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Androgen-independent prostate cancer cells DU-145 express a number of G protein-coupled receptors, including histamine H1 receptors. There is evidence for the presence of beta-adrenoceptors in the human prostate, and in this work we set out to characterise the expression of beta-adrenoceptors by DU-145 cells, their linking to cyclic AMP (cAMP) formation and the possible modulation by histamine H1 receptors of beta-adrenoceptor function. Saturation [3H]-dihydroalprenolol binding indicated that DU-145 cells express moderate levels of beta-adrenoceptors (22.7+/-2.5 fmol/mg protein), which belong to the beta2-subtype as assessed by inhibition by the antagonists ICI-118,551 and CGP-20712A. Inhibition of [3H]-dihydroalprenolol binding by agonists (noradrenaline, adrenaline and isoproterenol) showed the presence of both high-(53-59%) and low-affinity binding sites. beta-Adrenoceptor stimulation with isoproterenol resulted in robust [3H]-cAMP accumulation (10-30-fold of basal, EC50 142 nM; pEC50 6.85+/-0.05). While not having effect of its own on basal [3H]-cAMP accumulation, histamine significantly augmented the beta2-adrenoceptor-induced response (overall effect 152+/-6% of isoproterenol alone) with EC50 1.35 microM (pEC50 5.87+/-0.06). This effect was independent of extracellular Ca2+, insensitive to antagonists/agonists at H1, H2 or H3/H4 receptors and mimicked by drugs containing an imidazole ring in their chemical structure and by imidazole itself. Taken together, our results show that in DU-145 cells histamine augments beta2-adrenoceptor-induced cAMP independently of the activation of known histamine receptors. The effect may involve other mechanisms such as allosteric modulation of beta2-adrenoceptors by the imidazole moiety of histamine.

Using histamine and the H3 receptor antagonist thioperamide, the roles of histamine receptors in NMDA-induced necrosis were investigated in rat cultured cortical neurons. Within 3 h of intense NMDA insult, most neurons died by necrosis. Histamine reversed the neurotoxicity in a concentration-dependent manner and showed peak protection at a concentration of 10(-7) m. This protection was antagonized by the H2 receptor antagonists cimetidine and zolantidine but not by the H1 receptor antagonists pyrilamine and diphenhydramine. In addition, the selective H2 receptor agonist amthamine mimicked the protection by histamine. This action was prevented by cimetidine but not by pyrilamine. 8-Bromo-cAMP also mimicked the effect of histamine. In contrast, both the adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine and the cAMP-dependent protein kinase inhibitor N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinolinesulfonamide reversed the protection by histamine. Thioperamide also attenuated NMDA-induced excitotoxicity, which was reversed by the H3 receptor agonist (R)-alpha-methylhistamine but not by pyrilamine and cimetidine. In addition, the protection by thioperamide was inhibited by the GABA(A) receptor antagonists picrotoxin and bicuculline. Further study demonstrated that the protection by thioperamide was due to increased GABA release in NMDA-stimulated samples. These results indicate that not only the H2 receptor/cAMP/cAMP-dependent protein kinase pathway but also the H3 receptor/GABA release pathway can attenuate NMDA-induced neurotoxicity.

The functional role of protein kinase C in the cAMP signaling cascade was investigated in human promyelocytic leukemia (HL-60) cells. Protein kinase C activation after short exposure to 100 nM phorbol 12-myristate 13-acetate (PMA) increased the intracellular cAMP level up to 3- to 5-fold after 30 min. Such enhancement was almost completely blocked by the selective protein kinase C inhibitor bisindolylmaleimide (GF 109203X). In addition, PMA, but not 4-alpha-PMA, synergistically elevated cAMP levels when adenylyl cyclase was activated directly by forskolin or indirectly by G protein activation after cholera toxin treatment or guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) treatment in digitonin-permeabilized cells. The results indicate that protein kinase C directly increases adenylyl cyclase activity and synergistically enhances it, when it is simultaneously activated otherwise. On the other hand, a 10-min treatment with PMA cut the cAMP accumulation induced by histamine, prostaglandin E2, or isoproterenol by 50-70%. However, the binding affinity and total binding of [3H]histamine to membrane receptors was not effected by PMA, suggesting that the site of protein kinase C's action is not at the receptor level. Western blot analysis of protein kinase C isozymes revealed that PMA (100 nM) caused translocation of cytosolic protein kinase C such as alpha, beta and epsilon to the particulate/membrane fraction. Treatment with a lower concentration of PMA (10 nM) translocated the protein kinase C-epsilon within 2 min, while it had little effect on the translocation of protein kinase C-alpha and -beta up to 20 min. However, simultaneous treatment with 10 nM PMA plus histamine for 5 min significantly inhibited the histamine-mediated cAMP generation, indicating that the protein kinase C-epsilon could be involved in the inhibition of receptor-mediated cAMP generation. Taken together, we conclude that PMA, through the activation of protein kinase C, has two opposite effects on the cAMP signaling cascade in HL-60 cells: a direct activation of adenylyl cyclase and an inhibition of receptor-mediated signal transduction.

