Radioprotective potential of histamine on rat small intestine and uterus.

The aim of this study was to improve knowledge about histamine radioprotective potential investigating its effect on reducing ionising radiation-induced injury and genotoxic damage on the rat small intestine and uterus. Forty 10-week-old male and 40 female Sprague-Dawley rats were divided into 4 groups. Histamine and histamine-5Gy groups received a daily subcutaneous histamine injection (0.1 mg/kg) starting 24 h before irradiation. Histamine-5Gy and untreated-5Gy groups were irradiated with a dose of whole-body Cesium-137 irradiation. Three days after irradiation animals were sacrificed and tissues were removed, fixed, and stained with haematoxylin and eosin, and histological characteristics were evaluated. Proliferation, apoptosis and oxidative DNA markers were studied by immunohistochemistry, while micronucleus assay was performed to evaluate chromosomal damage. Histamine treatment reduced radiation-induced mucosal atrophy, oedema and vascular damage produced by ionising radiation, increasing the number of crypts per circumference (239 ± 12 vs 160 ± 10; P<0.01). This effect was associated with a reduction of radiation-induced intestinal crypts apoptosis. Additionally, histamine decreased the frequency of micronuclei formation and also significantly attenuated 8-OHdG immunoreactivity, a marker of DNA oxidative damage. Furthermore, radiation induced flattening of the endometrial surface, depletion of deep glands and reduced mitosis, effects that were completely blocked by histamine treatment. The expression of a proliferation marker in uterine luminal and glandular cells was markedly stimulated in histamine treated and irradiated rats. The obtained evidences indicate that histamine is a potential candidate as a safe radioprotective agent that might increase the therapeutic index of radiotherapy for intra-abdominal and pelvic cancers. However, its efficacy needs to be carefully investigated in prospective clinical trials.

Estrogen receptor profiles: changes in mouse and rat mammary tumors by treatment with selective estrogen receptor modifiers.

OBJECTIVE: The aim of this work was to analyze the effect of estradiol (E(2)), medroxyprogesterone and the two selective estrogen receptor modulators (SERMs) (tamoxifen (Tam) and raloxifene (Ral)) on the estrogen receptor (ER) conformers profile performed by size exclusion HPLC in relation to hormone dependence of mammary tumors. MATERIALS AND METHODS: Two types of mammary tumors were studied: tumors transplanted in BALB/c mice that are medroxyprogesterone acetate (MPA)-dependent for growth, and tumors induced in Sprague-Dawley rats by intraperitoneal injection of N-nitroso-N-methylurea (NMU). Tumors from mice treated with MPA, E(2), Tam or Ral and NMU-treated rats were analyzed and compared to that of control. RESULTS: The tumor conformer profiles were as follows: control and MPA-treated mice showed only one peak (oligomeric form); E(2)-treated mice also showed only one peak (dimer); Tam-treated mice showed one peak corresponding to a possible proteolytic fragment, and Ral-treated mice showed two peaks (oligomeric and a possible proteolytic fragment). On the other hand, NMU-induced mammary tumors from rats showed three peaks (oligomeric, monomeric and proteolytic). CONCLUSION: Our findings may indicate that SERMs affect the aggregation state of ER and thereby its ability to modulate genomic transcription mechanisms related to growth rate.

Thiols and polyamines in the potentiation of malathion toxicity in larval stages of the toad Bufo arenarum.

Treatment with exogenous spermidine enhanced acute malathion toxicity during larval development of the toad Bufo arenarum Hensel. The polyamine was rapidly incorporated in the larvae with a subsequent metabolization to putrescine and spermine, which were excreted to the media. Endogenous polyamine levels were not changed by either spermidine or malathion treatments. However, 0.5-mM spermidine modified malathion uptake and bioavailability increasing the concentration of the xenobiotic in the larvae. The amount of reduced thiols was decreased by both compounds, but the depletion was insufficient to induce cytotoxicity. The oxidative degradation of polyamines competes for the pool of reduced glutathione used in the conjugation of malathion in the larvae, thus leading to the reported potentiation of toxicity. Our results suggest that exposure to thiols-depleting agents may induce alteration of organophosphate degradation in amphibian larvae.

Histamine as an autocrine growth factor: an unusual role for a widespread mediator.

