Adenylate Cyclase In Homogenates Research Articles

In vitro effect of the racemic mixture and the (-)enantiomer of N-n-propyl-3-(3-hydroxyphenyl)-piperidine (3-PPP) on postsynaptic dopamine receptors and on a presynaptic dopamine autoreceptor.

The racemic mixture and the (-)enantiomer of the putative dopamine autoreceptor agonist 3-PPP were investigated in vitro using dopamine-sensitive adenylate cyclase in homogenates of rat striatum as a model for a postsynaptic D1-receptor type and inhibition of electrically-evoked tritium overflow from rat striatal slices preincubated with [3H]choline and [3H]dopamine as a model for a postsynaptic D2- and a presynaptic dopamine autoreceptor type, respectively. In contrast, to apomorphine, neither the racemic mixture nor the (-)enantiomer exerted any effect, suggesting agonistic properties in all three receptor models. However, both (+/-)3-PPP and (-)3-PPP were weak antagonists at postsynaptic D1- and D2-receptors. The results of the present investigation suggest that the in vivo effects of 3-PPP are either the result of metabolic activation or that this drug activates an other dopamine autoreceptor type, pharmacologically different from that one modulating dopamine release.

Adenylate cyclase sensitivity to catecholamines and forskolin in rat pia-arachnoid and cerebral microvessels

Adenylate cyclase in homogenates of perfused pia-arachnoid from the rat brain displayed a sensitivity for activation by dl'isoproterenol, l'epinephrine, l'norepinephrine (NE) and fenoterol that was greater than shown by partial beta 2 adrenergic agonists (metaproterenol and salbutamol), or partial beta 1 adrenergic agonists (tazolol and dobutamine) and an alpha adrenergic agonist (phenylephrine). The addition of the quanosine triphosphate (GTP) analog, Gpp(NH) p(5′-guanylyl imidodiphosphate) to the enzyme preparations resulted in an increased ability of all agents (except tazolol) to activate adenylate cyclase. The agent, forskolin, exerted a very potent activation of the catalytic site of adenylate cyclase in both pia-arachnoid and cerebral microvessels (capillary fraction). The order of potency for adrenergic antagonists to inhibit NE-induced stimulation of the pial enzyme was: propranolol (mixed beta) > butoxamine ( beta 2) > phentolamine ( alpha 1) > practolol ( beta 1). Subchronic injections of reserpine to rats resulted in a pial enzyme that was hyper-responsive to NE and isoproterenol. Similarly, the capillary enzyme displayed an enhanced activity to NE and dopamine (DA). Both high and low K m forms of cyclic AMP (cAMP) phosphodiesterase were detected in developing and adult pia-arachnoid and capillaries. The addition of a calmodulin fraction plus calcium ions did not elicit activation of the high K m enzyme. Moreover, adenylate cyclase during development was sensitive to activation by NE and forskolin. Thus, the pia-arachnoid possesses an adenylate cyclase receptor-coupled system with a mixed response to catecholamines but which is primarily beta 2 in nature. In addition, this system, as well as the capillaries, possesses a capacity to respond to manipulation of monoamine levels.

Demonstration of adenylate cyclase coupled adenosine receptors in guinea pig ventricular membranes

Adenylate cyclase in homogenates of guinea pig ventricles was inhibited by the stable adenosine analogs N 6-phenylisopropyl-adenosine (PIA) and 5′-N-ethylcarboxamidoadenosine (NECA). Inhibition required GTP and was enhanced by sodium ion. The maximum inhibition observed was 35.1±1.1%, the EC50 (95% confidence limits,n) for PIA and NECA were 0.20μM (0.17–0.25μM, 6) and 0.66 μM (0.26–1.7 μM, 4) respectively. 8-Phenyltheophylline (10 and 100 μM) and isobutylmethylxanthine (100 μM) antagonized the inhibitory effects of the adenosine analogs. These results indicate that adenosine receptors of the inhibitory type (R I or A 1) are present in guinea pig myocardium and may mediate some of the cardiac responses to adenosine.