This study demonstrates the presence of histamine H1 and H2 receptors and purinoreceptors A1 and A2 on endothelial cells derived from human brain microvessels (HBEC). Histamine induced formation of both inositol triphosphate (IP3) (EC50 = 10.2 +/- 0.9 microM) and cyclic adenosine monophosphate (cAMP) (EC50 = 5.2 +/- 0.9 microM) in HBEC in a concentration-dependent fashion. IP3 formation was inhibited by H1 receptor antagonists mepyramine maleate and chlorphenyramine, but not by H2 receptor antagonist cimetidine. Production of cAMP was efficiently inhibited by cimetidine. Selective A1 receptor agonists decreased, whereas A2 receptor agonists increased cAMP production in HBEC. When added together with histamine to HBEC cultures, both A1 and A2 receptor agonists diminished histamine-induced IP3 stimulation. This effect was reversed in the presence of specific A1 and A2 receptor antagonists, respectively. Marked augmentation of histamine-induced cAMP production by HBEC was observed in the presence of A2 agonist. This response was dependent on H1 receptors, since it was reduced in the presence of H1-receptor antagonist. It is suggested that interaction between histamine and adenosine modulating induction of second messengers in HBEC may influence endothelium-dependent responses of brain microvascular compartments.

We have examined the effect of venom sac extract (VSE), prepared from two hymenopteran species, on intracellular cyclic AMP (cAMP) accumulation in a cultured human cell line. VSE prepared from the oriental hornet (Vespa orientalis) and from the paper wasp (Polistes carolina) induced an increase in accumulation of cAMP in human, transformed, non-pigmented, ciliary epithelial cells. The effect of V. orientalis VSE on intracellular cAMP was dose-dependent. Blocking the response of adenylate cyclase-linked beta-adrenergic receptors was without effect on this cellular response to VSE. On the other hand, the response to VSE prepared from both species was suppressed almost totally by the H2-histamine receptor-specific antagonist, cimetidine. The findings are discussed in the light of earlier observations that described a significant reduction in intraocular pressure in vertebrate animals treated with V. orientalis VSE.

Histamine, acting via H1 receptors, augments adenosine-induced cAMP accumulation in slices of guinea pig cerebral cortex by an indirect mechanism that appears to involve an intracellular messenger(s). To better characterize this process, the time course of this augmentation was examined in slices prelabeled with [3H] adenine. When histamine (1 mM) was added after the cAMP level had reached steady state with adenosine (0.1 mM), the cAMP level rose to a new steady level within 10 min (t 1/2, 2-3 min). There was no measurable delay in this response, indicating rapid activation of the augmentation after receptor occupation. Studies using the H1 receptor antagonist mepyramine indicated that the continued presence of the histamine stimulus was required to maintain the augmentation. Addition of mepyramine (10 microM) between 1 and 14 min after histamine caused cAMP levels to fall to a level similar to that obtained previously with adenosine alone, but with a delay of 2-3 min. This gives an upper estimate of the lifetime of any intracellular messenger involved in the augmentation process. To determine whether histamine acts by stimulating synthesis of cAMP or by inhibiting its breakdown, the fall in tissue cAMP content was studied after rapid removal of the adenosine stimulus by addition of adenosine deaminase. The initial fall was significantly faster in slices incubated with 0.1 mM adenosine plus 1 mM histamine than in slices with 0.1 mM adenosine alone, indicating increased synthesis and breakdown of cAMP in the presence of histamine. However, the higher breakdown rate probably reflects stimulation of the degradation process by the higher initial level of cAMP with histamine because, at equivalent levels, cAMP content fell at similar rates in both conditions. This was confirmed in other experiments in which similar steady state cAMP levels were achieved with and without histamine by appropriate choice of adenosine concentrations. It is therefore concluded that the direct effect of histamine is primarily to potentiate cAMP synthesis.

