Abstract
Abstract— l‐Isopropylnorepinepherine (IPNE), 3‐isobutyl‐1‐methylxanthine (IBMX) and N6,O2′‐dibutyryl cyclic AMP have been found to stimulate the conversion of glycogen phosphorylase (GPase) from b to a forms in rat caudate nucleus slices. The average percentage of total GPase in the a form in control incubations was 32%. The percentage of total GPase in the a form was increased to 1.5 times the control value in the presence of 1 mM‐IBMX, to twice the control value in the presence of 0.05 mM‐IPINE and to 2.5 times the control in the presence of 0.05 mM‐IPNE and 1 mM‐IBMX in combination. The increase in GPase activation correlated well with the elevation of cyclic AMP levels by these agents in caudate slices. The percentage of total GPase in the a form was also increased to 2.5 times the control by 1 mM dibutyryl cyclic AMP. Dopamine (DA) and 2‐chloroadenosine (2‐CI‐Ado), which also elevate cyclic AMP levels in rat caudate slices, were without significant effect on GPase. The results indicate that the β‐adrenergc adenylate cyclase in the rat caudate nucleus plays a role in the regulation of glycogen metabolism, while the DA‐stimulated adenylate cyclase is not significantly involved. 2‐CI‐Ado does have effects on glycogen metabolism in the caudate, but these effects do not appear to be mediated by GPase activation.
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