Biomedical subjects

A Giachetti

Publications and source records attributed to A Giachetti.

At least 91 records · Page 5Linked to original sources

PubMed1989

Role of muscarinic receptor subtypes in the regulation of migrating myoelectric complex in the dog.

The role played by muscarinic receptor subtypes in the regulation of the migrating myoelectric complex was investigated in 7 dogs chronically implanted with bipolar electrodes along the small intestine. Pirenzepine (3-300 micrograms/kg i.v.) and atropine (1-30 micrograms/kg i.v.) were used as selective and unselective antagonist, respectively. Atropine (30 micrograms/kg) significantly delayed the onset of the next complex. On the contrary, pirenzepine displayed a biphasic action: low doses (less than 100 micrograms/kg) shortened the cycle period, whereas at 300 micrograms/kg the drug behaved like atropine. Pirenzepine affected the cycle period in the low-dose range by reducing the length of phase I. Both atropine and pirenzepine impaired the migration of the ongoing complex, and significantly reduced the migration velocity of the following one. These findings suggest that the initiation of the migrating myoelectric complex in the dog is under an inhibitory influence mediated by the M1 muscarinic receptor subtype; on the other hand, M2 receptor activation is needed for the onset of the activity front. Finally, both receptor subtypes determine the normal migration of phase III.

Animals↗

PubMed1989

Multiple sources of calcium for contraction of the human urinary bladder muscle.

1. KCl, carbachol, neurokinin A and endothelin produced concentration-dependent contractions of mucosa-free muscle strips from the dome of the human urinary bladder. The maximal response to carbachol or neurokinin A exceeded that to KCl, while the maximal response to endothelin approached that to KCl. 2. Nifedipine (1 microM) abolished the response to KCl, reduced the response to carbachol or neurokinin A but had no effect on the response to endothelin. Bay K 8644 (1 microM) markedly potentiated the response to KCl but had little or no effect on the response produced by the other stimulants. 3. Superfusion of the strips with a nominally calcium (Ca)-free medium containing EDTA (1 mM) for 30 min markedly reduced the response to carbachol, neurokinin A and endothelin, although a small response was still evident at high concentrations. Likewise, after a prolonged (60 min) superfusion of the strips with a high K (80 mM) Ca-free medium plus EDTA (1 mM) these three agonists still produced a small contractile response. 4. The nifedipine (1 microM) resistant response to carbachol, neurokinin A or endothelin was markedly depressed by LaCl3 (1 mM). In contrast, the nifedipine-(1 microM) resistant response to carbachol was not modified by NiCl2 (0.1 mM) or omega-conotoxin (0.1 microM). 5. Caffeine produced divergent effects depending upon the temperature of incubation: a relaxation at 37 degrees C and a concentration-dependent (2.5-20 mM) contraction at 25 degrees C. The latter was markedly inhibited by procaine (3 mM) but unaffected by nifedipine (1 microM). 6. After a prolonged (60 min) superfusion with a high K, Ca-free medium containing EDTA the response to carbachol (100 microM) was abolished by previous exposure to procaine (3 mM). Conversely, the response to endothelin (1 microM) was unaffected by procaine. The response to endothelin in these experimental conditions was also resistant to LaCl3 (1 mM). 7. These findings indicate that multiple sources of Ca are mobilized for contraction of the human bladder muscle by different stimulants. Dihydropyridine- and voltage-sensitive Ca channels provide the major if not the sole source of Ca for the response to KCl, play some role in the response to muscarinic (carbachol) or NK-2 tachykinin receptor stimulation but are not involved in the response to endothelin. Carbachol, neurokinin A and endothelin all mobilize a Ca pool (either extracellular or located at membrane level) which is LaCl3-sensitive but nifedipine-resistant. Neither T- nor N-type channels appear to be involved in the response to carbachol. In addition, these agents mobilize a tightly bound Ca pool independently from membrane depolarization. This latter pool is probably a procaine-sensitive intracellular source of activator Ca mobilized by caffeine and carbachol. The failure of procaine to prevent the response to endothelin in high K, Ca-free medium raises the possibility that this peptide mobilizes an intracellular source of activator Ca, distinct from the caffeine- and carbachol-sensitive pool.

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

PubMed1989

Octylonium bromide interacts competitively with the PAF receptor.

