Role and Function of the Clinical Tutor in Mental Health Nursing in Ireland

The clinical tutor (CT) in mental health nursing is a role aimed at supporting the learning needs of mental health nursing students undertaking a 12-month post-registration programme. This paper aims to examine the role of the clinical tutor in mental health nursing in Ireland by describing the experience of nursing students and key service stakeholders. A qualitative descriptive design was employed using focus group discussions and semi-structured interviews. Two focus groups were conducted with 14 nursing students in the final week of their one-year programme. Semi-structured interviews were undertaken with seven service stakeholders and service leaders. Participants reported positive experiences of working with the clinical tutor and valued the role in terms of educational and pastoral support. Participants suggested the role strengthened the link between theory and practice and enhanced the relationship between the higher education institute and clinical sites. However, a lack of clarity existed in terms of role description. Participants suggested the CT role enhanced the link between the university and clinical areas providing benefits to both student and service stakeholders. Implementing similar roles may benefit post-registration mental health nursing students in other jurisdictions. Further investigation on how the role operates from the perspective of those in the post may provide more clarity and enhance the development of such roles in the future.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), TRAIL receptors, and the soluble receptor osteoprotegerin in human gestational membranes and amniotic fluid during pregnancy and labor at term and preterm

We have studied TNF-related apoptosis-inducing ligand (TRAIL) and its membrane-bound (R1-R4) and soluble receptors [osteoprotegerin (OPG)] in gestational membranes to assess their significance in preterm parturition and premature rupture of membranes (PROM). TRAIL was detected by ELISA in extracts of term choriodecidual (but not amnion) tissues and explant-conditioned media. Concentrations of OPG (determined using ELISA) in gestational membranes were 20- to 50-fold greater than those of TRAIL. Median OPG concentrations in amniotic fluid (AF) at 15-17 wk gestation were similar to those at term before and during labor, whereas levels in pregnancies sampled preterm were significantly elevated. OPG levels in AF from women with preterm PROM were similar to those from women in preterm labor. In contrast, in pooled AF samples (n = 23-33), TRAIL concentrations at term with and without labor were elevated compared with samples from preterm deliveries. TRAIL-R3 and -R4 decoy receptors were detected in term amnion and choriodecidual extracts by immunoblotting and were localized by immunohistochemistry to amnion epithelial cells and chorionic trophoblasts. TRAIL (100 ng/ml) had little or no effect on amnion or choriodecidual cell viability or apoptosis, although these tissues responded to TNF-alpha with increased prostaglandin E(2) production. Our findings suggest that OPG is abundant in gestational membranes and, in concert with TRAIL decoy receptors, may protect resident cells of the fetal membranes against the proapoptotic effects of TRAIL and other related ligands during pregnancy.

Three families with autosomal dominant nephrogenic diabetes insipidus caused by aquaporin-2 mutations in the C-terminus

The vasopressin-regulated water channel aquaporin-2 (AQP2) is known to tetramerize in the apical membrane of the renal tubular cells and contributes to urine concentration. We identified three novel mutations, each in a single allele of exon 4 of the AQP2 gene, in three families showing autosomal dominant nephrogenic diabetes insipidus (NDI). These mutations were found in the C-terminus of AQP2: a deletion of G at nucleotide 721 (721 delG), a deletion of 10 nucleotides starting at nucleotide 763 (763-772del), and a deletion of 7 nucleotides starting at nucleotide 812 (812-818del). The wild-type AQP2 is predicted to be a 271-amino acid protein, whereas these mutant genes are predicted to encode proteins that are 330-333 amino acids in length, because of the frameshift mutations. Interestingly, these three mutant AQP2s shared the same C-terminal tail of 61 amino acids. In Xenopus oocytes injected with mutant AQP2 cRNAs, the osmotic water permeability (Pf) was much smaller than that of oocytes with the AQP2 wild-type (14%-17%). Immunoblot analysis of the lysates of the oocytes expressing the mutant AQP2s detected a band at 34 kD, whereas the immunoblot of the plasma-membrane fractions of the oocytes and immunocytochemistry failed to show a significant surface expression, suggesting a defect in trafficking of these mutant proteins. Furthermore, coinjection of wild-type cRNAs with mutant cRNAs markedly decreased the oocyte Pf in parallel with the surface expression of the wild-type AQP2. Immunoprecipitation with antibodies against wild-type and mutant AQP2 indicated the formation of mixed oligomers composed of wild-type and mutant AQP2 monomers. Our results suggest that the trafficking of mutant AQP2 is impaired because of elongation of the C-terminal tail, and the dominant-negative effect is attributed to oligomerization of the wild-type and mutant AQP2s. Segregation of the mutations in the C-terminus of AQP2 with dominant-type NDI underlies the importance of this domain in the intracellular trafficking of AQP2.

Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus

Over 155 mutations within the V2 vasopressin receptor (AVPR2) gene are responsible for nephrogenic diabetes insipidus (NDI). The expression and subcellular distribution of four of these was investigated in transfected cells. These include a point mutation in the seventh transmembrane domain (S315R), a frameshift mutation in the third intracellular loop (804delG), and two nonsense mutations that code for AVPR2 truncated within the first cytoplasmic loop (W71X) and in the proximal portion of the carboxyl tail (R337X). RT-PCR revealed that mRNA was produced for all mutant receptor constructs. However, no receptor protein, as assessed by Western blot analysis, was detected for 804delG. The S315R was properly processed through the Golgi and targeted to the plasma membrane but lacked any detectable AVP binding or signaling. Thus, this mutation induces a conformational change that is compatible with endoplasmic reticulum (ER) export but dramatically affects hormone recognition. In contrast, the W71X and R337X AVPR2 were retained inside the cell as determined by immunofluorescence. Confocal microscopy revealed that they were both retained in the ER. To determine if calnexin could be involved, its interaction with the AVPR2 was assessed. Sequential coimmunoprecipitation demonstrated that calnexin associated with the precursor forms of both wild-type (WT) and mutant receptors in agreement with its general role in protein folding. Moreover, its association with the ER-retained R337X mutant was found to be longer than with the WT receptor suggesting that this molecular chaperone also plays a role in quality control and ER retention of misfolded G protein-coupled receptors.

Pharmacological chaperones rescue cell-surface expression and function of misfolded V2 vasopressin receptor mutants

Over 150 mutations within the coding sequence of the V2 vasopressin receptor (V2R) gene are known to cause nephrogenic diabetes insipidus (NDI). A large number of these mutant receptors fail to fold properly and therefore are not routed to the cell surface. Here we show that selective, nonpeptidic V2R antagonists dramatically increase cell-surface expression and rescue the function of 8 mutant NDI-V2Rs by promoting their proper folding and maturation. A cell-impermeant V2R antagonist could not mimic these effects and was unable to block the rescue mediated by a permeant agent, indicating that the nonpeptidic antagonists act intracellularly, presumably by binding to and stabilizing partially folded mutants. In addition to opening new therapeutic avenues for NDI patients, these data demonstrate that by binding to newly synthesized mutant receptors, small ligands can act as pharmacological chaperones, promoting the proper folding and maturation of receptors and their targeting to the cell surface.

Functional studies of twelve mutant V2 vasopressin receptors related to nephrogenic diabetes insipidus: molecular basis of a mild clinical phenotype

X-linked nephrogenic diabetes insipidus (NDI) is a rare disease with defective renal and extrarenal arginine vasopressin V2 receptor responses due to mutations in the AVPR2 gene in Xq28. To study the cause of loss of function of mutant V2 receptors, we expressed 12 mutations (N55H, L59P, L83Q, V88M, 497CC-->GG, deltaR202, I209F, 700delC, 908insT, A294P, P322H, P322S) in COS-7 cells. Eleven of these, including P322H, were characterized by a complete loss of function, but the mutation P322S demonstrated a mild clinical and in vitro phenotype. This was characterized by a late diagnosis without any growth or developmental delay and a significant increase in urine osmolality after intravenous 1-deamino[D-Arg8]AVP administration. In vitro, the P322S mutant was able to partially activate the Gs/adenylyl cyclase system in contrast to the other V2R mutants including P322H, which were completely inactive in this regard. This showed not only that Pro 322 is important for proper V2R coupling, but also that the degree of impairment is strongly dependent on the identity of the substituting amino acid. Three-dimensional modeling of the P322H and P322S mutant receptors suggested that the complete loss of function of the P322H receptor could be due, in part, to hydrogen bond formation between the His 322 side chain and the carboxyl group of Asp 85, which does not occur in the P322S receptor.

An aquaporin-2 water channel mutant which causes autosomal dominant nephrogenic diabetes insipidus is retained in the Golgi complex

Mutations in the aquaporin-2 (AQP2) water channel gene cause autosomal recessive nephrogenic diabetes insipidus (NDI). Here we report the first patient with an autosomal dominant form of NDI, which is caused by a G866A transition in the AQP2 gene of one allele, resulting in a E258K substitution in the C-tail of AQP2. To define the molecular cause of NDI in this patient, AQP2-E258K was studied in Xenopus oocytes. In contrast to wild-type AQP2, AQP2-E258K conferred a small increase in water permeability, caused by a reduced expression at the plasma membrane. Coexpression of wild-type AQP2 with AQP2-E258K, but not with an AQP2 mutant in recessive NDI (AQP2-R187C), revealed a dominant-negative effect on the water permeability conferred by wild-type AQP2. The physiologically important phosphorylation of S256 by protein kinase A was not affected by the E258K mutation. Immunoblot and microscopic analyses revealed that AQP2-E258K was, in contrast to AQP2 mutants in recessive NDI, not retarded in the endoplasmic reticulum, but retained in the Golgi compartment. Since AQPs are thought to tetramerize, the retention of AQP2-E258K together with wild-type AQP2 in mixed tetramers in the Golgi compartment is a likely explanation for the dominant inheritance of NDI in this patient.

