| Abstract: | This work was designed to characterize the adenosine receptor (A1 or A2) involved in glucagon secretion. The most potent adenosine analogues on A1 receptors are the N6 substituted compounds, among them N6-phenylisopropyladenosine (PIA); furthermore L-PIA is 50 to 100 times more potent than D-PIA on the A1 receptor, whereas it is 3 to 5 times more potent on the A2 receptor; thus the A1 receptor shows a much higher stereoselectivity. The effects of L-PIA and D-PIA were studied on glucagon secretion from the isolated perfused rat pancreas. 1) L-PIA at 1.65 microM induced a transient glucagon secretion which was not greater than that induced by the same concentration of adenosine. 2) D-PIA at a 3 fold higher concentration (4.95 microM) elicited a secretion of glucagon comparable to that induced by L-PIA 1.65 microM; thus the involved receptor does not present a high stereoselectivity for L-PIA. These results support the fact that the receptor involved in glucagon secretion is not of the A1 type. |