Specific Muscarinic‐Cholinergic Desensitization in the Neuroblastoma‐Glioma Hybrid NG108‐15

The cholinergic agonist carbachol, epinephrine, and the opiate morphine all inhibit prostaglandin E1 (PGE1)-stimulated adenylate cyclase in homogenates from the neuroblastoma-glioma hybrid NG108-15. Pretreatment of the hybrid with 100 microM carbachol resulted in the rapid loss (desensitization) of the carbachol inhibition of adenylate cyclase (t1/2 less than 3 min). The desensitization of the carbachol inhibition was blocked by 0.1 microM atropine. Pretreatment with carbachol (1-24 h) did not significantly affect the inhibition of adenylate cyclase by either epinephrine or morphine, nor did it alter the PGE1-stimulated activity, that is, no supersensitization was observed. Cholate extracts of the particulate fraction from either carbachol-desensitized or of control NG108-15 were able to reconstitute adenylate cyclase activities of the coupling proteins (G/F)-deficient cyc- lymphoma cell membranes with equal efficacy. These results suggested that the coupling proteins of the adenylate cyclase were not altered by the carbachol pretreatment and that desensitization occurs at the receptor or at a receptor-associated level. However, the possibility remained that specific domains of the G/F, which interact only with muscarinic receptors, were altered.

Adrenergic stimulation of isolated rat gastric mucosal cells. Effect on adenylate cyclase and 14C-aminopyrine uptake.

Adrenergic stimulation of the adenylate cyclase (AC)-cAMP-system and 14C-aminopyrine accumulation, an indirect measure of parietal cell H+-production, was studied in a different preparations of gastric mucosal cells. The beta 2-adrenoceptor agonist hexoprenaline activated AC of crude homogenates from the gastric corpus of mouse, rat, guinea-pig, hog, dog and man. In isolated rat gastric cells (20% parietal cells), treated by low power sonication, 10(-8) to 10(-3) mol/l adrenaline and hexoprenaline activated AC equally potently and efficaciously by maximally 170%. Isoprenaline proved to be less effective activating up to 80%. 5.10(-5) mol/l GMP-PNP augmented basal activity 8.5 times and reduced the maximal efficacy. Adrenaline and hexoprenaline activated AC by maximally 120%, isoprenaline by 40%. The potency of adrenaline was 4 times lower, that of hexoprenaline 2 and that of isoprenaline 4 times higher in the presence of GMP-PNP. Adrenergic stimulation was inhibited by the beta-adrenoceptor antagonist propranolol, the effect of alpha-adrenoceptor-blockade by phenoxybenzamine was less pronounced. In fractions with 7-80% of parietal cells, prepared by isopycnic centrifugation with Percoll, adrenaline and hexoprenaline activated AC or hexoprenaline enhanced the cellular levels of cAMP in parietal cell poor and rich fractions. The degree of activation in response to histamine correlated with the number of parietal cells. 14C-Aminopyrine uptake was increasingly stimulated through 10(-8) to 10(-5) mol/l hexoprenaline, maximally by doubling the basal accumulation. 10(-4) mol/l histamine was 8 times more effective. 3.10(-7) mol/l propranolol inhibited the effect of 10(-5) mol/l hexoprenaline by 80%. The data suggest the localization of beta-adrenoceptors (likely beta 2-adrenoceptors) on parietal and other nonidentified gastric cells. At the parietal cell, adrenaline and hexoprenaline initiate activation of AC and hexoprenaline leads to H+-production. The responses are small compared to the effect of histamine. Thus, beta-adrenoceptor agonists exert intrinsic activity in relation to H+-production. Their influence on stimulated secretion of isolated cells remains to be elucidated.

