Neuronal Blocker Research Articles

From α and β to I1

There is no doubt that the sympathetic nervous system (SNS) plays an important role in the pathogenesis and maintenance of hypertensive disease, although many details concerning this association remain to be clarified. Over the years, several types of antihypertensive drugs have been developed that can impair SNS activity at virtually all levels of the system. Alpha and beta-adrenoceptor antagonists, postganglionic sympathetic neuron blockers and ganglioplegic agents are well-known examples of drugs with a predominantly peripheral activity. The CNS regulation of peripheral sympathetic activity offers a further possibility to counteract the influence of SNS activity. In particular, central catecholaminergic neurons and alpha-adrenoceptors have been analyzed in detail and are recognized as important targets for the classic centrally acting antihypertensives clonidine, guanfacine, and alpha-methyldopa. Initially, these drugs were assumed to reduce elevated blood pressure via the stimulation of central alpha-adrenoceptors in the brainstem, thus leading to peripheral sympathoinhibition and a reduction of elevated blood pressure, heart rate, and plasma catecholamines. In a later stage it has been recognized that central imidazoline (I1) receptors may also be involved in the central regulation of peripheral sympathetic activity and that they act as a target for centrally acting antihypertensives. Moxonidine and rilmenidine are the prototypes of such agents. Accordingly, the receptor profile of the various types of centrally acting antihypertensives can be characterized as follows: alpha-methyl-DOPA (through alpha-methyl-norepinephrine) alpha 2; clonidine (mixed agonist), alpha 2 + I1; moxonidine, rilmenidine, I1 > alpha 2. The various compounds mentioned will thus cause peripheral sympathoinhibition, initiated by different receptor targets in the CNS. Because most of the adverse reactions to clonidine and related drugs are mediated by central alpha-adrenoceptors, is is hoped that the imidazoline receptor agonists (moxonidine, rilmenidine) will show a more favorable pattern of side effects.

Ion transport across the jejunum in normal and cystic fibrosis mice.

Cystic fibrosis (CF) mice created by targeted disruption of the murine cystic fibrosis transmembrane conductance regulator gene lack adenosine 3',5'-cyclic monophosphate (cAMP)-mediated Cl- secretion and exhibit marked intestinal complications secondary to inadequate fluid secretion. The basal short-circuit current (Isc) in the normal murine jejuna [43.2 +/- 5.9 microA.cm-2, n = 10 (mean +/- SE)] exhibits marked spontaneous n = 10 (mean +/- SE)] exhibits marked spontaneous oscillations (amplitude = 47.9 microA.cm-2, n = 18), which were completely absent in the CF jejunum. Treatment of normal jejuna with the neuronal blocker tetrodotoxin completely eliminated the oscillations and decreased the Isc to levels not significantly different from the low basal Isc (5.4 +/- 2.8 microA.cm-2, n = 16) exhibited by CF tissue. Ion substitution studies revealed basal Isc in normal jejuna to be due primarily to Cl- secretion but these tissues appeared to be capable of HCO3- secretion as well. In contrast, CF jejuna spontaneously secreted neither Cl- nor HCO3-, which may indicate that CF jejuna have a defect in the ability to secrete both of these anions. Apical glucose elicited an electrogenic absorption of Na+ of identical magnitude in normal and CF jejuna. Without apical glucose, CF jejuna exhibited a very small Isc response to forskolin (delta 2.2 +/- 0.67 microA.cm-2, n = 10). However, in the presence of apical glucose, forskolin elicited an eightfold greater Isc response in the CF tissue (delta 17.2 +/- 4.8 microA.cm-2, n = 9).(ABSTRACT TRUNCATED AT 250 WORDS)

