Solid and Liquid Heat Capacities of n-Alkyl Para-aminobenzoates Near the Melting Point

The expression that relates the ideal mole fraction solubility of a crystalline compound to physico-chemical properties of the compound includes a term involving the difference in the heat capacities of the solid and liquid forms of the solute, C _P. There are two alternate conventions which are employed to eliminate this term. The first assumes that the term involving C _P, or C _P itself, is zero. The alternate assumption assigns the value of the entropy of fusion to the differential heat capacity. The relative validity of these two assumptions was evaluated using the straight-chain alkyl para-aminobenzoates as test compounds. The heat capacities of the solid and liquid forms of each of the para-aminobenzoates, near the respective melting point, were determined by differential scanning calorimetry. The data lead one to conclude that the assumption that the differential heat capacity is not usually negligible and is better approximated by the entropy of fusion.     

Immobilized Artificial Membrane (lAM)-HPLC for Partition Studies of Neutral and Ionized Acids and Bases in Comparison with the Liposomal Partition System

Purpose. To study the partitioning of model acids ((RS)-warfarin and salicylic acid), and bases (lidocaine, (RS)-propranolol and diazepam), with immobilized artificial membrane (lAM)-HPLC, as compared to partitioning in the standardized phosphatidylcholine liposome/buffer system. Methods. The pH-dependent apparent partition coefficients D were calculated from capacity factors (k_IAM) obtained by IAM-HPLC, using a 11-carboxylundecylphosphocholine column. For lipophilic compounds k_IAM, values were determined with organic modifiers and extrapolation to 100% water phase (k_IAMw) was optimized. Temperature dependence was explored (23 to 45° C), and Gibbs free energy (G), partial molar enthalpy (H) and change in entropy (S) were calculated. Equilibrium dialysis was used for the partitioning studies with the liposome/buffer system. Results. For extrapolation of k_IAMw, linear plots were obtained both with the respective dielectric constants and the mole fractions of the organic modifier. All tested compounds showed a similar pH-D diagram in both systems; however, significant differences were reproducibly found in the pH range of 5 to 8. In all cases, G and H were negative, whereas S values were negative for acids and positive for bases. Conclusions. In both partitioning systems, D values decreased significantly with the change from the neutral to the charged ionization state of the solute. The differences found under physiological conditions, i.e. around pH 7.4, were attributed to nonspecific interactions of the drug with the silica surface of the IAM column.     

Δ9-THC as a discriminative stimulus in rats and pigeons: Generalization to THC metabolites and SP-111

In a drug discrimination paradigm pigeons and rats were trained with an operant procedure to discriminate between the presence and absence of the effects of ⁹-THC (1.0 and 3.0 mg/kg, injected IM 90 min and I.P. 30 min before the start of the session). Once trained, various THC metabolites as well as a water-soluble derivative of THC (SP-111), were substituted for ⁹-THC to test for generalization to the training drug. Generalization to ⁹-THC occurred with the 11-hydroxy metabolites and the potency order was 11-OH-⁹-THC >11-OH-⁸-THC ⁹-THC. Among the other metabolites tested (8-OH-⁹-THC, 8, 11-di-OH-⁹-THC, 8-OH-⁹-THC, 8, 11-di-OH-⁹-THC), it was only 11-di-OH-⁹-THC that completely substituted for ⁹-THC in pigeons, albeit at very high dose levels (rats were not tested with these metabolites). SP-111 generalized to ⁹-THC in both species. However, the onset of action of SP-111 was slower than that for ⁹-THC, especially in pigeons. These studies show the importance of obtaining complete dose-effect determinations over time when assessing structure-activity relationships with drug-discrimination procedures.A brief account of the results, which are summarized in Neuropharmacology 18:1023–1024, 1979), was presented at the British Association for Psychopharmacology Summer Conference, July 15–17, Birmingham, England, 1979     

Influence of polymorphism on the surface energetics of salmeterol xinafoate crystallized from supercritical fluids

