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Biomedical subjects

R J Tallarida

Publications and source records attributed to R J Tallarida.

At least 55 records · Page 3Linked to original sources
PubMed1990

Studies on kinetics of [3H]beta-funaltrexamine binding to mu opioid receptor.

beta-Funaltrexamine (beta-FNA) was shown to be a reversible kappa agonist and an irreversible mu antagonist. [3H]beta-FNA at low concentrations (less than 10 nM) covalently binds to mu but not delta or kappa opioid receptors in brain membranes. The interaction between beta-FNA and mu opioid receptors was thought to involve two steps; a reversible ligand-receptor complex is formed before the formation of an irreversible complex, based on observations in bioassays in vitro. In this study, we investigated whether such a two-step process occurred in binding using bovine striatal membranes and determined the kinetic parameters by examining the time courses of both reversible and irreversible binding of [3H]beta-FNA to mu opioid receptors. Specific binding was defined as the difference between binding in the presence of levorphanol and dextrorphan (1 microM). Reversible binding was determined as the difference between membrane (reversible and irreversible) binding and irreversible binding. At 25 degrees, the rate of formation of irreversible [3H]beta-FNA-receptor complex increased as the concentration increased and reached a plateau at 2 nM; further increase in [3H]beta-FNA concentration did not enhance the rate of formation, indicating that the rate saturation effect exists for irreversible binding of [3H]beta-FNA to mu opioid receptors. At 10 degrees and low concentrations (less than 1 nM) of [3H]beta-FNA, appreciable reversible binding to opioid receptors occurred before any irreversible [3H]beta-FNA-receptor complex could be detected. These observations support the notion that reversible binding occurs before alkylation of the receptor. The binding of [3H]beta-FNA to mu opioid receptors was thus modeled to allow for such a two-step process: (formula; see text) A mathematical analysis method was derived to allow determination of all kinetic parameters (k+1, k-1, k2, and Kd) of such a two-step reaction. Values of k2, k+1, k-1, and Kd were determined at 10 degrees for 0.5, 0.25, and 0.125 nM [3H]beta-FNA and were found to be very similar among these three concentrations. Raising the incubation temperature from 10 degrees to 37 degrees greatly enhanced the values of k+1, k-1, and k2 without affecting Kd. At 37 degrees incubation without 200 mM NaCl significantly decreased the values of k+1, k-1, and k2 without affecting Kd. NaCl increased the irreversible binding, probably by shifting the equilibrium towards a conformation that binds more easily with beta-FNA. Under all conditions examined, the value of k-1 was found to be at least 5-fold greater than k2, indicating that the majority of the reversible complex dissociates and only a small portion proceeds to form irreversible complex. This finding is consistent with published observations that only a portion of beta-FNA binding to mu opioid receptors is irreversible. In conclusion, [3H]beta-FNA binds reversibly to mu opioid receptors before forming covalent bonding...

Animals↗
PubMed1989

Statistical analysis of drug-drug and site-site interactions with isobolograms.

The use of more than one drug to achieve a desired effect has been a common practice in pharmacologic testing and in clinical practice. For example, combinations of analgesics are frequently prescribed with a view to enhancing pain relief and reducing adverse effects. It is also well established that administration of more than one drug may give effects that are greater than, or less than, the additive effect of each drug given individually. A non-mechanistic method of characterizing the effect resulting from the administration of two compounds is the isobologram. It is relatively simple to draw and interpret isobolograms. However, this graphical technique, which employs equieffective concentrations of individual drugs and combinations of these, obtains the concentrations as random variables from concentration-effect data, usually transformed to a parallel line assay. Thus, statistical confidence limits from such assays, as well as from non-parallel designs, must be expressed on the isobologram if this diagram is to establish superadditive, subadditive, or merely additive effects. We now present a detailed statistical analysis of the isobolographic method illustrated with examples of the statistical procedures, a rational basis for selecting proportions of each drug in the combination, and a relatively novel application of the isobolographic concept, i.e., interactions involving different anatomical sites.

