SummaryEndothelioma cell lines transformed by polyoma vtrus middle T antigen (mTa) cause cavernous hemangiomas in syngenelc mice by recruitment of host cells. The production of nitric oxide (NO), as measured by nitrite and citruUine production, was s~gnificantly higher in mTa-transformed endothelial cells in comparison with nontransformed control cells. The maximal activity of NO synthase (NOS) was about 200-fold higher in cell lysates from the tEnd.1 endothelioma cell line than in lysates from nontransformed controls, whereas the affinity for arginine did not differ. The biochemical characterization of NOS and the study of mRNA transcripts indicate that tEnd.1 cells express both the inducible and the constitutive isoforms. NOS hyperactivity is not a simple consequence of celt transformation but needs a tissue-specific mTa expression. Since tEnd.Iconditioned medium induces NOS activity in normal endothelial cells, most likely NOS hyperactivity in endothelioma cells is atmbutabte to the release of a soluble factor. This NOSactivating factor, which seems to be an anionic protein, could stimulate tend.1 cells to express NOS by an autocrine way. By the same mechanism, tend.1 cells could induce NOS m the neighboring endothelial cells, and NO release could play a role in the hemangloma development. Such hypothesis is confirmed by our in vivo experiments, showing that the administration of the NOS inhibitor t-canavanme to endothehoma-bearmg mice significantly reduced both the volume and the relapse time of the tumor.N 'itnc oxide (NO) * is a short-hved free radical gas produced by various cell types, including vascular endothelial cells (1-3). In endothelium, NO is synthesized m response to a large number of stimuli and displays an enlarging spectrum of activities, such as smooth muscle relaxation, inhibition of platelet aggregation and adhesion, and decrease of smooth muscle cells prohferatlon (4,5). NO generation is catalyzed by a class of NADPH-dependent NO synthases t Abbrevtattons used m th~s paper eNOS, endothehal NOS, HUVEC, human umbthcal veto endothehal cells, 1NOS, mductble NOS, L-ArgMEE, L-argmme monoethylester, L-NAME, NC-mtro-t-argmme methylester, L-NMMA, NC-monomethyl-t-argmme hydrochlonde, MAEC, munne aorta endothehal cell, rata, middle T anttgen; NAF, NOS-actlvatmg factor, NO, mtnc oxide, NOS, mtrlc oxide synthase, Vmax, maximal rate (NOS), which favor the conversion of t-arginine m t-dtruUme and NO with a 1:1 stoichlometry, and are competitively inhibited by N~ t-arginine analogues (6, 7). At least three different lsoenzymes have been characterized (8,9). Both a constitutive, Ca2+-dependent NOS (cNOS or eNOS) and an inducible, CF +-independent enzyme (iNOS) have been detected in endothelial cells (10-13). Because of its short half-life, direct measurement of NO concentration is dif~cult, and several indirect techmques of detection have been developed. A simple and sensitive procedure monitors the conversion of [3H]arginine to [3H]citrulline, which is stoichiometric with NO (14,15) Established cell line...

No abstract

SummarySeveral studies in vitro and in vivo suggest that the nitric oxide (NO) production is impaired in diabetes mellitus. Reduced levels of NO could contribute to vascular alteration facilitating platelet-vascular wall interaction, adhesion of monocytes to endothelium, vascular smooth muscle proliferation and by decreasing endothelium-dependent vasodilation. In this study we evaluated the activity of the constitutive nitric oxide synthase (cNOS) in platelets of patients with insulin-dependent diabetes mellitus (IDDM) and with non-insulin-dependent diabetes mellitus (NIDDM). When compared to that of normal subjects, cNOS activity is significantly lower in patients with IDDM and with NIDDM (1.57 ± 0.25 vs. 0.66 ± 0.10 fmol/min/10 9 PLTs and 1.57 ± 0.25 vs. 0.67 ± 0.08, respectively; p <0.005). These data demonstrate that the platelet cNOS activity is decreased in diabetes mellitus.

Sequential opposed transdermal oestrogen replacement therapy was able to increase platelet cNOS activity in postmenopausal women with type 2 diabetes mellitus, suggesting that its use might be positive in preventing cardiovascular pathologies.