Activation of intestinal mucosal immunity in tumor-bearing mice by lactoferrin

We have previously demonstrated that oral administration of bovine lactoferrin (bLF) markedly increases CD4(+) and CD8(+) T cells and NK (asialoGM1(+) ) cells in the blood of tumor-bearing mice and enhances anti-metastatic activity. In this paper, we document that oral administration of bLF and bLF-hydrolysate (bLFH) is associated with strong increases in CD4(+) and CD8(+) T, as well as asialoGM1(+) cells in lymphoid tissues and lamina propria of the small intestine in mice, especially in tumor-bearing animals in which Co26Lu cells were implanted subcutaneously. Moreover, IgM(+) and IgA(+) B cells in lamina propria of the small intestine were also significantly increased by bLF and bLFH. Bovine apo-transferrin (bTF) did not exhibit such activity. In the colon, only CD8(+) cells were significantly increased by treatment with bLF, while asialoGM1(+) cells were significantly decreased. bLF and bLFH induced cytokines to activate T, B and asialoGM1(+) cells. Administration of bLF and bLFH, but not bTF, increased production of interleukin-18 (IL-18), interferon-gamma (IFN-gamma) and caspase-1 in the mucosa of the small intestine. Particularly high levels of IL-18 were found in the epithelial cells of the small intestine. Moreover, administration of bLF and bLFH, but not bTF, induced IFN-gamma presenting cells in the small intestine. Caspase-1, which processes proIL-18 to mature IL-18, was also induced in the epithelial cells of the small intestine following treatment with bLF and bLFH, but not with bTF. These results suggest that enhanced production of IL-18 and IFN-gamma and caspase-1 induction by treatment with bLF may be important for elevation of intestinal mucosal immunity.

Pinealectomy does not affect the entrainment to light nor the generation of the circadian demand-feeding rhythms of rainbow trout

The pineal organ and its secretory product melatonin are regarded as synchronizers of daily rhythms to the external light/dark (LD) cycle. In fish, the pineal organ acts as a direct photoreceptor, transducing light information into neural and humoral (melatonin) signals. In the present study, we investigate a possible role for the pineal organ and melatonin in the regulation of feeding rhythms of rainbow trout, Oncorhynchus mykiss. We used individual rainbow trout placed in an insulated room at constant temperature (14 degrees C). Fish were self-fed ad lib by means of self-feeders coupled to a computer that continuously recorded demand-feeding activity. Before and after pinealectomy, the fish were exposed to a LD cycle of 16:8 h and then constant light (LL) to test the effect of pinealectomy on demand-feeding rhythms. Feeding records revealed that trout fed exclusively during daytime (96% of feeding confined to the light phase), and that removal of the pineal organ did not disrupt this daily feeding profile, with synchronization to the LD cycle persisting. Moreover, the appearance of circadian feeding rhythms was not affected by pinealectomy: most of the operated fish free-ran with an average tau longer than 24 h. Plasma melatonin rhythms persisted in the pinealectomized trout, but with small amplitude. These results suggest that the pineal may not be the site of the pacemaker that controls feeding rhythms in trout, although further research is required to study the involvement of other photoperiod-transducing systems and melatonin (of nonpineal origin) in the regulation and expression of circadian rhythms in this species.

Milk and dairy products in cancer prevention: focus on bovine lactoferrin

Milk and dairy products constitute an important part of the western style diet. A large number of epidemiological studies have been conducted to determine effects of consumption on cancer development but the data are largely equivocal, presumably reflecting the different included components. It has been proposed that whereas fats in general could promote tumor development, individual milk fats like conjugated linoleic acid could exert inhibitory effects. There is also considerable evidence that calcium in milk products protects against colon cancer, while promoting in the prostate through suppression of circulating levels of 1,25-dihydroxyvitamin D3. Whey protein may also be beneficial, as shown by both animal and human studies, and experimental data have demonstrated that the major component bovine lactoferrin (bLF), inhibits colon carcinogenesis in the post-initiation stage in male F344 rats treated with azoxymethane (AOM) without any overt toxicity. The incidence of adenocarcinomas in the groups receiving 2% and 0.2% bLF were thus 15% and 25%, respectively, in contrast to the 57.5% control value (P<0.01 and P<0.05, respectively). Results in other animal models have provided further indications that bLF might find application as a natural ingredient of milk with potential for chemoprevention of colon and other cancers.

