Hormonal regulation of pancreatic islet adenyl cyclase

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Abstract
Adenylate cyclase activity of rat pancreatic islet membrane was increased by secretin, pancreozymin and isoproterenol; ACTH, glucagon, growth hormone and insulin had no effect. Both secretin and isoproterenol activations were enhanced by prostaglandin E1 (PGE1) and GTP. Isoproterenol activation was additive with PGE1, as was that of secretion with PGE1, but only in the presence of GTP. Secretin activation in the presence of PGE1 and GTP was equivalent to NaF stimulation. Kinetic analysis indicated that secretin and GTP increased the maximum velocity of the adenylate cyclase and tended to decrease the apparent affinity of the enzyme for ATP. Glucagon activation of islet membrane adenylate cyclase was dependent upon prior treatment of the membrane preparation with ethylene glycol bis(.beta.-aminoethyl ether)tetraacetic acid and the use of inhibitors of proteolytic enzymes during the collagenase digestion phase of islet preparation. Hormonal regulation of insulin secretion may be affected by PGE1 and guanine nucleotide modulation of the adenylate cyclase activation process.