Effects of histamine receptor stimulation on diseased gallbladder and cystic duct

The effects of histamine receptor stimulation on the motility of diseased human gallbladder and cystic duct were studied on tissue strips in vitro. Histamine produced concentration-dependent contractions in normal tissues and in tissues from each disease group, but the sensitivity of the strips to histamine as measured by the median effective dose was dependent upon the grade of disease: normal, 90.0 microM; mild chronic cholecystitis, 32.4 microM; advanced chronic cholecystitis, 12.5 microM; and acute cholecystitis, 3.0 microM. There were no differences in histamine sensitivity among different regions (body, neck, and cystic duct) of the biliary system. Studies with receptor-selective agonists and antagonists indicated that the contractile effects were mediated via histamine H1 receptors. Histamine H2 receptor agonists caused only small relaxant responses in about 30% of strips from gallbladder body, but were without effect in gallbladder neck and cystic duct. We conclude that the effects of histamine on the motility of diseased human gallbladder may depend upon the severity of the cholecystitis.

Heterogeneity of high affinity nitrobenzylthioinosine binding sites in mammalian cortical membranes: multiple forms of central nervous system nucleoside transporters?

Specific binding of [3H]nitrobenzylthioinosine to cortical membranes from several mammalian species was investigated. Rat, mouse, guinea pig, and dog membranes contained an apparent single class of binding sites; there was, however, a marked species-dependent variation in their affinity for [3H]nitrobenzylthioinosine. Rabbit cortical membranes contained two classes of binding sites and the high and low affinity components were similar to those found in guinea pig and dog cortical membranes, respectively. The [3H]nitrobenzylthioinosine binding sites in rat and the low affinity sites in rabbit were atypical in that they exhibited a low affinity for dipyridamole. It is proposed that these latter sites may represent a form of the central nervous system nucleoside transport system which is less susceptible to inhibition by dipyridamole.

Effects of prostaglandins on motility of gallbladders removed from patients with gallstones

Prostaglandins (PGs) affect smooth-muscle contractility and are also involved in the inflammatory reaction. They may therefore affect gallbladder motility in cholecystitis. The contractile effects of PGs were recorded in organ baths on strips from 63 fresh, surgically removed human gallbladders. Spontaneous rhythmic contractions were reduced or abolished by indomethacin, which inhibits endogenous PG synthesis. In strips with chronic cholecystitis, concentration-dependent contractions were produced by PGF2, PGB2 and PGD2; the responses to PGE1 and PGE2 were sometimes variable but there were concentration-dependent contractions after treatment of the strips with indomethacin. The majority of strips with acute cholecystitis responded poorly to PGs even after pretreatment with indomethacin. We concluded from this preliminary study that PGs could affect gallbladder motility and that indomethacin probably reduces the endogenous production of PGs in the gallbladder.

The effects of vasoactive intestinal polypeptide on the motility of human and guinea pig gallbladder

The effects of several preparations of vasoactive intestinal polypeptide (VIP) on the motility of strips of human and guinea pig gallbladder were investigated in vitro. VIP (10(-12) to 10(-6) M) had no measurable effects on the spontaneous activity, resting tone or cholecystokinin-octapeptide induced tone of human gallbladder strips. However, VIP (10(-12) to 10(-6) M) caused biphasic effects on the tone of guinea pig gallbladder strips. At low concentrations (10(-12) to 10(-10) M) contractions were observed that became smaller at higher concentrations (10(-9) to 10(-8) M). At still higher concentrations (10(-7) to 10(-6) M) relaxations were elicited. It appears that VIP is not as potent a relaxant of gallbladder muscle as first described. Human gallbladder tissue was totally unresponsive to the VIP preparations tested.

