Dysfunction of the endothelial nitric oxide signalling pathway in diabetes and hyperglycaemia

1. Vasodilatation induced by adenosine is mediated through the activation of A2-purinoceptors in endothelial and smooth muscle cells. 2. Adenosine induces a rapid and transient membrane hyperpolarization in endothelial cells. 3. Acute exposure to adenosine or A2-purinoceptor agonists activates the L-arginine-NO signalling pathway in human endothelial cells in vitro.

Expression of stress proteins heme oxygenase-1 and -2 in acute pancreatitis and pancreatic islet betaTC3 and acinar AR42J cells

Oxygen-derived free radicals have been implicated in the pathogenesis of acute pancreatitis, yet adaptive responses in the pancreas in vivo to oxidative stress remain poorly defined. We have investigated expression of the stress protein heme oxygenase in the intact pancreas of rats with caerulein-induced pancreatitis and in cultured pancreatic acinar and islet cell lines. Expression of inducible heme oxygenase-1 (HO-1) in the pancreas in vivo was enhanced 12-24 h after induction of pancreatitis. In murine islet (betaTC3) and rat acinar (AR42J) pancreatic cells, H2O2, methyl viologen, cadmium chloride and diethylmaleate enhanced HO-1 expression in a dose- and time-dependent manner, without altering expression of constitutive HO-2. Enhanced expression of HO-1 in the pancreas in vivo and pancreatic islet and acinar cells may contribute to cellular defences against oxidative stress associated with acute pancreatitis.

Modulation of vascular tone by low density lipoproteins: effects on L-arginine transport and nitric oxide synthesis

Low density lipoprotein (LDL) plays an important role in atherogenesis. Focal accumulation within the arterial intima of excess amounts of cholesterol-rich LDL leads to the migration and recruitment of monocytes, which then differentiate into macrophages after taking up large amounts of oxidatively modified LDL via their scavenger receptors and become lipid-laden 'foam cells' within the subendothelial space. It is generally accepted that oxidized LDL and hyperlipidaemia impair endothelial-dependent vascular relaxation, yet the existing literature on the effects of oxidatively modified LDL on endothelium-derived nitric oxide (NO) and prostacyclin (PGI2) release is inconclusive, since oxidized LDL has been reported to enhance or reduce NO and PGI2 production. Our studies using cultured human endothelial and smooth muscle cells have established that basal rates of L-arginine (NO precursor) transport, NO and PGI2 production and soluble guanylyl cyclase activity are unaffected by pretreatment (for 1 or 24 h) with native LDL, or with mildly or highly oxidized LDL. In contrast, highly oxidized LDL inhibited histamine-stimulated release of NO and PGI2 from human endothelial cells and induced an adaptive increase in the level of intracellular glutathione in human smooth muscle cells, a response which was prevented by the chain-breaking antioxidant alpha-tocopherol. Although initial rates of L-arginine transport and basal NO and PGI2 release from human endothelium are unaffected by oxidized LDL, agonist-stimulated release of these vasodilators is markedly attenuated. Elucidation of the mechanisms regulating these responses and their sensitivity to dietary antioxidants could lead to alternative strategies for reducing atherogenesis.

Noninvasive mechanical body contouring: a preliminary clinical outcome study

L.P.G.'s Endermologie is a massage method consisting of positive pressure rolling, in conjunction with applied negative pressure to both the, skin and subcutaneous tissues (L.P.G. Endermologie U.S.A., 3101 North Federal Highway, Suite 301 Fort Lauderdale, Florida 33306, U.S.A., (800) 222-3911). Devised in France during the 1970s, L.P.G.'s original purpose was to soften scars and standardize physical therapy; however, patients treated with the L.P.G. machine also showed an improvement in body contour and skin texture. Since then, several thousand machines have been in use in France as an alternative method for altering fat distribution in the subcutaneous plane. The authors began a study to determine the safety and efficacy of this machine. This study is composed of 22 women between the ages of 24 and 48. All 22 women completed at least seven sessions of treatments. Six of these 22 women completed all 14 sessions of the prescribed treatments. The study group exhibited a wide range of body habitus, initial weights, and final results. Of the 22 women who completed seven sessions of treatment, three had an increase in body weight and a mean index (see Materials and Methods) reduction in body diameter of 1.38 cm (0.5 in). Three of the six patients who completed all 14 treatment sessions had an increase in body weight and a mean index reduction in body diameter of 2.85 cm (1.12 in). All but one of the patients had a decrease in their mean body diameter index, regardless of their loss or gain in weight.

