Biocompatibility and immunologic properties of pericardial tissue stabilized by dye-mediated photooxidation

BACKGROUND AND AIMS OF THE STUDY

Bovine and porcine pericardial tissues stabilized by dye-mediated photooxidation have found application as bioprosthetic heart valve material.

METHODS

To help predict clinical performance, a series of tests were performed to assess the biocompatibility and immunologic properties of these materials.

RESULTS AND CONCLUSIONS

Photooxidized bovine or porcine pericardium sterilized with an iodine-based solution were found to be non-cytotoxic, non-hemolytic, and non-mutagenic. Oil or saline extracts of these tissues passed tests for intracutaneous toxicity (irritation), acute systemic toxicity, and subchronic toxicity. Histopathology of 90-day implants of these tissues in the rabbit model demonstrated no significant macroscopic reaction and only slight microscopic response. Using a rabbit model to assess immune response, both bovine and porcine pericardial tissues elicited low levels of antibody. Furthermore, tissue photooxidation or iodine sterilization did not increase the overall level of antibodies. Glutaraldehyde-treated tissue also elicited low antibody levels which were higher than photooxidized tissue-induced levels. Absorption studies indicated that the photooxidation process may generate new epitopes, possibly collagen cross-links. Using the juvenile sheep model to assess in vivo performance, bioprosthetic valves made with photooxidized tissue were implanted and allowed to serve as functional implants for up to two years. Upon explant, the photooxidized pericardial leaflets were found to be non-calcific and partially covered with a layer of host cells. Histological cross-sections stained with von Willebrand's factor confirmed this layer as endothelial cells.

Patterns of immunodominance in HIV-1-specific cytotoxic T lymphocyte responses in two human histocompatibility leukocyte antigens (HLA)-identical siblings with HLA-A*0201 are influenced by epitope mutation

Primary human immunodeficiency virus (HIV) infection is controlled principally by HIV-specific cytotoxic T lymphocytes (CTL) to a steady-state level of virus load, which strongly influences the ultimate rate of progression to disease. Epitope selection by CTL may be an important determinant of the degree of immune control over the virus. This report describes the CTL responses of two HLA-identical hemophiliac brothers who were exposed to identical batches of Factor VIII and became seropositive within 10 wk of one another. Both have HLA-A*0201. The CTL responses of the two siblings were very dissimilar, one donor making strong responses to two epitopes within p17 Gag (HLA-A*0201-restricted SLYNTVATL and HLA-A3-restricted RLRPGGKKK). The sibling responded to neither epitope, but made strong responses to two epitopes presented by HLA-B7. This was not the result of differences in presentation of the epitopes. However, mutations in both immunodominant epitopes of the p17 Gag responder were seen in proviral sequences of the nonresponder. We then documented the CTL responses to two HLA-A*0201-restricted epitopes, in Gag (SLYNTVATL) and Pol (ILKEPVHGV) in 22 other HIV-infected donors with HLA-A*0201. The majority (71%) generated responses to the Gag epitope. In the 29% of donors failing to respond to the Gag epitope in standard assays, there was evidence of low frequency memory CTL responses using peptide stimulation of PBMC, and most of these donors also showed mutations in or around the Gag epitope. We concluded that HLA class I genotype determines epitope selection initially but that mutation in immunodominant epitopes can profoundly alter the pattern of CTL response.

Positive selection of HIV-1 cytotoxic T lymphocyte escape variants during primary infection

Cytotoxic T lymphocytes (CTLs) are thought to play a crucial role in the termination of the acute primary HIV-1 syndrome, but clear evidence for this presumption has been lacking. Here we demonstrate positive selection of HIV-1 proviral sequences encoding variants within a CTL epitope in Nef, a gene product critical for viral pathogenicity, during and after seroconversion. These positively selected HIV-1 variants carried epitope sequence changes that either diminished or escaped CTL recognition. Other proviruses had mutations that abolished the Nef epitope altogether. These results provide clear evidence that CTLs exert selection pressure on the viral population in acute HIV-1 infection.