The involvement of histamine in cancer growth represents an old controversy and direct experimental evidence proving this hypothesis is not still available. In this paper we review the most relevant mechanisms referring to the role of histamine receptors, histidine decarboxylase and histamine release in the onset of an autocrine loop, that enables histamine to act as an autocrine growth factor. We postulate that this autocrine loop, that has been studied in an experimental mammary carcinoma model induced in rats, may be present in different human neoplasias. Therefore, the better understanding of this novel regulatory pathway that is controlled by histamine may contribute to identifying new therapeutic targets.

An experimental model of diabetes and cancer in rats.

The aim of this study was to develop an experimental model for the study of cancer associated with diabetes. For diabetes induction, Sprague-Dawley rats were given streptozotocin (STZ, 90 mg/kg body weight (BW), by intraperitoneal injection on the second day of life. For mammary tumour induction, rats were injected with 50 mg/kg BW of N-nitroso-N-methylurea (NMU) at 50, 80 and 110 days old. The neoplastic process and the effect of tamoxifen treatment was examined in non-diabetic and diabetic rats. The latency period, NMU-induced tumour incidence and the number of tumours per rat in diabetic rats versus controls were 117 +/- 7 days versus 79 +/- 9 days (P < 0.001); 93% versus 95% (NS); and 5.2 +/- 1.6 versus 2.7 +/- 0.5 (P < 0.02). A more benign histological pattern for tumours in diabetic animals was observed. Mammary tumours in diabetic rats grew more slowly than in controls. Tamoxifen (1 mg/kg/day) treated diabetic rats showed tumour regression in 67% of NMU-induced mammary tumours versus 53% in controls (NS). Our results show that tumour progression seems to be affected by diabetes in this experimental model. We suggest this is the result of changes to insulin-like growth factors and their receptors, which occur in diabetics, and our future research will examine this hypothesis.

Receptors characterization of intraperitoneally N-nitroso-N-methylurea-induced mammary tumors in rats.

Mammary adenocarcinomas induces in female Sprague-Dawley rats by three intraperitoneal injections of N-nitroso-N-methylurea were studied in order to characterize their estrogen (ER), progesterone (PgR), prolactin (PRLR) and epidermal growth factor (EGFR) receptors. All samples evaluated showed the presence of ER and PgR in the cytosol fraction and PRLR amd EGFR in the membrane fraction. Q (fmol/mg) and K(d) (nM) values were as follows: ER, 56 +/- 11 and 0.5 +/- 0.1; PgR, 109 +/- 25 and 2.2 +/- 0.5 and PRLR, 335 +/- 75 and 0.5 +/- 0.2, respectively. In all tumors studied, two specific sites were found for EGFR, one with Q(1) = 22 +/- 9 and K(d1) = 0.6 +/- 0.3, and the other with Q(2) = 125 +/- 33 and K(d2) = 2.1 +/- 0.5. Receptor content was found to be independent of tumor histopathological variety. Displacement index (DI) with estradiol and tamoxifen of [I(3)H]E2-ER binding showed great heterogeneity, with values ranging from 0.01 to1.54. No correlation between ER content and DI values was found. Antiestrogenic binding sites were not found in the microsomal fraction of ten mammary tumors examined. Proliferation of this experimental mammary tumor may be regulated by a complex interaction of steroid and polypeptide hormones, as well as growth factors.

H1 and H2 histamine receptors in N-nitroso-N-methylurea (NMU)-induced carcinomas with atypical coupling to signal transducers.

Two specific binding sites for histamine were characterized in the cell membrane of N-nitroso-N-methylurea (NMU)-induced tumors. The first one, with higher affinity (Kd = 4 +/- 2 nM), was further identified as an H2 type, while the lower affinity one (35 +/- 10 nM) corresponded to an H1 receptor. Histamine concentrations up to 50 nM, as well as H2 agonists, significantly enhanced the phosphoinositide turnover by acting through higher affinity H2 receptors. On the other hand, histamine at concentrations over 50 nM and H1 agonists produced a 100% increase in cAMP levels in a response specifically blocked by mepyramine. These H1 and H2 histamine receptors that exhibit different linkages to second messenger systems may prove to be a characteristic of cells with a high proliferating capacity, such as undifferentiated or transformed cells.

Induction of mammary tumors in rat by intraperitoneal injection of NMU: histopathology and estral cycle influence.

