The TOMMY trial: a comparison of TOMosynthesis with digital MammographY in the UK NHS Breast Screening Programme--a multicentre retrospective reading study comparing the diagnostic performance of digital breast tomosynthesis and digital mammography with digital mammography alone

BACKGROUND

Digital breast tomosynthesis (DBT) is a three-dimensional mammography technique with the potential to improve accuracy by improving differentiation between malignant and non-malignant lesions.

OBJECTIVES

The objectives of the study were to compare the diagnostic accuracy of DBT in conjunction with two-dimensional (2D) mammography or synthetic 2D mammography, against standard 2D mammography and to determine if DBT improves the accuracy of detection of different types of lesions.

STUDY POPULATION

Women (aged 47-73 years) recalled for further assessment after routine breast screening and women (aged 40-49 years) with moderate/high of risk of developing breast cancer attending annual mammography screening were recruited after giving written informed consent.

INTERVENTION

All participants underwent a two-view 2D mammography of both breasts and two-view DBT imaging. Image-processing software generated a synthetic 2D mammogram from the DBT data sets.

RETROSPECTIVE READING STUDY

In an independent blinded retrospective study, readers reviewed (1) 2D or (2) 2D + DBT or (3) synthetic 2D + DBT images for each case without access to original screening mammograms or prior examinations. Sensitivities and specificities were calculated for each reading arm and by subgroup analyses.

RESULTS

Data were available for 7060 subjects comprising 6020 (1158 cancers) assessment cases and 1040 (two cancers) family history screening cases. Overall sensitivity was 87% [95% confidence interval (CI) 85% to 89%] for 2D only, 89% (95% CI 87% to 91%) for 2D + DBT and 88% (95% CI 86% to 90%) for synthetic 2D + DBT. The difference in sensitivity between 2D and 2D + DBT was of borderline significance (p = 0.07) and for synthetic 2D + DBT there was no significant difference (p = 0.6). Specificity was 58% (95% CI 56% to 60%) for 2D, 69% (95% CI 67% to 71%) for 2D + DBT and 71% (95% CI 69% to 73%) for synthetic 2D + DBT. Specificity was significantly higher in both DBT reading arms for all subgroups of age, density and dominant radiological feature (p < 0.001 all cases). In all reading arms, specificity tended to be lower for microcalcifications and higher for distortion/asymmetry. Comparing 2D + DBT to 2D alone, sensitivity was significantly higher: 93% versus 86% (p < 0.001) for invasive tumours of size 11-20 mm. Similarly, for breast density 50% or more, sensitivities were 93% versus 86% (p = 0.03); for grade 2 invasive tumours, sensitivities were 91% versus 87% (p = 0.01); where the dominant radiological feature was a mass, sensitivities were 92% and 89% (p = 0.04) For synthetic 2D + DBT, there was significantly (p = 0.006) higher sensitivity than 2D alone in invasive cancers of size 11-20 mm, with a sensitivity of 91%.

CONCLUSIONS

The specificity of DBT and 2D was better than 2D alone but there was only marginal improvement in sensitivity. The performance of synthetic 2D appeared to be comparable to standard 2D. If these results were observed with screening cases, DBT and 2D mammography could benefit to the screening programme by reducing the number of women recalled unnecessarily, especially if a synthetic 2D mammogram were used to minimise radiation exposure. Further research is required into the feasibility of implementing DBT in a screening setting, prognostic modelling on outcomes and mortality, and comparison of 2D and synthetic 2D for different lesion types.

STUDY REGISTRATION

Current Controlled Trials ISRCTN73467396.

FUNDING

This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 19, No. 4. See the HTA programme website for further project information.

Variable size computer-aided detection prompts and mammography film reader decisions

Introduction

The purpose of the present study was to investigate the effect of computer-aided detection (CAD) prompts on reader behaviour in a large sample of breast screening mammograms by analysing the relationship of the presence and size of prompts to the recall decision.

Methods

Local research ethics committee approval was obtained; informed consent was not required. Mammograms were obtained from women attending routine mammography at two breast screening centres in 1996. Films, previously double read, were re-read by a different reader using CAD. The study material included 315 cancer cases comprising all screen-detected cancer cases, all subsequent interval cancers and 861 normal cases randomly selected from 10,267 cases. Ground truth data were used to assess the efficacy of CAD prompting. Associations between prompt attributes and tumour features or reader recall decisions were assessed by chi-squared tests.