Iontophoretic application of histamine H2-agonists depressed spontaneous firing of tuberal hypothalamic neurons in tissue culture. Perfusion with inhibitors of cyclic nucleotide phosphodiesterase increased the strength of these depressions, which persisted during perfusion with Ca2+-free medium. These results support a role of cyclic AMP as a mediator of histamine H2-elicited depressions of neuronal activity.

On guinea-pig heart we investigated whether cyclic AMP serves as a messenger for H1 - and/or H2-mediated responses to histamine. (1) On papillary muscle histamine elicited positive inotropic responses which were antagonized by burimamide but not by promethazine. The stimulation of H2-receptors was not only associated with an increase in contractility but also with an increase in cAMP. As shown by the time course of effects for 10(-5) M histamine, the maximal increase in cAMP preceded the maximum in contractility. The mechanical and biochemical responses to histamine were potentiated by the phosphodiesterase inhibitor papaverine, but antagonized by burimamide. (2) On the left guinea-pig atrium containing H1-receptors the inotropic response to histamine (10(-5) M) was not accompanied by increases in cAMP at stimulation frequencies of 0.5 and 2 Hz, respectively. In addition, in the presence of papaverine (3 X 10 (-5) M) no change in the cyclic AMP level occurred after application of histamine. Papaverine by itself, however, concomitantly increased contractility and cyclic AMP at a stimulation frequency of 0.5 Hz. In contrast, at 2 Hz papaverine increased only cAMP leaving the contractility unchanged. At this frequency the well-known Ca2+-antagonistic effect comes into prominence, thus masking the positive inotropic effect attributable to the inhibition of the phosphodiesterase. (3) On the right guinea-pig atrium the mediation of the positive chronotropic response to histamine by H2-receptors which is partly involved in the inotropic effect via the frequency-force relationship does not lead to a concomitant increase in cAMP. Also, in the presence of papaverine, histamine had no influence on the cAMP. However, papaverine potentiated the cardioacceleration produced by histamine. Although it is very likely that the cAMP in the sinus node rises, we were not able to detect an increase in cAMP in the whole atrial tissue. From the present results the conclusion can be drawn that the mediation of the inotropic effect due to stimulation of H2-receptors by histamine is associated with an increase of cyclic AMP, whereas that of H1-receptors is not. The view that cAMP may be the second messenger in the chronotropic action of histamine needs further elucidation by experiments on sino-atrial cells.

We have examined the interactions, in eliciting cAMP accumulation, between vasoactive intestinal polypeptide (VIP) and the three monoamines norepinephrine (NE), histamine (HIS), and serotonin (5-hydroxytryptamine, 5-HT) in mouse cerebral cortical slices. We have observed that NE and HIS, but not 5-HT, act synergistically with VIP to increase cAMP levels. The rank-order of potency of several adrenergic agonists in potentiating the effect of VIP on cAMP levels is the following: epinephrine greater than NE greater than phenylephrine much greater than clonidine, with EC50 of 2.2, 5, and 10 microM, respectively (clonidine being only marginally effective). This pharmacological profile is characteristic of the activation of alpha 1-adrenergic receptors. This contention is substantiated by the observation that the potentiating effect of NE is antagonized by the selective alpha 1-adrenergic antagonist prazosin at nanomolar concentrations. The potentiating effect of HIS is mediated by H1-histaminergic receptors since it is antagonized by the selective H1-receptor antagonist mepyramine but not by cimetidine, a selective H2-receptor antagonist. The synergistic interaction between VIP and NE is also observed in the presence of the adenosine antagonist theophylline, thus discarding the possibility of a mediation of the synergism by adenosine released by VIP.(ABSTRACT TRUNCATED AT 250 WORDS)

