Does sexuality matter? A cross-sectional study of drug use, social injecting, and access to injection-specific care among men who inject drugs in Melbourne, Australia

BACKGROUND

Gay, bisexual and other men who have sex with men (GBMSM) are overrepresented in cohorts of people who inject drugs. GBMSM's substance use is usually explored in the context of its contribution to sexual risk. We examined drug use practices, connectedness to other people who inject drugs, peer-to-peer injecting, and access to care among men who inject drugs in Melbourne, Australia. We aim to describe similarities and differences in these parameters for GBMSM and other men.

METHODS

Data were drawn from a prospective cohort study of people who inject drugs conducted in Melbourne, Australia, since 2009. This cross-sectional study used data collected between 2016 and 2021. Descriptive statistics were used to assess differences between GBMSM and other men.

RESULTS

Of 525 men who injected drugs over the study period, 48 (9%) identified as gay or bisexual, or reported sex with other men in the past 12 months. GBMSM and other men reported similar socio-demographics, drug practices (age of injecting initiation, most injected drug, peer-to-peer injecting, receptive syringe sharing) and access to injecting-specific care (drug treatment, source of needle-syringes). A significantly greater percentage of GBMSM reported past 12-month hepatitis C testing (69% vs. 52%, p = 0.028) and preferring methamphetamine (31% vs. 16%, p = 0.022). A higher percentage of GBMSM reported knowing > 50 other people who inject drugs (46% vs. 37%), but this difference was not statistically significant. Both groups primarily obtained injecting equipment from needle-syringe programs; a minority had accessed injecting-specific primary care.

CONCLUSION

Men who injected drugs in this cohort and those who identified as GBMSM reported similar drug and health-seeking practices. The higher prevalence of methamphetamine injecting among GBMSM may warrant different harm reduction support for this group. Health promotion should utilise opportunities to connect men who inject drugs in Melbourne to injecting-specific primary health care.

Constructing a 'target population': A critical analysis of public health discourse on substance use among gay and bisexual men, 2000-2020

BACKGROUND

Gay and bisexual men (GBM) have higher substance use prevalences than general population samples - often attributed to stigmatisation of sexual minority identities. We examined how influential public health research on substance use among GBM interprets this behaviour and what GBM-specific identities emerge through the discourses employed.

METHODS

We searched Web of Science for publications on substance use among GBM, selecting 60 of the most cited papers published during 2000-2020. We studied the language used to describe and interpret drug-using behaviour using critical discourse analysis, focusing on interpretive repertoires and subject positions.

RESULTS

Three distinct discursive tendencies were identified. First, in constructing a target population, GBM who use illicit drugs are positioned as deficient, socially irresponsible, and maladapted to dealing with stigmatisation and HIV risks. Second, in shifting the focus beyond the individual, the gay community is conceptualised as offering a safe space for socialisation. Nonetheless, gay community spaces are problematised as promoting substance use among vulnerable GBM through aggravating loneliness and normalising drug use as a form of maladaptive (avoidance) coping. Third, counterdiscursive movements add nuance, context, and comparisons that relativise rather than generalise substance use and focus on pleasure and self-determination. Such discourses centre the need for interventions that disrupt homophobic socio-structures instead of individualising approaches to limit non-conformity.

CONCLUSION

'Expert' assessments of substance use among GBM perpetuate pathologising understandings of this behaviour and promote abject subject positions, contributing to perpetuations of intergroup stigma and social exclusion based on drug and sexual practices. Our findings highlight the need for deliberate and critical engagement with prior research and a conscious effort to disrupt dominant discourses on GBM's substance use.

A scoping review of sexual transmission related HIV research among key populations in Malaysia: Implications for interventions across the HIV care cascade

The Malaysian government has committed to 'Fast Tracking the HIV Response' to achieve UNAIDS 2030 targets to end AIDS. The epidemic is concentrated among key populations and has shifted from people who inject drugs to HIV infection through sexual transmission among men who have sex with men, sex workers and transgender people. The aim of this scoping review was to examine social and behavioural research published since 2005 that can inform understanding of each stage of the 90:90:90 treatment cascade (as proposed by UNAIDS), including HIV risk behaviours and testing practices that precede entry. We found a concentration of studies related to predictors or correlates of HIV infections (mostly among men who have sex with men) and a shortfall in literature pertaining to sex workers or transgender people. While several studies examined factors associated with HIV testing, only one examined uptake of antiretroviral therapy and two explored issues of treatment adherence. No study examined broader care and support of people living with HIV. To scale-up effective programmes and apprise investment to achieve the ambitious targets set-out in the Malaysian National HIV/AIDS Strategic Plan, a combination of comprehensive strategic information and evidence generated through primary research is critical.

