Effects of various inhibitors of oxidative phosphorylation on energy metabolism, macromolecular synthesis and cyclic AMP production in isolated rat thymocytes. A regulating role for the cellular energy state in macromolecular synthesis and cyclic AMP production

Inhibitors of oxidative phosphorylation such as several triorganotin compounds, oligomycin, 2,4-dinitrophenol and carbonylcyanide p-trifluoromethoxyphenylhydrazone suppress energy metabolism of isolated rat thymocytes as indicated by a reduction of ATP levels, an increase in glucose consumption and by a marked accumulation of lactate. Also these compounds effectively inhibit the incorporation of DNA, RNA and protein precursors into acid-precipitable material of thymocytes. Moreover, the prostaglandin E₁-induced elevation of cAMP is markedly reduced by these inhibitors. A correlation is observed between the effects on energy metabolism, macromolecular synthesis and cAMP production, since (i) from a series of trialkyltin chlorides, tri-n-propyltin, tri-n-butyltin and tri-n-hexyltin are very effective inhibitors of these functions, while trimethyltin and tri-n-octyltin affect neither of them; (ii) other inhibitors of oxidative phosphorylation, each of them with quite different mechanisms of action, also inhibit macromolecular synthesis and cAMP production. The finding that a rise in intracellular ATP concentrations leads to a reversion of the tri-n-butyltin-induced inhibition of cAMP production and uridine incorporation, indicates a regulating role for the cellular energy state in these aspects of cellular function.     

Effects of tri-n-butyltin chloride on energy metabolism, macromolecular synthesis, precursor uptake and cyclic AMP production in isolated rat thymocytes

The inhibitor of oxidative phosphorylation tri-n-butyltin chloride (TBTC) causes membrane damage and disintegration of isolated rat thymocytes at concentrations higher than 1 microM. From a concentration of 0.1 microM, TBTC disturbs energy metabolism as indicated by an increase in methylglucose uptake, glucose consumption and lactate production and by a decrease in cellular ATP levels. Over the same TBTC concentration range, the incorporation of DNA, RNA and protein precursors are markedly reduced. Moreover the production of cyclic AMP upon stimulation of the cells with prostaglandin E1 is effectively inhibited. These effects cannot be explained by an inhibition of nucleoside kinase activity, amino acid uptake or adenylate cyclase activity. The effects of TBTC on macromolecular synthesis and cyclic AMP production are possibly due to a disturbance of the cellular energy state.     

Effects of various inhibitors of oxidative phosphorylation on energy metabolism, macromolecular synthesis and cyclic AMP production in isolated rat thymocytes. A regulating role for the cellular energy state in macromolecular synthesis and cyclic AMP production

Inhibitors of oxidative phosphorylation such as several triorganotin compounds, oligomycin, 2,4-dinitrophenol and carbonylcyanide p-trifluoromethoxyphenylhydrazone suppress energy metabolism of isolated rat thymocytes as indicated by a reduction of ATP levels, an increase in glucose consumption and by a marked accumulation of lactate. Also these compounds effectively inhibit the incorporation of DNA, RNA and protein precursors into acid-precipitable material of thymocytes. Moreover, the prostaglandin E1-induced elevation of cAMP is markedly reduced by these inhibitors. A correlation is observed between the effects on energy metabolism, macromolecular synthesis and cAMP production, since from a series of trialkyltin chlorides, tri-n-propyltin, tri-n-butyltin and tri-n-hexyltin are very effective inhibitors of these functions, while trimethyltin and tri-n-octyltin affect neither of them; other inhibitors of oxidative phosphorylation, each of them with quite different mechanisms of action, also inhibit macromolecular synthesis and cAMP production. The finding that a rise in intracellular ATP concentrations leads to a reversion of the tri-n-butyltin-induced inhibition of cAMP production and uridine incorporation, indicates a regulating role for the cellular energy state in these aspects of cellular function.     