Prevention of colon carcinogenesis and carcinoma metastasis by orally administered bovine lactoferrin in animals

Bovine lactoferrin (bLF), a milk protein known to have bacteriostatic properties was examined for its preventive effects on colon and other organ carcinogenesis and experimental metastasis. (Experiment 1) The influence on colon carcinogenesis was investigated in male rats treated with azoxymethane (AOM), then received 2 or 0.2% bLF for 36 weeks. Significant reduction in the incidence (27% and 46% of the control, respectively) and number of adenocarcinomas of the large intestine was observed. (Experiment 2) In BALB/c mice bearing subcutaneous (s.c.) implants of colon carcinoma 26 (Co 26Lu). bLF demonstrated significant inhibition of spontaneous lung metastasis (approximately 43% of the control). Number of cytotoxic asialoGM1+ and CD8+ cells in white blood cells increased (171% and 122% of control, respectively) after treatment. Results of those experiments indicate that bLF remarkably prevents colon carcinogenesis and lung metastasis of colon carcinoma cells, possibly due to increasing cytotoxic cells in the peripheral blood.

Female-soiled bedding induced fos immunoreactivity in the ventral part of the premammillary nucleus (PMv) of the male mouse

Previous studies have indicated that the ventral part of the premammillary nucleus (PMv) of rodents is involved in the regulation of aggressive and male mating behavior, although the precise physiological function of the PMv is still unclear. To analyze the physiological role of the PMv in male mating behavior, the effects of exposure to bedding soiled by female mice on Fos immunoreactivity (Fos-ir), an early marker of neuronal activation, were studied in the PMv and some sex-related nuclei. We observed that exposure to female-soiled bedding induced Fos-ir expression in the PMv of the male mouse. Although Fos-ir positive cells were found in the posterodorsal part of the medial amygdaloid nucleus and in the posteromedial cortical amygdaloid nucleus, which are terminals of the neuronal projections from the main and accessory olfactory bulbs, the numbers of Fos-ir cells in those nuclei were not affected by exposure to female-soiled bedding. Moreover, Fos-ir was not detected in the ventromedial hypothalamic nucleus. It is well established that soiled bedding is useful as a source of chemosensory substances, which include "pheromones." Thus, our findings, in agreement with previous behavioral and anatomical data, suggest that the PMv plays a role in initiating male copulative behavior that is induced by a female mice pheromone(s).

Proteins recognized by antibodies against isolated cytological heterochromatin from rat liver cells change their localization between cell species and between stages of mitosis (interphase vs metaphase)

Heterochromatin in the cell nucleus seems to concentrate various proteins, such as Drosophila heterochromatin protein 1, which maintain the repressed state of gene expression. However, it still remains obscure how protein composition related to chromatin structure is different between heterochromatin and euchromatin in interphase nuclei. We isolated cytological heterochromatin from sonicated interphase nuclei obtained from rat liver cells and prepared antisera against it. The dense heterochromatic bodies seen in the preparation of intact nuclei were duplicated in a relatively pure form during the preparation of heterochromatin. In the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, differences between the fractions of heterochromatin and euchromatin were noted by their protein composition. Isolated heterochromatin was then digested by DNase after partial digestion with trypsin and its dense structure changed to become highly sensitive to DNase. The prepared antibodies reacted with the heterochromatin region of rat liver cell nuclei and isolated cytological heterochromatin; however, they did not react with euchromatin. Using immunohistochemistry, the antibodies bound to each cell nucleus in all tissues observed; some cell types were distinguished by their differential stainability (e.g. staining in the cytoplasm). Staining of the mitotic cells showed that the proteins recognized by the antibodies were localized in the cytoplasm and, in part, on the chromosomes. Based on the results of molecular cloning from rat liver cDNA library using the antibodies as a probe, it seemed that the antibodies mainly recognized two proteins similar to arginase and general vesicular transport factor p115, respectively. The results obtained from these experiments reveal that some proteins located in the heterochromatin of interphase liver cell nuclei seem to play important roles in condensing a portion of the chromatin structure during interphase and suggest that proteins composing heterochromatin might be changed according to cell types or the stage of the cell cycle.

