The Mechanism of Uptake of Biodegradable Microparticles in Caco-2 Cells Is Size Dependent

Purpose. To study the uptake of biodegradable microparticles in Caco-2 cells. Methods. Biodegradable microparticles of polylactic polyglycolic acid co-polymer (PLGA 50:50) of mean diameters 0.1 m, 1 m, and 10 m containing bovine serum albumin as a model protein and 6-coumarin as a fluorescent marker were formulated by a multiple emulsion technique. The Caco-2 cell monolayers were incubated with each diameter microparticles (100 g/ml) for two hours. The microparticle uptake in Caco-2 cells was studied by confocal microscopy and also by quantitating the 6-coumarin content of the microparticles taken up by the cells. The effects of microparticle concentration, and incubation time and temperature on microparticle cell uptake were also studied. Results. The study demonstrated that the Caco-2 cell microparticle uptake significantly depends upon the microparticle diameter. The 0.1 m diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 m and 6 fold greater than the 10 m diameter microparticles. Similarly in terms of number the uptake of 0.1 m diameter microparticles was 2.7 × 10³ fold greater than the 1 m and 6.7 × 10⁶ greater than the 10 m diameter microparticles. The efficiency of uptake of 0.1 m diameter microparticles at 100 g/ml concentration was 41% compared to 15% and 6% for the 1 m and the 10 m diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 m) uptake increased with concentration in the range of 100 g/ml to 500 g/ml which then reached a plateau at higher concentration. The uptake of microparticles increased with incubation time, reaching a steady state at two hours. The uptake was greater at an incubation temperature of 37°C compared to at 4°C. Conclusions. The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 m) had significantly greater uptake compared to larger diameter microparticles. The results thus suggest that the mechanism of uptake of microparticles in Caco-2 cell is particle diameter dependent. Caco-2 cells are used as an in vitro model for gastrointestinal uptake, and therefore the results obtained in these studies could be of significant importance in optimizing the microparticle-based oral drug delivery systems.     

α-Adrenoceptor-mediated inhibitory effect of the sympathetic nervous system on the isoprenaline-induced increase in plasma renin concentration

Summary The importance of the sympatho-adrenal system for the isoprenaline-induced increase in plasma renin concentration was investigated in conscious rats. Ganglionic blockade by trimethidinium (10 mg kg^–1) increased the dose-dependent elevation of plasma renin concentration induced by isoprenaline (0.03–0.48 g kg^–1 min^–1). Also treatment of the rats with guanethidine (6 mg kg^–1) or reserpine (2.5 mg kg^–1, given 16 and 7 h prior to the experiments) further increased the effect of isoprenaline (0.5 g kg^–1 min^–1) on plasma renin concentration. Unilateral renal denervation combined with contralateral nephrectomy doubled the effect of the -sympathomimetic amine on renin release. The -adrenoceptor antagonist phenoxybenzamine (3 mg kg^–1) also enhanced the effect of isoprenaline on this parameter.It is concluded that apart from a stimulation of renin release via -adrenoceptors the sympathetic nervous system may inhibit renin release via stimulation of -adrenoceptors.Supported by DFG Me 541/1Partial preliminary communication: Meyer et al. (1976)     

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     

Identification of the neuroeffector transmitter in jejunal branches of the rabbit mesenteric artery

Summary Vasoconstriction or excitatory junction potentials (e.j.ps) evoked by nerve stimulation (15 field pulses at 2 Hz every 3 min) were recorded in rabbit isolated jejunal arteries. The resting diameter of the arteries and its decrease in response to stimulation was measured by a photoelectric method. Vasoconstriction was insensitive to prazosin 0.1 or 1 mol/l. Yohimbine 1 mol/l considerably enhanced, whereas ,-methylene ATP (,-meATP) 1 mol/l abolished the contractile response. In order to test the effect of exogenously applied transmitter candidates, noradrenaline (0.1–1 mol/l) and ATP (10–30 mol/l) were added in concentrations which evoked a vasoconstriction comparable to that induced by electrical stimulation. The action of noradrenaline was prevented by prazosin 0.1 mol/l, but was unaffected by both yohimbine 1 mol/l and ,-meATP 1 mol/l. ,-meATP 1 mol/l depressed the effect of ATP. The e.j.ps evoked by a train of 15 pulses showed facilitation up to the third response and thereafter depression; a partial summation was also observed. Prazosin 0.1 mol/l did not change the e j.p. amplitudes. By contrast, when yohimbine 0.1 or 1 mol/l was added to the prazosin-containing medium, both the late e j.ps in the train and the summation were enhanced in a concentration-dependent manner. ,-meATP 1 mol/l almost abolished the e.j.ps. In conclusion, in rabbit jejunal arteries, stimulation of postganglionic sympathetic nerves may release noradrenaline together with ATP which is probably the sole neuroeffector transmitter under our conditions. Transmitter release seems to be modulated by the activation of presynaptic ₂-adrenoceptors. Under the stimulation conditions of the present experiments the released transmitter does not activate postsynaptic ₁-adrenoceptors. Send offprint requests to P. Illes     