Results

There was a highly significant relationship between prompting and a decision to recall for cancer cases and for a random sample of normal cases (P < 0.001). Sixty-four per cent of all cases contained at least one CAD prompt. In cancer cases, larger prompts were more likely to be recalled (P = 0.02) for masses but there was no such association for calcifications (P = 0.9). In a random sample of 861 normal cases, larger prompts were more likely to be recalled (P = 0.02) for both mass and calcification prompts. Significant associations were observed with prompting and breast density (p = 0.009) for cancer cases but not for normal cases (P = 0.05).

Conclusions

For both normal cases and cancer cases, prompted mammograms were more likely to be recalled and the prompt size was also associated with a recall decision.

Influence of imaging on clinical decision making in the treatment of lower back pain

PURPOSE

To assess the impact of cross-sectional imaging with magnetic resonance (MR) imaging or computed tomography (CT) on clinical decision making for patients with lower back pain (LBP).

MATERIALS AND METHODS

A randomized controlled before-and-after study was performed in 145 patients who had symptomatic lumbar spinal disorders and had been referred to orthopedists or neurosurgeons. Participants were a subgroup within a multicenter pragmatic randomized comparison of two imaging policies on LBP treatment: "imaging" versus "no imaging," unless a clear indication developed. Paired assessments were made of diagnosis, diagnostic confidence, proposed treatment, treatment confidence at trial entry and follow-up, and expectations of imaging. Data were analyzed according to the groups as randomized.

RESULTS

At follow-up, there were no statistically significant differences between the groups with respect to diagnosis or treatment plans. Significant increases in diagnostic and therapeutic confidence between trial entry and follow-up were observed for both groups, with a significantly greater increase in diagnostic confidence (P =.01) in the imaging group.

CONCLUSION

Imaging may increase diagnostic confidence but has minimal influence on diagnostic or therapeutic decisions for patients with LBP. The results highlight the need for evidence-based guidelines for imaging in LBP treatment.

Recruitment to multicentre trials: the impact of external influences

A multicentre randomised controlled trial needs to recruit sufficiently large numbers of centres, clinicians and patients Delays in reaching recruitment targets are common and often necessitate extended recruitment periods with associated increased costs. The Scottish Back Trial and the MRC Laparoscopic Hernia Trial are used to illustrate how national clinical, economic and political factors can impact on the conduct of a multicentre trial. Changes in clinical practice, restructuring of the NHS and research and development funding, and changes in the procedures for obtaining local research ethics committee approval had adverse effects on recruitment. In addition, the extent to which changes in patient knowledge and attitudes to clinical trials could influence recruitment should not be ignored. In response to these obstacles both trials extended the recruitment period, identified additional recruitment centres and reduced the overall sample size. External factors which could compromise the successful completion of a d trial need to be recognised and addressed at an early stage.

A comparison of methods for measuring trunk list. A simple plumbline is the best

STUDY DESIGN

Trunk list was measured using three different techniques to compare accuracy, precision, and ease of use.

OBJECTIVE

To obtain a reproducible technique for further studies of the nature, cause, and clinical relevance of trunk list.

SUMMARY OF BACKGROUND DATA

Gravity-induced trunk list is a clinical sign that is frequently observed in patients with low back pain and has been associated with intervertebral disc lesions.

METHODS

Patients with trunk list participated in a comparison of three techniques to determine list magnitude and direction. Paired measurements of trunk list were obtained from each patient using three techniques: a plumbline, a projected shadow, and the 3SPACE Isotrak (McDonnell Douglas Electronics Company, Colchester, VT). In addition, intra- and interobserver reliability of list measurement was assessed by comparison of paired measurements by each of two observers.

RESULTS

List measurements assessed by the plumbline and the projected shadow techniques were not significantly different, but the Isotrak produced data that differed significantly (P < 0.05) from both of these techniques. Comparison of intra- and interobserver repeatability of list measurement using the plumbline technique indicated no significant difference between repeated measures by each observer or between two observers.

CONCLUSIONS

A plumbline is the most useful instrument for measuring static trunk list, but its limitations and the need for standardization of measurement technique must be recognized.

