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Biomedical subjects

M E Gerritsen

Publications and source records attributed to M E Gerritsen.

At least 91 records · Page 5Linked to original sources
PubMed1986

Regulation of hexose transport in cultured bovine retinal microvessel endothelium by insulin.

In microvessel endothelium obtained from young calf retinas, insulin stimulated the uptake of 2-deoxy-D-glucose in a dose-dependent manner. The maximal level of glucose uptake (50-100% over basal values) was observed at 1 ng ml-1 insulin. The effects of insulin on glucose uptake were time-dependent, with optimum stimulation of glucose transport observed after 90 min of insulin treatment. The effects of insulin were prevented by 15 min pretreatment with 2 micrograms ml-1 cycloheximide or by 2 micrograms ml-1 actinomycin D, suggesting a role for new protein synthesis in the actions of insulin on glucose transport in this cell type. These results demonstrate that cultured retinal microvessel endothelial cells exhibit an insulin-sensitive glucose transport system.

3-O-Methylglucose↗
PubMed1986

Dexamethasone inhibits prostaglandin release from rabbit coronary microvessel endothelium.

The effects of dexamethasone on prostaglandin secretion by cultivated rabbit coronary microvascular endothelial (RCME) cells were investigated. Incubation of RCME cells with dexamethasone resulted in a time- and concentration-dependent decrease in prostaglandin accumulation in the culture media and reduced basal and A23187-stimulated prostaglandin (PG) E2 and 6-keto-PGF1 alpha release. The maximal effects of dexamethasone (50-80% inhibition) were achieved after 16-18 h of incubation with the steroid at a final concentration of 10(-7) M. The effects of dexamethasone treatment were partially reversed 24 h after removal of the steroid from the culture media. Dexamethasone treatment did not reduce arachidonic acid-stimulated prostaglandin synthesis, indicating that the level of inhibition was proximal to that of cyclooxygenase. The inhibitory effects of dexamethasone could be prevented by pretreatment of the RCME cells with actinomycin D or cycloheximide, suggesting a requirement for protein synthesis in the inhibitory action of dexamethasone. Conditioned media from dexamethasone-treated cells contained a factor that inhibited porcine pancreatic phospholipase A2 (PLA2) in vitro. Transfer of conditioned media from dexamethasone-treated cells to untreated cells did not reduce basal or stimulated prostaglandin release; in contrast, a stimulatory action was consistently observed. Adherence of rabbit peripheral polymorphonuclear leukocytes (PMN) to RCME cells was reduced when the leukocytes were pretreated with 10(-7) M dexamethasone (4 h). However, dexamethasone pretreatment of the RCME cells did not significantly effect granulocyte adhesion. Thus coronary microvascular endothelial cell prostaglandin production is regulated by glucocorticoids, and glucocorticoid-pretreated microvascular endothelial cell release an inhibitor of PLA2 activity into the culture media.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Altered aortic and cremaster muscle prostaglandin synthesis in diabetic rats.

Alterations in the synthesis and release of prostaglandins have been reported in humans and animal models of diabetes mellitus. In the present study synthesis and release of prostaglandins by thoracic aorta and cremaster muscle of rats with streptozotocin-induced diabetes of 8 wk duration was compared with age-matched controls. Prostaglandin synthesis was assessed by the measurement of immunoreactive prostaglandin E2 (PGE2) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) release and by quantifying metabolism of exogenous [1-14C]arachidonic acid by thoracic aortic rings and minced cremaster muscle. The cremaster muscles from diabetic rats released significantly greater quantities of PGE2 and 6-keto-PGF1 alpha and PGE2. In contrast, the aortas from diabetic rats released smaller quantities of 6-keto-PGF1 alpha and PGE2 and exhibited reduced 6-[1-14C]keto-PGF1 alpha. These studies indicate that diminished prostacyclin (PGI2) and/or PGE2 production is not a general feature of all diabetic vascular tissues, suggesting that large and small blood vessels may not be similarly affected by diabetes in regard to the metabolism of exogenous arachidonic acid and the synthesis and release of prostaglandins. Furthermore, the vascular changes often observed in conjunction with diabetes, i.e., alterations in vascular reactivity and microangiopathy in small blood vessels and atherosclerosis of large blood vessels may be related in some way to the segmental differences observed in prostaglandin synthesis.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Effect of castration on prostaglandin-mediated changes in membrane potential and prostaglandin synthesis in guinea-pig seminal vesicle tissue.