Effects of sulfonylureas on membrane-bound low Km cyclic AMP phosphodiesterase in rat fat cells

The effects of sulfonylureas and a biguanide on membrane-bound low K_m cyclic AMP phosphodiesterase and lipolysis were examined in rat fat cells. Pharmacologically active sulfonylureas, such as tolbutamide (10 mM), acetohexamide (10 mM) and glibenclamide (200 μM) activated the phosphodiesterase when incubated with fat cells and suppressed lipolysis induced by isoproterenol. However, neither of these actions was observed in the presence of a pharmacologically inactive sulfonylurea, carboxytolbutamide (10 mM) and a biguanide, buformin (500 μM). Tolbutamide (0.5–10 mM) activated the enzyme, concentration dependently, and this manner of activation appears to coincide with that of the suppressive effect on the lipolysis. The time course of the enzyme activation was similar to that seen with insulin. K_m, optimal pH and sensitivity to temperature of the enzyme from tolbutamide-treated cells were the same as those of the enzyme from control and insulin-treated cells. Direct incubation of the enzyme from control cells with tolbutamide did not affect the activity, while as little as 10 μM 3-isobutyl-1-methylxanthine markedly inhibited the enzyme. Tolbutamide continued to activate the enzyme in cells in which insulin receptor had been destroyed by trypsin-pretreatment. These results are compatible with the idea that the enzyme activated by sulfonylurea and that activated by insulin may be the same species of phosphodiesterase and that the antilipolytic action of sulfonylurea may be mediated by the activation of the enzyme which does not occur through the insulin receptor.     

The effect of metabolites,papaverine, and probenecid on cyclic AMP efflux from isolated rat islets of Langerhans

The process of cyclic AMP efflux from rat islets of Langerhans has been studied. The dynamics of glucose-induced cyclic AMP efflux closely resembled the pattern of glucose-induced insulin release. Thus, both processes were dose-dependent for glucose having the same threshold concentrations (4–8 mmol/l glucose), with the time course of cyclic AMP efflux and insulin release from 0–60 min being very similar. Galactose did not affect insulin release, cyclic AMP efflux and intra-islet cyclic AMP accumulation. On the other hand, inosine, N-acetylglucosamine, α-ketoisocaproic acid, L-leucine and xylitol all promoted insulin release and cyclic AMP efflux. Except for L-leucine, all these substances enhanced the intracellular accumulation of cyclic AMP. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, greatly augmented all these parameters in the presence of glucose whereas in the absence of glucose, insulin release was not enhanced, while both cyclic AMP efflux and cyclic AMP accumulation were elevated. The drug, probenecid, did not alter either insulin release or intra-islet cyclic AMP levels, while cyclic AMP efflux was markedly reduced (though not abolished). Papaverine inhibited both insulin release and cyclic AMP efflux, but was found to augment the intra-islet cyclic AMP levels. The efflux of cyclic AMP correlates more closely with insulin release than with the cyclic AMP accumulation in most instances. The efflux is independent of either insulin secretory granule extrusion or intracellular fluctuations of the nucleotide, though it is not yet known whether cyclic AMP efflux may have some regulatory significance in insulin release.     

Regulation of rat brain (Na+ + K+)-ATPase activity by cyclic AMP

The interaction between the $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ and the adenylate cyclase enzyme systems was examined. Cyclic AMP, but not 5′-AMP, cyclic GMP or 5′-GMP, could inhibit the $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ enzyme present in crude rat brain plasma membranes. On the other hand, the cyclic AMP inhibition could not be observed with purified preparations of $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ enzyme. Rat brain synaptosomal membranes were prepared and treated with either NaCl or cyclic AMP plus NaCl as described by Corbin, J., Sugden, P., Lincoln, T. and Keely, S. ((1977) J. Biol. Chem. 252, 3854–3861). This resulted in the dissociation and removal of the catalytic subunit of a membrane-bound cyclic AMP-dependent protein kinase. The decrease in cyclic AMP-dependent protein kinase activity was accompanied by an increase in $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ activity. Exposure of synaptosomal membranes containing the cyclic AMP-dependent protein kinase holoenzyme to a specific cyclic AMP-dependent protein kinase inhibitor resulted in an increase in $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ enzyme activity. Synaptosomal membranes lacking the catalytic subunit of the cyclic-AMP-dependent protein kinase did not show this effect. Reconstitution of the solubilized membrane-bound cyclic AMP-dependent protein kinase, in the presence of a neuronal membrane substrate protein for the activated protein kinase, with a purified preparation of $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$, resulted in a decrease in overall $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ activity in the presence of cyclic AMP. Reconstitution of the protein kinase alone or the substrate protein alone, with the $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ has no effect on $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ activity in the absence or presence of cyclic AMP. Preliminary experiments indicate that, when the activated protein kinase and the substrate protein were reconstituted with the $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ enzyme, there appeared to be a decrease in the Na⁺-dependent phosphorylation of the Na⁺-ATPase enzyme, while the K⁺-dependent dephosphorylation of the $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ was unaffected.     