Animals↗
PubMed1988

Academic-industrial cooperative graduate program in clinical pharmacology.

Because a new level of sophistication among clinical investigators is necessary for the testing of new agents in human subjects, a close integration of basic science, clinical medicine, and pharmaceutical medicine is required. Experts from the Departments of Pharmacology and Medicine at Temple University School of Medicine and Smith Kline and French Laboratories have combined to form a joint training program in clinical pharmacology. This structured graduate program for physicians couples didactic courses with a defined program of independent research, leading to a Master of Science degree in pharmacology. The development of new technologies and the transfer of them from the "bench to the bedside" demands that the clinician have special competence in clinical pharmacology. This unique joint academic-industrial program sets the goals ensuring that this objective is met.

Clinical Trials as Topic↗
PubMed1988

Pharmacologic methods for identification of receptors.

Determinations of apparent equilibrium dissociation constants of drug-receptor interactions are made from both functional and radioligand binding studies. In each type of study, reversible reactions are assumed and the mass action law is applied. Functional studies are frequently used to determine the dissociation constant of a competitive antagonist but are less frequently used to obtain this constant for agonist compounds since the latter determination requires an experimental procedure that irreversibly inactivates a fraction of the receptors. In the present report, values of dissociation constant for prototype agonists and antagonists, determined from binding and from functional studies, are examined in two classical isolated preparations, rabbit aorta and guinea-pig ileum. In each preparation the dissociation constants from binding and functional experiments agree well for the antagonists but differ markedly for the agonists. Further, the dissociation constant values from binding are seen to be greater for the agonists than for the antagonists. When a chronic treatment regimen in the rabbit resulted in a pronounced change in the functional dissociation constant of subsequently administered norepinephrine, there was no significant change in either the binding constant of this agonist or in the pA2 value of the alpha antagonist, phentolamine. These, and the previously described results, are shown to be compatible with a simple two-state receptor model in which agonists bind with high and low affinity to each state while antagonists do not distinguish between the states. In this model, the ratio of low to high affinity states accounts for the failure of the binding procedure to detect changes in the agonists dissociation constant that are highly significant in the functional study. Whereas the model is based on data for these two classical preparations only, and may not be more generally applicable, the findings demonstrate the necessity for employing both functional and radioligand binding experiments when characterizing drug receptors.

Animals↗
PubMed1986

Estimation of the affinity of naloxone at supraspinal and spinal opioid receptors in vivo: studies with receptor selective agonists.

The apparent affinity of naloxone at cerebral and spinal sites was estimated using selective mu [D-Ala2, Gly-o15]-enkephalin (DAGO) and delta [D-Pen2, D-Pen5]enkephalin] (DPDPE) opioid agonists in the mouse warm water tail-withdrawal test in vivo; the mu agonist morphine was employed as a reference compound. The approach was to determine the naloxone pA2 using a time-dependent method with both agonist and antagonist given intracerebroventricularly (i.c.v.) or intrathecally (i.th.); naloxone was always given 5 min before the agonist. Complete time-response curves were determined for each agonist at each site in the absence, and in the presence, of a single, fixed i.c.v. or i.th. dose of naloxone. From these i.c.v. or i.th. pairs of time-response curves, pairs of dose-response lines were constructed at various times; these lines showed decreasing displacement with time, indicative of the disappearance of naloxone. The graph of log (dose ratio-1) vs. time was linear with negative slope, in agreement with the time-dependent form of the equation for competitive antagonism. From this plot, the apparent pA2 and naloxone half-life was calculated at each site and against each agonist. The affinity of naloxone was not significantly different when compared between agonists after i.c.v. administration. A small difference was seen between the affinity of i.th. naloxone against DPDPE and DAGO; the i.th. naloxone pA2 against morphine, however, was not different than that for DPDPE and DAGO. The naloxone half-life varied between 6.6 and 16.9 min, values close to those previously reported for this compound. These results suggest that the agonists studied may produce their i.c.v. analgesic effects at the same receptor type or that alternatively, the naloxone pA2 may be fortuitously similar for mu and delta receptors in vivo. Additionally, while the affinity of naloxone appears different for the receptors activated by i.th. DAGO and DPDPE, further work may be necessary before firm conclusions regarding the nature of the spinal analgesic receptor(s) can be drawn.

