Stimulation and Desensitization of Macrophage Adenylate Cyclase by Prostaglandins and Catecholamines

Preparations of peritoneal macrophages were obtained by selecting from a peritoneal exudate of guinea pigs those cells which adhere to glass.By preincubating the macrophages in a hypotonic pH 8.0 buffer, .homogenizationwas achieved under gentle conditions.The adenylate cyclase activity of homogenates was stimulated by catecholamines and by the prostaglandins E1 and E) (PGE1 and PGE2).Using inhibitors and other criteria the catecholamine receptor was classified as a P-adrenergic receptor.Since propranolol inhibits the catecholamine stimulation but not the prostaglandin stimulation of adenylate cyclase, it was concluded that these two classes of hormones interact with separate receptor sites.It is still unclear whether they afIect the same or different catalytic sites.Two types of experiments yielded information about the effects on adenylate cyclase activity of exposure of intact cells to hormones.Intact macrophages were incubated as monolayers with epinephrine or PGEz for 2 hours, after which the hormone was removed and the cells homogenized.Preincubation of macrophages with PGE, greatly reduced the subsequent response of adenylate cyclase to PGE2.The basal, epinephrine-stimulated, and NaF-stimulated adenylate cyclase activities were unaffected.Similarly, treatment of cells with epinephrine left the basal, PGES-stimulated and NaF-stimulated activities unaffected but markedly reduced the epinephrine-stimulated adenylate cyclase activity.This desensitization, i.e. loss of response to hormone due to treatment with hormone, was found to be dose-dependent over the range of lo-' to low4 M PGE,.Incubation of macrophage monolayers in a serum-containing medium leads to an increase in adenylate cyclase activity (basal) after 24 hours.Inclusion of PGE, in these cultures caused the basal adenylate cyclase activity to be markedly decreased relative to control cultures incubated without PGE2.This decrease was dose-dependent over the range of lo-' to 10e4 M PGEz and was not observed with prostaglandin Fl,.