Electrically-induced release of opioid peptides from the guinea-pig myenteric plexus preparation

Preparations of guinea-pig myenteric plexus-longitudinal muscle suspended in Krebs solution were stimulated electrically in the presence of cycloheximide and tetraethylammonium. The amounts of eleven endogenous opioid peptides released into the perifusing Krebs solution were determined and correlated with the decrease in the tissue contents induced by stimulation. For pro-enkephalin fragments the ratio of release to reduction in tissue contents was 29 to 43% for [Met]enkephalin, [Leu]enkephalin, [Met]enkephalyl-RF and [Met]enkephalyl-RGL. With [Met]enkephalyl-RRV-NH2 (BAM-8) the ratio was higher by 50% or more. However, it is of interest that there was no release of the probable precursor [Met]enkephalyl-RRVGRPEWWMDYQ(BAM-18). In this context it may be important that BAM-8 is the only endogenous opioid peptide having -NH2 at the C-terminal. The low tissue levels of pro-dynorphin derived peptide have made estimation of release unreliable.

Kappa-binding and degradation of [3H]dynorphin A (1-8) and [3H]dynorphin A (1-9) in suspensions of guinea pig brain membranes

Following incubation of [3H]dynorphin A (1-8) and [3H]dynorphin A (1-9) with suspensions of guinea pig brain membranes, analysis of the supernatants by HPLC has shown that both peptides are degraded at 25 degrees C and at 0 degrees C. Bestatin and captopril reduce degradation at 0 degrees C but for a similar degree of protection at 25 degrees C arginine-containing dipeptides are also required. The effects of these peptidase inhibitors on the degradation profiles indicate that [3H]dynorphin A (1-8) has three main sites of cleavage: the Tyr1-Gly2, Arg6-Arg7, and Leu5-Arg6 bonds. With [3H]dynorphin A (1-9) as substrate the Arg7-Ile8 and Ile8-Arg9 bonds are also liable to cleavage. In binding assays, in contrast to the effects of peptidase inhibitors on the degradation of unbound [3H]dynorphin A (1-8) and [3H]dynorphin A (1-9), bestatin and captopril have little effect on the binding characteristics of the tritiated dynorphin A fragments at the kappa-site at 0 degrees C. However, at 25 degrees C binding is low in the absence of peptidase inhibitors. When binding at mu- and delta-sites is prevented, the maximal binding capacities of [3H]dynorphin A (1-8), [3H]dynorphin A (1-9), and [3H](-)-bremazocine at the kappa-site are similar; [3H]dynorphin A (1-9) has 5-10 times higher affinity for the kappa-site than [3H]dynorphin A (1-8). Comparison of the effects of peptidase inhibitors on unbound dynorphin A fragments with their effects in binding assays suggests that the bound peptides are protected from the action of peptidases.

Species differences in the concentrations and distributions of opioid binding sites

Binding at the mu, delta- and kappa-types of opioid binding sites was compared in homogenates from the brains of guinea-pig, rabbit, rat and two mouse strains, under conditions of selective labelling. Species differences were shown by two observations. Firstly, analysis of saturation curves in homogenates of brain from which the cerebellum had been removed showed that in guinea-pig brain the opioid binding sites consist of 24% mu-sites, 32% delta-sites and 44% kappa-sites. In contrast, in rabbit brain the corresponding values are 43% mu-sites, 19% delta-sites and 37% kappa-sites and in rat brain, 46% mu-sites, 42% delta-sites and 12% kappa-sites. In the brains of DBA/2 mice the opioid binding sites are comprised of 51% mu-sites, 29% delta-sites and 20% kappa-sites and in C57BL/10 mice, of 44% mu-sites, 35% delta-sites and 21% kappa-sites; these strain differences are due to significant differences in the concentrations of the mu-sites. Secondly, species differences were found when the binding of single concentrations of tritiated ligands (1 X KD value in whole brain) was determined at mu-, delta- and kappa-sites in six brain regions from guinea-pig, rat or rabbit.

[3H]-Dynorphin A (1-8): degradation profile and binding characteristics in brain homogenates

[3H]-Dynorphin A (1-8) was degraded in brain homogenates at 25 degrees and even at 0 degree C. The peptidase inhibitors bestatin and captopril almost completely protected[3H]-dynorphin A (1-8) from degradation at 0 degree C but had only little effect on binding at this temperature. At 25 degrees C, the binding of [3H]-dynorphin A (1-8) was markedly improved by addition of bestatin, captopril and L-leucyl-L-arginine, which afforded some, but not complete protection from degradation. The results of saturation binding assays at 25 degrees C in the presence of the peptidase inhibitors were variable. However, it was found from saturation binding assays at 0 degree C that the maximum binding capacity for [3H]-dynorphin A (1-8) at the kappa-site is similar to that of [3H]-(-)-bremazocine and [3H]-dynorphin A (1-9).

