Induction of fatty liver by fasting in suncus

In vivo imaging of calcium dynamics in zebrafish hepatocytes

BACKGROUND AND AIMS

Hepatocytes were the first cell type for which oscillations of cytoplasmic calcium levels in response to hormones were described. Since then, investigation of calcium dynamics in liver explants and culture has greatly increased our understanding of calcium signaling. A bottleneck, however, exists in observing calcium dynamics in a noninvasive manner because of the optical inaccessibility of the mammalian liver. Here, we aimed to take advantage of the transparency of the zebrafish larvae to image hepatocyte calcium dynamics in vivo at cellular resolution.

APPROACH AND RESULTS

We developed a transgenic model expressing a calcium sensor, GCaMP6s, specifically in zebrafish hepatocytes. Using this, we provide a quantitative assessment of intracellular calcium dynamics during multiple contexts, including growth, feeding, ethanol-induced stress, and cell ablation. Specifically, we show that synchronized calcium oscillations are present in vivo , which are lost upon starvation. Starvation induces lipid accumulation in the liver. Feeding recommences calcium waves in the liver, but in a spatially restricted manner, as well as resolves starvation-induced hepatic steatosis. By using a genetically encoded scavenger for calcium, we show that dampening of calcium signaling accelerates the accumulation of starvation-related lipid droplets in the liver. Furthermore, ethanol treatment, as well as cell ablation, induces calcium flux, but with different dynamics. The former causes asynchronous calcium oscillations, whereas the latter leads to a single calcium spike.

CONCLUSIONS

We demonstrate the presence of oscillations, waves, and spikes in vivo . Calcium waves are present in response to nutrition and negatively regulate starvation-induced accumulation of lipid droplets.

METTL3 Regulated the Meat Quality of Rex Rabbits by Controlling PCK2 Expression via a YTHDF2–N6-Methyladenosine Axis

N6-methyladenosine (m⁶A) is the most prevalent internal mRNA modification in eukaryotes. The M⁶A modification plays an important role in transcription and cell function. The mechanism by which m⁶A modification regulates meat quality remains elusive. In this study, gene knockout and overexpression were used to explore m⁶A-modified regulation of meat quality. The content of PCK2 in blood increased significantly with the increase of Rex rabbits’ age. PCK2 expression levels in the longissimus lumborum and liver also increased significantly with the increase of Rex rabbits’ age. However, the expression level of PCK2 showed no significant difference in adipose tissue. In cell experiments, we found that METTL3 inhibited adipocyte differentiation by targeting the PCK2 gene via the recognition function of YTHDF2. Finally, the results of correlation analysis showed that PCK2 expression was positively correlated with intramuscular fat, whereas PCK2 expression was negatively correlated with total water loss rate at three different stages. In addition, PCK2 expression was also negatively correlated with reduced pH value at 75 and 165 days. Intramuscular fat content, pH and muscle water holding capacity are the main factors affecting the taste and flavor of muscle. Therefore, N6-methyladenosine regulated muscle quality by targeting the PCK2 gene.

Spontaneous Polycystic Kidneys with Chronic Renal Failure in an Aged House Musk Shrew (Suncus murinus)

Polycystic kidney disease is one of the most common inheritable renal diseases, characterized by the formation of multiple fluid-filled renal cysts. This disease is a progressive and unfortunately incurable condition. A case of polycystic kidney with chronic renal failure in house musk shrew (Suncus murinus) is described. At clinical presentation, a 16-month-old Suncus murinus showed weight loss and coarse fur. Regarding the biochemical profile, total protein concentrations increased, resulting in a declined albumin: globulin ratio. Blood urea nitrogen and creatinine concentrations were markedly elevated, indicating the end stage of chronic renal failure. Serum amyloid A levels increased and revealed inflammatory reaction during the cyst formation. Histopathologically, multiple cysts were lined by a single layer of epithelial cells or low cuboidal epithelium. The contents were homogenous eosinophilic materials (mucopolysaccharides or mucoproteins) and these cysts contained abundant macrophages. There were also regeneration and dilatation of renal tubes and interstitial fibrosis. The atrophic glomeruli and glomerular capsules were thickened and hyalinized by dense amorphous mucopolysaccharides. These histopathological findings suggested that the pathogenesis of polycystic kidney disease shared a common mechanistic feature across species.

