A Population Growth Model of Dissolution

Purpose. To develop a new approach for describing drug dissolution which does not require the presuppositions of time continuity and Fick's law of diffusion and which can be applied to both homogeneous and heterogeneous media. Methods. The mass dissolved is considered to be a function of a discrete time index specifying successive 'generations' (n). The recurrence equation: _n+1 = _n + r(l – _n)(1 – _n X ₀/) was derived for the fractions of dose dissolved _n and _{n +1}, between generations n and n + 1, where r is a dimensionless proportionality constant, X ₀ is the dose and is the amount of drug corresponding to the drug's solubility in the dissolution medium. Results. The equation has two steady state solutions, _ss = 1 when (X ₀/) 1 and _ss = /X ₀ when (X ₀/) > 1 and the usual behavior encountered in dissolution studies, i.e, a monotonic exponential increase of _n reaching asymptotically the steady state when either r < /X ₀ < 1 or r < 1 < /X ₀. Good fits were obtained when the model equation was applied to danazol data after appropriate transformation of the time scale to 'generations'. The dissolution process is controlled by the two dimensionless parameters /X ₀ and r, which were found to be analogous to the fundamental parameters dose anddissolution number, respectively. The model was also used for the prediction of fraction of dose absorbed for highly permeable drugs. Conclusions. The model does not rely on diffusion principles and therefore it can be applied under both homogeneous and non-homogeneous conditions. This feature will facilitate the correlation of in vitro dissolution data obtained under homogeneous conditions and in vivo observations adhering to the heterogeneous milieu of the GI tract.     

Pharmacological profile of a new potent and specific α2-adrenoceptor antagonist,L-657,743

Summary L-657,743, (2S,12bS)1,3-dimethylspiro (1, 3,4,5, 6,6, 7,12 b-octahydro-2-H-benzo[b]furo[2,3-a]quinolizine)-2, 4- pyrimidin-2-one, was tested in several in vitro and in vivo models for ₂-adrenoceptor antagonism. L-657,743 exhibited a high affinity ( 1 nM) for ₂-adrenoceptors labelled by [³H] rauwolscine or [3H]clonidine with a 240-fold selectivity versus ₁-adrenoceptors labelled by [³H]prazosin. L-657,743 was a potent, selective, and competitive ₂-adrenoceptor antagonist in the rat isolated vas deferens (pA₂ = 9.3 vs clonidine; pA₂ = 7.1 vs methoxamine). In vivo, L-657,743 potently blocked clonidine-induced mydriasis in the rat and stimulated cerebrocortical norepinephrine synthesis, two indices of central ₂-adrenoceptor antagonism. L-657,743 exhibited a comparatively low affinity for several monoamine receptor subtypes (D₁, D₂, 5-HT₁, 5-HT₂) in radioligand binding assays in vitro and a comparatively low potency to alter the synthesis of brain DA and 5-HT in vivo indicating a marked ₂-specificity versus other monoamine receptor mechanisms. Compared to yohimbine, L-657,743 had considerably higher ₂-antagonist potency and ₂/₁ selectivity and was significantly more ₂-specific (i.e., vs. DA, 5-HT receptors). Send of fprint requests to : D. J. Pettibone at the above address     

Presynaptic dopamine DA2-receptors in rabbit jejunal arteries

Summary Excitatory junction potentials (e.j.ps) evoked by nerve stimulation with 15 pulses at 1 Hz were recorded from muscle cells of rabbit isolated jejunal arteries. LY 171555 1 mol/l, SKF 38393 10 mol/l, dopamine 10 ol/l and clonidine 0.1 mol/l depressed all e j.ps in the train. The percentage inhibition was inversely related to the number of pulses. S- and R-sulpiride, 10 mol/l, domperidone 1 mol/l, SCH 23390 1 mol/l and rauwolscine 1 mol/l did not change, or even depressed the first e j.ps. Of these compounds only S- and R-sulpiride, 10 mol/l and rauwolscine 1 mol/l facilitated the late e.j.ps. The percentage facilitation increased with the number of pulses until a maximum was reached; rauwolscine 1 ol/l had the largest effect. S- and R-sulpiride, 10 mol/l, as well as domperidone 1 ol/l antagonized the action of LY 171555 1 mol/l. S-Sulpiride was more potent than its R-isomer. SCH 23390 1 mol/l and rauwolscine 1 mol/l blunted the effect of SKF 38393 10 mol/l. Rauwolscine 1 mol/l slightly reduced the inhibition by dopamine 10 mol/l; S-sulpiride 10 mol/l was antagonistic only in the presence of rauwolscine 1 mol/l. When rauwolscine 1 mol/l, prazosin 0.1 mol/l, propranolol 1 mol/l and cocaine 10 mol/l was added to the medium, dopamine 10 mol/l continued to produce the same depression of e j.ps, as in the absence of these compounds. Under such conditions S-sulpiride 10 mol/l also counteracted dopamine 10 gmol/l. Rauwolscine 1 mol/l prevented the effect of clonidine 0.1 mol/l. The antagonists were not absolutely selective against only one type of agonist. We suggest that both presynaptic DA₂- and postsynaptic DA₁-receptors are present in rabbit jejunal arteries. The activation of either receptor-type may depress the e j.ps. Dopamine interferes with neuroeffector transmission due to ₂-adrenoceptor agonist properties; its DA₂-effect is unmasked only after ₂-adrenoceptor blockade. There was no evidence for a co-transmitter function of dopamine. Send offprint requests to P. Illes at the above address     

