Determination of extraction constant,true partition coefficient and formation constant of ion-pair complexes of quaternary ammonium salts,tetrabutylammonium bromide and isopropamide iodide.with some organic anions by a solvent extraction technique

A new method of determining the extraction constant (K_e, the true partition coefficient (TPC) and the formation constant (K_f) of ion-pairs, was developed by the solvent extraction technique. K_e and TPC were estimated from the reciprocals of the intercept and the slope of the regression line obtained by plotting

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{vs}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}$

in the following equation.

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{=}\text{1}\text{K}{}_{\mathrm{e}}\text{+}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{x}\text{1}\text{TPC}$

where [A^T_W] and [B^T_W] are the total concentrations of the cationic compound A and that of the anionic compound B in the aqueous phase respectively, APC is the apparent partition coefficient of A, dA is the partition coefficient of cation A⁺. K_f, which is expressed by K_e/TPC, was then calculated. These constants were determined for the ion-pair extraction of tetrabutylammonium bromide and isopropamide iodide with 4 organic anions, i.e. benzoic acid, p-toluenesulfonic acid, salicylic acid and taurodeoxycholic acid. This new method might be applicable to other ion-pairs without further assumptions except that the molar ratio of the ion-pair formation be 1 : 1.     

The effects of cadmium, manganese and aluminium on sodium-potassium-activated and magnesium-activated adenosine triphosphatase activity and choline uptake in rat brain synaptosomes

The effects of Cd²⁺, Mn²⁺ and Al³⁺ on rat brain synaptosomal sodium-potassium-activated and magnesium-activated adenosine triphosphatase (Na-K-ATPase and Mg-ATPase) activity and choline uptake were studied. All three types of metal ions inhibited Na-K-ATPase activity more markedly than Mg-ATPase activity. The rank order of inhibition of Na-K-ATPase was: $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.4 μ}\text{M}\text{) >}\text{Mn}{}_{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 955 μ}\text{m}\text{) >}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 8.3}\text{mM}$). The rank order of inhibition of Mg- was:$\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 316 μ}\text{M}\text{>}\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.5}\text{mM}\text{>}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 21.9}\text{mM}\text{).}\text{Al}{}^{\mathrm{3+}}$ was most potent in inhibiting synaptosomal choline uptake ($\text{ic}{}_{50}\text{= 24μ}\text{M}$ in the absence of Ca²⁺ and 123 μ.M in the presence of 1 mM Ca²⁺). $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 363 μ}\text{M}\text{)}$ was a more effective inhibitor of choline uptake than $\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 1.2?1.5}\text{mM}\text{)}$ . The presence of 1 mM Ca²⁺ did not alter choline uptake, nor did it antagonize the inhibitory actions of the three metals. Our observations that Cd²⁺ and Al³⁺ inhibited synaptosomal choline uptake, but did not show parallel inhibitory effects on Na-K-ATPase activity directly contradicts the ionic gradient hypothesis. These results are also discussed in relation to the in vivo neurotoxicity of cadmium, manganese and aluminium.     

Kinetic studies on the deethylation of ethoxybenzamide: A comparative study with isolated hepatocytes and liver microsomes of rat

Kinetic parameters (K_m and V_max) of ethoxybenzamide deethylation in isolated rat hepatocytes and liver microsomes were compared. Adjustment of cofactors in microsomal deethylation, such as NADPH and Mg²⁺, to give optimum conditions, and appropriate correction of the apparent kinetic parameters for nonspecific binding and microsomal yield resulted in good agreement among the kinetic parameters of isolated hepatocytes [$\text{V}{}_{\mathrm{<mtext>max</mtext>}}\text{= 0.0863 μmole · min}{}^{\mathrm{?1}}\text{· (g liver)}{}^{\mathrm{?1}}$ and K_m = 0.459 mM] and microsomes [V_max = 0.124 μmoles · min^?1 · (gliver)^?1 and K_m = 0.378 mM].     

Toxic response as a quantitative function of body size.

