Physical Properties of Solid Molecular Dispersions of Indomethacin with Poly(vinylpyrrolidone) and Poly(vinylpyrrolidone-co-vinyl-acetate) in Relation to Indomethacin Crystallization

Purpose. To measure solid-state features of amorphous molecular dispersions of indomethacin and various molecular weight grades of poly(vinylpyrrolidone), PVP, and poly(vinylpyrrolidone-co-vinylacetate), PVP/VA, in relation to isothermal crystallization of indomethacin at 30°C Methods. The glass transition temperatures (Tg) of molecular dispersions were measured using differential scanning calorimetry (DSC). FT-IR spectroscopy was used to investigate possible differences in interactions between indomethacin and polymer in the various dispersions. The enthalpy relaxation of 5% w/w and 30% w/w polymer dispersions was determined following various aging times. Quantitative isothermal crystallization studies were carried out with pure indomethacin and 5% w/w polymers in drug as physical mixtures and molecular dispersions. Results. All coprecipitated mixtures exhibited a single glass transition temperature. All polymers interacted with indomethacin in the solid state through hydrogen bonding and in the process eliminated the hydrogen bonding associated with the carboxylic acid dimers of indomethacin. Molecular mobility at 16.5°C below Tg was reduced relative to indomethacin alone, at the 5% w/w and 30% w/w polymer level. No crystallization of indomethacin at 30°C was observed in any of the 5% w/w polymer molecular dispersions over a period of 20 weeks. Indomethacin alone and in physical mixtures with various polymers completely crystallized to the form at this level within 2 weeks. Conclusions. The major basis for crystal inhibition of indomethacin at 30°C at the 5% w/w polymer level in molecular dispersions is not related to polymer molecular weight and to the glass transition temperature, and is more likely related to the ability to hydrogen bond with indomethacin and to inhibit the formation of carboxylic acid dimers that are required for nucleation and growth to the crystal form of indomethacin.     

Spectroscopic Characterization of Interactions Between PVP and Indomethacin in Amorphous Molecular Dispersions

Purpose. To study the molecular structure of indomethacin-PVP amorphous solid dispersions and identify any specific interactions between the components using vibrational spectroscopy. Methods. Solid dispersions of PVP and indomethacin were prepared using a solvent evaporation technique and IR and FT-Raman spectra were obtained. Results. A comparison of the carbonyl stretching region of indomethacin, known to form carboxylic acid dimers, with that of amorphous indomethacin indicated that the amorphous phase exists predominantly as dimers. The hydrogen bonding of indomethacin is not as dimers. Addition of PVP to amorphous indomethacin increased the intensity of the infrared band assigned to non-hydrogen bonded carbonyl. Con-comitantly, the PVP carbonyl stretch appeared at a lower wavenumber indicating hydrogen bonding. Model solvent systems aided spectral interpretation. The magnitude of the spectral changes were comparable for an indomethacin-PVP solid dispersion and a solution of indomethacin in methylpyrrolidone at the same weight percent. Conclusions. Indomethacin interacts with PVP in solid dispersions through hydrogen bonds formed between the drug hydroxyl and polymer carbonyl resulting in disruption of indomethacin dimers. PVP may influence the crystallisation kinetics by preventing the self association of indomethacin molecules. The similarity of results for solid dispersions and solutions emphasises the 'solution' nature of this binary amorphous state.     

Thermal Stability of Mefruside–Polyvinylpyrrolidone Solid Dispersions

The stability of mefruside–polyvinylpyrrolidone (PVP) 30 solid dispersions at ratios of mefruside/PVP 30 of 9/1, 7/3, and 5/5 (g/g) after mechanical (tableting) and allothermic stressing (50, 60, and 70°C up to 240 hr) was investigated. Only the 5/5 (g/g) solid dispersion showed no recrystallization of mefruside, whereas a slight increase in crystallinity in the 7/3 (g/g) solid dispersion and a strong increase in the 9/1 (g/g) product were detected. The mechanisms of drug recrystallization in such high-energy products are discussed.     