Ｒｅｓｅｒｐｉｎｅ処置動物の血管条辺縁細胞Ｎａ‐Ｋ ＡＴＰａｓｅ活性に対するＬ‐ｔｈｒｅｏ‐ＤＯＰＳの影響

Na-K ATPase in the stria vascularis is known to participate in the active transport of Na+ and K+ ions, and plays essential role in producing cochlear endolymph. The mechanisms that control or maintain the stria vascularis function, however, remain unclear. In the present study, the K-NPPase activity, the second component of the Na-K ATPase complex, in the marginal cells was cytochemically investigated after reserpine and L-threo-DOPS administration. K-NPPase activity was completely inhibited after treatment with reserpine, whereas, following reserpine and L-threo-DOPS treatment, enzyme activity was detectable. As reserpine is an adrenergic neuron blocker, and L-threo DOPS is the precursor of L-noradrenaline, noradrenaline converted from L-threo DOPS was able to restore K-NPPase activity in the reserpine-treated animals. The present result suggests that catecholamines may play an essential role in the maintenance or control of the Na-K ATPase activity, and that the stria vascularis may be one of the target organs of catecholamines.

The role of L-threo DOPS in the control of Na-K ATPase activity of the marginal cells in the stria vascularis of reserpinized guinea pigs.

It is believed that the function of the stria vascularis in the cochlea is to produce endolymph. The mechanisms that maintain or control the function of the stria vascularis, however, remain unclear. In a previous study, we investigated the ultracytochemical effects of one-shot reserpine administration on the Na-K ATPase activity of the stria vascularis in guinea pigs. Na-K ATPase activity was shown to be completely inhibited 3-20 days after reserpinization, whereas in the present study at 20 days after reserpinization and following L-threo DOPS treatment, Na-K ATPase activity was detectable. As reserpine is an adrenergic neuron blocker, and L-threo DOPS is the precursor of noradrenaline, it seems that noradrenaline converted from L-threo DOPS was able to restore the Na-K ATPase activity in the reserpinized animals. These results suggest that catecholamines may play an essential role in the maintenance or control of the Na-K ATPase activity, and that the stria vascularis may be one of the target organs of catecholamines.

Trifluoperazine and calmidazolium have multiple actions on the release of noradrenaline from sympathetic nerves of mouse atria.

The aim of this study was to determine whether the calmodulin inhibitors trifluoperazine (TFP) and calmidazolium (CMZ) could decrease the action-potential-evoked release of noradrenaline from mouse isolated atria incubated with [3H]-noradrenaline in support of the hypothesis that calmodulin is involved in neurotransmitter release. TFP (10 microM and 30 microM) significantly enhanced stimulation-induced (S-I) outflow of radioactivity from mouse atria but had no effect at 1.0 microM or 70 microM. TFP (70 microM) also significantly increased the spontaneous outflow of radioactivity. The facilitatory effect of TFP (10 microM) on S-I outflow of radioactivity persisted in either the presence of 3-isobutyl-1-methylxanthine (100 microM) or atropine (0.3 microM) indicating that this effect of TFP was not mediated through either inhibition of phosphodiesterases or through interference with presynaptic muscarinic receptors, respectively. In the presence of phentolamine, the facilitatory effect of TFP (10 microM) on S-I outflow was reduced but there was no effect on S-I outflow at 70 microM. However, in the presence of a combination of both phentolamine (1.0 microM) and the neuronal uptake blocker desipramine (1.0 microM) a significant inhibitory effect of TFP (70 microM) on the S-I outflow of radioactivity was observed, indicating that effects of TFP on presynaptic alpha-adrenoceptors and neuronal uptake had disguised an inhibitory effect on S-I noradrenaline release. Another inhibitor of the Ca(2+)-calmodulin complex, calmidazolium (CMZ, 10 microM) inhibited the S-I outflow of radioactivity but had no effect at 1.0 microM. However, CMZ (10 microM) also induced a concomitant increase in the spontaneous outflow of radioactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Reserpine inhibits the nak ATPase activity of the stria vascularis in the cochlea

The function of the stria vascularis in the cochlea is believed to be the production of endolymph. The mechanisms that maintain or control the function of the stria vascularis, however, remain unclear. In the present study, the effects of one-shot reserpine administration on the NaK ATPase activity of the stria vascularis in guinea pigs were investigated. NaK ATPase activity was shown to be completely inhibited 3 to 20 days after reserpinization, and was detectable again 60 days after reserpinization. As reserpine is an adrenergic neuron blocker, these results suggest that catecholamines may play an essential role in the maintenance or control of NaK ATPase activity, and that the stria vascularis may be one of the target organs of catecholamines.