Evidence for a vasoconstriction-mediating receptor for UTP,distinct from the P2 purinoceptor,in rabbit ear artery

Summary 1. The mechanism of uridine 5-triphosphate-(UTP-)induced vasoconstriction was studied in the rabbit ear artery. The arteries were incubated and perfused at a constant rate of flow. Vasoconstriction was measured as an increase in perfusion pressure. 2. Noradrenaline, adenosine 5'-triphosphate (ATP) and UTP caused concentration-dependent vasoconstriction. ATP and UTP were approximately equipotent. 3. The vasoconstrictor effect of UTP 300 mol/l was enhanced by a mixture of atropine, diphenhydramine and methysergide (1 mol/l each) and not affected by indometacin 10 mol/l. 4. Prazosin (0.01 –1 mol/l) and phentolamine (1–10 mol/l) reduced the vasoconstrictor effect of UTP 300 mol/l by up to 34%. Prazosin 1 mol/l failed to diminish the vasoconstrictor effect of UTP 300 mol/l after the sympathetic nerves had been destroyed with 6-hydroxydopamine. 5. , -Methylene-ATP (10–50 ol/l) elicited transient vasoconstriction. Subsequently, vasoconstrictor responses to ATP 100 or 300 pmol/1 were reduced by 88%, whereas responses to UTP 100 gmol/1 were enhanced, responses to UTP 300 mol/l decreased by only 32% and responses to UTP 1000 gmol/1 reduced by 74%. After in vitro-denervation with 6-hydroxydopamine or in the presence of phentolamine 1 mol/l throughout, a, -methylene-ATP (10–50 mol/l) reduced the vasoconstrictor effect of UTP 300 mol/l by 44% and 43%, respectively. 6. We suggest that, in the rabbit ear artery, the non-adrenergic and , -methylene-ATP-resistant vasoconstrictor response to UTP is mediated by a separate receptor mechanism, distinct from the P₂ purinoceptor. Send offprint requests to K. Starke     

Muscarinic receptor interaction with full and partial β-adrenoceptor agonists in the rat colon strip

Summary -Adrenoceptor agonists inhibit contractile activity in isolated colon strips. In order to demonstrate that -adrenoceptors are located at different functional levels within the colon wall, increasing concentrations of muscarinic agonists were used to interact functionally with the -adrenoceptor-mediated inhibition of spontaneous colon activity. The effects of the full agonists isoprenaline and terbutaline and of the partial agonist prenalterol were functionally antagonized by carbachol (0.03 and 0.3 mol/l) and bethanechol (1,3 and 30 ol/l). This functional antagonism was parallelled by an increase in baseline tension and spontaneous contractile activity of the isolated colon strip. At lower concentrations of carbachol (0.003 and 0.01 ol/l) or bethanechol (0.03 and 0.31 mol/l) no effect on the contractile status of the smooth muscle or on the pD₂-values of the full agonists was seen. However, at these lower concentrations of muscarinic agonists a marked decrease in the maximal inhibitory response to the partial -adrenoceptor agonist prenalterol was demonstrated. The inhibitory response to prenalterol showed a biphasic concentration-response curve. The muscarinic antagonist atropine produced an increase in the maximal response of the high potency component of the concentration-response curve for prenalterol and an increase in the sensitivity to isoprenaline. These results demonstrate the presence of a high cholinergic tone in the colon preparation of a magnitude that clearly reduces the sensitivity to -adrenoceptor agonists. The different responses to full and partial -adrenoceptor agonists in the presence of increasing concentrations of muscarinic agonists may indicate that -adrenoceptors are located on two different functional units within the colon wall.     

