A MODULATING ROLE OF PITUITARY-ADRENAL AXIS IN CEREBRAL METABOLISM OF ADENOSINE 3'',5''-MONOPHOSPHATE

Abstract— The effect of adrenalectomy or hypophysectomy on the metabolism of adenosine 3',5'-monophosphate (cyclic AMP) in the cerebral cortex of male Wistar rats was investigated.
The bilateral removal of adrenal glands reduced significantly the activity of cerebral adenylate cyclase [EC 4.6.1.1]. whereas that of cyclic 3'.5'-nucleotide phosphodiesterase [EC 3.1.4.17] remained unchanged. The formation of cyclic AMP measured in cerebral cortical slices from adrenalectomized or hypophysectomized rats was also diminished. Decreases in the activity of adenylate cyclase and formation of cyclic AMP following adrenalectomy were antagonized by in vivo administration of dexamethasone or aldosterone, while those observed in hypophysectomized rats were restored by ACTH or dexamethasone. It is suggested that the pituitary adrenal axis has a modulating role in the metabolism of cerebral cyclic AMP, possibly by changing adenylate cyclase activity.     

Evidence for a defect in the number of β-adrenergic receptors and in the adenylate cyclase responsiveness to guanine nucleotides in fat cells after adrenalectomy

Receptor binding studies (?)-[³H]dihydroalprenolol as the ligand revealed, in adrenalectomized rat fat cells, a 50% decrease in the number of β-adrenergic receptors. er cell with no change in the receptor affinity for this ligand. Adrenalectomy caused no change in the binding affinity for isoproterenol of both high affinity and low affinity populations of the β-adrenergic receptors. Guanine nucleotide sensitivity of the agonist binding to β-receptors was also unaltered by adrenalectomy. Adrenalectomy caused a 30–40% decrease in the maximal response of adenylate cyclase to (?)-isoproterenol only when guanine nucleotides were present in the assay, without altering the (?)-isoproterenol concentration giving half-maximal adenylate cyclase stimulation (K_act values). The maximal response of adenylate cyclase to Gpp(NH)p also was lower in adrenalectomized membranes, indicating a defect at the guanine nucleotide regulatory site. Removal of adenosine by addition of adenosine deaminase failed to reverse the decreased adenylate cyclase response to isoproterenol in adrenalectomized rats. However, in intact fat cells, in which cyclic AMP accumulation in response to isoproterenol was decreased by adrenalectomy, removal of adenosine almost completely corrected this defect. These results indicate that the observed changes in the number of β-adrenergic receptors and in the ability of guanine nucleotides to stimulate adenylate cyclase, though explaining the decreased adenylate cyclase responsiveness to catecholamines, do probably not contribute significantly to the mechanism by which adrenalectomy decreases the lipolytic responsiveness of adipocyte to catecholamines. In addition, this study also suggests that the increased sensitivity to adenosine of lipolysis reported in adipocytes from adrenalectomized rats may result from an action of adenosine at a post-adenylate cyclase step, possibly on the cyclic AMP phosphodiesterase.     

Adipocyte G-proteins and adenylate cyclase. Effects of adrenalectomy.

Steroid hormones modulate the ability of cells to respond to hormones that act via cyclic AMP. In adipocytes of adrenalectomized rats, cyclic AMP accumulation and lipolysis in response to adrenaline are attenuated. However, the mechanism(s) of these effects are poorly understood. The effects of altered glucocorticoid status in vivo on the steady-state amounts of components of the hormone-sensitive adenylate cyclase were analysed in rat adipocytes. beta-Adrenergic receptors were analysed by using radioligand binding and immunoblotting with an anti-receptor antiserum. Neither the amount of radioligand binding nor the amount of beta-adrenergic-receptor peptide (Mr 67,000) was altered by adrenalectomy, whereas treatment of adrenalectomized rats with dexamethasone was found to increase both parameters by more than 25% with respect to the control. Forskolin-stimulated adenylated cyclase activity was unchanged in membranes isolated from adipocytes of adrenalectomized rats, but was decreased (50%) in those from dexamethasone-treated rats. The alpha-subunit of Gs was probed by using cholera-toxin-catalysed ADP-ribosylation. Immunoblotting was used to analyse the steady-state amounts of G-protein beta-subunits (beta-G35/36). Adrenalectomy was associated with decreases in the steady-state amounts of alpha-Gs (30%) and beta-G35/36 (50%). Dexamethasone treatment of adrenalectomized animals partially restored the lipolytic response of adipocytes to adrenaline and the amounts of alpha-Gs, increased the amounts of beta-G35/36 subunits from 50% to 150% of control values, increased beta-adrenergic receptors by more than 25% and decreased adenylate cyclase activity (50%). These results suggest that the steady-state amounts of components of hormone-sensitive adenylate cyclase are differentially regulated by glucocorticoids.     