Late escape from an immunodominant cytotoxic T-lymphocyte response associated with progression to AIDS

The precise role played by HIV-specific cytotoxic T lymphocytes (CTL) in HIV infection remains controversial. Despite strong CTL responses being generated during the asymptomatic phase, the virus persists and AIDS ultimately develops. It has been argued that the virus is so variable, and the virus turnover so great that escape from CTL recognition would occur continually, but so far there is limited evidence for CTL escape. The opposing argument is that evidence for CTL escape is present but hard to find because multiple anti-HIV immune responses are acting simultaneously during the asymptomatic phase of infection. We describe six donors who make a strong CTL response to an immunodominant HLA-B27-restricted epitope. In the two donors who progressed to AIDS, CTL escape to fixation by the same mutation was observed, but only after 9-12 years of epitope stability. CTL escape may play an important role in the pathogenesis of HIV infection.

Nonaldehyde sterilization of biologic tissue for use in implantable medical devices

Biologic tissue stabilized by dye-mediated photooxidation has found application in implantable devices. The desire to avoid aldehydes in the processing of photooxidized tissues led to the development of a nonaldehyde, iodine based sterilant. The interaction of tissue with iodine was indicated by a change in tissue shrinkage temperature, dependent upon solution and incubation parameters. The amino acid tyrosine also was altered, presumably because of aromatic ring iodination. Transmission electron microscopic study indicated no change in the quarter staggered array structure of collagen under controlled iodine treatment conditions. The D10 values for iodine kill of several organisms, in the absence of tissue, were determined in 0.1% iodine (pH 6.5) at 37 degrees C for Bacillus subtilis (12 min, Aspergillus niger, Escherichia coli, Candida albicans, Staphylococcus aureus, and Pseudomonas aeruginosa (all < 1 min). In a separate experiment, samples of 0.1% iodine (pH 6.5) containing photooxidized pericardial tissue were inoculated with 1.6 X 10(7) Bacillus subtilis, 4.6 X 10(6) Pseudomonas aeruginosa, or 7.2 X 10(6) Staphylococcus aureus and incubated at 37 degrees C. No survivors were detected on the tissue samples after exposure of 48 hr. Photooxidized pericardial tissue samples inoculated with either 3.2 X 10(5) porcine parvovirus or 1 X 10(9) infectious bovine rhinotracheitis were exposed to 0.1% iodine (pH 6.5) at 36 degrees C for 12 h. No viral particles were detected after exposure, yielding minimum viral log reduction factors of 3.0 and 6.5, respectively. The results presented indicate the potential for the nonaldehyde, iodine based solution to sterilize implantable devices containing biologic tissue.

Escape of human immunodeficiency virus from immune control

Cytotoxic T lymphocytes (CTL) play a crucial role in the attempt to control infection with human immunodeficiency virus (HIV). Variation in epitopes recognized by CTL is common and frequently offers potential escape routes for mutant virus. Proof of escape, however, requires demonstration of increased frequency of virus particles or provirus that carry the escape sequence. There are now several recorded examples of virus variants that escape from CTL and are then selected. Most dramatic are those in which the CTL response has been dominated by CTL recognizing a single epitope that has suddenly changed, resulting in escape to fixation. This has been seen both early and late in the infection, leaving no doubt that escape occurs. Such escape is likely to be favored when the antiviral CTL response is oligoclonal and focused on a small number of immunodominant epitopes. The heterogeneous CTL response seen in many HIV-infected patients may result from successive waves of virus escape followed by new CTL responses specific for subdominant epitopes. Mutant virus can escape by several different routes, including failure of the mutated peptide to bind to the presenting HLA molecule and altered interactions with T cell receptors (TCR), including antagonism.

Technical and methodologic considerations for performance of indirect calorimetry in ventilated and nonventilated preterm infants

OBJECTIVE

To evaluate and refine indirect calorimetry measurement techniques so that accurate metabolic measurements can be performed in mechanically ventilated and convalescing preterm infants who require supplemental oxygen.

DESIGN

Laboratory validation of an indirect calorimeter; clinical and laboratory assessments of technical problems in performing metabolic measurements; and clinical indirect calorimetry studies in mechanically ventilated and nonventilated preterm infants.

SETTING

Neonatal intensive care unit (ICU) in a tertiary care university hospital.

