Biomedical subjects

R B Raffa

Publications and source records attributed to R B Raffa.

At least 91 records · Page 5Linked to original sources

PubMed1992

Receptor regulation, competitive antagonism and pA2.

A growing body of evidence suggests that the number of drug receptors on cell surfaces is not fixed, but is dynamically regulated by circumstances that include exposure to the ligand itself. Because most traditional theories of drug action are based on the assumption of a fixed number of receptors, it is desirable to examine the importance of this regulatory process on the interpretation of dose-effect data. Of special interest is the impact of a variable receptor number on the equation of competitive antagonism and associated pA2 which, in the traditional theory, is a quantitative measure of antagonist-receptor affinity. Using a simple model of drug-induced endocytosis or exocytosis, it is shown that if the rate of either is appreciable, the pA2 is no longer a simple measure of affinity.

Binding, Competitive↗

PubMed1992

The effect of lowered extracellular Na+ concentration on ultraviolet light-induced relaxation of vasoconstricted rabbit isolated thoracic aorta.

The effect of lowering extracellular ion concentration on ultraviolet (UV) light-induced photorelaxation of norepinephrine(NE)-constricted rabbit isolated thoracic aorta was investigated. The magnitude of the photorelaxation response (similar to acetylcholine-induced, but not nitroprusside-induced, relaxation) progressively declined, in the absence of an effect on NE-induced vasoconstriction, as the total extracellular ion concentration was progressively reduced. This diminution in the photorelaxation response was duplicated by isosmotic lowering of the extracellular concentration of Na+, but not other ions, from 145 to 25 mM and was not restored by the replenishment of the Na+ deficiency by equimolar amounts of mannitol or Li+. In contrast, choline fully substituted for Na+. These findings suggest a fundamental difference in the ion dependency (and, hence, the mechanisms) of UV-induced photorelaxation and the vasorelaxations induced by acetylcholine or sodium nitroprusside.

Acetylcholine↗

PubMed1992

Supraspinal administration of [D-Met2]FMRFamide produces a naloxone-sensitive increase in heart rate in unrestrained spontaneously hypertensive rats.

Intracerebroventricular (i.c.v.) administration of either Phe-Met-Arg-Phe-NH2 (FMRFamide; molluscan cardioexcitatory neuropeptide; 3-30 micrograms) or the FMRFamide analog Phe-D-Met-Arg-Phe-NH2 ([D-Met2]FMRFamide; 15 micrograms) to conscious unrestrained spontaneously hypertensive rats (SHR) produced a relatively long lasting (greater than 1 h) increase in heart rate. The increase in heart rate produced by [D-Met2]FMRFamide was attenuated by i.c.v. injection of the opiate antagonist naloxone (2 micrograms). These results extend to a second endpoint an apparent opioid agonist-like (naloxone-reversible) action of [D-Met2]FMRFamide.

Animals↗

PubMed1992

Supraspinal antinociception produced by [D-Met2]-FMRFamide in mice.

The ability of Phe-Met-Arg-Phe-NH2 (FMRFamide) or [D-Met2]-FMRFamide to produce antinociception in mice, or to block morphine-induced antinociception, was examined using the tail-flick and tail-immersion (55 degrees C) tests. [D-Met2]-FMRFamide dose-dependently produced antinociception following intracerebroventricular (i.c.v.) administration with ED50 values (95% confidence limits) of 5.0 (2.2-7.2) and 12.8 (8.1-19.9) micrograms in the tail-flick and tail-immersion tests, respectively. FMRFamide did not produce a maximal effect in the tail-flick test. Naloxone (administered s.c. 20 min prior to the i.c.v. administration of [D-Met2]-FMRFamide) dose-dependently attenuated [D-Met2]-FMRFamide-induced antinociception. The shift in the [D-Met2]-FMRFamide dose-response curve was parallel and a pA2 value for naloxone of 6.3 +/- 0.3 was determined from a Schild plot analysis. Mice made tolerant to the antinociceptive effect of morphine were cross-tolerant to the antinociceptive effect of [D-Met2]-FMRFamide. FMRFamide and [D-Met2]-FMRFamide both produced rightward, parallel shifts of the morphine antinociceptive dose-response curve. The findings that [D-Met2]-FMRFamide both elicited naloxone-sensitive antinociception and attenuated morphine-induced antinociception are consistent with the view that FMRFamide-related peptides (FaRPs) are weak agonists at opioid receptors and, further, appear to reconcile the apparently chimeric agonist and antagonist properties of these peptides observed in vivo.

