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Biomedical subjects

M Parenti

Publications and source records attributed to M Parenti.

At least 19 recordsLinked to original sources
PubMed1995

The role of palmitoylation of the guanine nucleotide binding protein G11 alpha in defining interaction with the plasma membrane.

Mutations of Cys-9 to serine, Cys-10 to serine and a combination of both alterations were produced in a cDNA encoding murine G11 alpha to potentially interfere with the ability of the expressed polypeptides to act as substrates for post-translational palmitoylation. Each of these mutants and the wild-type protein were expressed in simian COS-1 cells. Mutation of either cysteine-9 or cysteine-10 decreased the degree of palmitoylation of the protein by some 80% compared with the wild-type, while the double mutant totally failed to incorporate [3H]palmitate. By contrast, in all transfections the endogenously expressed simian G11 alpha incorporated [3H]palmitate to similar levels. Particulate and cytoplasmic fractions from these cells were subjected to SDS/PAGE under conditions which allow resolution of primate and rodent forms of G11 alpha. Immunoblotting of these fractions demonstrated that in all cases the endogenously expressed simian G11 alpha was exclusively associated with the particulate fraction, as was the transfected and expressed wild-type murine G11 alpha. By contrast, each of the mutated forms of murine G11 alpha displayed a distribution in which approx. 70% of the expressed protein was present in the particulate fraction and 30% in the supernatant. To examine the conformation of the particulate expressed forms of murine G11 alpha, these fractions were treated with various concentrations of sodium cholate and immunoblots were subsequently performed on the solubilized and remaining particulate proteins. Whereas essentially all of the endogenous simian G11 alpha was solubilized by treatment with 1% (w/v) sodium cholate and some 50% with 0.32% cholate, expressed wild-type murine G11 alpha was more recalcitrant to solubilization. However, that fraction of wild-type murine G11 alpha which was solubilized behaved identically to the endogenous simian G11 alpha on Superose-12 gel-exclusion chromatography. The particulate fraction of the C9S/C10S double mutant of murine G11 alpha was highly resistant to solubilization by sodium cholate, whereas the particulate fractions of the two single cysteine to serine mutants were intermediate to the wild-type and double mutant in their ability to be solubilized by this detergent. These data demonstrate that the palmitoylation status of the cysteine residues at positions 9 and 10 in murine G11 alpha plays a central role in defining membrane association of this G-protein and indicate that much of the particulate fraction of the expressed palmitoylation-resistant mutants is likely to represent non-functional rather than correctly folded protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1995

The dynamic role of palmitoylation in signal transduction.

Guanine nucleotide binding protein (G protein)-linked receptors, the alpha-subunits of heterotrimeric G proteins and members of the Src family of nonreceptor tyrosine kinases are among many polypeptides that are posttranslationally modified by the addition of palmitate, a long-chain fatty acid. Attachment of palmitate to these proteins is dynamic and may be regulated by their activation. The presence of palmitate appears to play a key role in the membrane localization of either the entire polypeptide or parts of it, and may regulate the interactions of these polypeptides with other proteins.

Amino Acid Sequence↗
PubMed1995

Somatotropic dysregulation in old mammals.

In old mammals, including humans, the spontaneous growth hormone (GH) secretory pattern is markedly reduced resulting in lower amounts of GH released over 24 h, and the GH response to administration of GH-releasing hormone (GHRH) is reduced. In agreement with these in vivo findings, an impaired responsiveness to GHRH is evident in the pituitary of old male and female rats in vitro, and this is linked with a diminished stimulation of adenylate cyclase by GHRH. The poor GH responsiveness to GHRH in old mammals, which in the rat is coupled to a defective number of GHRH receptors in the somatotrophs, is likely due to a primary deficiency of GHRH availability, as implied by the diminished GHRH immunoreactivity and gene expression in and GHRH release from the hypothalamus of old rats. Attempts have been made to stimulate the sluggish somatotrophic function in elderly humans and dogs using GHRH; in either species positive results were obtained though, overall, it would seem that the GHRH hypofunction does not entirely account for the GH hyposecretory state during ageing. Concerning somatostatin, although the expression of this peptide decreases with age in the rat hypothalamus, secretion and activity of this hormone is increased, resulting in an altered relationship between GHRH and somatostatin gene expression and secretion. It is likely that defects, especially in catecholaminergic and cholinergic neurons, are instrumental in altering specific peptidergic neurons. Reportedly, catecholamines induce GH release by stimulating GHRH neurons and inhibiting somatostatin-releasing neurons; acetylcholine stimulates GH release via muscarinic receptors, in this way inhibiting the action of somatostatin neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Behavioral and biochemical evidence of opioidergic involvement in cocaine sensitization.