Purpose. To characterize the surface thermodynamic properties of two polymorphic forms (I and II) of salmeterol xinafoate (SX) prepared from supercritical fluids and a commercial micronized SX (form I) sample (MSX). Methods. Inverse gas chromatographic analysis was conducted on the SX samples at 30, 40, 50, and 60°C using the following probes at infinite dilution: nonpolar probes (NPs; alkane C5-C9 series); and polar probes (PPs; i.e., dichloromethane, chloroform, acetone, ethyl acetate, diethyl ether, and tetrahydrofuran). Surface thermodynamic parameters of adsorption and Hansen solubility parameters were calculated from the retention times of the probes. Results. The free energies of adsorption (-G_A) of the three samples obtained at various temperatures follow this order: SX-II > MSX SX-I for the NPs; and SX-II > MSX > SX-I for the PPs. For both NPs and PPs, SX-II exhibits a less negative enthalpy of adsorption (H_A) and a much less negative entropy of adsorption (S_A) than MSX and SX-I, suggesting that the high -G_A of SX-II is contributed by a considerably reduced entropy loss. The dispersive component of surface free energy (_s ^D) is the highest for MSX but the lowest for SX-II at all temperatures studied, whereas the specific component of surface free energy of adsorption (-G_A ^SP) is higher for SX-II than for SX-I. That SX-II displays the highest -G_A for the NP but the lowest _s ^D of all the SX samples may be explained by the additional -G_A change associated with an increased mobility of the probe molecules on the less stable and more disordered SX-II surface. The acid and base parameters, K_A and K_D, that were derived from H_A ^SP reveal significant differences in the relative acid and base properties among the samples. The calculated Hansen solubility parameters (_D, _P, and _H) indicate that the surface of SX-II is the most polar and most energetic of all the three samples in terms of specific interactions (mostly hydrogen bonding). Conclusions. The metastable SX-II polymorph possesses a higher surface free energy, higher surface entropy, and a more polar surface than the stable SX-I polymorph.     

Thermodynamics of Solutions I: Benzoic Acid and Acetylsalicylic Acid as Models for Drug Substances and the Prediction of Solubility

Purpose. To investigate the solution process of drug substances (exemplified by benzoic acid, BA, and acetylsalicylic acid, ASA), particularly the interrelation between enthalpic and entropic terms of Gibbs energy, in different solvents. To develop an approach for the estimation of standard solution enthalpies based on a self-consistent thermochemical scale. Method. Two independent methods, solubility experiments (concentrations of saturated solutions) and solution calorimetry (standard solution enthalpies) in aliphatic alcohols and individual organic solvents were used. Correlation between the thermodynamic functions in various solvents were analyzed by standard statistical methods. Multiple regression analysis between H ⁰ _sol values and the parameters of the solvents was run on the Koppel-Palm equation. Results. Based on experimental data, a compensation effect between thermodynamic functions was observed. Correlation was found between H ⁰ _sol (BA) and H ⁰ _sol (ASA) [where the H ⁰ _sol (BA)-values were used as a self-consistent thermochemical scale]. Furthermore, H ⁰ _sol correlated with the Koppel-Palm basicity of the solvents. Conclusions. The model based on solubility and solution experiments might be useful for the prediction of solubility or solvation of drug substances in different media. The regression equation based on the self-consistent thermochemical scale makes it possible to approximate the ability to solvate a drug substance in comparison with structure-relative substances.     

Evidence for separate neuronal mechanisms for the discriminative stimulus and catalepsy induced by Δ9-THC in the rat

The cataleptogenic effect of ⁹-THC was compared to its discriminative stimulus effects in rats. The ED₅₀s for the discriminative stimulus and catalepsy were 0.8 and 4.0 mg/kg, respectively, while their time courses were very similar. The ED₅₀ of ⁹-THC for catalepsy in experimentally naive rats was not different from that in rats trained with the drug discrimination procedure, indicating that the cataleptogenic effect was not appreciably attenuated by long-term exposure to low doses of ⁹-THC. Pharmacologically, the catalepsy produced by ⁹-THC more closely resembled that of haloperidol than of morphine, since anticholinergic pretreatment eliminated the ⁹-THC-induced catalepsy while pre-treatment with naloxone had no effect. Although the cataleptogenic effect of ⁹-THC could be pharmacologically manipulated by anticholinergic pre-treatment, its discriminative stimulus effects were not changed in the same animals. These results demonstrate that distinctive mechanisms of action exist for these cannabinoid-induced behaviors.     