Hyperoxic-induced alterations in lung cell structure and function: Effects on cellular cyclic AMP content and comparison to alterations produced by exogenous cyclic AMP

Hyperoxic exposure in vitro of two lung-derived cell types (the epithelial-derived L2 cells and WI-38 fibroblasts) inhibits cellular replication, produces striking morphologic changes and may result in cell death; these effects have been observed consistently in other cell types. Hyperoxic exposure of L2 cells is associated with an increase in cellular cyclic AMP content (cellular cyclic AMP content 454 ± 115 fmol/μg DNA in cells exposed to p_O2 677 Torr for 96 h compared to 136 ± 17 fmol/μg DNA in air-grown cells). Hyperoxic exposure of WI-38 fibroblasts is not associated with increased cyclic AMP content. Although cultivation of L2 cells in the presence of exogenous dibutyryl cyclic AMP does inhibit replication and produce morphologic alterations, similar effects are produced by sodium butyrate alone. Hyperoxic exposure alters cyclic AMP metabolism in some cell types, but the structural and functional alterations observed in L2 cells and WI-38 fibroblasts following hyperoxic exposure are not produced by changes in cellular cyclic AMP content.     

Enzyme-inhibitor interactions as a basis for heterogeneity of extracellular cyclic AMP phosphodiesterases in Dictyostelium discoideum

We have previously characterized three forms of cyclic-AMP phosphodiesterase obtained after dithiothreitol activation of the enzyme from the extracellular medium during late vegetative growth of Dictyostelium discoideum (Toorchen, D. and Henderson, E.J. (1979) Biochem. Biophys. Res. Commun. 87, 1168–1175). This communication presents evidence supporting the earlier hypothesis that the observed heterogeneity of enzyme species is due to formation of complexes between an endogenous inhibitor protein and a common catalytic polypeptide. Dithiothreitol inactivates the inhibitor, but does not cause its release from the catalytic unit. Additional evidence is presented for the presence of a similar catalytic polypeptide in the extracellular phosphodiesterase produced during the first 8 h of developmetn, except that this species is a phosphoprotein.     

The effects of Ca and guanylnucleotides on isoprenaline-stimulated cyclic AMP formation in rat reticulocyte ghosts

We have studied β-adrenergic stimulation of cyclic AMP formation in fragmented membranes and in unsealed or resealed ghosts prepared from rat reticulocytes. The maximal rate of isoprenaline-stimulated cyclic AMP formation with saturating MgATP concentrations and in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine was 5–8 nmol/min per ml ghosts are remained constant for at least 15 min. Transition from resealed ghosts to fragmented membranes was associated with a shift of the activation constant (K_a) for (±)-isoprenaline from 0.1 to 0.6 μM. The apparent dissociation constant for propranolol (0.01 μM) remained unchanged. The K_a values for isoprenaline in native reticulocytes and in resealed ghosts were identi The stimulating effect of NaF on cyclic AMP formation in resealed ghosts reached 15% of maximal β-adrenergic stimulation. Cyclic AMP formation, both in fragmented membranes and in ghosts, was half-maximally inhibited with Ca²⁺ concentrations ranging between 0.1 and 1 μM. GTP stimulated iosprenaline-dependent cyclic AMP formation in unsealed ghosts and in fragmented reticulocyte membranes by a factor of 3–5 but did not change the K_a value for isoprenaline. K_a values for the guanylnucleotides in different experiments varied between 0.3 and 2 μM. Ca²⁺ concentrations up to 4.6 μM reduced the maximal activation by GTP and Gpp(NH)p but did not affect their K_a values. Compared to GTP, maximal activation by Gpp(NH)p was higher in fragmented membranes, but much lower in ghosts. Our results suggest that the native β-receptor adenylate cyclase system of reticulocytes is more closely approximated in the ghost model than in fragmented membrane preparations. Membrane properties seem to modulate the actions of guanylnucleotides on isoprenaline-dependent cyclic AMP formation in ghosts. Some of these effects are not observed in isolated membranes.     