Chronic administration of cocaine produces sensitization to its behavioral effects in humans and experimental animals. In the present study, rats treated with cocaine (10 mg/kg, i.p.) once daily for 10 days showed an enhancement in the acute drug stimulation of locomotor activity and stereotypy. Biochemical analysis in the nucleus accumbens of chronic cocaine-treated animals indicated that sensitization of D1 dopamine (DA) receptors had also developed. In fact, stimulation of adenylyl cyclase activity by DA was increased in nucleus accumbens membranes from sensitized rats. Our findings suggest that a novel postsynaptic mechanism, i.e., an increased DA-D1 receptor function, may play a role in the sensitization. A causal relationship between the two events is supported by the observation that neither motor behavioral sensitization nor DA-dependent adenylyl cyclase hyperactivity developed when the opiate antagonist naltrexone (2 mg/kg, s.c.) was given daily for 10 days before cocaine. When given alone, naltrexone was inactive in all respects, which rules out any unspecific action and suggests that its effects may be due to competition at receptors with endogenous opioids mobilized by cocaine. This was indirectly supported by the finding that desensitization of opioid inhibition of adenylyl cyclase developed in nucleus accumbens membranes of cocaine-sensitized rats. Chronic blockade of opioid receptors by naltrexone also counteracted the reinforcing properties of cocaine; conditioned place preference, clearly displayed by cocaine-treated animals, was antagonized in a dose-related manner. Overall, these results confirm that endogenous opioid peptides play an important role in cocaine addiction.

Adenylyl Cyclases↗
PubMed1994

Prolonged very low calorie diet in highly obese subjects reduces plasma viscosity and red cell aggregation but not fibrinogen.

Epidemiological studies have shown that obesity, as well as haemorheological changes are risk factors for cardiovascular disease. The aim of this study performed in grossly obese subjects was to investigate: (a) the effects on haemorheological parameters of a 3 month period of very low calorie diet (VLCD, 514 and 470 Kcal/day in women and men respectively), and (b) the relationship between haemorheological test results at baseline and the different types of body fat distribution. Fifty-two obese healthy subjects (31 women), with BMI > 30, were examined at baseline; 34 of these (19 women), compliant with the diet, were also examined after 3 months VLCD. At baseline, the results of haemorheological variables were not significantly different for patients in the highest waist-to-hip ratio (WHR) tertile vs those in the other two tertiles. After VLCD, body weight and BMI decreased markedly. The values of Ht, plasma viscosity (PV), erythrocyte aggregation index (EAI) values (P < 0.001) and white blood cell (WBC) counts (P < 0.01) significantly dropped. Globulin levels decreased, while albumin levels increased leading to significantly (P < 0.001) higher A/G ratios. No significant changes in fibrinogen (Fgn) levels were recorded after diet. In conclusion, the present study demonstrates that prolonged VLCD associated with slimming in grossly obese subjects is effective in improving related haemorheological disorders, mainly of plasmatic type, except Fgn. Second, we found that, at least in these grossly obese subjects, there is no clear evidence of a relationship between the degree of haemorheological changes and WHR values.

Adult↗
PubMed1993

Effect of ethanol exposure on voltage-dependent calcium channels in in vitro cellular models.

