Human alpha-calcitonin gene-related peptide stimulates adenylate cyclase and guanylate cyclase and relaxes rat thoracic aorta by releasing nitric oxide

1. The signal transduction pathway for vasorelaxation induced by human alpha-calcitonin gene-related peptide (human alpha-CGRP) was studied in rat thoracic aortic rings preconstricted with noradrenaline (10(-7) M). 2. Vasorelaxation by human alpha-CGRP was inhibited by haemoglobin (10(-6) M) and methylene blue (10(-5) M) but was unaffected by ibuprofen (10(-5) M). 3. Acetylcholine caused a 16 fold increase in levels of guanosine 3':5'-cyclic monophosphate (cyclic GMP) with levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) being unaltered. Human alpha-CGRP caused a 12 fold increase in levels of cyclic GMP but, in contrast to acetylcholine, evoked a 2.5 fold rise in levels of cyclic AMP. The rises in cyclic nucleotides evoked by human alpha-CGRP and acetylcholine were dependent on the presence of an intact endothelium. 4. NG-nitro-L-arginine (L-NOARG: 10(-5) M), which inhibits nitric oxide synthetase, inhibited the relaxant response to human alpha-CGRP and cyclic GMP accumulation without affecting the cyclic AMP accumulation. 5. The data presented in this paper suggests that human alpha-CGRP relaxes the rat thoracic aorta by releasing nitric oxide and stimulating guanylate cyclase. The stimulation of adenylate cyclase by human alpha-CGRP probably precedes the activation of nitric oxide synthase but could be unrelated to the relaxant response.

Novel signal transduction pathway mediating endothelium-dependent beta-adrenoceptor vasorelaxation in rat thoracic aorta

1. Isoprenaline (3 x 10(-8)-10(-5) M), salbutamol (3 x 10(-7)-10(-4) M) and forskolin (3 x 10(-9)-3 x 10(-7) M) relaxed rat isolated thoracic aortic rings contracted with noradrenaline (10(-7) M). Removal of the endothelium from the aortic rings abolished the effect of acetylcholine (10(-6) M) and completely prevented the vascular relaxation induced by isoprenaline, salbutamol or forskolin. 2. The isoprenaline concentration-relaxation curve was shifted in parallel to the right about 10 fold by propranolol (3 x 10(-7) M) with no change in the maximum response, showing that the relaxation was mediated by a beta-adrenoceptor. 3. The inhibitor of nitric oxide synthesis, NG-nitro-L-arginine (L-NOARG; 10(-5) M), shifted the isoprenaline relaxation curve to the right and reduced the maximum response. 4. Isoprenaline (10(-6) M) relaxed noradrenaline-induced tone by approximately 95% and at the same time increased levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) 4 fold and guanosine 3':5'-cyclic monophosphate (cyclic GMP) 12 fold in the aortic rings. Sodium nitroprusside (3 x 10(-8) M) relaxed noradrenaline-evoked tone by 82% without changing levels of cyclic AMP but raised cyclic GMP 19 fold. 5. Forskolin (10(-7) M) relaxed noradrenaline-induced tone by approximately 41% and, like isoprenaline, increased levels of cyclic AMP (2.5 fold) and cyclic GMP (12 fold) in the aortic rings. 6. Removal of the endothelium abolished the relaxant effects of isoprenaline (10(-6) M) and also the associated accumulation of cyclic AMP and cyclic GMP.7. L-NOARG (10- M) inhibited the relaxant responses and accumulation of cyclic GMP induced by isoprenaline (10-6 M) and forskolin (10- M) without affecting the associated cyclic AMP accumulation.8. It is concluded that, in the rat aorta, isoprenaline acts through a P-adrenoceptor on the endothelium to raise cyclic AMP and that this may, directly or indirectly, release nitric oxide to evoke vascular relaxation via the increase in cyclic GMP. The importance of this novel transduction pathway for cardiovascular regulation remains to be determined.

Eye-tracking dysfunction in the affective psychoses and schizophrenia

Smooth pursuit eye movements to a sinusoidally moving target were recorded using the electro-oculogram in 49 subjects with bipolar disorder, 19 with major depressive disorder and 61 with definite schizophrenia, and compared with 145 normal controls. The signals were analysed in the frequency domain to yield a signal to noise ratio that is known to relate to accuracy of smooth pursuit. Smooth pursuit was found to be significantly poorer in schizophrenics than in bipolars, major depressed or controls. Eye-tracking performance was independent of the effects of neuroleptics, tricyclic antidepressants or lithium, and was not altered by the severity of depression in the affective psychoses. There was a small, but significant worsening of smooth pursuit with age in controls and schizophrenics, but this did not account for the group differences. The results support the view that among the major psychoses eye-tracking dysfunction is specific to schizophrenia.