Interindividual differences in the pharmacokinetics of digitoxin and digoxin during long-term treatment

Summary Patients suffering from congestive heart failure received maintenance doses of digitoxin (N=10) or digoxin (N=8). The plasma glycoside concentration was determined, and after a single dose of³H-digitoxin or³H-digoxin, the decline and excretion of radioactivity were measured over a period of 7 (digitoxin) and 3 days (digoxin). Plasma radioactivity declined with a ^x T_1/2 between 77 and 234 h (mean 138 h) in the case of digitoxin and with a ^x T_1/2 between 9.2 and 38.6 h (mean 23.5 h) for digoxin. A close correlation between ^x T_1/2 and excreted radioactivity and ^x T_1/2 and total plasma level was found for digitoxin. In 4 patients TLC of urine showed that interindividual variations in digitoxin elimination could possibly be attributed to variation in metabolism, resulting in the production of different metabolites. Predicted digitoxin plasma levels agreed well with measured values. The maintenance dose could be calculated from the total body clearance (V_Cl) and a presumed plasma glycoside level. The recommended technique facilitates dosage calculations in patients treated with digitoxin.Abbreviations AUC ₀ ^x area under curve - average steady state plasma concentration - F fraction of the dose which is absorbed - D dose - D_M maintenance dose - V_Cl plasma (body) clearance - dosage interval - kinetic parameter of the corresponding - ³H glycoside     

ATP and endogenous agonists inhibit evoked [3H]-noradrenaline release in rat iris via A1 and P2y-like purinoceptors

Summary Effects of ATP, adenosine and purinoceptor antagonists on field stimulation-evoked (3 Hz, 2 min) [³H]-noradrenaline overflow were investigated in the rat isolated iris.ATP and adenosine inhibited the evoked overflow of [³H]-noradrenaline. 1,3-Dipropyl-8-cyclopentylxanthine (DPCPX) shifted the concentration-response curve of ATP to the right in a concentration-dependent manner, but with a potency (–log K_B = 7.88) much lower than expected for an A1 adenosine receptor. In the continuous presence of DPCPX, the ATP-induced prejunctional inhibition was unaffected by suramin (100 mol/l) and DIDS (4,4-diisothiocyanatostilbene-2,2-disulfonic acid, 50 mol/l) but was antagonized by the P_2Y-receptor antagonist cibacron blue ( = reactive blue 2;30 and 100 mol/l, –log K_B = 4.7)and ,-methylene-ATP (10 mol/l). Whereas the evoked [³H]-noradrenaline overflow was unaffected by suramin and DIDS, cibacron blue and ,-methylene-ATP caused a small and transient increase. Cibacron blue at 30 mol/l failed to antagonize the inhibition of evoked [³H]-noradrenaline overflow that adenosine produced in the absence of DPCPX. Basal [³H]-noradrenaline overflow was enhanced by cibacron blue, not changed by ,-methylene-ATP and DIDS, and decreased by suramin.The results show that exogenous ATP inhibits sympathetic neurotransmission in the rat iris via A₁ and P_2Y-like purinoceptors. The latter have a low apparent affinity for cibacron blue and probably are blocked by ,-methylene-ATP. Under the present conditions, endogenous purines exert a tonic inhibition not only via A₁- but also via these P_2Y-receptors. Correspondence to: H. Fuder at the above address     

SK&F 104078, a post-functionally selective α2-adrenoceptor antagonist in the human saphenous vein in vitro

