Effects of a combination butaphosphan and cyanocobalamin product and insulin on ketosis resolution and milk production.

The objective of this study was to determine the effects of butaphosphan-cyanocobalamin (B+C), glargine insulin, and propylene glycol on resolution of ketosis and average daily milk yield after treatment. Cows from 16 herds in Ontario, Canada, and 1 herd in Michigan were tested at weekly intervals between 3 and 16 DIM. Ketosis was defined as blood ß-hydroxybutyrate (BHB) ≥1.2 mmol/L. All ketotic cows were given a baseline treatment of 3 d of 300 g of propylene glycol orally. Animals were then randomly assigned to treatment with 3 doses of either 25 mL of B+C or 25 mL of saline placebo and 1 dose of either 2 mL (200 IU) of glargine insulin or 2 mL of saline placebo in a 2 × 2 factorial arrangement. Outcomes of interest on all farms were ketosis cure (blood BHB <1.2 mmol/L 1 wk postenrollment), maintenance of ketosis cure (blood BHB <1.2 mmol/L 1 and 2 wk postenrollment), and blood BHB concentrations at 1 and 2 wk postenrollment. Milk weights were collected daily in 1 large freestall herd. Repeated measures ANOVA was used to evaluate blood BHB concentrations 2 wk after treatment and milk production for 30 d after treatment. Poisson regression was used to examine the effect of treatment on cure and maintenance of cure. Due to a regulatory delay causing temporary unavailability of B+C in Canada, data were analyzed in 2 sets of models: one for insulin and the corresponding placebo (n = 620) and one for the full trial (n = 380). Animals with blood glucose concentrations ≤2.2 mmol/L at the time of ketosis diagnosis were 2.1 times more likely (95% CI = 1.2 to 3.7) to be cured if treated with B+C. Animals in lactation 3 or higher that had blood glucose concentrations <2.2 mmol/L at enrollment produced 4.2 kg/d (95% CI = 1.4 to 7.1) more milk if treated with insulin versus placebo and 2.8 kg/d (95% CI = 0.9 to 4.7) more milk if treated with B+C versus placebo. Animals in lactation 3 or higher with blood glucose ≥2.2 mmol/L that were treated with insulin produced 2.3 kg/d (95% CI = 0.3 to 4.4) less milk than untreated controls. No interaction was observed between treatments. This evidence suggests that B+C and insulin may be beneficial for ketosis treatment in animals with blood glucose <2.2 mmol/L at ketosis diagnosis. It also suggests that blood glucose concentration may be an important predictor of success of ketosis treatment.

Randomized clinical field trial on the effects of butaphosphan-cyanocobalamin and propylene glycol on ketosis resolution and milk production.

The purpose of this study was to determine the effects of a butaphosphan-cyanocobalamin combination product (B+C) and 2 durations of propylene glycol treatment (PG; 3 versus 5 d) on ketosis resolution and early lactation milk yield. Cows from 9 freestall herds (8 in Ontario and 1 in Michigan) were tested at weekly intervals between 3 and 16 d in milk. Ketosis was defined as blood ß-hydroxybutyrate (BHB) ≥1.2 mmol/L. Ketotic cows were randomly assigned to treatment with 25 mL of B+C or 25 mL of saline placebo for 3 d and 3 or 5 d of 300 g of PG orally in a 2 × 2 factorial arrangement. Outcomes evaluated for all farms included ketosis cure (blood BHB <1.2 mmol/L at 1 wk after enrollment), maintenance of ketosis cure (blood BHB <1.2 mmol/L 1 and 2 wk after enrollment), and blood BHB concentrations at 1 and 2 wk after enrollment. Daily milk weights were collected in 3 herds. Poisson regression was used to evaluate cure and maintenance of cure, whereas repeated-measures ANOVA was used to evaluate blood BHB concentrations in the 2 wk after enrollment and average daily milk production in the 30 d after treatment. A total of 594 animals were enrolled in the study with 124 treated with B+C and 5 d of PG, 176 treated with B+C and 3 d of PG, 128 treated with saline and 5 d of PG, and 166 treated with saline and 3 d of PG. Animals with blood BHB >2.4 mmol/L at the time of enrollment were 1.7 times more likely [95% confidence interval (CI): 1.4 to 2.2] to cure and had a decrease of 0.25 ± 0.11 mmol/L blood BHB at 1 wk after enrollment if treated with 5 d of PG compared with 3 d, though this response was not seen in animals with BHB of 1.2 to 2.4 mmol/L at enrollment. Cows with blood glucose concentrations <2.2 mmol/L at enrollment produced 3.1 kg/d (95% CI: 1.3 to 5.0) more milk if treated with B+C and 3.4 kg/d (95% CI: 1.7 to 5.1) more milk if treated with 5 d of PG compared with their respective controls. This response was not seen in animals with blood glucose ≥2.2 mmol/L at enrollment and there was no interaction between treatments. These results indicate that extended PG treatment is beneficial in decreasing blood BHB concentrations in more severely affected animals. Additionally, both B+C treatment and extended PG treatment improved milk yield in animals with low blood glucose at the time of ketosis diagnosis.

