Cholinoreceptors of the dentis retractor muscle of the sea urchin Strongylocentrotus intermedius

Neostigmine increases and cholinergic blocking agents block contractions of Strongylocentrotus intermedius dentis retractor muscle caused by either acetylcholine or indirect stimulation. Both innervated and non-innervated parts of the muscle are sensitive to low acetylcholine concentration suggesting that there are both synaptic and extra-synaptic cholinoreceptors. Nicotinomimetics are more potent than muscarinomimetics. Both d-tubocurarine and atropine are weak blocking agents as compared to pentadecamethylene-bis-trimethylammonium or hexadecamethylene-bis-trimethylammonium, Kd being 1 X 10(-4) to 5 X 10(-5) and 5 X 10(-7) to 4 X 10(-7) M respectively. Disulphide bonds and carboxylic (or phosphate) groups were revealed in dentis retractor muscle cholinoreceptors using drugs modifying receptor structure. Cholinoreceptors of both nicotinic and muscarinic type were revealed in oesophagus longitudinal muscles of Strongylocentrotus intermedius.     

Identification and specific blockade of histaminergic receptors in guinea pig vasa deferentia

Histamine produces contractions of the guinea pig vas deferens. The present investigation was undertaken to characterize the nature of histaminergic receptors in this tissue. Histamine (1.6 X 10(-6) M to 3.2 X 10(-5) M) produced dose-related contractions of guinea pig vas deferens (GPVD). Mepyramine (5.3 X 10(-8) M and 1 X 10(-9) M) blocked the responses to histamine competitively. Metiamide (1.23 X 10(-5) M) did not block the responses to histamine significantly. Specific H1 and H2 receptor agonists, namely 2-(2'-pyridyl)ethylamine (PEA) (2.55 X 10(-6) M to 3.0 X 10(-5) M) and 4-methylhistamine (4-MH) (2.52 X 10(-5) M to 3.0 X 10(-4) M), respectively, produced dose-related contractions of GPVD. The responses to PEA were blocked competitively by mepyramine, whereas the responses to 4-MH were blocked by metiamide. Reserpine pretreatment (5 mg/kg, i.p., 24 h) did not alter the responses to histamine and PEA. Our data suggest the presence of both H1 and H2 receptors in the GPVD which are excitatory in nature.     

Studies of the mechanism of passive anaphylaxis in human airway smooth muscle

This investigation was carried out to study allergic contraction of passively sensitized human airway smooth muscle in response to specific antigen challenge. We attempted to determine the role played by histamine, slow reaction substances (SRSs), and cyclooxygenase products in the mediation of this response in tracheal smooth muscle. Tissues were passively sensitized with serum from ragweed-sensitive patients (15 h, 4 degrees C). Subsequent challenge with ragweed antigen produced a slowly developing contraction. The peak contraction to a dose producing a maximal response was 37 +/- 6% of the carbachol maximum. Mepyramine (5 X 10(-6) M) did not alter the contraction. Methylprednisolone (2 X 10(-5) M) attenuated the response to antigen but had no significant effect on the contractile response to arachidonic acid. Indomethacin (5.6-28 X 10(-6) M) enhanced the peak antigen-induced contractions by 25 +/- 11% whereas 5,8,11,14-eicosatetraynoic acid (6.4 X 10(-5) M) selectively attenuated the antigen-induced contraction by 86 +/- 12%. Nordihydroguarietic acid (6-12 X 10(-6) M) attenuated both the antigen plus arachidonate induced responses. FPL-55712 (1-2 X 10(-6) M) antagonized the contractions to antigen. Compound 48/80 and goat antihuman immunoglobulin E produced similar slowly developing contractions in sensitized and in some nonsensitized tissues. These responses, except for an early component of the response to 48/80, were independent of histamine and were reversed by FPL-55712. These findings suggest that arachidonic acid metabolites mediate (slow reacting substances) and modulate (prostaglandins) allergic contraction of human airway smooth muscle while any histamine released contributes little or nothing to the contraction in the larger airways.     