Relation between energy production and adenine nucleotide metabolism in human blood platelets

The relation between ATP production and adenine nucleotide metabolism was investigated in human platelets which were starved by incubation in glucose-free, CN^?-containing medium and subsequently incubated with different amounts of glucose. In the absence of mitochondrial energy production (blocked by CN^?) and glycogen catabolism (glycogen almost completely consumed during starvation), lactate production increased proportionally with increasing amounts of glucose. The generated ATP was almost completely consumed in the various ATP-consuming processes in the cell except for a fixed portion (about 7%) that was reserved for restoration of the adenylate energy charge. During the first 10 min after glucose addition, the adenine nucleotide pool remained constant. Thereafter, when the glycolytic flux, measured as lactate formation, was more than 3.5 μmol · min^?1 · 10^?11 cells, the pool increased slightly by resynthesis from hypoxanthine-inosine and then stabilized; at a lower flux the pool decreased and metabolic ATP and energy charge declined to values found during starvation. Between moments of rising and falling adenylate energy charges, periods of about 10 min remained in which the charge was constant and ATP supply and demand had reached equilibrium. This enabled comparison between the adenylate energy charge and ATP regeneration velocity. A linear relation was obtained for charge values between 0.4 and 0.85 and ATP regeneration rates between 0.6 and 3.5 ATP equiv. · min^?1 · 10^?11 cells. These data indicate that in starved platelets ATP regeneration velocity and energy charge are independent and that each appears to be subject to the availability of extracellular substrate.     

Cyclic nucleotides in the denervated rat diaphragm and the effect of cyclic AMP on ornithine and adenosylmethionine decarboxylases

The concentration of cyclic AMP and cyclic GMP were measured in the denervated rat diaphragm at various times following unilateral phrenicectomy. Cyclic AMP concentration was raised by the second day after operation, reached a peak by the third day, followed by another increase at around 10 days. By contrast, cyclic GMP concentration was decreased within a day after denervation and remained below control levels at all subsequent times studied. Epinephrine in vitro produced a comparable increase in the concentration of cyclic AMP in both normal and denervated tissue. The concentration of adenosine appeared unchanged in the denervated diaphragm by comparison with its innervated contorl. Activity of ornithine decarboxylase was elevated in the diaphragms of rats treated with dibutyryl cyclic AMP, but this effect could also be achieved with sodium butyrate alone. Adenosylmethionine decarboxylase activity was unaffected after treatment with either compound. These observations and others discussed are taken to indicate a lack of direct relationship between cyclic AMP concentrations and the activity of the rate-limiting enzymes of polyamine biosynthesis in the rat diaphragm.     

The effects of Ca2+ and guanylnucleotides on isoprenaline-stimulated cyclic AMP formation in rat reticulocyte ghosts

We have studied β-adrenergic stimulation of cyclic AMP formation in fragmented membranes and in unsealed or resealed ghosts prepared from rat reticulocytes. The maximal rate of isoprenaline-stimulated cyclic AMP formation with saturating MgATP concentrations and in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine was 5–8 nmol/min per ml ghosts are remained constant for at least 15 min. Transition from resealed ghosts to fragmented membranes was associated with a shift of the activation constant (K_a) for (±)-isoprenaline from 0.1 to 0.6 μM. The apparent dissociation constant for propranolol (0.01 μM) remained unchanged. The K_a values for isoprenaline in native reticulocytes and in resealed ghosts were identi The stimulating effect of NaF on cyclic AMP formation in resealed ghosts reached 15% of maximal β-adrenergic stimulation. Cyclic AMP formation, both in fragmented membranes and in ghosts, was half-maximally inhibited with Ca²⁺ concentrations ranging between 0.1 and 1 μM. GTP stimulated iosprenaline-dependent cyclic AMP formation in unsealed ghosts and in fragmented reticulocyte membranes by a factor of 3–5 but did not change the K_a value for isoprenaline. K_a values for the guanylnucleotides in different experiments varied between 0.3 and 2 μM. Ca²⁺ concentrations up to 4.6 μM reduced the maximal activation by GTP and Gpp(NH)p but did not affect their K_a values. Compared to GTP, maximal activation by Gpp(NH)p was higher in fragmented membranes, but much lower in ghosts. Our results suggest that the native β-receptor adenylate cyclase system of reticulocytes is more closely approximated in the ghost model than in fragmented membrane preparations. Membrane properties seem to modulate the actions of guanylnucleotides on isoprenaline-dependent cyclic AMP formation in ghosts. Some of these effects are not observed in isolated membranes.     