The role of glucocorticoids in the regulation of the diurnal rhythm of hepatic beta-hydroxy-beta-methylglutaryl-coenzyme A reductase and cholesterol 7 alpha-hydroxylase.

The microsomal activities of the hepatic enzymes hydroxymethylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase exhibit a diurnal rhythm with maximum activities observed during the dark period and minimum activities around noon (12:00h). This diurnal rhythm was maintained for both enzymes after adrenalectomy, but the amplitude of variation for the activity of both enzymes was greatly decreased. A single injection of cortisol administered to adrenalectomized rats 3h before the expected maximum in enzyme activity resulted in a twofold increase in the activity of both enzymes 3h later, at values similar to those observed for control rats killed at the same time. This response appeared to require protein synthesis, since it was blocked by actinomycin D. However, the administration of cortisol to adrenalectomized rats 3 h before the expected minimum did not result in significant change in the activity of hydroxymethylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase 3 h later. Kinetic studies of cholic acid metabolism in vivo demonstrated that adrenalectomy results in a significant decrease in the rate of synthesis of cholic acid and a considerable decrease in the pool size of cholic acid and its metabolic products. Treatment of adrenalectomized rats with cortisol increased the rate oonsistent with the effects of adrenalectomy and cortisol treatment on the activity of cholesterol 7alpha-hydroxylase.     

Does glucocorticoid deprivation promote the expression of adenosine receptor-sites stimulating adenylate cyclase in rat adipocyte membranes?

The influence of N⁶-phenylisopropyladenosine (PIA) on adenylate cyclase was compared in adipocyte membranes from adrenalectomized and sham operated rats. In the presence of 100 mM sodium, 10 μM GTP and adenosine deaminase, PIA inhibited basal adenylate cyclase activity in sham rats, but elicited biphasic effects in adrenalectomized rats: at concentrations up to 10 nM, PIA first stimulated the enzyme, after which higher concentrations produced inhibition. In the presence of theophylline, these biphasic effects could not be observed. When isoproterenol maximally-stimulated adenylate cyclase was studied, the same biphasic effects of PIA were also observed in adrenalectomized rats, provided that no sodium was added in the assay, since with 100 mM sodium, only inhibition was seen. Finally, the stimulatory but not the inhibitory effect of PIA was prevented by glucocorticoid administration, a phenomenon which suggests that glucocorticoid deprivation may promote the expression of adenosine receptorsites which activate adenylate cyclase and which are normally absent, cryptic or unfunctional in normal adipocytes.     

Studies on the mechanism of the decreased guanine nucleotide stimulatory effects on adenylate cyclase after adrenalectomy in rat adipocytes

In adipocyte membranes from adrenalectomized rats: (i) the defect in the stimulatory effects of guanine nucleotides on adenylate cyclase is greater with GTP than with GppNHp and appears to concern the GS-C complex and not the HR-GS-C ternary complex; (ii) the GTP-ase activity is enhanced; (iii) maximal alpha S-C interaction (tested by the responses to forskolin, cholera toxin or NaF) is unaltered and (iv) the alpha S affinity for guanine nucleotides and the GDP/GppNHp exchange reaction are both unimpaired. These data suggest that the enhanced GTP-ase activity together with a decrease in the catalytic activity of the alpha S-GTP-C complex are the likely mechanisms whereby adrenalectomy causes a defect in the fat cell adenylate cyclase response to guanine nucleotides.     

