Effects of omega-conotoxin GVIA on autonomic neuroeffector transmission in various tissues

1. The effects of omega-conotoxin GVIA (conotoxin), a potent inhibitor of neuronal N-type Ca2+ channels, have been examined on responses to stimulation of noradrenergic, cholinergic and non-adrenergic, non-cholinergic (NANC) nerves in a range of isolated tissues to investigate the role of conotoxin-sensitive Ca2+ channels in neurotransmission. 2. Contractions elicited by field stimulation of noradrenergic nerves in rat and mouse anococcygeus muscles, rabbit ear artery and rat vas deferens (epididymal portion) were inhibited by conotoxin. Responses to noradrenaline, and to adenosine triphosphate in the vas deferens, were not affected. 3. Positive chronotropic responses to field stimulation of noradrenergic nerves were inhibited by conotoxin in rat and mouse atria, but responses to noradrenaline and tyramine were not affected. 4. The stimulation-induced release of noradrenaline was inhibited by conotoxin in the rabbit ear artery and in rat and mouse atria. 5. Relaxations in response to stimulation of the noradrenergic perivascular mesenteric nerves were reduced or abolished by conotoxin in rat and rabbit jejunum. The response to noradrenaline in rat jejunum was not affected. 6. Contractions elicited by stimulation of cholinergic nerves were inhibited by conotoxin in rat jejunum and mouse ileum (perivascular mesenteric nerves), and in guinea-pig taenia caeci (field stimulation). Responses to acetylcholine in rat jejunum and mouse ileum were not affected. 7. Contractions elicited by stimulation of the cholinergic plus NANC pelvic nerves were inhibited by conotoxin in rabbit colon, and to a lesser extent in guinea-pig colon. The stimulation-induced contraction of the guinea-pig colon was inhibited by conotoxin by a greater proportion in the presence than in the absence of atropine. Responses to acetylcholine were not affected in the rabbit colon but were slightly reduced in the guinea-pig colon. 8. Relaxations in response to field stimulation of NANC nerves were inhibited by conotoxin in guinea-pig taenia caeci and rat gastric fundus strips, and in rat anococcygeus muscle when the tone was raised by guanethidine but not when it was raised by carbachol. The relaxations produced by sodium nitroprusside in the rat gastric fundus and anococcygeus were not affected. 9. Contractions of the rat bladder elicited by stimulation of the peri-urethral nerves, which are NANC- and cholinergically mediated, were relatively insensitive to inhibition by conotoxin. The response were almost completely abolished by tetrodotoxin. 10. The conotoxin-induced inhibitions of responses to nerve stimulation developed slowly and persisted after removal of conotoxin. The responses were almost completely abolished by tetrodotoxin. 10. The conotoxin-induced inhibitions of responses to nerve stimulation developed slowly and persisted after removal of conotoxin. 11. The inhibitory effect of conotoxin was inversely proportional to the frequency of stimulation (in several preparations) and to the Ca2+ concentration in the bathing solution (in rat vas deferens). These observations suggest that the inhibition by conotoxin of the Ca2+ influx required for excitation-secretion coupling in autonomic nerve terminals is not absolute, and can be overcome by repeated stimulation or by raising the Ca2 + concentration.

The effect of endothelin on noradrenergic transmission in rat and guinea-pig atria

Pre-and postjunctional effects of 10 nM endothelin have been studied in rat and guinea-pig spontaneously beating isolated atria. Endothelin increased the rate and force of contraction of atria from both species, but decreased the positive inotropic and chronotropic responses to stimulation of intramural sympathetic nerves by approximately 60% in rat and by 10-15% in guinea-pig atria. The stimulation-induced release of noradrenaline from either rat or guinea-pig atria was not significantly changed by endothelin.