Nature and recurrence of AVPR2 mutations in X-linked nephrogenic diabetes insipidus

X-linked nephrogenic diabetes insipidus (NDI) is a rare disease with defective renal and extrarenal arginine-vaso-pressin V2 receptor responses due to mutations in the AVPR2 gene in Xq28. We analyzed 31 independent NDI families to determine the nature and recurrence of AVPR2 mutations. Twenty-one new putative disease-causing mutations were identified: 113delCT, 253del35, 255de19, 274insG, V88M, R106C, 402delCT, C112R, Y124X, S126F, W164S, S167L, 684delTA, 804insG, W284X, A285P, W293X, R337X, and three large deletions or gene rearrangements. Five other mutations--R113W, Y128S, R137H, R181C, and R202C--that previously had been reported in other families were detected. There was evidence for recurrent mutation for four mutations (R113W, R137H, S167L, and R337X). Eight de novo mutation events were detected (274insG, R106C, Y128S, 167L [twice], R202C, 684delTA, and R337X). The origins were maternal (one), grandmaternal (one), and grandpaternal (six). In the 31 NDI families and 6 families previously reported by us, there is evidence both for mutation hot spots for nucleotide substitutions and for small deletions and insertions. More than half (58%) of the nucleotide substitutions in 26 families could be a consequence of 5-methyl-cytosine deamination at a CpG dinucleotide. Most of the small deletions and insertions could be attributed to slipped mispairing during DNA replication.

Mutations in the vasopressin V2 receptor gene in families with nephrogenic diabetes insipidus and functional expression of the Q-2 mutant

Nephrogenic diabetes insipidus (NDI) is characterized by a resistance of the kidney towards arginine vasopressin (AVP). Following molecular cloning of the vasopressin V2 receptor, we identified different mutations in the V2 receptor gene in families with X-linked NDI, which segregated with the disease. The Hopewell mutation (W71X) causes the disease in the largest North American NDI pedigree, with most of its members residing on Nova Scotia. Different mutations were found in three families from the Quebec area (Q-2: R137H, Q-3: R113W, Q-5: 804delG) and in the large Cannon kindred residing in Utah (L312X). In an Iranian family (O-1), another mutation was detected (A132D). Three of the six mutations (Hopewell, Cannon, Q-5) are predicted to cause the expression of a truncated V2 receptor and are therefore unlikely to function. The functional consequences of missense mutations (Q-2, Q-3, O-1) are less obvious. We therefore introduced the Q-2 mutation into wild-type cDNA. When expressed in COS.M6 or Ltk cells, the Q-2 mutant bound AVP with normal affinity. However, cells expressing the Q-2 mutant failed to respond to AVP with an increase in adenylyl cyclase activity. Thus the Q-2 mutant is unable to interact with or to activate the stimulatory G-protein Gs. The present data indicate that X-linked NDI is frequently attributable to a mutation in the V2 receptor gene. In addition, the data prove biochemically that the Q-2 mutation is the cause of NDI in the Q-2 family.

Predicting operative mortality after coronary artery bypass surgery in males

The general practitioner often requires a simple and reliable method of determining the potential risks of surgical intervention. We derived and tested a simple clinical scoring system for the preoperative prediction of 30-day mortality after coronary artery bypass surgery. From a national register of all open heart operations in the Republic of Ireland 1984-1989, we identified 4276 male patients who had primary isolated non-emergency coronary artery bypass surgery. Using logistic regression, we derived a clinical scoring system to predict operative (30-day) mortality in patients operated on between 1984 and 1987. We then prospectively evaluated the score on patients seen over the next two years. Variables identified for our scoring system were age, recent myocardial infarction, left ventricular failure, extensive distal coronary artery disease and body surface area. Five risk categories were defined; mortality in the high-risk group was 9.7-fold (95% CI: 4.6-20.7) greater than in the low-risk group. When tested on new patients, the relative mortality between the two risk groups was 15.2 (4.6-50.5). The observed and predicted mortalities in each risk group showed close agreement. This clinical scoring system, easily used by a general practitioner, can predict operative mortality in males for whom primary isolated coronary artery bypass surgery is contemplated.