Modulation of cholinergic neurotransmission by vasoactive intestinal peptide in ferret trachea

We studied the effect of vasoactive intestinal peptide (VIP) on the contractile responses to electrical field stimulation (EFS) in isolated ferret tracheal segments. VIP did not change resting tension up to 2 X 10(-7) M, but it showed a biphasic effect on the responses to EFS. In concentrations up to 10(-9) M, VIP potentiated the response; at higher concentrations VIP reduced responses. Thus, at a concentration of 10(-9) M, VIP decreased the mean (+/- SE) log EFS frequency, producing 50% of maximum contraction significantly from a control value of 0.476 +/- 0.062 to 0.214 +/- 0.057 Hz (P less than 0.01); at a concentration of 2 X 10(-7) M VIP increased the half-maximal frequency from a control value of 0.513 +/- 0.086 to 0.752 +/- 0.053 Hz (P less than 0.05). The potentiating effect of VIP (10(-9) M) was not inhibited by hexamethonium, indomethacin, pyrilamine, methysergide, or [D-Pro2,D-Trp7,9] substance P. The inhibitory effect of VIP (2 X 10(-7) M) was also not inhibited by hexamethonium, indomethacin, or naloxone. In contrast to EFS-induced contraction, contractions produced by acetylcholine (10(-9) to 10(-3) M) were not affected by VIP at concentrations of 10(-9) and 2 X 10(-7) M. These results suggest that VIP modulates contractions produced by EFS via presynaptic cholinergic mechanisms and probably through a specific VIP receptor.     

Inhibition of cholinergic neurotransmission in human airways by beta 2-adrenoceptors

The purpose of the study was to determine whether catecholamines modulate cholinergic neurotransmission in isolated human airway smooth muscle. Bronchial rings were suspended in organ baths for isometric measurement of tension, and contractions were induced by either electrical field stimulation (EFS) or exogenous acetylcholine (ACh). Isoproterenol, epinephrine, and norepinephrine in that order of potency produced concentration-dependent inhibition of comparable responses to EFS and ACh. However a potency difference of 100-fold for isoproterenol (IC50 = 4.80 X 10(-8) M for EFS and 3.70 X 10(-6) M for ACh) and 10-fold for both epinephrine and norepinephrine was observed for inhibition of responses to EFS compared with responses to ACh. The inhibitory effects of isoproterenol on responses to EFS were prevented by propranolol and ICI 118551 (a beta 2-antagonist) but not by betaxolol (a beta 1-antagonist). Tyramine had no effect on contractions elicited by EFS. These experiments demonstrate that beta-agonists inhibit cholinergic nerve-induced contractions of human bronchi more potently than contractions induced by exogenous ACh, suggesting modulation of cholinergic neurotransmission by prejunctional beta 2-receptors.     

Inhibitor effect of omeprazole in isolated human myometrial smooth muscle.

The aim of the present study was to investigate the effect of omeprazole, an H+-K+-ATPase inhibitor, in myometrial smooth muscle strips from women undergoing elective caesarean section at term. Isolated myometrial strips taken with informed consent were obtained from eight pregnant women undergoing elective caesarean section at term (not in labour) and mounted in organ baths for recording of isometric tension. We recorded the effect of increasing concentrations of omeprazole on spontaneous and Ca2+-induced contractions of myometrial smooth muscle and on contractions of myometrial smooth muscle pretreated with indomethacin (3 x 10(-6) M) and L-NAME (3 x 10(-5) M). Omeprazole (10(-4)-10(-3) M) decreased the amplitude and frequency of spontaneous contractions in a time- and concentration-dependent manner in all myometrial smooth muscle isolated from pregnant women. The decrease in amplitude of contractions in myometrial smooth muscle reached statistical significance beginning from the concentration of 3 x 10(-4) M. Addition of indomethacin (3 x 10(-6) M) and L-NAME (3 x 10(-5) M) in to the organ baths 30 min before did not change relaxation responses to omeprazole. When 8 mM Ca2+-precontracted in Ca2+-free medium myometrial smooth muscle were exposed to increasing concentrations of omeprazole (10(-5)-10(-3) M), omeprazole produced relaxation responses in a time- and concentration-dependent manner, reaching statistical significance at 10(-4) M. These results show: (1) omeprazole time- and concentration-dependently decreased spontaneous contractile activity in myometrial smooth muscle isolated from pregnant women, (2) omeprazole-induced relaxations was not influenced by indomethacin and N(G)-nitro-L-arginine methyl ester (L-NAME), suggesting that it is not mediated by cyclooxygenase products and nitric oxide, and (3) omeprazole brought about time- and concentration-dependently relaxation of myometrial smooth muscle precontracted by 8 mM Ca2+ in Ca2+-free medium. This effect of omeprazole may be due to blockade of the calcium channels.     

