Equivalent inhibition of in vivo platelet function by low dose and high dose aspirin treatment

In vitro platelet function was inhibited in healthy volunteers by two different doses of aspirin, as confirmed by measurement of maximum serum production of thromboxane B2 (TXB2) by platelets. 75 mg aspirin did not fully inhibit serum TXB2 production after 24 hours, whereas 300 mg aspirin did. Inhibition of platelet function in vitro was maintained by both 75 mg/day aspirin or 300 mg/alternate day aspirin. In contrast, in vivo production of TXB2, measured as urinary levels of the 11-keto-TXB2 metabolite, was inhibited similarly by both doses of aspirin throughout the study. These findings suggest that 75 mg/day aspirin may be sufficient adequately to inhibit platelet aggregation in vivo.     

Short-term therapy of atherosclerosis with low dose indomethacin: an experimental study

The effects of low dose indomethacin therapy in primary prevention of diet-induced atherosclerosis of rhesus monkeys was studied. The parameters studied were serum cholesterol concentration, thromboxane A2 (T x B2), prostacyclin (6-keto-PGF1 alpha) in serum/plasma, and the extent and intensity of coronary atherosclerosis. Although indomethacin did not affect serum cholesterol, it reduced serum T x B2 significantly (P less than 0.01). Plasma 6-keto-PGF1 alpha was not restored to the pretreatment level. A significant protective role of the drug was noted as far as coronary atherosclerosis is concerned (P less than 0.01).     

Therapeutic value of intravenous heparin in microvascular surgery: an experimental vascular thrombosis study

In an attempt to decrease a 10 to 15 percent vascular thrombosis rate leading to graft occlusion, low-dose human-grade heparin was studied to determine if carefully monitored intravenous therapy would increase 7-day patency in a known potent thrombosis model. In New Zealand white rabbits, the type of infusate administered intravenously, either saline (30 animals) or heparin (35 animals), was selected at random after completing a 2-mm arterial inversion graft in the femoral artery. A 72-hour infusion was used in all animals; the control group received sterile saline and the experimental group received a heparin infusion at 45 microliters per hour after a 500-unit bolus. All grafts in both groups were patent at the time of groin closure. Patency in the heparin-perfused group was 67 percent (24 of 35) as compared to 19 percent (6 of 30) in the control group (p less than 0.05) 1 week postoperatively. Scanning electron microscopy showed significantly less dense fibrin deposition and a decrease in the number of aggregated platelets in the heparin-perfused grafts. Partial tissue thromboplastin time values in the experimental group ranged between 55 and 75 seconds (control 20 to 25 seconds). We have shown that heparin, an inexpensive and readily available agent, maintains 1-week microarterial patency and results in few complications in a reliable, reproducible, and versatile thrombosis model. The clinical ramifications of using an antiplatelet agent that diminishes fibrin deposition in microsurgery are apparent.     

Repeated administration of low dose ketamine for the treatment of monoarthritic pain in the rat

The aim of the present study was to observe the effect of repeated subcutaneous (sc) injections of low doses of ketamine for the treatment of acute inflammatory pain in a complete Freund's adjuvant-induced monoarthritic pain model in rats. The results show: (1) sc injection of ketamine at a dose of 2 mg x kg(-1) or 10 mg x kg(-1) produced significant analgesia (P<0.01) in arthritic rats starting from the 2nd week and 3rd week, respectively. (2) Repeated administration of ketamine produced a significant reduction of the circumference of the arthritic ankle (P<0.05 and P<0.01 with different doses). (3) The body weight of the rats was not affected by continuous administration of ketamine for 4 weeks. No abnormal locomotor behavior was observed (It was concerned but not systemically evaluated in this study). The results suggest that repeated sc injection of ketamine for 4 weeks significantly reduce inflammatory pain in monoarthritis without notable aversive side effects.     

Biochemical changes induced by grape seed extract and low level laser therapy administration during intraoral wound healing in rat liver: an experimental and in silico study

In the present study, the changes that occur in rat liver tissue as a result of the use of grape seed extract (GSE) and low level laser therapy (LLLT) in intraoral wound (IW) healing are analyzed using biochemical parameters. Diode laser application groups received 8 J/cm² dose LLLT once a day for 4 days (810 nm wavelength, continuous mode, 0.25 W, 9 s). As a result of the biological parameter analysis, it was determined that the oxidative damage caused by the IWs and recovery period on 7th and 14th days could be substantially removed with GSE applications that have antioxidant capacity especially in rat liver tissue. In addition, the active compound of grape seed, catechin is studied in the active site of glycogen synthase kinase 3 (GSK3) target using molecular modeling approaches. Post-processing molecular dynamics (MD) results for catechin is compared with a standard GSK3 inhibitor. MD simulations assisted for better understanding of inhibition mechanism and the crucial amino acids contributing in the ligand binding. These results along with a through free energy analysis of ligands using sophisticated simulations methods are quite striking and it suggests a greater future role for simulation in deciphering complex patterns of molecular mechanism in combination with methods for understanding drug-receptor interactions.     