Room temperature housing results in premature cancellous bone loss in growing female mice: implications for the mouse as a preclinical model for age-related bone loss.

UNLABELLED: Room temperature housing (22 °C) results in premature cancellous bone loss in female mice. The bone loss was prevented by housing mice at thermoneutral temperature (32 °C). Thermogenesis differs markedly between mice and humans and mild cold stress induced by standard room temperature housing may introduce an unrecognized confounding variable into preclinical studies. INTRODUCTION: Female mice are often used as preclinical models for osteoporosis but, in contrast to humans, mice exhibit cancellous bone loss during growth. Mice are routinely housed at room temperature (18-23 °C), a strategy that exaggerates physiological differences in thermoregulation between mice (obligatory daily heterotherms) and humans (homeotherms). The purpose of this investigation was to assess whether housing female mice at thermoneutral (temperature range where the basal rate of energy production is at equilibrium with heat loss) alters bone growth, turnover and microarchitecture. METHODS: Growing (4-week-old) female C57BL/6J and C3H/HeJ mice were housed at either 22 or 32 °C for up to 18 weeks. RESULTS: C57BL/6J mice housed at 22 °C experienced a 62 % cancellous bone loss from the distal femur metaphysis during the interval from 8 to 18 weeks of age and lesser bone loss from the distal femur epiphysis, whereas cancellous and cortical bone mass in 32 °C-housed mice were unchanged or increased. The impact of thermoneutral housing on cancellous bone was not limited to C57BL/6J mice as C3H/HeJ mice exhibited a similar skeletal response. The beneficial effects of thermoneutral housing on cancellous bone were associated with decreased Ucp1 gene expression in brown adipose tissue, increased bone marrow adiposity, higher rates of bone formation, higher expression levels of osteogenic genes and locally decreased bone resorption. CONCLUSIONS: Housing female mice at 22 °C resulted in premature cancellous bone loss. Failure to account for species differences in thermoregulation may seriously confound interpretation of studies utilizing mice as preclinical models for osteoporosis.

Differential association of insulin resistance with cognitive and somatic symptoms of depression.

AIM: To examine the associations of depressive symptoms with insulin resistance, evaluating somatic and cognitive depressive symptoms separately. METHODS: A total of 328 individuals (mean age 60 years) referred for exercise stress testing, taking part in the Mechanisms and Outcomes of Silent Myocardial Ischemia study, completed the Beck Depression Inventory II. A fasting venous blood sample was collected for assessments of insulin and glucose level; the HOMA-IR (homeostatic model assessment of insulin resistance) was calculated. In principal component analysis, Beck Depression Inventory II items were forced to load onto two components (somatic and cognitive depressive symptoms). Adjusting for age, sex, BMI, medication use, smoking, physical activity, diabetes and cardiovascular disease, general linear model analyses were conducted to examine the associations between the components and log HOMA-IR . RESULTS: Principal component analysis showed that nine items loaded onto a cognitive depressive symptoms component and 10 items loaded onto a somatic depressive symptoms component. When examined separately, both components were significantly associated with log HOMA-IR however, when including both components simultaneously in the model, only somatic depressive symptoms remained significantly associated with log HOMA-IR. Back-transformed, a one-unit change in somatic depressive symptoms was associated with a 1.07 (95% CI 1.002, 1.14) change in HOMA-IR and a one-unit change in cognitive depressive symptoms was associated with a 1.03 (95% CI 0.97, 1.14) change in HOMA-IR. CONCLUSION: Somatic depressive symptoms seem to be more strongly associated with insulin resistance than do cognitive depressive symptoms. Monitoring somatic depressive symptoms may be more appropriate than monitoring cognitive depressive symptoms among depressed individuals with high insulin resistance.