Chronic ethanol exposure alters calcium movements and the number of dihydropyridine (DHP) binding sites in the animal brain and in cultured neural cell lines. The present study investigates the effect of ethanol treatment on dihydropyridine- and omega-conotoxin (CgTx)- labelled calcium channels in undifferentiated and differentiated NG 108-15 cells. Following differentiation, the binding of [3H] -PN 200-110 increased by 48% while [125I]-CgTx binding increased by six fold. In accordance with data in the literature, undifferentiated cells exposed to ethanol (3 days) showed a large increase (70%) in DHP binding sites. In contrast, CgTx binding sites were unmodified by the treatment. Using differentiated cells, ethanol exposure induced a significant decrease (53%) in CgTx binding sites without altering those labelled by PN 200-110 (isradipine). These findings indicate that the effect of ethanol exposure on calcium channels may be dependent on the type of channel considered and on the status of the cells treated.

Animals↗
PubMed1992

Lipid, lipoprotein, and apolipoprotein assessment during an 8-wk very-low-calorie diet.

The influence of a very-low-calorie diet (VLCD) on lipid pattern is controversial. To evaluate the long-term effect of semistarvation on lipid patterns, a group of severely obese patients [aged 37 +/- 12 y, body mass index (BMI) 40.0 +/- 0.9] underwent a VLCD for 8 wk. Total cholesterol (TC), LDL cholesterol (LDL-C), and HDL cholesterol (HDL-C), triglycerides (TGs), apolipoproteins A1 (apo A1) and B (apo B) were analyzed every week. TC (6.07 +/- 0.23 vs 5.53 +/- 0.25 mmol/L, P less than 0.0008), HDL-C (mmol/L 1.26 +/- 0.06 vs 1.04 +/- 0.05 mmol/L, P less than 0.0001), TGs (1.46 +/- 0.19 vs 1.06 +/- 0.10 mmol/L, P less than 0.0008), and apo A1 (1.57 +/- 0.06 vs 1.32 +/- 0.06 g/L, P less than 0.0002) decreased, whereas LDL-C and apo B showed a biphasic behavior: they significantly fell during the first 3 wk, but during the last weeks returned to their initial values.

Adult↗
PubMed1992

Pancreatic exocrine carcinoma producing adrenocorticotropic hormone.

A rare case of pancreatic exocrine carcinoma with an endocrine component secreting adrenocorticotropic hormone (ACTH) is reported and discussed in relation to other cases previously published. The patient initially presented with a severe form of diabetes, which was treated accordingly. Persistence of hyperglycemia, along with other metabolic alterations and marked hypokalemia, led to the suggestion of abnormal ACTH secretion. In this patient, however, a florid Cushing's syndrome was not observed. The patient also developed hematological alterations, mainly leukopenia and thrombocytopenia, whose origins were unclear. At autopsy, a poorly-defined mass was discovered between the body and tail of the pancreas. Standard histology showed a moderately-differentiated adenocarcinoma. Immunohistochemical analysis of the tumor specimen demonstrated the presence of some neoplastic cells immunoreactive for chromogranin A, neuron-specific enolase and ACTH. These findings are consistent with the existence of an endocrine component within the exocrine carcinoma with ACTH differentiation.

ACTH Syndrome, Ectopic↗
PubMed1992

G protein modulation of omega-conotoxin binding sites in neuroblastoma x glioma NG 108-15 hybrid cells.