Possible chemopreventive effects of bovine lactoferrin on esophagus and lung carcinogenesis in the rat

A milk component, bovine lactoferrin (bLF), previously shown by us to be a strong chemopreventive of colon carcinoma development, was examined for its influence on other organs using a rat multi-organ carcinogenesis model. Male F344 rats, aged 6 weeks, were treated sequentially with diethylnitrosamine (DEN, i.p.), dihydroxy-di-N-propylnitrosamine (DHPN, in drinking water) and N-nitrosomethylbenzylamine (NMBA, s.c.) during the first 8 weeks (DDN treatment), and then bLF was administered in the basal diet, at a dose of 2, 0.2, 0.02 or 0.002%. Other groups were given DDN treatment or bLF alone as controls. All surviving animals were killed at week 41, and major organs were examined histopathologically for neoplastic lesions. In the esophagus, a tendency for reduction in development of papillomas was evident in the bLF-treated animals, along with a significant suppression of relatively large-sized papillomas (more than 50 mm3 volume) at the 0.2% dose (P<0.05, 11% of the control). The multiplicity of tumors (adenomas and carcinomas) in the lung was also decreased in animals fed 0.02% bLF (1.98+/-0.41 per cm2 lung tissue section, P<0.05) compared to the control group (3.48+/-0.33). No enhancing or inhibitory effects of bLF on tumor development in other organs were noted. The present results indicate that bLF exerts chemopreventive effects in the esophagus and lung in addition to the colon.

Inhibitory effects of bovine lactoferrin on colon carcinoma 26 lung metastasis in mice

In order to determine the effects of the multifunctional iron-binding glycoprotein, lactoferrin (LF), and related compounds on tumor growth and metastasis, bovine LF (bLF), and bLF hydrolysate and lactoferricin (bLFcin), active products generated by acid-pepsin hydrolysis were administered orally to BALB/c mice bearing subcutaneous (s.c.) implants of the highly metastatic colon carcinoma 26 (Co 26Lu). bLF and the bLF hydrolysate demonstrated significant inhibition of lung metastatic colony formation from s.c. implanted tumors without appreciable effects on tumor growth. bLFcin displayed a tendency for inhibition of lung metastasis. On the other hand, bLF did not exert marked anti-metastatic activity in athymic nude mice bearing Co 26Lu, though bLF had a tendency to inhibit the lung metastatic colony formation associated with anti-asialoGM1 antibody (Ab) treatment. AsialoGM1+ and CD8+ cells in white blood cells were increased after treatment with bLF. In vitro, the viability of Co 26Lu-F55 cells was markedly decreased when co-cultured with white blood cells from mice administrated bLF p.o., but recovered on treatment with anti-asialoGM1 Ab or anti-CD8 mAb and complement. The results suggest bLF and related compounds might find application as tools in the control of metastasis and that asialoGM1+ and CD8+ cells in the blood are important for their inhibitory effects.

Inhibitory effects of bovine lactoferrin on intestinal polyposis in the Apc(Min) mouse