Analgesia↗
PubMed1985

The concept of a changing receptor concentration: implications for the theory of drug action.

Drugs are considered to produce their effects on biological tissues either by altering some physical property of cells or by interacting with specific cellular components, called receptors. Most drugs and endogenous neurotransmitters act on highly selective receptors located on the outer surface membrane of cells. These receptors were believed, until recently, to be stationary on the cell surface and to be present in unvarying numbers. Consequently, most early theorists modeled the drug-receptor interaction on the basis of stationary and static receptor molecules. The substantial advances in our understanding of drug action based on these models have partly justified this view. However, recent electron microscopic studies have revealed the presence of structures, including "coated" pits and vesicles, that appear to provide a mechanism by which cell surface receptors might be internalized in a process of endocytosis. The precise intracellular fate of these internalized receptors is unknown, but based on present understanding, it seems reasonable to believe that some are destroyed intracellularly whereas others are recycled to the cell surface. The importance of such processes to pharmacologic theory is a new awareness of a cellular pathway that is capable of internalizing drugs, receptors, or both. The implications of such a process to the theory of drug action extends to some unexplained drug phenomena such as down regulation, drug tolerance, tachyphyllaxis, and partial agonism. We present herein the theoretical framework for a model of drug action that incorporates the possibility of receptor internalization and subsequent degradation, recycling, or replacement.

Biological Transport↗
PubMed1985

Measurement of thermodynamic parameters for norepinephrine contraction of isolated rabbit thoracic aorta.

The thermodynamic quantities of change in free energy (delta G degree'), change in enthalpy (delta H degree') and change in entropy (delta S degree') were determined for the interaction of norepinephrine with the alpha-1 adrenoceptor of vascular smooth muscle. Specifically, a standard isolated rabbit thoracic-aorta preparation was used to examine the effect of temperature on norepinephrine-induced isometric tension development. Dissociation constants (KA) for norepinephrine were determined at several temperatures over the range 25-40 degrees C from equiactive concentrations obtained before (A) and after (A') partial irreversible receptor blockade by phenoxybenzamine, plotted as 1/A against 1/A' (KA = (slope-1)/intercept). The values of KA increased with temperature over the range 25-40 degrees C, indicating that the affinity of norepinephrine for the alpha-1 adrenoceptor is an inverse function of temperature over this range. From these results, the thermodynamic quantities delta H degree' and delta S degree' were determined from a van't Hoff plot of In (KA) against 1/T. The relative magnitudes of the change in enthalpy (delta H degree' = -25.58 kcal mol-1) and the change in entropy (delta S degree' = -0.052 kcal mol-1 deg-1) suggest that the reaction between norepinephrine and the alpha-1 adrenoceptor (delta G degree' = -9.15 kcal mol-1) is enthalpy driven, which is consistent with radioligand binding studies of other adrenoceptor subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

An evaluation of tamoxifen as a partial agonist by classical receptor theory--an explanation of the dual action of tamoxifen.

Tamoxifen is known to have both agonist and antagonist properties. Classical receptor theory predicts that given the relative concentrations of a partial agonist and full agonist acting on the same receptor, the partial agonist may reduce the effect of the full agonist. The immature rat uterine model is an excellent system to evaluate the interactions of estradiol and tamoxifen by application of receptor theory. Using this model, tamoxifen demonstrates both additive and antagonistic effects to estradiol in the fashion predicted by theory. The effects of tamoxifen are additive at low doses of estradiol and antagonistic over higher estradiol doses. It is possible that the dualism of agonism and antagonism seen in other target organs and species is a function of these basic characteristics of a partial agonist.