Generalization of the discriminative stimulus properties of x0394; 9 in rats

Rats were trained in a water maze to discriminate between IP injections of 3 mg/kg ⁹- (⁹⁽¹¹⁾-THC) and its vehicle. Both ⁸- and ⁹⁽¹¹⁾ were generalized to the training drug. In contrast to our observations in rhesus monkeys, where ⁹-THC is at least 100 times less potent than ⁹-THC, ⁹⁽¹¹⁾ was found to be only seven times less potent in the rat. Relative potencies, expressed as the dosage at which 50% of the animals gave drug responses (ED₅₀) were 1.8 mg/kg and 12.2 mg/kg for ⁹-THC and ⁹⁽¹¹⁾ respectively. Twenty-four hours after receiving 7×ED₅₀=12 mg/kg ⁹ the tests showed intermediate results when conducted with the training dosage; 4×ED₅₀=50 mg/kg ⁹-THC 48 h prior to the training dosage of 3 mg/kg ⁹-THC completely blocked drug-appropriate responses. Coinjection of ED₅₀ dosages of ⁹- and ⁹⁽¹¹⁾-THC led to 90% drug responses, demonstrating the additivity of the cannabis-like effect of both cannabinoids. Differences in the individual sensitivity of the rats to the tested cannabinoids were observed. Findings are interpreted in terms of the receptor mechanism for cannabis-like activity.This paper is dedicated to the memory of Dr. M. Binder who died on February 15, 1984     

Δ2-Valproate biotransformation using human liver microsomal fractions

The metabolism of 2-n-propyl-2-pentenoate (²-VPA) was evaluated in human hepatic microsomal fractions. Two biotransformation pathways have been particularly investigated. In the presence of the cytochrome P-450 co-factor, NADPH, the main metabolites recovered were ³-VPA, ^2,4-VPA and VPA. The glucuronidation of ²-VPA was also studied on various hepatic microsomal fractions using Brij^® 35 as activator and UDP-glucuronic acid as co-factor. A large interindividual variability occurred in this metabolic pathway.K _m andV _max were 0.85 mmol/l and 1.75 nmol·min^–1·mg^–1, respectively, for ²-VPA and 1.11 mmol/l and 5.71 nmol·min^–1·mg^–1 for VPA, respectively. The good correlationr=0.82; p<0.001) observed between the glucuronidation of VPA and ²-VPA as well as the mutual inhibition of each other's glucuronidation strongly suggests that (a) common single UDP-glucuronosyltransferase isoenzyme(s) was (were) involved in this glucuronidation step. The glucuronidation of specific substrates for various UDP-glucuronosyltransferase isoenzymes showed a good relationship between the glucuronidations of ²-VPA and morphine, a substrate for UDP-glucuronosyltransferase-2B. Moreover, morphine competitively inhibits A -VPA glucuronidation. It seems the same isoenzyme or, at least, (a) very closely related isoenzyme(s) belonging to UDP-glucuronosyltransferase-2 isoenzyme, is involved in ²-VPA glucuronidation.     

Comparative Investigation by Two Analytical Approaches of Enthalpy Relaxation for Glassy Glucose,Sucrose, Maltose,and Trehalose

No HeadingPurpose. In an effort to understand the stability of glassy sugars such as glucose, sucrose, maltose, and trehalose, the molecular mobility below the glass transition temperature (T_g) was investigated by an enthalpy relaxation measurement with differential scanning calorimetry (DSC).Methods. The glassy sample was aged over several days at (T_g – 10) K to (T_g – 30) K, before a DSC heating scan was taken. The relaxed enthalpy (H_relax) was estimated from the endothermic peak area. The enthalpy relaxation time was analyzed from the time course of H_relax using two different approaches; Kohlrausch-Williams-Watts (KWW) and extended Adam-Gibbs (exAG).Results. ^KWW, which is defined as the mean average enthalpy relaxation time in a distribution, and ^eff₀ and ^eff, which correspond to the enthalpy relaxation time of the initial minimum and final maximum cooperative rearrangement region, were estimated by KWW and exAG, respectively. And three activation energies for enthalpy relaxation were calculated from the Arrhenius plot.Conclusions. Although these Es originated from different theoretical backgrounds, almost the same trend was observed for a comparison of the values of the four sugars. The finding that the Es of glassy trehalose were the largest among the four sugars may support the reason that glassy trehalose is an effective stabilizer.     

