—The accumulation of cyclic adenosine 3′,5′‐monophosphate (cyclic AMP) was studied in cell‐free homogenates of guinea pig brain. Homogenates, prepared in Krebs‐Ringer buffer, responded markedly to the addition of neurohormones with an increased rate of cyclic AMP synthesis; preparations from cerebellum, cerebral cortex, and hippocampus responded to a degree approximating that achieved with slices of these areas of guinea pig brain. Adenylatc cyclase activity was seen only when cyclic AMP was measured by a [3H]adenine prelabelling technique or when total cyclic AMP was measured by radioimmunoassay; [32P]ATP did not serve as a substrate for this preparation of the enzyme. The adenylate cyclase was paniculate and required a Krebs Ringer buffer; use of tris, or tris with Mg2+ and Ca2+, resulted in a preparation totally devoid of hormonal stimulation. Digestion by purified beef heart cyclic nucleotide phosphodiesterase, Dowex chromatography, solubility in Ba(OH)2‐ZnSO4 mixtures, and two thin layer chromatographic systems demonstrated that the product of the hormonally stimulated adenylate cyclase preparation was cyclic AMP. The selectivity of hormonal stimulation and the adrenergic character of the hormonal receptors from different brain areas were maintained in the cell‐free preparation. However, simultaneous stimulation with two different neurohormones resulted in additive responses, rather than in the potentiation observed in preparations of slices of brain.

Five areas of guinea pig brain were examined to determine the properties of the receptor sites mediating increases in [3H]adenosine 3',5'-monophosphate (cyclic AMP).Both epinephrine and histamine were effective in causing increases in cyclic AMP in slices derived from cerebral cortex, hippocampus or amygdala, but not in diencephalon or brainstem. Stimulation of slices of cerebral cortex by either epinephrine or histamine resulted in a small, but reproducible, decrease in specific radioactivity of the [3H]-cyclic AMP produced, as did stimulation of the hippocampus by epinephrine. The catecholamine receptor was an a-adrenergic receptor in all three areas where epinephrine was effective; a-adrenergic stimulation, but not 8-adrenergic stimulation, increased levels of [3H]-cyclic AMP. Furthermore, a-, but not 8-adrenergic blocking agents, prevented the epinephrineinduced increase of both [3H]-and total cyclic AMP in cerebral cortex and hippocampus. Only antihistaminic agents were capable of antagonizing the histamine-induced increase of both [3H]-and total cyclic AMP in these two brain areas. The catecholamine receptor in the amygdala also appeared to be an a-adrenergic receptor. The effects of histamine and epinephrine together were far greater than the sum of effects ofeither hormone alone in both cerebral cortex and hippocampus.

The appearance of the characteristic crystalloid core of rat liver peroxisomes is emulated by the electron microscopic (EM) appearance of highly purified urate oxidase prepared from the same tissue. The purity of the enzyme preparation was established by gel electrophoresis under various conditions and the specific enzyme activity was at least as high as any previously reported. The amino acid composition of urate oxidase was determined. As additional evidence for close association of the peroxisomal core with urate oxidase, it was demonstrated that the biphasic changes in rat liver urate oxidase activity in response to prolonged starvation were paralleled by changes in the EM appearance of peroxisomes. Under comparable conditions catalase, another peroxisomal enzyme, did not show the same changes in activity as did urate oxidase. Evidence for the possible identity of urate oxidase with the peroxisomal crystalloid of rat liver has been presented, all materials having been obtained from, and experiments performed with, the rat.

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