Amitraz-induced glucose intolerance in rats: antagonism by yohimbine but not by prazosin

Amitraz (N-[2,4-dimethylphenyl]-N-[(2,4-dimethylphenyl)imino]-N-methylmethanimidamide) is a formamidine insecticide/acaricide that increases plasma glucose and decreases plasma insulin concentrations in dogs when applied topically. Because amitraz activates ₂-adrenoceptors in numerous tissues, in this study we used rats as a model to determine whether these effects of amitraz are mediated by ₂-adrenoceptors. The i. v. injection of amitraz (0.1, 0.3, and 1 mg/kg) followed by i.v. glucose injection (1 g/kg) induced a dose-dependent glucose intolerance characterized by hypoinsulinemia. At 1 mg/kg, amitraz completely blocked the insulin release induced by i. v. glucose administration. The ₂-adrenoceptor antagonist yohimbine (1 mg/kg, i.v.) prevented the effects of amitraz, but the ₁-adrenoceptor antagonist prazosin (0.3 mg/kg, i.v.) did not. The results suggested that one mechanism by which amitraz prolongs glucose-induced hyperglycemia is via inhibition of insulin release and this effect is mediated by ₂-adrenoceptors.     

Plasma concentration of α-methyldopa and sulphate conjugate after oral administration of methyldopa and intravenous administration of methyldopa and methyldopa hydrochloride ethyl ester

Summary The plasma concentrations of free -methyldopa and methyldopa sulphate conjugate were measured in 7 hypertensive patients with normal renal function following -methyldopa (1 g) orally. Five of these patients subsequently received -methyldopa ethyl ester (250 mg) (methyldopate) intravenously and two further patients received 250 mg of -methyldopa intravenously. After oral administration a large amount of total plasma -methyldopa was present as sulphate conjugate. There were wide interindividual differences in the ratio of free: conjugated -methyldopa in plasma (ratio at 4 hours ranged from 3.73 – 0.83) suggesting that individual differences in the extent of sulphate conjugation may occur. There was no close correlation between the degree of conjugation and the fall in arterial pressure. At all time intervals examined, plasma concentrations were higher following intravenous -methyldopa than -methyldopate. The plasma concentration of -methyldopa (free and esterified) 60 minutes after i.v. -methyldopate was 1.7±0.3 µg/ml wile at the same time after the same dose of methyldopa by the same route the mean concentration was 5.9 µg/ml. Although small amounts of sulphate conjugate were detected after i.v. -methyldopate, insignificant quantities of conjugate were found after i.v. -methyldopa. The average fall in mean arterial pressure was 27 mm Hg following i.v. -methyldopa but only 2.7 mm Hg following -methyldopate. These results suggest that sulphate conjugation of -methyldopa occurs in the gastrointestinal tract during absorption. Hydrolysis of -methyldopa ethyl ester does not appear to be instantaneous and pharmacokinetic differences between the ester and free -methyldopa have been demonstrated.     

Vasoconstriction mediated by postsynaptic α2-adrenoceptor stimulation

Summary The postsynaptic -adrenoceptors involved in vasoconstriction brought about by B-HT 933 (2-amino-6-ethyl-4,5,7,8-tetrahydro-6H-oxazolo-[5,4-d]-azepin) administered i.v. to pithed, normotensive rats were characterized. The rate of onset of the hypertensive response to i.v. B-HT 933 is slower than that induced by (–)-phenylephrine, an agonist of ₁-adrenoceptor. The antagonism of the -adrenoceptor blocking drugs rauwolscine, yohimbine and corynanthine was quantified towards B-HT 933-induced increases in diastolic pressure. Rauwolscine (pA₂=7.06) and yohimbine (pA₂=6.83) were effective antagonists, whereas corynanthine proved much less potent (pA₂=5.03). On the basis of the reported selectivity of yohimbine and its two diastereoisomers rauwolscine and corynanthine for ₁- and ₂-adrenoceptor, it is concluded that the postsynaptic -adrenoceptors triggered by B-HT 933 are of the ₂-type. B-HT 933 identifies a subclass of postsynaptic ₂-adrenoceptor in vascular smooth muscle distinct from postsynaptic ₁-adrenoceptor. Both types of -adrenoceptors are likely to be involved in the mediation of vasoconstriction.Preliminary data were presented at the 21th Spring Meeting of the German Pharmacological Soceity, Mainz, March 18–21, 1980 (Timmermans, 1980)     