Amino Acid Sequence↗

PubMed1992

Opioid and nonopioid components independently contribute to the mechanism of action of tramadol, an 'atypical' opioid analgesic.

Tramadol hydrochloride produced dose-related antinociception in mouse abdominal constriction [ED50 = 1.9 (1.2-2.6) mg/kg i.p.], hot-plate [48 degrees C, ED50 = 21.4 (18.4-25.3) mg/kg s.c.; 55 degrees C, ED50 = 33.1 (28.2-39.1) mg/kg s.c.] and tail-flick [ED50 = 22.8 (19.2-30.1) mg/kg s.c.] tests. Tramadol also displayed antinociceptive activity in the rat air-induced abdominal constriction [ED50 = 1.7 (0.7-3.2) mg/kg p.o.] and hot-plate [51 degrees C, ED50 = 19.5 (10.3-27.5) mg/kg i.p.] tests. The antinociceptive activity of tramadol in the mouse tail-flick test was completely antagonized by naloxone, suggesting an opioid mechanism of action. Consistent with this, tramadol bound with modest affinity to opioid mu receptors and with weak affinity to delta and kappa receptors, with Ki values of 2.1, 57.6 and 42.7 microM, respectively. The pA2 value for naloxone obtained with tramadol in the mouse tail-flick test was 7.76 and was not statistically different from that obtained with morphine (7.94). In CXBK mice, tramadol, like morphine, was devoid of antinociceptive activity after intracerebroventricular administration, suggesting that the opioid component of tramadol-induced antinociception is mediated by the mu-opioid receptor. In contrast to the mouse tail-flick test and unlike morphine or codeine, tramadol-induced antinociception in the mouse abdominal constriction, mouse hot-plate (48 degrees or 55 degrees C) or rat hot-plate tests was only partially antagonized by naloxone, implicating a nonopioid component. Further examination of the neurochemical profile of tramadol revealed that, unlike morphine, it also inhibited the uptake of norepinephrine (Ki = 0.79 microM) and serotonin (0.99 microM). The possibility that this additional activity contributes to the antinociceptive activity of tramadol was supported by the finding that systemically administered yohimbine or ritanserin blocked the antinociception produced by intrathecal administration of tramadol, but not morphine, in the rat tail-flick test. These results suggest that tramadol-induced antinociception is mediated by opioid (mu) and nonopioid (inhibition of monoamine uptake) mechanisms. This hypothesis is consistent with the clinical experience of a wide separation between analgesia and typical opioid side effects.

Animals↗

PubMed1992

Thermodynamic analysis of the temperature dependence of the dissociation constant of naloxone at opioid delta receptors in the mouse isolated vas deferens.

Dissociation constants (KB) for naloxone inhibition of the actions of DPDPE in the mouse isolated vas deferens preparation (inhibition of electrically induced twitch) were determined at five temperatures ranging between 25 and 40 degrees C. The values of KB tended to increase with temperature over the range examined, indicating that the affinity of naloxone for the opioid delta receptor is an inverse function of temperature. Using these data, the thermodynamic quantities delta G zero' (change in free energy), delta H zero' (change in enthalpy) and delta S zero' (change in entropy) were calculated from a van't Hoff plot of in (KB) against 1/T. The thermodynamic quantities determined in this study in vivo (delta G zero' = -10.59 kcal mol-1, delta H zero' = -15.73 kcal mol-1 and delta S zero' = -0.0168 kcal mol-1 zero K-1) are consistent with data reported from radioligand binding studies in vitro and suggest that the interaction between naloxone and the opioid delta receptor in the mouse isolated vas deferens is enthalpy driven. These data represent the first evaluation of the thermodynamics of opioid antagonist/receptor interaction in a physiological assay.