Paradoxical effects of endothelin on cardiovascular noradrenergic neurotransmission

1. Pre- and postjunctional effects of endothelin (1-10 nmol/L) have been studied in the rabbit isolated ear artery and in rat isolated atria. 2. Endothelin produced concentration-dependent increases in arterial perfusion pressure, and had positive chronotropic and inotropic effects in rat atria. 3. Vasoconstrictor responses of the arteries to sympathetic nerve stimulation were reduced by 1 nmol/L endothelin and abolished by 10 nmol/L endothelin. In rat atria, the chronotropic responses to nerve stimulation were markedly reduced by 10 nmol/L endothelin. 4. In rabbit ear artery, vasoconstrictor responses to noradrenaline were enhanced by 1 nmol/L endothelin, but were reduced by 10 nmol/L endothelin. In rat atria, endothelin reduced the chronotropic response to isoprenaline. 5. Endothelin (10 nmol/L) increased the stimulation-induced release of radioactivity in arteries and atria labelled with [3H]-noradrenaline by 91% and 23%, respectively. 6. The pre- and postjunctional effects of endothelin persisted in both arterial and atrial preparations for at least 30 min after its removal.

Recording of monophasic action potentials in the horizontally perfused guinea pig heart. An in vitro method to study drug-induced changes in cardiac electrophysiology

An in vitro technique has been developed for the recording of monophasic action potentials to enable the measurement of changes in the duration of repolarization and in rise time produced by known concentrations of drugs and ions. Guinea pig hearts were perfused horizontally at constant pressure (60 cm H2O) and temperature (37 degrees C) with Krebs-Henseleit buffer. Epicardial monophasic action potentials were recorded from the right ventricular base using a bipolar Ag/AgCl electrode to which a suction pressure of 400 mm Hg was applied. The monophasic action potential signals had smooth depolarization and repolarization phases with amplitudes of 25-65 mV; repeated measurements of monophasic action potential duration at the 50, 75, and 90% repolarization levels (MAPD 50, 75, and 90) and rise time, determined by computer analysis, were reproducible for at least 150 min of perfusion. There was an excellent linear correlation between heart rate and monophasic action potential duration. The ability of the method to detect drug-induced changes was confirmed using clofilium (10(-9) to 10(-5) M), which significantly prolonged monophasic action potential duration 50, 75, and 90 in a concentration-dependent manner, and tocainide (3 x 10(-4) M), which significantly decreased monophasic action potential duration 50, 75, and 90 and increased rise time.

Evaluation of the addition of cromolyn sodium to bronchodilator maintenance therapy in the long-term management of asthma

Three hundred ninety-seven patients, aged 5 to 63 years, took part in a year-long international multicenter, double-blind, placebo-controlled trial. The patients, whose asthma was considered not adequately controlled, were divided into two groups according to their principal medication at entry (group A, oral and/or inhaled beta 2-bronchodilators; group B, methylxanthines, with or without beta 2-agonists) and randomly allocated to additional treatment with cromolyn sodium (metered-dose inhaler, 2 mg, four times a day, or capsules, 20 mg, four times a day) or matching placebo. A 2-month baseline preceded 10 to 12 months of treatment. After 4 to 8 weeks of treatment, patients were encouraged to reduce bronchodilator usage. Patients used diary cards to record asthma severity, sleep difficulty, morning and evening peak expiratory flow rates, days of disruption of normal activity, use of test treatments, and concomitant medication. Significant differences favoring cromolyn sodium (p less than 0.05 and better) were observed for most of the treatment period in respect to (1) asthma severity, (2) morning and evening peak expiratory flow rates, and (3) days of disruption of normal activity. Patients receiving cromolyn sodium experienced fewer exacerbations and tended to use less concomitant medication than patients receiving placebo. Patients' opinions of treatment significantly favored cromolyn sodium. These results demonstrate the value of the addition of cromolyn sodium to existing therapy in the long-term management of asthma and endorse its use as a first-line treatment.

Rubella immunity in 14-18 year old females: assessment in a city practice

We have undertaken a pilot study to assess the rubella immunity status of 88 females aged 14-18 years in a Dunedin suburban general practice. According to practice records, only 60% were found to have a record of immunisation. The low response rate of only 58% of those requested to participate was of concern given the publicity about the dangers of the congenital rubella syndrome. All the girls who responded were shown to be immune against rubella. While 40% of the study group apparently escaped immunisation recording, they nonetheless acquired immunity. One explanation for this finding may be incomplete record keeping and transmission of the vaccination history of the patient. These results remind us that we should not be complacent as to the efficiency of our present immunisation efforts and to be alert to opportunities for ensuring protection in the patient population.