HIV self-testing intervention experiences and kit usability: results from a qualitative study among men who have sex with men in the SELPHI (Self-Testing Public Health Intervention) randomized controlled trial in England and Wales

Objectives

SELPHI (HIV Self‐Testing Public Health Intervention) is the largest randomized controlled trial (RCT) of HIV self‐testing (HIVST) in a high‐income setting to date, and has recruited 10 000 men who have sex with men (cis‐ and transgender) and transgender women who have sex with men. This qualitative substudy aimed to explore how those utilizing self‐tests experience HIVST and the implications for further intervention development and scale‐up. This is the first qualitative study in Europe investigating experiences of HIVST among intervention users, and the first globally examining the experience of using blood‐based HIVST.

Methods

Thirty‐seven cisgender MSM SELPHI participants from across England and Wales were purposively recruited to the substudy, in which semi‐structured interviews were used to explore testing history, HIVST experiences and intervention preferences. Interviews were audio‐recorded, transcribed and analysed through a framework analysis.

Results

Men accessed the intervention because HIVST reduced barriers related to convenience, stigma and privacy concerns. Emotional responses had direct links to acceptability. Supportive intervention components increased engagement with testing and addressed supportive concerns. HIVST facilitated more frequent testing, with the potential to reduce sexually transmitted infection (STI) screening frequency. Substudy participants with an HIV‐positive result (n = 2) linked to care promptly and reported very high acceptability. Minor adverse outcomes (n = 2; relationship discord and fainting) did not reduce acceptability. Ease of use difficulties were with the lancet and the test processing stage.

Conclusions

Intervention components shaped acceptability, particularly in relation to overcoming a perceived lack of support. The intervention was broadly acceptable and usable; participants expressed an unexpected degree of enthusiasm for HIVST, including those with HIV‐positive results and individuals with minor adverse outcomes.

Motivations and values associated with combining sex and illicit drugs ('chemsex') among gay men in South London: findings from a qualitative study

OBJECTIVES

There is considerable public health concern about the combining of sex and illicit drugs (chemsex) among gay men. With a view to inform supportive therapeutic and clinical interventions, we sought to examine the motivations for engaging in chemsex among gay men living in South London.

METHODS

Community advertising recruited 30 gay men for qualitative semi-structured interview. Aged between 21 and 53 years, all lived in South London in the boroughs of Lambeth, Southwark and Lewisham and all had combined crystal methamphetamine, mephedrone and/or γ-hydroxybutyric acid/γ-butyrolactone with sex in the past 12 months. Transcripts were subjected to a thematic analysis.

RESULTS

We broadly distinguished two groups of reasons for combining sex and drugs, within which we described eight distinct motivations. The first major group of motivations for combining drugs with sex was that drugs provide the means by which men can have the sex they desire by increasing libido, confidence, disinhibition and stamina. The second major group of motivations for chemsex was that drugs enhance the qualities of the sex that men value. Drugs made other men seem more attractive, increased physical sensations, intensified perceptions of intimacy and facilitated a sense of sexual adventure.

CONCLUSION

Analysis revealed that sexualised drug use provides both motivation and capability to engage in the kinds of sex that some gay men value: sex that explores and celebrates adventurism. Those services providing (talking) interventions to men engaging in chemsex should consider these benefits of sexualised drug use alongside the harms arising.

Illicit drug use in sexual settings ('chemsex') and HIV/STI transmission risk behaviour among gay men in South London: findings from a qualitative study

BACKGROUND

'Chemsex' is a colloquial term used in the UK that describes sex under the influence of psychoactive substances (typically crystal methamphetamine, mephedrone and gamma-hydroxybutyric acid (GHB)/gamma-butyrolactone (GBL)). Recently, concern has been raised as to the impact of such behaviour on HIV/sexually transmitted infection (STI) transmission risk behaviour, which this qualitative study aimed to explore via semistructured interviews with gay men living in three South London boroughs.