Effects of prostacyclin on the canine isolated basilar artery.

Prostacyclin (PGI2) produced a biphasic response in canine isolated basilar arteries. In low doses (1 X 10(-8)M-1 X 10(-7)M) PGI2 caused a slight but consistent relaxation of resting muscle tone. In low concentrations (1 X 10(-8)M-1 X 10(-6)M) PGI2 antagonized muscle contractions caused by serotonin or prostaglandin (PG) F2 alpha. This relaxant effect with low doses of PGI2 on the isolated cerebral artery contrasts with findings obtained with other PGs and supports the hypothesis that PGI2 is a mediator of vasodilatation. However, in 1 X 10(-5)M concentrations PGI2 contracted the arterial muscle and did not antagonize contractions induced by serotonin or PGF2 alpha.     

The effect of leukotriene D4 on the isolated stomach and colon of the rat

The effect of synthetic leukotriene D4 (LTD4) was evaluated on isolated gastric longitudinal or circular smooth muscle and distal colon of the rat. The concentrations of LTD4, 2.5 X 10(-10)M to 5 X 10(-7)M, evoked minimal to maximal contractile responses. In addition, selected prostaglandins were used to identify the mediator of LTD4-induced contraction of gastric smooth muscle. FPL 55712 inhibited LTD4-induced contractions of gastric longitudinal or circular muscle. Indomethacin inhibited only LTD4-induced contractions of the longitudinal muscle. A combination of FPL 55712 and indomethacin produced greater inhibition of LTD4-induced contractions of longitudinal muscle than either agent alone. However, the same combination of inhibitors showed no greater effect than FPL 55712 alone on LTD4-induced contractions of circular smooth muscle. Unlike PGI2, PGF2, PGA2, or PGD2, PGE2 evoked contraction of the longitudinal muscle and relaxation of the circular muscle of the stomach. The dissimilar effect of PGE2 in the two smooth muscle layers of the rat stomach may signify that PGE2 is the prostaglandin released by LTD4 from the longitudinal and circular gastric muscle. However, the opposing pharmacologic effects following LTD4-induced release of prostaglandins in the circular muscle of the stomach would preclude the appearance of an inhibitory effect of indomethacin in this tissue. In contrast, PGE2 and other prostaglandins contract gastric longitudinal muscle in response to LTD4. Thus, these studies clearly suggest that LTD4 has both a direct and indirect effect on gastric smooth muscle of the rat. Unlike the stomach, LTD4-induced contraction of the distal colon was not inhibited by indomethacin while FPL 55712 antagonized contractions. Thus, these findings indicate a differential mechanism of stimulation of rat gastrointestinal tissue by LTD4.     

Effect of prostaglandin F2 alpha on propulsive activity of the isolated segmental colon of the guinea-pig.

The effects of prostaglandin F2alpha (PGF 2alpha) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated. Using experimental conditions under which spontaneous propulsive activity was negligible, PGF2alpha (5X10(-8)X1X10(-6)M), added to the bathing medium increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1X10(-7)g/ml). The contractions produced by PGF2alpha (5X10(-7) -1X10(-5)M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1X10(-7) g/ml). From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF2alpha may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.     