Lethal response (96-hr) studies were conducted exposing mature male guppies (Poecilia reticulata) in lots representing different weight classes to ambient concentrations of six discrete toxicants: dieldrin, potassium pentachlorophenate, potassium cyanide, and copper, zinc, and nickel chlorides. Linear regressions with high correlation coefficients were defined for each toxicant by the equation, $\text{Y = a ? b}\text{log}\text{(}\text{M}\text{W}{}^{\mathrm{h}}\text{)}$, where Y = % mortality as probits, M = mean toxicant concentration, W = weight of each lot, and h = an exponent of weight. The computed value of h was 0.81 for dieldrin, 0.72 for pentachlorophenate, cyanide, and copper, 0.67 for nickel, and 0.30 for zinc. Additional lethal response studies were conducted exposing mature females of different size, juveniles of different size, and newborn guppies of similar size to dieldrin. The dose-response functions of each age group were found to incorporate the weight factor previously computed for adult males, i.e., W^0.81. Discrete, parallel regressions represented each life stage and sex. When compared on a weight factor basis, guppies became progressively more susceptible to dieldrin with each successive age class. Comparing adults only, males were more resistant than females. Evidence was gathered from the literature to show that the above equation applies furthermore to dose-response studies in which animals of varying size are given known amounts of toxicant, toxin, or drug. Consequently, the above equation may be generally employed to empirically establish the character of the relationship between dose and response when the size of the animals differ. Relative measures of toxic potency, e.g., LD50 and LC50, representing different sizes of an animal may be derived from the above equation and expressed in the useful form, LD50 = XW^h, where X is the antilog of the abscissal value of $\text{log}\text{(}\text{M}\text{W}{}^{\mathrm{h}}\text{)}$ corresponding to the 50% response level. This latter equation may also be derived from the commonly used function log LD50 = log a + b log W.     

Inhibition of hepatic microsomal lipid peroxidation by drug substrates without drug metabolism

Experiments were performed to study the mechanism of action of drug substrates on lipid peroxidation in rat hepatic microsomes. Addition of the drug substrates, aniline, β-diethylaminoethyl diphenylpropylacetate (SKF-525A), aminopyrine, benzo[a]pyrene or ethylmorphine, to hepatic microsomes causes almost complete inhibition of NADPH-induced (enzymatic) lipid peroxidation. These substrates also produce similar inhibition of ascorbate-induced (non-enzymatic) lipid peroxidation in microsomes in which drug-metabolizing enzymes were inactivated by heat treatment. The substrate concentrations producing half-maximal inhibition ($\text{K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ are also similar for NADPH- and ascorbate-induced lipid peroxidation. Addition of metyrapone, an inhibitor of drug metabolism, has no effect on either the $\text{K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ values or on the maximal substrate inhibition of NADPH-induced lipid peroxidation. All five drug substrates also inhibit Fe²⁺-stimulated oxidation of linoleic acid. These results demonstrate that inhibition of lipid peroxidation in hepatic microsomes by drug substrates is independent of drug metabolism and is probably due to the antioxidant properties of the substrates.     

Dansylarginine N-(3-ethyl-1,5-pentanediyl)amide: A potent and selective fluorescent inhibitor of butyrylcholinesterase

Interactions between dansylarginine N-(3-ethyl-1,5-pentanediyl)amide (DAPA) and the cholinesterases were examined by the techniques of enzyme kinetics and fluorescence spectroscopy. When tested with partially purified enzyme preparations, DAPA was a potent inhibitor of butyrylcholinesterase $\text{(}\text{IC}{}_{50}\text{= 2 × 10}{}^{\mathrm{?7}}\text{M}\text{)}$ but not of acetylcholinesterase $\text{(}\text{IC}{}_{50}\text{= 4 × 10}{}^{\mathrm{?4}}\text{M}\text{)}$. For a detailed study of the effects of DAPA on butyrylcholinesterase (BuChE), the enzyme was purified to homogeneity from horse serum, with the aid of affinity chromatography on N-methyl acridinium. The kinetics of the inhibition of purified BuChE by DAPA were complex, having both competitive and non-competitive features, and it was not possible to estimate K_i unambiguously. Spectroscopic measurements showed that the fluorescence of the dansyl moiety was strongly affected by the binding to BuChE. With excitation at 330 nm, total fluorescence emission from bound DAPA (at 450 nm and above) was 21-fold greater than from free DAPA. In a titration experiment, this enhancement of fluorescence intensity was used to calculate that each monomer of BuChE has two apparently independent DAPA-binding sites with a K_d of 4.5 × 10^?7 M. Further measurements showed that the fluorescence emission of bound DAPA was markedly blue-shifted (to 502 nm from 570 nm in free solution) and that the fluorescence lifetime of this form was greatly prolonged (to 24 nsec from 2.7 nsec). These observations indicate that the high affinity binding sites on BuChE lock DAPA in a highly non-polar environment.     

