Amylin and insulin in rat soleus muscle: dose responses for cosecreted noncompetitive antagonists

Abstract

Increasing concentrations of amylin progressively depressed the maximal insulin-stimulated radioglucose incorporation into soleus muscle glycogen, but did not substantively change the EC50 (range 0.78 to 1.52 nM); these findings show noncompetitive, insurmountable antagonism of insulin action by amylin. The results from 36 combinations of different insulin and amylin concentrations were used to construct a response surface that can be used to predict the response for any combination of insulin and amylin concentration. The predicted response to a constant ratio of insulin and amylin concentration is a bell-shaped curve. The experimentally determined response to increasing amounts of an amylin-insulin mixture (molar ratio of 0.14:1, within the range measured for pancreatic secretion and plasma levels) gave a bell-shaped response rather than the sigmoidal response seen with insulin alone. The amylin dose-response relation in the soleus system provides a useful bioassay for amylin agonists. The dose response for highly purified, synthetic human amylin obtained by measuring amylin concentrations by radioimmunoassay in the incubation medium gave an EC50 of 456 pM (+/- 0.18 log units). Human amylin had a potency greater than or equal to that of human insulin in this highly insulin-sensitive preparation.

Amylin injection causes elevated plasma lactate and glucose in the rat

“…After 2.hours infusion with somatostatin (S-9129, Sigma, St Louis, MO) at 3.4 nmolW, which then continued throughout the experiment. animals were injcctcd with a 100/11 150 mM NaCl containing 25.5 nmol freshly dissolved rat amylin (IoI# ZG485, Bachem, Torrance, CA), The biological activiky of peptidc to be used in this study was first verilicd using the solcus muscle-based assay [14] 3. Subcutaneous amylin injection without somatostatin infusion (n=5).…”

Different pharmacological characteristics in L6 and C2C12 muscle cells and intact rat skeletal muscle for amylin, CGRP and calcitonin

“…Both amylin and CGRP can inhibit insulin-stimulated incorporation of [U-_4C]-glucose into glycogen in skeletal muscle Deems et al, 1991a;Leighton et al, 1989;Young et al, 1992;Rossetti et al, 1993;Beaumont et al, 1995b). Amylin increases glycogen phosphorylase activity and reduces glycogen synthase activity in skeletal muscle (Deems et al, 1991b;Young et al, 1991;Lawrence & Zhang, 1994;Pittner et al, 1995a), promoting glycogenolysis and lactate release Pittner et al, 1995a).…”

Selective amylin antagonist suppresses rise in plasma lactate after intravenous glucose in the rat

“…This finding has been confirmed and extended in vitro [3] and in vivo and appears to result from activation of glycogen phosphorylase [4] and inhibition of glycogen synthase [S]. Amylin stimulation has been proposed [4] as underlying the previously unexplained increment in phosphorylase a activity observed after oral glucose [6].…”

“…]hCGRP from CGRP receptors (SK-N-MC cells [19]), and with 38-fold greater potency than that with which it displaces ['*'I]salmon calcitonin from calcitonin receptors (T47D cells [20]). Second, when present at 30 nM, AC187 reverses the inhibitory action of 100 nM rat amylin on insulin-stimulated incorporation of [U-i4C]glucose into glycogen in isolated rat soleus muscle [3] by 50%.…”