Nucleoside transport in heart: species differences in nitrobenzylthioinosine binding, adenosine accumulation, and drug-induced potentiation of adenosine action

The site-specific binding of the potent and selective nucleoside transport inhibitor, [3H]nitrobenzylthioinosine (NBMPR), to the nucleoside transport system of cardiac membranes of several species was investigated. The affinity of [3H]NBMPR for these sites ranged from 0.03 nM in rat to 0.78 nM in dog. The maximal binding capacity of cardiac membranes for [3H]NBMPR was also species dependent and was greatest in bovine and guinea pig heart (2551 and 1700 fmol/mg protein, respectively) and least in rat (195 fmol/mg protein). The affinities of recognized nucleoside transport inhibitors and benzodiazepines for these transport inhibitory sites in guinea pig and rat heart were estimated by studying the inhibition of the site-specific binding of [3H]NBMPR in competition experiments. These values were compared with their inhibitory effects on the transporter-dependent accumulation of [3H]adenosine in guinea pig and rat cardiac muscle segments and with their ability to potentiate the negative inotropic action of adenosine in electrically driven guinea pig and rat left atria. In guinea pig heart, the recognized nucleoside transport inhibitors and benzodiazepines had an order of affinity (dilazep greater than hydroxynitrobenzylthioguanosine greater than dipyridamole greater than hexobendine much greater than lidoflazine much greater than flunitrazepam greater than diazepam greater than lorazepam greater than flurazepam) for the NBMPR site which was similar to those for the inhibition of [3H]adenosine accumulation and for potentiation of adenosine action. In contrast, in rat heart, where the maximal binding capacity of [3H]NBMPR was lower (eightfold), the nucleoside transporter dependent accumulation of [3H]adenosine was also lower (sixfold) and the negative inotropic action of adenosine was not significantly potentiated.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin constricts the canine cystic duct

The effects of cholecystokinin and cholecystokinin-octapeptide on the canine cystic duct have been studied. The resistance to flow through the duct in vivo, assessed by measuring the flow rate of saline that was perfused through the duct at constant pressure, was increased by cholecystokinin in a dose-dependent manner. Cholecystokinin also produced the well-recognized, dose-dependent elevations of gallbladder intraluminal pressure. Comparison of dose-response curves prepared in each animal indicated that the sensitivity of the cystic duct was significantly lower than that of the gallbladder. Isolated strips of cystic duct and gallbladder in vitro were contracted by cholecystokinin or cholecystokinin-octapeptide; again, cystic duct muscle displayed a lower sensitivity than gallbladder to the contractile effects of these agents. It is not known whether cholecystokinin can affect cystic duct resistance under physiologic conditions.

Adenosine and ATP effects on isolated guinea pig gallbladder

Effects of adenosine, ATP and several derivatives of adenosine were measured in isolated strips of guinea pig gallbladder. Adenosine caused relaxations which were antagonized by theophylline and potentiated by an inhibitor of adenosine uptake, 6-(1-hydroxy-5-nitrobenzylthio)-guanosine (HNBTG). Among several adenosine derivatives, 2-chloroadenosine and 5'-N-ethylcarboxy-midoadenosine were similarly effective while 1-N6-phenylisopropyladenosine was only a weak relaxant. None of the derivatives caused maximal relaxations at 100 microM, and thus absolute potencies could not be determined. ATP caused predominantly contractile effects, with relaxations sometimes being evident at high concentrations. Indomethacin abolished contractile effects of ATP, suggesting prostaglandin involvement, and only relaxations were evident in its presence. Adenosine deaminase abolished the effects of adenosine and partly reduced the relaxant effects of ATP in the presence of indomethacin. In view of the low potency of adenosine and ATP, physiological roles for these compounds in gallbladder motility are not readily evident.

Benzodiazepine inhibition of nucleoside transport in human erythrocytes

The interaction of several benzodiazepines (BDZs) with the nucleoside transport system of fresh erythrocytes from humans was investigated. The affinities of BDZs for the nucleoside transport system were estimated by measuring BDZ inhibition of (a) the site-specific binding of nitrobenzylthioinosine, a potent and specific inhibitor of nucleoside transport, and (b) the uridine transport processes, zero-trans influx, zero-trans efflux, and equilibrium exchange influx. The BDZs inhibited both the inward and outward transport processes, and, for individual agents, inhibition constants (Ki) were similar for the inhibition of each transport process and for the inhibition of the site-specific binding of nitrobenzylthioinosine. The order of potencies of the BDZs in their interactions with the nucleoside transport mechanism (Ro 5-4864 greater than diazepam greater than clonazepam greater than lorazepam greater than flurazepam) is distinct from the potencies of these compounds at BDZ recognition sites. The affinities of the BDZs for the nucleoside transport system, which are about 1000-fold lower than for BDZ recognition sites, suggest that significant inhibition is unlikely to occur with the plasma concentrations (less than 1 microM) that result from usual anxiolytic doses of these agents.