Summary The present study investigated the effects of SK&F 104078 (6-chloro-9-[(3-methyl-2-butenyl)oxy]-3methyl-1H,2,3,4,-tetrahydro-3-benzazapine) at pre- and post functional ₂-adrenoceptors in the human isolated saphenous vein. Noradrenaline (0.001–100 mol/l) produced concentration-dependent contractions of the human saphenous vein which were competitively antagonised by the ₁-adrenoceptor antagonist prazosin (0.01–1.0 mol/l) and the ₂-adrenoceptor antagonist, rauwolscine (0.01–1.0 mol/l), indicating the presence of both post functional ₁- and ₂-adrenoceptors in this preparation. The selective ₂-adrenoceptor agonist, UK-14,304 (0.01–100 mol/l) also produced concentration-dependent contractions of the human saphenous vein which were antagonised by both rauwolscine (0.1 mol/l) and prazosin (0.1 mol/l). In the presence of angiotensin II (0.05 mol/l), which itself produced a transient contraction, rauwolscine (0.1 mol/l) produced a rightward shift of the UK-14,304 concentration-response curve while prazosin (0.1 mol/l) had no effect. SK&F 104078 (10.0 mol/l) under these conditions also produced a rightward shift of the concentration-response curve to UK-14,304, but was at least 100-fold less potent than rauwolscine. At pre functional ₂-adrenoceptors, exogenous noradrenaline (0.01 and 0.1 gmol/l) induced a concentration-dependent inhibition of stimulation-evoked [7-³H]-noradrenaline release from the human saphenous vein in vitro, which was antagonised by rauwolscine (0:1 mol/l) and tolazoline (10.0 mol/l) but not by SK&F 104078 (10.0 gmol/l).Rauwolscine (0.1 mol/l) produced a small increase in stimulation-evoked [7-³H]-noradrenaline release while both tolazoline and SK&F 104078 failed to produce any enhancement in release in the absence of exogenous agonist atconcentrationsupto10 gmol/l.Insummary, noradrenaline and UK-14,304 contracted the human isolated saphenous vein by an action at both postfunctional ₁- and ₂-adrenoceptors. These data demonstrate that SK&F 104078 discriminates between post- and pre-junctional ₂-adrenoceptors in the human isolated saphenous vein. Send offprint requests to M. V. Sennitt at the above address     

DDT increases hepatic testosterone metabolism in rats

DDT and its metabolites are considered as endocrine disruptors able to promote hormone-dependent pathologies. We studied the effects of technical-grade DDT on hepatic testosterone metabolism and testosterone hydroxylase activity ratios in the rat. Male and female Wistar rats were treated by gavage with a single dose of technical-grade DDT (0, 0.1, 1, 10, and 100 mg/kg body weight) and killed 24 h later. Hepatic microsomes were incubated with [4-¹⁴C]-testosterone and the metabolites were separated by thin-layer chromatography and quantified by radio scanning. DDT increased testosterone biotransformation and modified the profile of metabolites produced in a sex-dependent manner. Males treated with a representative dose (10 mg/kg) produced relatively less androstenedione (AD), 2-hydroxytestosterone (OHT), and 16-OHT but higher 6-OHT whereas treated females produced less 7-OHT and AD but higher 6-OHT and 6-OHT than their respective controls. In both sexes DDT decreased the relative proportion of AD and increased that of 6-OHT suggesting that the androgen-saving pathway was affected. The testosterone 6-/15-OHT ratio, a proposed indicator of demasculinization, was increased in treated males. This effect was in agreement with the demasculinizing ability proposed for DDT. The effects on 6-/16-OHT and 6-dehydrotestosterone/16-OHT ratios followed a similar tendency, with the ratio 6-/16-OHT being the most sensitive marker. Interestingly, these ratios were reduced in treated females suggesting that technical-grade DDT shifted testosterone hydroxylations toward a more masculine pattern. Thus, technical-grade DDT altered the hepatic sexual dimorphism in testosterone metabolism and decreased the metabolic differences between male and female rats.     

Retrospective study on the reliability of an “approximate LD50” determined with a small number of animals

Based on 364 LD₅₀ determinations in mice and rats after intravenous and oral administration of drugs, the reliability of an approximate LD₅₀ was retrospectively tested.The difference between approximate LD₅₀ and LD₅₀ is — independent of species and route of administration — not greater than ± 20% of the LD₅₀ in 90% of the cases.Four to five doses — uniformly distributed over the dose-mortality range can suffice in reliably determining the approximate LD₅₀.The probability is 10% that an approximate LD₅₀ and LD₅₀ are significantly different from each other.152 parallel studies on male and female animals show that the LD₅₀ or approximate LD₅₀ must not be determined for both sexes. It is sufficient to test a dose near the LD₅₀ in the opposite sex. A 50–75% reduction of expenditure in animal material is possible in most of LD₅₀ determinations.     

