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Results for “Microvessels”

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PubMed1989

Stimulation of glucose analogue uptake by cerebral microvessel endothelial cells by a product released by astrocytes.

Astroglial cells, both normal and neoplastic, secreted a product that stimulated glucose uptake by cerebral microvessel endothelial cells by 23% and 50%, respectively. Neither cerebral microvessel smooth muscle cells nor oligodendrocytes affected endothelial cell glucose uptake. The astrocytic product(s) did not affect glucose uptake by aortic endothelial cells. The effect on the cerebral microvessel endothelial cells increased with increasing time of exposure of the cells to the astroglial product(s), and required the constant presence of the astrocytic product to be maintained. The presence of a protein synthesis inhibitor during endothelial cell exposure to the astroglial conditioned medium blocked the stimulation of glucose uptake. Treatment of the astrocytic product with a protease destroyed its effectiveness. These results support the hypothesis that astrocytes induce the expression of at least one blood-brain barrier property by the cerebral microvasculature, and suggest that this induction may be produced by a protein released by the astrocytes.

3-O-Methylglucose↗

PubMed1998

Neutral endopeptidase and angiotensin-converting enzyme inhibitors increase nitric oxide production in isolated canine coronary microvessels by a kinin-dependent mechanism.

Bradykinin is a substrate for both neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE). Our previous studies showed that ACE inhibitors can stimulate nitric oxide production in coronary microvessels, which is mediated by local kinins. Whether inhibition of NEP also can affect local vascular NO production has not been established. To determine the role of NEP in the control of NO production, coronary microvessels were isolated from seven mongrel dogs. Two NEP inhibitors, phosphoramidon and thiorphan, and an ACE inhibitor, ramiprilat, were used. Nitrite, the metabolite of NO in aqueous solution, was measured by using the Griess reaction. Phosphoramidon and thiorphan (10(-6) M) increased nitrite production from 80 +/- 6 to 136 +/- 6 and 144 +/- 7 pmol/mg, respectively. Ramiprilat (10(-8) M) increased nitrite production from 78 +/- 6 to 155 +/- 7 pmol/mg wet weight. The effect of these agents on nitrite release was blocked by L-NAME, which inhibits NO synthase, HOE-140, which blocks bradykinin B2-receptor, and dichloroisocoumarin, which blocks kinin-forming enzymes. These results clearly indicate that inhibition of kinin metabolism by using neutral endopeptidase inhibitors increases NO production from coronary microvessels. Thus neutral endopeptidase plays an important role in local kinin-modulated NO production in the coronary microcirculation and NEP inhibitors may be useful clinical tools in treatment of cardiovascular disease.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2003

Lymphatic microvessels in the rat remnant kidney model of renal fibrosis: aminopeptidase p and podoplanin are discriminatory markers for endothelial cells of blood and lymphatic vessels.

ABSTRACT. Rat remnant kidney is an established model of renal tubulointerstitial fibrosis and progression to end-stage renal failure. The morphologic lesions comprise nephron loss and regeneratory tubular hypertrophy, interstitial infiltration, predominately by macrophages, and progressive fibrosis. A critical role in this complex pathology was assigned to tubulointerstitial blood microvessels that regulate the supply of oxygen and nutrients of tubuli. Whereas some investigations reported a rarefaction of the vascular network in association with the degenerative cortical changes, others observed an increase in vascularization. Here these discrepant findings are addressed by reinvestigation of the vascularization of rat remnant kidneys by the use of two novel endothelial lineage specific, discriminatory markers, i.e., the membrane mucoprotein podoplanin with specificity for lymphatic endothelia, and the glycosyl-phosphatidylinositol (GPI)-anchored membrane enzyme aminopeptidase P that is recognized by a monoclonal antibody designated JG12 and that is specifically expressed by endothelial cells of blood vessels only. The results obtained confirm a regional rarefaction of aminopeptidase P-positive blood microvessels; they also establish major changes in the renal lymphatic vasculature. Massive proliferation of lymphatic vessels was observed in fibrotic tubulointerstitial regions, whereas in kidneys of sham-operated rats, only a few lymphatic vessels were found adjoined with arteries. The lymphatic vessels frequently contained mononuclear cells that were also encountered in the interstitial spaces and expressed relative large amounts of vascular endothelial growth factor-C mRNA by in situ hybridization. Collectively, these results indicate that a large proportion of the microvessels encountered in the cortex of remnant kidneys are of lymphatic origin and cannot be discriminated by common endothelial markers, such as CD34, that are expressed by both lymphatic and blood endothelia cells. As lymphatic endothelial cells secrete chemokines that attract dendritic cells, it is possible that the increase in lymphatic vascularization could enhance the immunologic surveillance of remnant kidneys.