A regulatory element in the beta 2-microglobulin promoter identified by in vivo footprinting

Expression of the beta 2-microglobulin (beta 2-m) and major histocompatibility complex (MHC) class I genes is coordinately regulated. By ligation-mediated polymerase chain reaction, we have analyzed in vivo factor binding to the promoter region of the murine beta 2-m gene. In adult spleen, in which beta 2-m is expressed, strong protection was found in three elements. Two of these elements, the beta 2-m NF-kappa B binding site and the interferon consensus sequence, are homologous to the regulatory elements of the MHC class I genes and were also found to be protected in spleen. A third protected element, PAM, identified in this work, is unique to the beta 2-m gene. None of the elements showed protection in brain tissue, in which neither the beta 2-m nor the MHC class I gene is expressed. In vivo footprinting was also performed with F9 embryonal carcinoma cells, in which expression of the beta 2-m and MHC class I genes is induced at a low level only upon stimulation with retinoic acid (RA). No in vivo protection was detected before and after RA treatment of F9 cells, indicating that RA induction of beta 2-m (and MHC class I) expression occurs without detectable in vivo factor occupancy, whereas EL4 T lymphocytes expressing beta 2-m at a high level exhibited strong protection similar to that in spleen. Despite the lack of in vivo occupancy, the nuclear factors specific for each of the three elements were present in brain tissue and F9 cells as well as in spleen tissue and EL4 cells. We show that PAM, an element identified by its in vivo protection, binds nuclear factors ranging from 40 to 50 kDa in size and is capable of enhancing transcription of a reporter in F9 and other cells. Taken together, these results indicate that in vivo factor occupancy for the beta 2-m and MHC class I promoters is coordinated and occurs through a mechanism other than mere expression of relevant factors.

X-linked nephrogenic diabetes insipidus mutations in North America and the Hopewell hypothesis

In X-linked nephrogenic diabetes insipidus (NDI) the urine of male patients is not concentrated after the administration of the antidiuretic hormone arginine-vasopressin. This disease is due to mutations in the V2 receptor gene that maps to chromosome region Xq28. In 1969, Bode and Crawford suggested that most NDI patients in North America shared common ancestors of Ulster Scot immigrants who arrived in Halifax in 1761 on the ship Hopewell. A link between this family and a large Utah kindred was also suggested. DNA was obtained from 17 affected male patients from the "Hopewell" kindred and from four additional families from Nova Scotia and New Brunswick who shared the same Xq28 NDI haplotype. The Utah kindred and two families (Q2, Q3) from Quebec were also studied. The "Hopewell" mutation, W71X, is a single base substitution (G-->A) that changes codon 71 from TGG (tryptophan) to TGA (stop). The W71X mutation was found in affected members of the Hopewell and of the four satellite families. The W71X mutation is the cause of X-linked NDI for the largest number of related male patients living in North America. Other families (Utah, Q2 and Q3) that are historically and ethnically unrelated bear other mutations in the V2 receptor gene.

Regulation of MHC class I and beta 2-microglobulin gene expression in human neuronal cells. Factor binding to conserved cis-acting regulatory sequences correlates with expression of the genes

MHC class I molecules are coexpressed with beta 2-microglobulin (beta 2-M) on many somatic cells. However, these proteins are normally not present on cells of the central nervous system (CNS). Cells derived from human neuroblastomas were used as a model for investigating the molecular basis for the paucity of MHC class I and beta 2-M gene expression in neural cells and for the induction of these genes by two cytokines, IFN-gamma, and TNF-alpha. These cytokines independently increased MHC class I and beta 2-M cell surface expression on the neuroblastoma cell lines. IFN-gamma or TNF-alpha also increased MHC class I and beta 2-M steady-state RNA levels and the expression of MHC class I and beta 2-M CAT reporter constructs transiently transfected into the neuroblastoma cell lines, indicating that the cytokines acted by increasing the transcription of these genes. MHC class I and beta 2-M genes share two conserved regulatory elements, an NF kappa B-like site and the IFN consensus sequence, that act as a constitutive enhancer and an IFN-responsive element, respectively. Low MHC class I and beta 2-M gene expression in these cells was accounted for by undetectable to low factor binding activity specific for the above regulatory elements of these genes. TNF-alpha increased factor binding activity specific for the NF kappa B-like elements and IFN-gamma increased factor binding activity specific for the IFN consensus sequence elements of the MHC class I and beta 2-M genes, but not vice versa. Taken together, our results indicated that IFN-gamma and TNF-alpha increased MHC class I and beta 2-M gene expression in the neuroblastoma cell lines by inducing factor binding to the regulatory elements present in both genes.