Electrophysiological evidence shows that voltage-dependent calcium channel (VDCC) activity can be regulated by a large number of neurotransmitters. In particular, guanine nucleotide binding regulatory protein (G protein)-mediated inhibitory modulation of the channel activity has been deduced from evidence that GTP analogues and purified G proteins are able to mimic this effect. The G proteins involved are pertussis toxin (PTx) sensitive. The purpose of the present study was to investigate, using biochemical techniques, whether G protein activation modulates the recognition site for omega-conotoxin GVIA (CgTx), a peptide neurotoxin that selectively labels a population of high-threshold VDCC. Undifferentiated and differentiated (1 mM dibutyryl cyclic AMP, 4 days) NG 108-15 cells were used. In both crude cellular extracts specific binding of 125I-CgTx was characterized. Differentiation induced a sixfold increase in the number of binding sites and doubled the KD value. The in vitro addition of guanylylimidodiphosphate (GMP-PNP; a nonhydrolyzable analogue of GTP) to extracts prepared from differentiated cells reduced the 125I-CgTx binding by 48%. This effect, observed in undifferentiated cells as well, was also caused by other triphosphate guanine nucleotides, such as GTP, but not by guanosine 5'-O-(2-thiodiphosphate) or adenine nucleotides. Treatment of the cells with PTx prevented the GMP-PNP effect. Moreover, the results obtained after preincubation with specific antisera raised against the alpha subunits of Gi1-2 and Go suggest that Go is the G protein responsible for the observed effect.

Animals↗
PubMed1991

Pertussis toxin-sensitive G-protein mediates galanin's inhibition of scopolamine-evoked acetylcholine release in vivo and carbachol-stimulated phosphoinositide turnover in rat ventral hippocampus.

The effects of intracerebroventricular (i.c.v.) injections of pertussis toxin were investigated on the inhibitory action of galanin on acetylcholine release and phosphoinositide breakdown stimulated by muscarinic agents in rat ventral hippocampus. Pertussis toxin (0.6 micrograms, i.c.v., 96 h) counteracted the in vitro inhibitory effect of galanin (3.1 nmol) on phosphoinositide breakdown stimulated by carbachol without altering the stimulatory action of the cholinergic agonist on signal transduction, in miniprisms from rat ventral hippocampus. Pertussis toxin also abolished the in vivo effect of galanin on scopolamine-stimulated acetylcholine release in vivo but did not affect basal acetylcholine release. The results indicate that pertussis toxin-sensitive G-protein(s) mediates the galanin receptor regulation of pre- and postsynaptic cholinergic functions in the ventral hippocampus.

Acetylcholine↗
PubMed1991

Pertussis toxin pretreatment affects opiate/nonopiate and stress-induced analgesia differently.

Intracerebroventricular injection of pertussis toxin (PTX, 1 microgram/rat) six days before the hot plate test abolished analgesia induced by central morphine. The toxin did not affect analgesia evoked by central neurotensin or ASU 1-7 eel calcitonin. PTX pretreatment also attenuated footshock-induced analgesia (FSIA) delivered to all four paws. When the shock was restricted to the front paws, PTX consistently lowered postshock tail flick latencies, but did not reduce analgesia resulting from shock delivered to the hind paws. It thus appears that PTX-sensitive G-proteins are an essential transduction step needed to initiate the molecular events underlying opiate analgesia evoked by either morphine or shock. In contrast, the signal transduction mechanism subsequent to the stimulation of neurotensin or calcitonin receptors, and to the nonopiate FSIA, appears not to involve PTX-sensitive G-proteins.

Animals↗
PubMed1991

Age-related changes of growth hormone secretory mechanisms in the rat pituitary gland.

The mechanisms underlying the age-related decrease and increase in somatotroph responsiveness to growth hormone-releasing factor (GHRF) and somatostatin respectively were studied in rat pituitary membranes in vitro. Basal adenylate cyclase (AC) activity was similar in pituitary membranes from rats of 8 days (either sex) and male rats of 3 months, but it was almost threefold higher in membranes from male rats of 21-23 months. GHRF induced a lower percentage stimulation of AC activity in membranes from infant and old than adult rats. Somatostatin inhibited stimulation of AC induced by forskolin more effectively in membranes from adult than infant and old rats. In parallel experiments, since the tissue we used is formed by a mixed population of pituitary cells, we evaluated, for comparison, the effect on AC of neurohormones, i.e. vasoactive intestinal polypeptide (VIP) and dopamine which act primarily on lactotrophs. VIP induced a lower fold-stimulation of AC activity in membranes from infant and old than adult rats. Dopamine inhibited forskolin-induced stimulation of AC in the following rank order of magnitude: old, adult and infant rats, and was also more effective in inhibiting basal AC activity in old than in adult rats. The stimulatory and inhibitory G proteins (Gs and Gi) coupled to AC were measured indirectly by evaluating stimulatory and inhibitory effects of different concentrations of GTP on AC. GTP, at stimulatory concentrations, increased AC activity in membranes from infant and adult rats similarly whereas its effect was significantly greater in membranes from old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1990

Pertussis toxin modifies the effect of central morphine on rat intestinal motility.