Protein Aggregates Seem to Play a Key Role Among the Parameters Influencing the Antigenicity of Interferon Alpha (IFN-α) in Normal and Transgenic Mice

Purpose. During long-term treatment of various malignant or viral diseases with IFN- up to 20% of patients develop anti-IFN- antibodies for as yet unknown reasons. Methods. To address this issue, a mouse model using Balb/C mice was established and the relevance of several potentially anti-IFN- antibodies inducing factors was studied. Results. The model revealed that both a higher frequency of injections and a higher dosage of IFN- were more immunogenic and that the route of administration affected the antibody response to IFN-. The intrinsic immunostimulatory activity of IFN- itself also enhanced the immune response. IFN- protein aggregates (IFN--IFN- and human serum albumin (HSA)-IFN- aggregates), which were recently identified in all marketed IFN- products, were significantly more immunogenic than IFN- monomers. These aggregates broke the tolerance against human IFN- monomers in human IFN- transgenic mice. Conclusions. Based on these animal studies it is proposed that the immune response to IFN- in humans is most probably elicited by a combination of several factors among which IFN- protein aggregates seem to play a key role.     

Naloxone protein binding in adult and foetal plasma

Summary Binding of naloxone hydrochloride was determined at 37°C, by equilibrium dialysis against 0.067 M phosphate buffer, pH 7.4, in plasma obtained from 18 healthy adults, and 18 samples of umbilical cord venous (foetal) plasma. The percentage free fraction (% free) in plasma was independent of naloxone concentration (9 ng/ml to 2.5 µg/ml). Percent free naloxone in adult (x=54.0) was lower (p<0.01) than in foetal (x=61.5) plasma. In buffered solutions of purified HSA, %free naloxone (x=68.7) was independent of HSA concentration over the range 3.0 g/dl to 5.5 g/dl. Adult plasma concentrations of ₁-acid glycoprotein (₁-AGP) and -lipoprotein were higher (p<0.01) than foetal concentrations. Furthermore %free naloxone in foetal plasma decreased with the in-vitro addition of purified ₁-AGP. It is suggested that qualitative differences in adult and foetal albumin and quantitative differences in plasma levels of ₁-AGP and perhaps -lipoprotein are responsible for naloxone plasma binding differences between adults and the newborn.     

α1A and α1B-adrenoceptors enhance inositol phosphate generation in rat renal cortex

Summary We have studied the role of _1A and _1B-adrenoceptors in noradrenaline- and methoxamine-stimulated inositol phosphate accumulation in rat renal cortical slices. [³H]Prazosin binding studies with and without inactivation of _1B-adrenoceptors by chloroethylclonidine treatment suggested that noradrenaline lacks relevant selectivity for ₁-adrenoceptor subtypes. Both agonists stimulated [³H]inositol phosphate accumulation with similar maximal effects. The _1A-selective antagonists 5-methyl-urapidil and (+)-niguldipine inhibited inositol phosphate formation by both agonists with shallow biphasic curves but the high affinity component was only 15%–31% and 38%–41%, respectively. The irreversible _1B-selective antagonist chloroethylclonidine inhibited inositol phosphate generation by both agonists by 54%–57%. In contrast to our previous data in rat cerebral cortical slices; we conclude that in rat renal cortex both _1A- and _1B-adrenoceptors are involved in noradrenaline-and methoxamine-stimulated inositol phosphate generation.     