Regulation of MHC class I and beta 2-microglobulin gene expression in human neuronal cells. Factor binding to conserved cis-acting regulatory sequences correlates with expression of the genes

MHC class I molecules are coexpressed with beta 2-microglobulin (beta 2-M) on many somatic cells. However, these proteins are normally not present on cells of the central nervous system (CNS). Cells derived from human neuroblastomas were used as a model for investigating the molecular basis for the paucity of MHC class I and beta 2-M gene expression in neural cells and for the induction of these genes by two cytokines, IFN-gamma, and TNF-alpha. These cytokines independently increased MHC class I and beta 2-M cell surface expression on the neuroblastoma cell lines. IFN-gamma or TNF-alpha also increased MHC class I and beta 2-M steady-state RNA levels and the expression of MHC class I and beta 2-M CAT reporter constructs transiently transfected into the neuroblastoma cell lines, indicating that the cytokines acted by increasing the transcription of these genes. MHC class I and beta 2-M genes share two conserved regulatory elements, an NF kappa B-like site and the IFN consensus sequence, that act as a constitutive enhancer and an IFN-responsive element, respectively. Low MHC class I and beta 2-M gene expression in these cells was accounted for by undetectable to low factor binding activity specific for the above regulatory elements of these genes. TNF-alpha increased factor binding activity specific for the NF kappa B-like elements and IFN-gamma increased factor binding activity specific for the IFN consensus sequence elements of the MHC class I and beta 2-M genes, but not vice versa. Taken together, our results indicated that IFN-gamma and TNF-alpha increased MHC class I and beta 2-M gene expression in the neuroblastoma cell lines by inducing factor binding to the regulatory elements present in both genes.

X-linked nephrogenic diabetes insipidus: from the ship Hopewell to RFLP studies

Nephrogenic diabetes insipidus (NDI; designated 304800 in Mendelian Inheritance in Man) is an X-linked disorder with abnormal renal and extrarenal V2 vasopressin receptor responses. The mutant gene has been mapped to Xq28 by analysis of RFLPs, and tight linkage between DXS52 and NDI has been reported. In 1969, Bode and Crawford proposed, under the term "the Hopewell hypothesis," that most cases in North America could be traced to descendants of Ulster Scots who arrived in Nova Scotia in 1761 on the ship Hopewell. They also suggested a link between this family and a large Mormon pedigree. DNA samples obtained from 13 independent affected families, including 42 members of the Hopewell and Mormon pedigrees, were analyzed with probes in the Xq28 region. Genealogical reconstructions were performed. Linkage between NDI and DXS304 (probe U6:2.spl), DXS305 (St35-691), DXS52 (St14-1), DXS15 (DX13), and F8C (F814) showed no recombination in 12 families, with a maximum lod score of 13.5 for DXS52. A recombinant between NDI and DXS304, DXS305, was identified in one family. The haplotype segregating with the disease in the Hopewell pedigree was not shared by other North American families. PCR analysis of the St14 VNTR allowed the distinction of two alleles that were not distinguishable by Southern analysis. Carrier status was predicted in 24 of 26 at-risk females. The Hopewell hypothesis cannot explain the origin of NDI in many of the North American families, since they have no apparent relationship with the Hopewell early settlers, either by haplotype or by genealogical analysis. We confirm the locus homogeneity of the disease by linkage analysis in ethnically diverse families. PCR analysis of the DXS52 VNTR in NDI families is very useful for carrier testing and presymptomatic diagnosis, which can prevent the first manifestations of dehydration.

Molecular identification of the gene responsible for congenital nephrogenic diabetes insipidus

Antidiuretic hormone (arginine vasopressin) binds to and activates V2 receptors in renal collecting tubule cells. Subsequent stimulation of the Gs/adenylyl cyclase system promotes insertion of water pores into the luminal membrane and thereby reabsorption of fluid. In congenital nephrogenic diabetes insipidus (CNDI), an X-linked recessive disorder, the kidney fails to respond to arginine vasopressin. Here we report that an affected male of a family with CNDI has a deletion in the open reading frame of the V2 receptor gene, causing a frame shift and premature termination of translation in the third intracellular loop of the receptor protein. A normal receptor gene was found in the patient's brother. Both the normal and the mutant allele were detected in his mother. A different mutation, causing a codon change in the third transmembrane domain of the V2 receptor, was found in the open reading frame of an affected male but not in the unaffected brother belonging to another family suffering from CNDI.

Occupancy of upstream regulatory sites in vivo coincides with major histocompatibility complex class I gene expression in mouse tissues