Animals↗

PubMed1991

XAMI and DCDM, agonists at cAMP-associated octopamine receptors in cockroach nerve cord, produce centrally mediated antinociception in mice.

The ability of XAMI (2,3-xylylaminomethyl-2'-imidazoline), the most potent agonist of cAMP-associated octopamine-sensitive adenylate cyclase in cockroach (Periplaneta americana) nerve cord yet reported, and DCDM (N-demethylchlordimeform), a partial octopamine agonist in this preparation, to produce centrally mediated antinociception in mice was evaluated. The antinociception produced by these compounds was compared to that previously reported for p-octopamine, a phenylethylamine and endogenous mammalian hydroxyphenolic analog of norepinephrine. Consonant with the reported greater agonistic activity of XAMI on octopamine-sensitive adenylate cyclase, XAMI was more potent than p-octopamine by spinal or supraspinal administration in the abdominal constriction test (E50 = 0.013 micrograms i.t., 1.45 micrograms i.c.v.) and in the 48 degrees C hot-plate test (ED50 = 0.06 micrograms i.t., 0.4 micrograms i.c.v.), but was inactive in the tail-flick test (up to 4.0 micrograms i.c.v. or i.t.). Unlike p-octopamine, both XAMI and DCDM were active by peripheral routes of administration. DCDM was orally active in the mouse acetylcholine-induced abdominal constriction test (ED50 = 9.98 mg/kg p.o.) and was active via the s.c. route in this test (ED50 = 2.36 mg/kg), the 48 degrees C hot-plate test (ED50 = 5.40 mg/kg) and the tail-flick test (ED50 between 15 and 30 mg/kg). It appeared to be a full agonist against these endpoints. XAMI produced dose-related antinociception in the abdominal constriction test (ED50 = 0.10 mg/kg s.c.) and in the 48 degrees C hot-plate test (ED50 = 3.71 mg/kg p.o. and 0.46 mg/kg s.c.), where the antinociceptive response persisted for at least 60 min following subcutaneous or oral administration. Both compounds were less potent via peripheral routes than clonidine (as reference) in these tests. Mechanistically, XAMI-induced antinociception was antagonized by yohimbine and idazoxan, but not the opiate antagonist naloxone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclase Inhibitors↗

PubMed1991

Central and peripheral administration of serotonin produces opposite effects on mouse colonic propulsive motility.

The effects of central or peripheral administration of serotonin on colonic expulsion time (CE) of a glass bead were evaluated after i.p. or free hand i.c.v. administration to mice. Serotonin (5-HT) caused an inhibition of CE when administered centrally but stimulated propulsion after i.p. administration. Several selective serotonin agonists were then tested. Inhibition after i.c.v. administration was produced by 8-OH-DPAT (5-HT1a), RU-24969 (5-HT1b), and 2-methyl serotonin (5-HT3), but not DOI (5-HT2) which augmented propulsion. Relative potencies for inhibition (ED50S) were RU (0.9 micrograms, 3.9 nM) greater than 8-OH-DPAT (3 micrograms, 9.1 nM) greater than 5-HT (7.8 micrograms, 20.1 nM) greater than 2-methyl serotonin (43 micrograms, 140 nM). After i.p. administration 5-HT stimulated propulsive motility (ED50 = 16.1 micrograms, 41.4 nM) while 8-OH-DPAT (ED50 = 55 micrograms, 167 nM) and RU-24969 (ED50 = 54 micrograms, 236 nM) inhibited. DOI and 2-MS had no dose-related activity. The finding that several of the serotonin receptor agonists were capable of inhibiting propulsive motility either by i.p. or i.c.v. administration is a new finding and may help to explain drug-induced constipating activity in man. No selective agonist completely mimicked the effect of serotonin.

Animals↗

PubMed1991

Endothelin-1, -2 and -3 directly and big-endothelin-1 indirectly elicit an abdominal constriction response in mice.