Mechanism of action of leukotrienes on the guinea pig bronchus

The pharmacological activity of leukotrienes (LT) A4, C4, D4, E4, and histamine was investigated on guinea pig upper and lower bronchi. The contractions of the upper bronchi to histamine, LTA4, C4 and D4 were enhanced by cyclooxygenase inhibitors aspirin (1.67 X 10(-5) and 1.67 X 10(-6) M) and indomethacin (2.8 X 10(-6) and 2.8 X 10(-5) M) whereas the responses to LTE4 were not affected. The myotropic activity of the lower bronchi to all agonists were either very slightly or not at all modified by the presence of cyclooxygenase inhibitors. The thromboxane synthetase inhibitor OKY-046 (1.77 X 10(-5) and 1.77 X 10(-6) M) did not change the responses of higher bronchi to the agonists which suggested that the response of the upper bronchi may be mediated by prostaglandins but not by thromboxanes. The responses of the lower bronchi to leukotrienes A4, C4, D4 and E4 were inhibited by compound OKY-046. Blockade of thromboxane receptors together with inhibition of lipoxygenases by compound L-655,240 (2.53 X 10(-8) to 2.53 X 10(-5) M) had a slight effect on the stimulation of upper and lower bronchi by leukotrienes and histamine. The compound FPL-55712 (1.92 X 10(-6) and 1.92 X 10(-5) M) strongly reduced the contractions of the upper and lower bronchi to leukotrienes but did not affect the responses to histamine. These results suggest that the contractile effects of leukotrienes on upper bronchi is modulated by bronchorelaxant prostaglandins whereas the responses of the lower bronchi are mediated by thromboxanes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of mepacrine on uterine contractile responses

Mepacrine is a potent inhibitor of uterine contractile responses in vitro. Pretreatment of isolated rat uterine horns with mepacrine (1.3 X 10(-4)M) for periods of time ranging from 15 s to 5 min prior to the addition of carbachol (1.0 X 10(-4)M) showed that mepacrine could significantly reduce carbachol-induced uterine contractile responses within 15 s of exposure. The maximal inhibitory effects of mepacrine on uterine contractile responses were observed within 2 min of mepacrine treatment. A dose-response study related to the effect of increasing concentrations of mepacrine (7.5 X 10(-6) to 1.3 X 10(-4)M) on carbachol-induced (1 X 10(-4)M) uterine contractions revealed that a dose of 3.1 X 10(-5)M mepacrine reduced the carbachol-induced contraction by 50%. A dose of 7.8 X 10(-5)M mepacrine produced the maximal inhibitory effect on the carbachol-induced uterine contractions. Two doses of mepacrine (3.1 X 10(-5) and 1.3 X 10(-4)M) significantly reduced maximal contractile responses and shifted contractile dose-response curves of carbachol, oxytocin, prostaglandin F2 alpha, and BaCl2 to the right. Based on the nonselective inhibition by mepacrine of contractile responses induced by different uterotonic agents, these results suggest that mepacrine cannot be used to characterize the role of phospholipase in regulating the actions of hormones in uterine tissue.     

