Biomedical subjects

C Missale

Publications and source records attributed to C Missale.

At least 55 records · Page 3Linked to original sources

PubMed1991

Lack of coupling of D-2 receptors to adenylate cyclase in GH-3 cells exposed to epidermal growth factor. Possible role of a differential expression of Gi protein subtypes.

Exposure of GH-3 cells to epidermal growth factor for 4 consecutive days induced the expression of both D-2(415) and D-2(444) dopamine-receptor isoforms. Epidermal growth factor also promoted a remarkable increase in the content of Gi3 protein, which is responsible for receptor-induced activation of potassium channels in GH-3 cells. D-2 receptors in this model apparently activate a specific transducing pathway, leading to opening of potassium channels and inhibition of prolactin release by cAMP-independent mechanisms. This is shown by: 1) the selective D-2 agonist quinpirole, while inactive on vasoactive intestinal peptide-induced prolactin release, strongly inhibited the hormone secretion induced by neurotensin; 2) quinpirole, up to 100 microM, did not inhibit cAMP production evoked by vasoactive intestinal peptide both in intact cells and in broken cell membrane preparations; and 3) quinpirole and other D-2 agonists strongly potentiated Rb+ efflux when measured in a nominally calcium-free reaction solution containing 100 mM potassium (voltage-dependent component), but did not modify Rb+ efflux if measured in a reaction solution containing 1 mM calcium and 5 mM potassium (calcium-activated, cAMP-dependent component).

Adenylyl Cyclases↗

PubMed1991

Low doses of l-sulpiride down-regulate striatal and cortical dopamine receptors and beta-adrenoceptors.

There is now clinical evidence that l-sulpiride has antidepressant effects when administered at low, non-neuroleptic doses. Down-regulation of beta-receptor-linked adenylate cyclase is a well-documented adaptive response to chronic administration of antidepressant drugs. In this study, we investigated dopamine receptor and beta-adrenoceptor changes induced by chronic administration of low doses of l-sulpiride. The data indicate that striatal D1 and D2 receptor function was desensitized by the treatment, which suggests that at low doses l-sulpiride preferentially blocks D2 autoreceptors, leading to increased dopamine release. l-Sulpiride also induced a selective down-regulation of beta-receptor-associated adenylate cyclase activity in the frontal cortex, but not in the striatum, which does not receive norepinephrine projections. Taken together these data suggest that cortical noradrenergic terminals may be endowed with dopamine D2 receptors controlling norepinephrine release and that blockade of this dopaminergic inhibitory modulation may be involved in the antidepressant effects of l-sulpiride.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1991

Epidermal growth factor induces the functional expression of dopamine receptors in the GH3 cell line.

GH3 cells are a clonal strain from a rat pituitary tumor that synthesizes and secretes both PRL and GH. The peculiarity of these cells is that they do not express receptors for dopamine; thus the hormone release is insensitive to the inhibitory effect of dopamine and D2 receptor agonists. Exposure of GH3 cells to epidermal growth factor for 4 consecutive days markedly altered the cell morphology, from a spherical appearance to an elongated flattened shape, and increased the cell size. These morphological changes were accompanied by the functional expression of D2 dopamine receptors as shown by the presence of a specific, saturable, and stereoselective high affinity binding for [3H]spiroperidol in epidermal growth factor-treated cells and by the fact that the selective D2 agonist quinpirole recovered the property to inhibit PRL secretion in the cell cultures exposed to the neurotrophic factor. The effect of EGF on the functional expression of D2 receptors was dose dependent (EC50 = 8 pM) and reversible. These data suggest that EGF elicits major effects on the expression of specific genes leading to the differentiation of GH3 cells into lactotroph-like cells endowed with dopamine D2 receptors.

Animals↗

PubMed1990

Repeated administration of lisuride down-regulates dopamine D-2 receptor function in mesostriatal and in mesolimbocortical rat brain regions.