When injected intraperitoneally into mice, endothelins ET-1, ET-2, ET-3 and big-endothelin-1[1-38] (big-ET-1[1-38]) produced a dose-related, robust and easily quantified abdominal constriction response within 20 min. The ED50 values for this response were 0.026, 0.005, 0.131, and 0.043 mg/kg, respectively. Hence, this test could provide a convenient in vivo endpoint for endothelin activity. The results also imply that ET-1, ET-2, ET 3 or big-ET-1[1-38] may be nociceptive under certain conditions. Morphine (4 mg/kg, s.c.) administered 30 min prior completely blocked the response produced by ET-1. Thus, in conjunction with other indicators, the test may also serve as an in vivo screen for agents useful in the treatment of abdominal or visceral pain. The effect of big-ET-1[1-38], but not ET-1, was blocked by pretreatment with the enzyme inhibitor phosphoramidon (10 mg/kg, s.c., 30 min prior), implying that the big-ET-1[1-38] must first be enzymatically cleaved, presumably to ET-1, in order to elicit the abdominal constriction response. This test might also serve as a discriminative antinociceptive screen, because the response to ET-1 was not blocked by acetaminophen (400 mg/kg, p.o.), ibuprofen (75 mg/kg, p.o.) or indomethacin (1.0 mg/kg, p.o.).

Abdomen↗

PubMed1991

Endothelin-1-induced nociception.

Intracerebroventricular (i.c.v.) or intrathecal (i.t.) administration of morphine to mice antagonized the abdominal constriction induced by an i.p. injection of endothelin-1 (ET-1; 0.1 mg/kg). The ED50 values (95% confidence intervals) were 39.3 (16.5-80.2) ng and 1.5 (0.8-4.9) ng, respectively. The antagonism of ET-1-induced abdominal constriction by morphine was blocked by naloxone (1.0 mg/kg, s.c.) or by 24 h pretreatment with beta-funaltrexamine (beta-FNA; 8.84 micrograms, i.c.v.). These results demonstrate for the first time that the stimulus resulting from an i.p. injection of ET-1 is transmitted via ascending (pain) pathways that are subject to attenuation by opioid (mu) receptor activation. Hence, ET-1-induced abdominal constriction is a new pain model which, given the other pharmacology of ET-1, might represent a unique model with potential specific utility for anginal or other visceral pain.

Animals↗

PubMed1991

Centrally-mediated antinociceptive action of RWJ-22757 (formerly McN-5195): involvement of spinal descending inhibitory pathways (an hypothesis).

The present studies were an attempt to examine the mechanism of action of the novel antinociceptive compound RWJ-22757, (+/-)-trans-3-(2-bromophenyl)-octahydroindolizine (McN-5195). Intracerebroventricular (i.c.v.) administration of RWJ-22757 produced dose-related antinociception in the mouse tail-flick (48 degrees C) and rat hot-plate (51 degrees C) tests (ED50 = 243.3 and 261.3 micrograms, respectively). In contrast, intrathecal (i.t.) administration was without effect. The antinociception produced by peripherally (i.p.) or centrally (i.c.v.) administered RWJ-22757 was attenuated by i.t. administration of 2 micrograms phentolamine, 5 micrograms yohimbine, or 10 micrograms methysergide. I.t. administration of naloxone, at a dose (0.5 micrograms) that significantly attenuated the antinociceptive effects of peripherally or centrally administered morphine, had no effect on RWJ-22757-induced antinociception. We conclude from these results, coupled with the overall pharmacological and neurochemical profile of RWJ-22757, that the data are consistent with the hypothesis that RWJ-22757 produces antinociception predominantly at a site or sites located supraspinally with little or no activity at the spinal level and that RWJ-22757 activates adrenergic and serotonergic descending inhibitory pathways, increasing the tonic activity of endogenous antinociceptive systems.

Analgesics↗

PubMed1990

The novel anticonvulsant loreclezole (R 72063) does not produce diazepam-like anterograde amnesia in a passive avoidance test in rats.