To clarify the nature of the interaction of octylonium bromide with the PAF receptor, saturation studies of 3H-PAF binding were made in the presence of increasing concentrations of the radioligand (from 0.06 to 7.4 nM) and of octylonium bromide (1 X 10(-8), 5 X 10(-8) and 1 X 10(-7) M) or of a potent PAF antagonist L 652,731 (2.5 X 10(-7) M), or in the absence of competing drugs. Saturation binding data were plotted according to the non-linear fitting analysis and to Scatchard transformation. Both mathematical models indicated that the presence of added drugs decreased the affinity of the complex 3H-PAF/PAF receptors, leaving unaffected the maximum number of PAF binding sites. Receptor parameters in the absence of competitors were: KD = 1.2 nM, Bmax = 950 fmoles 3H-PAF bound/10(8) platelets. Octylonium bromide increased, in a concentration-dependent manner, KD values from 1.5 to 2.1 nM, while Bmax ranged from 910 to 980 fmoles 3H-PAF specifically bound/10(8) platelets. Likewise, L 652,731 did not influence Bmax (980 fmoles) but increased KD (1.9 nM). The binding behaviour of octylonium bromide and L 652,731 indicates that the two compounds inhibit competitively the binding of 3H-PAF to its receptors.

Animals↗

PubMed1988

Aversive conditioning of homozygous and heterozygous D.I. Brattleboro rats in the light-dark box.

Active and passive avoidance, and conditioned freezing acquisition and retention were studied in HODI and HEDI Brattleboro rats. All animals were from the same source and of the same age and sex. The light-dark box test was employed. 0.6 and 2.0 mA footshocks were administered for the same number (7) of daily trials. Extinction time-course was followed for seven consecutive daily trials. Passive avoidance: the conditioned response was acquired and retained equally well by all Ss and for both shock intensities. Active avoidance: for 0.6 mA shocks HODI Ss acquired and retained the response significantly better than HEDI Ss; for 2.0 mA shocks the response was acquired equally by both groups of Ss, and retained significantly better by HODI Ss. Freezing: in general, HODI Ss exhibited less freezing then HEDI Ss. The diverse conditioned behavior of HODI and HEDI Ss in this paradigm, which allows the contemporaneous investigation of several aversive responses, does not support the hypothesis that vasopressin deficiency impairs learning and memory in the rat.

Animals↗

PubMed1988

Pharmacological characterization of muscarinic receptors involved in McN-A-343-induced effects on intestinal motility and heart rate in conscious dogs.

1. Intravenous injection of the muscarinic agonist, McN-A-343, in conscious dogs equipped with an ileal Thiry fistula produced a dose-related inhibition of intestinal phasic contractile activity, and an increase in heart rate. 2. The inhibitory action of McN-A-343 on motility was antagonized with different potencies by antimuscarinic drugs. The non-selective drug, N-methylatropine, blocked the McN-A-343 effect as well as the reflex phasic activity. The M1-selective compound, pirenzepine (1-30 micrograms kg-1), was a potent antagonist of the McN-A-343 effect, whereas the cardioselective M2-antagonist, AF-DX 116, and the smooth muscle selective compound, 4-diphenylacetoxy-N-methyl piperidine (4-DAMP), were completely ineffective at the doses tested. 3. The McN-A-343-induced inhibition of intestinal motility was blocked by locally applied lignocaine, suggesting the involvement of a neural inhibitory pathway. The resistance to hexamethonium and (alpha 1-, alpha 2- and beta-) adrenoceptor blocking drugs excluded transmission through a nicotinic synapse or release of catecholamines. 4. McN-A-343-induced tachycardia was also the result of muscarinic receptor activation. It was very sensitive to antagonism by 4-DAMP, while being completely unaffected by AF-DX 116. Pirenzepine displayed an intermediate profile, reducing tachycardia at doses fully active in reversing the agonist-mediated effect on intestinal motility. Propranolol partially reduced McN-A-343 tachycardia, suggesting catecholamine release. 5. The two McN-A-343 effects investigated in the present study appear to be mediated by different muscarinic receptor subtypes. While the inhibitory action on intestinal motility results from stimulation of Ml-muscarinic receptors, the tachycardia is mediated by receptors blocked selectively by 4-DAMP.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗

PubMed1988

Muscarinic M1 receptors stimulate a nonadrenergic noncholinergic inhibitory pathway in the isolated rat duodenum.