Enhancement of Solubility and Bioavailability of β-Lapachone Using Cyclodextrin Inclusion Complexes

Purpose. To explore the use of cyclodextrins (CD) to form inclusion complexes with -lapachone (-lap) to overcome solubility and bioavailability problems previously noted with this drug. Methods. Inclusion complexes between -lap and four cyclodextrins (-, -, -, and HP-CD) in aqueous solution were investigated by phase solubility studies, fluorescence, and ¹H-NMR spectroscopy. Biologic activity and bioavailability of -lap inclusion complexes were investigated by in vitro cytotoxicity studies with MCF-7 cells and by in vivo lethality studies with C57Blk/6 mice (18-20 g). Results. Phase solubility studies showed that -lap solubility increased in a linear fashion as a function of -, -, or HP-CD concentrations but not -CD. Maximum solubility of -lap was achieved at 16.0 mg/ml or 66.0 mM with HP-CD. Fluorescence and ¹H-NMR spectroscopy proved the formation of 1:1 inclusion complexes between -CD and HP-CD with -lap. Cytotoxicity assays with MCF-7 cells showed similar biologic activities of -lap in -CD or HP-CD inclusion complexes (TD₅₀ = 2.1 M). Animal studies in mice showed that the LD₅₀ value of -lap in an HP-CD inclusion complex is between 50 and 60 mg/kg. Conclusions. Complexation of -lap with HP-CD offers a major improvement in drug solubility and bioavailability.     

The binding spectrum of narcotic analgesic drugs with different agonist and antagonist properties

Summary Four groups of narcotic analgesic drugs have been assessed for their opiate activities by using three binding assays and three pharmacological bioassays. In the binding assays, their inhibition constants (K _I, nM) were determined against the binding of the -ligand, [³H]-[d-Ala ² ,MePhe ⁴ , Gly-ol⁵]enkephalin, of the -ligand, [³H]-[d-Ala ² ,d-Leu ⁵]enkephalin and of the -ligand, [³H]-(±)-ethylketazocine after suppression of - and -binding by 100 nM of the unlabelled -ligand and 100 nM of the unlabelled -ligand. The pharmacological agonist or antagonist activities were assayed on the guinea-pig ileum, mouse vas deferens and rat vas deferens.The first group of compounds were pure agonists in all three pharmacological bioassays. The majority of the compounds showed preference to -binding but phenazocine and particularly etorphine had also high affinities to the - and -binding sites.The second group consisted of N-allyl and N-cyclopropylmethyl homologues of the morphine, 3-hydroxymorphinan and normetazocine series which had agonist and antagonist activities in the guinea-pig ileum and mouse vas deferens but were pure antagonists in the rat vas deferens. In the binding assays, -binding and -binding were prominent.The third group was made up by the ketazocine-like compounds which in the guinea-pig ileum and mouse vas deferens were pure agonists and in the rat vas deferens pure antagonists. The binding spectrum showed particularly high binding to the -binding site.The fourth group was the antagonists which were devoid of agonist activity with the exception of diprenorphine and Mr 2266 which had retained some agonism. The binding spectrum showed considerable variation, naloxone in low concentration being a selective -antagonist, Mr 2266 having high affinities to the - and -binding sites and diprenorphine having considerable affinities to the -, - and -binding sites.Since each of the four groups of compounds, whether pure agonists, agonist-antagonists, ketazocine-like drugs or pure antagonists, shows independent varittions in the affinities to the - and -binding sites, their different pharmacological behaviour cannot be solely due to difference in the binding spectra.     

Der Einfluß des Prednison- und Prednisolonbisguanylhydrazons auf die Na+ + K+-stimulierte Membran-ATPase des Meerschweinchenherzens

Zusammenfassung Prednison- und Prednisolonbisguanylhydrazon hemmen ebenso wie k-Strophanthin eine aus Meerschweinchenherzen gewonnene durch Na⁺ + K⁺ stimulierte Membran-ATPase. Eine 50%ige Hemmung erfolgt bei Konzentrationen von 3,8 M Prednisonbisguanylhydrazon, 0,28 M Prednisolonbisguanylhydrazon bzw. 1,3 M k-Strophanthin. Dieses Wirksamkeitsverhältnis der drei Verbindungen entspricht etwa der Hemmung des aktiven Ionentransportes an Meerschweinchenerythrocyten und dem positiv inotropen Effekt am isoliert durchströmten Meerschweinchenherzen.