The differential mechanisms of mild irritants on adaptive cytoprotection.

The protective action of mild irritants has been established. However, the mechanisms as to how they antagonize the injurious action produced by the subsequent challenge with an ulcerogenic stimulus are still unclear. The present study examined the different protective mechanisms of an oral administration of the three mild irritants, 20% ethanol, 0.3 mol/L HCl or 5% NaCl against the gastric injurious actions of absolute ethanol in rats. In an attempt to clarify the pathways and mediators involved in the adaptive cytoprotection, [D-Pro2, D-Trp7,9]-substance P (substance P antagonist), Nw-nitro-L-arginine methyl ester (L-NAME), indomethacin, capsaicin, lidocaine, atropine or hexamethonium was given. The protective action of 20% ethanol but not the other two mild irritants, was antagonized by L-NAME, indomethacin and capsaicin, which are the inhibitors of nitric oxide (NO) and prostaglandins (PG) synthesis, and afferent sensory neuron blocker, respectively. Substance P antagonist, lidocaine or atropine given alone, prevented mucosal damage; however, only substance P antagonist enhanced the anti-lesion action of 20% ethanol, while atropine and lidocaine increased the protective effect of NaCl and HCl. The three mild irritants increased the residual gastric secretion. Only 20% ethanol and 5% NaCl but not 0.3% HCl significantly increased the basal adherent mucus and also attenuated the mucus depletion by absolute ethanol. It is concluded that the cytoprotective action of either ethanol or NaCl seems to be mediated through the increase of residual gastric secretion and adherent mucus. In the ethanol-treated group, these actions could act through the afferent sensory fibres, with NO and PG as the possible mediators.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy-Dependent Accumulation of Neuron Blockers Causes Selective Inhibition of Neurotransmitter Uptake by Brain Synaptic Vesicles

The effects of neuron blockers on neurotransmitter accumulation in synaptic vesicles were investigated. Upon addition of ATP, brain synaptic vesicles accumulated chlorpromazine, haloperidol, and propranonol against concentration gradients of more than 100-fold. Bioenergetic analysis indicated that the transmembrane pH gradient (ΔpH) established by the vacuolar-type H+-ATPase is a direct driving force for these uptakes. Essentially the same results were obtained with vesicles from bovine adrenal chromaffin granules and proteoliposomes reconstituted with purified vacuolar H +-ATPase, indicating that the energy-dependent accumulation is due to diffusion and does not involve transport carriers specific for the blockers. Incubations of the two organelles with the blockers resulted in dissipation of ΔpH and slight increase of membrane potential (ΔΨ) without affecting ATPase activity. Under the same conditions, uptake of dopamine or γ-aminobutyrate (ΔpH-driven transport) was inhibited by neuron blockers, whereas uptake of glutamate (ΔΨ-driven transport) was slightly stimulated. Thus, neuron blockers inhibited ΔpH-driven uptake of neurotransmitter by dissipating the driving force. These results strongly suggest that synaptic vesicles are one of the target sites of neuron blockers.

Molluscivorous Conus Toxins as Probes for Voltage and Ligand Gated Ion Channels in Molluscs

Venomous Conus snails are highly specific in their feeding ecology, and include a group of some 50 species that feed only on other molluscs. The present work was based on the hypothesis that molluscivorous Conus toxins have undergone targeting to unique sites in prey excitable systems, and may therefore serve as selective probes for molluscan ion channels. Over the past four years we have examined molluscivorous Conus venoms using in vivo bioassays (Patella, Mytilus), and pharmacological experiments in Helix CNS. Parallel assays have been performed by collaborating groups using clectrophysiological techniques on isolated Aplysia or Lymnaea neurons. A series of mollusc selective toxins have been characterized both chemically and pharmacologically. All the toxins are small (16-32 amino acid residues) cysteine-rich peptides. They differ from most previously characterized conotoxins in their charge, and in their relatively high content of hydrophobic residues. From the pharmacological point of view three categories of toxins have been characterized so far: (1) neuronal acctylcholine receptor blockers; (2) sodium channel blockcrs; and (3) toxins that slow inactivation of sodium channels. In addition, recent observations in Lymnaea systems suggest the existence of a number of calcium channel blockers in molluscivorous Conus venoms. These toxins provide useful tools for neurobiologists working with molluscan models, and are extremely selective probes for ion channel structure and function.

