Effect of prostaglandins on skin tumorigenesis

Summary Concomitant administration of prostaglandins E₂ (PGE₂) and F₂ a(PGF₂ a) with a carcinogen, 3-methylcholanthrene (MCA) to mice for 2 months markedly enhanced the occurrence of squamous cell carcinomas. Only epidermal cell hyperplasia occurred in mice treated with MCA alone by that time. Radioactivity measurements and electron microscopic autoradiography revealed that prostaglandins stimulate DNA, RNA and protein synthesis in neoplastic cells. These findings indicate that PGE₂ and PGF₂ a can act as cocarcinogens on skin tumorigenesis.     

Effects of pCai and pHi on cell-to-cell coupling

Summary Internal longitudinal resistance (r_i), a determinant of cardiac conduction, is affected by changes in intracellular calcium and protons. However, the role and mechanism by which H⁺ and Ca²⁺ may modulate r_i is uncertain. Cable analysis was performed in cardiac Purkinje fibers to measure r_i during various interventions. In some experiments, intracellular pH (pH_i) was recorded simultaneously to study the pH_i-r_i relation. Both intracellular Ca²⁺ and H⁺ independently modified r_i. However, internal resistance of cardiac fibers was insensitive to pH_i changes compared to other tissues. A latent period preceded the pH_i-related changes in r_i and the amount of change depended upon methodology. The results suggest that direct action of protons on r_i may be subordinate to other regulatory processes. Ionic regulation of internal longitudinal resistance may occur by more than one mechanism: i) direct cationic binding to sites on junctional membrane proteins; and ii) H⁺- or Ca²⁺-dependent phosphorylation of junctional proteins.     

Effect of hydrogen peroxide on the binding of Merocyanine 540 to human erythrocytes

The fluorescent dye Merocyanine 540 (MC540) is often used as a probe to monitor the molecular packing of phospholipids in the outer leaflet of biomembranes. In a previous study we showed that the increased staining of erythrocytes with a perturbed membrane structure was mainly due to an increase in the fluorescence yield of cell-bound MC540, rather than to an increase of the number of bound molecules. Erythrocytes and ghosts exposed to continuous fluxes of H₂O₂ exhibited pronounced lipid peroxidation. Further, red blood cells subjected to this form of oxidative stress also showed increased staining with MC540. It appeared that this was caused by a strong increase in binding of MC540, together with a slight red shift of the fluorescence emission maximum and a small increase in the fluorescence yield of bound MC540. The changed MC540 binding characteristics were not observed when lipid peroxidation was suppressed by the presence of the antioxidant BHT in the incubation medium. However, open ghosts exposed to H₂O₂ showed no increase of MC540 binding, excluding a direct involvement of lipid peroxidation. Measurement of fluorescence emission spectra and gel filtration studies showed that MC540 can bind to H₂O₂-exposed hemoglobin. Experiments with erythrocytes lysed in hypotonic medium after exposure to H₂O₂ revealed that peroxidation of lipids with H₂O₂ induced a non-specific permeabilization of the plasma membrane to MC540, thereby allowing MC540 to bind to the oxidatively denatured, more hydrophobic hemoglobin. These results indicate that conclusions about packing of phospholipids in the outer leaflet of the membrane based on increased MC540-staining should be drawn with care. Received 27 September 1996; received after revision 5 November 1996; accepted 27 November 1996     

Influence of castration and testosterone replacement on hypothalamic tyrosine hydroxylase activity in the rat

Summary Hypothalamic tyrosine hydroxylase (TH) activity of castrate rats is modulated by testosterone propionate (TP) in vivo. Kinetic studies revealed that bothV _max andK _m were virtually unaltered for substrate tyrosine in the presence of an excess of DMPH₄ cofactor. TP replacement to castrate rats increased theK _m for added DMPH₄ cofactor, whileV _max decreased. These results suggest that TP decreases TH activity of castrate rats by inhibiting the enzymereduced pteridine cofactor complex.     