Similar activities of nerve growth factor and its homologue proinsulin in intracellular hydrogen peroxide production and metabolism in adipocytes: Transmembrane signalling relative to insulin-mimicking cellular effects

Generation of hydrogen peroxide in adipocyte plasma membrane and its intracellular metabolism and regulatory role have been shown by Mukherjee and co-workers to be a major effector system for insulin [Fedn Proc.35, 1694 (1976); Archs Biochem. Biophys.184, 69 (1977); Biochem. Pharmac.27, 2589 (1978); Fedn Proc.37, 1689 (1978); and Biochem. Pharmac.29, 1239 (1980)]. The possible involvement of this mechanism in the action of structurally similar polypeptides having some insulin-like metabolic effects was investigated. The β-subunit of nerve growth factor (2.5 S NGF, mol. wt 13,500) which has a striking structural homology with proinsulin and has been reported to exert certain insulin-like metabolic effects in its own target tissues (e.g. growing neurites and sympathetic ganglia), and the insulin-derived polypeptides, desalanine-insulin and desoctapeptide-insulin, as well as proinsulin, were examined for their effects on rat adipocytes, employing the technique of formate oxidation. Both NGF and proinsulin caused increased [¹⁴C]formate oxidation, showing similar intrinsic activities, up to a maximum of 140–160% of the basal rate; insulin increased the rate to 190–210% of the basal rate. The relative potencies of the hormones toward H₂O₂ formation and stimulation of the pentose phosphate pathway activity were: insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?11}}\text{M}\text{)}$, desalanine-insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?10}}\text{M}\text{)}$ , proinsulin $\text{(}\text{EC}{}_{50}\text{: 8 × 10}{}^{\mathrm{?9}}\text{M}\text{)}$, and NGF $\text{(}\text{EC}{}_{50}\text{: 10}{}^{\mathrm{?9}}\text{M}\text{)}$. The biologically inactive derivative, desoctapeptide-insulin, did not stimulate glucose oxidation, although it caused a small increase in formate oxidation, with an $\text{EC}{}_{50}\text{of}\text{5 × 10}{}^{\mathrm{?7}}\text{M}$, indicating a suboptimal level of H₂O₂ formation in the elevation of the hexose monophosphate shunt activity. 3-Amino-1,2,4,-triazole (50 mM), which irreversibly decomposes the peroxidatic compound II of the catalase: H₂O₂ complex, inhibited formate oxidation to a greater extent in the hormone-treated cells than in the control cells, whereas sodium azide, an inhibitor of the hemoprotein, catalase, completely inhibited it. The abilities of the polypeptides to stimulate H₂O₂ formation correlated with their abilities to promote lipogenesis from [U-¹⁴C]-D-glucose, as expected of insulin. The cellular GSH/GSSG ratio increased concomitantly with the stimulation of glucose oxidation via the shunt, indicating a tight coupling between these processes. The results confirm that the hydrogen peroxide production is a common basis of the metabolic actions of growth-promoting polypeptide hormones or mitogens beyond their respective receptors.     

Kinetic studies on the metabolism of ethylmorphine by isolated hepatocytes from adult rats

Hepatocytes of adult rats were isolated by infusion of a hyaluronidase collagenase mixture. High yields of cells excluding trypan blue were obtained. These cells, in Hank's buffer containing rat serum and 0.1% glucose, $\text{N-}\text{demethylate}\text{[}{}^3\text{H-CH}{}_3\text{-N]}$ethylmorphine. The formaldehyde initially formed is further metabolized to tritiated water. Fifteen per cent of the original metabolic activity was observed after 21 hr at 37° in 5% CO₂-air, and cumulative metabolism is linear for up to 90 min under these conditions. The K_m for the N-demethylation of [³H-CH₃-N]ethylmorphine is 50 μM, 20 per cent of the value observed for this reaction by musomal preparations. An active transport of the substrate into the cell is postulated to account for this difference.     

Effect of polychlorinated biphenyls on the immune responses of rhesus monkeys and mice.