Chemopreventive effects of bovine lactoferrin (bLF), previously shown to strongly inhibit intestinal carcinogenesis in rats (K. Sekine, E. Watanabe, J. Nakamura, N. Takasuka, D.J. Kim, M. Asamoto, V. Krutovskikh, T.H. Baba, T. Ota, M.A. Moore, M. Masuda, H. Sugimoto, H. Nishino, T. Kakizoe, H. Tsuda, Inhibition of azoxymethane-initiated colon tumor by bovine lactoferrin administration in F344 rats, Jpn. J. Cancer Res. 88 (1997) 523-526; K. Sekine, Y. Ushida, T. Kuhara, M. Iigo, H. Baba-Toriyama, M.A. Moore, M. Murakoshi, Y. Satomi, H. Nishino, T. Kakizoe, H. Tsuda, Inhibition of initiation and early stage development of aberrant crypt foci and enhanced natural killer activity in male rats administered bovine lactoferrin concomitantly with azoxymethane, Cancer Lett. 121 (1997) 211-216), on spontaneous intestinal polyp development were assessed in the ApcMin mouse, a model for both familial adenomatous polyposis and sporadic colon cancers. In the experiment, 54 mice at 6 weeks of age were given 2% bLF (15 mice), 0.2% bLF (15 mice) and AIN-93G (24 mice) as basal diet ad libitum for 8 weeks. An overall tendency for a reduction in the total number of polyps in the small intestine was evident in the bLF-treated animals, along with significant suppression in the jejunum at the 2% dose (P < 0.05, 68% of the control). In addition, body growth suppression, presumed to be due to anemia and/or intussusception as a consequence of numerous polyps in the intestine, was alleviated. No toxic effects were observed in the intestinal epithelium. Although not as obvious as observed for the rat case, the data suggest that bLF may be a chemopreventor of intestinal polyposis.

Proteasome inhibitors which induce neurite outgrowth from PC12h cells cause different subcellular accumulations of multi-ubiquitin chains

The effects of two proteasome inhibitors on neurite outgrowth from PC12h cells were investigated in terms of the mean length of the neurites and the frequency of occurrence of cells with long neurites. Benzyloxycarbonyl-leucyl-leucyl-leucinal (ZLLLal) and benzyloxycarbonyl-isoleucyl-t-butyl-glutamyl-leucinal (PSI) caused a significant elongation of PC12h cell neurites. Since ZLLLal is known to inhibit both calpain and proteasome activity, we examined the effects ofbenzyloxycarbonyl-leucyl-leucinal (ZLLal) which inhibits calpain activity to the same degree as ZLLLal, but which inhibits proteasome activity only weakly. ZLLal did not induce the significant elongation of neurites at any of the concentrations we studied. These results show that the inhibition of proteasome activity causes neurite elongation. We also quantified subcellular levels of multi-ubiquitin chains and free ubiquitin after treatments with PSI, ZLLLal and ZLLal. Treatment with ZLLal had no effects on levels of water- and urea-soluble multi-ubiquitin chains or of free ubiquitin either in the nucleus or in the cytoplasm. PSI and ZLLLal induced a large accumulation of water- and urea-soluble multi-ubiquitin chains and free ubiquitin in the nucleus. Similarly, PSI and ZLLLal increased cytoplasmic levels of urea-soluble multi-ubiquitin chains. On the contrary, PSI and ZLLLal had no effect on levels of water-soluble multi-ubiquitin chains or free ubiquitin in the cytoplasm. This is the first study to demonstrate subcellular differences in the accumulation of multi-ubiquitin chains and free ubiquitin during the neurite elongation induced by proteasome inhibitors.

Chromosomal mapping of the gene encoding serotonin N-acetyltransferase to rat chromosome 10q32.3 and mouse chromosome 11E2

Pineal melatonin is produced during the night. Its nocturnal increase regulates circadian rhythms and the photoperiodic reproductive response. Serotonin is acetylated to N-acetylserotonin by serotonin N-acetyltransferase (SNAT) and then methylated to form melatonin by hydroxyindole-O-methyltransferase (HIOMT). The rhythmicity of melatonin synthesis is regulated by the rhythmic activity of SNAT. Most laboratory mice do not have melatonin because of a genetic defect in the activity of SNAT and/or HIOMT. In a previous study using a recombinant inbred strain, we have found that the locus controlling pineal SNAT activity (Nat4) is located on mouse Chromosome 11. Recently, SNAT has been cloned in the rat. In the present study, the gene encoding SNAT was localized, using a rat cDNA fragment, on rat and mouse chromosomes by direct R-banding fluorescence in situ hybridization (FISH). In addition, using molecular linkage analysis with interspecific backcross mice, a gene encoding SNAT was mapped on a mouse chromosome. The gene encoding SNAT was localized to rat chromosome 10q32.3 and mouse Chromosome 11E2 by FISH. The molecular linkage analysis demonstrated that the gene encoding SNAT maps 1.5 cM distal to D11Mit11. The data suggest that Nat4 encodes SNAT. These chromosomal locations are in a region of conserved linkage homology between the two species.