L-NG-monomethyl arginine inhibits the vasodilating effects of low dose of endothelin-3 on rat mesenteric arteries

We have reported that low doses of endothelin-3 (ET-3) elicited continuous vasodilation of rat mesenteric arteries, which is possibly related to endothelium-derived relaxing factor (EDRF). In order to clarify whether or not the vasodilating effects of ET-3 are associated with EDRF, we examined the effects of L-NG-monomethyl arginine (L-NMMA), an analog of L-arginine, on low-dose ET-3 induced vasodilation of rat mesente-Hc arteries. Infusion of 50 microM L-NMMA inhibited the vasodilation induced by 10(-13) M ET-3 and rather elicited an increase in perfusion pressure, which itself was decreased by infusion of 150 microM L-arginine. In the presence of 50 microM L-NMMA, 10(-13) M ET-3 did not elicit any vasodilation of the mesenteric arteries preconstricted with NE, in which 150 microM L-arginine, but not D-arginine, caused considerable vasodilation. These data suggest that the vasodilating effects of low doses of ET-3 are associated with EDRF as an endothelium-derived nitric oxide.     

Low dose aspirin,platelet function and prostaglandin synthesis: Influence of epinephrine and alpha adrenergic blockade

The present investigation has evaluated the effects of low doses of oral aspirin on platelet prostaglandin synthesis and function. Whole (80 mg) or half (40 mg) tablets of baby aspirin given to adults had no effect on the response of their platelets to thrombin, ADP and epinephrine, but selectively inhibited aggregation induced by threshold concentrations of arachidonate 16–20 hours after ingestion. Larger amounts of arachidonate overcame the inhibition imposed by low dose aspirin, but not by adult aspirin tablets (600 mg). Epinephrine, in concentrations too low to cause aggregation, restored the sensitivity of aspirin-treated platelets to arachidonate. Studies with a-adrenergic agonists, antagonists and calcium channel blockers demonstrated that the corrective effect of epinephrine was mediated by an a-adrenergic receptor influence on calcium modulation of the platelet membrane.     

Sex-related difference in the effect of aspirin on prostaglandin metabolism in rat platelet and aorta

The effect of aspirin on the production of the arterial prostacyclin (PGI₂)-like substance and platelet malondialdehyde (MDA) was investigated in rats of both sexes. No significant sex difference observed with the arterial PGI₂-like substance. But, following the aspirin treatment, the production of the PGI₂-like substance was significantly decreased in male rats. There was significant sex difference in the production of platelet MDA before the aspirin treatment. And after the aspirin treatment, platelets of both sexes produced significantly less MDA. It is possible that sex difference in the effect of aspirin is related to the quantitative difference of cyclooxygenase activity between platelets and vasal wall.     

Prazosin treatment suppresses increased vascular permeability in both acute and passively transferred experimental autoimmune encephalomyelitis in the Lewis rat

Prazosin, an antagonist of the alpha 1-adrenoceptor, has been found to suppress the clinical and histologic expression of experimental autoimmune encephalomyelitis (EAE) in the Lewis rat. This effect appears to be specific for the alpha 1-receptor. To determine the effect of this drug on vascular permeability to serum proteins and inflammatory cells, leakage of serum proteins into the central nervous system (CNS) was measured with [125I]albumin, and quantitation of cellular inflammation was determined by an estimation of total DNA. The results show that in both actively induced and passively transferred models of the disease, treatment with prazosin significantly suppresses leakage of serum proteins into the CNS but does not significantly suppress the increase of DNA. The results of the [125I]albumin studies additionally support the conclusion that the extent of vascular permeability to serum proteins in the spinal cord is a significant correlate of clinical disease. The results of the DNA estimation were at variance with the histologic evidence of cellular infiltration. We conclude that treatment with prazosin has a significant effect on the development of vascular edema in EAE. These results additionally validate a role for the adrenergic receptor in the development of EAE, and support the hypothesis that the primary site of action of prazosin is on the vascular alpha 1-adrenoceptor.     