Effects of suramin and α,β-methylene ATP indicate noradrenaline-ATP co-transmission in the response of the mouse vas deferens to single and low frequency pulses

Summary Vasa deferentia from mice were field-stimulated by trains of 10 pulses delivered at 0.5 Hz. The pulses elicited separate twitches, the first of which (corresponding to a single pulse) exceeded the following ones in height and width and often was clearly biphasic. , -Methylene-ATP 1 mol/1 and suramin 100 mol/1 caused almost identical changes. They reduced the height of the first twitch in the train by about one half and also reduced its width in a manner indicating that only the second, slow phase remained, but reduced much more markedly the following twitches in which now a small second, slow phase also became detectable. Idazoxan 0.1 mol/1 or yohimbine 0.1 mol/l, when added in the presence of a, -methylene-ATP or suramin, further decreased the first twitch but enhanced twitches No. 2 to 10. These responses were then almost abolished by prazosin 0.1 mol/l. Successive addition of prazosin 0.1 mol/l and idazoxan 0.1 mol/1 to previously untreated vasa deferentia depressed the response to the first pulse by about one half in a manner indicating that only the first, rapid phase remained, but had comparatively little effect on the responses to the subsequent pulses. Suramin 100 mol/l almost abolished the contractions remaining in the presence of prazosin and idazoxan. The results indicate that the first, rapid phase of the neurogenic contractions elicited by single or low frequency pulses is mediated by ATP which substantially contributes to all responses in a train. The second, slow phase is mediated by noradrenaline which substantially contributes to the response to the first pulse only. The adrenergic contribution seems to be mediated by postjunctional ₁- as well as a ₂-adrenoceptors. Prejunctional ₂-adrenergic autoinhibition depresses the release of both ATP and noradrenaline. Send offprint request to I. v. Kügelgen at the above address     

A comparison of the effects of TMB-8 and nifedipine on pressor responses to α1- and α2-adrenoceptor agonists in pithed rats

TMB-8 has been characterized as an inhibitor of the release of Ca⁺ from intracellular pools. We have studied the modification of the pressor responses to selective _l-adrenoceptor agonists (methoxamine and phenylephrine), and to selective ₂-adrenoceptor agonists (B-HT 920 and B-HT 933) in pithed rats, produced by TMB-8. We have compared this modification with that produced by the calcium antagonist nifedipine. Nifedipine (100 g/kg, 300 g/kg, and 1000 g/kg) inhibited in a dose-dependent manner the pressor responses to the ₁- and ₂-adrenoceptor agonists, the dose-response curves to the ₂-adrenoceptor agonists being shifted further to the right. TMB-8 at a dose of 3000 g/kg did not modify the pressor effects of the _l-adrenoceptor agonists, and neither did it reinforce the inhibition of such responses produced by nifedipine. By contrast, TMB-8 pretreatment (0.03 g/kg, 0.3 g/kg, 3 g/kg, 30 g/kg, 300 g/kg and 3000 g/kg) inhibited the responses to both ₂-adrenoceptor agonists, the inhibition being more pronounced with B-HT 920. A similar effect was obtained with 0.03 g/kg TMB-8 and 0.3 g/kg TMB-8, particularly in the case of B-HT 920. It was stronger with higher doses, but similar for all doses over 3 g/kg. The inhibition of the pressor responses mediated by the stimulation of ₂-adrenoceptors by TMB-8 was less in rats treated with the Ca²⁺ entry promoter BAY K 8644 (300 g/kg), and could also be reduced by the continuous infusion of CaCl₂ (0.25 g/min). These results suggest that in pithed rats TMB-8 may also behave as an inhibitor of the Ca⁺ influx into vascular smooth muscle.     

Pharmacokinetics of sulfametopyrazine (Kelfizine W) effects of a single oral dose