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Summary Prednison- and Prednisolonbisguanylhydrazon inhibit like k-Strophanthin the Na⁺ + K⁺-stimulated ATPase from guinea-pig hearts. 50% inhibition was stated with concentrations of 3,8 M Prednisonbisguanylhydrazon, 0,28 M Prednisolonbisguanylhydrazon or 1,3 M k-Strophanthin. This difference in effectiveness of the compounds corresponds to the inhibition of the active ion-transport in erythrocytes of guinea-pigs and to the positive inotropic effect in isolated perfused guinea-pig hearts.

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Mit 1 TextabbildungDie Ergebnisse wurden auf der 5. Frühjahrstagung der Deutschen Pharmakologischen Gesellschaft am 28. April 1964 in Mainz vorgetragen. [Naunyn-Schmiedebergs Arch. exp. Path. Pharmak. 247, 341 (1964).]     

Differential inhibition of biphenyl hydroxylation in perfused rat liver

Summary A differential inhibition of biphenyl hydroxylation by -naphthoflavone and metyrapone was observed in isolated pefused rat liver. -Naphthoflavone inhibited 2- and 4-hydroxylation in livers from -naphthoflavone-pretreated animals but had no effect on both reactions in livers from phenobarbital-pretreated animals. Metyrapone inhibited 2- and 4-hydroxylation in phenobarbital-stimulated livers, but only insignificant inhibition of 2-hydroxylation and a slight enhancement of 4-hydroxylation by metyrapone was observed in -naphthoflavone-stimulated livers.Conjugation of 2-hydroxybiphenyl and 4-hydroxybiphenyl by isolated perfused livers was also studied. 4-Hydroxybiphenyl preferentially formed sulphates in livers from untreated animals but after induction glucuronidation was as effective as sulphation or even exceeded sulphation. Only glucuronic acid conjugates of 2-hydroxybiphenyl were detected.     

Biodegradable PLGA Microspheres Loaded with Ganciclovir for Intraocular Administration. Encapsulation Technique,in Vitro Release Profiles,and Sterilization Process

Purpose. The purpose of this work was to obtain a sterilized formulation consisting of biodegradable microspheres of poly (DL-lactide-co-glycolide) (PLGA) for intraocular sustained release of ganciclovir. Methods. Microspheres were prepared using a dispersion of ganciclovir in fluorosilicone oil (FSiO) that was further dispersed in an acetone solution of PLGA [50/50 and inherent viscosity 0.41 dl/g], and emulsified in silicone oil with a surfactant. Once prepared, the formulation was exposed with an effective radiation dose of 2.5 megarads. The release rate data of ganciclovir from the sterilized and nonsterilized batches were compared using the similarity factor (f₂). Results. The dispersion of the drug in FSiO contributed to achieving a drug payload of up to 95% of the theoretical in the 300-500 m microspheres. Ten mg released ganciclovir in vitroat 1.3 g/h for the first 21 days, but decreased to 0.2 g/h from day 25 until the end of the release study (42 days). No significant differences in the amounts of encapsulated drug (=0.05) were observed between the sterilized and nonsterilized microspheres. Furthermore, dissolution profiles of formulations behaved similarly before and after gamma radiation exposure. Conclusions. The technique of microsphere preparation described resulted in high ganciclovir loading (95%) and prolonged drug release. The ganciclovir formulation behaved similarly before and after the sterilization process.     