Effects of a low-protein diet on prolactin- and growth hormone-producing cells in the rat pituitary gland

BACKGROUND

It is well known that an unbalanced diet induces various changes in the pituitary gland. However, little attention has been paid to the molecular aspects of this perturbation. We studied the influence of a low-protein diet (LPD) on the prolactin (PRL) and growth hormone (GH) cells in the rat pituitary gland using immunohistochemical staining and in situ hybridization.

MATERIALS

Rats aged 20 days were fed a diet containing 27% protein or one with 8% protein (LPD) for 30 days. Pituitary glands were obtained and subjected to either immunohistochemistry or in situ hybridization. Quantitative morphological analysis was then conducted to determine cell number and area as well as the percentage of cells stained by the respective antisera and/or cDNA probe in each experimental group.

RESULTS

The average sectional areas of both PRL- and GH-producing cells in the LPD group were smaller in size than those in the controls. The cell numbers per unit area (mm2) of PRL-positive cells and PRL mRNA-positive cells were 3,596.5 and 3,948.6, respectively, in the LPD group, and 3,179.6 and 4,888.5, respectively, in the controls. The numbers per unit area of GH-positive cells and GH mRNA-positive cells in the LPD group were similar (2,252.3 and 2,224.4), as compared to 2,161.3 and 1,684.2, respectively, in the well-fed rats. Whereas PRL-positive cells comprised about 27% of the total number of cells in both animal groups, those given the LPD contained a lower percentage (29%) of PRL mRNA-positive cells as compared to the controls (44%). On the other hand, GH mRNA-positive cells numbered about 15% of the total cell population both animal groups; however, the malnourished rats contained a lower percentage (16%) of GH-positive cells than did their well-fed counterparts (20%).

CONCLUSIONS

Taken together, these results indicate that in the rat pituitary gland, administration of an LPD reduced the size of PRL- and GH-positive cells as well as differentially affecting a subpopulation of the PRL mRNA-positive cells and the GH-positive cells.

Light-dependent expression of pinopsin gene in chicken pineal gland

The phase of a circadian clock in the chicken pineal gland is reset by an environmental light signal, which is captured by the pineal photoreceptive molecule(s). Here we show that the mRNA level of pinopsin, a predominant photoreceptive molecule in the pineal gland, undergoes a diurnal fluctuation in chickens maintained on a light/dark cycle. The mRNA levels in the light were approximately six times higher than those in the dark. This fluctuation was not observed in constant darkness, where the mRNA levels remained low. Subsequent light exposure of chickens increased the amount of pinopsin mRNA regardless of the circadian time. Clearly, the expression of pinopsin gene is controlled by a light signal, independent of the circadian clock. In vitro experiments using cultured pineal glands isolated from the visual system also revealed the light-dependent increase in pinopsin mRNA level, indicating that the pineal photoreceptive molecule(s) is responsible for the induction. These results demonstrate the presence of a feedback loop through which the light signal captured by pinopsin stimulates the transcription of its own gene in the chicken pineal gland. In contrast, pinopsin protein remained at an almost constant level in chickens maintained under the same light/dark cycles. The protein level, however, decreased to approximately 50% of the light/dark level under constant darkness and subsequently increased upon exposure to light after the dark period. It is suggested that, under the light/dark cycles, the pinopsin protein level is kept constant by the light-dependent synthesis, which would compensate for a possible degradation of pinopsin in the daytime.