The relationship between lipid peroxidation, glutathione (GSH) content, and CCl₄-induced toxicity was investigated in rat hepatocytes isolated by a collagenase-perfusion technique. Two chemical initiators of lipid peroxidation, ferric ions complexed with adenosine diphosphate ($\text{ADP}\text{Fe}{}^{\mathrm{3+}}$) and diethyl maleate, were studied for comparison. CCl₄ caused a reduction of intracellular K⁺ and release of alanine aminotransferase (ALT) into the medium, but no evidence of lipid peroxidation, as measured by the absorbance of thiobarbituric acid (TBA)-reacting materials and lipid-extract diene conjugation. $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$ caused lipid peroxidation, but only a small loss of K⁺. Diethyl maleate caused a greater amount of lipid peroxidation and cell damage than did $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$. Neither response appeared to be related to the GSH content, which was reduced by diethyl maleate, but not by $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$, and by CCl₄ only at the highest dose. The results suggest that lipid peroxidation is not a requisite step in CCl₄-induced toxicity in isolated hepatocytes.     

Quantitative mechanistic studies in simultaneous fluid flow and intestinal absorption using steroids as model solutes

The interplay of flow-rate, aqueous boundary layer and membrane permeability coefficients, solute lipophilicity and intestinal length has been quantitatively determined for the in situ situation of bulk fluid flow and concurrent steady-state absorption of steroids in the small intestines of the rat. Seven steroids ranging in 3 orders of magnitude in n-octanol/water partition coefficients were used.The results followed the physical model predictions described by:

$\text{C(?)}\text{C(0)}\text{=exp}\text{?}\text{2πγ?}\text{Q}\text{·}\text{P}{}_{\mathrm{aq}}\text{1+P}{}_{\mathrm{aq}}\text{P}{}_{\mathrm{m}}$

where $\text{C}\text{?}\text{C}\text{(0)}$ is the fraction of steroid remaining in the intestinal lumen of length ?, r is the effective lumenal radius, Q is the flow-rate, P_aq and P_m are the respective aqueous boundary layer and membrane permeability coefficients. The log fraction of steroids remaining in the lumen was linear with intestinal length at various flow rates. The fraction absorbed increased with slower flow-rates at any given length due to the longer residence time. The fraction of steroid absorbed vs log partition coefficient profiles as a function of flow-rate were significantly sigmoidal. The absorption rates of progesterone were aqueous boundary layer-controlled and the less lipophilic hydrocortisone were membrane-controlled. It is significant that the permeability of the aqueous boundary layer is proportional to Q^0.44.     

A quantitative structure-activity relationship between partition coefficients and the acute toxicity of naphthalene derivatives in Artemia salina nauplii

The 1-octanol/water partition coefficient has been used frequently as a rapid predictor of organic pollutant bioconcentration potential in aquatic life. Harmful effects of aromatic compounds have been related to partition coefficients in a meaningful way. Acute toxicity tests were conducted by exposing 30-h posthatch Artemia salina larvae cultured at 19°C in artificial sea water to naphthalene, naphthalene derivatives, and other nonrelated chemicals for 24 h to determine immobilization concentrations (IC₅₀). The IC₅₀ value for each chemical was used to derive a quantitative structure-activity relationship (QSAR) which included the partition coefficient as the only parameter of molecular structure. A linear correlation resulted for all chemicals tested using Artemia:

$\text{log}\text{1}\text{IC}{}_{50}\text{=1.57(plusm 0.60)+0.88(plusm 0.12)×}\text{log}\text{P}$

where n = 11, r² = 0.968, and s = 0.226. The hydrophobic nature of the chemicals appeared to be the most important factor producing larval immobilization because the naphthalene congener set was not collinear with electronic and steric physicochemical properties. The IC₅₀ values were also correlated with the molecular weight and boiling point of each chemical, but a significant increase in the regression variance occurred in comparison to log P. The naphthalene QSAR was a good predictor of acute toxicity in Artemia nauplii.     

Mechanisms by which quipazine,a putative serotonin receptor agonist,alters brain 5-hydroxyindole metabolism

Quipazine (2-[1-piperazinyl] quinoline maleate) was shown to increase serotonin and decrease 5-hydroxyindoleacetic acid concentrations in whole brain, several brain regions, and the spinal cord of rats 1 hr after its administration (10 mg/kg, i.p.). In animals with transected spinal cords, quipazine induced stronger activation of extensor reflexes than 5-hydroxytryptophan, chlorimipramine, or Lilly 110140. This response could be blocked by methiothepin. In slices of rat cerebral cortex, quipazine inhibited the uptakes of [³H]-serotonin (EC₅₀ = 10^?6 M) and [³H]-norepinephrine ($\text{EC}{}_{50}\text{= 2 × 10}{}^{\mathrm{?6}}\text{m}$); it was equipotent with Lilly 110140 in inhibiting serotonin uptake, but less potent than chlorimipramine ($\text{EC}{}_{50}\text{= 10}{}^{\mathrm{?7}}\text{m}$). Quipazine administration to rats did not inhibit monoamine oxidase activity, and actually elevated brain tryptophan levels. These observations suggest that the effects of quipazine on brain serotonin and 5-hydroxyindoleacetic acid concentrations could have been caused by direct activation of central serotonin receptors (which would secondarily decrease impulse flow along serotonergic neurones), or by the inhibition of serotonin reuptake, or by both mechanisms.     