Summary The pharmacokinetics of sulfametopyrazine were studied for seven days after a single oral dose of 2 g. in healthy volunteers in order to establish its chemotherapeutic value. — The appearance and disappearance of the drug in the plasma were evaluated both for compounds with a free amino group and for total sulphonamides. The half-life and absorption, distribution, elimination and excretion coefficients were calculated, as well as the concentrations in plasma water and interstitial fluid. The estimated drug concentrations in the urine agreed with those calculated from the excretion coefficients. — In all subjects at the end of the seventh day the concentrations in all body compartments of active compounds exceeded the minimum required for a therapeutic effect. The highest concentrations found in the urine were always significantly lower than the drug's basal solubility at pH 5, thus excluding any risk of crystalluria.Glossary of symbols total binding capacity of plasma proteins for SMP - Specific gravity of blood ( Bl), and interstitial fluid (IF) - minimum inhibitory concentration for bacterial growth. Evaluation of against E. coli or other pathogenic bacteria in a medium free of antagonists [29] - ratio of dose interval to half-life - dose interval - safety factor. Proportionality constant between andc _min for a therapeutic efficacy of 95 per cent - fraction of the administered drug absorbed from the depot (gastrointestinal tract etc.) - distribution coefficient with respect to the drug concentration in blood plasma (ml/g) - D* initial dose of the drug - D maintenance dose - M molecular weight of the drug (280) - G weight of subject (kg) - F area between time axis and concentration curve (plotted c' values) - t _50% apparent biological half-life - w ¹ water content of plasma (ml/ml) - p protein concentration of plasma (pBl), or interstitial fluid (pIF) (g/l) - c _IF concentration in the interstitial fluid - C ₀ concentration in plasma at zero time after i.v. administration - c ₁ ⁰ concentration in plasma after oral absorption extrapolated to zero time - c ₁ concentration in plasma water of the drug with free amino function - c _min minimum inhibitory concentration needed in plasma water (minimum therapeutic concentration) - k ₀₁ rate constant for absorption - k ₁ rate constant for absorption determined at timet; (similarlyk₂) - K total elimination coefficient - k _el rate constant for elimination - k _F rate constant for formation of metabolites - k _D excretion coefficient of SMP with free amino function - k _U coefficient of metabolite excretion - D ₀ quantity of SMP in the body at time zero - D _B quantity of SMP in the body at timet - D _U quantity of SMP excreted in the urine at timet - M _F quantity of metabolites formed at timet - M _B quantity of metabolites present in the body at timet - M _U quantity of metabolites excreted in the urine at timet - K dissociation constant for the sulphonamide-protein complex - notation for quantities related to drug concentrations in plasma, e.g. c (corresponding term without refer to plasma water)     

Release-inhibiting α2-adrenoceptors at serotonergic axons in rat and rabbit brain cortex: evidence for pharmacological identity with α2-autoreceptors

The pharmacological properties of the presynaptic ₂-adrenoceptors modulating the release of serotonin in rat and rabbit brain cortex (₂-heteroreceptors) were compared with the properties of presynaptic ₂-autoreceptors in the same brain area. Brain cortex slices were preincubated with [³H]-serotonin or [³H]-noradrenaline and then superfused and stimulated by brief high-frequency pulse trains.The ₂-adrenoceptor agonist bromoxidine reduced the electrically evoked overflow of tritium in experiments with both [³H]-noradrenaline and [³H]-serotonin and in brain slices from either species. The antagonists phentolamine, idazoxan, (+)-mianserin, rauwolscine, 5-chloro-4(1-butyl-1,2,5,6-tetrahydropyridin-3-yl)-thiazole-2-amine (ORG 20350), 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane (WB 4101), (–)-mianserin and corynanthine caused parallel shifts of the concentration-inhibition curves of bromoxidine to the right. Negative logarithms of antagonist dissociation constants pK_d were calculated from the shifts. In the rat, the ₂-autoreceptor pK_d value of each single antagonist was similar to its ₂-heteroreceptor pK_d value, maximal difference 0.4, giving a close correlation, r = 0.97 (P<0.001). In the rabbit equally, the ₂-autoreceptor pK_d value of each single antagonist was similar to its ₂-heteroreceptor pK_d value, maximal difference 0.4, again yielding a close correlation, r = 0.96 (P < 0.001). However, antagonist pK_d values at rat ₂-autoreceptors differed from those at rabbit ₂-autoreceptors, r = 0.70 (P > 0.05), and antagonist pK_d values at rat ₂-heteroreceptors differed from those at rabbit ₂-heteroreceptors, r = 0.64 (P > 0.05). Comparison with radioligand binding experiments from the literature indicated that, in the rat, both auto- and heteroreceptors conformed best to the _2D subtype (r 0.97, P < 0.01 for pK_d correlation with binding sites in rat submaxillary gland) whereas, in the rabbit, they conformed best to the _2A subtype (r 0.93, P < 0.01 for pK_d correlation with binding sites in HT29 cells).It is concluded that, in both the rat and the rabbit, the ₂-adrenoceptors modulating the release of serotonin are pharmacologically identical with the presynaptic ₂-autoreceptors. However, rat ₂-autoreceptors and -heteroreceptors differ pharmacologically from rabbit ₂-autoreceptors and -heteroreceptors. Presynaptic ₂-auto-as well as -heteroreceptors are _2D in the rat and _2A in the rabbit. Correspondence to: N. Limberger at the above address     

Electrophysiological actions of adenosine and aminophylline in spontaneously beating and voltage-clamped rabbit sino-atrial node preparations