Action of cannabidiol on the anxiety and other effects produced by δ9-THC in normal subjects

The object of the experiment was to verify whether cannabidiol (CBD) reduces the anxiety provoked by ⁹-TCH in normal volunteers, and whether this effect occurs by a general block of the action of ⁹-TCH or by a specific anxiolytic effect. Appropriate measurements and scales were utilized and the eight volunteers received, the following treatments in a double-blind procedure: 0.5 mg/kg ⁹-TCH, 1 mg/kg CBD, a mixture containing 0.5 mg/kg ⁹-TCH and 1 mg/kg CBD and placebo and diazepam (10 mg) as controls. Each volunteer received the treatments in a different sequence. It was verified that CBD blocks the anxiety provoked by ⁹-TCH, however this effect also extended to marihuanalike effects and to other subjective alterations induced by ⁹-TCH. This antagonism does not appear to be caused by a general block of ⁹-TCH effects, since no change was detected in the pulse-rate measurements. Several further effects were observed typical of CBD and of an opposite nature to those of ⁹-TCH.These results suggest that the effects of CBD, as opposed to those of ⁹-TCH, might be involved in the antagonism of effects between the two cannabinoids.With a fellowship from Capesfrom CNP_q     

The mechanism of action of Δ 9 -tetrahydrocannabinol on body temperature in mice

The effect of ⁹-tetrahydrocannabinol ( ⁹-THC) on body temperature of the mouse was studied. A dose-response relationship (5–100 mg/kg) for the hypothermic effect of ⁹-THC was seen. The investigation as to the mechanism underlying the hypothermic action of ⁹-THC was also investigated. The relatively specific dopamine antagonist haloperidol potentiated ⁹-THC-induced hypothermia as did the -adrenoceptor antagonist phenoxybenzamine. However, depletion of serotonin with P-chlorophenylalanine reduced the hypothermic response to ⁹-THC as did pretreatment with the serotonin antagonist methysergide. Inhibition of re-uptake of serotonin with clomipramine potentiated the hypothermia following ⁹-THC. It is suggested that the hypothermic effect of ⁹-THC in the mouse is mediated to a large extent via serotonergic mechanisms.     

Dependence of the cardiovascular effects of pindolol on the individual sympathetic nervous activity

Summary To investigate the mechanism of the relative beta-antagonist and agonist properties of pindolol, the cardiovascular effects of i.v. pindolol 0.01 mg/kg were studied in 23 subjects with different baseline levels of cardiac beta-adrenergic function. Baseline cardiac beta-adrenergic activity was assessed by the decrease in heart rate following intravenous propranolol 0.2 mg/kg (HR) after parasympathetic blockade with intravenous atropine 0.04 mg/kg. Cardiac beta-adrenergic sensitivity was defined by the positive chronotropic effect of a three minute infusion of isoprenaline 0.005 µg/kg/min. The chronotropic effect of intravenous pindolol was negatively correlated with resting beta-adrenergic activity (R=–0.81, p<0.001). The traditional point of HR, at which pindolol shifted from beta-antagonist to beta-agonist action, was 17 beats/min, i.e. pindolol decreased heart rate in subjects with HR greater than 17 bpm, and increased heart rate in those with HR less than 17 bpm. The chronotropic effect of intravenous pindolol, however, was positively correlated with beta-sensitivity (R=+0.73, p<0.001). Thus subjects with the greatest increment in heart rate with isoprenaline had an increased heart rate with pindolol, while those with the lowest increment in heart rate with isoprenaline had a decreased heart rate with pindolol. Intravenous pindolol decreased cardiac index and increased total peripheral resistance in the group with HR more than 17 bpm, and it had the contrary actions in the group with HR less than 17 bpm. Blood pressure in both groups was not significantly changed by pindolol. Compared to endogenous catecholamines, pindolol was considered to possess higher beta-adrenocepter affinity and weaker beta-adrenoceptor stimulating action. Therefore, pindolol produced a net beta-blocking action in subjects with elevated cardiovascular sympathetic nervous activity and beta-stimulating action in subjects with reduced sympathetic nervous activity.     