Short communication: the effect of temperature on performance of milk ketone test strips.

Ketosis is estimated to affect 15% of early lactation dairy cows. A ketone test strip (Keto-Test; Elanco Animal Health, Greenfield, IN) allows producers a method to determine the concentration of ß-hydroxybutyrate (BHBA) in milk to track individual animal and herd incidence of ketosis. The objective of this study was to determine the effect of altering the temperature of milk and the test strips at the time of the test on the reliability of the Keto-Test. A total of 118 Holstein cows, ranging from 5 to 17 DIM, were selected from a commercial Holstein dairy herd in Michigan. A milk sample was collected from the right rear quarter of each cow during the a.m. milking. Each sample was tested under 4 temperature conditions: (1) Keto-Test strips and milk at room temperature (RT; 24.0 ± 0.1°C; control; manufacturer's instructions), (2) cold strips (10.8 ± 0.9°C) and milk at RT, (3) cold strips and fresh milk, and (4) strips at RT and fresh milk. Milk was recorded as negative (0-99 µmol/L), weak positive (100-199 µmol/L), positive (200-499 µmol/L), or highly positive (≥ 500 µmol/L). Blood samples were collected immediately following milk collection and analyzed for BHBA concentration using a ketone test meter. Cows with blood BHBA concentration of ≥ 1,400 µmol/L were considered positive for subclinical ketosis. Accuracy of the Keto-Test strips under the 4 conditions was determined by the κ coefficient of agreement, using the result of condition 1 as the accepted true value. Additionally, sensitivity and specificity were calculated using the blood BHBA concentrations and results of each of the 4 conditions. Using the Keto-Test 60.2% of cows tested negative for milk BHBA, 24.6% tested weak positive, 14.4% tested positive, and 0.8% tested highly positive. The weighted κ coefficient of agreement between the control condition (1) and condition 2, 3, and 4 and 95% lower and upper confidence intervals were as follows: condition 2=0.71 (0.62, 0.80), condition 3=0.69 (0.60, 0.78), and condition 4=0.63 (0.54, 0.73). These results indicate good agreement between the outcome of condition 1 and conditions 2, 3, and 4. The sensitivities/specificities for 1, 2, 3, and 4 were as follows: 0.77/0.79, 0.74/0.75, 0.69/0.88, and 0.69/0.84, indicating that the test in all temperature conditions had a strong ability to detect the presence of BHBA in milk. In conclusion, the reliability of the Keto-Test strips was not dependent on the temperature of the milk or the test strips.

Differential effects of hydrogen peroxide on indices of endothelial cell function.

The responses of pig aortic endothelial cells to sublethal doses of potentially toxic stimuli were investigated by monitoring K+ efflux, prostaglandin production, and the release of cytoplasmic purines. Xanthine plus xanthine oxidase reversibly stimulated these three parameters of endothelial cell function at doses that were not cytotoxic, as measured by chromium release, adenine uptake, and vital dye exclusion. The effects of xanthine plus xanthine oxidase were inhibited by catalase but not by superoxide dismutase, suggesting that H2O2 was responsible. Reagent H2O2 also reversibly stimulated K+ efflux, prostaglandin production, and the release of purines. The threshold concentration of H2O2 for these effects was approximately 10 microM, which was at least 30-fold lower than that which caused cytotoxicity. In addition to the direct effect of H2O2 in stimulating prostaglandin production (PGI2 and PGE2), prior exposure of endothelial cells to lower doses of H2O2 (less than 0.1 microM) at high oxygen tension inhibited the subsequent stimulation of prostaglandin production by ATP, A23187, and H2O2 itself. We conclude that H2O2 has substantial effects on endothelial physiology at doses up to 3,000-fold lower than those which induce cytotoxicity.