PATIENTS

Level II and level III mechanically ventilated (n = 10) and nonventilated (n = 14) neonatal ICU patients who required FIO2 levels ranging from 0.21 to 0.42.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

System calibration was assessed by combustion of 100% ethanol; the mean respiratory quotient was 0.667 +/- 0.001 (SEM). In addition, oxygen consumption (Vo2) and CO2 production (Vco2) were simulated by CO2/nitrogen infusions within the range expected for 0.5- to 7-kg infants. Mean relative errors were 0.6 +/- 0.3% and 1.8 +/- 0.3% for expected Vo2 and Vco2 values, respectively. In 27 mechanically ventilated patients with no audible endotracheal tube leak, measured endotracheal tube leak ranged from 0.0% to 7.5%. Fluctuations in FIO2 during mechanical ventilation were monitored in 30-min studies, using wall-source (n = 27) or tank-source (n = 11) supplemental oxygen. Mean FIO2 variation was 0.00075 +/- 0.00013 vs. 0.00011 +/- 0.00001 using wall-source and tank-source oxygen, respectively. Some of the difficulties of obtaining accurate measurements in supplemental hood oxygen studies were overcome by using tank-source vs. wall-source oxygen and a unique hood design.

CONCLUSIONS

Accurate indirect calorimetry studies can be performed in both ventilated and nonventilated infants weighing as little as 500 g, providing that sufficient attention is paid to technical and methodologic measurement details.

Hyperglycemia during childhood diarrhea

OBJECTIVE

To determine the cause of hyperglycemia in childhood diarrhea.

METHODS

During an 8-month period, patients admitted to a diarrhea treatment center in Bangladesh had their blood glucose concentrations determined. Sixteen patients aged 2 to 10 years with hyperglycemia (blood glucose concentration >10.0 mmol/L) and 20 patients in the same age group with a normal blood glucose concentration (3.3 to 9.0 mmol/L) had blood samples obtained on admission and 4 and 24 hours later for determination of glucoregulatory hormones and gluconeogenic substrates.

RESULTS

Prevalence of hyperglycemia among patients aged 2 to 10 years was 9.4%. Compared with the normoglycemic patients, hyperglycemic patients more often had severe dehydration (100% versus 10%, p <0.001), infection with Vibrio cholerae 0 1 or toxigenic Escherichia coli (94% vs 25%, p <0.001), and had similar duration of fasting (16 vs 14 hours, p = 0.677). Concentrations of epinephrine (7.15 vs 2.00 micromol/L), norepinephrine (10.35 vs 3.50 micromol/L), cortisol (1.38 vs 0.82 micromol/L), glucagon (36 vs 14 pmol/L), and C-peptide (1.22 vs 0.35 nmol/L) were all significantly (p < or = 0.014) higher in patients with hyperglycemia than in normoglycemic patients.

CONCLUSIONS

The development of hyperglycemia in diarrhea is caused by a stress response to hypovolemia.

Cytotoxic T lymphocytes and viral turnover in HIV type 1 infection

To understand the role of the immune system in limiting HIV type 1 replication, it is critical to know to what extent the rapid turnover of productively infected cells is caused by viral cytopathicity or by immune-mediated lysis. We show that uncultured peripheral blood mononuclear cells of many patients contain cytotoxic T lymphocytes (CTL) that lyse target cells-at plausible peripheral blood mononuclear cell-to-target ratios-with half-lives of less than 1 day. In 23 patients with CD4 counts ranging from 10 to 900 per microliter, the average rate of CTL-mediated lysis corresponds to a target cell half-life of 0.7 day. We develop mathematical models to calculate the turnover rate of infected cells subjected to immune-mediated lysis and viral cytopathicity and to estimate the fraction of cells that are killed by CTL as opposed to virus. The models provide new interpretations of drug treatment dynamics and explain why the observed rate of virus decline is roughly constant for different patients. We conclude that in HIV type 1 infection, CTL-mediated lysis can reduce virus load by limiting virus production, with small effects on the half-life of infected cells.