Aminopeptidases↗

PubMed2006

Proliferating endothelial cells, but not microvessel density, are a prognostic parameter in human cutaneous melanoma.

The induction of angiogenesis is crucial in the development of most human tumors. Angiogenesis is routinely assessed by the density of tumor microvessels. This technique reveals controversial results on the clinical and prognostic value of angiogenesis in melanoma. We investigated angiogenesis in tumor tissues of 58 cutaneous melanoma patients, of which a clinical follow-up of over 10 years was available, through assessment of microvessel density and by enumeration of the number of proliferating endothelial cells. To that end, vessels were immunohistochemically detected by CD31/CD34 staining, and proliferating endothelial cells were enumerated in a double staining with the proliferation marker Ki67. We found that microvessel density did not correlate with tumor stage or survival, neither in intratumoral nor in peritumoral areas. In contrast, proliferating endothelial cells were only observed in intratumoral areas and were correlated positively with tumor stage and the presence of distant metastases. In addition, a strong positive correlation was found with the number of proliferating tumor cells. Finally, high numbers of growing endothelial cells predicted short survival. Our results show that angiogenesis could best be measured by enumeration of proliferating endothelial cells and that this parameter has prognostic value in patients with cutaneous melanoma.

Adult↗

PubMed2004

Immunohistochemical study of microvessel density, CD44 (standard form), p53 protein and c-erbB2 in gallbladder carcinoma.

BACKGROUND: The purpose of the present study was to investigate microvessel density (MVD), and the expression of CD44 adhesion molecule, p53 protein and c-erbB2 in gallbladder carcinoma, and their relation to histological grade and tumor invasiveness. METHODS: Immunohistochemical staining with antibodies against factor VIIIRAg, CD44 standard form (CD44s), p53 protein and c-erbB2 was performed on paraffin sections from 33 cases of gallbladder carcinoma. RESULTS: Significant increase of MVD with increasing depth of invasion (P < 0.02) was observed. No association of MVD with histological differentiation, CD44s, p53 and c-erbB2 protein expression was found. The expression of p53 protein was significantly higher in deeply invasive tumors (P = 0.028) and in moderately and poorly differentiated carcinomas (P < 0.05). The CD44s expression was higher in well-differentiated carcinomas (P < 0.05). c-erbB2 expression was found in 30.4% of tumors studied, but did not relate to any other parameters. CONCLUSION: Microvessel density and p53 protein expression increase progressively with increasing tumor invasiveness in gallbladder carcinomas. Microvessel density, p53 protein, CD44s, and perhaps c-erbB2 expression may be implicated in gallbladder carcinoma evolution.

Aged↗

PubMed1981

Identification of beta-adrenergic receptor binding sites in rat brain microvessels, using [125I]iodohydroxybenzylpindolol.

Brain microvessels were prepared from rat cerebral cortex. The purity was confirmed by phase-contrast microscopy and by the measurement of an enzymatic marker, gamma-glutamyltranspeptidase. The microvessel preparation was subjected to radioreceptor assay using a 125I-labelled beta-adrenergic antagonist, hydroxybenzylpindolol (IHYP). The binding was linear with protein concentration up to at least 80% microgram per tube. It was saturated at 200 pM IHYP concentration. The KD value calculated by Scatchard analysis was 69.4 +/- 9.9 pM. The maximum binding (Bmax) was 107 +/- 4 fmol/mg protein. The binding reached equilibrium within 30 min and was dissociated by addition of (-)-propranolol. The inhibitory effects of isomers of propranolol and isoproterenol on this binding showed that (-)-isomers were two orders of magnitude more potent than the (+)-isomers. Other neurotransmitters did not affect IHYP binding. The characteristics of the binding, saturability, high affinity, reversibility and stereospecificity, suggest tha IHYP is bound to beta-adrenergic receptor sites located on brain microvessels.

Animals↗

PubMed1982

Microvessels from the spinal cord: isolation procedure and characterization of the fraction.

A simple method for the preparation of microvessels from the spinal cord is described. The fraction being enriched in the microvessels is characterized by morphological techniques and compared biochemically with the original suspension. The method makes possible detailed studies on the metabolism of microvessels and can be complementary to procedures that have been developed for separating the capillaries from other brain tissues.