To find whether the antipropulsive effect of morphine administered intracerebroventricularly (i.c.v.) depends on a G-protein-mediated mechanism, we studied the effect of i.c.v. pertussis toxin (PTX) pretreatment on morphine-induced inhibition of intestinal motility. The influence of PTX was evaluated on intestinal transit (charcoal meal test) and by monitoring of intestinal myoelectrical activity. The antitransit effect of morphine (10 micrograms/rat) was antagonized by about 70% 3, 6, 9 and 12 days after PTX pretreatment (1 microgram/rat) and it was partially restored after 25 days. I.c.v. morphine abolished the regular appearance of the myoelectric migrating complex (MMC) recorded in the rat jejunum and this effect was completely antagonized by PTX pretreatment. When morphine was injected 25 days after PTX, it significantly reduced MMC frequency, confirming the partial recovery seen in the transit experiments. The pertussis toxin-catalyzed ADP ribosylation of a 39-41 kDa substrate in membranes prepared from hypothalamus and midbrain of rats injected with toxin 6 days before was strongly reduced as compared to the controls. On the contrary, after 25 days, ADP ribosylation was the same in treated and control rats. Thus the antipropulsive effect of central morphine could be initiated at receptor sites which interact with G-protein substrates of pertussis toxin.

Adenosine Diphosphate↗
PubMed1990

Diabetic retinopathy in chronic pancreatitis.

Using fluorescein angiography, we studied the prevalence and characteristics of diabetic retinopathy in 40 patients with chronic pancreatitis complicated by diabetes and in 40 type 1 diabetics with comparable duration of diabetes. Retinopathy was found in 19 pancreatitis patients (47.5%) and in 20 type 1 diabetic patients (50%); it was background, minimal, or mild to moderate, without impairment of visual function, in all 19 pancreatitis patients and in 17 of the 20 type 1 diabetics. In the remaining three idiopathic diabetics, retinopathy was background of severe degree in two and proliferative, with impairment of vision, in one. No differences between patients with and without retinopathy were observed in fasting blood glucose, glycosylated hemoglobin, serum cholesterol, or triglyceride levels. The only significant difference (p less than 0.001) was the greater duration of diabetes in patients with retinopathy when compared with those without it (10.8 +/- 5.7 vs. 5.2 +/- 3.9 yr in pancreatitis patients; 11.2 +/- 5.0 vs. 5.1 +/- 3.5 yr in type 1 diabetics; mean +/- SD). Contrary to what is generally believed, the results indicate that the risk of retinopathy and the characteristics of this complication in patients with chronic pancreatitis and secondary diabetes are similar to those in patients with idiopathic diabetes.

Blood Glucose↗
PubMed1990

Pertussis toxin inhibits morphine analgesia and prevents opiate dependence.

Six days after intracerebroventricular pretreatment of rats with pertussis toxin (PTX 0.5 microgram/rat) there was a marked decrease in the antinociceptive effect of morphine, regardless of the route of opioid administration (into the periaqueductal gray matter, intrathecally or intraperitoneally) or the analgesic test used (tail flick and jaw opening reflex). PTX pretreatment also partially attenuated the naloxone-precipitated withdrawal syndrome in morphine-dependent rats, significantly reducing teeth chattering, rearing and grooming. These in vivo findings indicate that G-protein-dependent mechanisms are involved in morphine analgesia and dependence. The biochemical mechanism could be related to ADP ribosylation of Gi coupled to the adenylate cyclase system, but an interaction of PTX with other G-proteins linked to different second messengers or directly to ionic channels cannot be excluded.

Adenylate Cyclase Toxin↗