We examined the effect of the muscarinic agonist McN-A-343 (4-m-chlorophenylcarbamoyloxy-2-butynyl trimethyl ammonium) on in vitro preparations of rat small intestine. McN-A-343 (0.1-10 microM) induced a concentration-dependent relaxation of duodenum, jejunum and ileum. This effect was due to activation of muscarinic receptors of the M1 subtype, inasmuch as it was antagonized by atropine (pA2, 8.93) and by the selective M1 antagonists pirenzepine and dicyclomine with high affinity (pA2, 8.09 and 8.14, respectively). Tetrodotoxin, but not hexamethonium, abolished McN-A-343 relaxation indicating involvement of neural pathways and absence of nicotinic transmission. Moreover, in the presence of apamin (0.1 microM) McN-A-343 induced a contractile response. Unlike McN-A-343, acetylcholine contracted the rat duodenum; its concentration-response curve was significantly potentiated by tetrodotoxin, suggesting stimulation of the McN-A-343 sensitive receptor by acetylcholine (P less than .01). Prior treatment of animals with reserpine reduced the potency of McN-A-343 only by 2.5-fold. The gamma-aminobutyric acid (GABA) antagonist bicuculline inhibited McN-A-343 with an affinity comparable to that found for GABA(A) receptors (pA2, 5.52), indicating involvement of GABAergic fibers. ATP is also likely to play a role, as desensitization experiments showed that alpha-beta-methylene ATP induced a comparable decrease of both McN-A-343 and its own response. In contrast, desensitization induced by GABA occurred to a minor extent. Thus, in the rat duodenum, activation of an M1 muscarinic receptor induces relaxation by releasing GABA, and possibly ATP, from myenteric neurons.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗

PubMed1988

Binding and functional characterization of the cardioselective muscarinic antagonist methoctramine.

The antimuscarinic properties of the newly synthetized polymethylene tetramine derivative, methoctramine, were investigated in binding and functional assays. Methoctramine displaced the specific binding of [3H]-N-methylscopolamine [( 3H]NMS) and [3H] pirenzepine from membranes of rat tissues with the following order of affinities: heart = cerebellum greater than cortex greater than submandibular glands, the ratio of the affinities of the compound for the heart and the glands amounting to about 130. Computer fits of binding curves generated in cardiac and cortical membranes were compatible with an interaction at one binding site, whereas those in submandibular glands and cerebellum had slopes significantly lower than 1. Experiments performed in cardiac membranes to investigate the effect of methoctramine on the dissociation kinetics of [3H]-NMS showed that concentrations of compound up to 1 microM did not affect the dissociation of [3H]-NMS elicited by an excess of NMS. At greater concentrations (10-100 microM), methoctramine dose dependently inhibited [3H]-NMS dissociation, thus revealing an allosteric interaction. In in vitro functional assays, methoctramine displayed more than 100 times greater affinity for the muscarinic receptors mediating negative inotropic and chronotropic effects in guinea pig atria than for those responsible for tracheal contraction. Similarly, the compound was a more potent antagonist of the bradycardial response to bethanechol than of the bladder tonus increase, saliva secretion and hypotension induced by the muscarinic agonist in anesthetized cats. Finally, in the pithed rat, methoctramine preferentially inhibited cardiac M2 (vagal bradycardia) over ganglionic M1 (McN-A-343-induced hypertension) responses. The evidence appears to characterize methoctramine as being the most selective M2 muscarinic antagonist described to date.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Kinetic analysis of the interaction of mifentidine with gastric H2-receptors in the conscious dog.

The H2-receptor antagonists mifentidine and cimetidine were compared for their ability to antagonize the activation of H2-receptors in the conscious dog. Dose-response curves to dimaprit in stimulating gastric secretion were displaced to the right in a dose-related fashion by both drugs. Schild and Eadie-Hofstee analysis of these data indicated that mifentidine and cimetidine inhibited in vivo activation of H2-receptors in a manner compatible with competitive surmountable antagonism. Mifentidine displayed a 24fold greater potency than cimetidine as H2 antagonist in the conscious dog.

Animals↗

PubMed1987

WEB 2086. A potent PAF antagonist exerts protective effect toward PAF-induced gastric damage.

Single intravenous administration of platelet activating factor (PAF; 4 micrograms/kg) induced reproducible gastric damage in the conscious rat which was prevented by WEB 2086, a potent and specific PAF-antagonist. Intravenous and oral ED50s in protecting rats from gastric damage were 61 and 633 micrograms/kg, respectively. Because of the reported association between septic shock and gastrointestinal ulceration, the therapeutic potential of PAF-antagonists might be broader than previously thought.

Animals↗

PubMed1987

Effect of mifentidine on mepirizole-induced duodenal ulcer in the rat.

The H2-receptor antagonists mifentidine, famotidine, cimetidine and ranitidine were examined for their ability to prevent the duodenal ulcer caused by mepirizole (250 mg/kg p.o.), a non-steroidal anti-inflammatory agent, in the conscious rat. All the compounds exerted a dose-related protective effect and on the basis of their ED50s, the following rank order of potency was found: mifentidine = famotidine greater than ranitidine greater than cimetidine. The antiulcer activity displayed by the H2-receptor antagonists evaluated in this model reflects their potency in inhibiting basal and stimulated gastric acid secretion in rat. The results of these studies indicate mifentidine as a potent anti-ulcer agent.