Functional modifications of both D-1 and D-2 dopamine (DA) receptor subtypes following repeated administration of lisuride, a DA agonist that acts selectively on D-2 DA receptors were studied. The functional state of D-1 and D-2 DA receptors was evaluated from measurements of SKF 82526-stimulated and bromocriptine-inhibited adenylate cyclase activity in different brain regions of rats treated daily for 26 days with saline or lisuride (100 micrograms/kg i.p.). Persistent stimulation by lisuride of DA receptors in striatum, nucleus accumbens, substantia nigra, frontal cortex, hippocampus and pituitary gland induced a down-regulation of D-2 receptors without changing the functional activity of D-1 receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1990

Evidence for the presence of both D-1 and D-2 dopamine receptors in human esophagus.

Clinical and pharmacological evidence suggested that dopamine is involved in the control of esophageal motility. The present study was designed to determine whether or not dopamine receptors are present in human esophagus. With this aim we measured adenylate cyclase activity as a biochemical index of dopamine receptor function in esophageal specimens taken from five patients during surgery for upper esophageal carcinoma. The selective D-1 agonist fenoldopam stimulated cAMP formation in the lower esophageal sphincter, but not in the esophageal body; this effect was prevented by the selective D-1 antagonist SCH 23390 and by d-butaclamol. Bromocriptine, a selective D-2 stimulator, inhibited adenylate cyclase activity in the lower esophageal sphincter, an effect blocked by the D-2 antagonist (-)sulpiride. No effects of bromocriptine were found in the esophageal body. These data indicate that both D-1 and D-2 receptors are present in the lower esophageal sphincter, but not in esophageal body and emphasize the role of dopamine in the regulation of esophageal function.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1990

Dopaminergic regulation of aldosterone secretion. Biochemical mechanisms and pharmacology.

Aldosterone secretion is subject to both stimulatory and inhibitory controls. Angiotensin II (AII) is the primary regulator of aldosterone production and an inhibitory role of dopamine (DA) has been suggested recently. We have reported that two different DA receptors are present in rat adrenal glomerulosa: D-1, associated with stimulation of adenylate cyclase, and D-2, coupled in an inhibitory way with the cyclic AMP (cAMP) generating system. By measuring aldosterone secretion and cAMP formation in intact adrenal glomerulosa cells, we also found a specific functional interaction between D-2 receptors apparently associated with inhibition of cAMP formation and AII in the regulation of aldosterone production.

Adrenal Glands↗

PubMed1990

Beta 1- and beta 2-receptors are differentially desensitized in an experimental model of heart failure.

Recent reports suggested that a complex alteration in beta-receptor function occurs in failing human myocardium. We evaluated beta-receptor-subtype activity in an experimental model of monocrotaline (MCT)-induced cardiomyopathy in the rat. Through pulmonary hypertension, MCT causes right ventricular hypertrophy (RVH), either associated with heart failure or not, beta-Receptor function was evaluated in both failing-hypertrophic and hypertrophic hearts in binding studies with [125I]iodocyanopindolol (ICYP) and by measuring adenylate cyclase (AC) activity. In the right failing ventricle, beta 1- but not beta 2-receptor density was decreased. Lesion-associated modifications in the adenylate cyclase system were also observed: isoproterenol- and guanosine 5' [beta, gamma-imido]triphosphate [Gpp(NH)p]-stimulated cyclic AMP formation was reduced in the right failing ventricle, while the cyclic AMP responses to NaF and forskolin were unchanged. On the other hand, no changes in either beta-receptor density or function were found in hypertrophic ventricles. MCT-induced heart failure in the rat is thus associated with a selective decrease of beta 1-receptor density and function. These results suggest that MCT-induced cardiac failure may be an appropriate model in which to investigate heart insufficiency further.

Adenylyl Cyclases↗

PubMed1990

A mechanism additional to cyclic AMP accumulation for vasoactive intestinal peptide-induced prolactin release.

Vasoactive intestinal peptide (VIP) is a prolactin (PRL)-releasing factor which has been proposed to exert its secreting property by activating the adenylate cyclase enzyme. The present study shows that the omission of external Ca2+ did not affect the ability of VIP to induce PRL release while it completely abolished the VIP stimulatory effect on adenylate cyclase. We found that VIP (500 nM) stimulated PRL secretion in a time-dependent manner reaching a plateau at 3 min. This pattern was not changed when Ca2+ was omitted from the incubation medium. When tested at different concentrations, VIP stimulated PRL release with EC50 values of 1.3 nM in the presence of Ca2+ and 30 nM in the absence of Ca2+. On the other hand, Ca2+ removal completely suppressed the VIP-induced cAMP formation. VIP (200 nM) was also found to activate Ca2+ influx into pituitary cells. The increase in Ca2+ permeability showed a peak at 5 s and remained significantly higher than control values until 1 min. In conclusion, in an experimental condition where Ca2+ was omitted from the medium, VIP was found to induce PRL release without stimulating cAMP production. This cAMP-independent PRL release was blocked by preincubation of the cells with 1 microgram/ml pertussis toxin. An additional mechanism other than adenylate cyclase activation or Ca2+ entry is proposed to sustain VIP-induced PRL release.

