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Biomedical subjects

H Martens

Publications and source records attributed to H Martens.

At least 73 records · Page 4Linked to original sources
PubMed1995

Suppression of melatonin secretion in some blind patients by exposure to bright light.

BACKGROUND: Complete blindness generally results in the loss of synchronization of circadian rhythms to the 24-hour day and in recurrent insomnia. However, some blind patients maintain circadian entrainment. We undertook this study to determine whether some blind patients' eyes convey sufficient photic information to entrain the hypothalamic circadian pacemaker and suppress melatonin secretion, despite an apparently complete loss of visual function. METHODS: We evaluated the input of light to the circadian pacemaker by testing the ability of bright light to decrease plasma melatonin concentrations in 11 blind patients with no conscious perception of light and in 6 normal subjects. We also evaluated circadian entrainment over time in the blind patients. RESULTS: Plasma melatonin concentrations decreased during exposure to bright light in three sightless patients by an average (+/- SD) of 69 +/- 21 percent and in the normal subjects by an average of 66 +/- 15 percent. When two of these blind patients were tested with their eyes covered during exposure to light, plasma melatonin did not decrease. The three blind patients reported no difficulty sleeping and maintained apparent circadian entrainment to the 24-hour day. Plasma melatonin concentrations did not decrease during exposure to bright light in seven of the remaining blind patients; in the eighth, plasma melatonin was undetectable. These eight patients reported a history of insomnia, and in four the circadian temperature rhythm was not entrained to the 24-hour day. CONCLUSIONS: The visual subsystem that mediates light-induced suppression of melatonin secretion remains functionally intact in some sightless patients. The absence of photic input to the circadian system thus constitutes a distinct form of blindness, associated with periodic insomnia, that afflicts most but not all patients with no conscious perception of light.

Adolescent↗
PubMed1995

Cryptocrine signaling in the thymus network and T cell education to neuroendocrine self-antigens.

Both during phylogeny and ontogeny the thymus appears as a nodal point between the two major systems of cell-to-cell signaling, the neuroendocrine and immune systems. This review presents the experimental observations which support a dual role in T cell selection played by the thymic repertoire of neuroendocrine polypeptide precursors. Through the mode of cryptocrine intercellular signaling thymic neuroendocrine-related precursors synthesized in thymic epithelial cells have been shown to influence the early steps in T cell differentiation. In addition, thymic neuroendocrine-related polypeptides are a source of self-antigens which are presented by the major histocompatibility system of the thymic epithelium. Preliminary data also suggest that the intrathymic T cell education to neuroendocrine self-antigens is not strictly superimposible to the antigen presentation by dedicated presenting cells. Insulin-like growth factor-II (IGF-II) was identified as one dominant member of the insulin family expressed by thymic epithelial and nurse cells. The intrathymic presentation of IGF-II or IGF-II derived self-antigens is under current investigation. If further confirmed, the central tolerogenic properties of IGF-II could be considered in the elaboration of a strategy for an efficient and safe prevention of insulin-dependent diabetes.

Amino Acid Sequence↗
PubMed1994

Effects of parathyroid hormone and parathyroid hormone-related protein on the rates of absorption of magnesium, calcium, sodium, potassium and phosphate ions from the reticulo-rumen of sheep.