A possible role of the pineal gland in acute immobilization-related suppression of naloxone-induced LH release in ovariectomized estrogen-primed rats

It has been recently reported that acute immobilization stress almost completely suppresses the luteinizing hormone (LH) release induced by naloxone, a mu-opioid antagonist, in ovariectomized estrogen-primed rats. The present study examined the possible involvement of the pineal gland in the acute immobilization-related suppression of the naloxone-induced LH release. An intraventricular (ICV) injection of 15 microg naloxone produced an abrupt increase in circulating LH concentrations in non-stressed rats. The naloxone-induced LH release was completely eliminated when tested 60 min after the end of a 30 min session of acute immobilization. The same stress conditions did not affect LH-releasing hormone (LHRH)-induced LH release, suggesting that the stress-related suppression of the naloxone-induced LH release was a suprapituitary event. In chronically-pinealectomized rats, but not in sham-pinealectomized rats, naloxone injected 60 min after the end of the stress session evoked a significant increase in serum LH concentrations. However, naloxone injected ICV during the acute immobilization did not elicit LH release in either pinealectomized or sham-operated rats. Under non-stressed conditions, the LH secretory response to naloxone was similar in pinealectomized and sham-operated animals. The same stress (30 min immobilization) significantly increased pineal melatonin content as well as plasma melatonin concentrations in rats bearing intact pineal glands, indicating that stress actually affected the pineal function. These results provide evidence for a role of the pineal in the suppression of the LH response to naloxone after stress, but not during stress.

Inhibition of initiation and early stage development of aberrant crypt foci and enhanced natural killer activity in male rats administered bovine lactoferrin concomitantly with azoxymethane

The influence of concomitant administration of bovine lactoferrin (bLF) on induction of aberrant crypt foci (ACF) by azoxymethane was investigated in male F344 rats. Two percent bLF and 3% Bifidobacterium longum (B. longum), as a positive control, significantly decreased the numbers of ACF as well as the total numbers of aberrant crypts reproducibly in three independent studies (2% bLF, P < 0.01; 3% B. longum, P < 0.05). Most importantly large size foci composed of four or more crypts were always significantly decreased by 2% bLF (P < 0.05). Additional investigation of the natural killer activity of spleen cells demonstrated enhancement by bLF (P < 0.01) and B. longum (P < 0.01) in line with the levels of influence on foci induction, indicating a possible role for elevated immune cytotoxicity in the observed inhibition.

Inhibitory effects of oleic and docosahexaenoic acids on lung metastasis by colon-carcinoma-26 cells are associated with reduced matrix metalloproteinase-2 and -9 activities

In order to determine the effects of single unsaturated fatty acids (UFAs) or combinations on establishment of lung metastatic colonies, UFAs were administered orally to CDF1 mice bearing s.c. implants of the highly metastatic colon carcinoma 26. Oleic acid (OA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) demonstrated significant inhibition. In the case of DHA, this inhibitory potential was markedly reduced by co-administration of linoleic acid (LA) or EPA. Furthermore, while tumor cells treated with DHA showed a very low potential for lung colony formation when injected i.v., this again being partially reversed by co-administration of EPA. UFAs were found to be well absorbed into tumor tissues after oral administration, causing marked changes in relative levels, the arachidonic acid (AA) content, in particular, being markedly decreased by treatment with DHA or EPA, but not with DHA plus EPA or with DHA plus LA. Investigation of the gelatinolytic activity of the 57-kDa and 92-kDa isoforms of type-IV collagenase (MMP-2 and MMP-9, respectively) showed a clear reduction in the former by treatment with OA, while DHA, but not DHA plus LA or EPA, caused a decrease in the 92-kDa isoform, which was well correlated with AA content in tumor tissues (r = 0.900, p < 0.001). These results suggest that inhibition of metastasis due to treatment with OA and DHA might be due to depressed type-IV collagenase activity.

Characterization, guanosine 5'-O-(3-thiotriphosphate) modulation, daily variation, and localization of melatonin-binding sites in the catfish (Silurus asotus) brain