Effects of neutrophil elastase and other proteases on porcine aortic endothelial prostaglandin I2 production, adenine nucleotide release, and responses to vasoactive agents.

The effects of neutrophil elastase on endothelial prostacyclin (PGI2) production, nucleotide release, and responsiveness to vasoactive agents were compared with the effects of cathepsin G (the other major neutral protease of neutrophils), pancreatic elastase, trypsin, chymotrypsin, and thrombin. PGI2 production by pig aortic endothelial cells cultured on microcarrier beads and perfused in columns was stimulated in a dose-dependent manner by trypsin, chymotrypsin, and cathepsin G (1-100 micrograms/ml for 3 min). Thrombin, while active at low concentrations (0.1-10 National Institutes of Health U/ml), induced smaller responses. Neutrophil and pancreatic elastase had little or no effect on PGI2 production. Dose-dependent, selective release of adenine nucleotides was induced by neutrophil elastase (3-30 micrograms/ml). The other proteases were much less active; for example, trypsin (100 micrograms/ml) induced a response only approximately 5% as great as did 30 micrograms/ml neutrophil elastase. After exposure to 30 micrograms/ml neutrophil elastase, cells did not exhibit the characteristic burst of PGI2 production in response to extracellular ATP; responsiveness gradually returned after 40-120 min. This effect was not seen with the other proteases. Elastase partly inhibited responses to bradykinin and had no effect on PGI2 production that was stimulated by ionophore A23187. There was no evidence of cytotoxicity, as measured by release of lactate dehydrogenase. Neutrophil degranulation can generate concentrations of elastase and cathepsin G comparable with those tested in the present study, and the effects of these enzymes on endothelial function lead us to suggest that they may play a role in vasoregulation and vascular pathology.

Lysosomal hydrolases of human vascular cells: response to agonists of endothelial function.

Endothelial injury has been proposed as a feature of a wide variety of vascular diseases, and release of endothelial lysosomal hydrolases could contribute to the pathological changes seen. We have determined the relative activities of 14 glycosidases, two esterases and four peptide hydrolases in human umbilical vein endothelial cells and investigated whether known agonists of endothelial function, or materials known to modulate hydrolase secretion in other phagocytic cells, influenced the activity or secretion of these enzymes by human umbilical vein endothelial cells. Hexosaminidase, beta-galactosidase, beta-glucuronidase and alpha-iduronidase accounted for most of the measured glycosidase activity. Acid phosphatase activity greatly exceeded arylsulphatase activity, and most of the measured peptidase activity was due to acid peptidases. Optimum pH and apparent Km values were determined for the most abundant hydrolases. Exposure of human umbilical vein endothelial cells to bradykinin, thrombin or interleukin-1 resulted in negligible release of either hexosaminidase or lactate dehydrogenase (LDH), in contrast to phorbol myristate acetate, which caused a parallel, dose-dependent release of both enzymes. Treatment of these cells with calcium ionophore A23187, trypsin or platelet-activating factor, caused less than 10% release of either hexosaminidase or LDH. Agents known to modulate lysosomal enzyme secretion by other phagocytic cells failed to induce selective secretion of lysosomal enzymes by human umbilical vein endothelial cells.

Evidence for an early inflammatory response in the central nervous system of mice with scrapie.

In Alzheimer's disease, the most prevalent of the neurodegenerative diseases, inflammation of the CNS contributes to the pathology and is a target for therapy. In contrast, the group of neurodegenerative conditions known as the Prion Diseases have been widely reported as lacking any inflammatory elements despite the many similarities between the pathologies of Alzheimer's Disease and Prion Diseases We have found evidence for an inflammatory component in mouse scrapie, characterized by microglial activation and T-lymphocyte recruitment, which appears long before any clinical signs of the disease and spreads along well-defined anatomical pathways. These observations emphasize the potential value of murine scrapie as a model for studying the inflammatory pathology of other neurodegenerative diseases.