A histological method for studying the effects of drugs on mediator-induced airway microvascular leakage in rodents

Methods are described for studying the effects of drugs on increases in tracheobronchial microvascular permeability (leakage) induced by inflammatory mediators. A model in conscious guinea pigs (in which the leakage effects resulted from circulating mediator) and a model in anesthetized rats (in which the leakage effects resulted from application of the mediator to the airway lumen) are described. Inhibitor drugs were given i.v. 2 min before the mediator. In guinea pigs either histamine or leukotriene D4 (LTD4) and colloidal carbon (C, the tracer molecule for leakage) were administered together iv.; in rats 5-hydroxytryptamine (5-HT, 100 micrograms) was injected intratracheally followed by i.v. colloidal carbon. Tracheal and bronchial tissues were removed 15 min later from the killed animals and prepared for histology, and the number of C-labeled microvessels in the mucosal/submucosal region of 7-micron sections was counted. In guinea pigs, leakage produced by LTD4 or histamine was related to the dose administered and the relative potency of LTD4:histamine was approximately 123:1, on a molar basis. Leakage caused by histamine, but not by LTD4, was prevented by mepyramine (1 mg/kg) and LTD4-induced leakage was prevented by FPL 55712 (1 mg/kg). Terbutaline (1 mg/kg) attenuated leakage to both mediators but never abolished it. In rats, leakage was also seen to 5-HT, which was prevented by methysergide (1 mg/kg) and markedly attenuated by ketanserin (1 mg/kg) or by terbutaline (1 mg/kg). It is suggested that the colloidal carbon tracer technique has application to pharmacological studies designed to examine the effects of drugs on mediator-induced permeability to macromolecules in the tracheobronchial microcirculation.

Characterization of the O-methylation of catechol oestrogens by intact rabbit thoracic aorta and subcellular fractions thereof

In the present study we investigated the O-methylation of catechol oestrogens by intact rabbit thoracic aorta and subcellular fractions thereof. The O-methylation of 2-hydroxyoestradiol (2OHE2) and 2-hydroxyoestriol (2OHE3) displayed saturation kinetics in the intact tissue. The apparent Km and Vmax values for the O-methylation of 2OHE2 were determined to be 0.91 mumol/l and 104 pmol g-1 min-1, respectively, when 2OHE2 was used as substrate; and 1.14 mumol/l and 188 pmol g-1 min-1 when 2OHE3 was used as substrate. The inhibitors of the extraneuronal uptake process (viz; phenoxybenzamine 33 mumol/l; normetanephrine, 46 mumol/l; and deoxycorticosterone acetate 27 mumol/l) failed to inhibit the O-methylation of either 2OHE2 (3.4 mumol/l) or 2OHE3 (3.4 mumol/l) in intact segments of the rabbit thoracic aorta. (-)-Isoprenaline (40 mumol/l) abolished the O-methylation of 2OHE2 (3.4 mumol/l) and markedly reduced that of 2OHE3 (3.4 mumol/l). Pretreatment of tissues with phenoxybenzamine (33 mumol/l) partially restored the O-methylation of 2OHE2 and 2OHE3 in the presence of (-)-isoprenaline (40 mumol/l). The O-methylation of 2OHE2 (5 mumol/l) was significantly reduced in segments of aorta in which the endothelium was removed. The latter reduction could not be attributed to damage to components of the vessel media. The O-methylation of 2OHE2 and (-)-isoprenaline by subcellular fractions of the rabbit aorta also was examined. Both the microsomal and cytosolic fractions were shown to O-methylate 2OHE2 and (-)-isoprenaline, providing evidence for the existence of membrane-bound and soluble forms of COMT in the rabbit aorta. The O-methylation of 2OHE2 by cytosolic and microsomal fractions of the aorta was determined and compared to that of (-)-isoprenaline. The kinetic constants for the O-methylation of 2OHE2 by cytosolic (Km: 0.27 mumol/l; V max: 112 pmol g-1 min-1) and microsomal (Km: 0.15 mumol/l; Vmax: 161 pmol g-1 min-1) fractions were similar. In contrast, the kinetic constants for the O-methylation of isoprenaline by cytosolic (Km: 121 mumol/l; Vmax: 174 pmol g-1 min-1) and membranal (Km: 0.91 mumol/l; Vmax: 105 pmol g-1 min-1) fractions were very different. It is concluded that catechol oestrogens are excellent substrates for catechol-O-methyltransferase (COMT) in the rabbit aorta. Their O-methylation can occur in endothelial structures as well as in the smooth muscle-containing medial sections of the vessel.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac arrest and heart attack: an evaluation of lay knowledge