Subclassification of presynaptic α2-adrenoceptors: α2D-autoreceptors and α2D-adrenoceptors modulating release of acetylcholine in guinea-pig ileum

The study was designed to classify in terms of _2A, _2B, _2C and _2D the presynaptic ₂-autoreceptors, as well as the ₂-receptors modulating the release of acetylcholine, in the myenteric plexus-longitudinal muscle (MPLM) preparation of the guinea-pig ileum. A set of antagonists was chosen that was able to discriminate between the four subtypes. Small pieces of the MPLM preparation were preincubated with ³H-noradrenaline or ³H-choline and then superfused and stimulated electrically.The stimulation periods used (3H-noradrenaline: 3 trains of 20 pulses, 50 Hz, train interval 60 s; ³H-choline: single trains of 30 pulses, 0.2 Hz) did not lead to ₂-autoinhibition or inhibition of ³H-acetylcholine release by endogenous noradrenaline. The ₂-selective agonist 5-bromo6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) reduced the evoked overflow of tritium in both ³H-noradrenaline and ³H-choline experiments. Most (³H-noradrenaline) or all (³H-choline) of the 10 antagonists shifted the concentration-inhibition curves of UK 14,304 to the right. pK_d values of the antagonists were calculated from the shifts. pK_d values from ³H-noradrenaline experiments correlated with pK_d values from ³H-choline experiments (r = 0.981).It is concluded that ₂-autoreceptors and ₂-heteroreceptors modulating the release of acetylcholine in the MPLM preparation are of the same subtype. Comparison with antagonist affinities for prototypic native ₂ binding sites, binding sites in cells transfected with ₂ subtype genes, and previously classified presynaptic ₂-adrenoceptors — all taken from the literature — indicates that both are _2D. The results are consonant with the hypothesis that at least the majority of ₂-autoreceptors belong to the _2A/D branch of the ₂-adrenoceptor tree, across mammalian or at least across rodent and lagomorph species. The same may hold true for ₂-adrenoceptors on non-noradrenergic neurones.     

Effect of α-hexachlorocyclohexane on metabolism and excretion of pentetrazol (Cardiazol®) in the rat

Summary -Hexachlorocyclohexan (-HCH) has been shown to be a potent anticonvulsant when tested with pentetrazol. In the experiments reported here the question was examined whether or not the anticonvulsant properties of -HCH are based on an acceleration of pentetrazol breakdown in the rat.In this study the rat has been shown to metabolize pentetrazol extensively. The enzymatic activity is located in the microsomal fraction of the liver and requires NADPH and oxygen. It is inhibited by SKF-525 A and carbon monoxide. This is taken as evidence that P-450 containing mixed function oxidases are involved in the breakdown of pentetrazol.-HCH pretreatment leads to an acceleration of pentetrazol break-down by microsome preparations of about 140%. In vivo -HCH pretreated rats eliminate pentetrazol from brain and serum with a half life of 1.3 h, while this is 3.8 h in untreated rats.The earliest point in time at which -HCH pretreatment causes diminished brain levels of pentetrazol has been found 60 min after pentetrazol injection. Prior to this brain levels of pentetrazol were identically in untreated and -HCH-treated rats.As pentetrazol elicits convulsions within the first 30 min following oral or subcutaneous administration of a convulsive dose and -HCH is clearly active as an anticonvulsant under these conditions, the accelerated breakdown of pentetrazol cannot be the cause of the anticonvulsive action of -HCH.Supported by Deutsche Forschungsgemeinschaft.H. W. V. was the holder of a grant from Deutsche Forschungsgemeinschaft.     

DOPA decarboxylase inhibition does not influence the diuretic and natriuretic response to exogenous α-atrial natriuretic peptide in man

Summary The role of dopamine synthesis in the renal actions of human -atrial natriuretic peptide (ANP) was investigated in six dehydrated volunteers using the DOPA decarboxylase inhibitor carbidopa.Each subject received oral placebo or carbidopa (100 mg) followed by an infusion of ANP 10 pmol · kg^–1 · min^–1 for 1 h. The responses to placebo alone and to carbidopa alone were investigated on separate occasions. ANP produced a similar increase in plasma immunoreactive ANP whether placebo or carbidopa pretreatment had been given. Urinary dopamine excretion was increased by ANP. Carbidopa pretreatment substantially attenuated this increase without affecting the natriuretic or water-diuretic response to ANP. Carbidopa also failed to alter the change in filtration fraction produced by ANP.The results suggest that increased synthesis of intrarenal dopamine is not required for the renal effects of ANP in man.     