The effect of halothane on the stability of Ca2+ transport activity of isolated fragmented sarcoplasmic reticulum

The effects of the inhalation anaesthetic agent, halothane (CF₃CHBrCl), on the stability of the calcium transport system of isolated rabbit white skeletal muscle sarcoplasmic reticulum have been studied. Calcium transport activity was unaffected when suspensions of sarcoplasmic reticulum vesicles were preincubated at 37° and pH 6.8 at concentrations of halothane below 5 mM, but was progressively inactivated at higher concentrations. (Ca²⁺,Mg²⁺)-ATPase activity was enhanced during inactivation of calcium transport. At pH 6.3 and 5.8, halothane increased the first order rate constants of inactivation and effects were noted in the anaesthetic range of concentration (1–2 mM). The inulin inaccessible space of membrane vesicles did not change appreciably during the period of treatment with halothane, excluding increased permeability as an explanation of the inhibition of calcium accumulation. Inactivation was irreversible and highly temperature dependent, with an activation energy of 52.7 kcal/mol. Calcium ions had a protective effect against inactivation (K_{0.5 (Ca2+) = 1.5 × 10^?6M}), as did ATP ($\text{K}{}_{\mathrm{<mtext>0.5\; (</mtext><mtext>Atp</mtext><mtext>)</mtext>}}\text{? 10}{}^{\mathrm{?6}}\text{M}$). It is concluded that mild acid conditions and halothane act synergistically during inactivation of the calcium transport system of sarcoplasmic reticulum membranes. These studies suggest that halothane interacts with the (Ca²⁺, Mg²⁺)-ATPase protein at the ATP-specific binding site or that it disrupts protein-lipid associations in the membrane. In either case the destabilizing effect of halothane may be modified by the conformational state of the protein.     

The role of hydrophobic and electron donor properties in acetylcholinesterase inhibition by carbamates

The abilities of seven m-substituted phenyl methylcarbamates to inhibit acetylcholinesterases from honey bee and cotton leafworm (Spodoptera littoralis, Boisd.) were explored. The extra inhibition bestowed by m-substituted phenyl methylcarbamate as compared with the unsubstituted (Δ log k_i = log$\text{k}{}_{\mathrm{i}}\text{(X)}\text{k}{}_{\mathrm{i}}\text{H))}$ was well correlated with the calculated contribution of each substituent through its hydrophobic and electron donating properties (0.69 π – 0.95 σ + 1.19). The correlation coefficient r = 0.95 for cotton leafworm acetylcholinesterase and 0.92 for that of honey bee. Analysis of these data, in addition to those of the housefly from the literature, resulted in a direct linear relationship in spite of enzyme source, with r = 0.91. It was therefore postulated that hydrophobic interaction and electron donating properties of the substituent were involved in inhibition through complex formation with the enzyme acetylcholinesterase prior to the carbamylation step.     

Participation of superoxide free radical and Mn2+ in sulfite oxidation.

Sulfurous acid gas is a well-known air pollutant. The participation of superoxide ($\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$), a species of activated oxygen, in sulfite oxidation was investigated in relationship to this health hazard. The reduction of nitroblue tetrazolium (NBT) was markedly accelerated in the presence of the xanthine-xanthine oxidase system (X-XO), Mn²⁺ and SO₃^2?, but not by X-XO and Mn²⁺ or X-XO and SO₃^2? alone. This accelerated NBT reduction was partially suppressed by superoxide dismutase and was completely suppressed by allopurinol. Oxygen consumption was also markedly accelerated under to condition which caused the increase in NBT reduction. Lipid peroxidation of rat liver homogenate increased in the presence of X-XO, SO₃^2?, or both. This increased lipid peroxidation was definitely suppressed by Mn²⁺. From these observations, it is suggested that chain reactions involving sulfite oxidation are initiated by O₂^? generated from X-XO, and Mn²⁺ acts as a catalyst in the process.     