METHODS

Interviews were conducted with 30 community-recruited gay men (age range 21-53) who lived in the boroughs of Lambeth, Southwark and Lewisham, and who had used crystal methamphetamine, mephedrone or GHB/GBL either immediately before or during sex with another man during the previous 12 months. Data were subjected to a thematic analysis.

RESULTS

Chemsex typically featured more partners and a longer duration than other forms of sex, and the relationship between drug use and HIV/STI transmission risk behaviour was varied. While some men believed that engaging in chemsex had unwittingly led them to take risks, others maintained strict personal rules about having safer sex. Among many participants with diagnosed HIV, there was little evidence that the use of drugs had significantly influenced their engagement in condomless anal intercourse (primarily with other men believed to be HIV positive), but their use had facilitated sex with more men and for longer.

CONCLUSIONS

Analysis revealed that, within this sample, chemsex is never less risky than sex without drugs, and is sometimes more so. Targeted clinic-based and community-based harm reduction and sexual health interventions are required to address the prevention needs of gay men combining psychoactive substances with sex.

Perceptions of superinfection risk among gay men with diagnosed HIV who have unprotected anal intercourse

This paper explores how men who have sex with men (MSM) with diagnosed HIV who engage in unprotected anal intercourse (UAI) perceive the potential risk of superinfection and how they respond to it. Semistructured interviews were carried out with 42 MSM recruited via community-based agencies throughout England and Wales. The interviews examined sexual risk taking and the ways in which men sought to manage the risks they perceived. All participants had heard of superinfection and one-third considered it a personal risk when they had UAI with men with the same sero-status. The risk of being superinfected with HIV was often situated among a number of other concerns that men felt they needed to manage when having sex. There was significant uncertainty about the likelihood of acquiring an additional strain of HIV, which was exacerbated by competing, and often conflicting, advice from a variety of expert sources. Men frequently drew upon lay and expert understandings of viral load and infectiousness to rationalize engagement in UAI with other diagnosed positive men. HIV health-care providers should seek to find consensus on how to discuss superinfection with MSM, taking account of the array of other physical and social risks associated with sex.

Exact vortex nucleation and cooperative vortex tunneling in dilute Bose-Einstein condensates

With the imminent advent of mesoscopic rotating Bose-Einstein condensates in the lowest Landau level regime, we explore lowest Landau level vortex nucleation. An exact many-body analysis is presented in a weakly elliptical trap for up to 400 particles. Striking non-mean-field features are exposed at filling factors >>1. For example, near the critical rotation frequency pairs of energy levels approach each other with exponential accuracy. A physical interpretation is provided by requantizing a mean-field theory, where 1/N plays the role of Planck's constant, revealing two vortices cooperatively tunneling between classically degenerate energy minima. The tunnel splitting variation is described in terms of frequency, particle number, and ellipticity.

Anomalous hydrodynamics and normal fluids in rapidly rotating Bose-Einstein condensates

In rapidly rotating condensed Bose systems we show that there is a regime of anomalous hydrodynamics which coincides with the mean field quantum Hall regime. A consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show that there are constraints which connect spatial variations of density and phase and that the vortex positions are not the simplest description of the dynamics. We demonstrate, inter alia, a simple relation between vortices and surface waves. We show that the surface waves can emulate a "normal fluid," allowing dissipation by energy and angular momentum absorbtion from vortex motion in the trap. The time scale is sensitive to the initial configuration, which can lead to long-lived vortex patches--perhaps related to those observed at JILA.

X-linked myotubular myopathy in a family with three adult survivors

We describe a family with an extremely mild form of X-linked myotubular myopathy. Three affected males survived to adulthood with sufficient muscle strength to enable them to carry out normal daily activities. The mildness of the myopathy in this family is highlighted by the following: no neonatal or infant mortality resulting from the myopathy; one affected male who did not have neonatal asphyxia and had normal early motor milestones - this affected male was able to increase his muscle bulk and strength to normal by weightlifting; and a 55-year-old male who still lives an independent life. DNA sequencing identified a novel missense mutation - G469A (E157K) - in exon 7 of the MTM1 gene in this family. To our knowledge, this is the third X-linked myotubular myopathy family, with multiple adult survivors, to be reported in the literature.