Effects of adrenalectomy on CRH regulation of ACTH release: adenylate cyclase activity, cyclic AMP-dependent protein kinase activity and ACTH release

Corticotropin releasing hormone (CRH) stimulation of ACTH release and cyclic AMP-mediated events involved in the control of ACTH release were compared in sham-operated and adrenalectomized rats. CRH-stimulated adenylate cyclase activity was decreased in pituitary homogenates from adrenalectomized animals. CRH-stimulated cyclic AMP accumulation was essentially abolished and CRH-stimulated cyclic AMP-dependent protein kinase (A-kinase) activity was decreased in freshly prepared anterior pituitary cells from adrenalectomized animals. Basal and CRH-stimulated ACTH release was elevated in these cells. Since ACTH release is increased in adrenalectomized rats despite the down regulation of CRH-linked pituitary mechanisms, we speculate that the site of action of disinhibition by corticosterone of ACTH release (or synthesis) following adrenalectomy is distal to the generation of cyclic AMP and/or that non-CRH mediated mechanisms assume a greater role in ACTH regulation following adrenalectomy.     

Endocrine control of cytosolic factors stimulating adenylate cyclase in rat lung

Endocrine control of cytoplasmic factors modulating adenylate cyclase activity in rat lung membranes was investigated. Hypophysectomy, adrenalectomy and thyroidectomy showed an adverse effect on the body and organ weights. Lung protein, glycogen and DNA contents were decreased in the endocrine ablated animals which were restored to the normal values on hormone treatment. Phosphodiesterase and phosphorylase activities were increased and decreased in adrenalectomized and thyroidectomized animals, respectively. The activities of these enzymes were restored to normal values on hormone treatment. Adrenalectomy and thyroidectomy affected ATPases differently. Basal adenylate cyclase activity in rat lung membranes was not affected by adrenalectomy and hormone treatment. However, the total enzyme activity was increased by both dexamethasone (DEX) and thyroxine (T4) treatments. The activation of the particulate adenylate cyclase by the cytoplasmic factors was markedly decreased in the lung from hypophysectomized, adrenalectomized and thyroidectomized rats. This decrease in the cytoplasmic activation of adenylate cyclase was restored to or above the control values on hormone treatment. Alteration in the activation of enzyme by cytoplasmic factors did not appear to be due to the change in the responsiveness of the enzyme. Glucocorticoids appeared to have a specific effect on the cytoplasmic factors modulating the enzyme.     

The effect of glucocorticoids on adipocyte corticotropin receptors and adipocyte responses

A specific and sensitive assay for determining the binding of adrenocorticotropin (ACTH) to isolated rat adipocytes has been developed and utilized to study the effect of glucocorticoids on ACTH receptor. Measurement of the binding of tritiated ACTH (spec. act. 90 Ci/mmol) to adipocytes isolated from normal, adrenalectomized, and adrenalectomized dexamethasone-treated rats indicated that there are no differences among these three populations in either the magnitude or the affinity of the binding reaction. The binding interaction was found to be of high affinity (K_d = 5.23 + 1.92 · 10^?9 M) and paralleled closely the stimulation of lipolysis (K_m = 2.09 ± 0.35 · 10^?9 M). About 16 300 receptors were calculated to be present per adipocyte. Hormone-induced cyclic 3′,5′-adenosine monophosphate production remained intact after adrenalectomy, thereby confirming that receptors are not lost during steroid deprivation. The lipolytic response did, however, become less sensitive to both ACTH and epinephrine following adrenalectomy. Pre-treatment of adrenalectomized rats with dexamethasone resulted in an increase in basal and hormone-stimulated levels of cyclic AMP and glycerol production to super-normal values. In adipocyte ghost preparations, ACTH and epinephrine sensitive adenylate cyclase activity was not decreased by adrenalectomy and dexamethasone administration did not result in a selective enhancement of ACTH sensitive adenylate cyclase activity. Our results indicate that glucocorticoids do not cause their permissive effects by specific regulation of the ACTH receptor on the adipocyte.     