Comparison of cloned and pharmacologically defined rat tissue α1-adrenoceptor subtypes

Multiple ₁-adrenoceptor subtypes have been defined by pharmacological and receptor cloning techniques, but the precise alignment of cloned and pharmacologically-defined subtypes is still unclear. We have compared the affinities of 8 subtype-selective compounds at three cloned ₁-adrenoceptor subtypes (rat _1B, bovine _1C rat _1A/D) with those previously determined by the same methods in rat spleen, cerebral cortex, and kidney (Naunyn-Schmiedeberg's Arch. Pharmacol. 348: 385–395, 1993). Among all compounds tested to date at cloned ₁-adrenoceptor subtypes (+)-tamsulosin appears to be the most selective with a rank order of potency _1C > _{1A/D 1B}. Affinities for the _1A-selective 5-methyl-urapidil, methoxamine, oxymetazoline, phentolamine and (–)- and (+)-tamsulosin and for noradrenaline and SDZ NVI-085 at the splenic _1B-adrenoceptors and at their low affinity sites in cerebral cortex and kidney correlated best with those at the cloned _1B-adrenoceptor. Affinities of these drugs at their high affinity sites in cerebral cortex (pharmacologically-defined _1A-adrenoceptor) were matched best by those at the cloned _1C-adrenoceptor. Rat kidney appears to contain two chloroethylclonidine-resistant ₁-adrenoceptor subtypes one of which is similar to the cloned at _1C- and one to the cloned _1A/D-adrenoceptor. We conclude that the cloned _1B-adrenoceptor is the genetic correlate of the pharmacologically-defined _1B-adrenoceptor. An ₁-adrenoceptor subtype corresponding to the cloned _1A/D-adrenoceptor appears to exist in rat kidney. Among cloned ₁-adrenoceptor subtypes, the bovine _1C-adrenoceptor bears the closest resemblance to the pharmacologically-defined _1A-adrenoceptor in rat cortex and to one of the chloroethylclonidine-insensitive subtypes in rat kidney.     

Binding of aprindine and moxaprindine to human serum, α1-acid glycoprotein and serum of healthy and diseased humans

Summary A comparison was made between the binding of the anti-arrhythmic agents aprindine and moxaprindine to human serum, to human serum albumin (HSA), to ₁-acid glycoprotein (₁-AGP) and to a mixture of HSA and ₁-AGP. In serum from healthy volunteers (n=4) the binding of aprindine-HCl 5 µg/ml (13.8 µM) was 93.8% (SD±1.0), and that of moxaprindine-HCl 5 µg/ml (12.8 µM) was 94.1% (SD±1.1). Their binding to the mixture of ₁-AGP and albumin approximated their binding to serum. For ₁-AGP, the binding was similar for both compounds, whereas for HSA the binding of aprindine was more pronounced than that of moxaprindine: for both products the affinity coefficient for binding to ₁-AGP was about 100 times greater than that for binding to albumin. In serum from rheumatoid patients and from patients with renal failure a small but significant increase in binding of aprindine and moxaprindine was observed, approximately 1%. Increased and decreased binding was seen in serum from cirrhotic patients; for example, for aprindine the range in cirrhosis was 96.7%–79.8%, and the range in controls was 95.0%–92.4%. Free drug fraction and ₁-AGP concentration were inversely correlated. The results show that ₁-AGP plays an important role in the binding of aprindine and moxaprindine, and that alteration in the binding of the two compounds in disease states to a large extent can be explained by changes in serum ₁-AGP concentration.     

Synthesis and pharmacological study of some alkylamini esters and amides of α,α-diarylaliphatic acids

Conclusions Sixteen alkylamino esters and amides of ,-diphenyl--ethoxyacetic acid and ,-diphenylpropionic acid have been synthesized and investigated pharmacologically. All the compounds prepared possess spasmolytic and cholinolytic properties. Derivatives of ,-diphenyl--ethoxyacetic acid are also characterized by the presence of analgesic and anti-cough action. Loading the alcoholic or acid part of the molecule, or replacement of the ester bond by an amide bond, leads to weakening of activity.Translated from Khimiko-Farmatsevticheskii Zhurnal, No. 1, pp. 9–14, January, 1970.     