Reprogramming of glucocorticoid receptor function by hypoxia

Here, we investigate the impact of hypoxia on the hepatic response of glucocorticoid receptor (GR) to dexamethasone (DEX) in mice via RNA-sequencing. Hypoxia causes three types of reprogramming of GR: (i) much weaker induction of classical GR-responsive genes by DEX in hypoxia, (ii) a number of genes is induced by DEX specifically in hypoxia, and (iii) hypoxia induces a group of genes via activation of the hypothalamic-pituitary-adrenal (HPA) axis. Transcriptional profiles are reflected by changed GR DNA-binding as measured by ChIP sequencing. The HPA axis is induced by hypothalamic HIF1α and HIF2α activation and leads to GR-dependent lipolysis and ketogenesis. Acute inflammation, induced by lipopolysaccharide, is prevented by DEX in normoxia but not during hypoxia, and this is attributed to HPA axis activation by hypoxia. We unfold new physiological pathways that have consequences for patients suffering from GC resistance.

A Model Construction of Starvation Induces Hepatic Steatosis and Transcriptome Analysis in Zebrafish Larvae

Hepatic steatosis caused by starvation, resulting in non-alcoholic fatty liver disease (NAFLD), has been a research topic of human clinical and animal experiments. To understand the molecular mechanisms underlying the triggering of abnormal liver metabolism by starvation, thus inducing hepatic lipid accumulation, we used zebrafish larvae to establish a starvation-induced hepatic steatosis model and conducted comparative transcriptome analysis by RNA-seq. We demonstrated that the incidence of larvae steatosis is positively correlated with starvation time. Under starvation conditions, the fatty acid transporter (slc27a2a and slc27a6-like) and fatty acid translocase (cd36) were up-regulated significantly to promote extrahepatic fatty acid uptake. Meanwhile, starvation inhibits the hepatic fatty acid metabolism pathway but activates the de novo lipogenesis pathway to a certain extent. More importantly, we detected that the expression of numerous apolipoprotein genes was downregulated and the secretion of very low density lipoprotein (VLDL) was inhibited significantly. These data suggest that starvation induces hepatic steatosis by promoting extrahepatic fatty acid uptake and lipogenesis, and inhibits hepatic fatty acid metabolism and lipid transport. Furthermore, we found that starvation-induced hepatic steatosis in zebrafish larvae can be rescued by targeting the knockout cd36 gene. In summary, these findings will help us understand the pathogenesis of starvation-induced NAFLD and provide important theoretical evidence that cd36 could serve as a potential target for the treatment of NAFLD.

Genetic ablation of solute carrier family 7a3a leads to hepatic steatosis in zebrafish during fasting

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder caused by abnormal lipid metabolisms, such as reduced hepatic fatty acid oxidation (FAO), but intracellular control of FAO under physio- and pathological conditions remains largely undefined. Here, we demonstrate that deprivation of Slc7a3a leads to hepatic steatosis in fasted zebrafish as a result of defects in arginine-dependent nitric oxide (NO) synthesis. Fast-induced hepatic steatosis in slc7a3a-null mutants can be rescued by treatments with NO donor, cyclic guanosine monophosphate analog, adenosine-monophosphate-activated protein kinase (AMPK) activator, or peroxisome proliferator-activated receptor alpha (PPAR-α) agonist. In contrast, inhibitors of NO synthases, AMPK, or soluble guanylate cyclase and liver-specifically expressed dominant negatives of peroxisome proliferator-activated receptor-gamma coactivator 1 alpha and PPAR-α are sufficient to induce hepatic steatosis in fasted wild-type larvae. Moreover, knockdown of Slc7a3 in mice or SLC7A3 in human liver cells impaired AMPK-PPAR-α signaling and resulted in lipid accumulation under fasting or glucose starvation, respectively.

CONCLUSION

These findings have revealed a NO-AMPK-PPAR-α-signaling pathway that is crucial for the control of hepatic FAO in vertebrates.

Hepatic lipotoxicity and the pathogenesis of nonalcoholic steatohepatitis: the central role of nontriglyceride fatty acid metabolites

A significant body of evidence now forces us to rethink the causes of NASH. Once thought to be a disease caused by triglyceride accumulation in hepatocytes with subsequent oxidant stress and lipid peroxidation causing inflammation and fibrosis, new data from animal studies and a limited number of human studies now provide convincing evidence that triglyceride accumulation does not cause insulin resistance or cellular injury in the liver. The lipotoxic liver injury hypothesis for the pathogenesis of NASH suggests that we need to focus our therapeutic efforts on reducing the burden of fatty acids going to the liver or being synthesized in the liver. This can be accomplished by improving insulin sensitivity at the level of adipose tissue to prevent inappropriate peripheral lipolysis and by preventing unnecessary de novo lipogenesis in the liver. Excess carbohydrates are the major substrates for de novo lipogenesis, and thus, reducing carbohydrate consumption through dietary changes and increasing muscle glucose uptake through exercise remain important cornerstones of treatment and prevention of lipotoxic liver injury, a disease hitherto called NASH.