Open access carotid duplex scanning: throughput and resultant surgical workload

It is now generally accepted that high-quality duplex scanning obviates the need for pre-operative angiography in the assessment of most cases of carotid disease. An information leaflet was circulated to all general practitioners and hospital doctors in early 1996. Indications, results of treatment and details of the open access service were described. This paper outlines the workload that followed, for both imaging and surgical departments.

Species-divergent regulation of human and mouse osteocalcin genes by calciotropic hormones

Although osteocalcin is the most abundant noncollagenous protein in bone, its role remains undefined. Recent studies have reported diametrically opposing responses in the vitamin D regulation of the mouse vs the human and rat osteocalcin genes. The aim of this study was to increase the understanding of these differences and further elucidate the physiological function and regulation of osteocalcin. Direct comparison of the regulation of both the endogenous mouse osteocalcin gene (mOC) and a human osteocalcin promoter-chloramphenicol acetyl transferase (hOC-CAT) reporter as integrated templates was undertaken in primary osteoblastic cultures from OSCAT transgenic mice. Expression of both genes was up-regulated with the onset of mineralization. Long-term chronic 1, 25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) treatment and acute (2 day) PTH treatment inhibited both mOC and hOC-CAT expression. At all stages of osteoblastic development studied, hOC-CAT was up-regulated by acute 1,25-(OH)(2)D(3), whereas mOC was unaffected or inhibited. Mouse osteopontin was strongly up-regulated by acute 1, 25-(OH)(2)D(3) treatment. Thus, the divergence of the osteocalcin responses to 1,25-(OH)(2)D(3) is specific for the osteocalcin gene and for an acute 1,25-(OH)(2)D(3) treatment regime. Elucidation of this unique aspect of bone physiology will provide valuable insights into the still incompletely understood roles of osteocalcin and 1, 25-(OH)(2)D(3) in bone.

Reconstruction of the lateral ligaments of the ankle using semi-tendinosis graft

Injury to the lateral ligaments of the ankle is one of the most common sports-related injuries. Although these injures generally resolve with non-operative treatment reconstruction of the lateral ligaments of the ankle is occasionally necessary. We report the surgical technique and result of reconstruction of the anterior talo-fibular ligament using a semi-tendinosis free graft in 26 patients with an average follow-up of 24 months. 81% of patients reported complete resolution or substantial improvement in instability, swelling and sharp pain. Episodes of functional instability persisted in five patients post operatively. No significant differences were noted between the operated and contra-lateral non-operated ankle in range of motion or uniaxial balance assessment. Kin-Com testing of hamstring strength showed no differences between sides. Short term results suggest that this ligament reconstruction provides good results without sacrifice of peroneal function and has minimal donor site morbidity.

Polyethylene sulfonate: a tight-binding inhibitor of 6-phosphogluconate dehydrogenase of Cryptococcus neoformans

Polyethylene sulfonate (PES) or polyvinyl sulfonate was found to be a potent inhibitor of a number of fungal enzymes, including 6-phosphogluconate dehydrogenase from Cryptococcus neoformans. The inhibition was apparently competitive versus either NADP or 6-phosphogluconate, with 50% inhibition at PES concentrations below 10 nM. Replots of slopes of double-reciprocal plots versus inhibitor concentration were sharply concave upward, whereas replots of slope versus [PES]3 were linear. The inhibition was freely reversible upon dilution of the enzyme-PES complex. A model is presented that involves initial binding of the long (M(r) 50,000) polyanionic PES at a remote site on the enzyme, followed by interaction of the end of the tethered polymer with the binding site for NADP or for 6-phosphogluconate.

Peribulbar and retrobulbar anesthesia with prilocaine: a comparison of two methods of local ocular anesthesia

Prilocaine (Citanest) has been shown to be a satisfactory alternative to lignocaine, with certain important advantages, including superior diffusion. The latter may be especially important in peribulbar anesthesia, where the level of diffusion is a critical factor in providing a timely, high-quality block. In a prospective randomized study, we compared the effectiveness of peribulbar vs retrobulbar administration of prilocaine. Eighty-seven patients undergoing elective intraocular surgery were randomized to receive either retrobulbar or peribulbar anesthesia with prilocaine 3% with felypressin and hyaluronidase. Pain of injection, akinesia, and anesthesia were evaluated at predetermined intervals after injection. Except for the fact that lid akinesia occurred earlier in the peribulbar group, there was no difference in the quality or rate of onset of overall akinesia in the two groups. Nor were there any differences in the pain associated with injection. Both groups had excellent operative anesthesia and akinesia.

