The influence of taurocholate and dehydrocholate choleresis on plasma disappearance and biliary excretion of indocyanine green in the rat

Summary The pharmacokinetics of indocyanine green (ICG; 3.9 moles/kg and 12.9 moles/kg) were investigated in rats given infusion of either saline, taurocholate (106 moles/h) or dehydrocholate (106 or 268 moles/h). During the infusion of saline and taurocholate the plasma concentration of ICG decreased in a mono-exponential manner. However, with dehydrocholate the clearance of ICG from plasma showed two phases with different half lives. The half life of the rapid component (2.2 min) was about the same as the one found in the control experiments.After injection of 12.9 moles/kg ICG the biliary excretion of the dye increased by 138% during taurocholate administration, while an equimolar dehydrocholate infusion resulted in a mean increament of 55%. Under these circumstances the bile flow was stimulated by 195% and 297% resp.With the lower dose of ICG (3.9 moles/kg) however, there was no stimulation of the biliary ICG excretion with taurocholate. At this dose level an infusion of dehydrocholate (106 mol/h) enchanced the biliary output of ICG by approximately 54%, while administration of 268 mol/h resulted in a slight but significant decrease of 31%.These observations can be explained by assuming interaction of the bile acids with the hepatic transport of ICG at different sites. The appearance of the second component of the plasma curve during dehydrocholate infusion is possibly related to a diminished hepatic storage capacity for ICG and is not due to an effect on the primary hepatic uptake or biliary output of the dye.     

Frequency- and train length-dependent variation in the roles of postjunctional α1- and α2-adrenoceptors for the field stimulation-induced neurogenic contraction of rat tail artery

Summary The present paper examines the roles of postjunctional ₁- and ₂-adrenoceptors for the noradrenaline (NA)-induced neurogenic contractile response to field stimulation mainly with 1–100 pulses at 2 or 20 Hz, in the tail artery of adult normotensive rats. Pharmacological tools were employed to isolate and characterize the ₁- and ₂-adrenoceptor-mediated components of this response. The degree to which the drugs influenced NA release or reuptake was assessed by their effects on the electrochemically determined, stimulation-induced rise in the NA concentration at the innervated outer surface of the media. This response was unaffected by ,-methylene ATP (10 M) or suramin (500 M), added to desensitize or block P₂-purinoceptors, respectively prazosin (0.1 M) or SK&amp;F 104078 (6-chloro-9-[(3-methyl-2-butenyl)oxyl]-3-methyl-1H-2, 3, 4, 5-tetrohydro-3-benzazepine, 0.1 M), used to block postjunctional ₁- and ₂-adrenoceptors respectively, nifedipine (10 M), blocker of Ca²⁺ influx through L-type channels, and ryanodine (10 M), which blocks mobilization of Ca²⁺ from intracellular stores; it was moderately enhanced by yohimbine (0.1 M), blocker of pre- and postjunctional ₂-adrenoceptors, and strongly enhanced by cocaine (3 M) or desipramine (1 M), blockers of NA reuptake. Judging from their inhibitory effects on the contractile responses to the ₁- and ₂-adrenoceptor agonists, phenylephrine andxylazine, prazosin (0.1 M)and SK & F 104078 (0.1 M) could be used to selectively block ₁- and ₂-adrenoceptors respectively, while yohimbine (0.1 M) was less selective, strongly depressing ₂- and slightly depressing ₁-adrenoceptor-mediated responses. The ₁-adrenoceptor-mediated component of the contractile response to short trains at 20 Hz was fast in onset, brief in duration and abolished by ryanodine; that mediated by ₂-adrenoceptors was more delayed, prolonged and insensitive to ryanodine. Both components were dose-dependently depressed by nifedipine (0.1–10 M). The small contractile responses to single pulses, or up to 50 pulses at 2 Hz, or short train (< 4 pulses) at 20 Hz, were more markedly depressed by 0.1 M yohimbine or SK & F 104078 than by 0.1 M prazosin and, hence, mediated mainly by ₂-adrenoceptors. The reverse was true of the much larger response to longer trains at 20 Hz, which thus probably was mediated mainly by ₁-adrenoceptors. Cocaine or desipramine, as well as ,-methylene ATP or suramin, amplified both components of the NA induced contractile response especially that mediated via a₁-adrenoceptors and caused by single pulses or short trains.The main conclusions are (i) that the small NA-induced contractile responses of this artery to single pulses, or pulses at low frequency, or in short trains at high frequency, are mediated mainly via ₂-, and the larger responses to longer trains at high frequency increasingly via ₁-adrenoceptors, (ii) that the ₁- and ₂-adrenoceptor-mediated components interact cooperatively, probably at least in part by utilizing two different pathways to increase the intracellular Ca²⁺, (iii) that neuronal reuptake of NA strongly restricts both components of the NA-induced contraction, especially the ₁-adrenoceptor-mediated response to single pulses or short trains, and (iv) that both components of the NA-induced contraction, especially that mediated by ₁-adrenoceptors, may be depressed by ATP released by field stimulation and acting via P_2x-purinoceptors on smooth muscle. Based on these results a novel working hypothesis is proposed, in which it is assumed that the geometry of NA-mediated neuromuscular transmission in this vessel varies with the frequency and number of impulses in a stimulus train.Correspondence to J.-X. Bao at the above address     