The histamine-stimulated accumulation of [3H]cAMP (formed by prelabeling with [3H]adenine) was characterized pharmacologically in a vesicular preparation of guinea pig cortex. The H2 antagonist cimetidine maximally blocked 80% of the response, whereas only 45% of the response could be inhibited by H1 antagonists. A combination of H1 and H2 antagonists completely abolished the response. These and other findings show that both H1 and H2 receptors mediate the response, but 25% of the response may require simultaneous activation of both receptors. A role for adenosine as a mediator of the histamine response was investigated. Adenosine deaminase (EC 3.5.4.4., 2.5 units/ml) decreased basal [3H]cAMP levels, abolished the cimetidine-resistant component of the histamine response, and reduced maximal H1 antagonism of the histamine response to 30%. Treatment with a combination of adenosine deaminase and the calcium chelator EGTA (2 mM) appeared to eliminate the H1 component completely. Under these latter conditions only H2 receptors appeared to mediate the histamine response. Thus, both H1 and H2 receptors stimulate [3H]cAMP accumulation in the vesicular preparation, but the H1 response seems to require either concomitant adenosine or H2 receptor stimulation and may be calcium dependent. These findings differ from those found in broken cell membrane preparations, where only H2 receptors appear to be coupled to adenylate cyclase activation.

On helically cut strips of the rabbit's mesenteric artery, a temperature decrease from 42 degrees C to 25 degrees C reduced the contractile responses to histamine. Metiamide shifted the dose-response curve of the histamine-induced contraction towards higher values at 25 degrees C, but not at 42 degrees C. Furthermore, on arterial strips contracted by phenylephrine histamine evoked a dose-dependent relaxation at 25 degrees C whereas at 42 degrees C only slight relaxing responses to histamine occurred. Metiamide was capable of preventing the relaxation induced by histamine in a competitive manner. At 25 degrees C the relaxation as produced by histamine was accompanied by increases in cyclic AMP which occurred prior to the relaxing effects. Metiamide abolished the cyclic AMP increase in response to histamine. At 42 degrees C histamine was unable to elevate the cyclic AMP content. Thus, it is concluded that a cyclic AMP-mediated relaxation due to stimulation of H2-receptors counteracts the histamine-induced contraction and reduces the contractile responses to histamine at low temperatures. In addition, clear-cut evidence exists from the present study that also on artery smooth muscle the H2-receptor-mediated responses are closely associated to cyclic AMP.

Beta-adrenoceptor-mediated cyclic AMP formation was found to be increased in leukocytes from manic-depressive patients during untreated depression when compared with euthymic patients treated with antidepressants. The difference was dependent on the stimulation used (isoprenaline or a combination of noradrenaline and phentolamine) and was only significant when the combination was used. Histamine-stimulated cyclic AMP formation in leukocytes was enhanced in patients with untreated depression, both when compared with euthymic patients suffering from manic-depressive illness, with or without treatment with antidepressant drugs, and also when compared with control persons without any known psychiatric disease. Although at variance with the results of some other studies on the same topic, the results of the present study indicate that changes in receptor function in leukocytes may be a state-dependent marker in depressive illness.

Norepinephrine, histamine, adenosine, glutamate, and depolarizing agents elicit accumulations of radioactive cyclic AMP from adenine-labeled nucleotides in particulate fractions from Krebs-Ringer homogenates of guinea pig cerebral cortex. The particulate fractions contain sac-like entities, which apparently are associated with a significant portion of the membranal adenylate cyclase. Particulate fractions from sucrose homogenates are a less effective source of such responsive entities. Activation of the adenine-labeled cyclic AMP-generating systems by norepinephrine is by means of alpha-adrenergic receptors, while activation by histamine is through H1- and H2-histaminergic receptors. Adenosine responses are potentiated by the amines and are antagonized by alkylxanthines. Glutamate and depolarizing agents appear to elicit accumulations of cyclic AMP via "release" of endogenous adenosine. It is proposed, based on the virtual absence of an alpha-adrenergic or H1-histaminergic response in the presence of a combination of potent adenosine and H2-histaminergic antagonists, that alpha-adrenergic and H1-histaminergic receptor mechanisms do not activate adenylate cyclase directly in brain slices or Krebs-Ringer particulate fractions, but merely facilitate activation by beta-adrenergic, H2-histaminergic, or adenosine receptors.