Effects of cyclic AMP and butyrate on cell cycle,DNA, RNA,and purine synthesis of cultured astrocytes

Dibutyryl cyclic monophosphate (dBcAMP) has been shown to inhibit growth, and alter the morphology of astrocytes. However, the potential contribution of its hydrolytic product, butyrate, in inducing some of the changes that have been attributed to dBcAMP, is not clear. DNA, RNA, and purine synthesis were therefore studied in primary astrocyte cultures after 24 hours of exposure to varying concentrations of butyrate, dBcAMP, and agents that increase intracellular cAMP levels. Progression of cells through cell cycle was also studied by flow cytometry. Dibutyryl cAMP partially arrested cells in Go/G1 phase of cell cycle while sodium butyrate increased the percentage population of cells in G2/M phase. DNA synthesis and de novo purine synthesis were inhibited after treatment with dBcAMP, sodium butyrate, and various drugs that increase intracellular cAMP levels. RNA synthesis was increased with cAMP but was not affected by sodium butyrate. Our study shows that at millimolar concentrations, butyrate is capable of altering the cell cycle and inhibiting DNA synthesis in primary astrocyte cultures, in a manner that is similar although not identical to the effects of dBcAMP.     

Impact on energy metabolism of quantitative and functional cyclosporine-induced damage of kidney mitochondria

In this study we have measured, under experimental conditions which maintained efficient coupling, respiratory intensity, respiratory control, oxidative phosphorylation capacity and protonmotive force. Succinate cytochrome-c reductase and cytochrome-c oxidase activities were also studied. These investigations were carried out using kidney mitochondria from cyclosporine-treated rats (in vivo studies) and from untreated rats in the presence of cyclosporine (in vitro studies). Inhibition of respiratory intensity by cyclosporine did not exceed 21.1% in vitro and 15.9% in vivo. Since there was no in vitro inhibition of succinate cytochrome-c reductase and cytochrome-c oxidase activities, the slowing of electron flow observed can be interpreted as a consequence of an effect produced by cyclosporine between cytochromes b and c₁. Cyclosporine had no effect on respiratory control either in vitro or in vivo. Statistically significant inhibition of the oxidative phosphorylation was observed both in vitro (6.6%) and in vivo (12.1%). Moreover, cyclosporine did not induce any change of membrane potential either in vivo or in vitro. Our findings show that cyclosporine is neither a protonophore, nor a potassium ionophore. In cyclosporine-treated rats we noticed a decrease of protein in subcellular fraction, including the mitochondrial fraction. The role of the inhibition respiratory characteristics by cyclosporine in nephrotoxicity in vivo must take account of these two parameters: inhibition of the respiratory characteristics measured in vitro and diminution of mitochondrial protein in cyclosporine-treated rats.     

31P-NMR studies on phospholipid structure in membranes of intact,functionally-active,rat liver mitochondria

³¹P-NMR studies of intact functional rat liver mitochondria at 37°C demonstrate that the large majority (?95%) of endogenous phospholipids exhibit motional properties consistent with bilayer structure. This property is unaffected by oxidative phosphorylation processes or the presence of Ca²⁺.     