Hydrolysis of human and pig brain natriuretic peptides, urodilatin, C-type natriuretic peptide and some C-receptor ligands by endopeptidase-24.11

Endopeptidase-24.11 (E-24.11, EC 3.4.24.11) is widely believed to play a physiological role in metabolizing atrial natriuretic peptide (ANP). Since the discovery of ANP, new natriuretic peptides have been isolated and other peptides synthesized as receptor ligands. The hydrolysis in vitro of six related peptides by the endopeptidase has been studied, mainly by h.p.l.c. The initial attack on the 32-residue form of pig brain natriuretic peptide (pBNP-32) was shown to be at the Ser20-Leu21 bond, as had been previously shown for the 26-residue form. In contrast, human brain natriuretic peptide-32 (hBNP-32), which differs in ten residues from pBNP-32, was attacked first at the Met4-Val5 bond, releasing the N-terminal tetrapeptide, and only later at bonds within the ring: at Arg17-Ile18 and subsequently at four other sites. Urodilatin, which has a four-residue extension at the N-terminus compared with alpha-human atrial natriuretic peptide-28 (alpha-hANP), was degraded at about half the rate of the latter, though the C-terminal Phe-Arg-Tyr was released at the same rate. The 22-residue C-type natriuretic peptide was hydrolysed more rapidly than alpha-hANP, as were two C-receptor ligands (peptides with deletions within the ring): C-ANP4-23 (rANP4-23 des-Gln18,Ser19,Gly20,Leu21,Gly22) and SC 46542 (hANP5-28 des-Phe8,Gly9,Ala17,Gln18). Angiotensin-converting enzyme failed to hydrolyse pBNP-32, hBNP-32 or 125I-rat (r) ANP, even after prolonged incubation. Km and kcat values were determined for the hydrolysis of alpha-hANP, porcine BNP-26, porcine BNP-32 and 125I-rANP by E-24.11. Ki values were determined for six peptides, alpha-hANP, urodilatin, hBNP-32, C-type natriuretic peptide (CNP), SC 46542 and C-type natriuretic peptide (C-ANP4-23), in radiometric assays of E-24.11 with either [125I] insulin B chain or [125I] rANP as substrate. The Ki values (2.5-13 microM) for CNP were the lowest of any of the group, whereas those for hBNP-32 (151-172 microM) were the highest. The physiological significance of these results is discussed, especially in regard to the relative resistance of hBNP-32 to attack and the ability of the C-receptor ligands to compete with natriuretic peptides for hydrolysis by E-24.11.

Cellular reorganisation of membrane peptidases in Wallerian degeneration of pig peripheral nerve

Immunohistochemical techniques have been used to study a group of membrane peptidases in the distal segment of the ulnar nerve of piglets 7 and 14 days after surgical section. Five peptidases were studied, all of which have a wide distribution on the surfaces of many cell types and have roles in metabolising neuropeptides. In normal pig nerves, endopeptidase-24.11 is expressed by both myelin- and nonmyelin-forming Schwann cells. Peptidyl dipeptidase A (angiotensin converting enzyme), aminopeptidase-N and dipeptidyl peptidase IV are present in the microvessels, and aminopeptidase-N is also seen in the perineurial connective tissue. Of this group of peptidases, only aminopeptidase-W is a neuronal marker in normal nerve. Macrophages were identified by two antibodies, 74-22-15 and 40D (which recognises Ia). Short-term cultures of macrophages obtained by alveolar lavage were positively stained by both antibodies and about half of the cells also expressed aminopeptidase-N and dipeptidyl peptidase IV. Staining by 40D and 74-22-15 revealed the presence of significant numbers of macrophages in normal nerve, but none of the membrane peptidases colocalized with these cells. Seven days after section of the nerve, the distal segment showed morphological changes typical of Wallerian degeneration. Endopeptidase-24.11 was no longer visible in myelin sheaths, but remained a marker for the surface of Schwann cells (defined also by staining for glial fibrillary acidic protein). The macrophage markers revealed marked changes in the morphology of these cells, often consistent with their phagocytic activity. Two peptidases, aminopeptidase-N and aminopeptidase-W, also appeared at this time to be associated with cells exhibiting the morphology of activated macrophages. This association could be confirmed in many instances by double staining with 74-22-15 and antibodies to the peptidases. Angiotensin converting enzyme retained its single location in microvessels at 7 days after section, but at 14 days a new pattern emerged as it, too, was expressed by macrophages. Dipeptidyl peptidase IV was not shown to be a macrophage marker in the degenerating nerve. Thus Wallerian degeneration leads to remarkable changes in the cellular expression of membrane peptidase; endopeptidase-24.11 reflects the changed morphology of Schwann cells while aminopeptidase-N, aminopeptidase-W and angiotensin converting enzyme become expressed by the actively phagocytosing macrophages.