Dimethylnitrosamine inhibits the glucagon-stimulated adenylate cyclase activity of rat liver plasma membranes and decreases plasma membrane fluidity

The effect of the hepatocarcinogen dimethylnitrosamine on rat liver plasma membrane adenylate cyclase activity and lipid fluidity was assessed. Glucagon-stimulated adenylate cyclase activity exhibited a complex response to increasing concentrations of dimethylnitrosamine, whereas fluoride-stimulated adenylate cyclase activity was progressively inhibited. Maximal inhibitory effects were observed at a concentration of 15 mM in both cases. The activity of detergent-solubilized adenylate cyclase was unaffected by dimethylnitrosamine. ESR analysis using a fatty acid spin probe showed that dimethylnitrosamine produced a marked, dose-dependent reduction in the fluidity of the plasma membrane with a maximal effect occurring at 20 mM. Dimethylnitrosamine also elevated the temperature at which the lipid phase separation occurred in rat liver plasma membranes, from 28 degrees C to 31 degrees C. The non-carcinogenic but structurally similar compound, dimethylamine hydrochloride neither inhibited adenylate cyclase nor decreased plasma membrane fluidity. It is suggested that the decrease in membrane fluidity, induced by dimethylnitrosamine, via its effects on membrane fluidity, could influence plasma membrane function and cellular regulation.     

Biochemical evidence for PGI2 and PGE2 receptors in the rabbit renal preglomerular microvasculature

It has been proposed that a portion of the biologic actions of vasodilator prostaglandins occurs via an interaction with specific adenylate cyclase-linked receptors. This hypothesis was explored further in the renal microvasculature by examining the effects of PGI2, PGE1, and PGE2 on rabbit preglomerular microvascular adenylate cyclase. A membrane preparation derived from freshly isolated rabbit renal preglomerular microvessels was used in these studies. NaF, forskolin, or 5'-guanylyl imidodiphosphate were found to be effective in increasing adenylate cyclase activity in the absence of exogenous guanosine-5'-triphosphate. A dose-dependent stimulation of adenylate cyclase was also observed with guanosine-5'-triphosphate. PGE1, PGE2, and PGI2 produced a dose-dependent stimulation of adenylate cyclase activity only in the presence of guanosine-5'-triphosphate suggesting that this nucleotide is essential for prostaglandin-induced stimulation of the enzyme. PGI2 exhibited a time-dependent increase in adenylate cyclase activity and this increased activity reached a plateau at 20-25 min. When PGE1 and PGE2 were added together, no additive effect on adenylate cyclase stimulation was noted whereas PGI2 and PGE2 when added together produced an additive stimulatory effect. When viewed together, these data suggest the presence of separate PGI2 and PGE adenylate cyclase-linked receptors in rabbit renal preglomerular microvessels. These findings also suggest that in the renal microvasculature, cyclic AMP may be a second messenger mediating the vasodilatory effects of both PGI2 and PGE2.     

Acidic phospholipid species inhibit adenylate cyclase activity in rat liver plasma membranes.