Diet and gastrointestinal signal on T1-weighted magnetic resonance imaging of mice

In magnetic resonance (MR) imaging of small animals, the gastrointestinal contents may give rise to intense signals on T1-weighted images. The aim of this study was to determine the optimal dietary preparation to reduce gastrointestinal signals in mice and to evaluate the usefulness of this approach. Images of the mouse trunk were obtained using a T1-weighted, three-dimensional fast low-angle shot sequence under various dietary conditions and were compared with respect to the gastrointestinal signals and image quality. The dietary preparation studied included giving alternative diets for 24 h, intestinal cleansing, and 6-h fasting. Mice with and without dietary preparation underwent MR lymphography using gadofluorine 8, and the visualization of abdominal lymph nodes was compared. In the absence of dietary preparation, hyperintense areas were conspicuous in the gastrointestinal system, whereas on the images taken from mice fed potato or sweet potato for 24 h before imaging, gastrointestinal hyperintensity was less prominent. This preparation also reduced artifactual signals and resulted in higher-quality images of the kidneys. Intestinal cleansing, which consisted of 24-h fasting and laxative intake, did not reduce the gastrointestinal signals and caused signal changes that were indicative of fatty liver development. Some of the abdominal lymph nodes of the mice that did not receive dietary preparation were visualized on MR lymphography source images but not on maximum intensity projection (MIP) images. In contrast, on the MIP images of mice fed potato, all the lymph nodes delineated on the source images were successfully visualized. In conclusion, feeding mice potato or sweet potato for 24 h before MR imaging reduces the gastrointestinal signals and image degradation due to artifacts. Appropriate dietary preparations facilitate the display of target structures on MIP images and are expected to enhance the capabilities of small animal MR imaging.

ICAM-1 and beta2 integrin deficiency impairs fat oxidation and insulin metabolism during fasting

Intercellular adhesion molecule 1 (ICAM-1) and beta2 integrins play critical roles in immune responses. ICAM-1 may also participate in regulation of energy balance because ICAM-1-deficient mice become obese on a high-fat diet. We show that mice deficient in these adhesion receptors are unable to respond to fasting by up-regulation of fatty acid oxidation. Normal mice, when fasted, exhibit reduced circulating neutrophil counts and increased ICAM-1 expression and neutrophil recruitment in liver. Mice lacking ICAM-1 or beta2 integrins fail to show these responses--instead they become hypoglycemic with steatotic livers. Fasting ICAM-1-deficient mice reduce insulin more slowly than wild-type mice. This produces fasting hyperinsulinemia that prevents activation of adenosine mono-phosphate (AMP)-activated protein kinase in muscles and liver, which results in decreased import of long chain fatty acids into mitochondria. Thus, we show a new role for immune cells and their adhesion receptors in regulating metabolic response to fasting.

The evolutionarily conserved gonadotropin-releasing hormone II modifies food intake

GnRH is an evolutionarily conserved peptide of which there are multiple structural variants. One form, GnRH II, is the most widespread in vertebrates, but its primary function remains unclear. In female musk shrews, administration of GnRH II, but not GnRH I, reinstates mating behavior previously inhibited by food restriction. Because this finding suggests that the function of GnRH II may be linked to energetic status, we tested whether GnRH II directly affects food intake. Adult female musk shrews were maintained on ad libitum feeding or food restricted for 48 h, after which they were infused centrally with GnRH I (1 microg), GnRH II (1 microg), or saline. Food intake was recorded 90 min, and 3, 6, 24, and 48 h after infusion. GnRH II administration, but not saline or GnRH I, reduced 24-h food intake in ad libitum animals. Short-term food intake (90 min and 3 h) of both ad libitum and underfed shrews receiving GnRH II was also reduced by as much as 33%, relative to the food intake of saline-infused controls. GnRH I infusion did not affect short-term food intake differently than saline infusion in shrews fed ad libitum. In underfed females, GnRH I had an effect on short-term food intake that was intermediate to saline and GnRH II. We conclude that, in addition to its permissive role in regulating reproduction, GnRH II may also modulate food intake in mammals. Because GnRH II is present in primate brain, it may also serve a similar function in humans.