Assay of adenylate cyclase in homogenates of control and Duchenne human skeletal muscle

The wide range of values reported for activity of adenylate cyclase (AC) in human skeletal muscle prompted re-evaluation of conditions used for homogenization and assay. Adenylate cyclase activity in the same normal muscle differed with different techniques of homogenization. In pH 7.5 isotonic Tris buffer, basal and catecholamine-activated activities declined rapidly in homogenates kept at 4°C. Loss of basal activity was prevented by addition of a chelator of divalent cations. Loss of response to isoproterenol was prevented by addition of guanylnucleotides. Enzyme activity was maximal at 37°C and pH 7.6. Enzyme activity was lower when theophylline was used to prevent degradation of labelled 3',5' cyclic adenosine monophosphate (cyclic AMP) than when unlabelled cyclic AMP was used to this purpose. Basal activity increased with increased MgCl 2 concentration up to 50 mmol/l, but isoproterenol-activated activity was maximal at 4 mmol/l MgCl 2. AC was inhibited by exogenous adenosine, but addition of adenosine deaminase to the assay mixture did not increase AC activity. Based upon these observations, standardized procedures of homogenization and assay were devised and used to measure AC activity in muscles of boys with Duchenne muscular dystrophy: basal and isoproterenol-stimulated activities were abnormally low.

Opioids, noradrenaline and GTP analogs inhibit cholera toxin activated adenylate cyclase in neuroblastoma x glioma hybrid cells.

D-Ala2-Met5-enkephalin, morphine, and noradrenaline inhibit the adenylate cyclase in homogenates of neuroblastoma x glioma hybrid cells in a dose-dependent manner even after the enzyme has been preactivated by cholera toxin. Half-maximal inhibition and extent of inhibition are the same with native or cholera toxin-activated enzyme. The inhibition caused by opioids or noradrenaline are antagonized by naloxone or phentolamine, respectively. The effect of D-Ala2-Met5-enkephalin on cholera toxin-activated enzyme is immediate in onset and rapidly reversed by the addition of naloxone. Guanyl-5'-yl-imidodiphosphate stimulates basal activity but inhibits the enzyme activated by cholera toxin or prostaglandin E1. Stimulation occurs at a concentration of 100 microM or above, inhibition even at 0.1 microM. The inhibitory effect of the non-hydrolysable GTP analog is antagonized by GTP. Guanyl-5'-yl-methylenediphosphonate, another nonhydrolysable GTP analog, inhibits basal as well as cholera toxin-stimulated or prostaglandin E1-stimulated adenylate cyclase. Other guanine derivatives such as GDP, GMP, cyclic GMP, guanyl-5'-yl-phosphoric acid amide and guanosine have no effect under the same conditions. The results may be taken as a piece of evidence for two separate guanyl nucleotide-binding sites accompanying the adenylate cyclase in the hybrid cells and mediating, respectively, stimulation and inhibition of the enzyme by hormones.

Dopaminergic mechanisms in the teleost retina. I. Dopamine-sensitive adenylate cyclase in homogenates of carp retina; effects of agonists, antagonists, and ergots.

A specific dopamine-sensitive adenylate cyclase has been identified in homogenates of the teleost (carp) retina. Maximal stimulation by 100 microM-dopamine resulted in a 5--10-fold increase in adenylate cyclase activity with half-maximal stimulation occurring at a concentration of 1 microM. l-Noradrenaline and l-adrenaline were some 10 times less potent than dopamine whilst the alpha- and beta-adrenoreceptor agonists, l-phenylephrine and dl-isoprenaline were inactive. Apomorphine elicited a partial stimulation of adenylate cyclase activity whilst various ergot alkaloids produced mixed agonist/antagonist responses. Dopamine-stimulated adenylate cyclase activity was potently antagonised by various neuroleptic drugs including fluphenazine, alpha-flupenthixol and alpha-piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone. The benzamide derivatives, metoclopramide and sulpiride, together with the alpha- and beta-adrenoreceptor blocking agents, phentolamine and propranolol respectively were essentially inactive at blocking dopamine-stimulated adenylate cyclase activity. These data suggest the presence of a highly specific dopamine-sensitive adenylate cyclase in homogenates of teleost retina possessing similar pharmacological properties to the dopamine-sensitive adenylate cyclase observed in the mammalian central nervous system.