Mechanisms of the contractile effects of flosequinoxan

In guinea-pig papillary muscles the positive inotropic effect of flosequinoxan (BTS) starting at 100 mol/1 amounted to 287.6 ± 34.2% at 300 mol/l without any effects on time to peak tension (103.9 ± 2%) and relaxation time (107.1 ± 6.7% of predrug value, respectively). 10 mol/l carbachol attenuated the positive inotropic effect of 300 mol/l to 166.5 ± 11.6% (n = 10). The phosphorylation state of the inhibitory subunit of troponin (TnI) and phospholamban(PLB) in [³²P]-labeled guinea-pig ventricular myocytes was increased starting at 100 mol/l amounting to 142.5 ± 12.6% and 130.9 ± 2.2% at 300 mol/l, respectively (n = 5). Furthermore, BTS (300 mol/l) decreased phosphorylase phosphatase activity by 23.1%. It is concluded that the contractile effects of BTS are accompanied by enhanced phosphorylation of regulatory proteins which could in part be due to inhibition of phosphorylase phosphatase activity.     

Metal concentrations in oldsquaw (Clangula hyemalis) during an outbreak of avian cholera, Chesapeake Bay, 1994

Forty out of 41 oldsquaw carcasses collected during a 3 month avian cholera outbreak in Chesapeake Bay, USA, in 1994 were culture positive for Pasteurella multocida. Pasteurella-positive birds collected in February had greater (p 0.05) mean (geometric) liver concentrations of cadmium (7.35 versus 3.71 g per g dry weight) and lower concentrations of selenium (9.90 versus 12.5 g per g dry weight) than Pasteurella-positive birds collected during March and April. The mercury content of the livers and cadmium content of the kidneys did not differ (p> 0.05) between birds collected early in the die-off and those collected in March and April. The liver and kidney concentrations of metals in the Pasteurella-positive birds collected in 1994 were compared to apparently healthy oldsquaw (n = 67) collected from Chesapeake Bay during 1985--1987, because healthy oldsquaw were not collected during the avian cholera outbreak in 1994. Compared to the apparently healthy oldsquaw collected in 1985--1987, the mean concentrations of cadmium (liver 4.32 versus 2.65 g per g dry weight and kidney 22.7 versus 11.5 g per g dry weight) were greater (p 0.05) in the oldsquaw which succumbed to avian cholera in 1994. In contrast, the liver concentrations of selenium (11.9 versus 17.8 g per g dry weight) and mercury (0.389 versus 1.83 g per g dry weight) were lower (p 0.05) in the birds from the 1994 die-off than for the apparently healthy oldsquaw collected in 1985--1987. Three birds from the 1985--1987 cohort and none of the birds from the 1994 cohort had liver lead concentrations greater than 4 g per g dry weight. The results of this study indicate a possible link between high cadmium tissue concentrations and susceptibility to avian cholera in oldsquaw     