ADP plays a key role in thrombogenesis in rats.

The relative importance of ADP, arachidonic acid metabolites and serotonin as thrombogenic factors was evaluated in rats by comparing, after oral administration, the effects of two inhibitors of ADP-induced platelet aggregation (ticlopidine and PCR 4099), three cyclo-oxygenase inhibitors (aspirin, triflusal and indobufen) and a selective serotonin 5HT2 receptor antagonist (ketanserin) on platelet aggregation, in four platelet-dependent thrombosis models and on bleeding time. Platelet aggregation induced by ADP and collagen was completely inhibited by ticlopidine and PCR 4099 whereas only the collagen aggregation was reduced by the cyclo-oxygenase inhibitors. Ketanserin or a depletion of platelet serotonin by reserpine did not affect platelet aggregation. Ticlopidine and PCR 4099 greatly prolonged rat tail transection bleeding time. This is probably related to their known ability to inhibit ADP-mediated platelet aggregation. In contrast, the cyclooxygenase inhibitors did not affect bleeding time at all. Reserpine and ketanserin prolonged bleeding time by interfering with the action of serotonin on the vascular wall. Ticlopidine and PCR 4099 were very potent antithrombotics in all the models. Aspirin, only at a high dose, inhibited poorly thrombus formation on a silk thread in an arterio-venous shunt, suggesting that the inhibition of cyclo-oxygenase was not responsible. Triflusal was inactive in all models while indobufen slightly reduced thrombus formation in the silk thread and metallic coil models. Ketanserin and reserpine reduced thrombus only in the metallic coil model. Thrombus formation was greatly reduced in fawn-hooded rats, which lack ADP in their platelet dense granules because of a genetic storage pool deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Purinoceptors in the rat heart.

The effects of an intracoronary bolus of adenosine triphosphate (ATP), alpha, beta-methylene ATP (APCPP), beta, gamma-methylene ATP (APPCP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and adenosine on coronary tone and ventricular myocardial contraction were investigated in the perfused rat heart. Adenine nucleotides, given by bolus injection were negatively inotropic in amounts greater than 3 X 10(-7) mol. The potency order was ATP greater than ADP greater than AMP. Adenosine (less than 1 X 10(-5)mol) had no effect on ventricular myocardial contraction. Adenine nucleotides and adenosine (1 X 10(-10)-1 X 10(-7) mol) reduced coronary tone. The potency order was ATP greater than ADP greater than AMP = adenosine. The ATP analogue APPCP was less active than ATP at reducing coronary tone, and APCPP had no vasodilator effect. This suggests the presence of a P2-purinoceptor, subclass P2Y, which mediates vasodilation. ATP and ADP increased the concentration of prostacyclin (measured as 6-keto prostaglandin F1 alpha) in the perfusate, but only after injection of greater than 3 X 10(-7) mol, suggesting that the vasodilator responses to ATP and ADP were not mediated by prostacyclin. AMP and adenosine had no effect, even at 1 X 10(-5) mol. At a dose of 3 X 10(-9) mol, approximately 40% of ATP and 70% of ADP was converted to AMP and adenosine whilst passing through the heart. The amounts of AMP and adenosine formed, however, were insufficient to account for the vasodilator effects of ATP and ADP. 6 Vasodilatation mediated by AMP and adenosine was inhibited by an infusion of 8-phenyltheophylline (8-PT; 2 x 10-5 M) indicating interaction with a P1-purinoceptor. Vasodilatation induced by ATP (at doses at which AMP and adenosine had no action) was also depressed by 8-PT indicating either an action of ATP on PI-purinoceptors, or an effect of 8-PT on P2y receptors. 7 Vasodilatation induced by AMP was unaltered during an infusion of alpha,beta-methylene ADP (2 x 10-6 M, which inhibited breakdown of AMP to adenosine by 54.2 +/- 1.5%, n = 4). This suggests that AMP acted directly, and it did not require conversion to adenosine to induce vasodilatation. 8 The ATP analogues APCPP (1 x 10-9_1 x 10-8 mol) and APPCP (1 x 10-8_l x 10-7mol) increased coronary tone, as did high doses (I x 10-5 mol) ofATP and ADP, indicating the presence of an additional P2-purinoceptor, subclass P2X, mediating vasoconstriction.