Activation of A2-purinoceptors by adenosine stimulates L-arginine transport (system y+) and nitric oxide synthesis in human fetal endothelial cells

1. Human umbilical vein endothelial cells were challenged acutely with adenosine and its analogues to examine whether adenosine modulates L-arginine transport (system y+) and synthesis of nitric oxide (NO) and prostacyclin (PGI2). 2. L-Arginine transport was stimulated by adenosine (10 microM, 2 min) and the A2-receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS-21680; 100 nM), but not by the A1-receptor agonist N6-cyclopentyladenosine (CPA). 3. Activation of L-arginine transport was inhibited by the A2-receptor antagonists ZM-241385 and 3,7-dimethyl-1-propargylxanthine (DMPX), but unaffected by the A1-receptor antagonists 8-cyclopentyl-1,3-dipropylxanthine and 8-phenyltheophylline or the adenosine transport inhibitor nitrobenzylthioinosine. 4. Adenosine and CGS-21680 evoked a rapid membrane hyperpolarization. 5. Adenosine and CGS-21680 induced increases in intracellular cGMP levels, whereas release of PGI2 was unaffected. NG-nitro-L-arginine methyl ester (an NO synthase inhibitor) and the A2-receptor antagonists ZM-241385 and DMPX prevented increases in cGMP accumulation. 6. Our findings provide the first evidence that activation of human fetal endothelial cell A2-purinoceptors, but not A1-purinoceptors, leads to a membrane hyperpolarization and stimulation of basal rates of L-arginine transport and NO biosynthesis.

Actions of oestrogen on vascular endothelial and smooth-muscle cells

The overall effects of oestrogen on the vasculature are beneficial as a result of its antioxidant properties and ability to enhance relaxation by modulating synthesis of endothelium-derived vasodilators and smooth-muscle cell Ca2+ signalling. Although the protective effects of oestrogen are well accepted, only limited and conflicting data are available on the cellular mechanisms mediating steroid action in the vasculature. Discrepancies in cell culture experiments may reflect differences in culture conditions, the origin of cells and/or hormonal status. For example, umbilical vein endothelial cells isolated from gestational diabetic pregnancies exhibit phenotypic changes that are maintained during prolonged cell culture [42,75]. As gender differences in vascular reactivity have long been reported [76-78], gender needs to be taken into account in interpreting vascular responses to oestrogen in animal models. Further research is required to characterize the non-genomic actions of oestrogen in the vasculature. Whether activation of non-genomic receptors by physiologically relevant plasma concentrations of oestrogen modulates the activity of endothelial cell NOS, cyclo-oxygenase and superoxide dismutase and smooth-muscle cell Ca2+ ion channel activity remains to be investigated. Prolonged exposure of the vasculature to circulating steroid hormones may more closely reflect in vivo conditions, since oestrogen is known to enhance endothelium-dependent relaxation in response to some agonists [79].

Diabetes and insulin-induced stimulation of L-arginine transport and nitric oxide synthesis in rabbit isolated gastric glands

1. The properties of L-arginine transport have been characterized and correlated with cGMP production (index of nitric oxide (NO)) in whole gastric glands isolated from non-diabetic and alloxan-diabetic rabbits. 2. In non-diabetic and diabetic glands, transport of L-arginine was stereoselective, Na+ and pH independent and inhibited by other cationic amino acids. L-Arginine transport was slightly inhibited by L-leucine and L-phenylalanine, but unaffected by other neutral amino acids. 3. Diabetes enhanced the Vmax for saturable L-arginine transport from 10.7 +/- 1.0 to 17.7 +/- 0.5 pmol (mg protein)-1 s-1, with negligible changes in K(m). 4. Accumulation of the membrane potential-sensitive probe tetra[3H]phenylphosphonium (TPP+) was increased 2-fold in diabetic compared with non-diabetic gastric glands, suggesting a membrane hyperpolarization. 5. Basal intracellular cGMP levels were elevated 2-fold in diabetic gastric glands, and in non-diabetic glands histamine, vasoactive intestinal peptide, and bradykinin increased cGMP levels. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (100 microM) abolished basal cGMP accumulation. 6. Addition of extracellular L-arginine induced a concentration-dependent increase in cGMP levels in gastric glands isolated from non-diabetic rabbits, but had no effect on elevated cGMP levels in diabetic glands. 7. Insulin induced a rapid (5 min) concentration-dependent increase in cGMP levels in non-diabetic gastric glands, but reduced elevated cGMP levels in diabetic gastric glands. 8. The present study has identified a specific transport system for L-arginine in gastric glands which resembles the classical system y+. Our findings also provide the first direct evidence that diabetes increases the basal activity of system y+ and NO synthase in gastric glands. The differential modulation of L-arginine transport by insulin and L-arginine identified in non-diabetic and diabetic glands, may be of importance in protecting the gastric mucosa from injuries associated with diabetes.