Summary Effects of adenosine (30 to 200 mol/l) on the spontaneous action potentials and the membrane currents in rabbit sino-atrial node (SA) preparations were examined. Adenosine (30 mol/l) lengthened the action potential duration and the cycle length. At 100 mol/l, adenosine also hyperpolarized the maximum diastolic potential. However, the action potential amplitude and the maximum rate of depolarization _max) were unaffected. In the presence of adenosine (200 mol/l) addition of aminophylline (an antagonist) (23–46 mol/l) shortened the cycle length and depolarized the maximum diastolic potential to the contrary. Aminophylline did not antagonize the prolongation of the action potential. Aminophylline (46 mol/l) alone decreased the cycle length and the maximum diastolic potential, but did not affect the action potential amplitude, the action potential duration and the _max. In the presence of aminophylline (46 mol/l). addition of adenosine (200 mol/l) increased the cycle length and the action potential duration, and decreased _max. In voltage-clamp experiments, adenosine greatly shifted the background current in the outward direction. Holding potential was –40 mV. Adenosine reduced a slow inward and a time-dependent outward current, in a concentration-dependent manner. Adenosine did not affect the time constant of inactivation phase and the voltages of the half-maximum activation and inactivation for the slow inward current. The activation curve for the outward current was also unaffected. A hyperpolarization-activated inward current was decreased. In the presence of aminophylline (46 mol/l), adenosine (200 mol/l) decreased the slow inward current, the time-dependent outward current and the hyperpolarization-activated inward current. These results suggest that adenosine produces its actions on the heart by inhibition of ionic currents and activation of the outward background current.Correspondence to H. Satoh at the above address     

Opposite modulation of ouabain cardiotoxicity by hexamethyleneamiloride and phenylephrine

Summary To see whether the Na/H antiporter plays a role in digitalis cardiotoxicity, we investigated the influence of modulators of Na/H exchange on the toxic effects of ouabain in isolated, paced (0.4 Hz) rat left atria. Ouabain (1 mmol/l) caused a transient positive inotropic effect followed by toxic events, including a complete loss of developed force and a gradual increase in resting force. In the presence of hexamethyleneamiloride (3 and 10 mo1/l), an inhibitor of Na/H exchange, ouabain (1 mmol/l) caused a sustained positive inotropic effect without toxicity. By contrast, phenylephrine (100 mol/ 1) an -adrenoceptor agonist reported to stimulate the antiporter, hastened the development of ouabain's toxicity. Neither ouabain, at a subtoxic concentration (650 ol/l), nor phenylephrine (100 mol/l) affected diastolic force, but in their combined presence, a substantial contracture developed and twitch contractions disappeared. Phenylephrine (30 or 100 mol/l) or adrenaline (30 mol/l), in the presence of a -adrenoceptor antagonist, increased the intracellular pH by up to 0.15 pH unit, as measured using ion-selective microelectrodes in quiescent preparations. This effect on pH₁ was prevented by hexamethyleneamiloride (10 mol/l). Consistent with phenylephrine's ability to stimulate Na⁺ influx via the Na/H antiporter, phenylephrine (100 mol/l) increased intracellular Na⁺ activity by about 3 mmol/l in ouabain (650 mol/l)-treated atria. These findings indicate that modulators of Na/H exchange affect the cardiotoxicity of digitalis glycosides and imply that the stimulation of myocardial -adrenoceptors may aggravate digitalis toxicity.This work was conducted in part under the auspices of the Association for US/French Biomedical Cooperation Send offprint requests to S. M. Vogel at the above address     

The modulation of [3H]noradrenaline and [3H]serotonin release from rat brain synaptosomes is not mediated by the α2B-adrenoceptor subtype

Summary The present study aimed at relating the presynaptic ₂-adrenoceptors, known to modulate noradrenaline and serotonin release, with the recently described _2A- and _2B-adrenoceptor subtypes. The effects of the agonist oxymetazoline (selective for _2A subtype) and of three adrenoceptor antagonists (idazoxan, 1-(2-pyrimidinyl)piperazine (PmP) and prazosin, the last one known to be _2B selective) were evaluated on [³H]noradrenaline and [^H]serotonin release in superfused synaptosomes from rat brain cortex. These drugs were also tested in [³H]yohimbine binding to human platelet membranes (containing only _2A receptors) and to neonatal rat lung membranes (containing only _2B receptors).The affinity pattern of these compounds at _2A-adrenoceptors in binding studies was oxymetazoline > = idazoxan > PmP > prazosin; at _2B-adrenoceptors it was idazoxan > = prazosin > PmP = oxymetazoline. Oxymetazoline inhibited with high and similar potencies the K⁺-evoked [³H]noradrenaline and [³H]serotonin release, IC₅₀ 18 and 7 nM, respectively; in the same conditions, the IC₅₀ values of noradrenaline were 42 and 168 nM, respectively. The antagonist affinity pattern (antagonism against noradrenaline) was idazoxan > PmP > prazosin, either on [³H]serotonin release.These results indicate that presynaptic ₂ auto- or heteroreceptors do not belong to the _2B subtype and suggest that the modulation of noradrenaline and serotonin release may be mediated by the _2A-adrenoceptor subtype. Send offprint requests to M. Gobbi at the above address     