Control of opiate receptor-adenylate cyclase interactions by calcium ions and guanosine-5′-triphosphate

Adenylate cyclase of homogenates of NG108-15 neuroblastoma × glioma hybrid cells is activated by low concentrations of Ca 2+ ions and is inhibited by higher ( 0.1mM) concentrations of Ca 2+ ions. Activation of either opiate receptors by 10 μM morphine or α-adrenergic receptors by 10 μM norepinephrine inhibits adenylate cyclase by 55% in the absence of Ca 2+ ions, and inhibits the Ca 2+-dependent activation of adenylate cyclase by more than 90%. Concentrations of Ca 2+ ions 0.1mM inhibit adenylate cyclase and also reduce the extent inhibition of adenylate cyclase by morphine but not by norepinephrine. Guanosine-5′-triphosphate (0.1–1 μM) is required for inhibition of adenylate cyclase by morphine. The results show that morphine inhibits adenylate cyclase by a guanosine-5′-triphosphate-dependent process and that the extent of inhibition of adenylate cyclase by morphine or norepinephrine is a function of the Ca 2+ ion concentration and the proportion of adenylate cyclase molecules that are activated or inhibited by Ca 2+ ions.

Localization of dopamine-sensitive adenylate cyclase within the rat olfactory tubercle

There are three histological layers within the rat olfactory tubercle: plexiform, pyramidal, and polymorphic. We have assayed dopamine-sensitive adenylate cyclase in homogenates of frozen sections cut parallel to these layers. Consecutive sections (16 micrometer) were homogenized in groups of 6. Every seventh section was stained with toluidine blue to monitor the depth and orientation of the plane of section. I report the laminar distribution of dopamine-sensitive adenylate cyclase at two locations within the tubercle where the local topographies are quite different from one another. In the caudomedial tubercle where the parallel alignment of the neuronal layers is clearest, there is a marked gradient in the activity of dopamine-sensitive adenylate cyclase. Its distribution corresponds very closely to the distribution of pyramidal cell bodies and their dendrites in this region of the olfactory tubercle.

Dopamine receptor topography: Characterization of antagonist requirements of striatal dopamine-sensitive adenylate cyclase using protoberberine alkaloids

Representative protoberberine-related alkaloids, i.e. tetrahydroprotoberberines (THPB), quaternary protoberberine salts (Quat. PB) and quaternary dehydroprotoberberine salts (Dehyd. Quat. PB), have been used to characterize the geometric and stereospecific requirements of antagonists of the dopamine receptor. The optical isomers of 2, 3, 10, 11-THPB were tested for their ability to antagonize dopamine stimulated adenylate cyclase activity. The results indicate that (±)-2. 3, 10, 11-THPB inhibited the ability of 100 μM dopamine to elevate adenylate cyclase in homogenates of the rat caudate nucleus. The ic 50 was observed to be 6 μM. The S-(−)-isomer of 2, 3, 10, 11-THPB was a more potent antagonist of dopaminesensitive adenylate cyclase activity than the R-(+)-isomer. The ic 50 for (−)-THPB was 1μM whereas that for the (+)-isomer was 50 μM. The data also show that the positional isomer, 2, 3, 9, 10-THPB, antagonized dopamine activation of adenylate cyclase with the same degree of potency as 2, 3, 10, 11-THPB. Exhaustive O-methylation of THPB at all four hydroxyl positions, the 2, 3-position of the “a” ring and the 10, 11-position of the “d” ring as in xylopinine or the 2, 3-position of the “a” ring and the 9, 10-position of the “d” ring as in tetrahydropalmatine, rendered these compounds weak antagonists of the dopamine response. Selective O-methylation of the THPB molecule markedly altered the potency of the resultant compounds as antagonists depending on the position of the O-methyl substitution. Overall, these data are consistent with the idea that the orientation of the nitrogen atom in a fixed ( cis: gauche) position 2 carbon atoms from a catechol nucleus renders antagonist properties to these compounds which interact with the dopamine receptor.