Random samples of Dunedin residents were interviewed before and after the publication in the telephone directory of an information sheet on cardiac arrest and heart attack. Most subjects had heard of both cardiac arrest and heart attack but almost half of the samples were either wrong in identifying which was the more serious or they did not know. One-third of the post-publication sample had looked at the information sheet. Results indicate limited awareness of all but the most elementary medical facts and the existence of a variety of confusions and misconceptions in the two samples. Problems of comprehension and remembering are discussed in the context of the communication of medical information by doctors and health educators.

Evidence that 6-hydroxydopamine is an inhibitor of catechol-O-methyltransferase in intact tissue

The effect of in-vitro sympathetic denervation on the O-methylation of 2-hydroxyoestradiol was examined using the rabbit thoracic aorta. Aortic segments were exposed to 6-hydroxydopamine (400 mg litre-1, 10 min), incubated in 2-hydroxyoestradiol (5 microM, 60 min), and the 2-methoxyoestradiol formed was quantified using HPLC with electrochemical detection. Pre-exposure to 6-hydroxydopamine reduced O-methylation by 90% in intact aortic strips. However, O-methylation was also reduced (81%) in rabbit aorta that had been surgically denervated before exposure to 6-hydroxydopamine. Furthermore, the O-methylation of 2-hydroxyoestradiol (20 microM, 15 min) by partially purified soluble catechol-O-methyltransferase was inhibited by 6-hydroxydopamine (400 mg litre-1) by 95% and 51% in the absence and presence of antioxidant, respectively. These results suggest that the inhibition of catechol-O-methyltransferase by 6-hydroxydopamine reported for the purified enzyme, applies to the intact tissue and that the inhibition is dependent on oxidation of the 6-hydroxydopamine. Subsequent experiments using dialysis techniques demonstrated that the inhibition of soluble catechol-O-methyltransferase by 6-hydroxydopamine was irreversible in part, but the degree of irreversibility was influenced by pH and by the extent of in-vitro oxidation of 6-hydroxydopamine.

Kinetic constants of isoprenaline and corticosterone for extraneuronal uptake in different cell types from various tissues

Extraneuronal uptake of isoprenaline was studied in a number of different, histologically identified, cell types: trachealis smooth muscle cells, vascular smooth muscle cells and myocardial cells. Segments of cat, rat or rabbit trachea, dog coronary artery or cat atria were incubated in isoprenaline, in the presence of U-0521 (100 mumol l-1) to inhibit catechol-O-methyltransferase. The intensities of formaldehyde-induced fluorescence (due to accumulation of isoprenaline) were measured, using microphotometry, in the appropriate cells in histological sections of the tissue. Endogenous fluorescence in adrenergic nerves was removed by pretreatment of rats with 6-hydroxydopamine and of cats and rabbits with reserpine. Segments of dog coronary artery were incubated with 6-hydroxydopamine in vitro to remove neuronal fluorescence. This treatment was also shown to be effective in guinea-pig trachea without any influence on the determination of the kinetic parameters of isoprenaline uptake in the trachealis smooth muscle cells. Fluorescence in all cell types studied was shown to represent isoprenaline which had accumulated by extraneuronal uptake, in that fluorescence was reduced by drugs which inhibit extraneuronal uptake (corticosterone, normetanephrine, metanephrine and/or phenoxybenzamine), by exposure to a K+-Krebs solution and by incubating tissues in isoprenaline at 0 degree C rather than 37 degrees C. In each cell type, isoprenaline uptake obeyed Michaelis-Menten saturation kinetics, both in the absence and presence of corticosterone. Corticosterone was a competitive inhibitor of isoprenaline uptake in all the cell types.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular transport and packaging of prolactin: a quantitative electron microscope autoradiographic study of mammotrophs dissociated from rat pituitaries