Regulation of oxytocin, oestradiol and progesterone receptor concentrations in different uterine regions by oestradiol, progesterone and oxytocin in ovariectomized ewes

The regulation of oxytocin, oestradiol and progesterone receptors in different uterine cell types was studied in ovariectomized ewes. Animals were pretreated with a progestogen sponge for 10 days followed by 2 days of high-dose oestradiol to simulate oestrus. They then received either low-dose oestradiol (Group E), low-dose oestradiol plus progesterone (Group P) or low-dose oestradiol, progesterone and oxytocin (via osmotic minipump; Group OT). Animals (three to six per time-point) were killed following ovariectomy (Group OVX), at oestrus (Group O) or following 8, 10, 12 or 14 days of E, P or OT treatment. In a final group, oxytocin was withdrawn on day 12 and ewes were killed on day 14 (Group OTW). Oxytocin receptor concentrations and localization in the endometrium and myometrium were measured by radioreceptor assay, in situ hybridization and autoradiography with the iodinated oxytocin receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin. Oestradiol and progesterone receptors were localized by immunocytochemistry. Oxytocin receptors were present in the luminal epithelium and superficial glands of ovariectomized ewes. In Group O, endometrial oxytocin receptor concentrations were high (1346 +/- 379 fmol [3H]oxytocin bound mg protein-1) and receptors were also located in the deep glands and caruncular stroma in a pattern resembling that found at natural oestrus. Continuing low-dose oestradiol was unable to sustain high endometrial oxytocin receptor concentrations with values decreasing significantly to 140 +/- 20 fmol mg protein-1 (P < 0.01), localized to the luminal epithelium and caruncular stroma but not the glands. Progesterone treatment initially abolished all oxytocin receptors with none present on days 8 or 10. They reappeared in the luminal epithelium only between days 12 and 14 to give an overall concentration of 306 +/- 50 fmol mg protein-1. Oxytocin treatment caused a small increase in oxytocin receptor concentration in the luminal epithelium on days 8 and 10 (20 +/- 4 in Group P and 107 +/- 35 fmol mg protein-1 in Group OT, P < 0.01) but the rise on day 14 was not affected (267 +/- 82 in Group OT and 411 +/- 120 fmol mg protein-1 in Group OTW). In contrast, oestradiol treatment was able to sustain myometrial oxytocin receptors (635 +/- 277 fmol mg protein-1 in Group O and 255 +/- 36 in Group E) and there was no increase over time in Groups P, OT and OTW with values of 61 +/- 18, 88 +/- 53 and 114 +/- 76 fmol mg protein-1 respectively (combined values for days 8-14). Oestradiol receptor concentrations were high in all uterine regions in Group O. This pattern and concentration was maintained in Group E. In all progesterone-treated ewes, oestradiol receptor concentrations were lower in all regions at all time-points. The only time-related change occurred in the luminal epithelium in which oestradiol receptors were undetectable on day 8 but developed by day 10 of progesterone treatment. Progesterone receptors were present at moderate concentrations in the deep glands, caruncular stroma, deep stroma and myometrium in Group O. Oestradiol increased progesterone receptors in the luminal epithelium, superficial glands, deep stroma and myometrium. Progesterone caused the loss of its own receptor from the luminal epithelium and superficial glands and decreased its receptor concentration in the deep stroma and myometrium at all time-points. There was a time-related loss of progesterone receptors from the deep glands of progesterone-treated ewes between days 8 and 14. These results show differences in the regulation of receptors between uterine regions. In particular loss of the negative inhibition by progesterone on the oxytocin receptor by day 14 occurred only in the luminal epithelium, but is unlikely to be a direct effect of progesterone as no progesterone receptors were present on luminal epithelial cells between days 8 and 14.