Selectivities of opioid peptide analogues as agonists and antagonists at the delta-receptor

The endogenous opioid ligands interact with more than one of the mu-, delta- and kappa-binding sites. By the use of binding assays and bioassays, enkephalin analogues have been assessed for their selectivity for binding at the delta-binding site and for their agonist and antagonist activities at the delta-receptor. The electrically-induced contractions of myenteric plexus-longitudinal muscle preparations of the guinea-pig ileum were inhibited by mu- and kappa-receptor ligands. Inhibitions were seen with mu-, delta- and kappa-receptor ligands in the mouse vas deferens, mainly with mu-receptor ligands in the rat vas deferens and only with kappa-receptor ligands in the rabbit vas deferens. From observations on a considerable number of [Leu5] enkephalin analogues, it has been concluded that [D-Pen2, D-Pen5] enkephalin and [D-Pen2, L-Pen5] enkephalin are the most selective delta-agonists and that N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH is the most selective antagonist (Aib = alpha-aminoisobutyric acid). The binding of these peptides at the delta-site is 99% of the total binding. As to potency, the agonists are superior to the antagonists.

Radioligands for probing opioid receptors

The three endogenous opioid precursors of almost 30000 Da are pro-opiocortin, proenkephalin and prodynorphin. Pro-opiocortin contains beta-endorphin, melanotropins and ACTH. Proenkephalin yields one [Leu5]enkephalin, three [Met5]enkephalins, one [Met5] enkephalyl-Arg-Arg-Val-NH2 (metorphamide or adrenorphin), one [Met5]enkephalyl-Arg-Gly-Leu and one [Met5]enkephalyl-Arg-Phe. [Leu5]enkephalin is common to all fragments of prodynorphin; its carboxyl extension by Arg-Lys leads to alpha- and beta-neo-endorphin and its carboxyl extension by Arg-Arg gives two dynorphins A and B of 17 and 13 amino acids, respectively. Another endogenous peptide is dynorphin A (1-8). The three main opioid binding sites are mu, delta and kappa. Their analysis has been facilitated by the synthesis of analogues of peptides and non-peptide compounds, which have selective agonist or antagonist action at only one site. The various physiological roles of the three types of the opiate receptor have so far not been sufficiently investigated.

[3H]-dynorphin A (1-9): binding characteristics and degradation profile in brain homogenates

[3H]-Dynorphin A (1-9) is rapidly degraded in brain homogenates, even at 0 degree C. Although protection from degradation at O degree C, and to a lesser extent at 25 degrees C, was obtained with a combination of bestatin, L-leucyl-L-leucine, L-arginyl-L-arginine and captopril, these peptidase inhibitors had little effect on binding at 0 degree C. At the kappa-site, the maximum binding capacity of [3H]-dynorphin A (1-9) at 0 degree C was similar to that at 25 degrees C but it is suggested that, even after suppression of mu- and delta-binding, [3H]-dynorphin A (1-9) may bind to more than one site for which it has differing affinities at 0 degree C.

Spectrum of the mu, delta- and kappa-binding sites in homogenates of rat brain

1 In homogenates of rat brain, the binding characteristics of tritiated opiates and opioid peptides were examined and the relative capacities of mu-, delta- and kappa-binding sites of the opiate receptor determined by saturation analysis.2 In competition experiments, binding of the selective mu-ligand [(3)H]-[D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin at the mu-site was displaced by [D-Ala(2),D-Leu(5)]enkephalin with rather low affinity (K(I) = 12.6 nM) and more readily by the ketazocine-like compounds (-)-ethylketazocine (K(I) = 3.1 nM) and (-)-bremazocine (K(I) = 0.32 nM), which also displaced the binding of [(3)H]-[D-Ala(2),D-Leu(5)]enkephalin from the delta-site. In contrast, the binding to the kappa-site was easily displaced by ethylketazocine (1.0 nM) and bremazocine (0.37 nM) but not by the mu-ligand [D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin (K(I) = 2000-3000 nM) or the delta-ligand [D-Ala(2),D-Leu(5)]enkephalin (K(I) > 20,000 nM).3 The dissociation equilibrium constant (K(D)) and the binding capacity (pmol/g) of the mu-binding site were determined with the selective mu-ligand [(3)H]-[D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin. For the delta-site, [(3)H]-[D-Ala(2),D-Leu(5)]enkephalin was used in the presence of unlabelled [D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin in order to suppress cross-reactivity to the mu-binding site. For the estimation of kappa-binding, [(3)H]-(+/-)-ethylketazocine or [(3)H]-(-)-bremazocine were used in the presence of unlabelled mu- and delta-ligands for the suppression of cross-reactivities to the mu- and delta-binding sites.4 In rat brain the capacity of the mu-binding site was 7.3 pmol/g brain, that of the delta-binding site 6.7 pmol/g brain and that of the kappa-binding site 2.0 pmol/g brain. Thus, the kappa-binding site had the lowest value whereas in the guinea-pig brain the capacity of the mu-binding site was lower than that of the delta- or kappa-binding site.

