The calcitonin peptide family: relationship and mode of action

Effects on Bone

The actions of amylin on bone have been reviewed in several publications (MacIntyre, 1992a,b; MacIntyre et al., 1991; Reid and Cornish, 1996; Tamura et al., 1992a,b; Zaidi et al., 1990a,c, 1993b). MacIntyre proposed that amylin or its derivatives or agonists would be useful for treating bone disorders, such as osteoporosis, Paget's disease, or bone loss resulting from malignancy, endocrine disorders, autoimmune arthritides, breakage and fracture, immobility and disease, or hypercalcaemia (MacIntyre, 1995).

GSK3 involvement in amylin signaling in isolated rat soleus muscle

Amylin can evoke insulin resistance by antagonizing insulin in a non-competitive manner. Here, we investigated the glycogenolytic effect of amylin in isolated skeletal muscle and compared it to the effects of a calcitonin gene-related peptide (CGRP). Amylin alone had no statistically significant effect on glucose transport. However, amylin decreased insulin-stimulated glucose transport by about 30%. The involvement of cAMP could not be detected at the concentrations shown to promote glycogenolysis. Previously, it has been shown that increased glycogen synthase kinase 3 (GSK3) activity plays a role in insulin resistance. Here, the ratio of GSK3 alpha:beta isoforms in rat soleus was found to be 1.2:1. We found that amylin increased GSK3alpha activity, which in turn led to increased phosphorylation of glycogen synthase and decreased glycogen synthesis de novo.