Inhibition of platelet aggregation with intravenous and oral administration of carboprostacyclin in man

Intravenous infusion of carboprostacyclin, a chemically stable analogue of prostacyclin (PGI₂) resulted in ex-vivo inhibition of ADP-induced platelet aggregation at doses that did not produce significant changes in blood pressure or heart rate. Oral administration of relatively large doses of this compound also inhibited ex-vivo ADP-induced platelet aggregation but this was accompanied by headache, facial flush, tachycardia and changes in blood pressure.     

The protective activity of 2 normal immunoglobulin preparations for intravenous administration in experimental Pseudomonas aeruginosa infection

The antibody levels in 18 batches of the preparations of human immunoglobulin, Immunovenin and Immunovenin-Intact, for intravenous injection were determined in the enzyme immunoassay with the use of the mixture of P. aeruginosa lipopolysaccharide antigens of seven immunotypes. The average antibody titers in these preparations were identical. The preparations were found to have protective action against P. aeruginosa experimental infection in mice.     

Kinetic analyses of the effects of hyperoxia and hypoxia on vascular cyclooxygenase activity in vitro

Kinetic analyses were performed to understand the mechanism of hyperoxic induced inhibition of prostacyclin synthesis by human umbilical arteries. Brief exposure of arterial segments to oxygen resulted in over 30% decrease in Vmax of cyclooxygenase in treated vessels. In contrast, cyclooxygenase from hypoxic arterial segments showed approximately a 49% increase in Vmax. There were no significant differences in apparent Km values. These studies suggest that the decreased production of prostacyclin by hyperoxic tissue is due to cyclooxygenase inactivation.     

Enantioselective pharmacodynamics of the nonsteroidal antiinflammatory drug ketoprofen: in vitro inhibition of human platelet cyclooxygenase activity.

The pharmacological activity of ketoprofen enantiomers was investigated in humans by an in vitro method. The antiplatelet effect of ketoprofen was assessed by measuring the inhibition of platelet thromboxane B2 (TXB2) generation during the controlled clotting of whole blood obtained from each of four healthy volunteers. Ketoprofen was added separately to whole blood as a range of concentrations of (1) predominantly (S)-ketoprofen, (2) racemic ketoprofen, and (3) predominantly (R)-ketoprofen. (S)-Ketoprofen was found to be solely active at inhibiting human platelet TXB2 production; (R)-ketoprofen was devoid of such activity and did not modify the potency of its optical antipode. A relationship between the percentage inhibition of TXB2 generation and the unbound concentration of (S)-ketoprofen in serum was modelled according to a sigmoidal Emax equation. The mean (+/- SD) serum unbound concentration of (S)-ketoprofen required to inhibit platelet TXB2 generation by 50% (EC50) was 0.320 (+/- 0.062) ng/ml. This value for ketoprofen is considerably lower than previously reported values for (S)-ibuprofen and (S)-naproxen.     

Thromboxane production in the pregnant rat: differential recovery by platelets and uterus following aspirin administration

Radioimmunologic data provide evidence that the pregnant rat uterus produces thromboxane B2 (TXB2). To provide further evidence that this radioimmunologic compound is TXB2, an extract of media incubated with uteri from 21-day pregnant rats was passed through a silicic acid column and each 1-ml eluate was tested for its ability to displace tritiated TXB2 from antibody. One peak was found and it corresponded to that of authentic TXB2 eluted through an identical column. Rechromatographing the peak on a thin-layer plate, the radioimmunologic peak again corresponded with the TXB2 standard. Since blood platelets are a major source of thromboxane, their presence in the vasculature of tissues makes them a possible contaminating factor. Following aspirin (300 mg) intubation into rats on either gestational Day 18, 19 or 20, in vitro production of the TXB2 by isolated uteri and washed platelets was determined and compared to the same tissues from untreated rats. When aspirin was administered 1 day prior to autopsy, TXB2 production by uterine tissue was 32% of the control uterus. Platelet TXB2 production was 25% of control platelets. When aspirin was administered 2 days prior to autopsy, uterine TXB2 production increased to 60% of the control, while platelet TXB2 was 43% of the control. When aspirin was administered 3 days prior to autopsy, uterine TXB2 production was higher than that of control, while platelet TXB2 production was 54% of the control. The more rapid recovery of TXB2 by uterine tissue compared to platelets suggest that the TXB2 produced by uterine tissue is not due solely to platelet contamination.     