Differential channelling of liver lipids in relation to susceptibility to hepatic steatosis in two species of ducks

In the human, hepatic steatosis can be associated with an imbalance between synthesis, secretion and storage of hepatic lipids, and exhibits a genetic susceptibility. The effect of overfeeding on hepatic lipid channelling was investigated in two genotypes of ducks that differ in their susceptibility to fatty liver, i.e. the common duck, Anas platyrhynchos, and the Muscovy duck, Cairina moschata. Before overfeeeding, the Muscovy duck exhibited a lower subcutaneous adiposity and a higher muscular development, whereas hepatic composition was similar in both genotypes (>5% lipids and triglycerides accounting for 6-10% lipids). In the plasma lipoprotein profile, HDL predominated (5.5-7.8 g/l) over VLDL (0.09-0.25 g/l) and LDL (0.65-1.06 g/l). All lipid and lipoprotein concentrations were lower in the Muscovy duck. In response to overfeeding, the Muscovy duck exhibited a higher degree of hepatic steatosis (62 vs. 50% lipids), and a lower increase in adiposity and in the concentration of plasma triglycerides (6-fold vs. 10-fold) and VLDL (23-fold vs. 34-fold). Thus, certain genotypes may be more responsive to the dietary induction of fatty liver because of a less efficient channelling of hepatic lipids towards secretion into plasma and adipose storage, and the duck may represent a suitable model in which to study the development of hepatic steatosis and its pathogenesis.

Inflammatory liver steatosis caused by IL-12 and IL-18

Acute fatty degeneration in the liver is caused by various agents, such as aspirin, valproic acid, and ibuprofen, that directly inhibit mitochondrial beta-oxidation of fatty acid and oxidative phosphorylation. Endogenous molecules, such as cytokines and hormones, are also known to mediate microvesicular steatosis in liver failure. In this study, we examined how interleukin-12 (IL-12) and IL-18 cause steatosis in the liver. Administration of these cytokines in combination caused marked hepatosteatosis and weight loss in mice. There were marked increases in levels of interferon-gamma (IFN-gamma), nitrite (NO(2)/NO(3)), and fibrinogen in the circulation in these mice. On the other hand, the ATP concentration and blood flow in the liver were significantly reduced. These changes, except the production of IFN-gamma and NO, were partially inhibited by Z-VAD-fmk, a synthetic tripeptide inhibitor for NO-induced caspases. These results indicate that IL-12 and IL-18 may mediate inflammatory hepatosteatosis through impairment of the microcirculation, which leads to mitochondrial dysfunction in hepatocytes.

Fatty liver and hyperlipidemia in IDDM (insulin-dependent diabetes mellitus) of streptozotocin-treated shrews

Severe IDDM (insulin-dependent diabetes mellitus) was produced in the musk shrew (Suncus murimus, Insectivora) by a high dose (a single intraperitoneal injection of 100 mg/kg Body Weight) of streptozotocin (STZ) injection. All shrews that were administered a high dose of STZ exhibited hyperglycemia (449 +/- 16 mg/dl vs 73 +/- 4 mg/dl in controls) and hypoinsulinemia(0.25 +/- 0.07 ng/ml vs 10.96 +/- 1.97 ng/ml in controls) with ketosuria 10 days after injection. Their livers were enlarged and exhibited ayellowish-brown color with marked triglyceride (TG) accumulation (63.25 +/- 7.10 mg/g Liver vs 2.11 +/- 0.19 mg/g Liver in controls). It is probable that the increased influx of fatty acids into the liver induced by hypoinsulinemia and the low capacity of excretion of lipoprotein secretion from liver in the musk shrew resulting from a deficiency of apolipoprotein B synthesis play important roles in fatty liver formation. Hyperlipidemia was another feature in shrews with severe IDDM. The blood TG level was especially high in these shrews (899 +/- 178 mg/dl vs 23 +/- 5 mg/dl in controls). These results indicate that the IDDM shrew, induced by high doses of STZ, is a unique model characterized by fatty liver and hyperlipidemia and may be useful for studying lipid metabolism of IDDM.