The major histocompatibility complex (MHC) class I HLA-B7 transgene carrying a 660-bp upstream sequence is expressed in the mouse with tissue specificity that parallels that of the expression of endogenous mouse MHC class I (H-2) genes. We have performed in vivo genomic footprinting for the HLA-B7 transgene and the endogenous H-2Kb gene. We show that the upstream region of both the transgene and the endogenous gene was extensively occupied in spleen tissue, where these genes are expressed at high levels. In contrast, no occupancy was detected in brain tissue, where expression of these genes is virtually absent. Sites exhibiting in vivo protection correspond to cis elements previously shown to bind to nuclear factors in vitro, including the constitutive enhancer region I and the interferon response element. The strongest tissue-specific protection was detected at site alpha, located downstream from the interferon response element. Site alpha bound a constitutively expressed nuclear factor(s) in vitro that exhibited an overlapping specificity which may involve a nuclear hormone receptor, RXR, and an AP-1-related factor. Site alpha was functional in vivo, as it enhanced MHC class I transcription in lymphocytes. These results show that the tissue-specific occupancy of the MHC class I regulatory sequences in vivo correlates with their expression and suggest that in vivo occupancy is controlled by a mechanism other than the mere presence of factors capable of binding to these sites. Our results suggest that a sequence present in the 660-bp upstream region in a human leukocyte antigen gene directs tissue-specific occupancy of MHC class I genes in vivo, independently of their position and copy number, illustrating a potential advantage of using a transgene for delimitation of the sequence requirement for in vivo occupancy.

Vasopressin antagonist inhibition of clotting factor release in the rhesus monkey (Macaca mulatta)

The antidiuretic (V2) agonist, dDAVP, stimulates release of the clotting factors von Willebrand factor (vWF) and factor VIIIc (FVIIIc) in humans. The objective of these studies was to identify and characterize dDAVP stimulation of clotting factor release in pentobarbital-anesthetized rhesus monkeys using V2 receptor agonists (dDAVP, SK&F 101926, SK&F 104146, SK&F 104244) and a V2 receptor antagonist (SK&F 105494) given i.v. dDAVP (3.0 micrograms/kg) stimulated release of vWF, FVIIIc and renin and was associated with tachycardia and blood pressure-lowering activity. The V2 receptor antagonist, SK&F 105494 (30 micrograms/kg, i.v.), had no effect on clotting factor release, heart rate or blood pressure, but prevented dDAVP stimulation of clotting factor release and tachycardia. The V2 agonists SK&F 101926, SK&F 104146 and SK&F 104244 did not stimulate clotting factor release, blood pressure, heart rate or plasma renin activity in this species at the doses tested. Thus, the rhesus monkey is a nonhuman primate species in which dDAVP stimulation of FVIIIc and vWF occurs. The results support the hypothesis that dDAVP stimulation of clotting factor release is mediated by a low-affinity, V2-like receptor mechanism. The tachycardia and renin release associated with dDAVP administration are most likely secondary to vasodilation, also mediated by a V2-like mechanism.

Platelet vasopressin receptors in patients with congenital nephrogenic diabetes insipidus

Arginine-vasopressin (AVP), interacts with at least two types of receptors: V1 receptors which mediate the aggregating effects of AVP on human blood platelets and other AVP actions on vascular smooth muscle and hepatocytes; and V2 receptors which mediate the antidiuretic effects on renal tubules. Congenital nephrogenic diabetes insipidus (CNDI) is a rare X-linked disorder in humans with abnormal renal and extrarenal V2-receptor responses. However, the V1 receptor responses are apparently normal, since in these patients blood pressure increases in response to AVP. To assess V1 receptor responses, binding studies (3H-AVP) were done on intact platelets obtained from 6 male patients with CNDI, 10 normal subjects and 4 patients with autosomal dominant central diabetes insipidus (ADCDI). The affinity constant (0.68 +/- 0.04 vs. 0.59 +/- 0.06 nM) and the number of specific binding sites per platelet (101 +/- 6 vs. 86 +/- 12) were similar in the normal subjects and the patients with CNDI. However, the number of binding sites per platelet was increased in the patients with ADCDI (189 +/- 12). Platelet aggregation induced by AVP was equivalent in the three groups. Platelet-fraction AVP was elevated in patients with CNDI and undetectable in patients with ADCDI. These results suggest that the structure and the function of V1 platelet receptor-effector pathway are normal in patients with CNDI.

Physiological roles of Na+/Ca2+ exchange in Limulus ventral photoreceptors

In previous work we have presented evidence for electrogenic Na+/Ca2+ exchange in Limulus ventral photoreceptors (1989. J. Gen. Physiol. 93:473-492). This article assesses the contributions to photoreceptor physiology from Na+/Ca2+ exchange. Four separate physiological processes were considered: maintenance of resting sensitivity, light-induced excitation, light adaptation, and dark adaptation. (a) Resting sensitivity: reduction of [Na+]o caused a [Ca2+]o-dependent reduction in light sensitivity and a speeding of the time courses of the responses to individual test flashes; this effect was dependent on the final value to which [Na+]o was reduced. The desensitization caused by Na+ reduction was dependent on the initial sensitivity of the photoreceptor; in fully dark-adapted conditions no desensitization was observed; in light-adapted conditions, extensive desensitization was observed. (b) Excitation: Na+ reduction in fully dark-adapted conditions caused a Ca2+o-dependent depolarizing phase in the receptor potential that persisted beyond the stimulus duration and was evoked by a bright adapting flash. (c) Light adaptation: the degree of desensitization induced by a bright adapting flash was Na+o dependent, being larger with lower [Na+]o. Na+ reduction enhanced light adaptation only at intensities brighter than 4 x 10(-6) W/cm2. In addition to being Na+o dependent, light adaptation was Ca2+o dependent, being greater at higher [Ca2+]o. (d) Dark adaptation: the recovery of light sensitivity after adapting illumination was Na+o dependent. Dark adaptation after bright illumination in voltage-clamped and in unclamped conditions was faster in normal-Na+ saline than in reduced Na+ saline. The final sensitivity to which photoreceptors recovered was lower in reduced-Na+ saline when bright adapting illumination was used. The results suggest the involvement of Na+/Ca2+ exchange in each of these physiological processes. Na+/Ca2+ exchange may contribute to these processes by counteracting normal elevations in [Ca2+]i.

