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Biomedical subjects

P Spano

Publications and source records attributed to P Spano.

At least 55 records · Page 3Linked to original sources
PubMed1993

Nerve growth factor suppresses the transforming phenotype of human prolactinomas.

The most effective therapy of human prolactinomas is represented by dopamine D-2 receptor agonists; there is, however, a population of nonresponder patients who require surgical intervention. In the present study, we report that prolactinomas totally resistant to pharmacological therapy have a high potential of both growing in soft agar and forming tumors in nude mice and lack D-2 receptors for dopamine. These tumors express the receptors for nerve growth factor (NGF) and are sensitive to its differentiating activity. After exposure to NGF for 4 days, prolactinoma cells decreased their proliferation rate, lost their capability to form colonies in soft agar, lost their tumorigenic activity in nude mice, and reexpressed the lactotroph-specific D-2 receptor protein inhibiting prolactin release. These effects were permanent after NGF withdrawal and were reproducible in vivo in nude mice transplanted with the tumors. NGF in fact remarkably and lastingly depressed tumor growth and induced expression of D-2 receptors when injected intravenously once a day for 5 days into prolactinoma-bearing nude mice. These data suggest that NGF may induce a long-lasting switch of gene expression in human prolactinomas, modifying their transforming phenotype and reverting them to more differentiated, less malignant, dopamine-sensitive lactotroph-like cells. The possibility thus arises that short-term treatment with NGF may restore the refractory patients to conventional pharmacological therapy with D-2 agonists.

Animals↗
PubMed1992

Tolerance to hypoactivity and sensitization to hyperactivity after chronic treatment with a presynaptic dose of lisuride in rats.

We studied the adaptive changes of the locomotor effects of lisuride, a selective agonist for dopamine (DA) D2 receptors, and the functional state of D1 and D2 receptors after repeated administration of lisuride at a dose supposed to act preferentially on DA autoreceptors. Rats were treated daily with saline or lisuride, at a dose that causes a significant reduction in locomotor activity when given to naive rats (25 micrograms/kg i.p.), for 33 days and the effect of different challenging doses of the drug on locomotor activity was measured at different times during and after the treatment. The functional state of D1 and D2 DA receptors was evaluated by measuring SKF 82526-stimulated and LY 171555-inhibited adenylate cyclase (AC) activity in the caudatus/putamen, nucleus accumbens and substantia nigra and naive and chronically treated rats. There was a progressive decline in the ability of lisuride to decrease locomotor activity in rats given daily injections of lisuride, and there was a marked reduction in the threshold dose of lisuride for causing hypermotility. The functional state of DA receptors, positively or negatively linked to AC activity, was not modified by the treatment. The most suitable explanation of the reported adaptive behavioral changes is a down-regulation of DA autoreceptors after chronic treatment with presynaptic doses of lisuride.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1992

L-alpha-glycerylphosphorylcholine antagonizes scopolamine-induced amnesia and enhances hippocampal cholinergic transmission in the rat.

The effects of L-alpha-glycerylphosphorylcholine (alpha-GPC) on scopolamine-induced memory impairment and on brain acetylcholine (ACh) synthesis and release were investigated in rats. Oral administration of alpha-GPC 3 h before the behavioural test prevented the learning impairment induced by scopolamine given 30 min before the acquisition of a passive avoidance response. Similarly, retrograde amnesia induced by scopolamine, given immediately after acquisition training, was also completely reversed by the drug. These effects were dose-dependent with a maximum at 300 mg/kg. The mechanism of action of this compound was investigated by measuring hippocampal ACh synthesis and release both in vivo by means of the microdialysis technique and in vitro in tissue slices. alpha-GPC dose dependently increased ACh release with a maximum at 300 mg/kg. In addition, i.v. injection of [14C]alpha-GPC resulted in [14C]ACh formation. The data suggest that the behavioural effects of alpha-GPC may be related to its property to increase hippocampal ACh synthesis and release.

Acetylcholine↗
PubMed1992

Rat pituitary cells selectively express mRNA encoding the short isoform of the y2 GABAA receptor subunit.

The GABAA receptor belongs to the ligand-gated ion channel receptor superfamily and appears to be composed of from 4 to 5 subunits which interact with each other. Molecular cloning of cDNAs encoding the different subunits of the GABAA receptor has revealed an unexpected heterogeneity which includes at least 4 homologous classes of subunits: these classes, designated as alpha, beta, gamma, and delta contain multiple variants. We have measured the steady-state levels of mRNAs encoding different (alpha 1, alpha 4, beta 1, beta 2, beta 3, gamma 2 long, gamma 2 short and delta) GABAA receptor subunits in the rat anterior pituitary and cerebellum using a polymerase chain reaction (PCR)-derived method. We found that pituitary cells express mRNAs encoding the alpha 1, beta 1 and beta 3 GABAA receptor subunits whereas the transcripts for alpha 4, beta 2 and delta were undetectable. We also found that pituitary cells selectively express the short isoform of the gamma 2 subunit mRNA. These data indicate that the expression of the various GABAA receptor subunits is cell-specific and support the concept that the diversity in function and pharmacology of the GABAA receptor is based on the ability of cells to specify the expression of selective GABAA receptor subunits.

Animals↗
PubMed1992

Activation of dopamine D2 receptors linked to voltage-sensitive potassium channels reduces forskolin-induced cyclic AMP formation in rat pituitary cells.