The synergism between H1- and H2-receptors in the histamine-induced stimulation of cAMP accumulation was studied in slices from guinea pig hippocampus. Since H1-receptors appear to be coupled to the phosphatidylinositol cycle, the participation of the two branches of the cycle in this synergism was assessed by using phorbol esters and/or by removing Ca2+ from the external medium. The protein kinase C activator, 4 beta-phorbol 12,13-dibutyrate (4 beta-PDB), strongly potentiated, with an EC50 of 0.2 microM, the accumulation of cAMP elicited by dimaprit, an H2-receptor agonist used at supramaximal concentration (0.3 mM). The effect of 4 beta-PDB was also observed in the presence of impromidine, an H2-receptor agonist, and histamine. 4 beta-Phorbol 12-myristate, 13-acetate, another protein kinase C activator, also potentiated the effect of dimaprit in a concentration-dependent manner although less potently than 4 beta-PDB. In contrast, 4 alpha-phorbol or the phorbol esters, 4 alpha-phorbol 12,13-didecanoate or 4-O-methylphorbol 12-myristate, 13-acetate, all inactive on protein kinase C, had no potentiating effect. 2-Thiazolylethylamine (2-TEA), a predominantly H1-receptor agonist, increased the stimulation induced by dimaprit (0.3 mM), and this response was further enhanced in the presence of 4 beta-PDB in maximal concentration (1 microM). Mepyramine (0.1 microM) antagonized the H1-receptor-mediated effect in the absence as well as the presence of 4 beta-PDB. The phorbol ester did not significantly alter the EC50 of 2-TEA or the magnitude of its effect. In the absence of phorbol esters, removal of Ca2+ from the incubation medium did not change the response elicited by 0.3 mM dimaprit but reduced by 50% the response to a supramaximal concentration of 2-TEA. This effect was more marked when EGTA was added in the Ca2+-free medium. The EC50 value of 2-TEA was only slightly modified in the absence of Ca2+ (180 +/- 20 microM as compared with 70 +/- 4 microM in the presence of 2.6 mM Ca2+). In the presence of 4 beta-PDB (1 microM), removal of Ca2+, particularly in the presence of EGTA, did not affect or slightly increased the response to dimaprit, but still strongly reduced the response to 2-TEA. The Ca2+ ionophore A 23187 (10 microM) showed a tendency to mimic the potentiating effect of 2-TEA.(ABSTRACT TRUNCATED AT 400 WORDS)

The identification and characterization of histamine receptors in the organ systems of various species has been made possible in recent years by the introduction of relatively selective agonists and antagonists of H1 and H2 receptors. H2 receptors have now been clearly demonstrated in gastric mucosa, heart, rat uterus, brain, and adipose tissue. Less well-defined H2 receptor systems have also been described in the vasculature, bronchioles, and other smooth muscles as well as in the thyroid gland and lymphocytes. In tissues where it has been examined a close correlation between H2 receptors and the adenylate cyclase--cyclic AMP system has been found. With the exception of the central nervous system stimulation of H1 receptors does not seem to be involved with cyclic AMP. In the case of the brain the H1 receptor stimulation of adenylate cyclase can be differentiated from H2 receptor stimulation of the enzyme by the use of blocking agents and by the fact that the H1 receptor response is enhanced in the presence of adenosine. Studies of the involvement of histamine with the adenylate cyclase--cyclic AMP system have been concentrated on such tissues as gastric mucosa, heart, rat uterus, brain, and adipose tissue. The present review will concentrate on the literature concerning those tissues.

