Effects of imidazolines and derivatives on insulin secretion and vascular resistance in perfused rat pancreas

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The effects of imidazolines and derivatives were studied on insulin secretion and vascular resistance in the isolated perfused rat pancreas. On insulin secretion, two imidazoline α 2-adrenoceptor antagonists, efaroxan (1–100 μM) and RX821002 (10 μM), had a stimulating response; however, idazoxan, like the non-imidazoline α 2-adrenoceptor antagonist yohimbine, was ineffective at 10 μM. The oxazoline rilmenidine with α 2-adrenergic activity at 10 μM inhibited insulin release; this effect was reversed to a stimulation after the blockade of α 2-adrenoceptors. Antazoline (1–10 μM), an imidazoline devoid of α 2-adrenergic activity, also had an insulin-releasing effect. On pancreatic vessels, all imidazolines tested (efaroxan, RX821002, antazoline and idazoxan), in contrast to yohimbine, induced vasoconstriction. Rilmenidine did not have a vasoconstrictor effect after blockade of α 2-adrenoceptors. Furthermore, the efaroxan-induced insulin release or vasoconstriction was not affected by the blockade of α 2- and α 1-adrenoceptors. This study shows that imidazolines and derivatives are able to stimulate insulin release and induce vasoconstriction in the rat pancreas. These effects cannot be ascribed to an interaction with α-adrenoceptors but may involve different types of imidazoline sites.