Nucleoside transport in human erythrocytes. A simple carrier with directional symmetry in fresh cells, but with directional asymmetry in cells from outdated blood

Kinetic characteristics of the transport of uridine, a non-metabolized permeant in human erythrocytes, have been compared in erythrocytes from fresh and outdated stored blood. Uridine transport kinetics in fresh cells conformed to the predictions of a simple carrier model operating with directional symmetry, but in erythrocytes from outdated blood the kinetic characteristics of uridine transport were those of an asymmetric system. The latter result agrees with earlier reports by others. The mobility of the loaded and empty carriers differed by about 6- and 12-fold in fresh and outdated blood, respectively.

Saturable, high affinity binding of the nucleoside transport inhibitor, nitrobenzylthioinosine, to guinea pig cardiac membranes

The site-specific binding of the potent nucleoside transport inhibitor, [3H]nitrobenzylthioinosine ([3H]NBMPR), to guinea pig cardiac membranes was rapid, reversible and saturable. [3H]NBMPR bound with high affinity to a single class of sites at which the KD was 0.23 +/- 0.07 nM and which had a Bmax of 1700 +/- 290 fmol/mg protein. Several recognized nucleoside transport inhibitors and benzodiazepines inhibited the binding of [3H]NBMPR with an order of potency similar to that observed for the inhibition of the binding of [3H]NBMPR to human erythrocytes and guinea pig synaptosomes.

Stimulatory and inhibitory histamine receptors in canine cystic duct

1 The effects of histamine receptor stimulation were assessed on the resistance of the canine cystic duct in vivo and on the contractility of circular muscle preparations of canine cystic duct in vitro. 2 In anaesthetized dogs, the H1-receptor agonist, 2-pyridylethylamine (0.05 to 15 mumol, i.a.), elicited dose-dependent increases in cystic duct resistance, whereas the H2-receptor agonist, 4-methylhistamine (0.05 to 15 mumol, i.a.) decreased cystic duct resistance. These responses were antagonized by the H1-receptor antagonist, diphenhydramine, and the H2-receptor antagonist, cimetidine, respectively. 3 Histamine (0.1 to 3000 nmol, i.a.) also increased cystic duct resistance in vivo. In the presence of diphenhydramine, the stimulatory effect of histamine was antagonized and slight decreases in cystic duct resistance became apparent. Cimetidine or prazosin also antagonized the stimulatory effects of histamine. 4 Histamine (1 to 100 microM) or 2-pyridylethylamine (1 to 100 microM) contracted, whereas 4-methylhistamine (1 to 100 microM) relaxed, circular muscle preparations of cystic duct. These excitatory and inhibitory responses were antagonized by diphenhydramine and cimetidine, respectively. 5 These results indicate that the canine cystic duct possesses excitatory H1- and inhibitory H2-receptors. The predominant effect of histamine is an H1-receptor-mediated increase in cystic duct resistance. Histamine, which may be released in association with cholecystitis, may exert significant effects on the regulation of bile flow in and out of the gallbladder and may contribute to gallbladder stasis during biliary disease.

Species differences in nucleoside transport. A study of uridine transport and nitrobenzylthioinosine binding by mammalian erythrocytes

A kinetic study of the inward transport of uridine in erythrocytes of rabbit, human, mouse, rat and guinea-pig demonstrated that the apparent Km of this process was similar (about 0.2mM) in these cell types, but Vmax. values differed markedly. In this array of cell types, Vmax. values were proportional to the number of transport-inhibitory, high-affinity binding sites present per cell of each type. Transport of uridine or adenosine was not detected in dog erythrocytes, nor was saturable, high-affinity binding of nitrobenzylthioinosine demonstrable. These findings demonstrate that species differences in nucleoside transport capacity are attributable to differences in the cell-surface content of functional nucleoside transport sites, rather than to differences in the kinetic properties of these sites.