Nitric oxide synthesis inhibitors attenuate calcitonin gene-related peptide endothelium-dependent vasorelaxation in rat aorta

The effect of inhibitors of nitric oxide synthesis were examined on the endothelium-dependent relaxation induced by acetylcholine and human alpha-calcitonin gene-related peptide (CGRP) on rat isolated aortic rings preconstricted with noradrenaline. The endothelium-dependent vasorelaxation induced by acetylcholine and CGRP was inhibited by NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine (L-NOARG) in a concentration-related fashion. The inhibition of endothelium-dependent relaxation by L-NMMA and L-NOARG was partially reversed by L-arginine but not by D-arginine for both acetylcholine and CGRP. The data presented suggests that CGRP, like acetylcholine; relaxes the rat aorta via the release of nitric oxide.

Acoustic reflectometry for airway measurement. Principles, limitations and previous work

Acoustic pulse reflectometry is a relatively recent technique which allows the non-invasive measurement of human airways. The technique consists of guiding an acoustic impulse through the subject's mouth and into the airway. Suitable analysis of the resulting reflection (the 'echo') allows a reconstruction of the area-distance function. The non-invasive nature of the technique offers significant advantages over the established methods of x-ray cephalometry and CT scanning, and makes it very attractive for the investigation of ENT problems and sleep apnoea, and in the anaesthetic management of patients. This paper describes the theory and limitations of acoustic reflectometry, discusses previous work, and suggests some modifications: it is currently being implemented clinically.

Stasis oedema in the elderly: are diuretics necessary?

Diuretic therapy was discontinued in 15 elderly patients. None of these patients had evidence of uncontrolled cardiac failure or hypertension, and they all had received diuretics long-term. Two patients required resumption of diuretics due to the development of cardiac failure or severe leg oedema. In the remaining 13 patients, mean leg volume increased by 8.2%. Discontinuation of diuretic therapy in elderly patients is associated with a small but significant worsening of lower limb oedema.

A diathermy suppression filter for external pacemakers

Some patients undergoing cardiothoracic surgery require cardiac pacing. Surgical diathermy interferes with the operation of external pacemakers, and can cause a loss of cardiac output. The addition of a simple two-stage LC filter to the front end of the pacemaker enables cardiac output to be maintained during the use of surgical diathermy. (Although this article refers specifically to the Devices E4160 series pacemakers, the filter can, in principle, be used with any external pacemaker.

Automatic test equipment for rechargeable batteries

An automatic charger for the testing of a wide range of nickel cadmium and lead acid rechargeable batteries is described.

[Pharmacology of various aminosteroidal muscle relaxants]

A large number of analogues of pancuronium and vecuronium have been tested for neuromuscular blocking and other actions in anaesthetized cats, dogs, pigs and monkeys in an attempt to find a nondepolarizing substitute for succinylcholine. The results demonstrated an inverse relationship between dose and brevity of action; that is to say that grief duration was found only among compounds of relatively low potency. Two compounds given the code numbers Org 7617 and Org 9616 were found to possess promising properties. Both compounds are 17-butyrate analogues of vecuronium. Org 9616 also has an allyl group, in place of the methyl group, attached to the quaternary nitrogen at position 16. Both compounds have time courses similar to that of succinylcholine. They do not release histamine or produce ganglion block, and they are both considerably less potent than pancuronium in blocking the cardiac vagus. Both may produce a small fall in blood pressure. Electrophysiological analysis shows that neither compound is expected to occlude the receptor-operated ion channels of the motor endplate in concentrations likely to be achieved clinically.

Comparison of potassium hydroxide digestion and a modified Kato technique for the semi-quantitative estimation of Schistosoma mansoni eggs in faeces

A simple method for the semi-quantitative estimation of eggs of Schistosoma mansoni in stools, based on digestion of faeces in 4% potassium hydroxide (KOH), is described. The relative performance of KOH digestion and a modified Kato method showed that the former was more sensitive and that the KOH/Kato ratio for the geometric mean number of eggs per gram, in stools positive by both methods, was 3.51.