Adenylate Cyclase Toxin↗

PubMed1990

[The adrenergic beta system in an experimental model of heart failure].

Reports in the literature have suggested that a complex alteration in beta-receptor pathway takes place in failing human myocardium. The purpose of our study was to evaluate the beta-adrenergic receptor system in an experimental model of heart failure induced by monocrotaline in rats. Monocrotaline, administered with a single intraperitoneal injection (50 mg/Kg), causes pulmonary hypertension and right ventricular hypertrophy, associated with congestive heart failure. beta 1 and beta 2-receptors were characterized in the right ventricle by direct radioligand binding utilizing [125I] Iodocyanopindolol and selective beta 1-(CGP 20712A) and beta 2-(ICI 118551) antagonists. Adenylate cyclase was measured in basal condition and in the presence of different stimulators as isoproterenol with ICI 118551 (beta 1-receptor-stimulated activity), isoproterenol with CGP 20712A (beta 2-receptor-stimulated activity), Gpp(NH)p, NaF and forskolin. In the right ventricle of the failing hearts the beta 1-receptor density decreased selectively (-55.8%) while the beta 2-receptor density was unchanged. Modifications in the adenylate cyclase system were demonstrated: a reduction in the basal and beta 1- and beta 2-stimulated adenylate cyclase activity; a decrease in adenylate cyclase activation elicited by Gpp(NH)p, but not by forskolin and NaF. In conclusion, these data suggest that in monocrotaline-induced heart failure in the rat there is a selective beta 1-receptor down-regulation and an impaired coupling efficiency of G proteins. These results are in line with biochemical changes found in patients with heart failure.

Adenylyl Cyclases↗

PubMed1990

[Regulation mechanisms in prolactin secretion. Possible role of the hypophyseal renin-angiotensin system].

Recent studies have shown a possible role of different factors in the regulation of prolactin secretion. In fact many neurotransmitters (dopamine) and peptides can modulate prolactin release from anterior pituitary lactotrophs. In vitro and in vivo studies, Angiotensin II has been shown to increase prolactin release. On the basis of these data we have studied the effects of enalapril (ACE-Inhibitor) on baseline plasma prolactin in nine hypertensive post-menopausal women. The results indicate that 15-day inhibition of angiotensin-converting enzyme by enalapril significantly reduced serum prolactin levels. These data suggest that the Angiotensin II may play a role in the control of prolactin secretion in hypertensive women.

Aged↗

PubMed1989

Repeated reserpine administration up-regulates the transduction mechanisms of D1 receptors without changing the density of [3H]SCH 23390 binding.

Behavioural studies have shown that stimulation of D1 receptors, which is uneffective in normal rats, induced strong hypermotility in rats pretreated with reserpine for 5 days. On this basis, we investigated D1 receptor plasticity using the 5-day treatment with reserpine (1 mg/kg; s.c.) as an experimental model. The function of striatal D1 receptors was determined both in binding studies with [3H]SCH 23390 and by measuring formation of cAMP in response to the selective agonist, SKF 82526. The results indicate that the responsiveness of adenylate cyclase (AC) to D1 receptor stimulation was markedly increased after reserpine administration, while no significant changes were found in [3H]SCH 23390 binding site density. Moreover, formation of cAMP after stimulation of Gs protein with GppNHp was markedly enhanced in dopamine (DA)-depleted rats; the responsiveness of AC to forskolin, which directly stimulates the AC catalytic unit, was not affected by reserpine administration. These data indicate that reserpine-induced D1 receptor up-regulation is apparently mediated by a marked enhancement of the coupling efficiency of Gs protein, suggesting that the D1 behavioral supersensitivity does not correlate with the density of D1 receptors, but is reflected by a selective up-regulation of their transduction mechanisms.