Novel, cross-restricted, conserved, and immunodominant cytotoxic T lymphocyte epitopes in slow progressors in HIV type 1 infection

HIV-specific cytotoxic T lymphocytes (CTLs) play an important role in the immune response to HIV infection. Long-term nonprogressors (LTNPs) or slow progressors (SPs) in HIV infection may make qualitatively different CTL responses compared to those generated by seropositive individuals who progress to disease at a faster rate. The class I molecule HLA-B*57 has been identified as one restriction element overrepresented in SP groups studied, and, together with the closely related molecule HLA-B*58, occurs commonly in ethnic groups where HIV is most prevalent. In this study, we have identified five new HLA-B*57-restricted CTL epitopes recognized by SP donors, one of which is also HLA-B*5801 restricted. These HLA-B*57-restricted responses represent the dominant HIV-specific CTL response in each of the SP donors tested. These and other such epitopes may be an important component in future vaccine design.

Photoperiod mediates the ability of serotonin to release prolactin in the turkey

Photostimulation (PS) of turkeys increases the number of hypothalamic vasoactive intestinal peptide (VIP)-immunoreactive neurons, the number of anterior pituitary VIP binding sites, and prolactin (PRL) secretion. Serotonin (5-HT) was recently shown to stimulate PRL secretion through VIP. This study tested the hypothesis that 5-HT's ability to induce PRL secretion is mediated by reproductive status and/or photoperiod in normally cycling turkey hens. Initially, saline or 5-HT was infused into the third ventricle of nest-deprived, previously incubating (ND) hens for 60 min at rates of 0.1, 1.0, or 10 nmol/min. The results led to use of the 10 nmol/min infusion rate for the remaining 5-HT infusions. Next, 5-HT was infused into short-day (SD;6), laying (6), ND (5), and photorefractory (P/R;6) hens. Plasma PRL was elevated in all groups except for the SD hens (P < 0.05). In Experiment 3, VIP was infused into the median eminence of SD (6), laying (5), and P/R (5) hens, increasing circulating PRL levels in all three groups (P < 0.05). Finally, SD hens were photostimulated for 0, 3, or 10 days and then infused with 5-HT. Only the birds which were photostimulated for 10 days exhibited elevated plasma PRL (P < 0.05). In conclusion, PS regulates PRL secretion at the hypothalamic level and more than 3 days of PS are required for 5-HT-ergic stimulation of PRL secretion.

Tenacious Binding of Fibrinogen and Albumin to Pyrolite Carbon and Biomer

Adsorption of bovine fibrinogen from dilute plasma and human serum albumin (HSA) from buffered HSA solution to low-temperature isotropic (LTI) pyrolytic carbon (Pyrolite) and polyetherurethane urea (Biomer) was measured. Whereas fibrinogen adsorption to Biomer passed through a maximum at intermediate plasma dilution (a typical Vroman peak), maximal adsorption to Pyrolite occurred from undiluted plasma; i.e., there was no Vroman effect. Protein elution by sodium dodecyl sulfate (SDS) surfactant was also measured. The amount of fibrinogen eluted from both substrates by SDS was less when the protein was adsorbed from more dilute plasma or eluted after 4 days postadsorptive residence time. Under all conditions, fibrinogen retention by Pyrolite was greater than that by Biomer. Binding of a monoclonal anti-fibrinogen (against residues 402-411 of the gamma chain) to substrates preadsorbed with human plasma was measured using an ELISA. Antibody binding (normalized to the amount of fibrinogen adsorbed) to plasma preadsorbed Pyrolite was much less than that to preadsorbed Biomer. On both surfaces, normalized antibody binding was much greater when fibrinogen adsorption had occurred from more dilute plasma. Monolayer adsorption of HSA to Pyrolite was observed. HSA retention was greater when the protein was adsorbed from more dilute solution. These results demonstrate that proteins are tenaciously bound to Pyrolite compared with Biomer. Therefore, the thromboresistance of Pyrolite may be partly due to the lowered reactivity of the platelet binding domain, as well as a lessened ability of tightly bound fibrinogen to interact with platelets.