Characteristics, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) modulation, daily variation, and localization of melatonin-binding sites in the brain of a nocturnal teleost, the catfish Silurus asotus, were studied by radioreceptor assay using 2-[125I]iodomelatonin as the radioligand. The specific binding was rapid, stable, saturable, and reversible. The radioligand binds to a single class of receptor site with an affinity (Kd) of 30.7 +/- 7.3 pM and total binding capacity (Bmax) of 9.76 +/- 0.79 fmol/mg protein (mean +/- SE, n = 5). The binding sites were highly specific for 2-iodomelatonin and melatonin. The specificity was almost identical to that of functional melatonin receptors in the dermal and epidermal melanophores in this species and that of ML-1 subtype melatonin receptors in vertebrates, including melatonin-binding sites in the goldfish brain. GTPgammaS treatment altered both the Kd and Bmax values, indicating that melatonin-binding sites in the catfish brain are coupled to G protein. The Bmax values exhibited no daily variation under light-dark cycles of 12 hr light:12 hr dark whereas plasma melatonin levels and Kd fluctuated in a rhythmic fashion. The density of melatonin-binding sites in discrete brain areas was determined to be highest in optic tectum-thalamus and hypothalamus, intermediate in telencephalon, cerebellum, and medulla oblongata, and lowest in olfactory bulbs. These results suggest that melatonin secreted from the pineal organ and/or retina plays neuromodulatory roles in the catfish brain via G protein-coupled melatonin receptors. Characteristics of melatonin receptors seem to be highly conserved during evolution, although the density of melatonin receptors is not regulated by melatonin itself in this species.

5-Fluorouracil derivatives. XXII. Synthesis and antitumor activities of 1-carbamoyl-5-fluorouracils

Fifty-four 1-carbamoyl-5-fluorouracils were synthesized from 5-fluorouracil and isocyanate or amine. Antitumor activity was tested in the L-1210 tumor system, and 11 compounds gave better values of therapeutic ratio than HCFU (1-hexylcarbamoyl-5-fluorouracil). 1-(4-Methoxycyclohexylcarbamoyl)-5-fluorouracil gave the best result.

Photic and circadian regulations of melatonin rhythms in fishes

Photic and circadian regulations of melatonin rhythms in the pineal organ and the retina of several teleosts were studied to investigate the regulatory mechanisms of melatonin rhythms in fishes. In the eyecup preparations of the goldfish, Carassius auratus, both time of day and lighting conditions affected melatonin production, with high melatonin production observed only in the dark-treated group incubated during the 'subjective' night. Thus, in the goldfish retina, local photoreceptors and an ocular circadian clock seem to regulate melatonin production, as in the zebrafish retina and in the pineal organ of a number of teleosts, including the goldfish. However, this circadian regulation of melatonin rhythms is not universal among fishes. Although the superfused pineal organ of the masu salmon Oncorhynchus masou secreted melatonin in a rhythmic fashion under light-dark (LD) cycles, the rhythm disappeared under constant darkness (DD), as in the rainbow trout, with a large amount of melatonin released both during the subjective day and the subjective night. These results suggest that all salmonids lack circadian regulation of melatonin rhythms. Furthermore, when ocular melatonin rhythms were compared in two cyprinids, the ugui Tribolodon hakonensis and the oikawa Zacco platypus occupying different ecological niches, ocular melatonin contents exhibited daily variations, with higher values during the dark phase of LD cycles in both species. The rhythmic changes persisted in the ugui under DD, with higher levels at subjective midnight than at subjective midday; however, ocular melatonin levels in the oikawa were consistently high under DD. Thus, the circadian regulation of melatonin rhythms in fishes is influenced not only by phylogeny, but also by the ecological niches of the animals. These results suggest that the physiological functions of melatonin in the circadian and photoperiodic systems differ among fishes.

Unusual responses to light and darkness of ocular melatonin in European sea bass

Regulation by light and darkness of melatonin rhythms in the plasma and eye of the European sea bass (Dicentrarchus labrax) was studied. During light-dark cycles, plasma and ocular melatonin exhibited day-night changes with higher levels at mid-dark and at mid-light, respectively. Circulating melatonin levels were low in constant light but high in constant darkness (DD); ocular melatonin levels showed the reverse pattern. Plasma melatonin exhibited circadian rhythm for 1 cycle but the rhythm was no longer apparent on day 2. There was no circadian rhythm in ocular melatonin. Acute light exposure in DD decreased plasma melatonin but increased ocular melatonin. These results suggest that circulating melatonin may be used as a signal for darkness but ocular melatonin is used as a signal for the light phase.