Mobilisation of triacylglycerol stores

Triacylglycerol (TAG) is an energy dense substance which is stored by several body tissues, principally adipose tissue and the liver. Utilisation of stored TAG as an energy source requires its mobilisation from these depots and transfer into the blood plasma. The means by which TAG is mobilised differs in adipose tissue and liver although the regulation of lipid metabolism in each of these organs is interdependent and synchronised in an integrated manner. This review deals principally with the mechanism of hepatic TAG mobilisation since this is a rapidly expanding area of research and may have important implications for the regulation of plasma very-low-density lipoprotein metabolism. TAG mobilisation plays an important role in fuel selection in non-hepatic tissues such as cardiac muscle and pancreatic islets and these aspects are also reviewed briefly. Finally, studies of certain rare inherited disorders of neutral lipid storage and mobilisation may provide useful information about the normal enzymology of TAG mobilisation in healthy tissues.

Peroxisome proliferator-activated receptor alpha mediates the adaptive response to fasting

Prolonged deprivation of food induces dramatic changes in mammalian metabolism, including the release of large amounts of fatty acids from the adipose tissue, followed by their oxidation in the liver. The nuclear receptor known as peroxisome proliferator-activated receptor alpha (PPARalpha) was found to play a role in regulating mitochondrial and peroxisomal fatty acid oxidation, suggesting that PPARalpha may be involved in the transcriptional response to fasting. To investigate this possibility, PPARalpha-null mice were subjected to a high fat diet or to fasting, and their responses were compared with those of wild-type mice. PPARalpha-null mice chronically fed a high fat diet showed a massive accumulation of lipid in their livers. A similar phenotype was noted in PPARalpha-null mice fasted for 24 hours, who also displayed severe hypoglycemia, hypoketonemia, hypothermia, and elevated plasma free fatty acid levels, indicating a dramatic inhibition of fatty acid uptake and oxidation. It is shown that to accommodate the increased requirement for hepatic fatty acid oxidation, PPARalpha mRNA is induced during fasting in wild-type mice. The data indicate that PPARalpha plays a pivotal role in the management of energy stores during fasting. By modulating gene expression, PPARalpha stimulates hepatic fatty acid oxidation to supply substrates that can be metabolized by other tissues.

Periodontitis in the house musk shrew (Suncus murinus): a potential animal model for human periodontal disease

BACKGROUND

Our understanding of periodontal diseases has been facilitated greatly by the use of animal models. However, no animal model has been identified that truly reflects the disease seen in humans. Suncus murinus, a rat-sized laboratory house musk shrew, has received attention as a valuable animal model due to ease of handling. In the studies described here, periodontal conditions in Suncus murinus were evaluated to determine the usefulness of the shrew as an experimental model for understanding various aspects of periodontal diseases.

METHODS

Periodontal tissues of 34 Suncus murinus (18 to 430 days old) were examined macroscopically, morphometrically, histologically, and ultrastructurally.

RESULTS

Dentition pattern is I3/1, C1/1, P2/1, M3/3. Spontaneous gingival swelling with accumulation of plaque was observed in more than two-thirds of animals older than 200 days. Morphometric analysis of alveolar bone demonstrated a pattern of bone loss that correlated closely with animal age. Histologically, periodontal lesions varying from gingivitis to periodontitis, similar to those observed in humans, were noted. Marked infiltration of lymphocytes and plasma cells in the connective tissue was noted, usually not seen in periodontal lesions of rodents. Although osteoclastic alveolar bone resorption was noted, active bone resorption was not a frequent feature in specimens obtained from chronic inflammatory lesions. Ultrastructurally, degradation of collagen fibers in the inflamed area and ingestion of collagen fibrils by fibroblasts in the deeper connective tissue were often seen.

CONCLUSIONS

These results indicate the potential utility of Suncus murinus as a model to study periodontal disease; e.g., chronic nature of the inflammatory periodontal lesions, similar to those in humans, as well as other advantages including size and ease of handling and housing of these animals.

Neuromuscular transmission and innervation in the urinary bladder of the insectivore Suncus murinus

In isolated preparations of the urinary bladder detrusor of the house musk shrew Suncus murinus (order: insectivora; family: Soricidae), electrical field stimulation (0.5-32 pulses/s) evoked neurogenic contractile responses that were markedly attenuated by atropine (1 microM). The non-cholinergic component was reduced but not abolished by the P2-purinoceptor antagonist, suramin (300 microM). Thus, neuromuscular transmission in the suncus urinary bladder is effected by cholinergic and purinergic nerves together with an as-yet unidentified component. Using immunohistochemical methods, the suncus urinary bladder was seen to be supplied by nerves containing neuropeptide Y, tyrosine hydroxylase, vasoactive intestinal polypeptide, galanin, substance P, calcitonin gene-related peptide and type I nitric oxide synthase. The pattern of responses to electrical field stimulation was more similar to that of humans and Old World primates, than to that of rodents or lagomorphs. The pattern of innervation of the bladder wall, in terms of the distribution of populations containing a given neuropeptide, was very similar to that in humans. Hence, Suncus murinus may provide a novel species for modelling the neuropharmacology of the human bladder, and also for studying the evolution of autonomic innervation.

