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 skeletal muscle glucose utilization. The mechanism responsible for this modification is unknown. Therefore an investigation was made of the insulin-sensitive glucose transporter (GLUT-4) in three skeletal muscles from six lactating (peak of lactation) and six non-lactating goats. GLUT-4 protein content was assessed in crude membrane preparations and Triton 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. tensor fasciae latae and longissimus dorsi) than in oxidative muscles (-0.20 in masseter). Down-regulation of the insulin-sensitive glucose transporter (GLUT-4) expression in skeletal muscles from lactating goats may be responsible for the decrease in insulin responsiveness of glucose utilization previously observed in vivo.