Kinetics of amiloride in rat following oral and intravenous administration

The disposition profile of amiloride, a potassium sparing agent, was studied in rats by using an HPLC method coupled to spectrofluorometric detection. Amiloride was administered orally and intravenously at the dose of 10 mg/Kg. The most relevant pharmacokinetic parameters are described for both administration routes.     

Pharmacokinetics of propetamphos following intravenous administration in the F344 rat

Propetamphos [(E)-l-methylethyl 3[[(ethylamino)methoxyphosphinothioyl]oxy]-2-bu-tenoate], the active ingredient in Safrotin,® is an organophosphate developed by Sandoz, Ltd.® (Switzerland) as an insecticide (1). Although metabolism of propetamphos has been previously investigated (2,3), there is no pharmacokinetic data available in the literature. The current studies were undertaken to investigate the pharmacokinetics of propetamphos following intravenous administration in male and female Fischer 344 (F344) rats. Rats were dosed via an indwelling jugular cannula at a dose of 12 mg/kg (one-tenth the oral LD-50). Blood samples were withdrawn via the cannula at predetermined timepoints to quantitate plasma concentrations of propetamphos over time. Propetamphos is highly bound to plasma proteins (free fraction = 0.06). Free propetamphos concentration in plasma vs. time data were analyzed by noncompartmental methods. The terminal elimination rate constant, λ, was significantly different for males versus females (0.015 min^?1 for males and 0.037 min^?1 for females, p = 0.001). Plasma was cleared of unbound propetamphos at rates of 0.559 ± 0.069 and 0.828 ± 0.181 L/min/kg for males and females (mean ± standard error). Mean residence times (MRTs) for propetamphos in the body for males and females were 28.3 ± 5.7 and 14.4 ± 3.5 min, and the volume of distribution at steady state (Vss) was 14.7 ± 2.6 and 12.3 ± 4.5 L/kg. The differences in these parameters, clearance (CI), MRT, and Vss, were not statistically significant at the p < 0.05 level for males versus females, but MRT was nearly significantly different (p = 0.08). Because of the rapid elimination of propetamphos from plasma following intravenous administration, it is unlikely that propetamphos would bioaccumulate in environmentally exposed animals. Although the pharmacokinetic parameters were not statistically different for males and females in these studies, there was a clear clinical difference in their susceptibility to propetamphos toxicity. Female rats presented with overt signs of organophosphate intoxication, whereas males were only slightly effected. The observed gender-related clinical difference in susceptibility to toxicity suggests that there may be a difference in the extent of elimination due to activation versus detoxication of propetamphos in males and females. Another possible explanation for the clinical difference in propetamphos toxicity is that inhibition of acetyl-cholinesterase by the activated, oxygenated form of propetamphos (propetamphos oxon) may be greater in females than in males.     

Hypophysial portal vascular infusion of TRH in the rat: an ultrasturctural and radioimmunoassay study.

The hypophysial portal vessels and anterior pituitary gland of adult male Wistar rats were exposed surgically. A hypophysial portal vessel was cannulated and infused for one minute with saline or thyrotrophin (TRH). Anterior pituitary glands were collected at 1,5,15,30 or 60 minutes after cessation of infusion, for light and electron microscopic examination. Before and immediately after cannulation of a portal vessel, a 1-ml sample of blood was collected at 1,5,15,30, or 60 minutes, from the femoral vein for radioimmunoassay (RIA) of growth hormone. Thyrotrophs from anterior pituitary glands of rats infused with TRH displayed emiocytic activity at all time-periods studied. Rough endoplasmic reticular (RER) cisternae were dilated at 15 minutes following infusion and remained dilated at 30 and 60 minutes. TRH was observed to stimulate emiocytic activity in most pituitary cell-types. Extensive dilations of RER cisternae were also observed in mammotrophs and gonadotrophs, but were not observed in somatotrophs or adrenocorticotrophs. The demonstration that thyrotrophs, mammotrophs, somatotrophs, and gonadotrophs respond to TRH suggests that some common features may be shared by these cells. Preliminary analysis of the RIA data show that TRH was potent in elevating radioimmunoassayable growth hormone levels. Significant increases (p less than 0.02) in plasma GH levels were present at the earlier time periods studied (1,5, and 15 minutes) following the infusion of TRH, but no at 30 or 60 minutes. These findings provide additional support for the non-specific action of TRH upon hte various adenohypophysial cell types, and demonstrate that TRH stimulates these cells by a direct action on the adenohypophysis.