Dispersed pituitary cells prepared from estrogen-treated female rats were subjected to pulse labeling with [3H]leucine (5 min) followed by a chase incubation (up to 3 h) in order to study intracellular transport of PRL in mammotrophs. Sites of synthesis, rates of transport, and sites of packaging and storage of PRL were determined by quantitative electron microscopic autoradiography. Results of grain counts show that label is initially (end of pulse) distributed randomly over the rough endoplasmic reticulum (ER), but rapidly (5--15 min of chase) moves to the stacked Golgi cisternae where concentration into secretion granules takes place. The label moves successively from small (Type I) immature granules (15--55 min of chase) to large (Types II and III) polymorphic granules (55--115 min) in the Golgi region, to rounded or ovoid mature (Type IV) granules (55--185 min) usually found in the peripheral cytoplasm, indicating that these types of granules represent successive stages in granule concentration and assembly. Analysis of the relative grain density (percentage of total grains/percentage of total area) confirmed that there was progressive concentration (up to 20--150 times) along the transport route with the concentration lowest in the ER, higher in the Golgi, and highest in immature and mature secretion granules. These data indicate that synthesis of PRL occurs randomly in the ER, transport to the Golgi occurs rapidly (within 5--10 min), and is completed rapidly (90% within 15--20 min), and concentration into granules and aggregation of small granules into larger forms also occurs rapidly (by 15--20 min), but goes on over a prolonged period of time (up to 3 h). Use of dispersed cells has allowed a more precise determination of the location and kinetics of steps in the intracellular processing of PRL than has been possible previously using other systems.

Alterations of the glomerular epithelium in acute aminonucleoside nephrosis. Evidence for formation of occluding junctions and epithelial cell detachment

The visceral glomerular epithelium of rats made nephrotic by daily injections of puromycin aminonucleoside was examined from the time of onset of proteinuria (day 6) to the time when many animals die (day 15) in order to establish the chronology of the pathologic alterations which occur during the course of the disease. In addition, the structure of the residual epithelial slits was examined using special fixatives and freeze-fracture. Changes seen early in the disease (7 to 9 days) are: (1) a reduction in the number of foot processes and filtration slits; (2) occurrence of occluding junctions in many of the residual slits coupled with displacement of the slit diaphragms; (3) thinning of the dense central portion of the basement membrane (lamina densa) with a corresponding widening of the space (lamina rara externa) between it and the epithelium; (4) heightened epithelial pinocytosis with increased numbers of protein absorption droplets or lysosomes. In freeze-fracture preparations the occluding junctions were seen to be limited in extent and made up of only a few strands, indicating they are incomplete and represent occluding maculae or fasciae rather than zonulae. Later on in the disease (10 to 15 days) no further changes in the number or arrangement of slits is evident, but other alterations occur: (1) denuded regions of basement membrane are seen where there is initially partial and eventually complete detachment of the epithelium from the basement membrane; (2) increasing numbers of large vacuoles or phagosomes and decreasing numbers of fully condensed lysosomes are present; and (3) basement membrane-like material is seen in the spaces between the partially detached epithelium and basement membrane. The new findings in this study are: (1) the clarification of early (reversible) versus late (probably irreversible) changes in the glomerular epithelium in a acute aminonucleoside nephrosis; (2) delineation of the structure of the residual epithelial slits; (3) the description of progressive loosening of the attachment between the epithelium and the basement membrane leading to focal or complete epithelial cell detachment; (4) the presentation of evidence indicating that exhaustion of the lysosomal system of the glomerular epithelium (in protein absorption and concentration) occurs late in the disease. The available evidence is summarized and indicates that the glomerular basement membrane, the main glomerular filter, is defective in aminonucleoside nephrosis and allows increased protein leakage. However, it seems likely that the main site of action of aminonucleoside is on the epithelium leading to the production of defective basement membrane.

Health service planning in a British new town

The initial postwar development of new towns in Britain took place at a time when the present British National Health Service was in its infancy, and few attempts were made to integrate health service planning into the overall planning process. The more recent new towns have been the object of better social planning and, at the same time, the National Health Service has been substantially unified, at first functionally and, in 1974, administratively. In consequence, attempts have been made to use the opportunities which such towns present for planning health services in a comprehensive and integrated manner. The evolution of a planning and implementation structure for health services in Milton Keynes, a new town with a target population of 250,000, is described, together with some of the implications for the administratively unified National Health Service which came into being in 1974.