The effect of oxytocin and oestradiol on the action of conceptus secretory protein in progesterone-treated ovariectomized ewes

In intact cyclic ewes intrauterine infusion of conceptus secretory proteins results in the suppression of both endometrial oxytocin receptor concentrations and oxytocin-induced prostaglandin F2 alpha release. However, similar infusion in progesterone-treated ovariectomized ewes, while suppressing endometrial oxytocin receptors, does not fully inhibit oxytocin-induced prostaglandin F2 alpha release. To examine whether this anomaly resulted from an inadequate simulation of the luteal phase in the ovariectomized ewe treated with progesterone alone, the effects of additional treatment with two other ovarian hormones, oestradiol-17 beta and oxytocin, was investigated. Rather than permitting conceptus secretory protein to successfully inhibit oxytocin-induced prostaglandin F2 alpha release, treatment with oestradiol-17 beta in addition to progesterone actually resulted in an advancement in the timing of release. However, treatment with oxytocin, alone or in combination with oestradiol, permitted the full inhibition of oxytocin-induced prostaglandin F2 alpha release. To confirm that this effect did not result from the action of oxytocin alone, independently of the action of conceptus secretory protein, a second experiment was undertaken using a similar protocol but without the infusion of conceptus secretory protein. In this situation, oxytocin-induced prostaglandin F2 alpha release was only partially inhibited suggesting that both luteal oxytocin and conceptus secretory proteins are necessary to facilitate the full inhibition of luteolysis during early pregnancy in the ewe.

Periovulatory endocrinology in high ovulating Meishan sows

The present study was designed to investigate the hormone profiles (oestradiol, LH, FSH, inhibin, progesterone) in high ovulating Meishan sows (MS; n = 9) and in contemporary Large-White hybrid control sows (LW; n = 9) during the follicular phase, the periovulatory period and the early luteal phase. Ovulation rate was higher in MS than LW animals (23.7 and 16.6 respectively; P < 0.001) and overall was correlated with the area of the oestradiol peak (P < 0.05) and inhibin concentrations (P < 0.05). Both the duration of and the area of the oestradiol peak were greater in MS than LW (P < 0.01; P < 0.02), as were inhibin concentrations both before and after the LH surge (P < 0.05). Neither basal nor peak concentrations of LH or FSH differed between the breeds (P > 0.05), although FSH concentrations were correlated with the area under the oestradiol peak (P < 0.05). Finally, the time-interval from the onset of the LH surge until the rise in plasma progesterone was shorter in MS than LW (54.5 and 74.3 h respectively; P < 0.01). In conclusion, these results show for the first time that the higher ovulation rate in MS is associated with enhanced oestradiol and inhibin secretion with no significant difference in LH or FSH concentrations. The more rapid luteinization response to the LH surge by MS in terms of plasma progesterone concentrations may be important in ensuring the high level of embryo survival in this breed.

Activation of L-arginine transport (system y+) and nitric oxide synthase by elevated glucose and insulin in human endothelial cells

1. Modulation of L-arginine transport (system y+) and release of nitric oxide (NO) and prostacyclin (PGI2) by elevated glucose and insulin were investigated in human cultured umbilical vein endothelial cells. 2. Elevated glucose induced a time- (6-12 h) and concentration-dependent stimulation of L-arginine transport, which was reversible and associated with a 3-fold increase in intracellular cGMP accumulation (index of NO synthesis) and 75% decrease in PGI2 production. 3. Elevated glucose had no effect on the initial transport rates for L-serine, L-citrulline, L-leucine, L-cystine or 2-deoxyglucose. 4. Resting membrane potential was unaffected by elevated glucose whereas basal intracellular [Ca2+] increased from 65 +/- 5 nM to 136 +/- 16 nM. 5. Insulin induced a protein synthesis-dependent stimulation of L-arginine transport and increased NO and PGI2 production in cells exposed to 5 mM glucose. 6. In cells exposed to high glucose, insulin downregulated elevated rates of L-arginine transport and cGMP accumulation but had no effect on the depressed PGI2 production. 7. Our findings suggest that insulin's normal stimulatory action on human endothelial cell vasodilator pathways may be impaired under conditions of sustained hyperglycaemia.

Role of oxidative stress in the pathogenesis of acute pancreatitis

During the last 10 years, the role of oxidative stress in pancreatitis and the benefits or otherwise of antioxidants has been the subject of numerous research papers. There is general agreement that glutathione and other sulphydryl compounds are depleted while lipid peroxidation is increased in pancreatic tissue during the development of acute pancreatitis. Treatment with antioxidants has been shown to reduce acinar cell injury and oedema in various animal models of pancreatitis, suggesting that the sustained generation of reactive oxygen species depletes cellular antioxidant defences. Evidence for a role for bradykinin and nitric oxide in pancreatitis has been conflicting with some studies suggesting these agents might ameliorate pancreatic dysfunction by enhancing pancreatic blood flow and secretion in response to bradykinin-stimulated generation of nitric oxide from endothelium, while other studies suggest that nitric oxide potentiates pancreatic oxidative stress. Thus, there is clearly a need for well-designed clinical trials to evaluate the protective role of antioxidant therapy in acute pancreatitis.