Effect of K+ channel blockers on the α2-adrenoceptor-coupled regulation of electrically evoked noradrenaline release in hippocampus

Summary The question whether presynaptic ₂-adrenoceptors regulating noradrenaline release in hippocampus directly couple to tetraethylammonium chloride (TEA) or -dendrotoxin (-DTX)-sensitive K⁺ channels was investigated. Hippocampal slices, prelabelled with [³H] noradrenaline, were superfused in the presence of (+)-oxaprotiline and electrically stimulated with 4 pulses delivered at 100 Hz, in order to avoid autoinhibition due to released noradrenaline.TEA enhanced the evoked [³H]noradrenaline release in rabbit hippocampus in a concentration-dependent manner, yielding an approximately 4-fold increase at 30 mmol/l, whereas the spontaneous outflow of tritium was only slightly affected at this concentration. The ₂-adrenoceptor agonist clonidine, at 10–100 nmol/l inhibited the evoked [³H]noradrenaline release between 77% and 96%. The inhibitory effect of the ₂-agonist was distinctly diminished in the presence of 30 mmol/l TEA but was restored in low Ca²⁺/high Mg²⁺ buffer. Therefore, the diminution of the ₂-agonist effect by TEA observed in experiments with normal Ca²⁺ can be explained by an increase of the Ca²⁺ availability for the release process due to the prolongation of action potentials. In rabbit hippocampus -DTX (10–200 nmol/l) did neither affect the evoked release of [³H]noradrenaline nor its ₂-agonist-induced modulation. However, in rat hippocampus -DTX significantly increased the evoked transmitter release and diminished the effect of clonidine.Taken together, the present data for the rabbit hippocampus exclude the possibility that activation of presynaptic ₂-adrenoceptors inhibits depolarization-evoked [³H]noradrenaline release by inducing an outward K⁺ current through TEA- or -DTX-sensitive K⁺ channels. However, there are species differences between the rabbit and the rat so that in the rat the ₂-adrenoceptors could actually be coupled to K⁺ channels — provided that the release-enhancing properties of -DTX do not account for the ₂-antagonism observed.Correspondence to C. Allgaier at the above address     

A novel electrophysiological approach to monitor pulse by pulse the concentration of released noradrenaline at the presynaptic α2-adrenoceptors of sympathetic nerves in rat tail artery

The excitatory junction current (EJC) evoked by electrical stimulation of postganglionic sympathetic nerves of rat tail artery with 100 pulses at 2 Hz, at 1.3 mmol/l external Ca²⁺, was used as a measure of the per pulse release of ATP. In controls the EJCs were initially facilitated, then gradually depressed during the stimulus train. The first EJC was slightly depressed by the ₂-adrenoceptor antagonist yohimbine, but starting from the 4th pulse the EJCs were enhanced. Yohimbine increased the early facilitation without markedly modifying the subsequent depression. The yohimbine-induced enhancement of EJCs caused by pulses 11–100 was, thus, constant. The noradrenaline reuptake blocker cocaine depressed the EJCs, abolished the early facilitation and slightly enhanced the depression. These effects of cocaine were reversed by further addition of yohimbine. The ₂-adrenoceptor agonist xylazine (1 and 10 mol/1) dose dependently depressed the EJCs starting from the first pulse. The inhibitory effect of 1 mol/l xylazine, but not that of 10 mol/l xylazine, declined with train length.The inhibition of individual EJCs caused by activation of presynaptic ₂-adrenoceptors was used to monitor the concentration of released noradrenaline at these receptors. The ratio of individual EJCs in the presence and absence of yohimbine was assumed to reflect, pulse by pulse, the relative concentration of released noradrenaline at the presynaptic ₂-adrenoceptors, and hence termed [NA] ₂. For comparison, the concentration of endogenous noradrenaline was monitored electrochemically by differential pulse amperometry with a carbon fibre microelectrode; this signal is termed [NA]_CF. [NA] ₂ and [NA]_CF grew during the first 7 – 10 or 14 – 16 pulses, respectively, and then remained relatively constant throughout the stimulus train. Cocaine caused [NA] ₂ and [NA]_CF to continue to grow during the first 35 and 50 pulses, and enhanced their peak levels by 180% and 320%, respectively. For comparison with the effects on the EJCs mediated via presynaptic ₂-adrenoceptors, those caused by varying external Ca²⁺ level were examined. At 0.65 mmol/1 Ca²⁺ the amplitude of the first EJC was smaller than that at 1.3 mmol/1 Ca²⁺, but the facilitation of later EJCs was enhanced and the subsequent depression reduced. An increase in external Ca²⁺ to 2.6 mmol/1 had the opposite effects. All effects on EJCs caused by changes in external Ca²⁺ were maximal for the first EJC and then declined with train length.The results show (i) that changes in the amplitude of individual EJCs during a 2 Hz train, caused by activation of presynaptic ₂-adrenoceptors, may by used to monitor pulse by pulse the concentration of neurally released noradrenaline at these receptors ([NA] ₂), (ii) that [NA] ₂ grows during the first ten pulses to a plateau which is maintained until the end of the stimulus train, (iii) that an exogenous ₂-adrenoceptor agonist or changes in the external Ca²⁺ concentration affect the release probability in all varicosities uniformly, (iv) that activation of presynaptic ₂-adrenoceptors by released endogenous noradrenaline preferentially inhibits release from weak varicosities while strong varicosities were immune, and (iv) that the degree of activation of these receptors controls the per pulse release, and thereby the level of the [NA] ₂ plateau at steady state.     