Animals↗

PubMed1987

Effects of detention and illumination on rats' exploratory behavior in a two-box apparatus.

The effects of detention and lighting intensity on the exploratory behavior of male Wistar rats have been investigated by means of several types of two-box apparatus. Experiments consisted of six consecutive daily trials. Step-through latency values were taken up to 180 sec. Even a very short detention (10 sec) within the starting box exerted a powerful inhibitory influence on the exploratory behavior of the subjects. Uniformly well-lighted surroundings (both boxes) exerted an equally powerful inhibitory influence on the same behavior. This inhibition was only slightly decreased by the availability of visual cues. Only in the apparatus in which at least one box was dark was the exploratory behavior well maintained. Both detention and bright lighting inhibited selectively the exploratory, locomotor behavior of these animals and did not inhibit other motor activities. In fact, groomings and attempts (abortive passages from one box into the other) were repeatedly performed during the increased step-through latency. These activities are discussed as indicators of a conflict between drives.

Animals↗

PubMed1987

Central muscarinic activation elicits compulsive drinking behaviour in the rat.

Injection of bethanechol into the lateral cerebral ventricle of the rat induces a marked increase in drinking, within 30 min from administration. The response is dose-related, maximal water intake (6.1 +/- 0.55 mL; mean +/- s.e.) occurring at 10 micrograms of bethanechol. Peripheral administration of the agonist (up to 3 mg kg-1 i.p.) fails to elicit drinking. Among several specific antagonists only antimuscarinic drugs produced a significant inhibition of the response, suggesting that the compulsive drinking behaviour in the rat is caused by activation of central muscarinic receptors. The drinking behaviour emerges as a reliable test to assess central muscarinic activity of both agonists and antagonists.

Animals↗

PubMed1987

AF-DX 116, a cardioselective muscarinic antagonist.

The M2 subtype of the muscarinic receptor was investigated using the antagonist AF-DX 116. In "in vitro" and "in vivo" experiments, AF-DX 116 behaved as a competitive antagonist and exhibited a selectivity for cardiac muscarinic-mediated functions. It antagonized negative chronotropic and inotropic effects exerted by muscarinic receptor activation in the guinea pig atria with an affinity (pA2) 10-fold greater than that estimated in intestinal and tracheal smooth muscle preparations. It also reversed the negative chronotropic effect induced by peripheral vagal stimulation, intrasinus node injection of bethanechol and central vagal activation by clonidine. In all these in vivo functions, AF-DX 116 was approximately 10 times less potent than atropine, while being several hundred-fold less potent in antagonizing acetylcholine-mediated bronchoconstriction and gastric emptying. These results are consistent with the hypothesis that the cardiac muscarinic receptors constitute a subclass of the M2 subtype.

Animals↗

PubMed1987

(R)-nipecotic acid ethyl ester: a direct-acting cholinergic agonist that displays greater efficacy at M2 than at M1 muscarinic receptors.

Previous reports have suggested that the ethyl ester of (R)-nipecotic acid ethyl ester [(R)-NAEE] displays cholinomimetic properties in vivo. The present study was undertaken to characterize more fully this action by examining the effects of (R)-NAEE in a number of pharmacological and biochemical tests of cholinergic action. (R)-NAEE was found to produce negative inotropic and chronotropic effects on the guinea pig atria (pD2 = 5.91 and 5.62, respectively), and was capable of stimulating contractions in the guinea pig ileum (pD2 = 5.95) and rat jejunum (pD2 = 5.40) at concentrations similar to bethanechol. Both the cardiac and intestinal effects of (R)-NAEE were reversed by atropine. Moreover, (R)-NAEE competed with N-[3H]methylscopolamine and [3H]pirenzepine for muscarinic binding sites in a variety of tissues. Like carbachol, (R)-NAEE inhibited GTP-stimulated adenylate cyclase in rat striatal membranes (EC50 = 52 microM), whereas, unlike carbachol, (R)-NAEE was unable to stimulate inositol phosphate accumulation in rat cerebral cortical slices, behaving as an antagonist in this latter system (pA2 = 5.0). The results indicate that (R)-NAEE interacts directly with cholinergic muscarinic receptors, being an agonist for the M2 subtype and an antagonist at M1 sites.

Adenylyl Cyclase Inhibitors↗

PubMed1987

N-butyl hyoscine exerts local spasmolytic effect in the small and large bowel of the conscious dog.