Differential effects of prostaglandin E2 on contractions of airway smooth muscle

In an in vitro muscle bath, the active tension generated by strips of canine tracheal smooth muscle responding to cumulative additions of either histamine (10(-8) to 10(-3) M) or acetylcholine (10(-9) to 10(-3) M) was measured in the absence and presence of prostaglandin E2 (PGE2) (10(-6) to 10(-5) M). When contractile responses of equal magnitude were compared, the contractions elicited by acetylcholine were resistant to the inhibitory effects of PGE2, relative to comparable contractions elicited by histamine. To assess the role of adenylate cyclase in determining the different responses to histamine and acetylcholine in the presence of PGE2, we assayed adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and found that acetylcholine, but not histamine, decreased PGE2-stimulated adenylate cyclase activity by 48 +/- 2% (mean +/- SE; n = 5). However, in other experiments, we found that even large pharmacological increases in tissue adenosine 3',5'-cyclic monophosphate (cAMP) content only partially inhibited muscarinic tone. Also, exogenously applied analogues of cyclic AMP inhibited contractions induced by histamine more effectively than comparable contractions induced by acetylcholine. We concluded that acetylcholine decreased adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and that this effect may have contributed to, but did not completely account for, the relative resistance of muscarinic contractions to the inhibitory effects of PGE2.     

Thromboxane effects on canine trachealis neuromuscular function

The objective of this study is to determine which inflammatory mediators had direct effects on canine trachealis muscle neuromuscular control to identify candidate mediators of the hyperresponsiveness observed in vitro after O3 exposure. Studies were carried out in the sucrose gap at 29 degrees C and in the muscle bath at 37 degrees C. Leukotriene (LT) B4, LTD4, and prostaglandin (PG) D2 had neither direct nor significant effects on the excitatory junction potentials (EJP's), the secondary membrane potential oscillations, or the associated contractions that followed field stimulation of cholinergic nerves. U 46619, a stable analogue of thromboxane (Tx) A2, enhanced (10(-10)-10(-7) M) the duration and the amplitude of secondary oscillations and associated contractions without affecting the EJP's. In the muscle bath, U 46619 enhanced field-stimulated contractions; this was antagonized competitively by SQ 29548. In both the sucrose gap and the muscle bath, higher concentrations (10(-9) M and higher) caused direct effects, small depolarizations, and contractions. These effects of U 46619 were unaffected by indomethacin or guanethidine but were abolished by SQ 29548, an antagonist selective at TxA2-PGH2 receptors. U 46619 at 10(-9) M did not affect electrical or mechanical responses to acetylcholine and at 10(-9) M did not increase the sensitivity to acetylcholine. Platelet-activating factor (PAF) was inactive in all muscle-bath and most sucrose-gap experiments. In 7 of 20 of the latter, it caused effects qualitatively like those of U 46619, but whether it acted through release of TxA2 could not be tested because of the rapid tachyphylaxis to PAF. We conclude that TxA2 may mediate the hyperresponsiveness found in vitro after O3 treatment.     

Effects of stimulation of nervous fibres upon contractile activity of the tracheobronchial lymphatic node capsules' smooth muscles

The contractile activity of smooth muscle of tracheobronchial lymph nodes' capsules was recorded in vitro. The field electric stimulation (0.5 ms pulses, 55 V nominal, 4 min trains at frequencies 0.5, 1, 2, 4, 8, 16 and 32 Hz) of strips from lymph node produced a frequency-dependent increase in baseline tension and frequency of phase contractions. Evoked contractions were significantly (about 80%) reduced by tetrodotoxin (1 x 10(-6) M). The blockage of M-cholinoreceptors with atropine (1 x 10(-6) M) did not affect the field-evoked responses. Contractile field-evoked effects were significantly reduced by the phentolamine (1 x 10(-7)-1 x 10(-6) M) but not completely. Field-evoked contractions were slightly affected by the propranolol (1 x 10(-7)-1 x 10(-6) M). We conclude that the contractile activity of bovine tracheobronchial lymph node capsular smooth muscle is modulated by excitatory adrenergic nerves.     