Evidence in favour of a selective α1-adrenoceptor blocking action of WB 4101 in vivo

Summary The -adrenoceptor blocking potency of WB 4101 at ₁- and ₂-adrenoceptors has been investigated in pithed rats.WB 4101 was approximately 97 times more potent at antagonizing the vasopressor responses produced by the selective ₁-adrenoceptor agonist phenylephrine, than those produced by the selective ₂-adrenoceptor agonist M-7.A dose of WB 4101 (3 mg/kg) that caused extensive blockade of vascular ₁-adrenoceptors, but little or no blockade of vascular ₂-adrenoceptors, exerted no significant blockade of the presynaptic ₂-adrenoceptors in the rat heart.The results support the view that WB 4101 is a highly selective antagonist at ₁-adrenoceptors in vivo.     

Synthesis and antimicrobial action of α-(5-nitrofuryl-2)quinoxaline and its derivatives

Conclusions -(5-Nitrofuryl-2) quinoxaline, and its -cyano- and -oxyderivative were synthesized by nitration of the respective furylquinoxalines with a nitrating mixture. When 2-oxy-3-(furyl-2) quinoxaline is subjected to nitration with excess of nitric acid a dinitro-derivative is formed which is presumably 6-nitro-3-(5-nitrofuryl-2)-2-oxyquinoxaline. The antibacterial, tuberculostatic, and fungistatic activities of the -(furyl-2)- and -(5-nitrofuryl-2) quinoxalines and their derivatives were studied in vitro.Translated from Khimiko-Farmatsevticheskii Zhurnal, No. 10, pp. 14–17, October, 1968.     

α1-adrenoceptor subtype affinities of drugs for the treatment of prostatic hypertrophy

Summary We have used radioligand binding and inositol phosphate accumulation studies to determine the affinity at mixed _1A- and _1B-adrenoceptors (rat cerebral cortex and kidney), _1A-adrenoceptors (rat cerebral cortex and kidney following inactivation of _1B-adrenoceptors by chloroethylclonidine treatment) and _1B-adrenoceptors (rat spleen) for drugs currently under investigation for the treatment of benign prostatic hypertrophy, alfuzosin, naftopidil and (–)- and (+)-tamsulosin. Alfuzosin and naftopidil had similar affinities in all model systems (approximately 10 nM and 130 nM, respectively) and lacked relevant selectivity for ₁-adrenoceptor subtypes. Their potency to inhibit noradrenaline-stimulated inositol phosphate formation in cerebral cortex matched their affinities as determined in the binding studies. Tamsulosin had higher affinity at _1A- than at _1B-adrenoceptors, and was slightly more potent than alfuzosin and naftopidil at _1B- and considerably more potent at _1A-adrenoceptors. However, the interaction of the tamsulosin isomers with chloroethylclonidine-insensitive (_1A-like) adrenoceptors was complex. A detailed analysis of the tamsulosin data and those obtained with other drugs, most notably noradrenaline and oxymetazoline, suggested that chloroethylclonidine-insensitive ₁-adrenoceptors may be heterogenous and that this heterogeneity may differ between cerebral cortex and kidney of the rat.     