Rats were injected intraperitoneally with loreclezole (R 72063), diazepam, or scopolamine 60 min prior to acquisition of a passive avoidance task and tested 18 h later for retention of the learned (passive) behavior. The known impairment of performance produced by diazepam in this test is believed to be a model for the clinically observed diazepam-induced anterograde amnesia in humans. We report in this study that (1) consistent with the literature, pretreatment with diazepam (2.0-16.0 mg/kg i.p.) or scopolamine (3.0 mg/kg i.p.) produced impairment in passive avoidance performance of rats (anterograde amnesia), but (2) pretreatment with loreclezole (R 72063) (2.0-80.0 mg/kg i.p.) did not impair the acquisition, retention, or the retrieval (tested 18 h later) of passive avoidance behavior by rats at any dose. The results suggest that the anticonvulsant activity of loreclezole is mediated by a mechanism distinct from the one coupled to diazepam-like disruption of cognitive functions involved in the acquisition or posttraining information processing of passive avoidance behavior.

Amnesia↗

PubMed1990

The actions of FMRF-NH2 and FMRF-NH2 related peptides on mammals.

Since the initial isolation and characterization of FMRFamide (Phe-Met-Arg-Phe-NH2) from a molluscan source, the potential for the interaction of this neuropeptide with opioid systems has been suspected. Immunoreactive FMRFamide-like material is found in mammals (particularly in brain, spinal cord and GI tract) and mammalian-derived FMRFamide-related peptides (FaRPs) have been identified. A considerable amount of data supports the hypothesis that FMRFamide or mammalian FaRPs function as endogenous antiopiates, particularly with regard to opioid-induced antinociception and other opioid-induced behaviors. They have also been reported to be capable of altering the rate of morphine tolerance development and precipitating withdrawal in morphine-dependent animals. These data imply that FMRFamide or FaRPs are competitive antagonists at opiate receptors. The relatively low affinity for opiate receptors also suggests other possibilities, including mammalian FMRFamide (or FaRP) receptors equivalent to those in invertebrates, partial agonism at opiate receptors or, an indirect (modulatory) role. Whatever the actual mechanism, FMRFamide-like peptides and other 'anti-opiate' peptides might have critical roles in the development of opioid tolerance and dependence or in the pharmacologic study or clinical treatment of these phenomena.

Animals↗

PubMed1990

[D-Met2]-FMRFamide (DMFa): production of naloxone-sensitive antinociception in mouse tail-flick test.

Considerable data support the hypothesis that mammalian FMRFamide (Phe-Met-Arg-Phe-NH2) or mammalian FMRFamide-related peptides (FaRPs) function as endogenous antiopiates (for review see Raffa, 1988). We report here that central administration (i.c.v.) of a FaRP with D-amino acid substitution in the second position, i.e. [D-Met2]-FMRFamide (DMFa), produces dose-related, naloxone-reversible antinociception in the mouse tail-flick test. Hence, this modification appears to confer agonist-like activity.

Analgesics↗

PubMed1990

Effect of Phe-D-Met-Arg-Phe-NH2 and other Phe-Met-Arg-Phe-NH2-related peptides on mouse colonic propulsive motility: a structure-activity relationship study.

The effect of several i.c.v.-administered FMRFamide (Phe-Met-Arg-Phe-NH2)-like peptides (FaRPs) on mouse colonic propulsive motility was examined. Dose-related inhibition of propulsive motility (measured as an increase in the time of colonic bead expulsion) was produced by analogs with either the sequence (-)F[X]RFamide or with the FMRFamide sequence containing D-amino acid substitutions. The C-terminal dipeptide sequence Arg-Phe-NH2 was sufficient to produce this effect. D-amino acid substitution in the second position, i.e., [D-Met2]-FMRFamide (DMFa), conferred significantly enhanced activity (nearly maximal obtainable response under the test conditions) in this preparation (ED25 = 2.3 micrograms = 3.8 nmol). DMFa did not block the action of morphine but, like morphine, was blocked by the opioid antagonist naloxone and was attenuated by 24-hr pretreatment with the selective mu-1 opioid antagonist naloxonazine (35 mg/kg s.c.). It is concluded that a variety of FaRPs, particularly those with a nonpolar residue in the first position and with Arg in the third position, behave as opioid-like agonists, not antagonists, on mouse colonic propulsive motility. DMFa is identified as the most active FaRP studied to date on this endpoint.