Human alpha-calcitonin gene-related peptide (CGRP) is a potent vasodilator in human mesenteric vasculature

1. The effect of human alpha-calcitonin gene-related peptide (CGRP) and sodium nitroprusside have been measured on human isolated mesenteric vasculature and on rings of human superior mesenteric artery and saphenous vein. 2. When noradrenaline (10(-5) M) was used as the vasoconstrictor in preparations perfused with Krebs solution at constant flow, human alpha-CGRP was 10 times more potent than sodium nitroprusside in evoking dose-dependent falls in perfusion pressure. 3. Human alpha-CGRP and sodium nitroprusside were about equipotent at relaxing rings of superior mesenteric artery contracted by noradrenaline (10(-6) M). When the tone of saphenous vein rings was raised by noradrenaline (10(-6) M), human alpha-CGRP did not relax the vascular smooth muscle. 4. The results show that human alpha-CGRP is a potent vasodilator in human arterial preparations and may act preferentially on arterioles rather than large arteries.

Central cardiovascular effects of calcitonin gene-related peptide: interaction with noradrenaline in the nucleus tractus solitarius of rats

The haemodynamic responses to microinjections of rat or human calcitonin gene-related peptide (CGRP) into the nucleus tractus solitarius (NTS) of rats were studied. 40 fmol rCGRP did not significantly modify cardiovascular parameters, but 0.2 pmol decreased blood pressure and heart rate (HR), whereas 2 pmol produced a pressor response with no effect on HR. hCGRP elicited a transient fall in blood pressure when administered at the highest dose (2 pmol), but had no effects when given at 0.2 pmol. A possible functional relationship with catecholamines was also investigated. The hypotensive response to 20 nmol noradrenaline (NA) was significantly modified by simultaneous administration of a low dose (40 fmol, ineffective alone) of rCGRP. When rCGRP (40 fmol) was coinjected simultaneously with an ineffective dose (10 pmol) of NA, a hypotensive response was observed. Our results provide evidence that rCGRP may play a role in the control of cardiovascular homeostasis in the NTS, and suggest a functional interaction between this peptide and NA.

A microvolt calibrator

A simple, versatile calibrator for use with electrophysiological instrumentation is described. A novel feature of the device is the simulation of patient electrode resistances.

Postjunctional inhibition of contractor responses in the mouse vas deferens by rat and human calcitonin gene-related peptides (CGRP)

The effects of rat and human alpha-calcitonin gene-related peptide (CGRP) were compared in the mouse and rabbit isolated vas deferens preparation contracted by either field stimulation or acetylcholine. The peptides were about equipotent at inhibiting twitch responses of the mouse vas deferens to field stimulation at 0.2 Hz (IC50 12 +/- 4 nM and 15 +/- 3 nM, rat and human alpha-CGRP respectively). Rat alpha-CGRP was less potent at inhibiting responses to 10 Hz than to either 0.2 Hz or 1.0 Hz stimulation. The potency of rat alpha-CGRP at 1.0 Hz was unaltered by halving the calcium concentration of the Krebs solution. The inhibitory effect of human alpha-CGRP was not antagonized by either propranolol (300 nM) or idazoxan (300 nM), although in the same tissues these latter two drugs reduced responses to isoprenaline and clonidine respectively. Rat alpha-CGRP (100 nM) and human alpha-CGRP (1.0 microM) did not alter the uptake of [3H]-noradrenaline (30 nM) into mice isolated vasa deferentia. Rat alpha-CGRP (3-100 nM) did not alter the fractional release per pulse (1.0 Hz, 100 pulses) of tritium from vasa preloaded with [3H]-noradrenaline, although at the same time the peptide inhibited responses of the smooth muscle to field stimulation. Rat and human alpha-CGRP were equipotent at inhibiting contractions of the mouse vas deferens evoked by acetylcholine although the peptides were less potent than against twitch responses. In the rabbit vas deferens neither rat nor human alpha-CGRP (3 nM-1 microM) inhibited either twitch responses or acetylcholine contractions. 7 These results suggest that rat and human alpha-CGRP inhibit contractor responses of the mouse vas deferens not by interference with adrenergic mechanisms, but through postjunctional (possibly CGRP) receptors. A similar mechanism may underlie effects ofCGRP in other tissues. The rabbit vas deferens appears to lack the CGRP 'receptors'.