Regulation of adenylate cyclase activity in hamster adipocytes

Summary In ghosts of hamster adipocytes, the regulation of adenylate cyclase (ATP: pyrophosphate lyase, cyclizing; EC 4.6.1.1) activity by prostaglandins, -adrenergic agonists and nicotinic acid was studied. These three classes of antilipolytic agents caused adenylate cyclase inhibition without an apparent lag phase. Maximal inhibitions observed ranged between about 45% (by -adrenergic agonists) and 60% (by prostaglandins and nicotinic acid). The order of potency for the inhibitory prostaglandins (PG) was PGE₁ PGE₂>PGF₂PGI₂>PGD₂>6-keto PGF₁. The IC₅₀ values obtained were about 0.007, 0.06, 0.3 and 1 M for PGE₁, PGF₂, PGD₂ and 6-keto PGF₁, respectively. -Adrenergic agonists, studied in the presence of the -adrenergic blocking agent, propranolol (30 M), inhibited the fat cell enzyme with the order of potency (1)-adrenaline > (1)--methylnoradrenaline (1)-noradrenaline > clonidine tetryzoline > (1)-phenylephrine. The IC₅₀ values obtained for (1)-adrenaline and (1)-noradrenaline were about 3 and 10 M, respectively. The inhibitory effect of (1)-adrenaline was blocked by the -adrenergic antagonists with the potency order yohimbine phentolamine > prazosin. These findings suggest that an ₂ of receptors is involved in this catecholamine-induced inhibition. Nicotinic acid (10 M) reduced adenylate cyclase activity by about 60% with half-maximal effectiveness at about 0.6 M. The nicotinic acid derivatives, nicotinamide, -pyridylcarbinol and NAD (up to 100 M), had no effect on enzyme activity.Inhibition of the hamster adipocyte adenylate cyclase by the antilipolytic agents required the presence of both GTP, which reduced basal activity by about 80% at 10 M, and sodium ions, which specifically activated the GTP-affected from of the enzyme. Inhibition was also observed in the presence of ACTH, which in a GTP-dependent manner increased adenylate cyclase activity. Pretreatment of the enzyme preparation with NaF (10 mM) partially reduced the inhibitory effect, and preactivation with the stable GTP analogue, guanylyl 5-imidodiphosphate (100 M), abolished the adenylate cyclase inhibition by the antilipolytic agents.Abbreviations PG prostaglandin - GMP-P(NH)P guanylyl 5-imidodiphosphate Some of the data were presented in abstract form (Aktories et al., 1979a)     

Effect of phorbol esters and polymyxin B on modulation of noradrenaline release in mouse atria

Summary Phorbol 12-myristate 13-acetate (PMA; 0.03, 0.1 and 1.0 mol/l), a protein kinase C activating phorbol ester, significantly enhanced the stimulation-induced (S-I) outflow of radioactivity at 5 Hz stimulation in mouse atria preincubated with [³H]-noradrenaline, whereas a phorbol ester which does not activate protein kinase C, phorbol 13-acetate (0.1 mol/l), had no effect. This suggests that protein kinase C may have a role in modulating sympathetic neurotransmission.Polymyxin B (7 and 21 mol/l), an inhibitor of protein kinase C, had no effect on the S-I outflow of radioactivity. However, it had a significant inhibitory effect in a concentration of 70 mol/l. Polymyxin B (21 mol/l) reduced the facilitation of the S-I outflow of radioactivity produced by PMA (0.03 mol/l), 8-bromo-cyclic AMP (90 mol/l), tetraethylammonium chloride (300 mol/l), and idazoxan (0.1 mol/l). Furthermore, when a higher frequency of stimulation was applied (10 Hz rather than 5 Hz), polymyxin B (21 pmol/1) by itself inhibited the S-I outflow of radioactivity.In the presence of a concentration of PMA (0.1 mol/l) that was maximally effective in enhancing the S-I outflow of radioactivity, both idazoxan (0.1 mol/l) and 8-bromocyclic AMP (90 mol/l) still enhanced the S-I outflow. This suggests that these agents are not operating through protein kinase C and further suggests that the inhibitory effect of polymyxin B on these agents cannot be due to inhibition of protein kinase C. The effects of clonidine on the S-I outflow were not affected by a maximally effective concentration of PMA (0.1 mol/l). These results suggest that protein kinase C is not involved in a ₂-adrenoceptor mediated modulation of noradrenaline release. Send offprint requests to I. F. Musgrave at the above address     

The effectiveness of β-adrenoceptor stimulation and the contribution of β1-adrenoceptors increase from the proximal to the distal part of the canine saphenous vein