Discriminative effects of combinations of Δ9-Tetrahydrocannabinol and pentobarbital in pigeons

The purpose of the present study is to examine potentially additive effects of pentobarbital and ⁹-Tetrahydrocannabinol ⁹-THC using a drug discrimination paradigm. Three groups of pigeons were trained to discriminate between the effects induced by i.m. administrations of either (a) 0.25 mg/kg ⁹-THC and vehicle, (b) 4 mg/kg pentobarbital and saline, and (c) ⁹-THC and pentobarbital. Test probes under extinction conditions produced orderly dose generalization gradients among the drug-vs nondrug-trained animals. ED₅₀ for pentobarbital was 1.60 mg/kg and ED₅₀ for ⁹-THC was 0.10 mg/kg. Tests in birds discriminating between pentobarbital and ⁹-THC suggested a sharpening of the drug cue effects; tests with the vehicles resulted in approximately a random key selection (33%–66%) while tests with combinations of the two training drugs suggested that ⁹-THC was the more salient cue in this group. Tests with combinations of various doses of pentobarbital and ⁹-THC in the drug-vs nondrug-trained birds did not increase responding on the respective drug-training associated key. Thus the cue effects of pentobarbital and ⁹-THC were not summational under these experimental conditions. In conclusion, rather low doses of pentobarbital and ⁹-THC are effective as discriminative cues in pigeons and the cues thus induced are different. Combinations of the two drugs are not necessarily summational, and the pentobarbital vs the ⁹-THC discriminations augmented the discriminable effects of the two drugs. In addition, the analeptic drug, bemegride, antagonizes the pentobarbital (4 mg/kg) stimulus in the group trained to discriminate between this barbiturate and saline, which agrees with earlier drug antagonism data obtained among mammals (gerbils and rats), required to discriminate between barbiturates and the nondrug condition.     

Effect of cannabinoids on the turnover rate of acetylcholine in rat hippocampus,striatum and cortex

Summary The effects of ⁹-tetrahydrocannabinol, (⁹THC) the major psychoactive compound of marijuana, and cannabidiol (CBD), a non-psychoactive component, on the acetylcholine (ACh) concentration and the turnover rate of ACh (TR_ACh) have been studied in various regions of the rat brain. Neither ⁹THC doses from 0.2 to 10 mg/kg nor CBD (10 or 20 mg/kg) alter the ACh concentration in the brain areas examined 30 min, after the intravenous injection. However, ⁹-THC (doses from 0.2 to 10 mg/kg) causes a marked dose-related decrease in the TR_ACh in hippocampus whereas CBD is without effect in this brain region even when 20 mg/kg is given. Furthermore, high doses of ⁹-THC (5 mg/kg) and CBD (20 mg/kg) that produce a significant decrease in the TR_ACh of striatum fail to change the TR_ACh in parietal cortex. The low doses of ⁹-THC required to reduce hippocampal TR_ACh suggest that an action on these cholinergic mechanisms may play a role in the psychotomimetic activity of ⁹-THC.     

Clinical effects and plasma levels of Δ9-Tetrahydrocannabinol (Δ9-THC) in heavy and light users of cannabis

⁹-Tetrahydrocannabinol (⁹-THC) was administered in a crossover design by smoking and IV injection to groups of heavy and light users of marihuana. Plasma concentrations of ⁹-THC were similar for the groups after IV injection of 5.0 mg ⁹-THC, but the AUC_{0–240 min} showed a trend towards lower values for the heavy user group. To achieve a maximum desired high, both groups smoked similar amounts (about 13 mg) of ⁹-THC. Heavy users tended to have higher plasma levels than light users. The systemic availability of smoked ⁹-THC was significantly higher for the heavy users (heavy users 23±16% vs 10±7% for light users). These results also indicate that heavy cannabis users smoke more efficiently than casual smokers.Both light and heavy users showed more clinical effect following IV administration than after smoking. The response of the heavy users, both with respect to effect on heart and high, was quite comparable to that of light users.The present study does not suggest that tolerance readily develops in heavy users.     