Arachidonic acid stimulated an increase in transmural electrical potential difference (p.d.) in guinea-pig seminal vesicle tissue in vitro. Pretreatment with indomethacin abolished this response. Indomethacin pretreatment did not prevent the p.d. from increasing in response to theophylline. Changes in p.d. in response to arachidonic acid were greatly attenuated, and the response to theophylline was abolished in seminal vesicle tissue taken from castrated guinea-pigs. Seminal vesicles, aorta and ileum taken from castrated guinea-pigs synthesized and released more prostaglandins than did those from control animals. It is concluded that the effects of arachidonic acid on p.d. are mediated by its metabolism to prostaglandins; the inability of seminal vesicles from castrated animals to respond to arachidonic acid is not a result of a decrease in prostaglandin production, but is more likely a result of other degenerative changes attendant upon castration; and androgens appear to have some regulatory function on prostaglandin synthesis in a variety of tissues.

Animals↗
PubMed1985

Insulin binding and effects of insulin on glucose uptake and metabolism in cultured rabbit coronary microvessel endothelium.

Microvascular endothelial cells were isolated from rabbit cardiac tissue, and cultivated by standard tissue culture techniques. The conversion of [U-14C]glucose to CO2 and lipids was significantly enhanced by insulin treatment. Insulin stimulated uptake of 2-[3H]deoxyglucose and enhanced the transport of 3-O[3H]methyl-D-glucose. Specific binding of [125I]insulin to RCME cells, displaceable by cold insulin, was also observed. These data demonstrate that insulin is capable of regulating metabolic activities in coronary microvascular endothelium.

3-O-Methylglucose↗
PubMed1983

PGD2 formation in the vasculature: characteristics of rat tail vein prostaglandin endoperoxide-D isomerase.

Rat tail vein homogenates, microsome and high speed supernatant fractions were incubated with [1-(14) C]prostaglandin endoperoxide (PGH2) and products separated and identified by radio-thinlayer chromatography. PGI2 synthase was localized to the microsomal fraction, but exhibited low activity compared to rat tail arteries prepared in the same manner. PGH-D isomerase was identified in the cytosolic fraction of tail veins. The isomerase was maximally active in the presence of reduced glutathione at pH 7.5-8.0, exhibited a Km for PGH2 of 33 microM, and was inhibited sulfhydryl-directed reagents. The similarities of this enzyme to PGD synthase of the rat cerebral microvasculature are discussed.

Animals↗
PubMed1983

Arachidonic acid and prostaglandin endoperoxide metabolism in isolated rabbit and coronary microvessels and isolated and cultivated coronary microvessel endothelial cells.

Isolated microvessels and isolated and cultured microvessel endothelial cells were prepared from rabbit cardiac muscle. Pathways of arachidonic acid metabolism were determined by measurement of exogenous substrate utilization [( 1-14C]arachidonic acid incorporation and release from intact tissue and cells; [1-14C]prostaglandin H2 (PGH2) metabolism by broken cell preparations) and by quantification of endogenous products (immunoreactive 6-keto-prostaglandin F1 alpha (PGF1 alpha) and prostaglandin E (PGE) release) by selective radioimmunoassay. Rabbit coronary microvessels and derived microvascular endothelial cells (RCME cells) synthesized two major products of the cyclooxygenase pathway: 6-keto-PGF1 alpha (hydrolytic product of prostaglandin I2) and PGE2. A reduced glutathione requiring PGH-E isomerase was demonstrated in coronary microvessels and RCME cells, but not in rabbit circumflex coronary artery or aorta. In addition, a minor amount of a compound exhibiting similar characteristics to 6-keto-PGE1 was found to be produced by microvessels and RCME cells. Measurement of endogenously released prostaglandins indicated that under basal and stimulated conditions, PGE release exceeded that of 6-keto-PGF1 alpha. Microvessels and microvessel endothelial cells derived from cardiac muscle of rabbit exhibit pathways of arachidonate metabolism that are different from those of many large blood vessels and derived endothelial cells.