Alkaline Phosphatase↗

PubMed1983

Effects of vasoactive intestinal polypeptide, monoamines, prostaglandins, and 2-chloroadenosine on adenylate cyclase in rat cerebral microvessels.

Adenylate cyclase in microvessels isolated from rat cerebral cortex was stimulated by guanine nucleotides, catecholamines, prostaglandin E1, prostaglandin E2, and 2-chloroadenosine. Catecholamine stimulation was mediated by interaction with beta-adrenergic receptors. The order of relative potency was: isoproterenol greater than epinephrine greater than norepinephrine. Activation of microvessel adenylate cyclase by prostaglandins E1 and E2 as well as by 2-chloroadenosine was dose related. Twenty-two peptides were tested for possible effects on the microvessel adenylate cyclase. Only vasoactive intestinal polypeptide (VIP) was stimulatory. No inhibitory action was observed. Activation by VIP required guanosine triphosphate and was dose dependent from 10 nM to 1 microM (ED50 = 0.1 microM). At 30 degrees C, stimulation of adenylate cyclase by the peptide increased linearly with time for up to 15 min. The effect of VIP was not inhibited by phentolamine or propranolol, suggesting that its action was not elicited by interaction with alpha- or beta-adrenergic receptors. Activation achieved by VIP and isoproterenol, prostaglandin E1, or 2-chloroadenosine was the sum of the individual stimulations, suggesting that receptors for VIP were distinct from those for isoproterenol, prostaglandin E1, and 2-chloroadenosine.

2-Chloroadenosine↗

PubMed1992

Steroid inhibition of neural microvessel morphogenesis in vitro: receptor mediation and astroglial dependence.

Steroid hormones alter several aspects of microvascular function within the CNS. Both microvessel formation and blood-brain barrier expression appear to be influenced by interactions between astrocytes and endothelial cells. To determine if steroids alter astrocyte-endothelial interactions, we studied their effects on astroglial-induced microvessel morphogenesis in vitro. C6 astroglial cells induce bovine retinal microvascular endothelial cells to differentiate into capillary-like structures. Dexamethasone, hydrocortisone, and progesterone at 10 nM inhibited C6-induced microvessel morphogenesis by 75, 35, and 30%, respectively. Inhibition by dexamethasone was both time and concentration dependent, reaching 80-100% at 1 microM. Tetrahydrocortisone and 17 alpha-hydroxyprogesterone had only marginal inhibitory effects. Cortexolone, a glucocorticoid receptor antagonist, blocked inhibition by dexamethasone. Progesterone receptors were expressed in C6 but not bovine retinal microvascular endothelial cells, identifying the astroglial cell as the likely effector of progesterone-mediated inhibition. Astroglial cells were further implicated as the effectors of steroid-mediated inhibition because none of the steroids inhibited astroglial-independent capillary-like structure formation in response to a reconstituted extracellular matrix, Matrigel. These findings are evidence that steroids modulate neural microvascular endothelial cell functions indirectly through perivascular astrocytes via a receptor-mediated mechanism.

Animals↗

PubMed1983

Influence of diabetes on the reactivity of mesenteric microvessels to histamine, bradykinin and acetylcholine.

1 Noradrenaline (NA) evoked a vasoconstrictor response in rat mesenteric microvessels in situ, the latency and nature of which was analogous in normal and alloxan-diabetic animals.2 Histamine and bradykinin (Bk) were capable of antagonizing the response to NA in normal but not in diabetic animals. In contrast, acetylcholine (ACh) was equally effective as an antagonist to NA in both groups of animals.3 The altered responses to histamine and Bk were not associated with hyperglycaemia since fasting rendered the diabetic animals normoglycaemic and yet did not restore the reactivity of microvessels. Previous administration of insulin to diabetic animals corrected the impaired responses to histamine and Bk.4 A similar condition of impaired responses to histamine and Bk was produced in normal animals by the intravenous injection of 2-deoxyglucose although ACh remained fully active.5 Apparently, the functional changes observed in the response to histamine or Bk, as antagonists of the vasoconstrictor reaction to NA, were not associated with a defective response of all smooth muscle. First, because ACh remained active in diabetic animals, and, second, because extravascular smooth muscles obtained from either normal or diabetic rats were equally relaxed by histamine or Bk in vitro.6 It is suggested that histamine and Bk antagonized the vasoconstrictor response of microvessels to NA through an action on lining endothelial cells resulting in increased vascular permeability and hyperosmolarity of extracellular fluids.7 The process depended on the availability of insulin, and, therefore, might be affected by intracellular glucopaenia as occurring in diabetes.8 Intracellular glucopaenia markedly affected other structures. Reduced atria rates were observed in diabetes, despite the fact that the isolated preparation responded normally to NA, ACh or tyramine. Partial substitution of glucose in the bathing fluid by 2-deoxyglucose or addition of NaF to the organ bath evoked similar changes in atria from normal animals.9 ACh which has little effect on vascular permeability must exert its vasodilator effects through mechanisms which are different from those influenced by the biochemical changes occurring in diabetes.