3,4-Dihydroxyphenylethylamine (dopamine) D2 receptor agonists, including BHT 920 and bromocriptine, and the potassium channel opener minoxidil share the property of hyperpolarizing the plasma membrane by activating voltage-dependent potassium channels. These drugs were tested for their ability to inhibit the cyclic AMP formation induced by forskolin either in intact or in broken pituitary cells. In contrast to bromocriptine, which was active in both experimental systems, BHT 920 and minoxidil inhibited the forskolin-induced cyclic AMP formation in intact-cell but not in broken-cell preparations. The effects of BHT 920 were (a) concentration dependent, with a calculated IC50 of 0.7 microM, (b) dopaminergic in nature, being specifically antagonized by sulpiride, (c) not additive with those induced by minoxidil, and (d) less effective in the presence of potassium channel blockers, such as 4-aminopyridine and tetraethylammonium. These data indicate that the inhibition of forskolin-induced cyclic AMP formation by BHT 920 in intact pituitary cells is not a primary consequence of receptor occupation, but a late event, possibly related to the opening of voltage-dependent potassium channels elicited by this drug through the activation of a subtype of dopamine D2 receptors uncoupled to adenylyl cyclase.

Adrenergic alpha-Agonists↗
PubMed1991

Various Ca2+ entry blockers prevent glutamate-induced neurotoxicity.

In the present study we investigated the effect of different Ca2+ entry blockers on the onset of neuronal damage induced by glutamate, kainate or alpha-amino-3-hydroxy-5-methyl-5-isoxazolo propionate (AMPA) in primary culture of rat cerebellar granule cells. We found that the dihydropyridine derivative, nifedipine used at 100 nM concentration, significantly counteracted the neuronal death induced by 15 min application of 50 microM glutamate. This effect was dependent on the presence of nifedipine before the exposure of granule cells to glutamate and was dose-related (IC50 = 10 nM). The nifedipine response was reproduced by isradipine and by verapamil with IC50 values of 9 and 100 nM, respectively. The activation of voltage sensitive Ca2+ channels elicited by 100 nM Bay K 8644, greatly enhanced glutamate-mediated neurotoxicity. Moreover, 100 nM isradipine was significantly active in blocking the neuronal death produced by 24 h exposure of cerebellar granule cells to 10 microM AMPA or 60 microM kainate. These results reveal a 'preventive' role of the Ca2+ entry blockers on the development of the neurodegeneration induced by overstimulation of various glutamate receptor subtypes.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
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↗
PubMed1991

Characterization of monoaminergic receptors in hypothalamic nuclei mediating feeding behavior in rats.

It has been proposed that receptors mediating the action of dopamine (DA), serotonin and norepinephrine exist in the hypothalamus to control feeding behavior in the rat. To further characterize the receptor subtypes involved in this phenomenon and determine their locus within specific hypothalamic nuclei, measurements of adenylate cyclase (AC) activity, as a biochemical index of monoaminergic receptors, were taken after administration of various monoaminergic agonists and antagonists. It was first found that DA and selective D2 agonists, such as quinpirole and lisuride, strongly reduced AC activity in homogenates from the lateral perifornical hypothalamus (PFH), where previous evidence has shown DA agonists to inhibit feeding. These inhibitory effects were stereospecifically antagonized by the D2 antagonist (-)-sulpiride. The selective D1 agonist SKF 82526, up to 100 microM, was completely inactive in modifying the basal enzyme function in PFH. In homogenates from rat paraventricular nucleus (PVN), DA (100 microM), quinpirole (10 microM) and SKF 82526 (100 microM) were unable to affect AC activity, consistent with previous pharmacological evidence showing DA in the PVN to have no effect on feeding. These results suggest the presence of D2 receptors in the PFH but not in the PVN and the absence of D1 receptors in both areas. Under the same experimental conditions, the alpha 2 adrenoceptor agonist clonidine was able to inhibit AC in the PVN, and this effect was reversed by the alpha adrenoceptor antagonist phenoxybenzamine. These results supported the previously described PVN alpha 2 adrenergic system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
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↗
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

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↗
PubMed1988

Dopamine selectively inhibits angiotensin II-induced aldosterone secretion by interacting with D-2 receptors.

Aldosterone secretion is subject to both stimulatory and inhibitory controls. Angiotensin II (AII) is the primary stimulator of aldosterone production and an inhibitory role of dopamine (DA) has been suggested recently. In this study we investigated the interactions between DA and AII in the intracellular events leading to aldosterone secretion. By measuring aldosterone secretion and cyclic AMP (cAMP) formation in intact adrenal glomerulosa cells we show that AII induced a sustained stimulation of aldosterone secretion (EC50, 0.41 nM) and a rapid and transient increase in intracellular cAMP content (EC50, 4 nM). DA inhibited both aldosterone secretion (IC50, 300 nM) and cAMP formation (IC50, 100 nM) elicited by submaximal concentrations of AII; in contrast, DA did not attenuate either basal or adrenocorticotropic hormone-stimulated cell activity. The pharmacological characterization of DA effects with dopaminergic agonists and antagonists strongly indicated an involvement of D-2 receptors. Indeed, selective D-2 agonists were more effective than DA in inhibiting the glomerulosa cell responses to AII; in addition, the effects of DA on both aldosterone secretion and cAMP formation were prevented by D-2 antagonists, such as (-)-sulpiride and domperidone, but not by the selective D-1 antagonist SCH 23390. These data suggest a specific functional interaction between D-2 receptors apparently associated with inhibition of cAMP formation and AII in the regulation of aldosterone production.

Adrenal Cortex↗