Permeable analogues of cGMP promote hepatic calcium inflow induced by the synergistic action of glucagon and vasopressin but inhibit that induced by vasopressin alone.

Treatment of perfused rat liver with the nitric oxide-generating reagent molsidomine led to substantial increases in cGMP without itself affecting basal Ca2+ fluxes. Under these conditions the ability of glucagon plus vasopressin to induce Ca2+ influx was greatly enhanced. The permeable analogue of cGMP (8-bromo-cGMP) enhanced glucagon plus vasopressin-induced Ca2+ influx to a similar extent as that with molsidomine. This suggests that the effect of the latter is attributable to the generation of cGMP which itself enhances the ability of the two hormones to induce synergistic Ca2+ influx. While 8-bromo-cGMP (or molsidomine) did not influence Ca2+ fluxes induced by glucagon, these agents strongly inhibited Ca2+ influx induced by vasopressin alone. These data show that while 8-bromo-cGMP has no effect on basal Ca2+ fluxes, it is able to modify the Ca2+ influx induced by glucagon and vasopressin action in hepatic tissue.

Eosinophilia in nude rats and nude mice after infection with Fasciola hepatica or injection with its E/S antigens.

Peripheral blood and bone marrow eosinophilia occurred in nude rats and nude mice following F. hepatica infection, with the magnitude of the response in nude rats greater than that in nude mice. Injection of E/S antigens induced eosinophilia in nude rats and a limited eosinophilia in nude mice. Bone marrow eosinophilia was greatly enhanced in Fasciola-infected nude rats, particularly 14 days after infection and later. In nude mice, bone marrow eosinophilia developed soon after infection and persisted for the duration of the experiment, but was not as marked as in nude rats. Bone marrow eosinophils in antigen-injected animals were also elevated, and again this was more marked in nude rats. The number of colonies formed in agar culture from bone marrow cells of both nude rats and nude mice also increased following infection and remained significantly elevated throughout the experiment. Bone marrow colonies in antigen-injected nude rats increased on day 8, while in injected nude mice, the number of colonies rose rapidly following injection with antigens. Thus, nude rats and nude mice develop T-cell-independent eosinophilia, which appears to originate in the bone marrow. The magnitude of eosinophilia is greater in nude rats and it has yet to be determined whether these effects have any relevance to the ability of rats, but not mice, to develop resistance to reinfection with F. hepatica.

IL-5-deficient mice have a developmental defect in CD5+ B-1 cells and lack eosinophilia but have normal antibody and cytotoxic T cell responses.

Mice deficient in interleukin-5 (IL-5-/- mice) were generated by gene targeting in embryonal stem cells. Contrary to previous studies, no obligatory role for IL-5 was demonstrated in the regulation of conventional B (B-2) cells, in normal T cell-dependent antibody responses or in cytotoxic T cell development. However, CD5+ B cells (B-1 cells) in the peritoneal cavity were reduced by 50%-80% in 2-week-old IL-5-/- mice, returning to normal by 6-8 weeks of age. The IL-5-/- mice did not develop blood and tissue eosinophilia when infected with the helminth Mesocestoides corti, but basal levels of eosinophils with normal morphology were produced in the absence of IL-5. IL-5 deficiency did not affect the worm burden of infected mice, indicating that increased eosinophils do not play a significant role in the host defence in this parasite model.

Do nitric oxide and cGMP play a role in calcium cycling?

The biological molecule NO and its cyclic nucleotide effector molecule cGMP, are involved in a variety of biological systems. This article reviews evidence supporting a role for these molecules in signal transduction. Over the last 10 years, it has become evident that these molecules are important in Ca2+ regulation, particularly in excitable cells. In these cells, cGMP-dependent mechanisms appear to both directly and indirectly regulate Ca2+ transport. Until recently, reports of the actions of cGMP in non-excitable cells have been contradictory, presenting a confusing plethora of effects. In these cells, the cGMP-Ca2+ regulation pathway appears to be concentration-dependent, possibly representing a negative feedback mechanism. Ca2+ entry appears to be activated when low concentrations of cGMP are present, and inhibited at higher concentrations. The role of cGMP in Ca2+ regulation in non-excitable cells has been largely overlooked and further investigation of this issue may provide clues as to the nature of various unknown components that induce Ca2+ entry into these cells.

Does nitric oxide play a role in liver function?

Nitric oxide (NO) is becoming increasingly recognised as a signalling molecule in many organs, although its role in the liver remains to be fully elucidated. There is no doubt that liver cells can produce NO in response to a variety of stimuli including Corynebacterium parvum-infection, lipopolysaccharide (LPS) and a variety of cytokines. Within the liver, NO modulates some fundamental intracellular functions such as protein synthesis, mitochondrial electron transport and components of the citric acid cycle. Intercellular roles for NO in the liver may include drug metabolism and blood storage. Also, NO acts to protect the liver from immunological damage in models of hepatic inflammation. Understanding the role of NO in the liver may provide insight into the functioning of this organ in health and disease.

Eosinophil differentiation in response to Fasciola hepatica and its excretory/secretory antigens.

Bone marrow cells from mice infected with Fasciola hepatica, from mice injected with F. hepatica excretory/secretory (ES) antigens, and from uninfected or uninjected control animals were cultured in the presence of F. hepatica ES antigens or the eosinophil differentiation cytokine IL-5. Eosinophil maturation in cultures was assessed quantitatively by measuring eosinophil peroxidase (EPO) activity and qualitatively by visual appraisal in stained preparations over a week. It was found that the presence in all cultures (including those from control animals) of either ES antigens at an optimal concentration of 100 micrograms ml-1 (established in preliminary trials) or IL-5 at 500 units ml-1 led to enhanced EPO activity. EPO activity in cultures without IL-5 or ES antigens remained static or fell over the culture period. At day 3 in all cultures containing IL-5 or ES antigens, there was maintenance of or only a slight decline in, the number of eosinophils that were present when cultures were initiated, and more of them were mature than at day 0 as evidenced by their EPO activity. However, there was a marked fall in eosinophil numbers in all cultures in the absence of IL-5 or ES antigens. The results indicate that F. hepatica ES antigens, like IL-5, stimulate eosinophil maturation in bone marrow with a consequent rise in EPO activity in the cells. Whether the antigen(s) acts directly or indirectly on the eosinophils or their precursors has yet to be established. Nevertheless, it seems clear that F. hepatica produces a molecule with a functionally similar effect to that of IL-5.

Eosinophil responses to Fasciola hepatica in rodents.

Qualitative and quantitative cellular changes in the peripheral blood and bone marrow of resistant (rat) and susceptible (mouse) hosts of Fasciola hepatica have been examined. Eosinophil numbers in the peripheral blood and bone marrow of both hosts increased almost immediately following infection. Rats responded more rapidly than mice. Bone marrow colony formation in both rats and mice was greatly enhanced following F. hepatica infection. Injection of excretory/secretory (E/S) antigens of the fluke into rats and mice caused peripheral eosinophilia. Eosinophil levels in mice dropped by day 7 post-injection, but those in rats remained high. Eosinophil precursors in the bone marrow of injected animals also rose. Bone marrow colony formation in antigen-injected mice peaked sharply at day 7 but then fell rapidly. Rats injected with E/S antigens had about twice the level of bone marrow colonies as controls, 12 days post-injection. For most parameters measured, the magnitude of the responses of rats was greater than mice, which may be significant in the context of the rat's ability to acquire resistance to reinfection.