Acetylcholine↗

PubMed2005

Microvessels in chronic total occlusions: pathways for successful guidewire crossing?

Arterial chronic total occlusions (CTO) are a common and clinically relevant problem in patients with coronary artery disease. Percutaneous coronary intervention (PCI) success rates in a wide range of CTO are low, primarily due to inability of guidewire crossing. The pathophysiology of CTO is poorly understood and limits our ability to introduce innovative therapies. Recent studies from our laboratory have suggested that microvessel formation within arterial CTO is a complex process with temporal and regional differences. Moreover, there is evidence from pilot studies that the presence of either microvessels or the particular extracellular matrix environment in the adjacent perivascular tissue can facilitate guidewire crossing and successful PCI. Currently, studies are underway in our experimental CTO model to delineate the pathophysiology of microvessel formation in CTO and its potential role in PCI.

Animals↗

PubMed1999

Tumor microvessels in melanoma express the beta-2 chain of laminin. Implications for melanoma metastasis.

The ultrastructural localization of an amorphous matrix to the interface between microvessel endothelium and tumor cells has been recently reported in a series of melanomas. Laminin expression as documented by immunohistochemistry was localized to microvessels in melanomas showing the amorphous matrix. In order to identify more precisely the type of laminin present in this amorphous material, immunostaining was carried out on cryostat sections from 16 human melanoma specimens. Four murine monoclonal antibodies directed against the alpha-3, beta-2, beta-3 and gamma-2 laminin chains were employed. In the melanomas studied, alpha3, beta3 and gamma2 laminin chains showed only minimal focal vascular positivity. In contrast, the beta2 (16/16 cases) laminin chain exhibited a consistent positivity in an angiocentric pattern about tumor microvessels. In all melanomas, some tumor cells seemed to spread along the abluminal surface of the small vessels, exhibiting a pericytic location, particularly along the intratumoral projections formed by the beta2 laminin chain. Given the role of laminin in migration and tumor progression, the results suggest a role of the beta2 laminin chain in melanoma spread, promoting tumor migration along the abluminal surface of vessel, a phenomenon which has been termed extra-vascular migratory metastasis.

Adult↗

PubMed2006

Relationship between atrial natriuretic peptide-immunoreactive cells and microvessels in rat gastric mucosa.

AIM: To investigate the ultrastructural localization of atrial natriuretic peptide (ANP)-synthesizing cells and the relationship between ANP-synthesizing cells and microvessels in rat gastric mucosa. METHODS: Immunohistochemistry techniques and postembedding immunoelectron microscopy techniques were used to validate the findings regarding the expression of ANP-synthesizing cells and the ultrastructural localization of ANP-synthesizing cells in the gastric mucosa. Histochemistry techniques and the tannic acid-ferric chloride method (TA-Fe staining method) were used to reveal microvessel density and the distribution of ANP-synthesizing cells in different regions of the stomach. RESULTS: Cells expressing ANP were localized and ANP-synthesizing cells were identified as enterochromaffin (EC) cells in the gastric mucosa. ANP-synthesizing cells existed in different regions of the stomach. The percentage ANP-synthesizing cells in the mucosa was greatest in the fundus (46.7%+/-5.3%), intermediate in the antrum (40.1%+/-4.5%), and least in the body (21.6%+/-3.6%). There was a positive relationship between the percentage of ANP-synthesizing cells and the density of microvessels in the antral mucosa, but not in the fundus or body mucosa. CONCLUSION: ANP is synthesized by EC cells in rat gastric mucosa, and ANP-synthesizing cells are most dense in the gastric fundus. ANP may act not only as a regional autocrine and/or paracrine regulator, but also as an endocrine regulatory peptide in the gastrointestinal tract.