Effects of Sucrose and Trehalose on the Preservation of the Native Structure of Spray-Dried Lysozyme

Purpose. To investigate the effects of sucrose, trehalose, sucrose/dextran mixtures, and sucrose/trehalose mixtures on the preservation of the native structure of spray-dried lysozyme in the solid state. Methods. The intensity of the -helical band and the melting enthalpies (H_m ) of spray-dried lysozyme in the dried form and in aqueous solution were obtained using second derivative FTIR and differential scanning calorimetry (DSC) respectively. Results. The intensity of the -helical band and the H m of spray-dried lysozyme obtained were linearly correlated and both suggest that the stabilization of lysozyme in the dried form was excipient concentration-dependent with a close to maximum stabilization being conferred by sucrose or trehalose at a mass ratio 1–2 (sugar:enzyme). Sucrose appeared to be more effective than trehalose on a weight by weight basis whilst stabilizing effects of dextran/sucrose or trehalose/sucrose mixtures were found to be additive. Conclusion. Dehydration during spray drying was considered the main stress to the denaturation of lysozyme. A major effect of the sugars in protecting lysozyme against dehydration was attributable to hydrogen bonding between the sugar and protein molecules, which lead to an increase in the change in the negative value of the free energy between native and denatured states.     

Withdrawal-like behaviour induced by inhibitors of biogenic amine reuptake in rats treated chronically with Δ 9-tetrahydrocannabinol

The effects of the biogenic amine reuptake inhibitors fluoxetine, clomipramine and imipramine on the behaviour of rats after chronic treatment with ⁹ tetrahydrocannabinol ( ⁹-THC) for 5 and 10 days were examined. Rats with permanently in-dwelling IV cannulae were injected twice daily with doses of ⁹-THC (2–6 mg/kg). ⁹-THC treatment reduced the rate of body weight gain and induced the typical biphasic modifications of behaviour. Tolerance developed to both of these effects. On days 6 and 11 of the experiment, rats were injected IP with 15 mg/kg imipramine HCl, clomipramine HCl or fluoxetine HCl, and behaviour, consisting of writhes, backward kicks, jumps and wet shakes, was observed for the next 30 min. Each of the amine reuptake inhibitors induced changes in behaviour, the severity of which appeared to correlate with their ability to inhibit the reuptake of 5-hydroxytryptamine (5-HT). It is suggested that tryptaminergic mechanisms are involved in the production of a withdrawal-like behaviour after chronic ⁹-THC treatment.     

CB<Subscript>1</Subscript> receptor mediation of cannabinoid behavioral effects in male and female rats

Rationale Cannabinoids have been shown to produce greater behavioral effects in female than male rats. Although central nervous system CB₁ receptors are known to mediate cannabinoid-induced behavioral effects in male rats, it is not known whether the same is true for females.Objective To determine if cannabinoid-induced antinociception and catalepsy are similarly mediated by central CB₁ receptors in male and female rats.Methods The ability of SR141716A, a CB₁ receptor selective antagonist, administered ICV (1–1000 g) or IT (1–600 g) to block 10 mg/kg IP ⁹-THC-induced antinociception (paw pressure) and catalepsy (bar test), was compared in male and female rats.Results ⁹-THC alone produced slightly greater antinociception, and significantly greater catalepsy in females than males. When administered ICV, SR141716A partially antagonized ⁹-THC-induced antinociception in both females and males. IT SR141716A also antagonized ⁹-THC-induced antinociception in both sexes; it was slightly more potent in males but equally effective in males and females. SR141716A antagonized ⁹-THC-induced catalepsy in a similar manner in males and females when given ICV or IT.Conclusions These results confirm that ⁹-THC-induced behavioral effects are mediated by central CB₁ receptors in male and female rats.     

Thermodynamic In Vitro Studies as a Method to Investigate the Pharmacodynamic Behavior of Adenosine A1 Receptor Ligands

Purpose. A thermodynamic analysis of the binding to rat cortex adenosine A₁, receptor of N⁶-substituted (full agonists) and N⁶-substituted-deoxyribose (partial agonists) adenosine derivatives was performed. The intrinsic activity of the compounds was evaluated by measurements of the inhibition of forskolin stimulated 3, 5-cyclic adenosine mono-phosphate (c-AMP) levels in isolated epididymal rat adipocytes. Methods. The thermodynamic parameters G° (standard free energy), H °(standard enthalpy), and S° (standard entropy) of the binding equilibrium were determined by means of affinity measurements carried out at different temperatures (0, 10, 20, 25, 30° C). Levels of c-AMP were evaluated performing competitive protein binding assays. Results. The binding of the ligands increases with temperature enhancement and, as a consequence, is totally entropy driven. Standard entropy values correlate significantly with intrinsic activity ones. Conclusions. It is proposed the data obtained by these in vitro experiments can be used to investigate the in vivo pharmacodynamic of A₁, full and partial agonists.