Membrane peptidases in the peripheral nervous system of the pig: their localization by immunohistochemistry at light and electron microscopic levels

The presence and cellular localization of five membrane peptidases has been investigated in peripheral nerves, including those of the autonomic nervous system, in the pig. Endopeptidase-24.11 ("enkephalinase") peptidyl dipeptidase A, aminopeptidase N, aminopeptidase W and dipeptidyl peptidase IV were studied by both enzymic assays of membranes prepared from samples of nerve and by immunoperoxidase histochemistry at light and in two cases, endopeptidase-24.11 and aminopeptidase W, at electron microscopic levels. All five peptidases could be quantified by enzymic assay, though the activities were about 1% of those in renal microvilli and less than those of choroid plexus membranes. Endopeptidase-24.11 was associated with Schwann cell membranes in all types of nerve examined, including major nerves containing predominantly myelinated fibres as well as autonomic nerves, such as the vagus and splenic nerves and the sympathetic chain, staining being observed in membranes associated with myelinated and unmyelinated fibres. The Schwann cell location of endopeptidase-24.11 was confirmed by correlation with immunostaining for glial fibrillary acidic protein and by electron microscopy. This peptidase is known to have a wide repertoire of susceptible substrates among neuropeptides which was here shown to include vasoactive intestinal polypeptide (Km 268 microM, kcat 568 min-1), one of a number of neuropeptides present in peripheral nerve fibres. Three of the peptidases, peptidyl dipeptidase A, aminopeptidase N and dipeptidyl peptidase IV, were associated with microvessels of peripheral nerves. Aminopeptidase N was also observed in connective tissue elements, including the perineurium. Aminopeptidase W was unique among the five peptidases in having a neuronal localization. This was observed in unmyelinated and myelinated nerves and was supported by comparison with the pattern of staining observed for neurofilament protein and by electron microscopic immunoperoxidase staining. This observation was unexpected since aminopeptidase W has not been detected as a neuronal marker in the brain. Some possible roles for the membrane peptidases in peripheral nerves are discussed.

The hydrolysis of brain and atrial natriuretic peptides by porcine choroid plexus is attributable to endopeptidase-24.11

The hydrolysis of the porcine 26-residue brain natriuretic peptide (BNP-26) and its counterpart human 28-residue atrial natriuretic peptide (alpha-hANP) by pig membrane preparations and purified membrane peptidases was studied. When the two peptides were incubated with choroid plexus membranes, the products being analysed by h.p.l.c., alpha-hANP was degraded twice as fast as BNP. The h.p.l.c. profiles of alpha-hANP hydrolysis, in short incubations with choroid plexus membranes, yielded alpha hANP' as the main product, this having been previously shown to be the result of hydrolysis at the Cys7-Phe8 bond. In short incubations this cleavage was inhibited 84% by 1 microM-phosphoramidon, a specific inhibitor of endopeptidase-24.11. BNP-26 was hydrolysed by choroid plexus membranes, kidney microvillar membranes and purified endopeptidase-24.11 in a manner that yielded identical h.p.l.c. profiles. In the presence of phosphoramidon, hydrolysis by the choroid plexus membranes was 94% inhibited. Captopril had no effect and, indeed, no hydrolysis of BNP-26 by peptidyl dipeptidase A (angiotensin-converting enzyme) was observed even after prolonged incubation with the purified enzyme. The stepwise hydrolysis of BNP-26 by endopeptidase-24.11 was investigated by sequencing the peptides produced during incubation. The initial product resulted from hydrolysis at Ser14-Leu15, thereby opening the ring. This product (BNP') was short-lived; further degradation involved hydrolysis at Ile12-Gly13, Arg8-Leu9, Gly17-Leu18, Val22-Leu23, Arg11-Ile12 and Cys4-Phe5. Thus endopeptidase-24.11 is the principal enzyme in renal microvillar and choroid plexus membranes hydrolysing BNP-26 and alpha-hANP.