6-Ketoprostaglandin F1 alpha↗
PubMed1981

Prostaglandin D synthase in microvessels from the rat cerebral cortex.

Microvessels, a mixture composed predominantly of small arterioles and capillaries (7-80 micro diameter), were isolated from the rat cerebral cortex by selective nylon sieving and glass bead elutriation. The morphology and purity of the microvessel and cerebral cortex filtrate (virtually free of vascular contamination) were monitored by light microscopy and by the activity of several enzymes: gamma -glutamyl transpeptidase, GSH-S-transferase, prostacyclin synthase and PGD synthase. Prostacyclin and PGD synthesizing activities as well as gamma-glutamyl transpeptidase activity were localized to the microvessels of the rat cerebral cortex whereas GSH-S-Transferase was restricted to the non-vascular filtrate fraction. The characteristics of the PGD synthase were similar to those of the purified enzyme previously described for the rat brain. The microvessel (MV) PGD synthase was localized to the cytosol fraction of the microvessels and did not require reduced glutathione for activity. The enzyme was inhibited by pre-incubation with p-hydroxymercuribenzoate (ImM) or N-ethylmaleimide (ImM). The MV RGD synthase saturated at 15-20 microM PGH2, exhibited an apparent Km of 9.6 microM, and a pH optimum of 8.0-8.1. These findings suggest roles for both prostacyclin and PGD synthesis by the rat cerebral vasculature in the autoregulation of cerebral blood flow and/or neural function. These studies also indicate that the major source of PGI2 and PGD2 synthesis by rat brain homogenates is the microvasculature.

Animals↗
PubMed1981

Sites of prostaglandin synthesis in the bovine heart and isolated bovine coronary microvessels.

Metabolically active coronary microvessels (generally less than 100 micrometers in diameter) were isolated from bovine hearts. These preparations were virtually free of contaminating myocytes and consisted of a mixture of arterioles, venules, capillaries, and collagen fibers. The prostaglandin biosynthetic capacity of isolated coronary microvessels was assessed by quantitating conversion of 14C-arachidonic acid and 14C-prostaglandin endoperoxide (PGH2) to prostaglandins. Coronary microvessels were found to exhibit low cyclooxygenase activity, i.e., minimal conversion (less than 1%) of arachidonic acid (AA) to prostaglandins when compared with either the coronary artery (3.6% conversion of AA) or coronary vein (3.3%). Isolated myofibril fractions demonstrated virtually no cyclooxygenase activity (less than 0.1%). Two enzymatic endoperoxide metabolizing activities were evident in the microvessels, prostacyclin synthetase and PGE isomerase. When compared on a microsomal protein basis, the coronary artery exhibited higher prostacyclin synthetase activity than the microvessels but was devoid of PGE isomerase activity. In contrast, whereas PGE isomerase activity was detectable in the coronary vein, the activity was lower than that of the microvessels; further, it could not be demonstrated in the other myocardial fractions. A glutathione-enhanced PGD-forming activity was present in high speed supernatants derived from the coronary artery and vein preparations, but was not present in the coronary microvessel or isolated myofibril fractions. From these studies we conclude that (1) the major source of prostaglandins released into the coronary circulation is the coronary vasculature, and (2) the resistance elements of the coronary circulation differ from the larger elements (i.e., arteries and veins) in the enzymes of the prostaglandin biosynthetic pathway present and thus in the nature and perhaps quantity of prostaglandins biosynthesized.

Animals↗
PubMed1980

Prostaglandin endoperoxide metabolism by bovine cerebral microvessels.