Development and trends in the drug treatment of essential hypertension

A brief survey is given of the development of the drug therapy of essential hypertension over five decades, followed by a discussion on newer antihypertensive drugs and principles. Virtually all levels and elements of the sympathetic nervous system can be modulated by drugs in such a manner that elevated blood pressure is lowered, for instance with the use of central alpha 2-adrenoceptor agonists (clonidine, alpha-methyldopa), ganglioplegic drugs, peripheral adrenergic neurone blockers, and alpha- and beta-adrenoceptor antagonists. The beta-blockers have been maintained as a very major group of antihypertensive therapeutics. Among alpha-adrenoceptor antagonists, only the selective alpha 1-blockers are useful as antihypertensive drugs, although some interest has developed in newer alpha 2-adrenoceptor antagonists which are selective for postsynaptic alpha 2-adrenoceptors. Diuretics, in spite of some criticism, are still a cornerstone in antihypertensive drug treatment. Their position has been reinforced by the results of the recent Systolic Hypertension in the Elderly Program, Swedish Trial in Old Patients with Hypertension and Medical Research Council (Elderly) trials. Calcium antagonists have been extended by several new dihydropyridines which appear to be more vasoselective than the classical compounds. Various new ACE inhibitors have been introduced, but so far they have not clearly offered major advantages over the established compounds. Renin inhibitors and angiotensin II-receptor antagonists are being studied for their potential as antihypertensive drugs and they are also important because they may modulate the renin-angiotensin-aldosterone system. Inhibitors of neutral endopeptidase will cause an accumulation of endogenous atrial natriuretic peptide, and hence lower blood pressure by counteracting several effects of the renin-angiotensin-system. Potassium channel openers are vasodilators and potential antihypertensive drugs with additional anti-ischaemic activity.

Acute depolarization block of A10 dopamine neurons: interactions of morphine with dopamine antagonists

Extracellular single-unit recording techniques were used to determine the effects of morphine, administered either systematically (intravenous) or locally (microiontophoresis), on ventral tegmental area (A10) dopamine (DA) neuronal activity in animals pretreated with D1 (SCH 23390) or D2 (primozide) DA receptor antagonists. In rats pretreated with the D2 antagonist primozide, A10 DA neurons readily entered a state of apparent depolarization block in response to either i.v. or iontophoretically applied morphine. Whether the inactivation of DA neurons was induced by systemic or local morphine, it was reversed in 22 of 27 cases by iontophoretic administration of the inhibitory amino acid transmitter γ-aminobutyric acid (GABA), suggesting depolarization block as the underlying mechanism. Pretreatment of rats with the D1 antagonist SCH 23390 did not significantly alter the tendency of A10 DA neurons to enter apparent depolarization block in response to morphine. These data support recent behavioral evidence suggesting that the combination of systemic pimozide and ventral tegmental area morphine can result in depolarization inactivation of the mesoaccumbens DA reward system.

Increase of plasma neuropeptide Y-like immunoreactivity following chronic hypoxia in the rat.

In an attempt to understand the changes of circulating neuropeptide Y (NPY) during hypoxia, the plasma level of NPY was investigated by radioimmunoassay. Exposure of rats to hypobaric hypoxia at an altitude of 18,000 ft for 4 weeks causes an increase of pulmonary pressure and an elevation of plasma NPY-like immunoreactivity (NPY-LI). However, the systemic blood pressure was not elevated by this chronic hypoxia. Also, plasma noradrenaline (NA) estimated by chromatographic analysis (HPLC-ECD) was not markedly raised. Failure of bretylium and guanethidine, sympathetic neuron blockers, in reducing the plasma NPY-LI level of these rats ruled out the participation of adrenergic nervous terminals. Adrenal medulla seems responsible for this elevation of plasma NPY-LI because this magnitude disappeared in adrenalectomized rats. These data suggest that chronic hypoxia induced an elevation of circulating NPY from the adrenal gland of rats.