Animals↗

PubMed1993

Permeability of disrupted cerebral microvessels in the frog.

1. This study reports the results of varying the hydrostatic pressure on measurements of permeability coefficient to the low molecular weight impermeant dye carboxyfluorescein (MW = 376) in single leaky cerebral microvessels. A mathematical model, that solved the convective diffusion equations used to analyse the measurements, showed that the measurements were consistent with leakiness being due to 22 nm wide parallel-sided slits between endothelial cells. 2. Microvessels on the surface of the frog's brain were cannulated with a micropipette and perfused with an artificial cerebrospinal fluid containing the dye. Vessels were occluded with a glass microneedle and the rate of change in dye concentration in a 12 microns length section was measured using video-intensified microscopy. 3. It was found that the rate of dye loss at all points along the occluded microvessel segment could be accounted for by a model for convection and diffusion, and that changes in dye concentration at a point remote from the segment entrance can give a good measure of diffusive permeability. 4. When series of measurements were carried out on a single vessel, permeability rose over the course of 20 min. Mean permeability for all measurements was 3.01 x 10(-5) cm sec-1, n = 64 (mode, 2.0; range, 0.48-9.6). The hydrostatic pressure applied during the perfusion had no effect on the measured permeability. 5. The dye concentration along the vessel axis was measured at the steady state and was shown to respond to changes in hydrostatic perfusion pressure in a way predicted by the model. This indicates that hydrostatically driven bulk flow can be important, and thus convection may account for effects previously ascribed to vesicular transcytosis. 6. The possible anatomical basis for the porous pathway is discussed in the light of recent observations on the presence of 0.5 microns perijunctional gaps, the possibility of transendothelial channels, and the unzipping of tight junctions to leave a 22 nm wide slit.

Animals↗

PubMed2006

Topographical heterogeneity of K(IR) currents in pericyte-containing microvessels of the rat retina: effect of diabetes.

Although inwardly rectifying potassium (K(IR)) channels are known to have important functional roles in arteries and arterioles, knowledge of these channels in pericyte-containing microvessels is limited. A working hypothesis is that K(IR) channel activity affects the membrane potential and thereby the contractile tone of abluminal pericytes whose contractions and relaxations may regulate capillary perfusion. Because pericyte function is thought to be particularly important in the retina, we used the perforated-patch technique to monitor the ionic currents of pericytes located on microvessels freshly isolated from the rat retina. In addition, because changes in ion channel function may contribute to microvascular dysfunction in the diabetic retina, we also recorded from pericyte-containing microvessels of streptozotocin-injected rats. Using barium to identify K(IR) currents, we found that there is a topographical heterogeneity of these currents in the pericyte-containing microvasculature of the normal retina. Specifically, the K(IR) current detected at distal locations is strongly rectifying, but the proximal K(IR) current is weakly rectifying and has a smaller inward conductance. However, soon after the onset of diabetes, these differences diminish as the rectification and inward conductance of the proximal K(IR) current increase. These diabetes-induced changes were reversed by an inhibitor of polyamine synthesis and could be mimicked by spermine, whose concentration is elevated in the diabetic eye. Hence, spermine is a candidate for mediating the effect of diabetes on the function of microvascular K(IR) channels. In addition, our findings raise the possibility that functional changes in K(IR) channels contribute to blood flow dysregulation in the diabetic retina.

Animals↗

PubMed2004

Modulation of cyclic AMP production by signal transduction pathways in preglomerular microvessels and microvascular smooth muscle cells.