In order to obtain an experimental model we induced mammary tumors in female Sprague-Dawley rats. The carcinogen N-nitroso-N-methylurea (NMU) was injected intraperitoneally (i.p.) at doses of 50 mg/kg body weight when animals were 50, 80 and 110 days old. Tumor sizes were measured with a caliper and their growth parameters and histopathological properties were tested. For 100 rats, 88.4% of developed lesions were ductal carcinomas, histologically classified as 52.8% cribiform variety, 30.6% solid carcinoma. Metastases in liver, spleen and lung were present. Other primary tumors were detected with low incidence. The influence of the rat estrous cycle during the first exposure to intraperitoneal NMU injection was studied. The latency period in estrus, proestrus and diestrus was 82 +/- 15, 77 +/- 18 and 79 +/- 18 days, respectively. Tumor incidence was significantly higher in estrus (95.2%) than proestrus (71.4%) or diestrus (77.4), (P < 0.01). Mean number or tumors per animal was similar among the three groups (4.4 +/- 3.2, 3.8 +/- 3.6, 3.2 +/- 1.8). The procedure described appears to be the simplest method for inducing experimental mammary tumors in rats.

Histamine as an autocrine growth factor in experimental mammary carcinomas.

In order to determine the role of endogenous histamine in the regulation of cell growth, the in vitro action of fluoromethyl-histidine (MFMH) was studied in experimental mammary carcinomas induced in rats. Tumor cells were cultured in soft agar using the clonogenic agar technique. The MFMH was added in different concentrations (0.01-100 microM). The effect observed was a 60% inhibition on colony formation with a maximal effect at concentrations over 10 microM. This action was completely reverted by the H2 agonists dimaprit and arpromidine with an IC50 value of 1 microM. The action of the H2 agonists when added alone was a significant increase in cell proliferation (135%), while the H1 agonist produced a dose-dependent inhibition on cell growth. In these experimental carcinomas endogenous histamine is critical for cell proliferation and one of its major effects may be the stimulation of cell growth by acting on specific H2 membrane receptors.

Effect of histamine on growth and differentiation of the rat mammary gland.

The presence of H1 and H2 histamine receptors and their associated second messenger systems were studied during the development of the rat mammary gland. In the tissue of the young female, histamine presented a double receptor site as previously described for experimental mammary tumors, namely a high affinity H2 site (Kd = 10 +/- 2 nM, Bmax = 1068 +/- 71 fm/mg prot.), which mediated its effect via the products of phosphoinositide hydrolysis and a low affinity H1 receptor (Kd1 = 5 +/- 2 nM, Bmax = 188 +/- 33 fm/mg prot. and Kd2 = 41 +/- 20 nM, Bmax = 1980 +/- 790 fm/mg prot. when characterized with 3H-mepyramine), coupled to adenylyl cyclase activation. On the other hand, the mammary gland of the adult rat presented these receptors coupled to the classical second messenger systems described for mammalian cells, that is, the H2 receptor produced an increase in intracellular cAMP levels and the H1 receptor increased the phosphoinositide turnover. We conclude that histamine plays a critical role during development and differentiation of the normal rat mammary gland.

Histamine receptors in an experimental mammary carcinoma.

An experimental mammary carcinoma was induced in Sprague-Dawley rats by the ip administration of N-nitroso-N-methylurea (NMU) in three doses of 50 mg/kg. In order to study the expression of histamine receptors in these experimental tumors, the presence of specific binding sites for histamine was studied. Using [3H]-histamine as a radioligand, two specific binding sites were characterized on the cell membrane. The first site, of high affinity, Kd = 4 +/- 2 nM, was further characterized as an H2 type using [3H]-cimetidine and [3H]-tiotidine as radioligands and by displacement experiments with different histamine agonists and antagonists. The second one of low affinity, Kd = 35 +/- 14 nM, needs further characterization. The determination of cAMP levels showed that histamine and the H2 agonist dimaprit, produced a significant decrease in the nucleotide concentration 6 minutes after stimulation, in a response that was specifically abolished by H2 antagonists. Based on these results, we conclude that neoplastic cells from NMU induced tumors express H2 histamine membrane receptors which are coupled to a transductional pathway different from cAMP production, which may be involved in the regulation of tumor growth.

Effect of exogenously applied polyamines on malathion toxicity in the toad Bufo arenarum Hensel.