Electrophysiological, biochemical, and behavioral studies of acute haloperidol-induced depolarization block of nigral dopamine neurons

The electrophysiological, biochemical and behavioral responses produced by administration of haloperidol were studied in intact rats and in rats with 6-hydroxydopamine-induced partial lesions of the nigrostriatal dopamine pathway. In both control rats and rats tested four to 10 days postlesion, the electrophysiological response of nigral dopamine neurons to increasing doses of haloperidol consisted of either: (1) an increase in firing rate which reached a plateau at six to 10 spikes per second, or (2) no response (i.e., less than 20% change in firing rate). Administration of additional doses of haloperidol up to lethal levels did not elicit further changes in dopamine cell firing in these rats. In contrast, in 6-hydroxydopamine-treated rats tested four to six weeks postlesion, acute administration of haloperidol was not only more consistent in producing increases in dopamine cell firing rate, but also caused six out of seven dopamine neurons tested to cease firing upon entering a state of depolarization block. In all cases in which depolarization block was observed, dopamine cell firing was reinstated by either iontophoretic application of γ-aminobutyric acid or intravenous administration of apomorphine. In parallel studies, haloperidol caused an increase in the extracellular dopamine levels measured by microdialysis in the striatum of control rats, whereas administration of the same dose of haloperidol to 6-hydroxydopamine-treated rats four to six weeks postlesion did not elicit any change in extracellular dopamine levels. In addition, administration of haloperidol at a dose which was ineffective in control rats produced gross motor deficits in the 6-hydroxydopamine-treated rats when tested four to six weeks postlesion. These results show that 6-hydroxydopamine-induced dopamine depletions produce a time-dependent change in the responsivity of the nigrostriatal dopamine system to acute haloperidol administration. In this altered system, the induction of depolarization block of spike activity in nigral dopamine neurons by haloperidol was not associated with a corresponding decrease in extracellular dopamine levels measured in the striatum. However, it appeared that depolarization block did prevent haloperidol-induced increases in extracellular dopamine levels. The occurrence of depolarization block in the dopamine-depleted animal may limit the capacity of this system to respond to additional compromise, in spite of the compensatory processes that contribute to maintaining motor function.

Relative contributions of ATP and noradrenaline to the nerve evoked contraction of the rabbit jejunal artery. Dependence on stimulation parameters.

Isotonic contractions of the rabbit jejunal artery were evoked by perivascular nerve stimulation with trains of 10 or 100 stimuli at 2 Hz or 10 Hz. Short trains of stimuli elicited contractions that were totally resistant to alpha-adrenoceptor blockade (0.1 mumol/l prazosin) but blocked by alpha,beta-methylene ATP (1 mumol/l). A substantial noradrenergic component of contraction comprising about 50% of the total could be evoked by adjusting the stimulation parameters (increasing the frequency and/or number of stimuli in a train). The noradrenergic and the purinergic components are derived from sympathetic nerves as both were blocked by TTX and the adrenergic neurone blocker guanethidine (3 mumol/l). It is concluded that the contraction of the rabbit jejunal artery to short trains of stimuli is predominantly purinergic, a noradrenergic component only being revealed at higher frequencies of stimulation or during longer trains of stimuli. The purinergic component of contraction is derived from sympathetic nerves and not from a separate population of purinergic nerves.

Modules of cortical neurons and their "self-assembly".

The data we have by now accumulated on the cytoarchitectonics of the cerebral cortex, as well as published data, suggest that some of the neurons are structurally combined into compact clusters (ensembles, blocks), and that the majority of them participate in the construction of these clusters by directing the terminal branches of their axons to them. The collaterals of projection, associative, and callosal nerve cells, as well as the axons of interneurons which accomplish local interneuronal closures, can combine individual elements of the ensembles into a unified morphofunctional system. The collaterals of the axons of a block of neurons spread divergently to neurons disposed along the perimeter, while the axons of the latter converge reciprocally to the neurons of the cluster, forming a maximum (focus) of the arborization of the axonal terminals there; this makes it possible actively to isolate modules of nerve cells by accomplishing their self-assembly.