Dopaminergic control of prolactin secretion in the turkey

The stimulatory and inhibitory effects of dopamine (DA) upon avian prolactin (PRL) secretion suggest that, in birds, these actions are mediated by multiple DA receptors. To test this hypothesis, combined intracranial infusions of DA and selective D1 or D2 DA receptor blockers, plus electrical stimulation (ES) of the brain and vasoactive intestinal peptide (VIP) immunoneutralization, were used to characterize the actions of DA on PRL secretion in the turkey. Blockade of D1 DA receptors prevented the increase in circulating PRL observed in response to infusion of stimulatory concentrations of DA or to ES. Stimulatory infusions of DA also failed to increase circulating PRL in birds immunized against VIP. Results from infusion of the D2 DA receptor antagonist were unclear. Low concentrations had no effect, while the highest concentration (100 nmol/min) produced an increase in plasma PRL. At the high concentration the drug may be affecting PRL secretion by (1) acting nonspecifically, (2) acting as a partial DA agonist on D1 DA receptors, or (3) diffusion to the pituitary and blockade of D2 receptors there. These data suggest that avian PRL secretion is mediated by D1 DA receptors within the brain and that the stimulatory effect of DA upon PRL secretion requires an intact VIPergic system.

Shrinkage temperature versus protein extraction as a measure of stabilization of photooxidized tissue

A rise in thermal denaturation temperature has been utilized as an indication of stabilization of collagen-containing materials such as pericardial tissue and porcine heart-valve leaflets following treatment with glutaraldehyde, Denacol, or other chemical agents. In contrast, stabilization of bovine pericardial tissue by dye-mediated photooxidation does not result in a significant rise in shrinkage temperature comparable with these treated materials. It was therefore hypothesized that a rise in shrinkage temperature is not a necessary indication for tissue stabilization. A sensitive protein extraction assay has been developed which can be used to monitor the stabilization of pericardial tissue by a variety of treatment methods, including photooxidation. A reduction in extractable protein, as analyzed by polyacrylamide gel electrophoresis, is noted for pericardial tissue treated with photooxidation, glutaraldehyde, or Denacol. Loss of extractable protein, as a function of treatment time, correlates well with a significant rise in shrinkage temperature for pericardium treated with glutaraldehyde or Denacol but not with photooxidation. This difference is attributed to the stabilization processes of glutaraldehyde and Denacol, which involve extensive crosslinking and polymer formation within and in addition to the native pericardial matrix, leading to a rise in matrix complexity and thermal stability. In contrast, photooxidation is a catalytic process involving modification and crosslink formation within existing matrix components, resulting in a material with little added matrix complexity.

Calcification of polyurethanes implanted subdermally in rats is enhanced by calciphylaxis

Calcification complicates the use of the polymer polyurethane in cardiovascular implants. To date only costly experimental circulatory animal models have been useful for investigating this disease process. In this paper we report that polyurethane calcification in rat subdermal implants is enhanced by overdosing with a vitamin-D analog. The calcification-prone state, known as calciphylaxis, was induced in 4-week old rats by oral administration of a vitamin-D analog, dihydrotachysterol. We studied two commercially available polyurethanes (Biomer and Mitrathane) and two proprietary polyurethanes (PEU-2000 and PEU-100). PEU-100 is unique because it is derivatized with ethanehydroxy-bisphosphonate (EHBP) for calcification resistance. Polyurethane calcium and phosphate levels and morphological changes due to calciphylaxis were compared with those of control rat subdermal explants in 60-day studies. Increased polyurethane mineralization was observed due to calciphylaxis with 60-day rat subdermal explants of Biomer, Mitrathane, and PEU-2000 (calcium levels, respectively, 4.13 +/- 0.56, 18.61 +/- 2.73, and 3.37 +/- 0.22 microgram/mg, mean +/- standard error) as compared to control explants (calcium levels, respectively, 1.22 +/- 0.1, 12.57 +/- 0.86, and 0.20 +/- 0.86 microgram/mg). The study also demonstrated that with 60-day implants calciphylaxis had no side effects on somatic growth and serum calcium levels. Explant surface morphology of these polyurethane explants examined by scanning electron microscopy, back scattering electron imaging coupled with energy dispersive X-ray spectroscopy, and light microscopy demonstrated the presence of predominantly surface-oriented calcification. PEU-100, derivatized with 100 n.moles/ mg of EHBP, resisted calcification with explant calcium levels 0.51 +/- 0.01 (calciphylaxis) and 0.38 +/- 0.01 (control) microgram/mg. It is concluded that calciphylaxis enhances superficial polyurethane calcification in rat subdermal implants and that an EHBP-modified polyurethane resists calcification despite calciphylaxis. Rat subdermal implants using calciphylaxis may be generally useful for evaluating the calcification potential of various biomedical polymers.