Adenylyl Cyclases↗

PubMed1989

Properties of benzodiazepine binding sites in peripheral blood lymphocytes.

Benzodiazepine (BDZ) binding sites were studied by using 3H-diazepam and 3H-Ro 5-4864 in intact lymphocytes from peripheral blood (PBL), in comparison to kidney and cerebellum. Experiments with 3H-diazepam performed at equilibrium and measuring kinetics revealed that BDZ binding sites are indeed present in rat PBL. The binding is saturable (Bmax 557 fmoles/10(6) cells), with high affinity (KD = 9.3 nM) and reversible. Specific binding sites are also observed by saturation experiments with 3H-Ro 5-4864 (Bmax 175 fmoles/10(6) cells, KD 2.2 nM). In addition, analysis of saturation isotherms obtained with 3H-diazepam indicates that BDZ binding sites are also present in human PBL. Scatchard plot of binding isotherms revealed an apparent single population of sites in all cases. The pharmacological characterization of BDZ binding sites in PBL, as compared with those of kidney and cerebellum, showed that these sites belong to the so-called "peripheral type."

Animals↗

PubMed1989

Angiotensin II differentially affects cyclic AMP formation in intact adrenal glomerulosa cells and in purified membrane preparations.

In the present study we have investigated the cyclic AMP (cAMP) responses to angiotensin II (AII) in isolated rat adrenal glomerulosa cells and in purified membrane preparations. When cells were incubated with 10 nM AII cAMP cellular content increased 2-fold at 5 min and 3-fold at 10 min, then rapidly declined. The effect of AII was dose-dependent with EC50 of 4 nM and was mediated by AII receptors as shown by the pharmacological characterization with AII analogs and AII receptor antagonists. Since AII inhibited cAMP formation in purified adrenal cortical membrane preparations, the stimulatory effect observed in intact cells could be indirect and mediated by other intracellular events.

Adenylyl Cyclases↗

PubMed1989

Potassium channels involved in the transduction mechanism of dopamine D2 receptors in rat lactotrophs.

1. Radioactive rubidium (86Rb+) efflux was used to measure potassium (K+) permeability in a study designed to asses both the presence and the sensitivity to ions and drugs of the K+ channels in the plasma membrane of rat lactotrophs. 2. Rb+ efflux from Rb+-pre-loaded lactotrophs into nominally calcium-free solution containing 5 mM-K+ was linear from 1 to 60 s, with a calculated rate of about 0.1%/s. Raising K+ concentrations to depolarize the cells stimulated the Rb+ efflux (0.2%/s), which was already significant after 1 s of exposure of the cell to 100 mM-K+. This component of Rb+ efflux has been designated component V (sensitive to voltage and Ca2+ independent). 3. Addition of Ca2+ to 5 mM-K+ solution had no effect on resting Rb+ efflux (0.1%/s), but did further stimulate Rb+ efflux into K+-rich solutions. This component, which has been designated component C, was completely inhibited by 0.5 mM-cadmium. These data fit the view that the increase in intracellular Ca2+ concentration during depolarization opens certain (Ca2+-activated) K+ channels. 4. K+ efflux was differently affected by K+ channel blockers. Tetraethylammonium (TEA) inhibited both V and C components while 4-aminopyridine (4-AP) inhibited the component V without modifying the C component of Rb+ efflux. 5. Dopamine appears to affect both types of Rb+ efflux components. Dopamine increased the efflux of Rb+ in a nominally Ca2+-free medium containing 5 mM-K+ (component V). This effect was statistically significant 15 s after exposure of the cells to 10 nM-dopamine. Increasing the concentrations of K+ to gradually depolarize the cells enhanced the rate of increase of Rb+ efflux induced by dopamine, being evident in the initial 2-5 s of incubations. Dopamine also increased Rb+ efflux in a 5 mM-K+ solution containing 1 mM-Ca2+ (component C). This effect was rapid (2-5 s) and inhibited by 0.5 mM-cadmium. The combined action of dopamine on both component C and V caused the cells to be less sensitive to depolarizing concentrations of K+. The increase in Rb+ efflux and the enhancement of prolactin release induced by high concentrations of K+ were, indeed, prevented by exposure of the cells to 10 nM-dopamine. 6. The effects of dopamine on either component V or component C were pharmacologically characterized as D2 receptor mediated, being mimicked by selective D2 receptor agonists (quinpirole and RU 24213) and stereospecifically blocked by the D2 receptor antagonist sulpiride.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗

PubMed1989

Dopaminergic receptor mechanisms modulating the renin-angiotensin system and aldosterone secretion: an overview.