Comparison of phospholipid effects on insulin-sensitive low Km cyclic AMP phosphodiesterase in adipocyte plasma membranes and microsomes

Both adipocyte plasma membranes and microsomes possess insulin-sensitive low K_m cyclic AMP phosphodiesterase activity. The activity of the enzyme from both sources was susceptible to activation by several anionic phospholipids. Activators of the plasma membrane enzyme were lysophosphatidylglycerol > lysophosphatidylcholine > lysophosphatidylserine > phosphatidylserine > phosphatidylglycerol. These same phospholipids activated the microsomal enzyme but the extent of activation by each phospholipid was reversed. Neutral phospholipids and other anionic phospholipids were without effect. The phospholipids had no effect on high K_m cAMP phosphodiesterase in either membrane. The results suggest that the phospholipid headgroup was an important determinant for enzyme activation by phospholipid. The increased susceptibility of the plasma membrane enzyme to lysophospholipid may be attributed to a difference in the plasma membrane enzyme compared to the microsomal membrane enzyme or to differences in plasma membrane and microsomal membrane phospholipid composition and their ability to regulate low K_m cAMP phosphodiesterase activity.     

Lanthanum stimulates the accumulation of cyclic AMP and inhibits secretion and thromboxane B2 formation in human platelets

La³⁺ was found to inhibit the secretion of 5-hydroxytryptamine and the production of thromboxane B₂ by washed platelets exposed to collagen or thrombin. In addition, La³⁺ inhibited secretion in response to sodium arachidonate, although the conversion of arachidonate to thromboxane B₂ was not affected.La³⁺ was also found to enhance the accumulation of cyclic AMP under basal conditions and in response to prostaglandin E₁, in washed platelets. The inhibition of cyclic AMP accumulation by ADP was prevented by La³⁺, suggesting that the effect of ADP on cyclic AMP metabolism was dependent upon the presence or flux of calcium at the platelet membrane.La³⁺ inhibited the activity of adenylate cyclase in platelet lysates both in response to prostaglandin E₁ and to F^?, indicating a possible effect at the catalytic subunit of the enzyme. None of the observed effects of La³⁺ could be reversed by the addition of Ca²⁺ up to 10 mM. The stimulation of cyclic AMP production by La³⁺ may largely explain the inhibitory effect of La³⁺ upon platelet secretion and thromboxane B₂ production. These results also suggest that Ca²⁺ localised at the platelet plasma membrane may be important in the regulation of cyclic AMP metabolism.     

Effect of ambient temperature on perinatal variations of cyclic AMP and cyclic GMP in rat brown adipose tissue

The level of cyclic AMP in the brown adipose tissue of perinatal rats was found to increase by the end of pregnancy and decrease during the first two days of life. It then increased in newborn rats maintained at either 28° or 16°. However, in the 16° group, the cAMP level remained high until the 21st day whereas, in the 28° group decreases were noted after the tenth day. These variations are discussed in regard to norepinephrine content and lipid metabolism in the tissue. Inverse variation of cAMP and cGMP levels were not observed during the period studied.     

Accumulation of inositol phosphates and cyclic AMP in guinea-pig cerebral cortical preparations: Effects of norepinephrine,histamine, carbamylcholine and 2-chloroadenosine

Norepinephrine and serotonin augment by about 2-fold the accumulation of cyclic [3H]AMP elicited by 2-chloroadenosine in [³H]adenine-labeled guinea-pig cerebral cortical slices. Histamine causes a 3-fold augmentation. The first two agents have no effect on cyclic AMP alone, while histamine has only a small effect alone. The augmentation of the 2-chloroadenosine response appears to be mediated by α₁-adrenergic, 5HT₂-serotonergic and H₂-histaminergic receptors. VIP-elicited accumulations of cyclic AMP are also augmented through stimulation of α₁-adrenergic, 5HT₂-serotonergic and H₁-histaminergic receptors. Activation of these amine receptors also increases the turnover of phosphatidylinositols in [³H]inositol-labeled guinea pig cerebral cortical slices. Norepinephrine causes a 5-fold, serotonin a 1.2-fold, and histamine a 2.5-fold increase in accumulations of [³H]inositol phosphates. 2-Chloroadenosine, vasoactive intestinal peptide, baclofen, and somatostatin have no effect on phosphatidylinositol turnover, nor do the last two agents augment accumulations of cyclic AMP elicited by 2-chloroadenosine. The data suggest a possible relationship between turnover of phosphatidylinositol and the augmentations of the cyclic AMP accumulations elicited by biogenic amines in brain slices.