Cultured chick sympathetic neurons: ATP-induced noradrenaline release and its blockade by nicotinic receptor antagonists

The ATP-induced increase in tritium outflow from cultured chick sympathetic neurons prelabelled with [³H]-noradrenaline was investigated.Seven days-old dissociated cell cultures of embryonic paravertebral ganglia, loaded with [³H]-noradrenaline (0.05 M), were superfused in the presence of (+)-oxaprotiline and exposed to ATP, ATP-analogues, or 1,1-dimethyl-4-piperazinium (DMPP) for 2 min. ATP (3 LM-3 mM), 2-methylthio-ATP (3–100 M), as well as DMPP (10 and 100 M) induced a significant overflow of tritium. The EC₅₀-value of ATP was 20 M. Both the ATP-induced and the DMPP-induced tritium overflow was Ca²⁺-dependent and sensitive to tetrodotoxin (0.3 M) and -conotoxin (0.1 M); in addition, it was inhibited by the ₂-adrenoceptor agonist 5-bromo-6-(2-imidazoline-2-ylamino)-quinoxaline (UK-14,304; 1 M). The effects of ATP and DMPP were not additive. The ATP-induced as well as the DMPP-induced overflow of tritium was diminished by the P₂-purinoceptor antagonists suramin (300 M) and reactive blue 2 (3 M); in all 4 cases, the inhibition amouted to approximately 40%. The tritium overflow induced by ATP or DMPP was almost abolished by the nicotinic receptor antagonist mecamylamine (10 M) and markedly inhibited by hexamethonium (100 M). Neither ATP nor electrical stimulation caused an overflow of tritium from cultures loaded with [³H]-choline.The results suggest that ATP at molar concentrations induces noradrenaline release from cultured chick sympathetic neurons via an action on a subclass of the nicotinic cholinoceptor.     

Neonatal exposure to zearalenone causes persistent anovulatory estrus in the rat

The effect of neonatal administration of zearalenone on the female reproductive system was studied in the rat. A single subcutaneous injection of 1.0 mg zearalenone to 3- or 5-day-old rats caused persistent vaginal estrus in adulthood. Ovaries in these animals contained many large follicles but no newly formed corpora lutea. The same effects were observed in rats which had received 100 g estradiol-17 in the neonatal period. Most rats which had received 100 g zearalenone or 10 g estradiol-17 showed regular 4-day estrous cycles and had newly formed corpora lutea in their ovaries. These results demonstrate that neonatal exposure to zearalenone produces persistent anovulatory estrus in the rat, the potency being about one tenth that of estradiol-17.     

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     

P2-purinoceptor antagonists discriminate three contraction-mediating receptors for ATP in rat vas deferens

The sites of action at which ATP elicits contraction of the rat vas deferens were studied by means of the P₂-purinoceptor antagonists pyridoxalphosphate-6-azophenyl-2,4-disulfonic acid (PPADS), suramin and reactive blue 2.Increasing concentrations of PPADS (up to 1 mM), suramin (up to 1 mM) and reactive blue 2 (up to 320 M) reduced and eventually abolished contractions elicited by the P_2X-purinoceptor-selective agonist ,-methylene ATP 3 M with IC₅₀ values of 2.1, 10.1 and 27.0 M, respectively. In contrast, PPADS and suramin caused only a partial inhibition of contractions elicited by ATP 1 mM, maximal reduction by about 40%, IC₅₀ values 1.3 and 5.0 M, respectively; reactive blue 2 did not change ATP-induced contractions. In tissues exposed to PPADS 320 M throughout, increasing concentrations of reactive blue 2 or suramin decreased contractions elicited by ATP 1 MM, IC₅₀ values 2.6 and 14.5 M, respectively. In tissues exposed to suramin 320 M throughout, increasing concentrations of PPADS decreased contractions elicited by ATP 1 mM, IC₅₀ 37.9 M, whereas reactive blue 2 slightly enhanced these contractions. In tissues exposed to reactive blue 2 100 M throughout, increasing concentrations of PPADS reduced contractions elicited by ATP 1 MM, IC₅₀ 26.6 M, whereas suramin caused no change. Pre-exposure to ,-methylene ATP 1 M to desensitize P_2X-purinoceptors reduced the response to ATP 1 mM by 91% in otherwise untreated tissues, but did not reduce the response to ATP 1 mM in tissues exposed throughout to PPADS 320 M, suramin 320 M or reactive blue 2 100 M. Neither PPADS nor suramin nor reactive blue 2 altered contractions elicited by KCl 35 mM. The P₁-purinoceptor antagonist 8-(p-sulfophenyl) theophylline 100 M did not change contractions elicited by ,-methylene ATP 3 M or ATP 1 mM.It is concluded that ATP 1 mM elicits contraction of the rat vas deferens through three sites: P_2X-purinoceptors which are blocked by PPADS, suramin and reactive blue 2; P_2Y-purinoceptors blocked by reactive blue 2 and suramin but resistant to PPADS; and non-P_2X-non-P_2Y-purinoceptors blocked by PPADS but resistant to inhibition by suramin and reactive blue 2. Correspondence to: R. Bültmann at the above address     