Animals↗
PubMed1984

Receptor theories and quantitative effect versus dose-concentration relationship.

Both in vivo and in vitro, the dissociation constant K not equal to D50. This was shown for morphine in vivo and for several vasoconstrictors in isolated vascular smooth muscle. When Schild plots are made for a pure competitive antagonist the underlying theory requires that the regression line be constrained to slope -1, for only in this case does pA2 = -log KB, and each has the same confidence limits. Further, even where the slope of the conventional (unconstrained) regression line differs only slightly from -1, the confidence limits of pA2 differ appreciably from those of -log KB. Values of K obtained from pharmacologic methods can discriminate among receptor subtypes. A proper determination of K permits knowledge of the stimulus-response relation, a drug-independent property of the effector system. A perturbation of the drug-receptor equilibrium is a way of determining both k1 and k2; so far, however, we have been successful only with alpha-adrenergic vasoconstrictors in which UV light is a suitable stimulus. Radiolabeled binding appears to be a precise way of determining K's for agonists and antagonists. However, it does not measure an effect; hence we do not know that such binding sites are true receptors unless we can find a correlation between the values obtained for a series of drugs with this method and those obtained with appropriate pharmacologic methods.

Binding, Competitive↗
PubMed1983

Ketazocines and morphine: effects on gastrointestinal transit after central and peripheral administration.

The mu agonist, morphine, and the prototype kappa agonists, ketocyclazocine and ethylketocyclazocine (EK), were studied for their effects on gastrointestinal transit. Following s.c. administration, both morphine (0.3-3 mg/kg) and ketocyclazocine (0.3-10 mg/kg) antagonized transit of an opaque marker through the small intestines of mice. Morphine (0.1-1 microgram) was also effective after intracerebroventricular (icv) administration in mice whereas ketocyclazocine (0.3-30 micrograms) was not. Similarly, while both morphine (0.3-5 mg/kg) and EK (0.6-10 mg/kg) slowed transit after s.c. injection to rats, only morphine (1-10 micrograms), but not EK (0.3-300 micrograms), was active following icv administration. Icv infusion of the mu benzomorphan, phenazocine (10-100 micrograms), slowed transit in a dose-related manner. These results indicate that there may be an anatomically distinct distribution of receptors for benzomorphan kappa agonists in both the mouse and rat, with these opiate receptors not being located near the lateral cerebral ventricles. The difference in efficacy between morphine and ketazocines in slowing gastrointestinal transit after icv administration to rodents suggests that (a) inactivity in this endpoint is a characteristic of benzomorphan kappa compounds and (b) the model may serve as a useful screen when establishing in vivo profiles of kappa agonists in mice and rats.

Animals↗
PubMed1983

Subclasses of opioids based on body temperature change in rats: acute subcutaneous administration.

Morphine and a number of opioid agonists and agonist-antagonists were injected into rats to examine their effects on body temperature after acute systemic administration. Dose- and time-response curves were constructed for each drug alone and in the presence of the antagonist naloxone. Based on these data, the opioids could be subdivided into several groups. The first group, made up of morphine, heroin, l-methadone, etorphine, fentanyl and levorphanol, caused hyperthermia at lower doses and hypothermia at higher ones. Both effects could be blocked by naloxone. A second group, consisting of buprenorphine, nalbuphine and l-pentazocine, produced only a naloxone-sensitive increase in body temperature, whereas the group comprising ethylketazocine, ketazocine, l-cyclazocine and normeperidine caused only a decrease. This fall in temperature was relatively less sensitive to naloxone blockade. Still another group of drugs (meperidine, normorphine and d-pentazocine) had little effect themselves but, in combination with naloxone, induced hypothermia. The fifth group (N-allylnormetazocine, d-cyclazocine, dextrorphan and d-methadone) had no effect whether alone or in the presence of the antagonist. These findings can be explained in terms of a two-receptor model by ascribing distinct thermoregulatory functions to each receptor type.

