Responses of plasma glucose metabolism to exogenous insulin infusion in sheep-fed forage herb plantain and exposed to heat

The use of herbal plants as traditional medicines has a century long history. Plantain ( Plantago lanceolata L.) is a perennial herb containing bioactive components with free radical scavenging activities. An isotope dilution technique using [U- 13 C]glucose was conducted to determine the effect of plantain on the responses of plasma glucose metabolism to exogenous insulin infusion in sheep. Six crossbred sheep (three wethers and three ewes; mean initial BW=40±2 kg) were fed either a mixed hay of orchardgrass ( Dactylis glomerata ) and reed canarygrass ( Phalaris arundinacea ) (MH-diet) or mixed hay and fresh plantain (1 : 1 ratio, dry matter basis, PL-diet) and exposed to a thermoneutral (TN, 20°C; 70% relative humidity (RH)) environment or a heat exposure (HE, 30°C; 70% RH) for 5 days using a crossover design for two 23-day periods. The isotope dilution was conducted on days 18 and 23 of the experimental period during TN and HE, respectively. Plasma concentration of α -tocopherol was greater ( P P =0.05) during HE compared with TN and remained comparable between diets. Plasma glucose turnover rate during the preinfusion period of insulin did not differ ( P =0.10) between dietary treatments and between environments ( P =0.65). The response of plasma glucose utilization to exogenous insulin administration was lower ( P =0.04) for the PL-diet than the MH-diet. Under present experimental conditions, the plantain group was found to be resistant to the effects of insulin infusion.