Effects of dexamethasone on [3H]choline uptake by rat forebrain synaptosomes

Summary Dexamethasone (3–300 mol/l) did not affect uptake of choline (1 mol/l) by rat forebrain isolated nerve terminals (crude synaptosomal fraction). At concentrations which have been shown to increase choline uptake by rat superior cervical ganglion, dexamethasone had no effect on synaptosomal choline uptake at choline concentrations between 0.1 and 30 mol/l, nor on choline uptake which had been partially inhibited either by hemicholinium-3 (0.1 mol/l) or by reducing the NaCl concentration (0-140 mmol/l).     

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

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

Pharmacokinetics of cefradine, sulfamethoxazole and trimethoprim and their metabolites in a patient with peritonitis undergoing continuous ambulatory peritoneal dialysis

Cefradine and co-trimoxazole pharmacokinetics were studied in a patient with peritonitis that complicated continuous ambulatory peritoneal dialysis (CAPD). Concentrations in the plasma reached after oral administration of 500 mg cefradine four times daily and 400/80 mg co-trimoxazole four times daily were for cefradine 100g/ml, for trimethoprim 15g/ml, and for sulfamethoxazole 100/ml, respectively. In the dialysate concentrations were reached of 35–70/ml cefradine, 2–5/ml trimethoprim and 8–17g/ml sulfamethoxazole. The values for sulfamethoxazole are regarded too low to be clinically effective. Half-lives protein binding values and CAPD clearances are presented. Low CAPD clearances were obtained during the night and high values during the day. The dosage yielded too high plasma trimethoprim concentrations, while sulfamethoxazole dialysate concentrations were too low. It seems questionable therefore whether co-trimoxazole can be used orally for the treatment of CAPD peritonitis.     

Characterization of an endothelial 5-hydroxytryptamine (5-HT) receptor mediating relaxation of the porcine coronary artery