Incubation of rat liver plasma membranes with liposomes of dioleoyl phosphatidic acid (dioleoyl-PA) led to an inhibition of adenylate cyclase activity which was more pronounced when fluoride-stimulated activity was followed than when glucagon-stimulated activity was followed. If Mn2+ (5 mM) replaced low (5 mM) [Mg2+] in adenylate cyclase assays, or if high (20 mM) [Mg2+] were employed, then the perceived inhibitory effect of phosphatidic acid was markedly reduced when the fluoride-stimulated activity was followed but was enhanced for the glucagon-stimulated activity. The inhibition of adenylate cyclase activity observed correlated with the association of dioleoyl-PA with the plasma membranes. Adenylate cyclase activity in dioleoyl-PA-treated membranes, however, responded differently to changes in [Mg2+] than did the enzyme in native liver plasma membranes. Benzyl alcohol, which increases membrane fluidity, had similar stimulatory effects on the fluoride- and glucagon-stimulated adenylate cyclase activities in both native and dioleoyl-PA-treated membranes. Incubation of the plasma membranes with phosphatidylserine also led to similar inhibitory effects on adenylate cyclase and responses to Mg2+. Arrhenius plots of both glucagon- and fluoride-stimulated adenylate cyclase activity were different in dioleoyl-PA-treated plasma membranes, compared with native membranes, with a new 'break' occurring at around 16 degrees C, indicating that dioleoyl-PA had become incorporated into the bilayer. E.s.r. analysis of dioleoyl-PA-treated plasma membranes with a nitroxide-labelled fatty acid spin probe identified a new lipid phase separation occurring at around 16 degrees C with also a lipid phase separation occurring at around 28 degrees C as in native liver plasma membranes. It is suggested that acidic phospholipids inhibit adenylate cyclase by virtue of a direct headgroup specific interaction and that this perturbation may be centred at the level of regulation of this enzyme by the stimulatory guanine nucleotide regulatory protein NS.     

Response of white adipocyte of mouse and rabbit to catecholamines and ACTH

The isolated intact white adipocyte of the Swiss mouse responds to both ACTH and catecholamines by an elevation of cAMP levels and an increase in lipolysis. However, in the isolated plasma membrane of the mouse adipocyte, adenylate cyclase loses its responsiveness to ACTH but retains its ability to respond to catecholamines. This lack of responsiveness to ACTH by adenylate cyclase of mouse adipocyte plasma membrane can be overcome, at least partially, by addition of GPP (NH)p, an analog of GTP, to the assay medium. The data on mouse adipocyte membrane suggests that the coupling of ACTH receptor to adenylate cyclase is dependent on GTP and that catecholamine-activation of adenylate cyclase is less dependent on this nucleotide. The isolated intact white adipocyte of adult New Zealand rabbit responds to ACTH, but does not (or only weakly) respond to catecholamines. In contrast to the mouse plasma membrane preparation, adenylate cyclase of adipocyte membrane of the rabbit responds to ACTH. And the addition of GPP(NH)P is not required to demonstrate the CTH: sensitive adenylate cyclase activity. The difference between mouse and rabbit adipocyte membrane in the requirement for GPP(NH)P in ACTH action is not readily explained. The lack of catecholamine sensitivity of rabbit membrane enzyme cannot be reversed by addition of GPP(NH)P or adenosine deaminase. These two adenylate cyclase model systems using mouse and rabbit adipocyte plasma membrane may be useful tools for the study of the specificity and mechanism of action of lipolytic hormones such as ACTH and catecholamines.     

Effect of andrenalectomy on cyclic 3',5'-guanosine monophosphate metabolism of rat liver and other tissues

Adrenalectomy increased guanyl cyclase and cyclic GMP phosphodiesterase activities in liver and other rat tissues. Liver guanyl cyclase activities from adrenalectomized rats were increased above those of normal controls according to kinetic analysis, gel filtration, ion-exchange chromatography, discontinuous sucrose gradient fractionation, sulfhydryl inhibition, and secretin activation. The effects of adrenal insufficiency on hepatic guanyl cyclase and cyclic GMP phosphodiesterase were prevented by cortisone acetate administration. Immunoassay of liver and skeletal muscle cyclic GMP after adrenalectomy showed markedly decreased levels in liver, but increased levels in skeletal muscle. In liver and other tissues, basal adenyl cyclase and cyclic AMP phosphodiesterase activities were unaffected by adrenalectomy. Hepatic levels of cyclic AMP were also unchanged by adrenalectomy. Hypophysectomy raised guanyl cyclase activity in liver but had no effect on liver cyclic GMP phosphodiesterase activity. These alterations are discussed in relation to possible glucocorticoid regulation of cyclic GMP metabolism.     

The epinephrine-sensitive adenylate cyclase of rat liver plasma membranes. Role of guanyl nucleotides.