The effect of hydrogen peroxide on the cyclin D expression in fibroblasts

Activation of mitogen-activated protein (MAP) kinase is essential for cyclin D1 expression and provides a link between mitogenic signalling and cell cycle progression. Hydrogen peroxide (H₂ O₂ ) activates MAP kinase; however, it is not known whether this leads to cyclin D expression. Sustained expression of cyclin D1 and D2 was observed when Her14 fibroblasts were incu-bated with 3 mM or higher H₂ O₂ concentrations. Similar results were obtained when cells were incubated in the presence of serum (FCS). However, the sustained expres-complex sion of cyclin D1 and D2 upon H₂ O₂ treatment was not due to the MAP kinase pathway, because MAP kinase kinase inhibitors did not inhibit cyclin D expression. Furthermore, cyclin D1 and D2 levels remained constant even after addition of a protein synthesis inhibitor, indicating that the effect of H₂ O₂ was not due to induction of protein synthesis. These results indicate that H₂ O₂ reversibly inhibits the ubiquitin-proteasome dependent degra-dation of cyclin D1 and D2, probably by transiently in-hibiting ubiquitination and/or the proteasome. Received 12 March 2001; received after revision 5 April 2001; accepted 9 April 2001     

Maternal influences on cardiovascular pathophysiology

Elevated blood pressure (BP) is of special clinical significance because of its association with pathophysiologies such as heart disease, renal failure, and stroke. We described the development of a protocol for use with hypertensive rats in which prepubertal exposure to a high salt (8% NaCl) diet results in a pathophysiological syndrome including rapid increase in BP, failure to maintain normal weight gain, renal damage, cerebrovascular lesions, and early mortality. These phenomena are described for the inbred spontaneously hypertensive rat (SHR), and for reciprocal F₁ hybrids of a cross between SHR and the Dahl salt-sensitive (SS/Jr) inbred strain. The study with reciprocal F₁s revealed striking effects of maternal environment on pathophysiological response to a high salt diet. F₁s nurtured by SHR mothers weighed less at 35 days of age, and after exposure to the high salt diet suffered more rapid BP increases, greater incidence of stroke, body weight loss, and mortality, than F₁s nurtured by SS/Jr dams. These results suggest that maternal mediation of the nutritional status of the animal may play an important role in determining susceptibility to elevated BP and subsequent pathophysiology associated with exposure to a high salt diet. The implication of these findings for human hypertension is briefly discussed.     

Effect of metabolic versus respiratory acid-base changes on isolated coronary artery and saphenous vein

Summary Experiments were performed on helically cut strips from coronary artery and saphenous vein to determine the relative influence of metabolic versus respiratory acid-base changes. Tensions were measured over a range of various HCO₃ ^– concentrations and pCO₂'s. The results suggest that tension is influenced by extracellular pH and is independent of pCO₂.Supported by USPHS grant No. HL24232.     

Effect of iron and hemoproteins on hydrogen peroxide-supported styrene oxidation to styrene oxide

Summary Fe²⁺, Fe³⁺ and their complexes with EDTA and hemin, methemalbumin and methemoglobin were active catalyzers of H₂O₂ supported styrene oxidation to styrene oxide. Methemoglobin was the most active compound; its peroxidative activity was comparable to that of cytochrome P-450 in liver microsomes of phenobarbital-treated rats. Cumene hydroperoxide supported styrene oxidation with methemoglobin and microsomal hemoproteins and was found to be more efficient than H₂O₂.This work was supported by C.N.R. (National Research Council) contract No. 79.03197.04.     

Amperometric study on lanthanum polytungstates

Zusammenfassung Es wurde die Zusammensetzung von Lanthanwolframat-Niederschlägen untersucht, die sich aus Lanthannitrat- und Natriumwolframat-Lösungen verschiedener Polymerisationsgrade bilden. Die Reaktionen wurden bei verschiedenem pH, in rein wässrigem oder wässrig-alkoholischem Milieu durch amperometrische Titration verfolgt. Im pH-Bereich von 5,5–6,5 bildet sich La₂O₃ · 3WO₃, bei einem pH von 4,2–5,5 La₂O₃ · 7WO₃.