Inhibition of adenosine accumulation into guinea pig ventricle by benzodiazepines

Several benzodiazepines were compared with dipyridamole for their ability to inhibit the nucleoside transporter specific accumulation of [3H] adenosine into guinea pig ventricle. Diazepam inhibited adenosine accumulation but was considerably less potent than dipyridamole. Lorazepam and flurazepam also inhibited accumulation, but were less potent than diazepam. Coronary vasodilation by diazepam or by dipyridamole probably is mediated via potentiation of adenosine following inhibition of the nucleoside transport system.

Antagonism of presynaptic adenosine receptors by theophylline 9-beta-D-riboside and 8-phenyltheophylline

Theophylline 9-beta-D-riboside and 8-phenyltheophylline were evaluated as presynaptic adenosine receptor antagonists in the rat vas deferens in vitro. Stimulation of presynaptic adenosine receptors, which results in an inhibition of the twitch response to electrical field stimulation, was achieved with 2-chloroadenosine, an adenosine analogue that appears not to be a substrate for the adenosine transport system. The presynaptic inhibitory action of 2-chloroadenosine was antagonized by theophylline (10 and 100 microM) and by 8-phenyltheophylline (10 microM) but not by theophylline 9-beta-D-riboside (100 microM). It is concluded that the addition of a ribose moiety to theophylline does not enhance the antagonist potency of the molecule but actually renders the compound inactive. However, 8-phenyltheophylline is approximately three times more potent than theophylline at presynaptic adenosine receptors.

Effect of adenosine uptake inhibition on the nature and potency of theophylline as a presynaptic adenosine receptor antagonist

The nature and potency of theophylline as a presynaptic adenosine receptor antagonist was investigated in rat vas deferens in vitro.Schild plots were constructed and the pA2 and the slope were determined when the presynaptic adenosine receptor agonist was (a) adenosine alone, (b) adenosine following adenosine uptake inhibition by hydroxynitrobenzylthioguanosine, and (c) 2-chloroadenosine, a potent adenosine analogue which appears not to be a substrate for the adenosine uptake system. The pA2 values for theophylline were 3.80, 4.58, and 5.61, respectively, and the slopes of the Schild plots were 0.58, 0.71, and 0.78, respectively.The variation in the apparent potency of theophylline as a presynaptic adenosine receptor antagonist is explained according to Furchgott's prediction that removal of an agonist from the vicinity of its receptor upsets the equilibrium between agonist and receptor and so may influence antagonist – receptor interactions.Because adenosine uptake varies among tissues, this process should be eliminated before attempting to compare potencies of adenosine receptor antagonists or to classify adenosine receptors by pA2 values.

Potentiation of the effects of adenosine on isolated cardiac and smooth muscle by diazepam

1. Adenosine (10(-7) to 3 x 10(-4) M) or 2-chloroadenosine (10(-8) to 10(-5) M) produced concentration-dependent inhibition of the responses of the rat isolated vas deferens to electrical field stimulation. In electrically driven (2 Hz) guinea-pig isolated left atria, adenosine (10(-6) to 10(-3) M) or 2-chloroadenosine (10(-8) to 10(-7) M) produced concentration-dependent decreases in isometric tension. 2. Diazepam (10(-6) and 10(-5) M) had no direct effect per se, but significantly potentiated the inhibitory action of adenosine on both tissues without altering the inhibitory effect of 2-chloroadenosine. 3. The adenosine uptake inhibitors, hydroxynitrobenzylthioguanosine (HNBTG, 10(-5) M) and dipyridamole (10(-5) M) also potentiated the inhibitory actions of adenosine in rat vas deferens, but not hose of 2-chloroadenosine. 4. Following adenosine uptake inhibition in rat vas deferens by HNBTG (10(-5) M), diazepam (10(-5) M) failed to produce any significant further potentiation of the inhibitory action of adenosine. 5. It is concluded that the potentiation of adenosine by diazepam is possibly due to an inhibition of adenosine uptake.