The spasmolytic activity of N-Butyl Hyoscine (NBH) (1) has been investigated in conscious dogs provided with ileal or colonic Thiry fistulas in which motility was stimulated by intraluminal distension. In ileal motility experiments, phasic motility index (PMI), intestinal tonus, contraction frequency and heart rate were monitored. Intravenous administration of NBH (10 to 100 micrograms/kg) depressed PMI (ED50 35.1 micrograms/kg) and the other motility parameters. Heart rate increases were observed at 100 micrograms/kg. Application of NBH directly into the fistula (300 to 3000 micrograms/kg) caused a long-lasting, potent inhibition (31-72%) of PMI; tonus and contraction frequency were only slightly affected, while heart rate was not altered. When NBH was administered into an ileal fistula adjacent to the one from which motility was recorded, changes of PMI and other parameters were observed only after a massive dose of the drug (10000 micrograms/kg). In colonic fistula experiments, intraluminal NBH administration (300 to 3000 micrograms/kg) depressed colonic motility (39-59%), without affecting heart rate. It is concluded that NBH present in the intestine, although poorly absorbed, exerts local spasmolytic action.

Animals↗

PubMed1987

Spontaneous and conditioned behavior of Wistar and Long Evans rats.

Spontaneous behavior (locomotion, feeding, drinking, and exploration in a two box apparatus) as well as conditioned behavior (passive and active avoidance responding, and freezing in the light-dark box apparatus) were studied in naive male Wistar and Long Evans rats. Concerning spontaneous behavior, Long Evans rats were more active during both light and dark periods, and showed better exploratory performance than Wistar rats. Concerning conditioned behavior, Long Evans rats acquired and retained better active and passive avoidance responses, and exhibited longer initial freezing than Wistar rats in the range of 0.6-1.4 mA footshocks. The results better define the important behavioral differences existing between the two strains, Long Evans rats showing consistently a higher level of alertness and a better conditioned performance.

Animals↗

PubMed1986

Cardioselective profile of AF-DX 116, a muscarine M2 receptor antagonist.

AF-DX 116 (see chemical name below) is a competitive antagonist of muscarine receptors in peripheral organs. In contrast to pirenzepine, its behaviour in functional experiments indicates selectivity for the M2 muscarinic subtype. In pithed rats AF-DX 116 inhibits vagally-induced bradycardia, an M2 response, (ED50 32 micrograms/kg i.v.) in preference to the M1-mediated pressor response to McN-A-343 (ED50 211 micrograms/kg i.v.). AF-DX 116 further discriminates among M2 receptors, showing a high affinity for the cardiac muscarine receptors. In isolated preparations, AF-DX 116 has a tenfold higher affinity for the muscarine receptors of the heart (pA2 7.33) than for those in smooth muscles (pA2 6.39-6.44). The same profile appears from animal studies, where the compound is a more potent antagonist of either endogenously or exogenously activated cardiac muscarine responses as compared to vascular, smooth muscle or secretory responses. In general, the ratios of potencies (ED50) observed in cardiac vs. other muscarine mediated functions ranged between 30 and 50. Atropine showed no discrimination, inhibiting all muscarine responses in the same range of doses. In the conscious dog intravenous AF-DX 116 increased basal heart rate, and completely reversed the reflex bradycardia induced by clonidine. Tachycardia was dose-related (ED50 79 micrograms/kg i.v.), and occurred independently of background sympathetic tone. AF-DX 116 clearly distinguishes between M1- and M2-mediated responses; it also emphasizes the long-recognized heterogeneity among the peripheral M2 subtypes. AF-DX 116, for its pronounced cardioselectivity, may have a therapeutic potential in the treatment of sinus bradycardia.

Animals↗

PubMed1986

Effect of pirenzepine and PGE2 on taurocholic acid-induced gastric lesions.

Cytoprotective activity of Pirenzepine (PZ) and Prostaglandin E2 (PGE2) was investigated in the gastric damage induced by taurocholic acid (TA) in the rat. Gastric mucosal potential difference (PD) and gross mucosal erosions were measured. Intravenous PZ (18 mg/kg) and PGE2 (5 micrograms/kg) prevented both the sharp decrease of PD and the gastric lesions caused by intragastric TA (40 mM). When TA administration preceeded drug treatment, both compounds reversed the PD fall but only PZ was able to restore gross mucosal integrity. It is thought that TA causes gastric damage by producing back-diffusion of H+ ions across the mucosal layer. It is speculated that antimuscarinic, such as PZ, might reduce gastric damage either by preventing, at the submucosal level, the spreading of cytolesive process triggered by H+ retro-diffusion and/or by inhibition of acid secretion in the depth of the gastric glands.

Animals↗