Summary The present study was undertaken to characterize -adrenoceptors of the canine saphenous vein and their distribution along this vessel. In a first series of experiments, concentration-response curves to isoprenaline and forskolin were compared on strips taken from proximal and distal portions of the vein. The tone of the strip was previously increased by phenylephrine to one of the three levels: about 85, 70 and 55% of the maximum, which corresponds to 3.08±0.16 and 2.96±0.17 (n = 6) N·g^–1, for proximal and distal strips, respectively. The maximal relaxation to isoprenaline was significantly larger in the distal than in the proximal portion, for responses starting at 85 and 70% of the maximum tone. In contrast, forskolin caused 100% relaxation, both proximally and distally, irrespective of the previous tone.In a second series of experiments, the relaxation to dobutamine and terbutaline was compared in proximal and distal portions after the tone had been elevated by adrenaline, noradrenaline and phenylephrine to about 70% of the maximum. When the tone was increased by adrenaline, the relaxation in response to 2.7 mol·l^–1 dobutamine was larger than that to 2.7 mol·l^–1 terbutaline both in proximal and distal portions, while when it was increased by noradrenaline, the relaxation to terbutaline was larger than that to dobutamine in the proximal portion; in the distal portion, dobutamine and terbutaline were equieffective. When the tone was increased by phenylephrine, dobutamine and terbutaline caused equivalent relaxations proximally, but distally the relaxation to dobutamine was larger than that to terbutaline.In a third series of experiments, the antagonism exerted by atenolol and by the compound ICI-118,551 on the relaxation to dobutamine and terbutaline was compared proximally and distally. Both proximally and distally atenolol was more effective against dobutamine than against terbutaline, while the compound ICI-118,551 was effective only against terbutaline.It is concluded that ₁- and ₂-adrenoceptors exist in the canine saphenous vein and that the effectiveness of -adrenoceptor stimulation increases from the proximal to the distal portion of this vessel due to a progressive increase in the density of ₁-adrenoceptors.Correspondence to S. Guimaraes at the above address     

The Effect of Low Concentrations of Molecularly Dispersed Poly(Vinylpyrrolidone) on Indomethacin Crystallization from the Amorphous State

Purpose. To investigate the effect of low concentrations of molecularly dispersed poly(vinylpyrrolidone) (PVP) on indomethacin (IMC) crystallization from the amorphous state using particle size effects to identify possible mechanisms of crystallization inhibition. Methods. Different particle sizes of amorphous IMC and 1, 2, and 5% PVP were stored dry at 30°C for 84 days. PXRD was used to calculate the rate and extent of crystallization and the polymorph formed. Results. Crystallization from amorphous IMC and IMC/PVP molecular dispersions yielded the polymorph of IMC. Crystallization rates were reduced at larger particle size and in the presence of 1, 2, and 5%PVP. Crystallization did not reach completion in some IMC/PVP samples, with the quantity of uncrystallized amorphous phase proportional to particle size. Conclusions. Low concentrations of molecularly dispersed PVP affected IMC crystallization from the amorphous state. Formation of -IMC at rates dependent on particle size indicated that surface nucleation predominated in both the absence and presence of PVP. Excellent correlation was seen between the extent of crystallization and simulated depths of crystal penetration, supporting the hypothesis that increasing local PVP concentration inhibits crystal growth from surface nuclei into the amorphous particle.     

The significance ofβ-adrenoceptor down regulation in the desipramine action in the forced swimming test

Summary The present studies were undertaken to clarify whether central-adrenoceptor down regulation is responsible for the greater effect of chronic treatment with desipramine (DMI) compared with acute treatment in the forced swimming test in rats. Repetitive administration of DMI activated the rat behaviour pattern and consequently reduced the duration of immobility. The degree of activation depended on the length of treatment, i.e. no effect when given in a single dose, moderate effect when given subchronically (3 doses) and marked activation after chronic (31 doses) treatment. Chronic treatment with DMI also produced a decrease in³H-dihydroalprenolol (³H-DHA) binding site in the cerebral cortex. Acute stimulation of brain-adrenoceptors by intracerebroventricular (i.c.v.) isoprenaline significantly, though partially, attenuated the behavioural effect of chronic DMI by ₁-adrenoceptor-related mechanisms. Similarly, chronic i.c.v. co-administration of atenolol or practolol, ₁-adrenoceptor antagonists, together with DMI attenuated both-adrenoceptor down regulation and the behavioural activation by chronic DMI. On the other hand, chronic i.c.v administration of isoprenaline, supposedly leading to down regulation of-adrenoceptors, facilitated the activating behavioural effect of DMI, as a single dose became effective. Changes, however, in³H-DHA binding parameters in the cerebral cortex were not observed after chronic isoprenaline. These results suggest that down regulation of-adrenoceptors in brain is reponsible, at least in part, for the marked activatory effect of chronic DMI in the forced swimming test, possibly by reducing an inhibitory function of ₁-adrenoceptor mediated mechanisms.     