Dopamine-sensitive adenylate cyclase in homogenates of rat nucleus accumbens: Structure-activity studies and effects of agonists and antagonists

A study has been made of the structural requirements for activity on the dopamine-sensitive adenylate cyclase present in homogenates of rat nucleus accumbens. The only active phenylethylamine derivatives tested were those containing hydroxy groups at the 3 and 4 positions on the benzene ring, a two carbon side chain and a terminal nitrogen, either unsubstituted or containing a single methyl group. The α- and β-adrenergic agonists, phenylephrine and isoprenaline respectively, were both inactive. Norsalsolinol was a weak agonist producing only a 50% stimulation of adenylate cyclase activity. The typical neuroleptic drugs, fluphenazine and cis-flupenthixol were both potent antagonists of the dopamine response as opposed to the atypical neuroleptics, metoclopramide and sulpiride, and the α- and β-adrenergic blocking agents, phentolamine and propranolol respectively, which were all inactive. Our results indicate that the dopamine receptors associated with adenylate cyclase in the nucleus accumbens are similar to those in the corpus striatum.

Opioid peptides derived from food proteins. The exorphins

Peptides with opioid activity are found in pepsin hydrolysates of wheat gluten and alpha-casein. The opioid activity of these peptides was demonstrated by use of the following bioassays: 1) naloxone-reversible inhibition of adenylate cyclase in homogenates of neuroblastoma X-glioma hybrid cells; 2) naloxone-reversible inhibition of electrically stimulated contractions of the mouse vas deferens; 3) displacement of [3H]dihydromorphine and [3H-Tyr, dAla2]met-enkephalin amide from rat brain membranes. Substances which stimulate adenylate cyclase and increase the contractions of the mouse vas deferens but do not bind to opiate receptors are also isolated from gluten hydrolysates. It is suggested that peptides derived from some food proteins may be of physiological importance.

Posterior pituitary adenylate cyclase: stimulation by dopamine and other agents

The posterior lobe of the pituitary gland contains dopaminergic and noradrenergic terminalsS,6, t4 as well as moderate levels of dopamine (DA) and norepinephrine is. In addition, the presence of receptors for DA in sheep posterior pituitary was indicated by binding studies employing [3H]-dihydroergocriptineS although negligible specific binding of another ligand, [3H]spiroperidol, was reported in a study of calf posterior pituitaryL A number of studies have suggested that monoamines and their receptors may be involved in the control of secretion of neurohypophysial hormones such as antidiuretic hormones (ADH) and oxytocin. Thus, a variety of agents including norepinephrine, epinephrine, reserpine, morphine, lithium chloride and antipsychotic drugs (e.g., chlorpromazine, perphenazine) which exert direct or indirect effect on monoaminergic transmission 4 influence ADH and oxytocin releasO1,12,15. Further, DA levels and release in the arcuate-median eminence DA cell group whose axons terminate in the posterior pituitary, are known to change following experimental manipulations (e.g., dehydration, suckling) affecting secretion of ADH and oxytocin~0,20. The levels of cyclic AMP in the posterior lobe are markedly elevated following acute treatment with reserpine, an amine depleting agent ~a, suggesting the possible presence of amine receptors linked to adenylate cyclase in the posterior pituitary. Also under conditions which increase ADH secretion in vivo, cyclic AMP levels in posterior pituitary are elevated 17. We report here the ability of DA, DA agonists and other agents to stimulate adenylate cyclase activity and a partial pharmacologic characterization of DA-stimulated adenylate cyclase in homogenates of rat posterior pituitary. Young adult male Sprague-Dawley rats weighing 200-300 g were sacrificed by decapitation and the posterior lobes of the pituitary glands rapidly dissected. The procedure used did not include separation of the intermediate lobe, although this tissue would represent only a minor component based on its relative tissue mass. The

Interaction of LSD and other hallucinogens with dopamine-sensitive adenylate cyclase in primate brain: Regional differences