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Acknowledgment: O. P.Sharma is grateful to the Council of Scientific and Industrial Research, New Delhi, for financial assistance and to Principal V. G.Garde for providing research facilities.     

Participation of ACTH1–10 and ACTH4–10 on the melatonin modulation of benzodiazepine receptors in rat cerebral cortex

In this study, we examined the effect of intracerebroventricular (i.c.v) injection of melatonin and/or ACTH_1–10 and ACTH_4–10 on [³H]flunitrazepam binding sites in the cerebral cortex of hypophysectomized rats. Hypophysectomy increased the B_max (maximum number of binding sites) of benzodiazepine (BNZ) receptors for at least 7 days after surgery, without changing K_D (dissociation constant). The i.c.v. injection of melatonin to hypophysectomized rats significantly increased B_max, whereas the same doses of melatonin were ineffective in sham-operated animals. In both cases, K_D values were unchanged. The i.c.v injection of ACTH_1–10 to hypophysectomized animals significantly increased B_max, an effect that was enhanced by simultaneous i.c.v. injection of ACTH_1–10+melatonin, reaching higher values of B_max than the i.c.v. injection of these hormones individually. No significant changes in K_D values were found after ACTH_1–10 and/or melatonin administration. However, the i.c.v. injection of ACTH_4–10 to hypophysectomized rats did not change B_max, although it significantly increased K_D values, indicating a decrease in the BNZ binding affinity. Melatonin injection counteracted this effect of ACTH_4–10, returning K_D to the control value. Moreover, although the lower dose of i.c.v. melatonin used, 10 ng, was unable to modify B_max of BNZ binding in the ACTH_4–10-injected group, the higher dose, 20 ng, significantly increased B_max. The results suggest that these ACTH-derived peptides can modulate the effect of melatonin on brain benzodiazepine receptors.     

Vitamin D receptors in heart: Effects on atrial natiuretic factor

We report that receptors for vitamin D exist in distinct regions of the heart in female and male mice, predominantly in the right atrium where most of the cardial atrial natriuretic peptide (ANF) is produced. Tritiated 1,25-dihydroxyvitamin D₃ (1,25-D₃, vitamin D, soltriol) and ANF are colocalized in nuclei and cytoplasm respectively in identical cardiomyocytes. Changes of ANF tissue and blood levels under dietary deficiency and treatment with 1,25-D₃ suggest direct genomic actions of vitamin D on myoendocrine cells of the atrium for the regulation of ANF manufacture and secretion. These results were obtained by combining thaw-mount autoradiography with immunocytochemistry using tritiated 1,25-D₃ and an antibody against rat ANF. This antibody was also used in a radioimmunoassay to determine atrial natriuretic factor in plasma, atria and ventricles of normal or vitamin D-deficient mice.     

The action of the peptidoleukotriene LTD4 on intracellular calcium in rat mesangial cells

The dose-dependent effect of CGP 45715A on the LTD₄-induced Ca²⁺ response of glomerular mesangial cells has been studied. Our results demonstrate that the LTD₄-dependent increase in the cytosolic Ca²⁺ concentration primarily involves an InsP₃-mediated release of Ca²⁺ from intracellular storage sites and to a minor extent an enhanced influx of Ca²⁺ through receptor-operated Ca²⁺ channels located in the plasma membrane. The action of CGP 45715A on the Ca²⁺ response is an inhibitory one and is convincingly explained by a displacement of LTD₄ from its receptor site(s). The contractile effect of LTD₄ on pulmonary smooth muscle is proposed to be mainly caused by a receptor-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate.     