(−)δ9 THC as an hypnotic

(–) ⁹ THC was found to significantly decrease the time it takes to fall asleep in physically healthy insomniacs. Once asleep, interruptions of sleep were not significantly altered over the whole night. The (–) ⁹ THC tended to be associated with some decrease in awakenings in the first half of the night.The primary side effect experienced by the subjects at all dose levels in the Pre-Sleep phase was temporal disorganization and mood alterations. There was an increase in intensity of side effects and number of subjects affected with increasing dosage.The most significant side effect, however, was a hangover phenomenon, or continued high the next day, with some residual of temporal disorganization. It increased in intensity and duration with increase in dosage. This hangover seems severe enough to eliminate the consideration of the 30 mg dose range of (–) ⁹ THC for clinical use as an hypnotic.Dr. Cousens is a 3rd Year Resident in Psychiatry at the Napa State Hospital, Napa, California     

The metabolism of the amyloid precursor protein and its relevance to Alzheimer's disease

Summary The pathology of Alzheimer's disease is primarily characterized by the deposition of -amyloid/A peptide as the major component of senile or neuritic plaques. The A peptide is produced as a result of proteolytic cleavage of the transmembrane protein precursor, APP, during its normal cellular metabolism. The free amino terminus of the A peptide is generated by an endopeptidic cleavage between Met⁶⁷¹-Asp⁶⁷² by a protease termed -secretase. Increased cleavage at this site takes place in a rare, inherited double mutation (Lys⁶⁷⁰-Met⁶⁷¹ to Asn⁶⁷⁰-Leu⁶⁷¹), leading to increased A production and consequent development of Alzheimer's disease on an accelerated time scale in the affected individuals, underscoring the pathological importance of -secretase activity. Cellular studies provide direct evidence that inhibition of -secretase activity would appear to be effective in inhibiting A production as a rational approach to developing therapeutics for the disease.     

Activation of central ATP-sensitive potassium channels produces the antinociception and spinal noradrenaline turnover-enhancing effect in mice

ICV cromakalim, a K⁺ channel opener, produced antinociception. This effect was completely antagonized by ICV glibenclamide, a selective adenosine triphosphate-sensitive K⁺ channel (K_ATP channel) blocker. Furthermore, direct opening of central K_ATP channels by ICV cromakalim increased the spinal noradrenaline (NA) turnover. On the other hand, the antinociception induced by ICV morphine ( opioid agonist), but not ICV U-50,488H ( opioid agonist) was markedly potentiated by cromakalim. These findings suggest that the opening of central K_ATP channels may elicit the antinociceptive effect and activate the descending NAergic pathway, and central K_ATP channels play an important role as a modulator of the antinociception induced by agonists but not agonists.     

The sympathetic axons innervating the sinus node of the rabbit possess presynaptic opioid к- but not μ- or δ-receptors

Summary The postganglionic sympathic nerves of rabbit isolated hearts were stimulated with pulses delivered at 5 Hz and train durations of 1–5 s. Ethylketocyclazone 0.01–1 mol/l and fentanyl 1 and 10 mol/l but not morphine 1 and 10 mol/l, Met-enkephalin 1 and 4 mol/l or d-Ala², d-Leu⁵-enkephalin 0.5 and 5 mol/l diminished the stimulation-evoked increase in heart rate. The effect of ethylketocyclazocine 0.1 mol/l was antagonized by naloxone 1 and 10 mol/l. In contrast, the effect of fentanyl was not changed by naloxone 10 mol/l. Ethylketocyclazocine 0.03 and 1 mol/l did not reduce the tachycardia elicited by exogenous noradrenaline. The results suggest that, under in vitro conditions, only presynaptic opioid - but not - or -receptors inhibit the release of noradrenaline from the sympathetic neurones innervating the sinus node.     