Interaction of [3H]flunitrazepam with the benzodiazepine receptor: Evidence for a ligand-induced conformation change

The interaction of [³H]flunitrazepam with benzodiazepine receptors in rat brain homogenates was studied in the presence of 2 μM endogenous GABA at 0° at pH 7.2. Equilibrium binding experiments showed a dominant component of high affinity with an equilibrium dissociation constant K = 0.86 ± 0.07 nM which accounted for 75% of total binding and another component of lower affinity (K ? 30 nM). The dissociation kinetics of the [³H]flunitrazepam complex at the high affinity site were strictly monophasic with a rate constant k_off = (7.7 ± 0.3) × 10^?4/sec. The association kinetics with the high affinity sites were studied with ligand concentrations [L]₀ in large excess over binding sites. The kinetics were in accordance with a single exponential with a reaction rate τ^?1. In the higher concentration range [L]₀ ? 10 nM, τ^?1 as a function of [L]₀ deviated from linearity and started to level off. The data are compatible with a two-step mechanism where R and L rapidly combine to form a pre-complex RL which then slowly isomerizes to the final complex C:

where $\text{K}{}_1\text{= (}\text{[}\text{R}\text{][}\text{L}\text{]}\text{([}\text{RL}\text{]}\text{)}$ and $\text{[}\text{RL}\text{]}\text{[}\text{C}\text{]}\text{=}\text{k}{}_{\mathrm{?2}}\text{k}{}_2\text{= k}{}_2$. Nonlinear parameter estimation yielded K₁24.2 ± 7.1 nM, k₂ = (2.8 ± 0.5) × 10^?2/sec and k_?2 = (9 ± 2) × 10^?4/sec. The isomerization step might reflect a ligand-induced conformation change of the high affinity site which is involved in the potentiation of GABA-ergic transmission produced by the benzodiazepines.     

Effect of diphenylhydantoin on the uptake and catabolism of l-[3H]norepinephrine in vitro in rat cerebral cortex tissue

The effect of diphenylhydantoin on the accumulation of [³H]norepinephrine in vitro was examined in brain slices prepared from rat cerebral cortex. High concentrations of diphenylhydantoin (10^?3 M) caused a significant reduction in the 5-min accumulation of [³H]norepinephrine. On the other hand, 10^?5–10^?4 M diphenylhydantoin facilitated the 20-min accumulation of [³H]norepinephrine. This facilitative action of diphenylhydantoin was (1) associated with a reduction in oxidative catabolism of [³H]norepinephrine and (2) abolished by the 2-hr pretreatment of rats with 100 mg/kg of nialamide (i.p.). The inhibitory action of diphenylhydantoin on the oxidative catabolism of [³H]norepinephrine was observed in both whole and lyzed crude synaptosomal preparations. When diphenylhydantoin and pargyline were compared, it was found that pargyline $\text{(}\text{id}{}_{50}\text{= 1.5 × 10}{}^{\mathrm{?6}}\text{M}\text{)}$ was 37 times more effective than diphenylhydantoin $\text{(}\text{id}{}_{50}\text{= 5.5 × 10}{}^{\mathrm{?5}}\text{M}\text{)}$ in inhibiting the oxidative deamination of [³H]norepinephrine. These results suggest that diphenylhydantoin alters norepinephrine metabolism in cerebral cortex slices by an inhibitory action on (1) monoamine oxidase activity and (2) the neuronal uptake system.     

The compressibility and compactibility of powder systems

This paper investigates the problem of compressibility and compactibility of powder systems. The term ‘compressibility’ is defined as the ability of a powder to decrease in volume under pressure, and the term ‘compactibility’ is defined as the ability of the powdered material to be compressed into a tablet of specified strength (i.e. radial tensile strength or deformation hardness). A novel approach leads to the following equation, which describes the deformation hardness P of the compact as a function of the applied pressure σ_c and the relative density ρ_r:

$\text{P = P}{}_{\max }\text{(1 ?}\text{exp}\text{( ? γσ}{}_{\mathrm{<mtext>c</mtext>}}\text{ρ}{}_{\mathrm{<mtext>r</mtext>}}\text{))}$

The parameter P_max is equal to the theoretically maximal possible deformation hardness at σ_cρ_r → ∞.P_max describes the compactibility and the parameter γ, termed the compression susceptibility, describes indirectly the compressibility. The equation is valid for pure substances as well as for binary mixtures An attempt is made to develop ‘additivity rules’ for the parameters P_max and γ in case of binary mixtures. For the general case it is necessary to introduce an interaction term, which can be explained qualitatively.