Interaction of p-nitrophenylalanine enkephalins with mu-, delta- and kappa-subtypes of the opiate receptor

Substitution of L-p-nitrophenylalanine for phenylalanine in position 4 of [D-Ala2, KLeu-NH2(5)]enkephalin analogues increased their affinity for mu-, delta- and kappa-binding sites in guinea-pig brain, increased their potency to inhibit electrically evoked contractions of the guinea-pig ileum and mouse vas deferens, and increased their analgesic potency in the mouse tail flick test, Introduction of L-adamantylalanine, but not of L-neopentylglycine, in position 5 resulted in a loss of activity.

Some 14 beta-substituted analogues of N-(cyclopropylmethyl)normorphine

A series of N-(cyclopropylmethyl)-14 beta-substituted-normorphine analogues was synthesized and tested for opioid agonist and antagonist activity in the guinea pig ileum and mouse vas deferens preparations. The 14 beta-bromo compound proved to be a pure antagonist equal in potency to naloxone in the guinea pig ileum assay. In contrast to N-(cyclopropylmethyl)-14 beta-hydroxynormorphine which was a pure antagonist, the corresponding sulfur analogue was about equal to nalorphine in agonist and antagonist potency.

Unexpected antagonism in the rat vas deferens by benzomorphans which are agonists in other pharmacological tests

The benzomorphans, ethylketazocine, bremazocine and MR 2034 are pure agonists in the guinea-pig ileum and mouse vas deferens but are competitive antagonists without agonist activity in the rat vas deferens.

Tobacco mosaic virus-enkephalin conjugates: potentiation of opioid activity

Covalent tobacco mosaic virus-enkephalin analogue conjugates containing between 5 and 450 agonist molecules attached through their C-terminal amino acids were prepared and assayed in pharmacological and binding assays that distinguish between mu- and delta-receptors. Increases in peptide- and receptor-specific potency and affinity were observed with a certain preference of mu- over delta-receptors. The results may become important for mapping receptors or for isolating opiate receptor-bearing membrane vesicles.

Comparison of the binding characteristics of tritiated opiates and opioid peptides

1 Binding assays on homogenates of guinea-pig brain showed that the maximal number of binding sites was different tritiated ligands interacting with the opiate receptors. 2 At 25 degrees C the binding capacity of morphine or dihydromorphine was only about 3 pmol/g fresh brain whereas etorphine and D-Ala2-L-Leu5- and D-Ala2-L-Met5-enkephalin amide had capacities of 13 to 15 pmol/g brain. D-Ala2-D-Leu5-enkephalin had an intermediate capacity of about 6 pmol/g brain. 3 The binding capacities of the natural methionine- and leucine-enkephalins measured at 0 degrees C were 5 to 6 pmol/g brain. At this temperature, the binding capacity of dihydromorphine, D-Ala2-D-Leu5-enkephalin and of the two enkephalin amides was only slightly lower than at 25 degrees C. 4 In assays in which unlabelled ligand competed with the same labelled ligand, the inhibition constants (KI) were equal to or not more than twice as large as the equilibrium dissociation constant (KD) determined in saturation assays. In contrast, the KI of unlabelled dihydromorphine against [3H]-D-Ala2-D-Leu5-enkephalin or of unlabelled D-Ala2-D-Leu5-enkephalin against [3H]-dihydromorphine was about 20 times higher than the respective KD values. 5 When for a given compound the ratio of the KI value against [3H]-D-Ala2-D-Leu5-enkephalin to the KI value against [3H]-dihydromorphine (discrimination ratio) is calculated, a high value indicates selectivity in favour of the mu-receptor and a low value selectivity in favour of the delta-receptor. The most selective mu-agonist known so far is normorphine with a discrimination ratio of 70 and the most selective delta-agonist is D-Ala2-D-Leu5-enkephalin with a ratio of 0.11. The selectivity of the known antagonists is in favour of the mu-receptor, since their discrimination ratios are larger than 1, varying between 10 for naloxone and 4 for Mr 2266.