Fused rhabdomeres (fur) in Drosophila: an eye mutation that alters rhabdomere morphology and retinal function

In the Drosophila compound eye, the photoreceptor cells are organized in highly precise units, the ommatidia. In each photoreceptor cell, the primary photopigment, opsin, is contained in the rhabdomere, an ordered array of densely packed microvilli. A genetic and phenotypic analysis of a new X-linked. P element-induced mutation, fur, (fused rhabdomeres) is presented. Light and electron microscope studies show that mutations at the fur locus result in the fusion of the adjacent rhabdomeres in the developing eye and the fusion takes place during the pupal stage of eye development. Electrophysiological experiments indicate that the fur mutant photoreceptors have reduced sensitivity to light and lack a PDA (prolonged depolarizing afterpotential), a response characteristic of normal photoreceptor cells. Recombination and deficiency mapping localize fur to the proximal region of the X chromosome. Reversion analysis indicates the fur mutant is the result of a P element insertion. These studies suggest that the fur locus encodes a gene that has specific roles in rhabdomere morphogenesis and retinal function.

Mortality in the first year after coronary artery bypass surgery. Irish Cardiac Surgery Register

In the three years 1983-1985 the Irish Cardiac Surgery Register (ICSR) recorded details on 1,534 patients who underwent primary isolated coronary artery bypass grafting (CABG). This unselected series of patients accounted for all such operations in the Republic of Ireland during this period and provides information on a wide spectrum of clinical subgroups of patients with ischaemic heart disease. There were 52 operative deaths (3.4%). At one year the number of deaths had risen to 75 (4.9%). Factors related to operative mortality were female sex, age greater than 60, left ventricular failure, history of myocardial infarction in the six weeks prior to surgery, poor left ventricular function and extensive disease of vessels to be grafted. All of the above factors except female sex were related to one year mortality. Analysis of late deaths (1.5%) separately showed evidence of pre-operative impaired left ventricular function to be an important prognostic indicator.

Epinephrine and dDAVP administration in patients with congenital nephrogenic diabetes insipidus. Evidence for a pre-cyclic AMP V2 receptor defective mechanism

We recently showed that the administration of the antidiuretic V2 specific agonist, 1-desamino[8-D-arginine]vasopressin (dDAVP), to seven male patients with congenital nephrogenic diabetes insipidus (CNDI) did not cause a decrease in blood pressure nor an increase in plasma renin activity or factor VIIIc or von Willebrand factor release. In normal subjects, plasma renin activity, coagulation factors and plasma cyclic AMP are stimulated not only by dDAVP but also by the administration of epinephrine. In the present study, we measured tissue plasminogen activator (activity and antigenicity), von Willebrand factor multimers, plasma and urinary cyclic AMP concentrations following dDAVP or epinephrine administration. We infused epinephrine into three male patients with CNDI. Factor VIIIc and tissue plasminogen activator augmented by 75 to 100% and von Willebrand Factor multimers were increased; plasma renin activity and plasma cyclic AMP concentration increased by 200%. None of these values changed when the same subjects as well as eleven other male patients with CNDI received dDAVP. Furthermore, dDAVP administration increased plasma cyclic AMP concentrations in normal subjects, but not in 14 male patients with CNDI. These results demonstrate the specificity of the extrarenal V2 receptor defect expressed in our patients. The lack of a plasma cyclic AMP response to the administration of dDAVP would suggest an altered pre-cyclic AMP stimulation mechanism.

