Alterations of cyclic AMP in cerebral ischemia.
Cyclic AMP levels were measured in brains of 21 cats after occlusion of a middle cerebral artery by a transorbital approach. Brain samples for determination of cAMP by a protein binding radioassay were obtained from the ischemic and contralateral temporal lobes before sacrifice, 1, 3, and 24 hours after occlusion of the right middle cerebral artery. At 1 hour, no difference between the 2 sides was observed; a mean of 17.4 pmoles/mg protein was observed from the side of the occlusion and 18.9 pmoles/mg protein from the contralateral side. At 3 hours, a mean value of 8.9 pmoles/mg protein on the ischemic side and a level of 21.7 pmoles/mg protein on the contralateral side were observed. At 24 hours, the cAMP level on the ischemic side remained below the nonischemic side; the values obtained were 13.7 pmoles/mg protein compared to 27.9 pmoles/mg protein compared to 27.9 pmoles/mg protein. These changes in cAMP as early as 3 hours after the onset of ischemia, when such a lesion is reversible, may indicate that in initial step in the alteration of cellular metabolism following ischemia is due to membrane perturbation and altered production of this second messenger.
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