Cardiovascular effects of human and rat CGRP compared in the rat and other species

In the anaesthetised rat, human and rat CGRP (calcitonin gene-related peptide) which differ by 4 out of 37 amino acids, when given intravenously, lowered blood pressure and increased heart rate. The effects of human CGRP were unaltered by either propranolol or by mepyramine plus cimetidine. In the rat isolated perfused heart the peptides decreased coronary perfusion pressure and evoked a tachycardia. The latter effect was not seen in the rabbit isolated heart, although human CGRP increased coronary flow. The two peptides were equipotent at increasing the rate and force of contraction in the rat isolated right atrium, effects unaltered by propranolol. In the guinea-pig isolated atrium, rat CGRP was 10 times as potent as a chronotropic agent than as an inotrope, unlike human CGRP which was equipotent. In conclusion, human and rat CGRP probably acted directly on the cardiovascular system to produce their qualitatively similar effects.

Human and rat alpha-CGRP but not calcitonin cause mesenteric vasodilatation in rats

A single gene encodes both calcitonin and the calcitonin gene-related peptide (CGRP). Human and rat alpha-CGRP were compared with sodium nitroprusside in the rat and rabbit isolated mesenteric vascular preparation perfused at constant flow. In the presence of the vasoconstrictor noradrenaline (10(-5) M), rat alpha-CGRP was about 10 times as potent as either human alpha-CGRP or sodium nitroprusside as a vasodilator in the rat mesenteric vasculature. In the rabbit mesenteric vasculature the order of potency was rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. Human and salmon calcitonin showed no vasodilator activity at doses 100 times greater than human alpha-CGRP. These results show that human and rat alpha-CGRP are potent vasodilators in the mesenteric vasculature, an effect not mimicked by the alternative gene product, the plasma calcium lowering hormone calcitonin.

Human alpha- and beta-CGRP and rat alpha-CGRP are coronary vasodilators in the rat

The effects of the recently described human alpha-calcitonin gene-related peptide (CGRP), human beta-CGRP and rat alpha-CGRP have been compared with those of the vasodilator sodium nitroprusside, on the rat and rabbit isolated heart. Hearts were perfused at constant flow and [Arg8]-vasopressin was used to increase coronary perfusion pressure. In the rat heart, the order of potency for evoking cumulative dose-dependent falls in perfusion pressure was human beta-CGRP greater than rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. In the same preparations the three CGRPs (but not sodium nitroprusside) elicited cumulative dose-related increases in heart rate. In the rabbit heart the order of potency for vasodilatation was rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. In marked contrast to results from the rat, neither rat alpha-CGRP nor human alpha-CGRP altered heart rate in the rabbit isolated heart. These results show that human alpha- and beta-CGRP and rat alpha-CGRP are vasodilators in the coronary vasculature, but that there is species variation as CGRP had a positive chronotropic effect in the rat heart but not in the rabbit heart.

Mains interference in ECG recording

Despite the increasing sophistication of ECG monitoring and recording equipment, the problem of mains interference and the techniques used to overcome it remain of fundamental importance. This paper presents simplified models of the instrumentation systems most commonly encountered in a hospital environment, concentrating on the ubiquitous isolated amplifier. Empirical values are given for the various parameters, and simple equations are developed to estimate the interference levels in practical situations.

Characterization and distribution of histamine H1- and H2-receptors in precapillary vessels

Selective H1- and H2-receptor agonists and antagonists are available to characterize histaminergic receptors and their distribution in the vasculature. Histamine can contract isolated vessels by acting on H1-receptors (i.e., mepyramine-sensitive) and induce relaxation (after inducing tone by, e.g., an alpha-adrenergic agonist) through H2-receptors (i.e., antagonized by burimamide, metiamide, or cimetidine) and H1-receptors. There are relatively few studies in which histamine receptors have been characterized using selective agonists to minimize problems arising from the coexistence of both types of receptor in the same tissue. The histamine H1- and H2-receptors in precapillary vessels may be similar to those in the guinea pig ileum and atria, respectively, but there are many results that appear to be at variance with this conclusion. The effect of histamine in vivo may be complicated by several factors, including distribution (e.g., leading to modification of transmission at sympathetic ganglia and post-ganglionic nerve terminals) and the method of administration. Intravenous injection of histamine produces hypotension, mediated predominantly by H1-receptors. After histamine infusion, the fall in blood pressure is mediated initially through H1-receptors, but there is also a sustained hypotensive effect (with a slower rate of onset) mediated by H2-receptors. In contrast to the systemic circulation, in the pulmonary circulation, histamine generally elicits vasoconstriction mediated by H1-receptors and vasodilatation by H2-receptors.