Effect of chylomicron remnants on apolipoprotein E synthesis in HepG2 cells

The effect of chylomicron remnants (CM-R) on apolipoprotein (apo) E synthesis by HepG2 cells was studied. The accumulation rate of apo E in the medium was increased in cells incubated with CM-R (chylo-cells) compared with that in the control cells. However, the abundance of apo E mRNA was not greater in chylo-cells than in control cells. The time course of apo E accumulation in the medium showed that apo E increased in the chylo-cells linearly up to 24 hours, whereas it increased in the control cells linearly only up to 6 hours, when it reached a plateau. The results suggest that the secretion rate of apo E was not affected by incubation with CM-R, but that uptake of the newly secreted apo E by the cells may be depressed by incubation with CM-R. Autoradiography of newly synthesized apo E showed that chylo-cells produced much more "larger" apo E than did the control cells. Two-dimensional electrophoresis of the apo E newly synthesized by the chylo-cells showed that the larger apo E was slightly acidic even after treatment with neuraminidase. Pulse-chase labeling of apo E showed that the larger apo E was secreted by both control and chylo-cells equally and that the larger apo E was converted to regular apo E in the medium more effectively in control cells than in chylo-cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine induces contractions in suncus ileum

Purinoceptor-mediated responses were characterized in the ileum of Suncus murinus. Adenosine as well as adenosine 5'-triphosphate (ATP) contracted the ileum in a concentration-dependent manner. Contractile responses to transmural electrical stimulation were attenuated by adenosine only at high concentrations. Theophylline competitively blocked the adenosine-induced contraction. Atropine also inhibited the adenosine-induced contraction but in a non-competitive manner. The ATP-induced contraction was not affected by theophylline, atropine or alpha, beta-methylene ATP. Indomethacin shifted the concentration-response curves for adenosine and ATP to the right. These results suggest that adenosine elicited contractions via direct stimulation of postsynaptic P1-purinoceptors and postsynaptic potentiation of the acetylcholine response. Suncus ileum will be a unique model for the analyses of purinoceptor-mediated responses.

Effect of FK409, a novel nitric oxide donor, on acute experimental myocardial ischemia

The anti-ischemic heart effect of (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]- 5-nitro-3-hexenamide (FK409), a novel nitric oxide donor, was studied in dog and rat preparations in vivo and in vitro. In anesthetized dogs with partially occluded coronary artery that were subjected to atrial pacing at a constant blood pressure, FK409 (1-100 micrograms/kg, i.v.) suppressed the ST-segment elevation on epicardial electrocardiograms. Glyceryl trinitrate (GTN; 10, 32 micrograms/kg) or dipyridamole (1000 micrograms/kg) failed to suppress the ST-segment elevation, although continuous i.v. infusion of GTN (32, 100 micrograms/kg/min) was effective. FK409 also suppressed the ST-segment elevation induced by methacholine in anesthetized rats by both i.v. (10, 100 micrograms/kg) and intraduodenal (i.d., 100, 1000 micrograms/kg) injections, while GTN (100 micrograms/kg, i.v.; 1000 micrograms/kg, i.d.) was effective only by the i.v. route. FK409 (0.32 microgram/kg/min, i.v.) and GTN (10 micrograms/kg/min) increased the blood flows of the endomyocardium (ENDO) and the epicardium (EPI) and the flow ratio of ENDO/EPI in the ischemic zone in anesthetized dogs with occluded coronary artery. Furthermore, in isolated dog vascular preparations, FK409 (4.6 x 10(-10)-4.6 x 10(-7) M) had a greater vasorelaxing effect on the large coronary artery [2.0-2.5-mm outer diameter (od)] than on the small coronary artery (0.3-0.5-mm od) or the saphenous artery. The results suggest that FK409 protects against acute experimental myocardial ischemia through relaxation of the large conductive coronary artery, and may be a useful oral drug for the treatment of angina pectoris.