Solasodine glycosides of Solanum unguiculatum (A.) Rich

Besides solasonine, three new glycosides, namely, 3-O--L-rhamnopyranosyl-(13)-solasodine, 3-O--L-rhamnopyranosyl-(12)--L-rhamnopyranosyl-(14)--D-galactopyranosyl solasodine, and 3-O--L-rhamnopyranosyl-(12)--D-galactopyranosyl solasodine, were isolated fromSolanum unguiculatum (A.) Rich. Their structures were determined on the basis of chemical and spectral methods.     

Tumor necrosis factor α decreases inositol phosphate formation and phosphatidylinositol-bisphosphate (PIP2) synthesis in rat cardiomyocytes

Treatment of neonatal rat cardiomyocytes for 72 h in the presence of tumor necrosis factor (TNF) (10 U/ml) lead to a decrease in basal and ₁-adrenoceptor-induced formation of the calcium-mobilizing second messenger inositol trisphosphate (IP₃) and its metabolites, IP₂ and IP₁, by 35 and 26%, respectively. The synthesis of phosphatidylinositol bisphosphate (PIP₂), the substrate of PI-specific phospholipase C, was decreased by 45% following the TNF (10 U/ml) exposure. Time courses of TNF (10 U/ml)-induced alterations in rat cardiomyocytes showed a parallel decline of basal inositol phosphate formation and PIP₂ synthesis suggesting that the decrease in inositol phosphate formation was due to the reduction in PIP₂ synthesis. As the TNF-induced decrease of PIP₂ synthesis was associated with a decreased synthesis of the phospholipid phosphatidylinositol (PI), the precursor of PIP₂, by 33%, the decreased availability of PIP₂ is apparently, at least in part, the result of the decreased synthesis of PI. As an apparent functional consequence of the decrease in IP₃ formation following the TNF exposure, the ₁-adrenoceptor-mediated induction of arrhythmias by 100 mol/l noradrenaline + 10 mol/l timolol was abolished in TNF-pretreated rat cardiomyocytes.To investigate one of the possible mechanisms of the TNF-induced decrease of PIP₂ formation, the effect of TNF pretreatment on glycerol-3-phosphate dehydrogenase (GDH), a key enzyme of lipogenesis, was studied: Exposure of the rat cardiomyocytes for 72 h to TNF induced a concentration-dependent decrease in GDH activity by maximally 55%.The result presented are consistent with the hypothesis that the decreased basal and ₁-adrenoceptor-induced formation of the second messenger IP₃ observed in chronic endotoxinemia and sepsis may be mediated by a TNF-induced decrease in the synthesis of PIP₂, the substrate of PI-specific phospholipase C. This mechanism occurs following long-term exposure to low TNF/ha concentrations and is apparently distinct from the short-term cardiac effects induced by high concentrations of TNF. Correspondence to: C. Reithmann at the above address     

Postjunctional α-adrenoceptors

Summary The postsynaptic -adrenoceptors in rat aorta and in pithed rat were investigated according to their sensitivity to nine -adrenergic agonists and to the selective antagonists yohimbine (₂) and prazosin (₁) and the non-selective one, phentolamine. In addition, in radioligand binding studies, the affinity and selectivity of the drugs were determined on rat cerebral cortex using [³H] yohimbine and [³H] prazosin.On rat aorta, prazosin is 1,000 times more potent than yohimbine against each -adrenoceptor agonist, whether ₁- or ₂-selective. Rat aorta probably contains only ₁-adrenoceptors.Pressor effects in pithed rats are mediated by post-junctional ₁- and ₂-adrenoceptors. The dose-response curve for -methylnorepinephrine in the presence of prazosin, using Hofstee's plots, revealed ₁- and ₂-adrenoceptors, respective proportions being 80.5 and 19.5%