α-Adrenoceptor Blockade by Phentolamine Inhibits β-Adrenergically and Cholinergically Induced Glucagon Secretion in the Mouse

Summary

Glucagon secretion is known to be stimulated by activation of the α-adrenoceptors. In this study, we investigated whether α-adrenoceptor blockade by phentolamine affects basal and stimulated glucagon secretion in the mouse.

Phentolamine was injected intraperitoneally to mice at dose levels varying from 2.6 to 260 μmol/kg. It was found that, while decreasing plasma glucose levels, phentolamine did not over this wide dose range affect basal glucagon concentrations indicating an inhibition of the hypoglycaemiainduced glucagon secretion. Further, phentolamine clearly inhibited the glucagon secretory response to β-adrenergic or cholinergic stimulation. Thus, phentolamine (2.6 μmol/kg), impaired the glucagon secretory response to the β₂-adrenoceptor agonist terbutaline by 51% (P < 0.01), and to the cholinergic agonist carbachol by 44% (P < 0.02).

We conclude that α-adrenoceptor blockade by phentolamine inhibits the glucagon secretion following hypoglycaemia or stimulation by α-adrenergic and cholinergic agonists. Thus, the β-adrenoceptors seem to be of great importance for glucagon secretion in the mouse.

Key-Words

Glucagon Secretion - α-Adrenoceptors - Cholinergic Stimulation - β-Adrenergic Stimulation - In Vivo - Mouse