The influence of D-lysergic acid diethylamide (LSD) and mescaline on adenylate cyclase activity was studied in homogenates of Cebus and rhesus monkey anterior limbic cortex (ALC), frontal cortex (FC), caudate nucleus and retina. Previous studies have shown these tissues to contain dopamine-stimulated adenylate cyclase (AC). In addition, we are now reporting the presence of a dopamine-sensitive adenylate cyclase in the auditory cortex. AC of ALC and auditory cortex was stimulated by LSD and mescaline, whereas activity of FC, caudate nucleus and retina was not stimulated by the same agents. In contrast to regional specificity for stimulation, LSD was capable of antagonizing dopamine-stimulated activity in all brain regions examined. LSD and mescaline produced similar maximal stimulation (about 70%) of AC of ALC homogenates, but the EC 50 for LSD (0.43 μM) was about one-tenth that for mescaline (4.5 μM). Similar relative potencies were also observed for the auditory cortex enzyme. Although much weaker than LSD, methamphetamine also produced a dose-dependent stimulation of ALC AC. Both agonist and antagonist effects of the hallucinogens appear to involve interaction with dopamine receptors; LSD- or methamphetamine-stimulated activity in ALC was blocked by haloperidol and fluphenazine, which are dopamine antagonists, but not by phentolamine, an α-receptor blocker. Antagonism of dopamine by LSD in both ALC and FC was found to be competitive and mescaline was an effective but weaker antagonist than was LSD. In addition, neither histamine — nor Gpp(NH)p — stimulated activity of FC was inhibited by LSD. It is proposed that the occurrence of dopamine agonistic action of hallucinogens in only certain regions of primate brain may provide a basis for at least some of the behavioral effects of LSD, mescaline and methamphetamine in primates.

H 1- and H 2-histamine receptors linked to adenylate cyclase in cell-free preparations of guinea pig cerebral cortex

Homogenates of whole or selected portions of guinea pig cerebral cortex prelabeled with [ 2 - 3H]adenine, were used to study the role of H 1- and H 2-histamine receptors in the activation of adenylate cyclase. Both the H 1-agonist 2-methylhistamine and the H 2-agonist 4-methylhistamine stimulated adenylate cyclase in homogenates of whole cortex and to an even greater degree in homogenates of the hippocampal portion of cortex. The H 1-antagonist tripelennamine inhibited the activation of adenylate cyclase by 2-methylhistamine but was relatively inactive against 4-methylhistamine. Whole cortex was more sensitive than hippocampus to inhibition by tripelennamine. The H 2-antagonist metiamide was equipotent against activation by 2-methylhistamine and 4-methylhistamine. The antidepressant maprotiline had the characteristics of an H 1-antagonist. This is the first cell-free study to demonstrate H 1-receptor-linked adenylate cyclase in guinea pig cerebral cortex. The results provide further support for the involvement of H 1- as well as H 2-receptors in the activation of brain adenylate cyclase.

Stable cholinergic-muscarinic inhibition of rat parotid adenylate cyclase

1. Introduction There are numerous reports describing cY-adrener- gic and cholinergic inhibition of CAMP accumulation in various tissues [ l-101 . The rat parotid gland pro- vides an excellent model system for the elucidation of inter-receptor interactions. The stimulation of a-adrenergic, /3-adrenergic and cholinergic-muscarinic receptors has been well characterized pharmacol- ogically, biochemically and morphologically and has been integrated into an overall scheme in [ 11 ,121. Cholinergic-muscarinic and a-adrenergic inhibition of CAMP accumulation, stimulated by activation of /3-adrenergic receptors in the rat parotid has been reported [13-IS]. Recent data from our laboratory demonstrated a different mechanism of action for the cholinergic and cu-adrenergic effect and also indicated adenylate cyclase as the target enzyme [ 16,171 . In the present communication we report a stable inhibi- tion of parotid adenylate cyclase in homogenates and washed membrane preparations following the ex- posure of tissue slices to carbamylcholine. 2. Experimental methods Male Wistar rats (120-200 g) were used through- out. Rats were fasted overnight prior to sacrifice. The