Summary The pharmacological properties of the endothelial 5-hydroxytryptamine (5-HT) receptors involved in relaxation of vascular smooth muscle were determined in rings of pig coronary artery contracted with 10 nmol/1 of the thromboxane A₂ receptor agonist 9,11-dideoxy-11,9-epoxy-methano-prostaglandin F₂ (U 46619).(1) In the presence of 10 mol/l ketanserin, relaxation was obtained with: 5-HT (apparent pD₂ value 7.00), 5-carboxamidotryptamine (5-CONH₂-T; 6.42), 5-aminotryptamine (5-NH₂-T; 5.96), 5-methoxytryptamine (5-OCH₃-T; 5.92), tryptamine, 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo(1,2-a)quinoxaline maleate (CGS 12066 A) and 5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole succinate (RU 24969). The maximum relaxation obtainable with the agonists was about 40–60% of the U 46619-induced contraction and the concentration-response curves for 5-HT, 5-NH₂-T and 5-OCH₃-T were bell-shaped. The endothelium-dependence of this effect (i. e. the failure to relax the artery in endothelium-denuded preparations) was demonstrated for 5-HT, 5-CONH₂-T, RU 24969, CGS 12066A and tryptamine.(2) 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 4-hydroxytryptamine, quipazine and yohimbine were ineffective in decreasing the tension of arteries with or without endothelium. Ipsapirone elicited full relaxation of U 46619-induced contraction, but this effect was not endothelium-dependent.(3) Metitepine (0.03-1 mol/l), 6-chloro-2-(1-piperazinyl)pyrazine (MK 212; 10 mol/l), methysergide (1 gmol/l) and cyanopindolol (0.1 mol/l) antagonized the relaxing effect of 5-HT in a non-surmountable manner, whereas metergoline (0.1 mol/l), quipazine (10 mol/l), yohimbine (1 mol/l), propranolol (1 mol/l) and (3-tropanyl)-1H-indole-3-carboxylic acid ester (ICS 205-930; 0.1 mol/l) did not. However, spiroxatrine (0.1 mol/l) and mesulergine (10 mol/l) enhanced the 5-HT-induced relaxation. The endothelium-dependent relaxation induced by 5-CONH₂-T was also inhibited by metitepine 1 gmol/l.(4) The 5-HT-induced relaxation was probably mediated by release of an endothelium-derived relaxing factor (EDRF). Gossypol, an inhibitor of EDRF, virtually abolished the 5-HT-induced relaxation while indometacin, an inhibitor of cyclooxygenase and accordingly of PGI₂ formation, did not.In conclusion, the failure of ketanserin and ICS 205–930 to counteract the relaxant effect of 5-HT receptor agonists excludes the involvement of 5-HT₂ and 5-HT₃ receptors, respectively, in the endothelium-dependent relaxation of the porcine coronary artery. The rather high potency of 5-CONH₂-T and the ability of certain 5-HT receptor antagonists, such as metitepine, methysergide and cyanopindolol, to counteract the effect of 5-HT are compatible with a 5-HT₁ character of the endothelial receptor. However, on the basis of the present data, no final classification, in particular with respect to the known 5-HT₁ receptor subtypes, is possible. Classification is also hampered by the bell-shaped character of the concentration-response curves for 5-HT receptor agonists and by their property to produce only partial relaxation. Send offprint requests to M. Gothert at the above address     

Methoxamine enhances the release of endogenous noradrenaline from rabbit ear artery: possible involvement of ATP

Summary The effect of methoxamine, an ₁-adrenoceptor agonist, on the electrically-evoked release of endogenous noradrenaline was examined in the isolated rabbit ear artery. Noradrenaline was quantified by high performance liquid chromatography-electrochemical detection. The release of adenine nucleotides and nucleosides by methoxamine was examined using high performance liquid chromatography-fluorescence detection.The release of noradrenaline evoked by electrical field stimulation (EFS) at 4 Hz was reduced by tetrodotoxin 0.3 mol/l and clonidine 1 mol/l by approximately 80% and 50%, respectively. On the other hand, methoxamine at 10 but not 1 mol/l enhanced the release of noradrenaline to approximately twice the control, and the enhancement was prevented by prazosin 1 mol/l. The facilitatory action of methoxamine was also abolished after desensitization of P₂-purinoceptors by ,-methylene ATP 30 mol/l as well as by the presumed P₂-purinoceptor antagonist suramin given at 10 mol/l. Exogenous ATP 10 mol/l significantly enhanced the EFS-evoked release of noradrenaline, and the enhancement was abolished by ,-methylene ATP and suramin. None of the drugs changed the spontaneous outflow of noradrenaline. These results indicate that endogenous ATP, acting at prejunctional purinoceptors, may participate in the facilitatory effect of methoxamine. Indeed, methoxamine 10 mol/l significantly enhanced the spontaneous outflow of ATP and, less so, ADP. The methoxamine evoked release of ATP and ADP was antagonized by prazosin 1 mol/l.It is concluded that methoxamine releases endogenous ATP from postjunctional sites which then, via prejunctional purinoceptors, facilitates action potential-evoked release of noradrenaline in rabbit ear artery.Supported by grants from the Mita Research Foundation, Matsue, Japan and Kanae Research Foundation, Osaka, JapanCorrespondence to K. Takeuchi 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     