Not only parathyroid hormone (PTH) but also parathyroid hormone-related protein (PTHrP) may play a role in calcium and phosphate homeostasis in ruminants. In five trained sheep, each with a large rumen cannula, the isolated rumen wash technique was used to measure electrolyte absorption rates from the rumen. After two control periods of measurement, 20 micrograms PTH(1-34) (n = 4), or PTHrP(1-34) (n = 5), was injected intravenously as a loading dose, followed by an infusion of 0.67 micrograms min-1 over 2 h. Both PTH(1-34) and PTHrP(1-34) significantly increased the absorption rates of calcium and phosphate from the reticulo-rumen. The increases in the absorption rates of magnesium, sodium and potassium observed were not significant. The same technique was also used to demonstrate that increasing the intraruminal calcium concentration from 1 to 4 mmol l(-1) caused corresponding increases in the net rate of absorption of both calcium and inorganic phosphate from the reticulo-rumen. Rumen epithelium was taken from four sheep and mounted in Ussing chambers so that fluxes of calcium could be measured in both directions using 45Ca. It was found that the addition of 100 ng ml-1 PTH(1-34) or PTHrP(1-34) to the serosal side increased the net calcium flux rates across the ruminal epithelium. It is concluded that both PTH and PTHrP can influence calcium and phosphate homeostasis in sheep not only by their recognized actions on bone and kidney but also on the absorption of these ions from the forestomachs.

Absorption↗
PubMed1994

Prognostic significance of the hepatitis B virus-DNA concentration in patients after orthotopic liver transplantation.

Hepatitis B virus-DNA was detected by polymerase chain reaction in 9 out of 10 patients after orthotopic liver transplantation. Three of these patients were at the same time positive for hepatitis B virus-DNA by dot-blot hybridization (hepatitis B virus-DNA > 1.5 pg/ml). In these three patients HBs-antigen (HBsAg) reappeared within a mean time of 12 weeks after orthotopic liver transplantation (range 7-18 weeks). Only two of the six polymerase chain reaction-positive and dot-blot-negative patients (hepatitis B virus-DNA between 0.4 fg/ml and 1.5 pg/ml) had recurrence of HBsAg within a mean time of 54 weeks (range 52-56 weeks). Passive immunoprophylaxis with anti-HBs antibodies (serum titers > 100 IU/l) did not prevent infection of the graft in the five reinfected patients. We conclude that a low concentration of serum hepatitis B virus-DNA after orthotopic liver transplantation, which is detectable only by polymerase chain reaction, indicates a delayed infection of the graft.

Adult↗
PubMed1993

Influences of extracellular matrix components on the growth and differentiation of ruminal epithelial cells in primary culture.

Primary cultures of ovine ruminal epithelial cells were made to study the influence of collagen types I and IV out of medium supplementation with various hormones and Na-n-butyrate on cell morphology and growth characteristics. Both collagen type I and type IV led to increased cell proliferation with the stimulatory effect being more pronounced in collagen IV. In cultures grown on collagen I, both non-stratified and stratified colonies were found, whereas cultures grown on collagen IV showed predominantly stratified growth. Cells in both stratified and non-stratified colonies were positive for cytokeratin antibody. In non-stratified colonies, positive staining with fibronectin antibodies (FN-15) was found in a network over and around the cells. It is suggested that the non-stratified ruminal epithelial cells are in some respects similar to a 'non-differentiating keratinocyte' strain, derived from newborn foreskin epidermis. Cells in stratified colonies bound Ulex europaeus (UEAI) lectin which has been shown to be specific for differentiated epithelial cells in ruminal mucosa. Supplementation of culture medium with glucagon and insulin increased the total cell-overgrown area of collagen I cultures, whereas this effect was absent in cultures grown on collagen IV. In both cultures grown on collagen I or IV, hydrocortisone led to an increase in total cell-overgrown area, whereas Na-n-butyrate inhibited proliferation.

Animals↗
PubMed1993

Mechanisms of sodium and chloride transport across isolated sheep reticulum.