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     

Influence of papaverine derivatives on phosphodiesterase activity,cyclic 3′,5′-AMP levels and relaxing effect on rabbit ileum

Summary The correlations between the relaxing effect of papaverine derivatives, inhibition of low K_m-phosphodiesterase (cAMP-PDE=EC 3.1.4.17) activity and cyclic 3,5-AMP (cAMP) levels in isolated rabbit ileum were investigated. There was a strong correlation between the relaxing effect, inhibition of PDE activity and cAMP content for eupaverine, ethylpapaverine and papaverine. Eupaverine was the most effective relaxing agent (I₅₀=7.5 M) and the most potent inhibitor of PDE activity (K_i=0.6 M), followed by ethylpapaverine (I₅₀=10 M); K_i=0.8 M) and papaverine (I₅₀=20 M; K_i=2 M). In contrast, there was a strong relaxing effect (I₅₀=6 M) but only slight inhibition of PDE activity (K_i=350 M) by tetrahydropapaveroline (THP). The adenylate cyclase stimulating effect of THP which was shown by others is most likely the reason for comparatively higher cAMP levels, which were found to be elevated about seven times over basal levels of 0.35 nmoles/g wet weight, and effective relaxation. Relaxation could be induced by exogenously added cAMP (I₅₀=45 M) and dibutyryl-cAMP (I₅₀=450 M). Our results support the assumption that smooth muscle relaxation in rabbit ileum is mediated by cAMP. Some of these observations have been published in abstract form (Schulz and Berndt, 1972).     

Interaction of adenine nucleotides,UTP and suramin in mouse vas deferens: suramin-sensitive and suramin-insensitive components in the contractile effect of ATP

Summary Effects of various nucleotides, nucleosides and noradrenaline on smooth muscle tension were studied in the isolated mouse vas deferens. ,-Methylene-ATP, ATPS, noradrenaline, ATP and UTP elicited contraction, with potency decreasing in that order; there was no contractile response to adenosine or uridine (up to 100 mol/l). Prolonged incubation with ,-methylene-ATP (concentration increased stepwise from 0 to 15 mol/l) selectively reduced contractions induced by ATP and UTP but not those induced by noradrenaline, and there was cross-tachyphylaxis between ATP and UTP. Suramin (10–300 mol/l) did not alter the response to noradrenaline but shifted the concentration-response curves for ,-methylene-ATP, ATPS, UTP and lower concentrations of ATP (0.1–1 ol/l) to the right. The pA₂-values of suramin were 5.2 against ,-methylene-ATP, 4.8 against ATPyS, 5.1 against UTP and 5.4 against lower concentrations of ATP. The effects of higher concentrations of ATP were largely resistant to suramin. The results indicate that the mouse vas deferens possesses contraction-mediating smooth muscle P_2X-receptors. UTP also acts at this receptor, and there is no evidence for a separate UTP receptor. The selective inhibition of nucleotide- but not noradrenaline-induced contractions by suramin confirms the view that suramin is a selective P₂-antagonist. The resistance against suramin of part of the effect of ATP suggests that ATP activates a suramin-insensitive site in addition to the P_2X-receptor.Send offprint requests to I. von Kügelgen at the above address     

Effects of locally applied dopamine to the nucleus accumbens on the motor activity of normal rats and following α-methyltyrosine or Reserpine

The motor activity of rats was investigated following bilateral application of various doses (0–80 g) of dopamine to the nucleus accumbens. A high dose (80 g) of dopamine increased the motor activity of normal as well as -methyltyrosine- and reserpine-treated rats. It also increased the late motor activity (6–9 min) of normal rats, probably due to stimulation of postsynaptic dopamine receptors. Lower doses (10–40 g) of dopamine suppressed initial (0–3 min) motor activity of normal rats, perhaps due to stimulation of dopamine autoreceptors on the dopamine nerve terminals in the nucleus accumbens with a subsequent inhibition of dopamine neurotransmission. An intermediate dose (40 g) of dopamine was able to restore the motor activity of -methyltyrosine-treated but not of reserpine-treated rats at all time intervals. This difference, indicating a restoration of the normal pattern of habituation by dopamine only in animals pretreated with -methyltyrosine, suggests that normal behaviour is dependent on release of dopamine by nerve impulses.     