Regulation of L-arginine transport and nitric oxide release in superfused porcine aortic endothelial cells

1. We have investigated whether changes in extracellular ion composition and substrate deprivation modulate basal and/or bradykinin-stimulated L-arginine transport and release of nitric oxide (NO) and prostacyclin (PGI2) in porcine aortic endothelial cells cultured and superfused on microcarriers. 2. Saturable L-arginine transport (Km = 0.14 +/- 0.03 mM; Vmax = 2.08 +/- 0.54 nmol min-1 (5 x 10(6) cells)-1) was pH insensitive and unaffected following removal of extracellular Na+ or Ca2+. 3. Cationic arginine analogues, including L-lysine and L-ornithine, inhibited L-arginine transport, whilst 2-methylaminoisobutyric acid, beta-2-amino-bicyclo[2,2.1]-heptane-2-carboxylic acid, L-phenylalanine, 6-diazo-5-oxo-norleucine, L-glutamine, L-cysteine and L-glutamate were poor inhibitors. 4. Deprivation of L-arginine (30 min to 24 h) reduced intracellular free L-arginine levels from 0.87 +/- 0.07 to 0.40 +/- 0.05 mM (P < 0.05) and resulted in a 40% stimulation of L-arginine, L-lysine and L-ornithine transport. 5. L-arginine and NG-monomethyl-L-arginine (L-NMMA), but not N omega-nitro-L-arginine methyl ester (L-NAME), trans-stimulated efflux of L-[3H]arginine. 6. Depolarization of endothelial cells with 70 mM K+ reduced L-arginine influx and prevented the stimulation of transport by 100 nM bradykinin, but agonist-induced release of NO and PGI2 was still detectable. 7. Basal rates of L-arginine transport and NO release were unaffected during superfusion of cells with a nominally Ca(2+)-free solution. Bradykinin-stimulated L-arginine transport was insensitive to removal of Ca2+, whereas agonist-induced NO release was abolished. 8. Although bradykinin-stimulated NO release does not appear to be coupled directly to the transient increase in L-arginine transport, elevated rates of L-arginine influx via system y+ in response to agonist-induced membrane hyperpolarization or substrate deprivation provide a mechanism for enhanced L-arginine supply to sustain NO generation.

Induction of L-arginine transport and nitric oxide synthase in vascular smooth muscle cells: synergistic actions of pro-inflammatory cytokines and bacterial lipopolysaccharide

1. The interactions between pro-inflammatory cytokines and bacterial lipopolysaccharide (LPS) on L-arginine transporter and inducible nitric oxide synthase (iNOS) activities were examined in rat cultured aortic smooth muscle cells. 2. LPS induced a concentration (0.01-100 micrograms ml-1) and time (8-24 h)-dependent stimulation of nitrite production which was accompanied by a parallel increase in L-arginine transport. 3. Unlike LPS, activation of smooth muscle cells with either interferon-gamma (IFN-gamma, 100 u ml-1), tumour necrosis factor-alpha (TNF-alpha, 300 u ml-1) or interleukin-1 alpha (IL-1 alpha, 100 u ml-1) failed to stimulate L-arginine transport or increase nitrite accumulation. 4. When applied in combination with LPS (100 micrograms ml-1) both IFN-gamma and TNF-alpha, but not IL-1 alpha, enhanced the effects observed with LPS alone. Furthermore, activation of cells with LPS and IFN-gamma had no effect on uptake of the neutral amino acid L-citrulline but selectively increased the Vmax for L-arginine transport 2.8 fold and nitrite levels from 24 +/- 7 to 188 +/- 14 pmol micrograms-1 protein 24 h-1. 5. The substrate specificity, Na- and pH-independence of saturable L-arginine transport in both unactivated (K(m) = 44 microM, Vmax = 3 pmol micrograms-1 protein min-1) and activated (K(m) = 75 microM, Vmax = 8.3 pmol micrograms-1 protein min-1) smooth muscle cells were characteristic of the cationic amino acid transport system y+. 6. Cycloheximide (1 microM) abolished induction of L-arginine transport and nitrite accumulation in response to LPS and IFN-gamma. In contrast, the glucocorticoid dexamethasone (10 microM, 24 h) selectively inhibited nitrite production. 7. Our results demonstrate that pro-inflammatory mediators selectively enhance transport of L-arginine under conditions of sustained NO synthesis by vascular smooth muscle cells. In addition, the differential inhibition of iNOS and L-arginine transporter activity by dexamethasone suggests that distinct signalling pathways mediate induction of the cationic transport protein and iNOS. The close coupling between substrate supply and NO production may have important implications in the pathogenesis of several disease states including endotoxin shock.