Clinical Atlas of Hypertension

Part 1 Epidemiology and natural history: measurement of blood pressure definitions of hypertension risks of hypertension determinants of blood pressure. Part 2 Mechanisms of blood pressure control: cardiac output and regulation venous circulation vasodilators and vasoconstrictors central regulation baroreceptors renin-angiotensin system other regulatory factors. Part 3 Pathogenesis and experimental models: experimental models physiology mechanisms of blood pressure control cellular changes. Part 4 Pathological consequences: vascular hypertrophy fibrinoid necrosis microangiopathic haemolytic anaemia arteriosclerosis atheroma cardiac effects CNS effects renal effects. Part 5 Known causes of hypertension: the nervous system the kidneys the endocrine system coarctation pregnancy drugs. Part 6 Clinical subgroups: children pregnancy the elderly hypertensive emergencies. Part 7 History and examination: medical, drug and family histories examination. Part 8 Investigation of the patient: urine and blood tests chest X-ray, ECG, ultrasound, pyelography, isotope scannings, CT scannings, plasma renin activity, gamma camera scanning and IVDSA pharmacological tests. Part 9 Drug action: diuretics - adrenoreceptor antagonists vasodilators calcium entry blockers inhibitors of the renin-angiotensin system - blockers centrally acting drugs ganglion blockers adrenergic neurone blockers new agents. Part 10 Treatment: data from the trials non-pharmacological methods - weight loss, sodium intake, potassium intake, calcium intake, alcohol intake, diet, exercise, yoga and relaxation pharmacological treatment - drug combinations, adverse effects special categories.

Effect of desipramine on norepinephrine metabolism in humans: interaction with aging

To determine whether differences in neuronal reuptake contribute to age-related changes of sympathetic nervous system activity, we compared norepinephrine (NE) release and metabolism during [3H]NE infusion and decay in six young (age 19-26 yr) and seven older (age 61-73 yr) healthy nonobese subjects. Subjects were studied on a control day and on a separate day after desipramine (DMI; 125 mg orally), a neuronal reuptake blocker. Compartmental analysis of plasma NE specific activity was used to determine several NE kinetic parameters. Plasma NE levels and NE spillover rates were higher in the elderly. Although plasma NE was unaffected by DMI in both age groups, both the metabolic clearance rate of NE from plasma and the rate of NE spillover into plasma fell in young and older groups during DMI. Furthermore, DMI dramatically lowered the mass of NE in the extravascular compartment and the rate of NE entry into the extravascular compartment. Thus neuronal uptake blockade has major effects on NE release as well as NE metabolism in humans. However, age-related differences in NE kinetics cannot be explained by differences in neuronal uptake.

Pavlovian conditioning in the rabbit during inactivation of the interpositus nucleus.

1. We have examined the role of the anterior interpositus nucleus (AIP) of the cerebellum in Pavlovian conditioning of the nictitating membrane response (NMR) of the rabbit with the use of reversible brain lesions produced by the local anaesthetic lidocaine. Previous experiments have demonstrated that destructive lesions of the AIP prevent the performance of conditioned NMRs (CRs). Microinjections of lidocaine into the AIP were used in the present experiment to determine whether the deficit in the performance of CRs resulted from a deficit in learning or memory. 2. A 3-phase procedure was employed to determine whether associative learning required the function of the AIP. In phase 1, rabbits were trained to make CRs to a flashing-light conditioned stimulus (CS) that was paired with an air-puff unconditioned stimulus (UCS) directed at the cornea. In phase 2, the AIP was anaesthetized during a session of conditioning in which a tone CS was paired with the UCS. Presentations of the light CS were interpolated throughout the tone conditioning in order to monitor the degree to which CRs were impaired by lidocaine. Phase 3 occurred after the effects of the lidocaine had dissipated and consisted of a test of retention to determine whether learning occurred during phase 2 but could not be expressed because of a performance deficit resulting from the inactivation of the AIP. 3. Infusion of lidocaine into the AIP abolished CRs to the light CS and prevented the performance of CRs to the tone CS in phase 2. The effect of the infusion was specifically due to a conduction block of neurons and/or fibres in the lateral aspect of the AIP. The infusion of lidocaine into regions surrounding the AIP did not affect CRs elicited by the light CS or prevent acquisition of CRs to the tone. Infusions of saline directly into the AIP did not impair the performance of CRs to either the tone or light CS. Quantitative analysis of diffusion revealed that the abolition of CRs was accompanied by anaesthetization of the AIP. 4. The retention test in phase 3 indicated that learning occurred normally during phase 2 when the AIP was inactivated and performance was abolished. When the function of the AIP was restored and performance had recovered, the subjects demonstrated a frequency of CRs to the tone CS that was indistinguishable from control subjects whose performance had never been impaired. 5. The CRs observed during the retention test provided an unequivocal measure of associative learning.(ABSTRACT TRUNCATED AT 400 WORDS)