Gamma-aminobutyric acid modulation of acetylcholine-induced contractions of a smooth muscle from an echinoderm (Sclerodactyla briareus)

This study provides pharmacological evidence for the presence of GABAergic neurons innervating the longitudinal muscle of the body wall (LMBW) of holothurians. Gamma-aminobutyric acid (GABA) A and B receptor subtypes were both present in this system and regulated spontaneous contractions as well as responses to acetylcholine (ACh) that stimulated contraction of the LMBW. GABA dose-dependently relaxed the resting tone of the LMBW. GABA (10(-5) M) inhibited ACh-induced (10(-4) M) contractions by 20%. The GABA B agonist, baclofen, relaxed the LMBW, an effect potentiated by GABA. Pretreatment with baclofen (10(-4) M) inhibited ACh (10(-4) M) contractions of the LMBW by 50%. Phaclofen, a GABA receptor B antagonist, caused a dose-dependent increase in resting tension. Phaclofen-induced (10(-5) M) contractions were reversed by the addition of GABA or baclofen (10(-4) M) and potentiated by the addition of another GABA B receptor antagonist, 2-hydroxy-saclofen (10(-5) M). Pretreatment with phaclofen (10(-5) M) caused a marked potentiation of ACh-induced (10(-4) M) contractions by 101%. 2-Hydroxy-saclofen (10(-5) M) had a toxic effect on the LMBW, rendering it completely unresponsive either to ACh or to a second exposure to GABA, and so exhibiting cross-desensitization. Muscimol, a GABA A receptor agonist, had no effect on the resting tension of the LMBW. Curiously, pretreatment of the muscle with muscimol (10(-5) M) potentiated ACh-evoked (10(-4) M) contractions by nearly 20%. Bicuculline (10(-5) M), a GABA A receptor antagonist, generated large, sustained contractions and partially blocked GABA-induced (10(-4) M) relaxation. Like 2-hydroxy-saclofen, bicuculline (10(-5) M) had a profound cross-desensitizing effect on the LMBW to subsequent exposures to GABA and ACh. ACh was unable to potentiate the sustained contractions induced by bicuculline.     

The influence of prostaglandin E2 (PGE2) on the acetylcholine-initiated contractions of isolated gastric muscularis muscle of Bufo marinus

Acetylcholine (ACh) (1.5 X 10(-5) M) elicited three different types of tonic and phasic contraction of muscularis muscle from different parts (cardiac, middle and pyloric) of the stomach of Bufo marinus. Prostaglandin E2 (PGE2) (10(-9)-10(-6) M) induced a concentration-dependent relaxation of tonic contractions elicited by ACh (1.5 x 10(-5) M) of strips from the cardiac part while potentiating the phasic contractions from the middle part of the stomach. PGE2 (10(-7) M) relaxed tonic contraction and potentiated phasic contraction concomitantly in preparations in which tonic and phasic contractions were elicited by ACh (1.5 x 10(-5) M). The effects of PGE2 on the preparation are related to the part of the stomach from where the strips are prepared and the muscle tone of the preparation.     

Endothelin: differential effects in vascular and nonvascular smooth muscle

Endothelin, a potent vasoconstrictor, produced concentration-dependent contractions in aorta, trachea and bladder body obtained from rat and rabbit. Contractions developed slowly, reaching maxiMum within 15-20 min. Although, in both rat and rabbit tissues, endothelin was 3- to 10-fold more potent in contracting vascular (approximate EC50, 1 nM) than nonvascular smooth muscle, rat trachea and rabbit bladder did contract in response to endothelin. Rat bladder body and rabbit trachea were the least sensitive tissues with only modest contractile responses to endothelin. To determine the role of calcium in these endothelin-induced contractions, the effects of diltiazem and nitrendipine were examined. Although diltiazem (5 x 10-5) M) or nitrendipine (10(-6) M) markedly attenuated contractions produced by KCl, neither agent significantly affected concentration response curves produced by endothelin in rabbit aorta or rat trachea. In rat aorta, nitrendipine had no effect on endothelin responses, whereas diltiazem modestly decreased the maximal contraction to endothelin. However, in rabbit bladder, both calcium channel blockers significantly decreased the maximum response to endothelin with no change in EC50. These results indicate that smooth muscle sensitivity to the contractile effects of endothelin may be both species and tissue specific.     