Several studies suggested that dopamine may be one of the inhibitory modulators of aldosterone secretion. Metoclopramide, a selective antagonist for dopamine D-2 receptors, increases both basal plasma aldosterone levels and the aldosterone response to angiotensin II (Ang II) in rats and humans kept on a high sodium intake, these effects being blocked by dopamine infusion. Dopamine, which has no significant effects on Ang II-induced aldosterone secretion in sodium-replete subjects, inhibits the hormonal response to Ang II infusion in sodium-depleted normal subjects, suggesting that the sodium balance state may be an important factor in the dopaminergic mechanisms controlling aldosterone secretion. The effect of dopamine on the hormone production is mediated by D-2 receptors in the adrenal cortex as shown by in vitro studies with isolated adrenal glomerulosa cells. Clinical studies have shown that dihydroergotoxine, a selective D-2 agonist, suppresses the aldosterone secretion induced by sodium depletion in hypertensive patients, an effect blocked by sulpiride. This mechanism could be of relevant therapeutic interest in its contribution to the natriuretic effects of dopaminergic agonists, which have clinical applications in the treatment of hypertension and congestive heart failure.

Adrenal Glands↗

PubMed1989

Inhibition of aldosterone secretion by dopamine, ibopamine, and dihydroergotoxine in patients with congestive heart failure.

There is now evidence for the presence of a dopaminergic inhibitory modulation of aldosterone production that is mediated by D-2 receptors in the adrenal cortex. In this study we evaluated the effects of dopamine and the dopaminergic agonists ibopamine and dihydroergotoxine on aldosterone secretion and plasma renin activity in 13 patients with chronic heart failure. Two groups of patients were noted: one responding to dopaminergic drugs with a decrease in plasma aldosterone and the other without dopamine agonist-related aldosterone suppression. No effect on plasma renin activity was found after each drug administration. A correlation was found between the response to dopamine agonists and basal plasma aldosterone levels. These data are of therapeutic value in showing the detrimental effect of the activation of the renin-angiotensin-aldosterone system occurring in heart failure: a drug reducing this activation appears promising for both its acute and long-term effects.

Aged↗

PubMed1988

Acute scopolamine treatment decreases dopamine metabolism in rat hippocampus and frontal cortex.

The aim of the present study was to correlate the impairment of cognitive function induced by scopolamine with the activity of dopaminergic synapses in brain areas which are innervated by the mesocortical limbic system (e.g. hippocampus and frontal cortex) or by the mesostriatal system (e.g. striatum and nucleus accumbens). The results indicate that acetylcholine receptor blockade induced by the intraperitoneal injection of 0.5 mg/kg scopolamine resulted in a selective decrease in the content of the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This effect appeared to be specific for the hippocampus and frontal cortex. Indeed, dopamine turnover in striatum and nucleus accumbens was not affected by scopolamine treatment. The scopolamine-induced decrease of dopamine turnover in both hippocampus and frontal cortex paralleled in terms of both time- and dose-dependence the drug-induced amnesic effects, as measured by a passive avoidance behavioral test.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1988

Pharmacological characterization of D1 and D2 dopamine receptors in rat limbocortical areas. I. Frontal cortex.

The mesolimbocortical dopaminergic system innervates several brain regions including the frontal cortex. The aim of our work was both to identify and to pharmacologically characterize the dopamine receptors located in this brain area. We found that different selective agonists for D1 receptors were able to increase adenylate cyclase activity, and these effects were antagonized by haloperidol and SCH 23390. Moreover different agonists for D2 receptors inhibited the cyclic AMP generating system, and these effects were prevented by (-)-sulpiride. According to the paradigm that D1 receptors are linked with adenylate cyclase in a stimulatory way, while D2 receptors are linked with the same enzyme in an inhibitory way, our results indicate the presence of both D1 and D2 receptors in rat frontal cortex.

Adenylyl Cyclases↗