1. 22Na+ and 36Cl- fluxes across isolated reticular epithelium of sheep were measured by using the Ussing-chamber technique. 2. Net NaCl absorption driven by Na(+)-K(+)-ATPase was observed under short-circuit conditions. 3. Evaluation of fluxes measured under voltage-clamp conditions indicated that Na+ absorption is mainly electroneutral. 4. Mucosal application of bumetanide, hydrochlorothiazide, or low dose amiloride (10(-4) M) produced no changes in Na+ transport whereas addition of higher doses of amiloride (> or = 10(-3) M) led to a reduction in net Na+ transport. Short chain fatty acids (SCFA) enhanced the amiloride-sensitive Na+ transport. 5. Alterations of JmsNa induced by inhibitors or by SCFA were always accompanied by qualitatively similar changes of JsmNa. Amiloride-sensitive JsmNa was also decreased at low mucosal Na+ concentration. 6. DIDS, SITS, and nitrate reduced both JmsCl and JsmCl. SCFA did not influence chloride transport. 7. It is concluded that Na+ transport is mediated by Na(+)-H+ exchange and by transport processes operating as Na+ self-exchange. Mucosal-to-serosal chloride transport seems partly to depend on anion exchange systems.

Acetazolamide↗
PubMed1993

Circadian sleep regulation in the absence of light perception: chronic non-24-hour circadian rhythm sleep disorder in a blind man with a regular 24-hour sleep-wake schedule.

Sleep disturbances and the failure to entrain circadian rhythms to the 24-hour day have been reported in the majority of totally blind subjects. The present case study of a totally blind man with a well-documented recurring sleep disturbance was designed to investigate the mutual relationship between sleep and the circadian timing system. The 63-year-old subject, a high school teacher with a regular work schedule, had suffered from cyclically recurring insomnia for the past 28 years. Analysis of a sleep log that he had kept for the past 15 years suggested that his circadian rhythms were not entrained to the 24-hour day. During a 3-month inpatient study, the period of the endogenous circadian pacemaker was assessed by analysis of ambulatory core body temperature, urinary excretion and a series of estimates of the phase of core body temperature cycles and plasma cortisol levels during constant routines. All circadian markers revealed periods in the range of 24.22-24.27 hours, with no evidence for a modulation of the observed periods by the sleep-wake cycle. During this 3-month inpatient study, a complete cycle of the subject's sleep disturbance and remission was polysomnographically documented while the subject lived on a regular 24-hour schedule. Because the subject's circadian rhythms were free-running and his sleep times were fixed, sleep occurred at virtually all circadian phases. Analysis of sleep latency, REM sleep latency, sleep duration, wake in sleep episode and REM sleep during sleep episode revealed a strong modulation by circadian phase. These findings in this blind man suggest that: 1) the period of his cyclically recurring sleep disturbance is directly related to the nonentrained period of an endogenous circadian pacemaker that drives circadian variation in core body temperature, urinary excretion, plasma cortisol and sleep propensity; 2) both his sleep structure and the severity of his daily sleep disruption are directly related to circadian phase and 3) his circadian pacemaker, which has an endogenous period that deviates only 0.2-0.3 hours from 24 hours, cannot be entrained by periodic daily exposure to nonphotic time cues, including a very regular 24-hour sleep-wake schedule.

Blindness↗
PubMed1993

Langerhans cell accumulation in chronic tinea pedis and pityriasis versicolor.

Persistence of chronic tinea pedis (CTP) and pityriasis (tinea) versicolor (PIVE) has been tentatively attributed to an impaired cellular immune response. Therefore immunophenotyping of the inflammatory infiltrates in both disorders was performed in order to detect possible defects in cellular defence. The results of the present study show a dominance of memory T cells, an accumulation of macrophages and lack of B cells. A very prominent feature in CTP and especially PIVE was a marked accumulation of Langerhans cells (LCs) in the epidermis, mostly without expression of CD4. Furthermore, reduced expression of cellular activation markers and the presence of suppressor T cells was noted. In general, the cellular response in PIVE appeared to be slightly stronger than in CTP. This composition of the inflammatory infiltrates in chronic dermatomycoses is similar to previous findings in a variety of dermatoses. However, in PIVE and CTP local reduction of delayed-type hypersensitivity may occur. The function of LCs in these infections is therefore of special interest.

Chronic Disease↗
PubMed1993

Influence of food deprivation on SCFA and electrolyte transport across sheep reticulorumen.