Uptake of 5-hydroxytryptamine by rat blood platelets and its inhibition by adenosine 5'-diphosphate.

1 The uptake of 5-hydroxytryptamine (5-HT) by rat blood platelets in citrated plasma was linear for at most 10 s and was substantially complete within 3 minutes. 2 Adenosine 5'-diphosphate (ADP) was a potent inhibitor of 5-HT uptake (Ki=0.38 muM) and kinetic analysis revealed that the inhibition was not competitive. 3 Inhibition of 5-HT uptake by ADP was abolished in the presence of prostaglandin E1 and 2-n-amylthio-AMP, which also inhibit the stimulant actions of ADP on blood platelets. 4 It is concluded that ADP could inhibit 5-HT uptake by changing the Na+/K+ distribution across the cell membrane, and the biological significance of this is discussed.

Stimulation of endothelial prostacyclin production plays no role in endothelium-dependent relaxation of the pig aorta.

Stimulation of prostacyclin production by pig aortic endothelial cells adhering to microcarrier beads superfused in columns, or 3H release from cells prelabelled with [3H]-arachidonate, was studied in response to a range of agents that induce endothelium-dependent vascular relaxation. Bradykinin, adenosine triphosphate (ATP) and ionophore A23187 each stimulated release of prostacyclin from unlabelled cells and of 3H from prelabelled cells but acetylcholine did not. Bradykinin induced a parallel, dose-dependent increase in 3H release and 86Rb efflux, measured simultaneously from columns of aortic endothelial cells preloaded with 86Rb and [3H]-arachidonate. The rank-order of effectiveness at inducing both 3H and 86Rb release, measured simultaneously from columns of aortic endothelial cells prelabelled with 86Rb and [3H]-arachidonate and challenged with maximal doses of each agonist, was: A23187 greater than bradykinin greater than ATP. The similarity between agonist-induced 3H release (from cells prelabelled with [3H]-arachidonate) and 86Rb efflux indicates that a common mechanism may be responsible, and the effectiveness of ionophore A23187 suggests that a rise in the intracellular level of calcium may be involved. The lack of effect of acetylcholine on release of prostacyclin from unlabelled cells or of 3H from cells prelabelled with [3H]-arachidonate provides further evidence that acetylcholine acts on endothelial cells by a mechanism that does not involve calcium mobilisation. Although bradykinin, ATP and ionophore A23187 each induced release of prostacyclin from aortic endothelial cells, prostacyclin did not relax the pig aorta. Furthermore, endothelium-dependent relaxation was unaffected by pretreating aortic strips with aspirin. It therefore appears that neither prostacyclin nor any other cyclo-oxygenase product mediates endothelium-dependent relaxation of the pig aorta.

Effects of sulphinpyrazone and aspirin on prostaglandin I2 (prostacyclin) synthesis by endothelial cells.

Synthesis of prostaglandin I2, (PGI2, prostacyclin) by vascular endothelium (assayed by the ability of cultured endothelial cells to inhibit platelet aggregation) was inhibited by aspirin. At 100 mumol/l aspirin completely blocked measurable PGI2 production, but endothelial cells had substantially recovered their ability to synthesize PGI2 24 h after removal of the drug. In contrast, the effect of 1 mmol/l aspirin was still evident 24 h after drug withdrawal. Sulphinpyrazone also inhibited PGI2 synthesis, but was about 100 fold less potent than aspirin, and the effect of the drug was lost within 24 h of its addition, even when endothelial cells were left in contact with the drug during this period.

5-Hydroxytryptamine and dopamine transport by rat and human blood platelets.