Isolated bovine cerebral microvessels were found to contain two prostaglandin endoperoxide-metabolizing activities: prostaglandin H2-E2 isomerase and prostacyclin synthetase. At low tissue protein concentrations (i.e., less than 1 mg/ml) and in the presence of reduced glutathione, formation of prostaglandin E2 was favored (about 80% of total prostaglandin products), whereas at higher protein concentrations, in the presence or absence of reduced glutathione, 6-keto-prostaglanding F1 alpha, the stable breakdown product of prostacyclin, was the major product (40-50% of total). Despite an increase in apparent prostacyclin formation, glutathione-enhanced prostaglandin E2 production was still evident at protein concentrations exceeding 1 mg/ml. No apparent enzymatic prostaglandin E2 forming activity was evident in whole cerebral cortex or pial artery homogenates although some GSH-enhanced prostaglandin E2 formation could be demonstrated in microsomes prepared from these tissues. These findings indicate that prostaglandin E2 formation is a dominant enzymatic endoperoxide-metabolizing activity in microvessels, and that this pathway may be primarily localized to the microvasculature. However, they also indicate that enzyme/substrate ratios and endogenous cofactor availability may affect the outcome of endoperoxide metabolism in the bovine cerebral microvasculature, Prostaglandin E2 and prostacyclin generated in the microvasculature could participate in the regulation of various functions, e.g., regional flow and capillary permeability.

Animals↗
PubMed1980

Prostaglandin E2 synthesis in pigeon aorta: comparison of atherosclerosis-resistant (Show Racer) and atherosclerosis-prone (White Carneau) breeds.

Microsomes prepared from the brachial artery and the thoracic aorta of atherosclerosis resistant (AR) Show Racer and atherosclerosis prone (AS) White Carneau pigeons were incubated with 14C-prostaglandin endoperoxide (PGH) and prostaglandin products analyzed. The microsomes demonstrated minimal prostacyclin (PGI2) synthetase activity; 6-keto-PGF1 alpha (the hydrolytic breakdown product of PGI2) accounting for less than 2% of total products. Reduced glutathione enhanced PGE2 formation in both the AR and AS preparations identifying an active PGH-PGE isomerase. The AR preparations demonstrated increased PGH-PGE formation with age, reaching maximal activity at 8-9 months, then decreasing at 14 months. The AS group also demonstrated a similar pattern of enzyme activity. These studies indicate that a) unlike the mammalian preparations prostacyclin synthetase does not appear to be a major enzymatic activity of the pigeon aorta, rather, b) PGH-PGE isomerase is the major endoperoxide metabolizing activity in the pigeon aorta and thus, c) a deficiency of prostacyclin production is not involved in the geneis of atherosclerosis in the pigeon.

Aging↗
PubMed1979

Urotensin I effects on intracellular content of cyclic AMP in the rat tail artery.

Rat tail artery strips were incubated in the presence of 4 x 10(-3) M theophylline and urotensin I (UI). At the concentrations of 1.50, 7.50 mU/ml but not of 0.75 mU/ml UI, the content of cAMP increased significantly. Cyclic AMP content and muscle tension were measured at 5--30 sec intervals during noradrenaline (NA)- and potassium chloride (KCl)-induced contractions and during subsequent urotensin I-induced relaxation. Cyclic AMP content declined initially after addition of NA but returned to baseline levels during the contraction. Significant dose-related increases in cAMP were noted upon addition of UI, prior to the onset of the relaxation response followed by a marked decrease during the relaxation response. An increase in cAMP was observed after initiation of the contractile response to KCl-contracted tissues, but no further increase in cAMP after addition of UI was detected. These findings suggest an involvement of cyclic AMP in the initial events leading to the relaxation response to urotensin I in the NA-contracted rat tail artery. Urotensin I-induced relaxation in KCl-contracted tissues appears to proceed by an alternative mechanism which does not require increased levels of cAMP.

Animals↗
PubMed1979

Effects of urotensin I on the isolated rat tail artery.

Urotensin I (UI) was found to elicit dose-related relaxation responses in isolated helical strips of the rat tail artery. The responses were not prevented by adrenergic, cholingergic or histaminergic blocking agents. Competitive and non-competitive components of antagonism were observed to noradrenaline-, 5-hydroxytryptamine-, and arginine vasopressin-induced contractions. Atropine caused a direct relaxation of the isolated vascular tissues, as well as a significant potentiation of UI responses.

Adrenergic alpha-Antagonists↗