The epinephrine sensitivity in vitro of the adenylate cyclase system in liver plasma membranes from adrenalectomized rats was increased by the addition of 1 to 100 muM GTP or GDP in the incubation medium. Basal and glucagon-stimulated cyclase activities were also enhanced by GTP and GDP. These effects occurred even in the absence of an ATP-regenerating system. They were mimicked by 5'-guanyl diphosphonate and a series of guanyl derivatives, indicating that the structural requirement for the GTP action is not very stringent. Guanyl nucleotides did not increase the affinity of the adenylate cyclase system for the activating hormones, nor did they protect the enzyme activity against denaturation. Their synergic effect was due to an enhancement of the affinity of the enzyme for the substrate MgATP and also to an increase of the maximal velocity of the reaction. It is proposed that the guanyl nucleotides act directly and primarily upon the catalytic component of the cyclase system, independently of their effects on the binding of the activating hormones to liver plasma membrane. Since the activating effects of epinephrine and glucagon are similar in the presence of GTP, but not in its absence, it is suggested that the lower efficiency of epinephrine under normal conditions is not due to intrinsic membrane characteristics, but rather, to superimposed extraneous modulations.     

Lysophosphatidylcholines can modulate the activity of the glucagon-stimulated adenylate cyclase from rat liver plasma membranes.

1. Synthetic lysophosphatidylcholines inhibit the glucagon-stimulated adenylate cyclase activity of rat liver plasma membranes at concentrations two to five times lower than those needed to inhibit the fluoride-stimulated activity. 2. Specific 125I-labelled glucagon binding to hormone receptors is inhibited at concentrations similar to those inhibiting the fluoride-stimulated activity. 3. At concentrations of lysophosphatidylcholines immediately below those causing inhibition, an activation of adenylate cyclase activity or hormone binding was observed. 4 These effects are essentially reversible. 5. We conclude that the increased sensitivity of glucagon-stimulated adenylate cyclase to inhibition may be due to the lysophosphatidylcholines interfering with the physical coupling between the hormone receptor and catalytic unit of adenylate cyclase. 6. We suggest that, in vivo, it is possible that lysophosphatidylcholines may modulate the activity of adenylate cyclase only when it is in the hormone-stimulated state.     

Regulation of calmodulin-sensitive adenylate cyclase by the stimulatory G-protein, Gs

Studies in bovine and rat brain membranes have suggested that calmodulin can potentiate neurotransmitter- and GTP-stimulated adenylate cyclase activities. To examine whether calmodulin and the stimulatory G-protein, Gs, are potentiative at a calmodulin-sensitive adenylate cyclase, Gs was purified from rabbit liver and reconstituted with a partially purified calmodulin-sensitive adenylate cyclase from bovine brain. Activated Gs (G*s) stimulated basal adenylate cyclase activity and enhanced the stimulation by calmodulin. The potentiation of the calmodulin-stimulated adenylate cyclase activity was dose-dependent with respect to G*s concentration. At the highest concentration of G*s tested (3 nM), a 2-fold enhancement of the calmodulin-stimulated adenylate cyclase activity was observed at all concentrations of calmodulin. The synergistic activation of adenylate cyclase by calmodulin and Gs was dependent on the presence of Ca2+ and occurred at physiologically relevant Ca2+ concentrations. The potentiation was not observed when either a nonactivated Gs or a mixture of activated Gi/Go was used. G*s was not able to stimulate or potentiate a calmodulin-stimulated adenylate cyclase purified from membranes pretreated with the nonhydrolyzable GTP analog, guanyl-5'-yl beta,gamma-imidodiphosphate. Photochemical cross-linking of 125I-calmodulin-diazopyruvamide to proteins having an Mr corresponding to the known Mr of adenylate cyclase was not enhanced by G*s. The results demonstrate that the guanyl nucleotide-dependent enhancement of calmodulin-stimulated adenylate cyclase activity is mediated by G*s and suggest that G*s modulates the enzymatic turnover of the calmodulin-stimulated activity.     