The effects of natural altered peptide ligands on the whole blood cytotoxic T lymphocyte response to human immunodeficiency virus

Cytotoxic T lymphocytes (CTL) directed against human immunodeficiency virus (HIV)-1 are detectable in the majority of infected individuals, and their early appearance as the initial viremia is suppressed is thought to represent a potent antiviral response. Variation which arises in CTL epitopes can affect recognition by CTL, and we have observed previously that variant epitopes in HIV-1 gag which arise in HIV-1-seropositive donors may act as T cell receptor (TCR) antagonists of their own CTL (Klenerman et al., Nature 1994, 369: 403). The most important question arising from these observations is the extent of these immune escape mechanisms in vivo. Here we show that fresh, uncultured lymphocytes taken directly from HIV-1-infected patients are susceptible to TCR antagonism by variants present within their own virus. In contrast to HLA Class II-restricted T cell responses, where anergy may be induced, we find that in vitro, natural variants may stimulate and sustain growth of CTL. These CTL lines retain lytic specificity exclusively for the original peptide. If this represents events in vivo, natural HIV altered peptide ligands (APL) have the capacity to inhibit the range of CTL directed against an epitope, not simply those clones selected in vitro. Partial activation of CTL by APL could also act to drive an ineffectual CTL response incapable of lysing infected cells bearing these natural antigenic variants. Distortion of lymphocyte populations and function by APL might represent a further mechanism of immune evasion by HIV.

Serotonergic stimulation of prolactin secretion is inhibited by vasoactive intestinal peptide immunoneutralization in the turkey

The neuronal mechanisms that govern prolactin (PRL) secretion in the turkey appear to involve monoaminergic systems. Considerable evidence indicates that serotonin (5-HT), acting centrally, is a potent stimulator of PRL secretion. This study, using birds actively immunized against VIP, tests the hypothesis that 5-HT stimulates PRL secretion by releasing vasoactive intestinal peptide (VIP). Nonimmunized turkeys were injected ip with saline, quipazine (5-HT agonist; 5 mg/kg), methysergide (5-HT antagonist; 8 mg/kg), or methysergide plus quipazine, and VIP-immunized birds were injected with saline or quipazine. Quipazine increased plasma PRL levels from 26.8 +/- 7.1 ng/ml at Time 0 to a peak value of 148.1 +/- 31.4 ng/ml 2 hr after infection. Pretreatment with methysergide or VIP-immunoneutralization abolished the PRL response to quipazine. Intraventricular infusion of 5-HT (1 nmol/min) caused plasma PRL to rise from a baseline of 16.3 +/- 2.6 ng/ml to 85.2 +/- 14.3 ng/ml after 30 min in nonimmunized control birds. Serotonin infusion did not induce PRL secretion in the VIP-immunized birds. These findings suggest that serotonergic stimulation of PRL secretion in the female turkey requires a functional VIPergic system.

Antigenic oscillations and shifting immunodominance in HIV-1 infections

A typical protein antigen contains several epitopes that can be recognized by cytotoxic T lymphocytes (CTL), but in a characteristic antiviral immune response in vivo, CTL recognize only a small number of these potential epitopes, sometimes only one, this phenomenon is known as immunodominance. Antigenic variation within CTL epitopes has been demonstrated for the human immunodeficiency virus HIV-1 (ref. 11) and other viruses and such 'antigenic escape' may be responsible for viral persistence. Here we develop a new mathematical model that deals with the interaction between CTL and multiple epitopes of a genetically variable pathogen, and show that the nonlinear competition among CTL responses against different epitopes can explain immunodominance. This model suggests that an antigenically homogeneous pathogen population tends to induce a dominant response against a single epitope, whereas a heterogeneous pathogen population can stimulate complicated fluctuating responses against multiple epitopes. Antigenic variation in the immunodominant epitope can shift responses to weaker epitopes and thereby reduce immunological control of the pathogen population. These ideas are consistent with detailed longitudinal studies of CTL responses in HIV-1 infected patients. For vaccine design, the model suggests that the major response should be directed against conserved epitopes even if they are subdominant.