Opioid peptides decrease noradrenaline release and blood pressure in the rabbit at peripheral receptors

Summary Effects of dynorphin-(1–13), Leu⁵-enkephalin,d-Ala²,d-Leu⁵-enkephalin (DADLE), and for comparison bremazocine, on plasma noradrenaline concentration and mean arterial pressure (MAP) were studied in pithed rabbits. In the first series of experiments, the sympathetic outflow was stimulated electrically via the pithing rod at 2 Hz twice for 3 min each (S₁, S₂). Drugs were administered before S₂. Bremazocine 10 g/kg+2g/kg/h and 100 g/kg+20 g/kg/h, dynorphin 1 and 3 g/kg/min, Leu⁵-enkephalin 100 g/kg/min and DADLE 10 and 30 g/kg/min all diminished the electrically-evoked increase in plasma noradrenaline and MAP. The effects were antagonized by naloxone. In the second series, an infusion of noradrenaline (2 g/kg/min) was given twice for 3 min each (N₁, N₂). Drugs were administered before N₂. Bremazocine 100 g/kg+20 g/kg/h slightly enhanced the pressor effect of exogenous noradrenaline, whereas dynorphin 3 g/kg/min, Leu⁵-enkephalin 100 g/kg/min and DADLE 30 g/kg/min caused no significant change. In the third series, the sympathetic outflow was stimulated continuously at 2 Hz, and the interaction of dynorphin and DADLE was studied. Dynorphin 1 g/kg/min and DADLE 10g/kg/min initially decreased MAP to a similar extent. The effect of DADLE faded with time. When, during continuous infusion of DADLE 10 g/kg/min, and after return of MAP to the pre-DADLE level, dynorphin 1 g/kg/min or DADLE 10 g/kg/min was infused additionally, the effect of dynorphin was unchanged, whereas that of DADLE was almost abolished. We conclude that the opioid peptides as well as bremazocine decrease action potential-evoked release of noradrenaline and, secondarily, blood pressure. They act at peripheral sites, presumably prejunctional opioid receptors at postganglionic sympathetic axons. Dynorphin on the one hand, and Leu⁵-enkephalin and DADLE on the other hand, appear to act at different receptors, dynorphin probably at a - and DADLE and Leu⁵-enkephalin at a -receptor.     

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)     

The anti-nociceptive effect of reserpine and haloperidol mediated by the nigro-striatal system: Antagonism by naloxone

Summary Reserpine (10 mg/kg) and haloperidol (2 mg/kg) injected intraperitoneally increased the reaction time of the tail-flick response in intact but not in pre-nigrally decerebrate or spinal rats. The anti-nociceptive effect of both drugs was antagonized by intraperitoneal injections of dopa (100 mg/kg), apomorphine (2mg/kg) or naloxone (1 mg/kg) as well as by bilateral micro-injections into the caudate nuclei of apomorphine (100 g and 20 g) and naloxone (10 g). It is concluded that the nigrostriatal feedback system is involved in the anti-nociceptive effect of reserpine and haloperidol.     

A new technique for the investigation of some analgesic drugs on a reflexive behavior in the rat

Summary The analgetic action of a series of analgesic and psychotropic agents was tested in a situation in which variable intensities of electric shock to a rat's feet were used to elicit two distinguishable reflexive responses: a flinching response at low shock values, and a jumping response at higher shock values,By using a modified method of limits, reliable threshold for the two responses were obtained.Chlorpromazine, perphenazine, morphine, codeine, nalorphine and acetylsalicylate were found to raise the threshold to jump, but had little or no effect on the threshold to flinch.PIH, JB 835, iproniazid, reserpine, tetrabenazine, and amphetamine were found to have no effect on either the jump or the flinch thresholds.A combination of amphetamine and codeine was found to produce a synergistic potentiation. A combination of morphine and nalorphine was found to produce an antagonism.The results were discussed in terms of Beecher's hypothesis that the analgetic action of drugs is due to a diminution of the emotional components of an animal's reaction to pain and in terms of the relationship of brain amine change to analgetic action.     

