Enhanced insulin-hypoglycemic activity in rats consuming a specific glycoprotein extracted from maitake mushroom.

Aim: Intraperitoneal glucose tolerance (ipGTT) and insulin challenge (ICT) tests were implemented to evaluate whether a specific glycoprotein extract of maitake mushroom (Grifola frondosa) known as SX-fraction enhances insulin sensitivity in spontaneously hypertensive rats (SHR).

Methods: SHR were divided randomly into a control group, a group receiving the antidiabetic drug, pioglitazone, in their diet, and three groups consuming three different concentrations of SX-Fraction derived from maitake mushroom in their food. The response of circulating glucose and insulin concentrations was examined at different time periods during an ipGTT. The major action of exogenous insulin during the ipGTT occurred within a 15-min period following injection of regular insulin. Accordingly, hypoglycemic activity was evaluated in SHR with and without glucose challenge over a short time frame in the ICT.

Results: Evidence gathered from the ipGTT and ICT tests suggests that the SX-fraction of Maitake in a proper dosage as well as pioglitazone enhance insulin sensitivity. Ingestion of SX-fraction produced a lower-circulating level of glucose after challenge despite no rise in circulating insulin. Compared to control, significantly lower-circulating glucose levels were seen in the groups consuming pioglitazone and higher doses of SX-fraction at 7.5 min after insulin challenge whether or not glucose was given concomitantly.

Conclusion: SHR in the pioglitazone and SX-fraction groups showed improved glucose tolerance despite no elevation of circulating insulin concentrations and showed enhanced sensitivity to exogenous insulin. Thus, a glycoprotein extract from Maitake mushroom (SX-fraction) should be considered as an alternative method for improving insulin sensitivity.