Dopamine D-2 receptors inhibit D-1 stimulated cyclic AMP accumulation in striatum but not limbic forebrain

Summary The effect of dopamine D-2 receptor activtion on dopamine D-1 stimulated cyclic AMP accumulation was investigated in slices of rat striatum and limbic forebrain (nucleus accumbens and tuberculum olfactorium). In striatal slices the dose-dependent increase in cyclic AMP accumulation due to dopamine (3–100 mol/1) was enhanced by selective D-2 receptor blockade using (–)-sulpiride (30 mol/1). In limbic slices the increase in cyclic AMP due to dopamine (3–50 mol/l) was unaffected by selective D-2 receptor blockade. The enhancement of cyclic AMP accumulation due to the selective D-1 agonist SKF 38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; 1 gmol/1) in striatal slices was attenuated in the presence of the selective D-2 receptor agonist LY 171555 (quinpirole hydrochloride; 10 mol/l). This attenuation was in turn blocked by (–)-sulpiride (10 mol/1). In limbic slices LY 171555 (10 mol/l) had no effect on SKF 38393 (1 mol/l) stimulated cyclic AMP accumulation. Conversely muscarine receptor activation, using carbachol (10 mol/l), attenuated D-1 stimulated cyclic AMP accumulation in both striatum and limbic forebrain. Dopamine D-2 or muscarine receptor stimulation in either striatal or limbic slices did not attenuate cyclic AMP accumulation due to VIP (vasoactive intestinal polypeptide; 0.5 mol/l), isoprenaline (10 mol/l) or 2-chloroadenosine (100 mol/l). This suggests that in striatal slices, D-2 receptors mediate a selective inhibition of D-1 stimulated cyclic AMP accumulation, but that in the limbic forebrain D-2 receptors are unlikely to be coupled to D-1 receptor-linked adenylate cyclase. These data indicate a fundamental difference in the properties of D-2 receptor-effector coupling in these brain regions. Send offprint requests to S. R. Nahorski at the above address     

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

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

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

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

Blockade of γ-aminobutyric acid-receptors of the B-subtype inhibits the dopamine-induced enhancement of the release of cholecystokinin-like immunoreactivity from slices of rat dorsal caudatoputamen

Summary When slices of rat dorsal caudatoputamen (= neostriatum) are incubated in vitro, Choecystokinin-like immunoreactivity (CCK-LI) is released upon addition of veratridine (3.75 mol/l). This release is affected by dopamine and by -aminobutyric acid (GABA)-receptor agonists. Dopamine enhances the release by stimulating dopamine D₂-receptors and decreases it via D₁-receptors. GABA_A-receptor agonists enhance the veratridine-induced release of CCK-LI, while GABA_B-receptor agonists decrease it. In the present investigation, it was examined whether GABA-receptors are involved in the effect which dopamine exerts via D₂-receptors. The GABA_A-receptor antagonist bicuculline (10 mol/l)and the blocker of the GABA_A-receptor ionophore picrotoxin (1 mol/l) did not affect the dopamine (0.1 mol/1)-induced increase in the release of CCK-LI. However, the GABA_A-receptor agonist muscimol (1 mol/l) not only enhanced the release of CCK-LI, but also prevented a further enhancement by dopamine (0.1 mol/l). This effect of muscimol was blocked by bicuculline (10 mol/l). In the presence of -amino-n-valeric acid (0.1 mmol/l), which has been described to block GABA_B-receptors, dopamine no longer enhanced the veratridine-induced release of CCK-LI. -Amino-n-valeric acid also inhibited the pronounced enhancement of the release of CCK-LI caused by dopamine (0.1 mol/l) and 1 mol/l in the presence of the preferential D₁-receptor antagonist SCH 23390. The effect of -amino-n-valeric acid persisted in the presence of bicuculline (10 mol/l and 100 mol/l). (+)-Baclofen, a partial agonist at GABA_B-receptors, and the stereoisomer (–)-baclofen, a full agonist, also prevented the effect of dopamine on the veratridine-induced release of CCK-LI. The effects of both drugs may be due to desensitization of GABA_B-receptors, which has been described to develop quite rapidly. It is concluded that -amino-n-valeric acid blocks GABA_B-receptors and in this way prevents the enhancement of the veratridine-induced release of CCK-LI caused by dopamine via D₂-receptors. These data are interpreted as evidence that dopamine and GABA-neurons can directly or indirectly interact in the rat neostriatum. Send offprint requests to D. K. Meyer at the above address     