Diabetes-induced activation of system y+ and nitric oxide synthase in human endothelial cells: association with membrane hyperpolarization

1. The activity of the human endothelial cell L-arginine transporter (system y+) has been correlated with cGMP production (index of nitric oxide) and prostacyclin (PGI2) release in umbilical vein endothelial cells cultured from normal or gestational diabetic pregnancies. 2. In non-diabetic and diabetic cells, transport of L-arginine was Na+ and pH independent, inhibited by other cationic L-arginine analogues and unaffected by neutral amino acids. 3. Diabetes was associated with an increased Vmax for saturable L-arginine transport (4.6 +/- 0.13 vs. 9.9 +/- 0.5 pmol (microgram protein)-1 min-1, P < 0.01), but had no effect on initial rates of transport for L-serine, L-citrulline, L-leucine or 2-deoxyglucose. 4. In non-diabetic and diabetic cells, elevated K+ resulted in a concentration-dependent inhibition in the initial rates of transport for L-arginine and the membrane potential-sensitive probe tetra[3H]phenylphosphonium (TPP+). 5. When resting membrane potential was measured using the whole-cell patch voltage clamp technique, diabetic cells were hyperpolarized (-78 +/- 0.3 mV) compared with non-diabetic cells (-70 +/- 0.04 mV, P < 0.04). Accumulation of [3H]TPP+ was also increased in diabetic compared with non-diabetic cells. 6. Basal intracellular cGMP levels were elevated 2.5-fold in diabetic cells, and L-NAME (100 microM), an inhibitor of nitric oxide synthase, abolished basal cGMP accumulation in non-diabetic and diabetic cells. 7. Histamine (10 microM) had no effect on L-arginine transport but evoked significant increases in cGMP in non-diabetic and diabetic cells, which were completely inhibited by L-NAME but unaffected by superoxide dismutase. 8. Basal and histamine-stimulated PGI2 release was decreased markedly in diabetic cells. 9. Our findings demonstrate that gestational diabetes is associated with phenotypic changes in fetal endothelial cells, which result in a membrane hyperpolarization, activation of the human endothelial cell L-arginine transporter (system y+), elevation of basal nitric oxide synthesis and decreased PGI2 production.

Insulin stimulates cationic amino acid transport activity in the isolated perfused rat pancreas

The effects of exogenous insulin, glucagon and streptozotocin-diabetes on influx (15 s) of L-lysine via a cationic amino acid transporter resembling system y+ were investigated in the isolated perfused rat pancreas. In non-diabetic pancreata, transport of L-lysine was saturable with an apparent Km of 2.11 +/- 0.29 mM and Vmax of 2.21 +/- 0.20 mumol min-1 g-1 (n = 6). Bovine insulin (100 mu u ml-1) increased the maximal transport rate (Vmax = 3.49 +/- 0.30 mumol min-1 g-1, n = 4, P < 0.05) for L-lysine 1.6-fold without altering the Km. L-Lysine transport was not elevated significantly in diabetic pancreata, although insulin (100 mu u ml-1) enhanced transport to values measured in non-diabetic preparations. Human glucagon (1.5 x 10(-9) M) had no stimulatory effect on L-lysine transport. These findings provide the first evidence that exogenous insulin stimulates cationic amino acid transport activity in the exocrine pancreatic epithelium. Activation of the cationic pancreatic amino acid transporter may provide a mechanism to enhance the supply of L-arginine and thus sustain nitric oxide-mediated pancreatic secretion in response to islet hormones and secretagogues.

Induction of the antioxidant stress proteins heme oxygenase-1 and MSP23 by stress agents and oxidised LDL in cultured vascular smooth muscle cells

Enhanced expression of the antioxidant stress proteins heme oxygenase-1 (HO-1) and macrophage stress protein (MSP23) by oxidative stress agents and oxidatively modified low density lipoproteins (LDL) was investigated in cultured porcine aortic smooth muscle cells. Treatment of smooth muscle cells with glucose oxidase, CdCl2 or diethylmaleate resulted in a time-dependent (6-48 h) induction of HO-1 and MSP23 expression. Exposure of cells to 100 micrograms protein/ml highly oxidised LDL increased the expression of HO-1 and MSP23 within 24 h, and the induction was dependent on the degree of LDL oxidation. The induction of HO-1 and MSP23 may thus play an important cytoprotective role against oxidative stress in atherogenesis.