Micronucleus induction in Vicia faba roots. Part 1. Absence of dose-rate, fractionation, and oxygen effect at low doses of low LET radiations

Micronucleus indication in Vicia faba roots has been evaluated after irradiation with 60Co gamma-rays. The dependence of the damage on dose, dose rate, fractionation, and oxygen has been studied. The best fit to the experimental data in the dose region between 7 and 190 cGy is represented, for single-dose exposures, by a linear + quadratic relationship. In the low-dose region, between 7 and 20 cGy, where the linear dose dependence is dominant, no dose-rate, fractionation, or oxygen effect could be observed. These effects were, however, present in the high-dose region, where the quadratic dependence is dominant.

Micronucleus induction in Vicia faba roots. Part 2. Biological effects of neutrons below 1 cGy

A dose-effect relationship has been established for high-energy neutrons (maximum energy 600 MeV) within a dose range of 0.2 to 80 cGy and for low-energy neutrons produced by a 252Cf source (mean energy 2.35 MeV) for doses between 0.2 and 5 cGy. The frequency of micronuclei was found to increase linearly with dose. The relative biological effectiveness (r.b.e) values calculated using 60Co radiation as a reference were, in the high-dose region, 4.7 +/- 0.4 and 11.8 +/- 1.3 for the high- and low-energy neutrons, respectively. At doses below 1 cGy constant values of 25.4 +/- 4.4 and 63.7 +/- 12 were reached for the respective neutron energies.

Stimulation-evoked release of [3H]-noradrenaline by 1, 10 or 100 pulses and its modification through presynaptic alpha 2-adrenoceptors

1 Mice isolated vasa deferentia were loaded with 1-[7,8-3H]-noradrenaline and subsequently field stimulated with 1, 10 or 100 pulses (2 ms pulse width, 1 Hz). The tritium overflow was separated into [3H]-noradrenaline and its 3H-metabolites. 2 The resting release of tritium contained about 7% [3H]-noradrenaline, 33% [3H]-3, 4-dihydroxyphenylglycol ([3H]-DOPEG) and 60% 3H-non-catechols with usually less than 1% [3H]-dihydroxymandelic acid ([3H]-DOMA). The proportion of the tritium as [3H]-noradrenaline increased with stimulation train length to 35% with 100 pulses; this increase in [3H]-noradrenaline was associated with falls in [3H]-DOPEG and 3H-non-catechols. Generally the proportional increase in [3H]-noradrenaline on stimulation was about 10 x total tritium when compared with the resting release. 3 The fractional release of [3H]-noradrenaline per pulse was independent of train length, averaging about 6 x 10(-6). This was reduced by the alpha 2-adrenoceptor agonist clonidine (0.3 - 30 nM) with an IC50 of 4.8 nM (10 pulses at 1 Hz). 4 The alpha 2-adrenoceptor antagonist, yohimbine (10 - 100 nM), did not alter the fractional release of [3H]-noradrenaline elicited by 1 pulse. The antagonist did not change the amount or composition of the resting or evoked tritium overflow. However, yohimbine (1 - 100 nM) increased the fractional release of [3H]-noradrenaline per pulse for trains of 10 or 100 pulses (1 Hz) in a concentration-dependent fashion. An increase above controls was significant only with 100 pulses and yohimbine, 30 nM. 5 The results show that the release of noradrenaline during trains of pulses in the mouse vas deferens can be regulated through presynaptic alpha 2-adrenoceptors. There was no evidence of inhibition by noradrenaline of its own release following a single pulse.

Calcium ions, morphine tolerance and noradrenergic transmission in the mouse vas deferens

The response of the isolated vas deferens of the mouse to electrical stimulation is inhibited by morphine and levorphanol via an opiate receptor, the inhibition decreasing with increasing stimulation frequency (0.2-16 Hz). Tolerance to the locomotor stimulant effect of morphine was induced over 48 h using a slow release preparation. Vasa from mice similarly treated with the slow release preparation showed a shift to the right of the morphine and levorphanol twitch inhibition curves. The reduction in the fractional release of [3H]noradrenaline by morphine and levorphanol was less in vasa from morphine-pretreated mice. Altering the Krebs solution by reducing the Ca2+ or Na+ or adding Mg2+ increased the effect of opiate agonists in vasa from naive and morphine-tolerant mice. Therefore, tolerance to morphine has not changed the ability of these ions to modulate opiate responses.