Interactions Between Vasoactive Intestinal Peptide and Dopamine in the Rabbit Retina: Stimulation of a Common Adenylate Cyclase

Although 3,4-dihydroxyphenylethylamine (dopamine, DA) and vasoactive intestinal peptide (VIP) have been reported to stimulate adenylate cyclase activity in the rabbit retina, possible interactions between VIP-sensitive and DA-sensitive adenylate cyclase systems have not been previously investigated. To elucidate the interactions between these two putative transmitter-stimulated cyclase systems, the effects of VIP, DA, and VIP + DA on the conversion of [alpha-32P]ATP to [32P]cyclic AMP in rabbit retinal homogenates were measured. VIP stimulated adenylate cyclase activity in a biphasic manner, suggesting that two classes of VIP receptors may be involved in the induction of cyclic AMP formation. DA was less potent than VIP, and stimulated cyclase activity with a monophasic dose-response curve. When assayed together, these stimulations were partially nonadditive, implying the existence of a common adenylate cyclase pool that may be stimulated by both putative neurotransmitters. The dopaminergic antagonist (+)-butaclamol completely blocked dopaminergic stimulation, but had no significant effect on VIP-induced stimulation, indicating that VIP interacts with specific VIP receptor sites, which are distinct from the dopaminergic receptor sites. Furthermore, the specific D-2 dopaminergic receptor agonist LY141865 demonstrated no inhibitory effect on adenylate cyclase activity, suggesting that the interaction between the VIP- and DA-sensitive adenylate cyclase systems does not result from a D-2 receptor-mediated cyclase inhibition in the rabbit retina. Finally, at maximally effective concentrations, DA and VIP were less potent than fluoride or forskolin in the stimulation of cyclic AMP formation, suggesting that adenylate cyclase pools that are not sensitive to DA and VIP may also be present in this retina.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between the cytoplasmic activator of adenylate cyclase and glycogen metabolism in rat lung

Summary The role of cytoplasmic activator of adenylate cyclase in rat lung metabolism was investigated. Mouse adrenal tumor (MAT) cells undergo differentiation in response to choleratoxin which acts through cyclic AMP. The activator of adenylate cyclase from rat lung also produced cyclic AMP in a disrupted MAT cell preparation. However, unlike choleratoxin, it did not induce MAT cell differentiation in whole cells. These results suggest impermeability of MAT cells, and possibly other cells, to the activator. Thus, means of altering activator activity in lung cytoplasm were sought, and changes in activator activity were related to lung glycogen. Adrenalectomy (ADX) in rats led to a reduction in activator activity that was accompanied by an elevation in lung glycogen. Dexamethasone treatment of adrenalectomized rats reversed both of these effects. Streptozotocin-induced diabetes in rats elevated activator activity and lowered lung glycogen. Insulin treatment of the diabetic rats restored activator activity to the normal control values. Preweaning of rats on day 16 instead of day 22 increased activator activity on the 19th day over the controls and there was a concomitant decrease in lung glycogen. Feeding the separated pups with homogenized milk restored glycogen and activator activity to the control values. These results indicate that activator activity in rat lung cytoplasm was dependent on the circulating levels of cortisol and insulin, and that there appeared to be an inverse relationship between activator activity and glycogen level in rat lungs.     

Hormonal control of the adenyl cyclase activity of adipose cell membranes prepared from badger, rabbit, fox and rat adipose tissues]

1. We have shown differences in hormonal regulation of adenylate cyclase activity in fat cell ghosts prepared from rat, rabbit, fox and badger adipose tissue, under the influence of catecholamines, ACTH and insulin. a) In the rat, catecholamines induced a large stimulation (+315%) of adenylate cyclase. b) In the rabbit, ACTH was the most effective hormone. c) In the fox and the badger, only catecholamines could stimulate adenylate cyclase. d) In both rat and rabbit, insulin did not reduce spontaneous enzymatic activity. Moreover, the activation of adenylate cyclase by ACTH in the rabbit was not altered by insulin, while in the rat, this hormone slightly decreased epinephrine stimulation. 2. Hormonal regulation of adenylate cyclase correlated with the lipolytic response.