Effects of treatment with buserelin on plasma concentrations of oestradiol and progesterone and cycle length in the cow

Treatment of cows with 10 micrograms of the gonadotrophin releasing hormone (GnRH) analogue, Buserelin (Receptal; Hoechst) 12 days after mating results in a 12% improvement in conception rate (Drew & Peters, 1991). We have now investigated the endocrine effects and possible mechanism of action underlying this effect. Treatment of cyclic cows (n = 5) with Buserelin on days 11 and 13 did not affect cycle length or plasma concentration of progesterone, but did significantly (P < 0.05) reduce plasma oestradiol concentration from day 12-16. We conclude that the Buserelin treatment acts by causing a fall in plasma oestradiol which results in a reduction in the strength of the luteolytic drive, improving the chance of an embryo being able to prevent luteal regression.

A role for gamma-glutamyl transpeptidase and the amino acid transport system xc- in cystine transport by a human pancreatic duct cell line

1. The roles of the gamma-glutamyl cycle and the anionic amino acid transport system xc- in mediating L-cystine uptake were investigated in cultured human pancreatic duct PaTu 8902 cells. This cell line exhibits morphological features of normal pancreatic duct cells and expresses gamma-glutamyl transpeptidase (gamma-GT, EC 2.3.2.2), an enzyme involved in the metabolism and regulation of intracellular glutathione (GSH). 2. Uptake of L-cystine (10 microM) was linear for up to 10 min, temperature dependent, Na+ independent, saturable (Michaelis-Menten constant (Km), 86 +/- 25 microM; maximal velocity (Vmax), 109 +/- 33 nmol (mg protein)-1 h-1) and reduced by 80-90% by a 50-fold excess concentration of L-glutamate and L-homocysteic acid, but not L-aspartate. These transport properties resemble those described for system xc-, which exchanges cystine for intracellular glutamate. 3. Acivicin, a known inhibitor of gamma-GT, decreased gamma-GT activity from 2.58 +/- 0.96 to 0.97 +/- 0.11 mU (mg protein)-1 and decreased the initial rates of L-cystine and L-glutamine uptake by 41-55%. Anthglutin (1-gamma-L-glutamyl-2-(2-carboxyphenylhyl)hydrazine), a structurally different inhibitor of gamma-GT, also caused a concentration-dependent (0.01-1 mM) decrease in gamma-GT activity and L-cystine uptake. 4. Neither acivicin nor anthglutin inhibited the uptake of L-glutamate, a poor substrate for gamma-GT. 5. In the presence of a 500-fold excess concentration of glutamate, which should abolish entry of cystine via system xc-, the remaining fraction of cystine transport was inhibited by 50% by acivicin, suggesting that transport is, in part, dependent on the activity of gamma-GT. 6. Cystine transport was also 60-80% inhibited by a series of gamma-glutamyl amino acids (5 mM) including gamma-glutamyl-glutamate, gamma-glutamyl-glutamine and gamma-glutamyl-glycine. alpha-Dipeptides inhibited cystine transport by only 6-22%. 7. These findings demonstrate that in human pancreatic duct PaTu 8902 cells, cystine uptake is mediated by system xc- (50-60%) and the gamma-glutamyl cycle. Our results provide the first evidence linking gamma-GT with cystine transport in human epithelial cells and are of relevance in view of the importance of cystine as a sulphur amino acid source for GSH synthesis in cells exposed to oxidative stress.

Progesterone inhibition of the development of the luteolytic signal in cows

Mated cows that subsequently undergo luteolysis have significantly lower plasma concentrations of progesterone than do cows in which pregnancy is maintained. Two groups of ovariectomized cows were treated with progesterone and oestradiol to recreate luteal phases exhibiting the extremes of plasma concentrations of progesterone (6.0 +/- 0.4 and 12.4 +/- 0.8 ng ml-1) normally seen in intact cows. The effect of this difference in progesterone on the development of the luteolytic signal was determined by monitoring the basal and oxytocin-stimulated plasma concentrations of the principal metabolite of prostaglandin F2 alpha' PGFM on days 12-16 of the simulated luteal phases. Basal PGFM concentrations were similar in the low and high progesterone groups on all days. The mean plasma concentration of PGFM showed a larger increase following oxytocin in the low progesterone group on days 13 and 14 (P < 0.05) and on days 15 and 16 (P < 0.1). These results demonstrate that a low plasma concentration of progesterone results in the development of a stronger luteolytic signal, and provide an explanation for the fact that cows with lower plasma concentrations of progesterone are more prone to embryo loss.