Cyclic AMP affects microvascular smooth muscle contraction and growth. Therefore, it is important to elucidate mechanisms regulating cyclic AMP production in microvascular smooth muscle. In this study, we determined whether several signal transduction pathways regulate receptor-induced cyclic AMP in isolated preglomerular microvessels and microvascular smooth muscle cells. Preglomerular microvessels were incubated with isoproterenol (beta-adrenoceptor agonist) and with and without U73122 (phospholipase C inhibitor), GF109203X (protein kinase C inhibitor), 1-butanol (phospholipase D inhibitor), CGP77675 (c-src inhibitor), HA1077 (Rho kinase inhibitor), Y27632 (Rho kinase inhibitor), LY294002 (phosphatidylinositol-3-kinase inhibitor), dipenyleneiodonium (NADPH oxidase inhibitor), or Tempol (superoxide dismutase mimetic). Cultured preglomerular microvascular smooth muscle cells were incubated with isoproterenol or forskolin (direct activator of adenylyl cyclase) and with or without U73122, C(2)-ceramide (phospholipase D inhibitor), or PP1 [src family inhibitor, 1-(1,1-dimethylethyl)-1-(4-methylphenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine]. All studies were conducted with 3-isobutyl-1-methylxanthine (broad-spectrum phosphodiesterase inhibitor) to eliminate changes in cyclic AMP degradation. In microvessels isoproterenol-induced cyclic AMP was not affected by Y27632, HA1007, LY294002, dipenylene-iodonium, or Tempol; was increased by U73122 and GF109203X; and was decreased by 1-butanol and CGP77675. In cells, U73122 increased and C(2)-ceramide and PP1 decreased isoproterenol-induced cyclic AMP. Forskolin-induced cyclic AMP was not altered. These results indicate that receptor-mediated activation of adenylyl cyclase is 1) not modulated by Rho kinase, phosphatidylinositol-3-kinase, NADPH oxidase, or superoxide; 2) is attenuated by phospholipase C and protein kinase C; and 3) is augmented by phospholipase D and src. Phospholipase C, phospholipase D, and src modulate receptor-induced cyclic AMP by affecting beta-adrenoreceptor/G protein/adenylyl cyclase coupling rather than by directly affecting adenylyl cyclase activity.

Adenylyl Cyclases↗

PubMed2004

Microvessel density and clinicopathological characteristics in hepatitis C virus and hepatitis B virus related hepatocellular carcinoma.

AIMS: To compare intratumorous microvessel density (MVD) and clinicopathological features in two different groups of hepatocellular carcinoma (HCC), namely: hepatitis B virus (HBV) related HCC (B-HCC) and HCV related HCC (C-HCC). METHODS: Fifty consecutive cases each of B-HCC and of C-HCC were studied. Microvessel numbers were assessed by staining for the antigen CD34; in each case, three areas with the highest numbers of microvessels were counted in both the intratumorous and the surrounding non-tumorous tissue; the mean value represented the final MVD. RESULTS: Patients with B-HCC were significantly younger than those with C-HCC (mean age, 60.1 (SD, 4.1) v 66.4 (4.3) years); no significant differences were seen for sex or Child's class distribution. The tumour diameter was larger in B-HCCs than in C-HCCs (mean, 5.6 (SD, 1.8) v 3.8 (1.8) cm). Tumour microsatellite formation was significantly higher in C-HCCs (12 v 4 cases). No differences were found for histological subtype, degree of differentiation, tumour encapsulation, and vascular invasion. The mean MVD value was significantly higher in tumorous (mean, 54 (SD, 13.8) v 38 (8.9)) and in the surrounding non-tumorous liver tissue (mean, 15 (SD, 4.3) v 7 (3.1)) of C-HCCs. CONCLUSIONS: C-HCCs present as smaller tumours in older patients, with a higher incidence of tumour microsatellite formation and higher MVD values both in the tumorous and the non-tumorous areas, suggesting a link between HCV infection, angiogenesis, and hepatocarcinogenesis.

Age Factors↗

PubMed1986

Diacylglycerol lipase and kinase activities in rabbit aorta and coronary microvessels.

Diacylglycerol lipase and kinase activities were measured in particulate and soluble fractions from rabbit aorta (intima-media) and coronary microvessels. With rabbit aorta, the hydrolysis at the sn-1 position of 1-palmitoyl-2-oleoyl-sn-glycerol had a pH optimum of 5-6 and was greater than hydrolysis at the sn-2 position (pH optimum of 6.5). Only the 2-monoacylglycerol accumulated during incubations at pH 5 and 6.5. These results are consistent with an ordered two-step reaction sequence where the fatty acid at the sn-1 position is released first, followed by the hydrolysis of the fatty acid from the 2-monoacylglycerol by a monoacylglycerol lipase with a neutral pH optimum. Lipase activity (sn-2 hydrolysis) at pH 6.5 was greater than kinase activity at all substrate concentrations. The presence of arachidonate at the sn-2 position of the diacylglycerol increased kinase activity but had little effect on lipase activity. Kinase activity was mainly particulate, whereas 50-60% of diacylglycerol lipase and 50% of monoacylglycerol lipase activity were soluble. Diacylglycerol lipase and kinase were also present in coronary microvessel preparations. Diacylglycerol lipase (sn-2 hydrolysis) activity in coronary microvessels was not enhanced by preincubation of the enzyme preparation with cAMP-dependent protein kinase.

Animals↗