Animals↗

PubMed1990

Antinociceptive action of McN-5195 in rodents: a structurally novel (indolizine) analgesic with a nonopioid mechanism of action.

McN-5195 [(+/-)-trans-3-(2-bromophenyl)-octahydroindolizine] inhibited at nontoxic doses the nociceptive response in tail-pinch, tail-flick and 48 degrees C hot-plate tests of mice, with ED50 values of 38.2, 33.9 and 30.9 mg/kg i.p., respectively, and of rats, with ED50 values (i.p.) of 33.2 mg/kg (tail-flick) and 33.3 mg/kg (hot-plate). The compound was p.o. active in the acetylcholine-induced irritant test (ED50 = 20.1 mg/kg) in mice and the air-induced irritant test (ED50 = 33.2 mg/kg) in rats. McN-5195 blocked thalamic activity (multiunit recordings from the ventral posterolateral nucleus) evoked by noxious stimulation of the contralateral hindlimb of anesthetized rats, but did not alter thalamic activity during non-noxious stimulation. The antinociceptive action of McN-5195 was not blocked by naloxone and was not diminished in morphine-tolerant animals. McN-5195 did not affect arachidonate metabolism and was not active against carrageenan-induced paw edema or in an adjuvant arthritis test in rats. McN-5195 did not bind to opiate, serotonin S1 or S2, dopamine D2, alpha-1, alpha-2, beta adrenergic or gamma-aminobutyric acid-A receptors and did not inhibit the synaptic uptake of norepinephrine, serotonin, dopamine or gamma-aminobutyric acid. McN-5195-induced antinociception was not affected by reserpine or phentolamine pretreatment and was not reduced in clonidine-tolerant animals. Ketanserin and yohimbine inhibited McN-5195-induced antinociception by an indirect mechanism. Tolerance did not develop to chronic administration of McN-5195 (120 mg/kg 3 times per day for 10 days). We conclude that McN-5195 is a structurally novel (indolizine) antinociceptive agent that produces its analgesic action via a nonopioid mechanism, not involving products of arachidonate metabolism.

Analgesics↗

PubMed1989

Central administration of p-octopamine to mice: assessment of antinociception.

Administration of p-octopamine by intracerebroventricular (i.c.v.) or intrathecal (i.t.) routes, but not orally, produced antinociception in the acetylcholine-induced abdominal constriction test (ED50 = 24.8 and 3.6 micrograms, respectively). Likewise, i.c.v. and i.t., but not peripheral (up to 200 mg/kg s.c.), administration increased latency in the 48 degrees C hot-plate test (ED50 = 11.5 micrograms i.c.v. and 0.2 micrograms i.t.). These actions were relatively long-lasting and not blocked by naloxone. Antinociception following i.c.v. administration was abolished in reserpinized mice or by pretreatment with i.t. phentolamine (2 micrograms). These results suggest a moderate antinociceptive action of p-octopamine involving non-opioid, reserpine-sensitive, central pathways.

Analgesics↗

PubMed1989

Thermodynamic analysis of the drug-receptor interaction.

Thermodynamic analysis of pharmacologic data potentially offers an insight into the molecular events underlying drug-receptor interactions not obtainable by other techniques. Embodied in thermodynamics are the laws governing the interconvertibility of heat and work and, hence, it is a particularly apt framework for the analysis of the transduction of information from ligand to biological tissue during the initiation of a drug effect. Implicit in thermodynamic analysis of pharmacologic data is quantitative measurement of the driving forces involved in the drug-receptor interaction (in place of less precise terms such as "affinity"). In addition, the cautious interpretation of thermodynamic analysis can give clues to the underlying mechanisms of the drug-receptor interaction that is beyond the resolving power of other parameters, such as the dissociation constant. The present review is an attempt to identify representative reports that have overtly analyzed pharmacologic data with thermodynamic analysis, to summarize the findings within and across studies (particularly regarding enthalpy- versus entropy-driven binding of agonists and antagonists), to point out and address some apparent inconsistencies that can arise, and to consider the application of thermodynamic analysis to data obtained using isolated tissue preparations.

Animals↗