Effects of end-tidal concentrations of cyclopropane, halothane and diethyl ether on peripheral autonomic neuroeffector systems in the rat

The effects of the inhalation anaesthetics, cyclopropane, halothane and diethyl ether were examined on peripheral neuroeffector systems in the pithed and in the conscious rat. 2 In the absence of a suitable means of accurately quantifying doses of inhalation anaesthetics given to small animals, an apparatus was constructed whereby end-tidal gas samples were collected semi-automatically from the mechanically ventilated rat. 3 Cyclopropane (15.3 and 29.3% end-tidal), halothane (0.20, 0.52 and 0.83% end-tidal) and diethyl ether (2% and 4% end-tidal) lowered the arterial pressure of the pithed rat. Heart rate was increased by diethyl ether 4%, decreased by halothane and unchanged by cyclopropane. 4 While each anaesthetic depressed the pressor responses to sympathetic nerve stimulation, cyclopropane increased and halothane and diethyl ether depressed the pressor responses to exogenous noradrenaline. 5 Each anaesthetic reduced the motor responses of the smooth muscle of the colon to parasympathetic stimulation. 6 The significance of the effects on peripheral neuroeffector systems is discussed in relation to the overall circulatory changes produced by these anaesthetics in the whole animal.

Cardiovascular effects of ketamine in the pithed rat, rabbit and cat

The effect of i.v. ketamine on arterial pressure and heart rate were examined in pithed rats, rabbits and cats. In all three species ketamine caused a brief decrease in arterial pressure and heart rate. In the rat, but not in the other two species, this initial decrease in arterial pressure was followed by a pressor response which was resistant to alpha-adrenoceptor blockade, depletion of tissue noradrenaline stores and adrenalectomy. It is concluded that the peripherally mediated pressor response found in the pithed rat is specific to this species, is not a result of liberation of peripheral catecholamines and does not explain the pressor effect of ketamine found in man and several animal species.

Effects of ketamine on the peripheral autonomic nervous system of the rat

The effects of ketamine (2-(o-chlorophenyl) 2-methylaminocyclohexanone) (2-50 mg/kg) on the responses of the pithed rat arterial pressure, anococcygeus muscle and colon to selective stimulation of the spinal autonomic outflows were examined. Ketamine depressed the vasopressor response produced by stimulation of the lumbar sympathetic outflow in a dose-dependent manner but did not significantly affect the pressor response to intravenous noradrenaline (NA) administration. Ketamine depressed the motor responses of the anococcygeus to stimulation of the pre-ganglionic lumbar sympathetic outflow or to stimulation of post-ganglionic fibres in the sacral region in a dose-dependent manner, the response to preganglionic stimulation being relatively more sensitive to such depression. The anococcygeus response to NA was significantly potentiated with doses of ketamine of 20 mg/kg and 50 mg/kg. Ketamine depressed the motor response of the smooth muscle of the colon to stimulation of the sacral parasympathetic outflow in a dose-dependent manner and at lower doses than were required to produce an equivalent depression of the sympathetic responses in the other tissues. A comparison was made of the effects of ketamine and cocaine on the motor responses of the anococcygeus muscle in vitro to NA, carbachol and field stimulation. Both ketamine and cocaine produced a non-specific depression of all responses at high doses whereas cocaine but not ketamine produced a large potentiation of NA and motor nerve responses at lower doses. The results are discussed in relation to the hypothesis that ketamine might elevate blood pressure in conscious animals and man by potentiating vascular adrenergic responses.

A technique for the study of muscle relaxants by stimulating the spinal motor nerve outflow in the pithed rat

The motor nerve outflow in the pithed rat was stimulated from the spinal column and contractions of individual skeletal muscles recorded. The preparation is anaesthetic-free and well suited to a study of muscle relaxants.