Effect of the level of oestradiol on oxytocin-induced prostaglandin F2 alpha release in the cow

We have investigated the effects of oestradiol-17 beta on the development of the luteolytic signal (prostaglandin F2 alpha (PGF2 alpha) release to an oxytocin challenge) using a steroid-treated ovariectomised cow model. Long-term ovariectomised cows were pre-treated with progesterone for 14 days followed by oestradiol-17 beta for 2 days to induce oestrus (day 0), and were then treated for a further 16 days with physiological doses of progesterone and oestradiol-17 beta to simulate a luteal phase. On day 11 oestradiol was either withdrawn (low group; n = 4), maintained (normal group; n = 4) or increased (high group; n = 4), generating mean (+/- S.E.M.) plasma concentrations of oestradiol from days 12-16 of 0.9 +/- 0.1, 2.3 +/- 0.4 and 3.7 +/- 0.2 pg/ml respectively. Basal and oxytocin-stimulated PGF2 alpha secretion was monitored by measuring concentrations of the principal metabolite of PGF2 alpha, 13,14-dihydro-15-keto PGF2 alpha (PGFM), in plasma samples collected before and after daily i.v. injection of 50 IU oxytocin from days 12-16. Basal PGFM was unaffected by the level of oestradiol treatment. In the normal group significant rises in plasma PGFM were seen following oxytocin on days 12, 13 and 14 (P < 0.05) as well as days 15 and 16 (P < 0.01). In the low group significant elevations in PGFM were only seen on days 15 and 16 (P<0.05), and were smaller (P<0.05) than those seen in the normal group.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of endometrial oxytocin receptors and prostaglandin F2 alpha production in cows by progesterone and oestradiol

We have investigated changes in endometrial oxytocin receptor concentrations and prostaglandin F2 alpha release in response to exogenous oxytocin treatment in ovariectomized cows treated with progesterone and oestradiol, and made comparisons with similar treatment in cyclic cows. In long-term ovariectomized cows, endometrial oxytocin receptors were present (300 fmol mg-1 protein), but no prostaglandin F2 alpha was released in response to oxytocin treatment until after the administration of progesterone. Subsequent administration of a concentration of oestradiol sufficient to induce oestrus resulted in the downregulation of these receptors and the loss of oxytocin responsiveness, which did not reappear within 20 days in the absence of further hormone treatment. When induced oestrus was followed by further treatment with luteal phase concentrations of progesterone and oestradiol, both oxytocin receptors and oxytocin-stimulated release of prostaglandin F2 alpha reappeared by day 16 after oestrus, in a pattern similar to that seen during the luteal phase of cyclic cows. These results demonstrate how progesterone and oestradiol control the development and responsiveness of endometrial oxytocin receptors in cows, and provide a valuable model in which to investigate further the precise control of the oxytocin receptor in this species.

Use of repeated biopsies to monitor endometrial oxytocin receptors in the cow

A transcervical biopsy technique was used for the repeated collection of samples of bovine endometrium from individual cows to monitor the development of oxytocin receptors. The collection of biopsies from three cyclic cows at two-day intervals between days 13 and 17 after oestrus did not result in any shortening of the length of the cycle (mean +/- sem 22.0 +/- 0.5 days). Furthermore, the assay of serial blood samples from three cows around the time of biopsy on days 15 and 17 demonstrated that the technique did not induce any release of prostaglandin F2 alpha (PGF2 alpha). Oxytocin receptors were undetectable (< 20 fmol/mg protein) on days 13 and 15 of the cycle, increased to a mean of 121 +/- 16 fmol/mg protein on day 17 (before luteolysis), and were highest in samples collected at oestrus (498 +/- 84 fmol/mg protein). To determine whether a single biopsy of endometrium would give a representative measure of the concentration of uterine oxytocin receptors, the concentrations were determined in samples of caruncular and intercaruncular endometrium collected from the upper, middle and lower proportions of uteri from three oestrous animals at slaughter. The concentrations were similar in both types of tissue (caruncular 730 +/- 15 fmol/mg protein, intercaruncular 727 +/- 48 fmol/mg protein) and there were no differences between the three regions of the uterus.