Cyclic GMP stimulation by vasopressin in LLC-PK1 kidney epithelial cells is l-arginine-dependent

Summary The l-arginine antagonist N^G-monomethyl-l-arginine has been shown to inhibit nitric oxide formation from l-arginine in endothelial cells. In the present study N^G-monomethyl-l-arginine was used to assess the role of l-arginine for cyclic GMP stimulation by vasopressin in a kidney epithelial cell line (LLC-PK₁). Preincubation of cells with 1 mol/l, 10 mol/l and 100 mol/l N^G-monomethyl-l-arginine decreased cyclic GMP stimulation at 1 mol/l vasopressin by 25%, 71% and 90%, respectively. This inhibition by N^G-monomethyl-l-arginine was markedly reduced by l-arginine (2 mmol/1) but not d-arginine (2 mmol/1). Cyclic GMP stimulation by the calcium ionophore A23187 was also inhibited by N^G-monomethyl-l-arginine and enantioselectively restored by l-arginine. However, N^G-monomethyl-l-arginine did not affect cyclic GMP stimulation by sodium nitroprusside that spontaneously releases nitric oxide. These results suggest that, in kidney epithelial cells, vasopressin induces nitric oxide formation from l-arginine leading to activation of soluble guanylate cyclase. It is concluded that nitric oxide formation from l-arginine is not only responsible for endothelium-dependent relaxation but may be a more general pathway with regulatory function for intracellular guanylate cyclase activity.Send offprint requests to K. Schror at the above address     

Inhibition by carbamazepine of various ion channels-mediated catecholamine secretion in cultured bovine adrenal medullary cells

The effects of carbamazepine (CBZ) on ²²Na⁺ influx, ⁴⁵Ca²⁺ influx, catecholamine secretion and cyclic GMP production were examined in cultured bovine adrenal medullary cells. 1 CBZ (40–120 mol/l) inhibited ²²Na⁺ influx evoked by carbachol in a concentration-dependent manner. CBZ inhibited carbachol-evoked ⁴⁵Ca²⁺ influx and catecholamine secretion at concentrations similar to those which suppressed ²²Na⁺ influx. 2 CBZ (4–120 mol/l) inhibited veratridine-induced ²²Na⁺ influx, ⁴⁵Ca²⁺ influx and catecholamine secretion. 3 CBZ (12 or 40–120 mol/l) suppressed 56 mmol/1 K⁺-evoked ⁴⁵Ca²⁺ influx and catecholamine secretion, respectively. 4 Combination of CBZ with nitrendipine or -agatoxin-IVA produced further inhibition of 56 mmol/l K⁺ - evoked ⁴⁵Ca²⁺ influx and catecholamine secretion, compared to the effect of CBZ alone, whereas CBZ plus -conotoxin-GVIA did not produce any further inhibition. 5 CBZ (40 mol/1) attenuated the production of cyclic GMP caused by muscarine. These results suggest that CBZ at therapeutic concentrations (16–48 mol/l: 4–12 g/ml) inhibits catecholamine secretion by interfering with nicotinic acetylcholine receptor-associated ion channels, voltage-dependent Na⁺ channels and N-type voltage-dependent Ca²⁺ channels, and may have an antimuscarinic effect in adrenal medullary cells.     

Study of Pharmaceutical Solid Dispersions by Microthermal Analysis

No HeadingPurpose. The main objective of the study was to determine the ability of microthermal analysis (TA) to assess the crystallinity of the drug in two noncommercial pharmaceutical solid dispersions.Methods. Pure substances, physical mixes, and solid dispersions were analyzed by TA. The thermal values obtained by TA were compared with data obtained by more conventional techniques like differential scanning calorimetry.Results. TA was able to detect the drug in the waxy matrix. The technique was capable of showing that relatively large amorphous drug domains (up to 70 m) are formed during the solidification of the solid dispersion. These amorphous domains are thermodynamically unstable and can crystallize upon aging.Conclusions. TA was successfully applied to the physical characterization of solid dispersions. Local thermal analysis (LTA) offers a unique way to probe a selected area on the surface of the sample. It is capable of melting the drug locally without melting the lower melting point excipient. These results gave an understanding of the poor dissolution performance of these solid dispersions upon aging.