Platelet desensitization by arachidonic acid is associated with the suppression of endoperoxide/thromboxane A2 binding to the membrane receptor

The inhibitory mechanism of high levels of exogenously added arachidonic acid on activation of washed human platelets was investigated. While low levels of arachidonic acid (5-10 microM) induced aggregation, ATP secretion and increase in cytoplasmic free Ca2+ concentration (first phase of activation), these platelet responses did not occur significantly at high concentrations (30-50 microM). However, much higher concentrations than 80 microM again elicited these responses (second phase). The first phase of platelet activation was inhibited by cyclooxygenase inhibitor, indomethacin, whereas the second one was independent of such treatment. Thromboxane B2 was produced dose-dependently until reaching a plateau at arachidonic acid concentrations higher than 20 microM, irrespective of the lack of aggregation and secretion at high concentrations. After that the amount of free arachidonic acid which remained unmetabolized in platelets gradually increased. High concentrations of arachidonic acid as well as other polyunsaturated fatty acids caused desensitization of platelets in response to U46619, and also depressed the specific [3H]U46619-binding to the receptor as well as other polyunsaturated fatty acids. The amount free arachidonic acid needed in platelets to suppress [3H]U46619 binding corresponded to that needed to inhibit platelet aggregation. Furthermore, arachidonic acid dose-dependently induced fluidization of lipid phase of platelet membranes as detected by 1,6-diphenyl-1,3,5-hexatriene. These results suggest that the inhibition of platelet response by high levels of arachidonic acid can be attributed to interference with endoperoxide/thromboxane A2 binding to the receptor, probably due to perturbation of the membrane lipid phase due to excess amounts of free arachidonic acid remaining in the membranes.     

Occurrence of a novel cardiac natriuretic peptide in rats

We established a specific radioimmunoassay for the ring structure of "iso-ANP" and detected iso-ANP[23-46]-like immunoreactivity (-LI) in the rat atrium (2.76 +/- 0.5 micrograms/g) and ventricle (13.9 +/- 5.7 ng/g). High performance-gel permeation chromatography revealed that iso-ANP[23-46]-LI in the rat heart was composed of two components with molecular weights of 10K and 5K. In reverse phase-high performance liquid chromatography, the retention times of these components were clearly different from that of synthetic iso-ANP. The 5K peptide was demonstrated to be present in the perfusate from isolated rat hearts and possessed binding ability to ANP receptors. This natriuretic peptide was, however, not detectable in other tissues including the brain. We conclude that the novel cardiac natriuretic peptide distinct from iso-ANP and ANP occurs in the rat heart and is secreted from the heart.     

Expression of active alpha-3 subunit of rat brain Na+,K+-ATPase from the messenger RNA injected into Xenopus oocytes

Cloned cDNA encoding the so-far uncharacterized alpha-3 subunit of rat brain Na+,K+-ATPase (Hara et al. (1987) J. Biochem. 102, 43-58, Shull et al. (1986) Biochemistry 25, 8125-8132) was incorporated into a vector carrying the SP6 promoter. The mRNA produced in vitro was injected into Xenopus oocytes with the mRNA encoding the Na+,K+-ATPase beta subunit of Torpedo electroplax. Increased Na+,K+-ATPase activity in the oocyte membrane was observed. This newly expressed activity was inhibited by ouabain (Ki = 1.5 x 10(-7) M), suggesting that the alpha-3 subunit of rat brain Na+,K+-ATPase is a highly ouabain-sensitive catalytic subunit.     

Isolation and sequence determination of rat cardiac natriuretic peptide

We have isolated a cardiac natriuretic peptide of 5K daltons from the rat atrium and determined its amino acid sequence. The 5K cardiac natriuretic peptide was elucidated to be a 45-amino acid peptide with the sequence of S-Q-D-S-A-F-R-I-Q-E-R-L-R-N-S-K-M-A-H-S-S-S-C-F-G-Q-K-I-D-R-I-G-A-V-S-R- L-G-C-D - G-L-R-L-F by sequencing the native peptide and its lysyl endopeptidase digests. The sequence of this peptide was identical to the amino acid sequence [51-95] of the rat brain natriuretic peptide (BNP) precursor deduced from the cDNA sequence. The 5K cardiac natriuretic peptide, or BNP[51-95], was identified as the major storage and secretory form derived from the BNP precursor in the rat heart.     

Endothelin in human plasma and culture medium of aortic endothelial cells--detection and characterization with radioimmunoassay using monoclonal antibody

We have developed monoclonal (KY-ET-1-I) and polyclonal (ET-F5) antibodies against endothelin-1 (ET-1) and established sensitive radioimmunoassays (RIAs) with different specificities. The RIA with KY-ET-1-I detected ET-1, ET-2 and ET-3, while the RIA with ET-F5 recognized ET-3 very weakly. Using these RIAs, we have investigated the concentration and molecular forms of ET-1-like immunoreactivity (-LI) in culture medium of bovine aortic endothelial cells and human plasma. Culture medium of endothelial cells contained two major components compatible with big ET and ET-1. ET-1-LI was also detected in human plasma. ET-1-LI in human plasma consisted of apparent two components, the small molecular form emerging at the position of ET-1 and the large form with the peak eluting at the preceding fraction of the elution position of big ET. The concentration of the small form of ET in human plasma was about 5 pg/ml.     