Pharmacokinetics,anticonvulsant efficacy,and adverse effects of trans-2-en-valproate after acute and chronic administration in amygdala-kindled rats

Summary Effects of adenosine and nucleotides on the release of previously stored [3H]-noradrenaline were studied in rabbit brain cortex slices. The slices were stimulated twice, in most experiments by 6 electrical field pulses delivered at 100 Hz.Adenosine and the nucleotides AMP, ADP, ATP, AMPS, ADPS, ATPyS, ,-imido-ATP and ,-methyl-ene-ATP all reduced the evoked overflow of tritiated compounds. For purines for which concentration-response curves were determined, the order of potency was adenosine > ATP ATPyS ,-imido-ATP ADP > ,-methylene-ATP. AMP 30 Etmol/l and AMPS 30 mol/l were approximately equieffective with 30 mol/l of adenosine and ATPS, and ADPS, 30 mol/l was approximately equieffective with 30 mol/l of ADP. ,-Methylene-ADP, 2-methylthio-ATP, UTP and GTPS did not change the evoked overflow of tritium. ,-Methylene-ATP caused an increase; however, the increase was small and became significant only after 59 min of exposure to ,-methylene-ATP or when the slices were stimulated by 30 pulses, 10 H₂. Neither adenosine deaminase (100 U/l) nor the blocker of 5-nucleotidase, ,-methylene-ADP (10 mol/l), attenuated the inhibition caused by ATP, ATPyS and ,-methylene-ATP, despite the fact that adenosine deaminase abolished the effect of adenosine. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX, 10 nmol/l) shifted the concentration-response curves of adenosine, ATPyS, ,-imido-ATP and ,-methylene-ATP to the right by very similar degrees. 8(p-Sulphophenyl)-theophylline (30 and 300 mol/l) also markedly antagonized the inhibition produced by ATPS. ,-Methylene-ATP (10 and 30 mol/l) and suramin (100 gmol/l) did not modify the effects of adenosine, ATPS and ,-methylene-ATP.It is concluded that nucleotides themselves can inhibit the release of noradrenaline in the rabbit brain cortex. The nucleotides and adenosine seem to act at the same site, i.e., the A₁ subtype of the P₁-purinoceptor. The results support the notion that metabolically stable, phosphate chain-modified nucleotides such as ATPS, ,-imido-ATP and ,-methylene-ATP can be potent P₁ agonists. No evidence was found for presynaptic P_2X-, P_2Y- or P₃-purinoceptors. Send offprint requests to I. von Kugelgen at the above address     

Electrophysiologic and inotropic effects of α-adrenoceptor stimulation in human isolated atrial heart muscle

Summary The effects of -adrenoceptor stimulation on force of contraction were investigated in human atrial heart muscle and compared with those of -adrenoceptor stimulation. The maximal positive inotropic effect produced by stimulation of -adrenoceptors with phenylephrine (in the presence of atenolol 10 mol/l) was significantly smaller than that seen in response to -adrenoceptor stimulation with isoprenaline. The maximal effect of phenylephrine (25% of the maximal effect of isoprenaline) required far higher concentrations (1 mmol/l) than isoprenaline (100 nmol/l); the EC₅₀ values amounted to 33.1 mol/l and 3.3 nmol/l, respectively. In the presence of the -adrenoceptor blocking agent phentolamine (1 mol/l), the concentration-response curve of phenylephrine was displaced to higher concentrations of the agonist; under these conditions, the EC₅₀ value amounted to 52.5 mol/l, The effects of the catecholamines noradrenaline and adrenaline on force of contraction remained unchanged in the presence of phentolamine (1 mol/l), or prazosin (1 mol/l), The positive inotropic effect of phenylephrine (1 mmol/l) was associated with a slight decrease in action potential duration; the effects on action potential were completely blocked in the presence of phentolamine (1 mol/l) These findings support the view that selective stimulation of -adrenoceptors may mediate a small but detectable positive inotropic effect in human atrial tissue under in vitro conditions. The requirement of high concentrations of -adrenoceptor agonists and the lack of effects of the endogenous catecholamines adrenaline and noradrenaline on -adrenoceptors (in concentrations which fully elicit the -adrenoceptors-mediated response) do not provide a basis for a functional role of -adrenoceptor-mediated effects under in vivo conditions. It is more likely that adrenaline- or noradrenaline-mediated changes in the force of contraction in the human atrium are virtually exclusively due to the stimulation of -adrenoceptors. Send offprint requests to H. Nawrath at the above address     

Quantitative Structure–Activity Relationship Analysis of Combretastatins: A Class of Novel Antimitotic Agents