Hemodynamic and coagulation responses to 1-desamino[8-D-arginine] vasopressin in patients with congenital nephrogenic diabetes insipidus

The antidiuretic hormone arginine vasopressin interacts with two types of receptors: V1, which mediates the effects of vasopressin on vascular smooth muscle, and V2, which mediates the antidiuretic effects on renal tubules. Resistance of the renal tubules to arginine vasopressin and to the antidiuretic V2-specific agonist 1-desamino[8-D-arginine] vasopressin (dDAVP) occurs in congenital nephrogenic diabetes insipidus, a rare X-linked disease, although the V1-receptor responses remain intact. The extrarenal actions of dDAVP in normal persons are a decrease in blood pressure, an increase in plasma renin activity, and stimulation of the release of factor VIIIc and von Willebrand factor. We measured the response of mean arterial pressure, pulse rate, plasma renin activity, factor VIIIc, and von Willebrand factor to an infusion of dDAVP (0.3 microgram per kilogram of body weight) in seven male patients with congenital nephrogenic diabetes insipidus, six obligatory carriers of the gene for nephrogenic diabetes insipidus, five patients with central diabetes insipidus, and four normal subjects. In the normal subjects and the patients with central diabetes insipidus, dDAVP decreased mean arterial pressure (by 10 to 15 percent) and increased pulse rate (by 20 to 25 percent), renin activity (by 65 percent), and the release of coagulation factors (twofold to threefold) (all changes were significant, P less than 0.01). None of these changes were observed in the patients with congenital nephrogenic diabetes insipidus, and minimal responses were observed in the obligatory carriers. These results confirm the existence of extrarenal vasopressin V2-like receptors, which may be defective in patients with congenital nephrogenic diabetes insipidus.

Human platelet fraction arginine-vasopressin. Potential physiological role

Arginine-vasopressin (AVP) immunoreactivity (Ir) has been found to be elevated in platelet-rich plasma. PlatAVP was defined as platelet-rich plasma Ir minus platelet-poor plasma Ir (Pavp). PlatAVP, Pavp, and synthetic AVP were found to have identical retention time on high performance liquid chromatography analysis and similar mobility on thin-layer chromatography. During a standard osmotic suppression-stimulation test, Pavp increased with plasma osmolality (Posm, mosmol/kg H2O); Pavp (pg/ml) = 0.98 (Posm -274.4), r = 0.57, P less than 0.001, n = 65; but PlatAVP was not significantly correlated with Posm and remained at 5 pg/ml. This PlatAVP concentration was estimated to represent a true intraplatelet AVP concentration of 0.4 to 3.7 X 10(-9) M. Binding studies on intact human platelets demonstrated specific binding sites for [3H]AVP (n = 16; BMax = 98 +/- 30 binding sites/platelet; Kd = 0.72 +/- 0.24 nM). This in vitro affinity association constant (Kd) was close to the estimated in vivo intraplatelet AVP concentration. Measurement of PlatAVP could estimate vasopressin bound to a specific platelet receptor.

Presynaptic and postsynaptic depressant effects of phenytoin sodium at the neuromuscular junction

1. Phenytoin sodium, 10 micrograms/ml (3.6 x 10(-5) M), reduces the amplitude of endplate potentials in mouse sternomastoid neuromuscular junctions. 2. The reduction in amplitude is due to a reduction both in the quantal content of endplate potentials and in the amplitude of the voltage response to quanta of acetylcholine. 3. The reduction caused by phenytoin in the amplitude of spontaneous miniature end plate potentials was due to a reduction in the time constant of decay of miniature endplate currents. 4. It is concluded that phenytoin depresses neuromuscular transmission by reducing both the amount of acetylcholine secreted in response to an action potential and by reducing the lifetime of postsynaptic channels activated by acetylcholine.

American mucocutaneous leishmaniasis

Presented is a well-documented, autochthonous case of mucocutaneous leishmaniasis, a protozoan disease endemic to Asia, Africa, Southern Europe, South America, and Central America, which until recently was not found in North America. Diagnosis is made by positive culture on NNN media, positive serodiagnosis, positive Montenegro skin test, the presence of Leishman-Donovan bodies on Giemsa stain with light microscopy, and the presence of the kinetoplast within the organism on electron microscopy. The recommended treatment is sodium antimony gluconate given intramuscularly, 600 mg daily for seven to ten days.

Changes on recovery in the concentrations of tryptophan and the biogenic amine metabolites in the cerebrospinal fluid of patients with affective illness

The concentration of the acid metabolites of dopamine, and 5-hydroxytryptamine (5-HT), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA) respectively, were estimated in the cerebrospinal fluid of patients suffering from either unipolar or bipolar affective illness, both before and after recovery. Significantly low concentrations of HVA and 5-HIAA (P<0·01 and 0·05 respectively) were found in the unipolar depressed group and these did not return to normal on recovery. Depressed bipolar patients had levels within normal limits. In bipolar manic patients the HVA concentration fell on recovery to a level significantly lower (P<0·05) than controls. There was no difference in the levels of tryptophan in the CSF of any of the groups of patients nor was there any alteration on recovery. There was a high correlation between 5-HIAA and HVA in the same CSF. These findings are against the amine hypothesis which postulated in depression a lowered concentration of transmitter amine at synaptic junction.