1 Uptake of 5-hydroxytryptamine (5-HT) by rat platelets in plasma was very rapid and diffusion did not contribute significantly at substrate concentrations that did not saturate the active transport.2 Under conditions which allowed measurement of initial rates of uptake, kinetic analysis revealed a high affinity uptake mechanism for 5-HT (K(m) = 0.7 muM).3 Uptake of dopamine was relatively slow and involved a lower affinity (K(m) = 70 muM) active transport process. Diffusion contributed significantly at concentrations that did not saturate the active transport.4 5-HT competitively inhibited uptake of dopamine, and vice versa; K(i) values for both amines were similar to their respective K(m) values for uptake.5 Chlorimipramine, desmethylimipramine and benztropine were tested as uptake inhibitors. Each was equipotent against 5-HT and dopamine, although the absolute potency of the drugs varied greatly. Chlorimipramine was the most potent (K(i)## 100 nM), and kinetic analysis revealed that the inhibition was competitive against both 5-HT and dopamine.6 Similar results were obtained in studies with human platelets: K(m) values for 5-HT and dopamine were about 1 muM and 100 muM respectively. Activity profiles of inhibitors were also similar: each compound tested was equipotent against 5-HT and dopamine, and the two amines each competitively inhibited uptake of the other.7 We conclude that dopamine is actively transported by platelets via the 5-HT uptake mechanism, but with a much lower affinity. There is no high-affinity dopamine-specific mechanism corresponding to that in the corpus striatum. Consequently although platelets may be valid models of transport in 5-hydroxytryptaminergic neurones, they should not be regarded as models for the dopamine transport mechanism found in dopaminergic neurones.

Endothelium-dependent relaxation of the pig aorta: relationship to stimulation of 86Rb efflux from isolated endothelial cells.

Bradykinin, adenosine triphosphate (ATP) and acetylcholine each relaxed histamine-contracted strips of pig aorta in a dose-dependent manner. These relaxations were abolished when the endothelium was removed. Relaxation induced by ATP was mimicked by adenosine diphosphate (ADP) but adenosine monophosphate (AMP) and adenosine were about 120 times less potent. Relaxation induced by acetylcholine was antagonized by atropine in a competitive manner, and carbachol induced the same degree of relaxation as acetylcholine, but was about 10 times less potent. The calcium ionophore, A23187, also induced a dose-dependent relaxation of pig aortic strips provided the endothelium was present, suggesting that a rise in the level of ionized calcium within the endothelial cells is one means by which vascular smooth muscle relaxation can be triggered. Bradykinin, ATP, ADP, AMP, adenosine and A23187 each induced a dose-dependent increase in 86Rb efflux from preloaded pig aortic endothelial cells. The dose-response curves for stimulation of 86Rb efflux and for endothelium-dependent relaxation were similar for each individual compound. ADP was equipotent with ATP, but AMP and adenosine were about 120 times less potent. Neither acetylcholine nor carbachol, in concentrations that induce endothelium-dependent relaxation, had any effect on 86Rb efflux from isolated aortic endothelial cells. Lanthanum, which blocks calcium influx, abolished the increases in 86Rb efflux induced by bradykinin and ATP, and the calcium ionophore A23187 was the most effective stimulant of 86Rb efflux, suggesting that the potassium transport induced by these agents is calcium-activated. It is concluded that endothelial responses to bradykinin and ATP can be assessed by monitoring 86Rb efflux, which probably reflects a calcium-activated efflux of potassium associated with the endothelium-dependent vascular relaxation induced by these agents. This pathway is apparently not involved in endothelial responses to acetylcholine.

The effects of radiographic contrast media on myocardial contractility and coronary resistance: osmolality, ionic concentration, and viscosity.