Stimulation of DNA repair synthesis of rat thymocytes by novobiocin and nalidixic acid in vitro without detectable DNA damage

Scheduled (SDS) and unscheduled (UDS) DNA synthesis as well as nucleoid sedimentation was investigated in vitro under the influence of novobiocin (NB) and nalidixic acid (NA) using intact thymic (T-cells) and splenic (S-cells) rat cells and cells which were exposed to X-rays, UV irradiation, methyl methanesulfonate (MMS), and DNA polymerase inhibitors. At concentrations of 56.25 (S-cells) and 225 g/ml (T-cells), respectively, NB inhibited SDS in a dose-dependent manner. Within a concentration range of 225–900 g NB/ml, UDS of S-cells decreased to values far below the tracer ([³H-methyl]-thymidine) incorporation of control cells, whereas UDS of T-cells increased by at least 200%. Within a concentration range of 450–1800 g/ml, NA enhanced SDS and UDS by about 30% in S-cells and by 100% in T-cells. The stimulating activity of NB and/or NA could be eliminated specifically by the DNA polymerase inhibitor 2',3'-dideoxythymidine. Enhanced nucleoid sedimentation was observed at NB concentrations 750 g/ml; S-cells revealed a higher sedimentation rate than T-cells. It is suggested that NB (and NA) influence DNA topology in a rather cell specific manner, stimulating UDS of T-cells by a DNA polymerase — dependent repair-like mechanism.     

Regulation of adenylate cyclase activity in hamster adipocytes

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

Cyclic nucleotide phosphodiesterases of human and rat gastric mucosa

Summary Cyclic adenosine-3,5-monophosphate (cAMP) phosphodiesterases (PDE) were partially purified from human and rat gastric mucosa. Drugs known to affect the cyclic nucleotide system and/or gastric secretion were tested for effects on the PDE-activities from both species.In rat gastric mucosa PDE-activity can be detected in the 100 000×g sediment (K _m =8.3 M; V _max=3.2 nmoles cAMP hydrolyzed/mg protein x min) and the cytoplasma (K _m =5.6 M; V _max=2.6 nmoles cAMP hydrolyzed/mg protein x min).The most effective inhibitors of the particle-bound activity are papaverine (K _i =4 M, non-competitive) and 3-isobutyl-1-methylxanthine (K _i=14 M, competitive). There was only a modest competitive inhibition by theophylline (K _i =495 M). PDE-activity in the cytoplasma was inhibited competitively by these three drugs (papaverine: K _i =6.5 M; 3-isobutyl-1-methylxanthine: K _i =37 M; theophylline: K _i =152 M.In human gastric mucosa PDE-activity can be detected in the particular fraction (K _m =23.9 M; V _max=1.2 nmoles cAMP hydrolyzed/mg protein x min), and the soluble fraction (K _m =12.1 M; V _max=2.4 nmoles cAMP hydrolyzed/mg protein x min).PDE-activity in the 100 000×g sediment was inhibited by papaverine (K _i =5.6 M, non-competitive), 3-isobutyl-1-methylxanthine (K _i =16 M, non-competitive), theophylline (K _i =165 M, non-competitive), and N₆-2-O-dibutyryl-cAMP (K _i =746 M, competitive).Inhibition in the 100 000×g supernatant was noncompetitive with 3-isobutyl-1-methylxanthine (K _i =7.1 M and papaverine (K _i =8.5 M), but competitive with N₆-2-O-dibutyryl-cAMP (K _i =170 M), and theophylline (K _i =225 M). This study indicates that PDE-activities of the two species are qualitatively similar, but quantitative differences exist.