Animals↗
PubMed1982

A comparison of the receptor constants of morphine and ethylketocyclazocine for analgesia and inhibition of gastrointestinal transit in the rat.

The efficacies and dissociation constants of proposed mu and kappa receptor agonists (morphine and ethylketocyclazocine, respectively) were compared using the method of partial irreversible blockade (with buprenorphine) and Stephenson's theory of drug action. While there was good agreement between the dissociation constant (KA) of morphine in analgesia (3.3 x 10(-5) M) and in inhibition of gastrointestinal transit (1.1 x 10(-5) M), the KA of ethylketocyclazocine differed by an order of magnitude in these endpoints (3.2 x 10(-6) M and 6.7 x 10(-5) M, respectively). The efficacies of morphine were found to be similar for the two effects studied (4.23 and 5.26), while those for ethylketocyclazocine differed markedly (2.06 and 10.39). The fraction of receptors remaining unblocked after buprenorphine was consistent for the test but not for the agonist, indicating a different distribution of receptors for the two endpoints. Our results strongly suggest that morphine induces analgesia, and slows transit in the small intestine, through the same type of receptor. The same conclusion cannot be drawn for ethylketocyclazocine.

Analgesia↗
PubMed1982

Pupillographic analysis of morphine action in the rabbit: role to the autonomic nervous system.

Pupillary response of albino rabbits were recorded using an infrared video pupillometer. The transient response to an i.v. injection of morphine (1-12 mg/kg) consists of three phases. Phase 1 is a brief mydriasis of 20 s duration. Phase 2 is a miosis that reaches a maximum within 2-4 min and is the only dose-related endpoint observed. Time-averaged pupil size is not decreased by morphine in a dose-related manner when measured 5 min after injection. Phase 3 is large amplitude fluctuation that reaches peak amplitude within 20 min and may last for several hours. Thus, dynamic pupillography reveals that the terms "miosis' and "mydriasis' may be insufficient to fully describe opiate-induced pupillary effects. All three phases are blocked by naloxone (0.1 mg/kg i.v.) and by topical pretreatment with scopolamine. These results are consistent with the theory that morphine alters pupil size by interaction with opiate receptors that are involved in the control of parasympathetic output to the iris.

Animals↗
PubMed1982

Morphine-receptor dissociation constant and the stimulus-effect relation for inhibition of gastrointestinal transit in the rat.

The dissociation constant (KA) of morphine for its receptors was determined by the method of partial irreversible blockade of the receptor population using inhibition of gastrointestinal transit of a forced charcoal meal as the pharmacological endpoint. The anti-motility effect of morphine was antagonized when rats were pretreated with buprenorphine (0.3 mg/kg s.c.), a narcotic antagonist analgesic, 30 min before morphine and the extent of gastrointestinal transit was estimated a further 45 min later. With this schedule of drug administration, the agonist action of buprenorphine is minimal and its antagonist action predominates. The value of KA was (1.1 +/- 0.2) x 10(-5) mol/kg, a value close to that previously reported (2.9 x 10(-5) mol/kg) by us with these compounds in the rat tail flick test. The value of [A50], found here was 2.15 x 10(-6) mol/kg, approximately 1/5 of that of KA. Also, the stimulus-effect relation of the tissue, defined in Stephenson's theory, was plotted and found to be nonlinear. This result, when coupled with the inequality of KA and [A50], argues against the application of classical drug-receptor theory to this system. The apparent agreement between KA values for antinociception and inhibition of gastrointestinal transit is interesting, but does not necessarily prove equivalent receptors mediating the two different effects.

Animals↗