SKELETAL-MUSCLE GLUCOSE-TRANSPORTER (GLUT-4) PROTEIN IS DECREASED IN LACTATING GOATS

Lactation in goats is associated with an insulin resistance manifested by an impairment of the ability of insulin maximally to stimulate ske letal muscle glucose utilization. The mechanism responsible for this m odification is unknown. Therefore an investigation was made of the ins ulin-sensitive glucose transporter (GLUT-4) in three skeletal muscles from six lactating (peak of lactation) and six non-lactating goats. GL UT-4 protein content was assessed in crude membrane preparations and T riton X-100 extracts by Western-blot analysis. Lactation resulted in a decrease in GLUT-4 protein content. This decrease was more pronounced in oxidoglycolytic muscles (proportionately -0.40 to -0.60 in m. tens or fasciae latae and longissimus dorsi) than in oxidative muscles (-0. 20 in masseter). Down-regulation of the insulin-sensitive glucose tran sporter (GLUT-4) expression in skeletal muscles from lactating goats m ay be responsible for the decrease in insulin responsiveness of glucos e utilization previously observed in vivo.