The effects of release and depletion of endogenous noradrenaline on the transmission of impulses in the mouse vas deferens

1 The effects of endogenous noradrenaline released by tyramine and the influence of depletion of the tissue noradrenaline with reserpine and/or alpha-methyl-p-tyrosine on the twitch responses of the field-stimulated mouse vas deferens have been studied.2 Tyramine (10-40 muM) inhibited the twitch responses to field stimulation and failed to produce a contraction. The inhibition decreased as the rate of stimulation increased.3 The inhibition produced by tyramine was antagonized by cocaine (10 muM) and by yohimbine (10 nM), which indicated that it was produced by released noradrenaline acting on presynaptic alpha-adrenoceptors.4 Depletion of the tissue noradrenaline by 39% by blockade of the synthesis of noradrenaline with alpha-methyl-p-tyrosine, was without effect on the twitch response but it reduced the inhibitory effect of tyramine.5 Depletion of the tissue noradrenaline by 96.5% with reserpine alone and by 99.4%, with a combination of reserpine and alpha-methyl-p-tyrosine, reduced the twitch responses by approximately 66% and virtually abolished the inhibition produced by tyramine. It also increased the rate of decline of the responses when the tissue was continuously stimulated. The remaining twitch was not antagonized by phenoxybenzamine (15 muM).6 Residual twitches were bigger in tissues depleted by 99.4% than in those depleted by only 96.5%. This difference was eliminated in the presence of yohimbine (128 nM).7 It is concluded that inhibition of the twitch responses by tyramine is produced by stimulation of presynaptic alpha-adrenoceptors and that the twitch response is associated with stimulation of the sympathetic neurone, but that it is not mediated by postsynaptic alpha-adrenoceptors.

alpha-Adrenoceptors in the mouse vas deferens and their effects on its response to electrical stimulation

1 Noradrenaline (ID50, 0.75 micrometer) and clonidine (ID50, 2.8 nM) produced a dose-related inhibition of the twitch response of the isolated vas deferens of the mouse to electrical stimulation, their effectiveness decreasing as frequency of stimulation increased from 0.2 to 16 hertz. 2 Phenylephrine (1.0--2.0 micrometer) produced a dose-related contraction of the mouse isolated vas deferens and potentiated the responses to field stimulation. 3 Yohimbine (10 nM) antagonized the inhibitory effects of noradrenaline and clonidine, but had no effect on the motor activity of phenylephrine. At a concentration of 128 nM yohimbine potentiated the twitch response by 110% at 1 Hz, but its effectiveness decreased with increasing frequency of stimulation up to 16 hertz. 4 Thymoxamine (0.3 micrometer) antagonized the effects of phenylephrine, but not those of clonidine. 5 From a consideration of the known characteristics of pre- and postsynaptic alpha-adrenoceptors, it is concluded that the inhibitory effect of noradrenaline is produced by stimulation of the former and the effects of phenylephrine by stimulation of the latter.

An inhibitory role for noradrenaline in the mouse vas deferens

1 Noradrenaline (0.1-3.0 muM) inhibited the twitch responses to single pulse field stimulation of the isolated vas deferens of the mouse. The higher concentrations of noradrenaline (ca. 0.3-3.0 muM) were required to make the tissue contract.2 Phentolamine (10 muM) abolished the contractor response to higher concentrations of noradrenaline and antagonized the inhibitory effect of lower concentrations on the twitch response.3 Propranolol (10 muM) potentiated both the contractor and the inhibitory effect of noradrenaline on the twitch response.4 Isoprenaline (0.1-3.0 muM) and salbutamol (1.0-3.0 muM) both inhibited the twitch response. Their effects were antagonized by propranolol (10 muM), but not by practolol (10 muM).5 The effects of uptake(1) and uptake(2) blocking agents were determined. Cocaine (10 muM) reduced the size of the twitch response in 2 out of 4 experiments. Imipramine (0.18 muM) also reduced the size of the twitch, as did oestradiol (3.7 muM) and a combination of cocaine and oestradiol.6 Contractor responses to exogenous noradrenaline showed tachyphylaxis, but when this was not very marked, the response could be shown to be potentiated by uptake blocking agents.7 The inhibitory effect of noradrenaline on the twitch response was greatly potentiated by cocaine (10 muM) and much less so by oestradiol (3.7 muM).8 It is concluded that the transmitter responsible for the twitch response is either an unknown substance released from the sympathetic neurone, or noradrenaline acting upon a receptor with none of the characteristics of known alpha- or beta-adrenoceptors. In either case, noradrenaline can inhibit the output, probably by stimulation of presynaptic alpha-adrenoceptors.