Insulin/insulin-like growth factor-I hybrid receptor abundance decreases with development in suckling pigs

The IGF-1 receptor and regulation of nitric oxide bioavailability and insulin signalling in the endothelium

The insulin-like growth factor-1 receptor (IGF-1R), like the insulin receptor (IR), plays a significant role in determining bioavailability of the critical signalling molecule nitric oxide (NO) and hence, modulates endothelial cell function, particularly in response to stimulation with insulin. In particular, the ability of the IGF-1R to form hybrid receptors with the IR appears to be highly significant in determining the sensitivity of the endothelial cell to insulin. This review will examine the structure of the IGF-1R and how this, with particular reference to the ability of the IGF-1R and the IR to form hybrid receptors, may have an effect both on endothelial cell function and the development of cardiovascular disease.

Aortic vasoreactivity during a postnatal critical window of the pancreas in rats

Changes in aortic vasoreactivity during the postnatal pancreatic critical window, where insulin and glucose, which modify vasoreactivity, are elevated, were studied and compared to those in control and metabolic syndrome (MS) rats. Twelve 21- and 28-day-old rats were used. To develop MS rats, male Wistar animals were given 30% sucrose in drinking water since weaning and used when 6 months old. Glucose and insulin levels were higher during suckling and decreased after weaning, and insulin and triglycerides levels increased in MS rats. Contraction elicited by norepinephrine (NE) was stronger than KCl contraction at all ages. KCl-induced contraction increased with, age being stronger in control rats; it further increased in MS rats. Norepinephrine-induced contraction increased from day 12 to day 28 but stabilized from day 21 to day 28; it was stronger in controls and increased in MS rats. Vasorelaxation to acetylcholine in NE precontracted rings did not change during the neonatal period, being similar to MS rats and lower than in controls. Insulin-induced increase in contraction elicited by KCl increased from day 12 to day 28 and increased from control to MS rats. There is a postnatal critical window in vasoreactivity that might predispose to cardiovascular diseases in adults.

Regulation of muscle growth in neonates

PURPOSE OF REVIEW

This review reports recent findings on the multiple factors that regulate skeletal muscle growth in neonates.

RECENT FINDINGS

Skeletal muscle is the fastest growing protein mass in neonates. The high rate of neonatal muscle growth is due to accelerated rates of protein synthesis accompanied by the rapid accumulation of muscle nuclei. Feeding profoundly stimulates muscle protein synthesis in neonates and the response decreases with age. The feeding-induced stimulation of muscle protein synthesis is modulated by enhanced sensitivity to the postprandial rise in insulin and amino acids. Insulin and amino acid signaling components have been identified that are involved in the feeding-induced stimulation of protein synthesis in neonatal muscle. The enhanced activation of these signaling components in skeletal muscle of the neonate contributes to the high rate of muscle protein synthesis and rapid gain in muscle protein mass in neonates.

SUMMARY

Recent findings suggest that the immature muscle has a heightened capacity to activate signaling cascades that promote translation initiation in response to the postprandial rise in insulin and amino acids thereby enabling their efficient utilization for muscle growth. This capacity is further supported by enhanced satellite cell proliferation, but how these two processes are linked remains to be established.

Developmental regulation of protein kinase B activation is isoform specific in skeletal muscle of neonatal pigs

The postprandial activation of the insulin signaling pathway that leads to translation initiation is enhanced in skeletal muscle of the neonate and decreases with development in parallel with the developmental decline in muscle protein synthesis. Our previous study showed that the activity of protein kinase B (PKB), a major insulin signaling component, was higher in 7- than in 26-d-old pigs. To examine the molecular mechanisms involved, we determined PKB isoform abundance and phosphorylation state, the abundance of its kinases, and PKB's association with its kinases. The abundances of total PKB, PKBalpha, and PKBgamma were higher in muscle of 7- than in 26-d-old pigs whereas PKBbeta abundance was similar in the two age groups. PKB phosphorylation at Thr308 was higher in 7- than in 26-d-old pigs but PKB phosphorylation at Ser473 was similar in both age groups. The association of PKB with 3'-phosphoinositide-dependent kinase-1 (PDK-1), a kinase that phosphorylates PKB at Thr308, and PDK-1 abundance were higher in 7- than in 26-d-old pigs. Moreover, PDK-1 phosphorylation at Ser-241, a site that is crucial for PDK-1 activation, was higher in 7- than in 26-d-old pigs. However, the association of PKB with integrin-linked kinase (ILK), a kinase that potentially phosphorylates PKB at Ser473, and ILK abundance were similar in both age groups. The result suggests that the developmental change in PKB activation is isoform specific and involves regulation by PDK-1.