Net absorption rates for SCFA, sodium, chloride, magnesium, and water were measured in the temporarily isolated and washed reticulorumen of sheep. The animals were either fed hay ad lib. plus concentrates once daily or were deprived of food for two days. Food deprivation led to decreased net absorption of all the substances tested. Comparing the solutes, the relative decreases varied between 43% (butyrate) and 56% (acetate). The decrease in solute absorption was accompanied by diminished water absorption. It is concluded that the reduction in absorption may be beneficial for the animal in that energy consumption is diminished and the reservoir function of the forestomach will be maintained longer. However, the reduced absorptive capacity may lead to a deficiency of magnesium, which is thought to be absorbed mainly by the forestomachs.

Absorption↗
PubMed1993

Membrane translocation and relationship with MHC class I of a human thymic neurophysin-like protein.

Thymic epithelial and nurse cells (TEC/TNC) synthesize an oxytocin (OT)-like peptide in association with a neurophysin (NP)-related protein in a way similar to in the hypothalamo-neurohypophysial (NHP) system. The central T-cell tolerance of the NHP neuroendocrine functions have been proposed to be mediated through these thymic NHP-related peptides due to their close homology with the NHP neurohormones OT and vasopressin (VP). In order to investigate their putative presentation by proteins of the major histocompatibility complex (MHC), human thymic membranes were purified and passed through an immunoaffinity column using mAb B9.12 directed to the monomorphic determinant of human MHC class I proteins. This methodology provided the following observations: (1) a NP-like protein is translocated in human thymic membranes and is retained by B9.12 on the column; (2) the MW of this NP-like material (50-55 kD) is quite different from the MW of hypothalamic NP proteins (10 kD), and (3) this thymic NP-like protein could be identified on Western blots with mAb B9.12. The precise extent of this relationship between the thymic NP-like protein and the Ig/MHC superfamily is actually investigated through the characterization of the genetic mechanisms responsible for the thymic expression of NHP-related peptides. Given the physiological importance of OT and of its binding to NP for transport along the axonal processes of the NHP tract, we postulate that, somewhat analogously, the thymic NP-/MHC class I-related protein could be involved in the presentation of the OT-like peptide to immature T-cells.

Amino Acid Sequence↗
PubMed1992

Elevated urinary excretion of orotic acid in sheep caused by intraruminal infusion of sodium propionate.

1. The effect of sodium propionate on urinary excretion of orotic acid was investigated. 2. Solutions containing sodium propionate or NaCl, 750 mM/day each, were continuously infused into the rumen for 10 days. 3. During NaCl infusion, an urinary orotic acid excretion of 290 +/- 80 micrograms/day was noted. The intraruminal infusion of sodium propionate raised the concentration of propionic acid in the rumen fluid from 14.0 +/- 0.9 to 26.9 +/- 1.9 mM. 4. During this experimental period the excretion of orotic acid via urine significantly increased to 492 +/- 30 micrograms/day. Parameters of nitrogen balance were not altered by propionate. 5. It is suggested that the site of propionate action in intact sheep is in the pyrimidine synthesis pathway.

Animals↗
PubMed1992

The recognition of hypothalamo-neurohypophysial functions by developing T cells.

Neuropeptide signals and specific neuropeptide receptors have been described in the thymus supporting the concept of a close dialogue between the neuroendocrine and the immune systems at the level of early T-cell differentiation. In this paper, we review recent data about neurohypophysial (NHP)-related peptides detected in the thymus from different species. We suggest that we are dealing in fact with other member(s) of the NHP hormone family, which seems to exert its activity locally through a novel model of cell-to-cell signaling, that of cryptocrine communication. This model involves exchange of signals between thymic epithelial cells and developing thymocytes. The NHP-related peptides have been shown to trigger thymocyte proliferation and could induce immune tolerance of this highly conserved neuroendocrine family.

Amino Acid Sequence↗