Autonomic innervation of the circular and longitudinal layers in swine myometrium.

Experiments were conducted on uteri excised from 44 gilts to clarify the autonomic innervation of the longitudinal (LM) and circular muscle (CM) layers of the myometrium. Functionally and biochemically, the two layers differed markedly in their reaction to transmitters. On transmural nerve stimulation (TMS) of isolated LM strips, relaxation was elicited and spontaneous contraction was inhibited in proportion to the electrical frequency imparted. Although the relaxation was accompanied by preliminary contraction in half the LM preparations tested, the relaxation phase predominated in all the LM strips. Relaxation was sensitive to carteolol (beta-blocker) and to guanethidine (adrenergic neuron blocker), whereas the contractile response in LM was sensitive to phentolamine (alpha-adrenergic antagonist). In the CM strips, contraction resulted from TMS, and though not responsive to hexamethonium, the contractions were enhanced by neostigmine and abolished by atropine. The amount of norepinephrine (NE) and the intensity of dopamine beta-hydroxylase activity were about 2.5 times greater in LM than in CM. Conversely, choline acetyltransferase activity, associated exclusively with cholinergic nerves, was about 8 times more intense in the CM. In line with the TMS responses, alpha-receptor-mediated contractions initiated by NE were enabled exclusively in the LM. Furthermore, beta-receptor-mediated inhibition elicited by isoproterenol was also paramount in the LM. We conclude that there are layer-specific variations in the functional innervation of the myometrium of the nulliparous pig uterus such that CM layer is primarily endowed with cholinergic innervation and the LM layer with adrenergic innervation.

Nicotine-induced release of noradrenaline and neuropeptide Y in guinea-pig heart: role of calcium channels and protein kinase C

The role of calcium, calcium influx through calcium channels, and activation of protein kinase C for the nicotine-induced release of noradrenaline and of the sympathetic co-transmitter neuropeptide Y (NPY) was investigated in the guinea-pig isolated perfused heart. In the coronary venous overflow noradrenaline and NPY were determined by high-pressure liquid chromatography and radioimmunoassay, respectively. In the presence of extracellular calcium (1.85 mmol/l) nicotine (1-100 mumol/l) evoked a concentration-dependent overflow of both transmitters with a molar ratio of approximately 1500 (noradrenaline):1 (NPY). The nicotine-induced (100 mumol/l) overflow of noradrenaline and NPY was in a linear manner related (r = 0.79 and 0.90, respectively; p less than 0.05) to the extracellular calcium concentration (0-1.85 mmol/l), and it was prevented by calcium-free perfusion. The L-type calcium channel blocker felodipine (100 nmol/l) did not affect the nicotine-induced (100 mumol/l) transmitter overflow. On the other hand, the neuronal (N-type) calcium channel blockers omega-conotoxin (100 nmol/l) and cadmium chloride (50 mumol/l) reduced the nicotine-induced (100 mumol/l) transmitter overflow to 20% of the control value, suggesting a role of N-type calcium channels in mediating the calcium influx for the nicotine-induced transmitter release. The nicotine-induced (30 mumol/l) overflow of both transmitters was two- to three-fold increased by activation of protein kinase C (phorbol 12-myristate 13-acetate; 100 nmol/l). The transmitter overflow was unaffected by 4 alpha-phorbol 12,13-didecanoate (100 nmol/l), a phorbol ester which does not stimulate protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)