Lymphocytes bear receptors for a wide variety of neurotransmitters, hormones, and other mediators that influence cellular functions in part through alterations in cyclic nucleotide metabolism. A sizable list of agents that increase cyclic AMP levels now includes adenosine (Ra), epinephrine (beta), glucocorticosteroids, histamine (H2), prostaglandins (A, E), and bacterial products (lipopolysaccharide, cholera toxin). We have found no evidence for lymphocyte cyclic AMP responses to adenosine Ri agonists or to enkephalins. Present data suggest a role for cyclic AMP in promoting the differentiation of immature lymphocytes, whereas elevated cyclic AMP levels are associated with inhibition of mature, differentiated lymphocyte functions. Opposing these effects of cyclic AMP are those of cyclic GMP and an expanding collection of compounds that increase its levels: acetylcholine (muscarinic), ascorbate, calcium ionophore, hydroperoxides of arachidonic acid, hypoxanthine derivatives, interleukin 1, serotonin, thymic hormones, and plant lectin mitogens. The biochemical pathways mediating cyclic GMP increases and mechanisms by which cyclic GMP may enhance immunological responses are being intensively studied.

Histamine influences the glomerular microcirculation and modulates immune-inflammatory responses. In the rat kidney, histamine is synthesized by glomeruli and stimulates cyclic nucleotide production specifically in glomeruli. We investigated the in vitro effect of histamine on cyclic nucleotide accumulation in rat cultured glomerular mesangial and epithelial cells. Histamine stimulated cyclic AMP (cAMP) accumulation in cultured mesangial cells (64.0 +/- 22.1 to 511.4 +/- 86.6 pmol/mg protein, n = 9) but had no effect on cAMP accumulation in epithelial cells. This effect was dose-dependent and time-dependent. Stimulation of cAMP accumulation occurred in the range of 5 X 10(-6) M-10(-4) M histamine with a half maximal stimulatory effect of 2 X 10(-5) M. Initial stimulation was noted by 30 s, and maximum stimulation was observed at 5 min. The H2 antagonist cimetidine (10(-4) M) abolished the stimulatory effect of histamine (10(-4) M), while equimolar concentrations of the H1 antagonist diphenhydramine had no significant effect on cAMP accumulation. Moreover, the specific H2 agonist dimaprit, but not the H1 agonist 2-pyridylethylamine, stimulated cAMP accumulation. Histamine had no effect on cAMP accumulation in epithelial cells or on cyclic guanosine monophosphate accumulation in epithelial or mesangial cells. Since the in vivo infusion of histamine reduces ultrafiltration coefficient and since mesangial cell contraction is thought to be responsible for the reduction in the ultrafiltration coefficient, we examined the effect of histamine on the contractile property of mesangial cells. Histamine (5 X 10(-6)-10(-4) M) contracted mesangial cells, and the H1 antagonist diphenhydramine (10(-4) M) but not the H2 antagonist cimetidine (10(-4) M) prevented histamine (10(-4) M) induced contraction. In addition, the H1 agonist 2-pyridylethylamine, but not the H2 agonist dimaprit, contracted mesangial cells. Histamine and its specific agonists and antagonists induced contraction of isolated glomeruli as assessed by glomerular planar surface area in a manner parallel to their effect on mesangial cells. Cinnarizine (10(-5) M), a Ca++ channel blocker, or Ca++, Mg++-free medium prevented histamine (10(-4) M) induced mesangial cell and glomerular contraction. Thus, histamine enhances cAMP accumulation specifically in mesangial cells via an H2 receptor. In contrast, histamine contracts mesangial cells and glomeruli via an H1 receptor, an effect that is dependent on extracellular Ca++ entry. These findings show that histamine potentially influences intraglomerular hemodynamics via effects on mesangial cell contraction. Moreover, our findings considered with the in vivo observation that histamine reduces kf via and H1 receptor provide further support of the hypothesis that mesangial cell contraction regulates the glomerular capillary surface area available for filtration. Our studies also show that this contractile effect of histamine is dependent on extracellular calcium. The presence of a cAMP system sensitive to histamine may have major implications in the pathogenesis of inflammatory glomerulopathies. Mesangial cells possess characteristics similar to circulating and tissue immune effector cells, including lysosomal enzyme release, oxygen radical production, and release of a number of immunomodulatory factors. Histamine and cAMP have been shown to modulate such characteristics of inflammatory cells. It is therefore conceivable that histamine, via its interaction with H2 receptors and subsequent generation cAMP, may have profound effects on such properties of mesangial cells, suggesting that this autacoid may modulate not only glomerular hemodynamics but also immune, inflammatory responses within the glomerulus.