of puerarin including the plasma glucose lowering effect and plasma BER elevating effect. In addition, naloxone and naloxonazine inhibited the plasma glucose lowering action of puerarin. Unlike in wild-type diabetic mice, puerarin failed to lower the plasma glucose in opioid p-receptor knockout diabetic mice. In conclusion, our results suggest that puerarin may activate α 1 -adrenoceptors on the adrenal gland to enhance the secretion of β-endorphin to result in a decrease of plasma glucose in STZ-diabetic rats.