Inhibitory adenosine A1-receptors on rat locus coeruleus neurones

Summary Intracellular recordings were performed in ₁-pontine slice preparation of the rat brain containing the locus coeruleus (LC). Adenosine (100, 300 mol/l) and its structural analogues, namely (–)-N⁶-(R-phenyliso-propyl)-adenosine (R-PIA; 3 – 30 mol/l) and S-PIA (10, 30 mol/l), as well as 5-N-ethylcarboxamido-adenosine (NECA; 3–30 mol/l) inhibited the firing rate of spontaneous action potentials and produced hyperpolarization; their rank order of potency was RPIA - NECA > S-PIA > adenosine. When applied by superfusion, all agonists strongly desensitized the LC cells; the hyperpolarization never surmounted 6 mV. Upon pressure ejection of adenosine 10 mmol/l from ₁- micropipette positioned close to an LC neurone, the membrane potential was raised by 14 mV and the apparent input resistance decreased by 20%. When the membrane potential was hyperpolarized by current injection to ₁- similar extent as adenosine did, the fall in input resistance was only 7%. The adenosine uptake inhibitor S-(p-nitrobenzyl)-6-thioguanosine (NBTG) 30 mol/l decreased the frequency of action potentials alone; on simultaneous bath-application with adenosine 300 mol/l it potentiated the hyperpolarization caused by the purine derivative. 8-Cyclopentyl-1,3-dipropylxanthine (CPDPX) 0.1 mol/l had no effect on its own, but it antagonized both R-PIA 30 mol/l and NBTG 30 mol/l. A higher concentration of CPDPX (1 mol/l) facilitated the spontaneous firing. In conclusion, both exogenous and endogenous adenosine activates somatic and/or dendritic A₁-receptors of LC neurones leading to an enhancement of potassium conductance and thereby to ₁- decreased firing rate and ₁- hyperpolarization. Send offprint requests to P. Illes at the above address     

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.     

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.     

Inhibition of furosemide-induced renin release by vasoconstrictors

Summary The effect of i. v. infused (asp¹--amid, val⁵)-angiotensin II (1.0 g/kg min), octapressin (phe², lys⁸-vasopressin) (10.0 mU/kg min) and of the -sympathomimetic amine phenylephrine (40.0 g/kg min) on the stimulation of renin secretion by furosemide (10.0 mg/kg i.v.) was investigated. The vasoconstrictors abolished the renin release induced by furosemide. Studies on the clearance of p-aminohippuric acid (PAH) (i.e. renal plasma flow) showed that the action of the vasoconstrictors cannot be explained by a decrease in access of furosemide to its intrarenal sites of action.The mechanism of the suppressive action of the vasoconstrictors on renin release is discussed.Supported by DFG grant Me 541/1.     

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).     

The mechanism of the drinking response to some hypotensive drugs: Activation of the renin-angiotensin system by direct or reflex-mediated stimulation of β-receptors

Summary The increase in water intake and plasma renin concentration (PRC) in response to the administration of the -receptor blocker phentolamine (10 mg/kg) were simultaneously diminished or abolished by ganglionic blockade with pempidine (10 mg/kg) or camphidonium (10 mg/kg) as well as by pretreatment with reserpine or 6-OH-dopamine. In contrast, the effects of the -mimetic agent, isoprenaline (250 g/kg), on both parameter remained unchanged. The (–)-isomer of propranolol (200 g/kg) selectively blocked the dipsogenic and PRC-raising effects of isoprenaline and phentolamine, thus demonstrating that a specific -receptor blockade antagonizes the drinking and increase in PRC induced by the drugs used.From these results it is concluded that the stimulation fo certain -receptors causes an increase in PRC. The -receptors may be stimulated either directly by -mimetic agents such as isoprenaline or indirectly by a reflex-mediated activation of the sympathetic nervous system brought about by hypotensive, drugs such as phentolamine.The activation of the renin-angiotensin system triggers off the drinking response.Some of the results were presented to the Deutsche Pharmakologische Gesellschaft (Meyer and Hertting, 1971).