Modulation of cholinergic neurotransmission in airways by enkephalin

We compared the effects of methionine enkephalin and leucine enkephalin on contractions of isolated canine tracheal smooth muscle strips induced by field electrical stimulation (ES) and exogenous acetylcholine (approximately 10(-5) M). Methionine and leucine enkephalin (10(-8) to 10(-5) M), when added at the peak of airway contractions induced by ES at 1 Hz, depressed the contractions in a concentration-dependent manner by a maximum of 95 and 99%, respectively. Acetylcholine-induced contractions of similar magnitude were depressed only 4% by methionine enkephalin and 12% by leucine enkephalin. Frequency-response curves (0.5-20 Hz) were also obtained before and after incubation of tracheal strips with 10(-5) M methionine and leucine enkephalin. Enkephalin depressed contractions induced by stimulation at 0.5 and 1 Hz by an average of 98 and 95%, respectively. The inhibitory effect of enkephalin progressively decreased at successively higher stimulus frequencies until at 20 Hz there was no significant difference between airway contractions obtained in the presence and absence of enkephalin. Naloxone (3 X 10(-5) M) antagonized the inhibitory effects of both enkephalins. We conclude that methionine and leucine enkephalins inhibit the release of acetylcholine from the postganglionic parasympathetic neurons that innervate airway smooth muscle.     

Studies of the innervation of rabbit myometrium and cervix

We characterized the innervation of isolated circular and longitudinal-oriented muscle strips from the nulliparous rabbit uterus and cervix by field stimulation (FS). FS with increasing frequency (2.5-50 pps) and voltage (2.5-70 V) caused graded increases in isometric contraction with no relaxation or inhibition of spontaneous activity. Tetrodotoxin (TTX, 3.1 X 10(-6) M) significantly reduced the FS response by 75% in all strips at higher stimulus frequencies. Contractile responses to FS were also significantly inhibited by atropine (3.5 X 10(-6) M) in circular uterus and in longitudinal cervix. Guanethidine (5 X 10(-6) M) reduced the response in all strips, as did phentolamine (3.6 X 10(-6) M) in longitudinal uterus and circular cervix. Propranolol (3.9 X 10(-6) M) did not significantly change the response in longitudinal uterus or circular cervix. In longitudinal uterus, combined guanethidine and atropine produced significant inhibition, but not statistically different from either drug alone. Similar results were seen in circular uterus. Electron microscopy and glyoxylic acid histofluorescence indicate that both blood vessels and smooth muscle in rabbit uterus are supplied with adrenergic nerves. The results suggest the presence of TTX-sensitive adrenergic and cholinergic excitatory innervation of rabbit uterus and cervix.     

Pre-junctional inhibitory action of prostaglandin E2 on excitatory neuro-effector transmission in the human bronchus

The effects of prostaglandin E2 (PGE2) and indomethacin on excitatory neuro-effector transmission in the human bronchus were investigated by tension recording and microelectrode methods. PGE2 (10(-10)-10(-9)M) suppressed the amplitude of twitch contractions and excitatory junction potentials (e.j.ps) evoked by field stimulation at a steady level of basal tension obtained by the combined application of indomethacin (10(-5) M) and FPL55712 (10(-6) M). In doses over 10(-8)M, PGE2 reduced the muscle tone and dose-dependently suppressed the amplitude of twitch contractions. Indomethacin (10(-5) or 5 x 10(-5) M) reduced the muscle tone and enhanced the amplitude of twitch contractions and e.j.ps evoked by field stimulation in the presence of FPL55712. PGE2 (10(-9) M) had no effect on the post-junctional response of smooth muscle cells to exogenously applied acetylcholine (ACh) (4 x 10(-7) M). However, indomethacin (10(-5) M) significantly enhanced the ACh-induced contraction of the human bronchus. These results indicate that PGE2 in low concentrations has a pre-junctional action to inhibit excitatory neuro-effector transmission in addition to a post-junctional action, presumably by suppressing transmitter release from the vagus nerve terminals in the human bronchial tissues.