With the ongoing development of new contrast agents, questions develop concerning the cardiac effects of these drugs. We used the perfused rat heart model to investigate the effects on cardiac and coronary function of hypertonic ionic (sodium chloride) and nonionic (glucose) solutions and conventional and low osmolality radiographic contrast media (RCM). We also evaluated the concurrent effects of RCM on prostacyclin and adenine nucleotide/nucleoside release. Hypertonic solutions of glucose had little effect on myocardial contraction (increase up to 7.7 +/- 0.9%), while NaCl solutions of similar osmolality were negatively inotropic (contractile force decreased up to 76.1 +/- 9.2%). Conventional RCM were negatively inotropic (decrease of 59.6 +/- 5.6% with Conray (Mallinckrodt Pharmaceuticals, St. Louis, MO), 32.2 +/- 3.2% with Angiovist 282 (Berlex Laboratories, Cedar Knolls, NJ]; two nonionic RCM, Iopamidol and Iotrol had little effect on myocardial contraction (reduction of 6.9 +/- 1.4% and increase of 12.0 +/- 2.9%, respectively). Hypertonic solutions of glucose and NaCl reduced coronary resistance in direct relationship to hyperosmolality. Conventional RCM also reduced coronary resistance, while the nonionic media caused minor alteration. None of the solutions tested altered prostacyclin or adenine nucleotide/nucleoside efflux from the heart. A solution of Ficoll 70 with a viscosity similar to that of RCM increased myocardial contraction by 9.6 +/- 3.6% and had no effect on coronary resistance, indicating that viscosity per se did not contribute to the negative inotropic effects or the reduction in coronary resistance. Hypertonic solutions, including conventional RCM, reduce coronary resistance as a result of their hyperosmolality Negative inotropic effects, however, are more related to high ionic concentration than to osmolality.

Human platelet reactivity during stressful diagnostic procedures.

Conscious subjects undergoing cardiac catheterization and other diagnostic procedures showed a rise in platelet-aggregation response to adenosine diphosphate (ADP) one hour before and during the procedure. The responses returned towards normal one hour afterwards. The response to glass beads was decreased one hour before the procedure, but was unchanged in subsequent samples. Plasma-free fatty acid (FFA) levels were increased during the procedure, and one hour afterwards, but had returned to normal by the following day. Platelet counts were slightly reduced on the day after the procedure. It is suggested that catecholamines released due to emotional stress may be responsible for the increased platelet responses to ADP and that this could influence the development of thrombosis and atherosclerosis.

Desensitization of agonist-stimulated prostacyclin release in human umbilical vein endothelial cells.

Prostacyclin (PGI2) release was studied in perfused columns of human umbilical vein endothelial cells cultured on microcarrier beads. Substantial homologous desensitization of PGI2 release occurred when cells were exposed to agonist for 2 min after a previous exposure; the extent depended on the concentration and duration of the first challenge. Recovery from exposure to ATP or bradykinin was complete in less than 80 min; recovery from thrombin was incomplete after greater than 80 min, and this was apparently related to its proteolytic activity. Experiments with ibuprofen, a reversible inhibitor of cyclo-oxygenase, demonstrated that homologous desensitization did not involve inactivation of cyclo-oxygenase. ATP and bradykinin did not induce heterologous desensitization. Thrombin and trypsin induced cross-desensitization, but neither agonist significantly reduced responses to ATP or bradykinin, suggesting that a common proteolytic mechanism is responsible for their ability to induce PGI2 synthesis. We conclude that desensitization of PGI2 release in response to physiological agonists is generally agonist-specific and involves modulation of molecular events at or close to the receptors involved, rather than inactivation of prostanoid biosynthesis.

Characteristics of the P2 purinoceptor that mediates prostacyclin production by pig aortic endothelial cells.

Release of prostacyclin was studied by superfusing small columns containing cells cultured on microcarrier beads. Transient dose-dependent stimulation of prostacyclin release by up to 500-fold was induced by adenosine 5'-triphosphate (ATP; 0.5-50 microM). Adenosine 5'-diphosphate (ADP) gave similar responses, whereas adenosine 5'-phosphate (AMP) and adenosine were essentially inactive. Of other natural nucleotides tested only uridine 5'-phosphate (UTP) was active. The L-enantiomers of ATP and ADP were inactive. 2-Cl-ATP was approximately 100 times more potent than ATP; 2-MeS-ATP was also more potent (threshold 0.05 microM) but its maximal effectiveness was less than 20% that of ATP; 2-EtS-ATP had a similar threshold to ATP but was even less effective than 2-MeS-ATP. Phosphorothioate nucleotide analogues of ATP or ADP were active, with no stereoselectivity between Rp and Sp diastereoisomers. No analogue tested showed antagonist activity. We conclude that ATP mediates endothelial prostacyclin release apparently via a P2Y receptor, although there are some striking differences from the previously described P2Y receptor mediating endothelium-dependent vasodilation in pig aorta.