Combretastatins and their synthetic analogues, having structural features resembling that of colchicine, also have similar modes of action. In this report we have correlated the cytotoxicity of combretastatins against the murine leukemic cell line L1210 with physicochemical parameters such as the summation of the Hansch-Fujita constant, which was used as an index of lipophilicity of the substituent groups on ring A (_a) and ring B (_b), the vector summation of the group dipole moments of ring A (µ_a) and ring B (µ_b), the nature of the linker chain between ring A and ring B (B_t-L), indicator parameters (NOH)_a and (NOH)_b, which represent the number of hydroxyl groups on ring A and ring B, respectively, and the summation of values of the substituents on the linker (_L). Cytotoxicity correlated well with (_b), (NOH)_a, (B_t-L), and (µ_b), and the dependency on (_b) was found to be parabolic.     

Influence of acetylator phenotype on the pharmacokinetics of a new vasodilator antihypertensive,endralazine

Summary Five and 10 mg single oral doses of a new vasodilator antihypertensive, endralazine (E) were given on separate occasions to 17 normal male volunteers (8 slow, 7 heterozygous fast and 2 homozygous fast acetylators). The homozygous fast acetylators were excluded from statistical comparisons. Only small differences were observed in the pharmacokinetics of E between the phenotypes and there was no evidence of non-linearity at the 2 dose levels studied. Terminal half-lives ranged from 2.59 to 7.14 h with a mean of 4.30±1.08 h for the 5 mg dose and 4.25±1.09 h for the 10 mg dose. There was no significant difference in half-lives between slow and heterozygous fast acetylators. The mean area under the plasma level-time curve (AUC ₀ ) was 18.2% lower (p<0.05) in the heterozygous fast acetylators than in the slow acetylators following the 5 mg dose and 11.0% lower (p>0.05) following the 10 mg dose. Extremely rapid absorption of the drug precluded accurate estimation of absorption rates. The AUC ₀ of the acetylation metabolite (methyltriazoloendralazine) was small compared to that of E although higher in the heterozygous fast acetylators than in the slow acetylators (p<0.01).     

Activation of β2-adrenoceptors by isoprenaline and adrenaline enhances noradrenaline release in cortical kidney slices of young spontaneously hypertensive rats

Summary The aim of the present study was to investigate -adrenoceptor modulation of noradrenaline release from sympathetic nerves in superfused cortical kidney slices of 4-week-old spontaneously hypertensive rats (SHR) and age-matched controls (WKY). After preincubation with ³H-noradrenaline the kidney slices were electrically stimulated in superfusion chambers. The stimulation induced (S-I) outflow of radioactivity was mainly composed of unmetabolized 3H-noradrenaline in both strains and thus taken as an index of noradrenaline release. There was a frequency-dependent (1.25–20 Hz) increase in the S-1 outflow of radioactivity. At all stimulation frequencies tested S-I outflow of radioactivity was similar or even slightly lower in SHR than in WKY kidney slices in either the absence or presence of cocaine (10 mol/l). The non-selective -adrenoceptor agonists isoprenaline (0.l gmol/1) and adrenaline (0.01 and 0.1 mol/l) enhanced S-I outflow of radioactivity. The facilitatory effects of isoprenaline (0.1 mol/l) and adrenaline (0.1 mol/l) were blocked by the selective ₂-adrenoceptor antagonist ICI 118551 (0.1 mol/l) but not by the selective ₁-adrenoceptor antagonist atenolol (0.3 mol/l). The cell-permeable CAMP analogue 8-bromo-cAMP (300 mol/l) enhanced S-1 outflow of radioactivity to a similar extent in both SHR and WKY kidney slices. A combination of 8-bromo-cAMP (300 mol/l) and adrenaline (0.1 mol/l) did not enhance S-1 outflow of radioactivity to a greater extent than 8-bromo cAMP (300 mol/l) alone in both strains. However, the facilitatory effects of isoprenaline (0.1 mol/l) and adrenaline (0.1 mol/l) but not that of adrenaline (0.01 mol/l) were significantly greater in SHR than in WKY. The results suggest that stimulation of prejunctional ₂-adrenoceptors by adrenaline even in the absence of a-adrenoceptor blockade enhances noradrenaline release in kidney cortex of young SHR and WKY. This ₂-adrenoceptor mediated effect may possibly be dependent on cAMP formation. The greater facilitatory effects of isoprenaline (0.1 mol/l) and adrenaline (0.1 mol/l) in SHR as compared to WKY are in accord with receptor binding studies which show a higher density of ₂-adrenoceptors in SHR than in WKY kidney cortex.Abbreviations SHR Spontaneously hypertensive rats - WKY WistarKyoto rats - cAMP 3-5-cyclic adenosine monophosphate - S-I stimulation induced Send offprint requests to: L. C. Rump