Acute effects of morphine and opioid peptides on the motility and responses of rat colon to electrical stimulation

1 Morphine and leucine- and methionine-enkephalins inhibited the contractile response of the pithed rat colon to electrical stimulation of the spinal motor outflows and inhibited motor responses of the isolated colon to field stimulation. 2 Morphine and the opioid peptides also had an excitatory action in the colon. In the pithed rat, opiates caused regular fluctuations in intracolonic pressure and in the isolated colon, caused regular waves of contraction. This excitatory response was produced by low concentrations of the enkephalins (2 X 10(-8) M, 2 X 10(-9) M), was stereospecific and was antagonized by naloxone. 3 Opiate-induced contractions in the isolated colon were inhibited by catecholamines, adenine nucleotides and by phosphodiesterase inhibitors. These contractions were unaffected by ergotamine and tolazoline, or by propranolol. 4 The excitatory action of opiates in the isolated colon was not antagonized and usually was potentiated by atropine, (+)-tubocurarine and hexamethonium. In the absence of opiates, these drugs also produced similar waves of contraction, which were unaffected by naloxone. 5 Opiate-induced contractions occurred in colon rendered unresponsive to 5-hydroxytryptamine (5-HT) and these contractions were potentiated by the 5-HT antagonist, lysergic acid diethylamide, which, when administered alone, caused similar contractions. The 5-HT antagonist, cyproheptadine, inhibited opiate-induced contractions but was non-specific, since it also inhibited responses of the colon to carbachol and KC1. 6 Opiate-induced contractions were unaffected by procaine and were potentiated by tetrodotoxin. Both of these drugs, when administered alone, produced waves of contractions, which were similar to those produced by opiates but were unaffected by naloxone. 7 Contractions produced in the isolated colon either by opiates, atropine or (+)-tubocurarine, or any combination of these drugs, were inhibited by field stimulation applied at the peak of a wave of contraction. This inhibitory response to field stimulation occurred at low frequencies of stimulation (less than 10 Hz), and persisted in colon from rats pretreated with reserpine to deplete, or 6-hydroxydopamine to destroy, adrenergic nerve endings. It was unaffected by guanethidine but abolished by tetrodotoxin. 8 The implications of these results are considered and it is concluded that the excitatory action of opiates in the rat colon is probably not mediated by the release of acetylcholine or 5-HT but instead, may be due either to a direct action on smooth muscle or to a presynaptic inhibitory action at a ganglionic site in a non-adrenergic inhibitory mechanism, which normally suppresses myogenic activity.

The inhibitory effects of presynaptic alpha-adrenoceptor agonists on contractions of guinea-pig ileum and mouse vas deferens in the morphine-dependent and withdrawn states produced in vitro

1 Isolated ilea from guinea-pigs implanted with morphine pellets were stimulated coaxially, either with or without morphine present in the bath fluid, and the longitudinal contractions recorded. 2 In the absence of morphine the inhibitory effects of the presynaptic alpha-adrenoceptor agonists, clonidine and oxymetazoline were much reduced and the dose-response curve was flat. This state of 'withdrawal' was readily reversed by morphine and levorphanol but not its inactive (+)-isomer, dextrophan. 3 The kappa-agonists, ketazocine and ethylketazocine, also restored the effects of clonidine as did the opioid peptides Tyr-D-Ala-Gly-Phe-D-Leu, acting preferentially on delta-receptors, and Tyr-D-Ala-Gly-MePhe-Met(O)-ol, acting mainly on micro-receptors. 4 The inhibitory effects of adrenaline and adenosine 3',5'-diphosphate were reduced at low but not at high concentrations. 5 In contrast, the inhibitory effect of clonidine on the electrically evoked contractions of vasa deferentia from mice implanted with morphine pellets was not abolished by the lack of morphine in the bath fluid or by addition of naloxone. 6 A possible explanation is suggested for the loss of the inhibitory effects of presynaptic alpha-adrenoceptor agonists in the withdrawn state of the dependent ileum.