Membrane peptidases in the pig choroid plexus and on other cell surfaces in contact with the cerebrospinal fluid

A comprehensive survey of 11 peptidases, all of which are markers for renal microvillar membranes, has been made in membrane fractions prepared from pig choroid plexus. Two fractionation schemes were explored, both depending on a MgCl2-precipitation step, the preferred one having advantages in speed and yield of the activities. The specific activities of the peptidases in the choroid-plexus membranes were, with the exception of carboxypeptidase M, lower than in renal microvillar membranes: those of aminopeptidase N, peptidyl dipeptidase A ('angiotensin-converting enzyme') and gamma-glutamyltransferase were 3-5-fold lower, those of aminopeptidase A and endopeptidase-24.11 were 12-15 fold lower, and those of dipeptidyl peptidase IV and aminopeptidase W were 50-70-fold lower. Carboxypeptidase M had a similar activity in both membranes. Alkaline phosphatase and (Na+ + K+)-activated ATPase were more active in the choroid-plexus membranes. No activity for microsomal dipeptidase, aminopeptidase P and carboxypeptidase P could be detected. Six of the peptidases and (Na+ + K+)-activated ATPase were also studied by immunoperoxidase histochemistry at light- and electron-microscopic levels. Endopeptidase-24.11 and (Na+ + K+)-activated ATPase were uniquely located on the brush border, and the other two peptidases appeared to be much more abundant on the endothelial lining of microvessels. Dipeptidyl peptidase IV and aminopeptidase W were also detected in microvasculature. Pial membranes associated with the brain and spinal cord also stained positively for endopeptidase-24.11, aminopeptidase N and peptidyl dipeptidase A. The immunohistochemical studies indicated the subcellular fractionation did not discriminate between membranes derived from epithelial cells (i.e. microvilli) and those from endothelial cells. The possible significance of these studies in relation to neuropeptide metabolism and the control of cerebrospinal fluid production is discussed.

A fluorimetric assay for aminopeptidase W

A novel two-step enzyme-linked assay for aminopeptidase W is described and validated by comparison with other assays. L-alpha-Glutamyl-L-tryptophan (Glu-Trp) is a favoured substrate for this enzyme. With the use of glutamate dehydrogenase (EC 1.4.1.2) in a second step, the assay measured the release of free glutamate from L-alpha-glutamyl-L-tryptophan by the increase in NADH fluorescence. In the presence of 5 mM-1,10-phenanthroline and 50 microM-cilastatin the contribution of other membrane peptidases, in particular aminopeptidases N and A and microsomal dipeptidase in kidney, was very small. Residual cytosolic activities hydrolysing Glu-Trp were sensitive to inhibition by 2.5 mM-N-ethylmaleimide. The activity of aminopeptidase W was unaffected by these inhibitors. There was good correlation between the fluorimetric assay and those in which the free tryptophan released by kidney membrane fractions was determined by h.p.l.c. or the aminopeptidase W was measured immunoradiometrically with a monoclonal antibody.

Boophilus microplus: the effect of histamine on the attachment of cattle-tick larvae--studies in vivo and in vitro

Circumstantial evidence suggests that the earlier detachment of Boophilus microplus larvae from highly resistant cattle follows the release of histamine at the attachment site. In vivo and in vitro experiments show that a proportion of the larvae will detach following injection or infusion of histamine. Other mediators such as bradykinin, prostaglandin E2, 5-hydroxytryptamine and dopamine have little or no effect on tick behaviour in vivo. Sensitivity to histamine declines as larval attachments stabilize, and repeated injections have no effect on the weight of larvae after 3 days on the host. Response to histamine is discussed in relation to host resistance, histology of the feeding lesion and larval behaviour.

Breast milk substitute: a bacteriological study

The increased susceptibility of infants fed on cows' milk preparations has been attributed, at least in part, to differences in the nature of the large-bowel content-owing to the acidity of the faeces and their high content of Lactobacillus bifidus. In an attempt to mimic these features of the breastfed infant in one who is fed artificially, a breast milk substitute was devised which resembles breast milk in several important ways. When this material was fed to newborn infants the faeces developed the characteristics of those of the breast-fed child.