The central effects of a novel dopamine agonist

A new peripheral dopamine agonist which causes dopaminergic renal vasolidation, was tested for central dopaminergic activity. SK & F 38393 stimulated the dopamine-sensitive adenylate cyclase in homogenates of rat caudate, as a partial agonist, and caused contralateral rotation in rats with unilateral 6-OHDA lesions of substantia nigra. Rotation was shown to be due to a direct effect on supersensitive dopamine receptors. Stimulation of cAMP formation and rotation were blocked by dopamine antagonists. In contrast to other dopamine agonists, SK & F 38393 did not cause stereotypy, emesis or inhibition of prolactin release, nor did SK & F 38393 affect dopamine turnover. The results suggest that SK & F 38393 may selectively stimulate supersensitive central dopamine receptors in vivo or may activate only a certain subclass of dopamine receptors including the receptor in the renal vasculature and the adenylate cyclase coupled postsynaptic receptor in the caudate.

5'guanylyl-imidodiphosphate actions on adenylate cyclase in homogenates of rat cerebral cortex plus neuronal and capillary fractions

A variety of neurohumoral agents activate adenylate cyclase in homogenates of rat frontal cortex (norepinephrine, isoproterenol, dopamine, apomorphine, histamine, 4-Me-histamine and prostaglandins E 1, E 2 and A 2). The enzyme in homogenates of isolated cortical neurons is likewise sensitive to norepinephrine, isoproterenol, dopamine, apomorphine, histamine, 2-Me- and 4-Me-histamine, and prostaglandin F 2α. Capillary-enriched fractions from the cortex possess an enzyme that is activated by norepinephrine, isoproterenol and dopamine. Addition of 5′-guanylyl-imidodiphosphate (Gpp(NH)p) to the cortical homogenates and neuronal fractions resulted in enhanced enzyme responses to norepinephrine, isoproterenol, dopamine, 2-Me- and 4-Me-histamine and the prostaglandins E 1 and E 2. The actions of histamine and apomorphine were not increased by the GTP analog. The sensitivity of the catecholamine-induced adenylate cyclase activation in cortical capillaries was augmented by Gpp(NH)p. Thus various cellular types within the cerebral cortex may possess different receptor characteristics with respect to stimulation of adenylate cyclase by neurohormones.

Actions in vitro and in vivo of chlorpromazine and haloperidol on cyclic nucleotide systems in mouse cerebral cortex and cerebellum

Three different procedures were utilized to study the action of chlorpromazine (CPZ) and haloperidol on adenylate cyclase-cyclic nucleotide systems in the mouse cerebral cortex and cerebellum. Using incubated tissue slices which in both tissues demonstrate an activation of adenylate cyclase by norepinephrine (NE), CPZ was found to be more effective than haloperidol in reducing this response. With the second method it was shown that adenylate cyclase in homogenates was stimulated in both tissues by NE while dopamine (DA) was active in only the cerebral cortex. With this broken cellular preparation, CPZ exerted greater antagonism than haloperidol on both the NE- and DA-sensitive enzymes. Moreover, the DA-responsive enzymes were blocked by both agents to a greater extent than was observed with the NE-induced stimulation. In the third experiment haloperidol and three doses of CPZ were injected into mice in vivo, at specified intervals; thereafter the tissues were rapidly inactivated by focused microwave irradiation (0.5 sec), and cyclic AMP and cyclic GMP levels were subsequently determined. In general, the acute injections ( 1 2 –8 hr) of CPZ and haloperidol diminished the steady-state levels of the two nucleotides. Subchronic administration (24–48 hr) usually resulted in elevated cyclic AMP amounts. The data indicate that under both in vitro and in vivo conditions, neuroleptics inhibit neurohumorally-induced activation of adenylate cyclase. Subchronic injections, however, suggest other factors become prominent i.e. inhibition of phosphodiesterase or enhanced receptor sensitivity.