The role of material surface chemistry in implant device calcification: a hypothesis

We proposed that a similar mechanism for calcification exists for poly(ether)urethanes and glutaraldehyde stabilized tissue. The mechanism is based on the propensity of the polyether component of the materials to complex calcium and provide initiating sites for ultimate formation of calcific deposits. Data evaluating the role ether containing materials have on calcification demonstrate that the rate of mineralization of either tissue valves or polymer valves can be controlled by paying attention to the basic chemical mechanism of complexation occurring at the surface and within the bulk of the implant devices. The molecular models described above, point out that the driving force for complexation with either the polyethers of the polyurethane or the polyether of glutaraldehyde is very strong, therefore, controlling the driving force may lead to medical devices with longer term durability.

The stimulatory and inhibitory effects of dopamine on prolactin secretion in the turkey

Dopamine (DA) was infused into the third ventricle of anesthetized laying turkey hens at various concentrations to determine its effect on both basal prolactin (PRL) levels and ongoing electrically induced PRL secretion. The infusion of DA at rates of 1.0 or 10.0 nmol/min resulted in dose dependent increases in plasma PRL. These infusions had no inhibitory effect on electrically stimulated PRL release. The infusion of DA at 100.0 or 500.0 nmol/min caused no stimulation of PRL secretion and totally inhibited the PRL response elicited by electrical stimulation of the medial preoptic nucleus. These results show that dopaminergic influences are involved in both stimulating and inhibiting avian PRL secretion and suggest possible biphasic actions of DA within the brain.

Active immunization with vasoactive intestinal peptide prevents the secretion of prolactin induced by electrical stimulation of the turkey hypothalamus

Immunoneutralization of endogenous vasoactive intestinal peptide (VIP) by active immunization with chicken VIP (cVIP) reduced both basal circulating prolactin (PRL) and steady-state levels of pituitary PRL mRNA in the turkey. This immunoneutralization severely curtailed the plasma PRL response induced by infusion of cVIP into the median eminence, and totally blocked the plasma PRL release effected by electrical stimulation of the medial preoptic nucleus. This is the first demonstration that a stimulated PRL secretion can be blocked by neutralizing VIP availability. These findings imply that among the neurochemicals released by electrical stimulation, only VIP directly stimulates PRL secretion. In addition to serving as a PRL releasing factor, VIP also appears to be involved in the regulation of pituitary PRL mRNA expression.

Role of vasoactive intestinal peptide in the control of prolactin-induced turkey incubation behavior. II. Chronic infusion of vasoactive intestinal peptide

Hyperprolactinemia is associated with incubation behavior in avian species. Increased nesting activity is a major indication of incubation behavior. Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion from the anterior pituitary. The goal of this study was to induce incubation behavior by stimulating PRL through chronically infusing VIP into the third ventricle of turkey brains. In experiment 1, porcine VIP (pVIP) was infused into the median eminence at a rate of 60 ng/min for 7 days by means of osmotic pumps implanted s.c.. Plasma PRL increased significantly in the pVIP-treated turkeys (p < 0.001). Although egg laying was not affected by the pVIP infusion, the mean oviduct weight decreased (p < 0.057). In experiment 2, saline or pVIP (30 or 60 ng/min) was infused into the third ventricle of laying turkeys for 12 days. Both pVIP treatments increased plasma PRL for 9 days (p < 0.05). The 30-ng pVIP/min infusion decreased nesting activity, plasma LH, ovary and oviduct weight, hypothalamic GnRH I, and anterior pituitary VIP receptors (p < 0.1). However, ovine PRL infusion (20.8 ng/min) into the same turkey flock increased nesting activity (p < 0.01). In conclusion, pVIP does not induce incubation behavior in laying turkeys.