Detection and characterization of endothelin-1-like immunoreactivity in rat plasma

Using two radioimmunoassays (RIAs) for endothelin-1 (ET-1) with and without a substantial cross-reactivity with ET-3, we have measured the plasma ET-1-like immunoreactivity (-LI) level in rat plasma. ET-1-LI was detected in plasma from male Wistar rats. ET-1-LI in rat plasma consisted of three components with molecular weights of 6K, 4K and 2.5K daltons by gel permeation chromatography. Two of the components were eluted at positions of big ET (4K) and synthetic ET-1 (2.5K). The remaining component was eluted at the preceding fraction (6K). No difference was observed in ET-1-LI of the small molecular form of ET (2.5K) between the two RIAs. Thus, there is little or no ET-3 in rat plasma, which has the sequence found originally in the rat genome. The concentration of the small molecular form of ET, presumably ET-1, in rat plasma was about 4 pg/ml.     

Counting statistics of 1/f fluctuations in neuronal spike trains

The mesencephalic reticular formation (MRF) neurons are regarded as contributing to the activation of the celebral cortex. In this paper, the statistical features of single neuronal activities in MRF of cat during dream sleep are investigated; the neuronal spike train exhibits 1/f fluctuations. Counting statistics is applied to the neuronal spike train giving rise to a variance/mean curve which follows at -law. For an interpretation of these findings, the clustering Poisson process is applied which not only gives rise to at -law but also suggests a generation mechanism. The MRF neuronal activities are closely fitted by the clustering Poisson process and the underlying statistical parameters can be estimated. These findings strongly suggest that neuronal activities can be interpreted as superposition of randomly occuring clusters ( = bursts of spikes).     

Immunohistochemical localization of atrial natriuretic polypeptide (ANP) in human atrial and ventricular myocardiocytes

To date, there have been few immunohistochemical investigations of atrial natriuretic polypeptide (ANP) in human cardiac tissue, especially the ventricles. In this study, myocardial tissue was obtained from two sources: the bilateral atria and ventricles at autopsy; and biopsy tissues from the right auricle and left ventricle of a patient with myocardial infarction undergoing surgery. These tissues were examined by the avidin-biotin immunoperoxidase technique using three kinds of primary ANP-antibodies. ANP-immunoreactivity was observed in the perinuclear region of myocytes of all tissues examined. The intensity of the reaction was stronger in atrial tissue, weaker in ventricular tissue. In the later tissue, the positive-staining myocytes were not part of the pulse-conducting system. Although the tissues we studied were not obtained from normal hearts, our data demonstrates that ANP-reactivity can be detected in ventricular myocytes outside the pulse-conducting system.     

Disposition of 125I-labeled recombinant human tumor necrosis factor in the tumor-bearing mouse

Disposition of [125I]rHu-TNF was elucidated in BALB/c mice bearing Meth A fibrosarcoma 7 days after transplantation. After i.v. administration, [125I]rHu-TNF measured by radioactivity and immunoreactivity biphasically decreased in plasma. Tumor level of [125I]rHu-TNF was the maximum at 1 h, then decreased and finally remained essentially constant. After i.t. administration, plasma level reached the maximum at 1 h. Tumor level decreased quickly and then became essentially constant. [125I]rHu-TNF was suggested to be degraded to small fragments in the tumor. Significant distribution of [125I]rHu-TNF was found in the kidney, lung, liver and tumor. Most tissue levels decreased with time in parallel with plasma levels. [125I]rHu-TNF radioactivity was found in proximal convoluted tubules of kidney and in those areas of tumor consisting of degenerating cells with pyknotic nuclei. Urine contained most of administered radioactivity, which being neither immunoreactive nor protein-bound.     

Immunohistochemical localization of atrial natriuretic polypeptide (ANP) in human atrial and ventricular myocardiocytes

Summary To date, there have been few immunohistochemical investigations of atrial natriuretic polypeptide (ANP) in human cardiac tissue, especially the ventricles. In this study, myocardial tissue was obtained from two sources: the bilateral atria and ventricles at autopsy; and biopsy tissues from the right auricle and left ventricle of a patient with myocardial infarction undergoing surgery. These tissues were examined by the avidin-biotin immunoperoxidase technique using three kinds of primary ANP-antibodies. ANP-immunoreactivity was observed in the perinuclear region of myocytes of all tissues examined. The intensity of the reaction was stronger in atrial tissue, weaker in ventricular tissue. In the later tissue, the positive-staining myocytes were not part of the pulse-conducting system. Although the tissues we studied were not obtained from normal hearts, our data demonstrates that ANP-reactivity can be detected in ventricular myocytes outside the pulse-conducting system.