The polyamines putrescine, spermidine, and spermine, are able to potentiate the toxicity of malathion in Bufo arenarum Hensel toad larvae. This action is synergistic and maximal with spermidine, which elevated up to 13-fold the mortality produced by this organophosphorus compound. Spermidine increased the degree of inhibition of acetylcholinesterase activity elicited by malathion, and impaired the recovery of this activity at the end of the treatment. Spermidine had no effect on the enzyme when applied alone. Toxic effects were also observed with the polyamines themselves when applied at concentrations similar to the intracellular levels described for rapid-growing organisms.

A simplified competition data analysis for radioligand specific activity determination.

Non-linear regression and two-step linear fit methods were developed to determine the actual specific activity of 125I-ovine prolactin by radioreceptor self-displacement analysis. The experimental results obtained by the different methods are superposable. The non-linear regression method is considered to be the most adequate procedure to calculate the specific activity, but if its software is not available, the other described methods are also suitable.

Alteración del metabolismo histamínico en tumores experimentales / Alteration of histamine metabolism in experimental tumors

Adenocarcinomas mamarios fueron inducidos en ratas Sprague-Dawley mediante N-nitraso-N-metil-urea (NMV). Una vez que el primer tumor se hacía evidente, los animales fueron tratados diariamente con una dosis oral de 4 mg/kg de animal de Levamisol (Leva). La actividad de histidina decarboxilasa (HDC), expresada dpm/(g,h), se determinó en el tumor y en el intestino con C-histidina por medición de actividad de CO2 con espectrometría de centelleo líquido. La histopatología demostró que todos los tumores inducidos eran adenocarcinomas mamarios más o menos diferenciados. Como fuera observado en otros casos, la actividad de HDC tumoral fue alta comparada con la de tejidos normales. El tratamiento con Leva durante 7 y 14 días no produjo influencias significativas sobre la actividad de HDC, si bien se evidenció una disminución de la actividad enzimática. La administración de Leva durante más de 20 días provocó una disminución significativa de la actividad de HDC. La actividad de dicha enzima dependió, en todos los casos, de la masa total del tumor (MTT). La actividad de HDC en función de MTT es una función lineal con coeficientes de correlación superiores a 0,9. Para las ratas tratadas con Leva durante 20 días o más, la pedndiente fue de 1,93 ñ 0,89. Para animales no tratados, la pendiente fue de 7,37 ñ 1,23. La diferencia es estadisticamente significativa de acuerdo al criterio de la distribución F (P <0,001). Nuestros resultados demuestran que un agente inmunomodulador exhibe un definido tiempo de retraso antes de ejercer su influencia sobre el metbolismo de la histamina, el cual anormal en diferentes tipos de tumores. En trabajos futuros se estudiará si este efecto está relacionado con la acción inmunomoduladora de la droga

Alteración del metabolismo histamínico en tumores experimentales / Alteration of histamine metabolism in experimental tumors

Adenocarcinomas mamarios fueron inducidos en ratas Sprague-Dawley mediante N-nitraso-N-metil-urea (NMV). Una vez que el primer tumor se hacía evidente, los animales fueron tratados diariamente con una dosis oral de 4 mg/kg de animal de Levamisol (Leva). La actividad de histidina decarboxilasa (HDC), expresada dpm/(g,h), se determinó en el tumor y en el intestino con C-histidina por medición de actividad de CO2 con espectrometría de centelleo líquido. La histopatología demostró que todos los tumores inducidos eran adenocarcinomas mamarios más o menos diferenciados. Como fuera observado en otros casos, la actividad de HDC tumoral fue alta comparada con la de tejidos normales. El tratamiento con Leva durante 7 y 14 días no produjo influencias significativas sobre la actividad de HDC, si bien se evidenció una disminución de la actividad enzimática. La administración de Leva durante más de 20 días provocó una disminución significativa de la actividad de HDC. La actividad de dicha enzima dependió, en todos los casos, de la masa total del tumor (MTT). La actividad de HDC en función de MTT es una función lineal con coeficientes de correlación superiores a 0,9. Para las ratas tratadas con Leva durante 20 días o más, la pedndiente fue de 1,93 ñ 0,89. Para animales no tratados, la pendiente fue de 7,37 ñ 1,23. La diferencia es estadisticamente significativa de acuerdo al criterio de la distribución F (P <0,001). Nuestros resultados demuestran que un agente inmunomodulador exhibe un definido tiempo de retraso antes de ejercer su influencia sobre el metbolismo de la histamina, el cual anormal en diferentes tipos de tumores. En trabajos futuros se estudiará si este efecto está relacionado con la acción inmunomoduladora de la droga (AU)