Lack of effects of 5-HT3 antagonists on normal and morphine-attenuated sexual behaviours in female and male rats

Although 5-HT₁ and 5-HT₂ receptor activity is known to influence copulation, the effects of 5-HT₃ receptor-selective drugs on sexual activity have yet to be systematically studied. The following experiments investigated the effects of the 5-HT₃-selective antagonists MDL 72222, ondansetron and ICS 205-930 on female sexual behaviour; male rats were studied using ondansetron and granisetron. These compounds influenced neither male nor female copulatory behaviours, suggesting that 5-HT₃ receptors contribute little to the modulation of sexual activity. 5-HT₃ receptor antagonists block certain opioid-induced behaviours and opioids selectively inhibit sexual behaviours; therefore, the ability of ondansetron and ICS 205-930 to modify morphine-attenuated copulatory activity was also tested. While morphine inhibited copulation, 5-HT₃ antagonists failed to reverse the effects.     

Influence of PGA1 on cartilage growth

Summary Using the Fell technique of organ culture of cartilage in a chemically defined medium, it has been shown that prostaglandin A₁ at a concentration of 25 g/ml caused chondrocyte death in chick embryonic limb rudiments. An equimolar concentration of PGE₂ was not toxic to the cells.Acknowledgments. We are grateful for the support of C. J. K. by the Medical Research Council and of D. L. G. by the Arthritis and Rheumatism Council for Research. Our thanks are due to Dame Honor Fell, F. R. S. for invaluable advice and guidance, to Dr J. Pike (Upjohn Co.) for supplies of prostaglandin A₁, and to Dr Sylvia Fitton-Jackson for the gift of culture medium.     

Evidence of a direct action of triiodothyronine (T3) on the cell membrane of GH3 cells: an electrophysiological approach

Summary Electrophysiological experiments demonstrate that triiodothyronine (T₃) exerts a direct effect on the membrane of a strain of cultured rat pituitary tumor cells, GH₃/B₆. These cells respond to pressure application of T₃ (2–5 nl, concentration 1·10^–10 M) with an increase in the membrane resistance (R_m) and a hyperpolarization. Spontaneously firing cells become silent.     

pHi regulatory ion transporters: an update on structure, regulation and cell function

Intracellular pH (pH_i) is a major regulator of various and critical cellular functions. A close regulation of pH_i is thus mandatory to maintain normal cellular activity. To this end, all cells express ion transporters that carry across their plasma membrane H⁺ or equivalent H⁺ into and out of the cell. Besides pH_i, these ion transporters are under the regulation of neurohormonal stimuli. This review summarises the molecular identity, regulation and function of the main membrane pH-regulatory ion transporters. Received 30 December 1998; received after revision 4 February 1999; accepted 9 February 1999     

A note on the mechanism of action of UV-irradiation of amphibian embryos

Summary The actions on amphibian embryos of UV-irradiation, exposure to Li⁺ or exposure to ouabain show interesting parallels with their effects on spontaneous release at the presynaptic terminals of the neuromuscular junction. It is suggested that these treatments serve to raise intracellular Ca²⁺ ([Ca²⁺ _i) in these examples, and that UV-promoted abnormalities in embryogenesis are a consequence of changes in [Ca²⁺]_i at critical stages in development.     

The impact of different energy options on atmospheric CO2 levels

Conclusions It is found that large differences in future atmospheric CO₂ concentration may be estimated due to different energy supply strategies. At present there seems to be no immediate need to reduce fossil fuel consumption. However, considering the magnitude of possible effects, efforts should be made to keep the increase of fossil fuel consumption as low as possible. Especially with regard to the CO₂ strategy given in figure 6 it should be borne in mind that fossil fuel plants which are planned today are expected to operate beyond the 1st decade of the next century     

Electrometric studies on the reaction between thorium and alkali tungstate

Zusammenfassung Es wurde die Reaktion zwischen Th⁴⁺ und WO₄ ^2–-Ionen durch amperometrische, pH und konduktometrische Titrationen zwischen Th(NO₃)₄ und Na₂WO₄ untersucht. Elektrometrisch konnte bewiesen werden, dass sich zwischen pH 4.50–5.75 normales Thoriumtungstat ThO₂ · 2WO₃ bildet.