Cumulative Dose-response Curves Research Articles

Tacrine does not alter the potency of succinylcholine in the rat.

Tacrine is a cholinesterase inhibitor used to manage Alzheimer's dementia. Given iv, it prolongs succinylcholine blockade in humans but the effects of chronic oral tacrine are not known. Groups of adult rats were given 2.5 mg.kg-1 tacrine (chronic groups) or l ml saline (control) twice daily by gavage for one, two, four or eight weeks. An additional (acute) group received 2.5 mg.kg-1 tacrine iv. Twelve to 18 hr after the last gavage of tacrine or saline, and -20 min after iv tacrine, cumulative dose-response curves of succinylcholine were determined in the tibialis and soleus muscles in anaesthetized, ventilated rats during monitoring of evoked twitch response to indirect (nerve) train-of-four stimulation. The ED50 and ED95 of succinylcholine in control rats were (mean +/- SD) 204 +/- 41 and 382 +/- 96 micrograms.kg-1, respectively in the tibialis muscle, and 280 +/- 52 and 629 +/- 168 micrograms.kg-1 in the soleus muscle (P < 0.05 between muscles). In the acute and chronic tacrine groups, the mean ED50 and ED95 ranged from 166-197 and 277-396 micrograms.kg-1., respectively, in the tibialis muscle, and 248-333 and 546-667 micrograms.kg-1, in the soleus muscle. Dose responses did not differ among acute and chronic tacrine groups and the control group. Chronic oral tacrine does not alter muscle response to succinylcholine in the rat. This may not apply to Alzheimer patients receiving chronic tacrine since the interaction between acute tacrine and succinylcholine in the rat differs from that in humans.

The Effects of Chronic Tacrine Therapy on d-Tubocurarine Blockade in the Soleus and Tibialis Muscles of the Rat

Tacrine (THA) is an anticholinesterase drug used to manage Alzheimer's dementia, but it is not clear how its chronic use might affect response to nondepolarizing muscle relaxants.We determined the magnitude and time course of the effects of chronic oral THA and of intravenous (IV) THA on d-tubocurarine (dTC) blockade at the soleus and tibialis muscles. Six groups of adult rats were given 10 mg/kg THA twice daily by gavage for 1,2,4, or 8 wk (chronic THA groups), or 1 mL of saline twice daily by gavage for 1-8 wk (control), or IV THA approximately 20 min before (acute), and the cumulative dose-response curves of dTC at the tibialis and soleus muscles were determined during indirect train-of-four stimulation in the anesthetized, mechanically ventilated rat. The 50% effective dose (ED50) and 95% effective dose (ED95) of dTC in control rats were (mean +/- SD) 30 +/- 10 and 61 +/- 18 micro g/kg in the tibialis and 32 +/- 8 and 75 +/- 19 micro g/kg in the soleus; respectively. IV THA increased the ED95 of dTC 2.5- to 3-fold (P < 0.05) but did not alter the ED50. Chronic THA increased both the ED50 and ED95 of dTC 1.5- to 2-fold (P >or=to 0.05), and this effect tended to decrease with duration of THA therapy. We conclude that chronic THA therapy in rats causes resistance to dTC, with a tendency for the resistance to decrease with time, probably because of down-regulation of postsynaptic acetylcholine receptors. The same may apply to Alzheimer's patients taking THA chronically. (Anesth Analg 1997;85:431-6)

The effects of chronic tacrine therapy on d-tubocurarine blockade in the soleus and tibialis muscles of the rat.

Tacrine (THA) is an anticholinesterase drug used to manage Alzheimer's dementia, but it is not clear how its chronic use might affect response to nondepolarizing muscle relaxants. We determined the magnitude and time course of the effects of chronic oral THA and of intravenous (IV) THA on d-tubocurarine (dTC) blockade at the soleus and tibialis muscles. Six groups of adult rats were given 10 mg/kg THA twice daily by gavage for 1, 2, 4, or 8 wk (chronic THA groups), or 1 mL of saline twice daily by gavage for 1-8 wk (control), or IV THA approximately 20 min before (acute), and the cumulative dose-response curves of dTC at the tibialis and soleus muscles were determined during indirect train-of-four stimulation in the anesthetized, mechanically ventilated rat. The 50% effective dose (ED50) and 95% effective dose (ED95) of dTC in control rats were (mean +/- SD) 30 +/- 10 and 61 +/- 18 microg/kg in the tibialis and 32 +/- 8 and 75 +/- 19 microg/kg in the soleus; respectively. IV THA increased the ED95 of dTC 2.5- to 3-fold (P < 0.05) but did not alter the ED50. Chronic THA increased both the ED50 and ED95 of dTC 1.5- to 2-fold (P > or = 0.05), and this effect tended to decrease with duration of THA therapy. We conclude that chronic THA therapy in rats causes resistance to dTC, with a tendency for the resistance to decrease with time, probably because of down-regulation of postsynaptic acetylcholine receptors. The same may apply to Alzheimer's patients taking THA chronically.

Cumulative vs. Acute Dose–Response Procedures Produce Differential BAC and Behavioral Functions for Ethanol

The discriminative stimulus attributes of ethanol (ETOH) were characterized in rats trained to discriminate between 1.25 g/kg ETOH and saline. The ETOH generalization functions were assessed using both acute and cumulative dosing procedures. The cumulative procedures differed in the individual incremented doses used to generate the functions. Acute dosing procedures produced discriminative functions that were significantly different from cumulative dose–response curves (DRCs). Similar cumulative DRC’s were generated within each cumulative dosing procedure, whereas significant differences were produced between the two dosing incremented procedures. When blood alcohol concentrations (BACs) were quantified, a cumulative testing procedure produced significantly lower BACs than acute testing procedures at every dose above the initial or starting dose. Interestingly, response rate functions did not differ within or between cumulative and acute procedures. These data may suggest that differential ETOH dosing procedures may differentially influence the behavioral choice and BAC functions in rats, and cautions against the use of cumulative procedures to assess shifts in DRCs during chronic treatments without a concomitant assessment of BACs.

Discrete versus cumulative dosing in dose–response discrimination studies

This study describes the results of a `side-by-side' comparison of two measurement techniques and two dosing regimens in a discrimination study using rats trained to either 10 mg/kg cocaine or 2 mg/kg 3,4-methylenedioxymethamphetamine (MDMA). The measurements employed were either quantal or quantitative; the former an all-or-none correct lever selection measure and the latter a measure of all responses made at the time that the criterion for selection was met. The dosing regimens were either a discrete single injection of lower doses than used in training or a cumulative dose administration sequence, in an ascending order, during one session on two separate occasions. Results indicate that the cumulative dose–response relationships, as indicated by both the slope of the curve or the generated ED 50 value, for the discrete and cumulative dose–response curves do not significantly differ. In addition, both the quantal and quantitative measurements yield almost identical ED 50 values, thus allowing for accurate comparability of drug-discrimination data using different techniques. The present experimentation employed two drugs known to produce heightened response rates which would not allow for behavioral suppression at the highest doses used either in discrete or cumulative regimens. The pharmacokinetics of the two drugs employed in the discrimination tests are considered and discussed in light of the advantages and disadvantages of each of the two methods employed.

Pipecuronium revisited: Dose-response and maintenance requirement in infants, children, and adults

To compare dose-response relationship and maintenance requirement of pipecuronium in anesthetized infants, children, and adults. Prospective, consecutive sample trial. Operating room at a university hospital. 15 infants (1-11 months), 15 children (3-10 years), and 15 adults (35-50 years) of ASA physical status I and II. Anesthesia was induced and maintained with N2O:O2 2:1 and 1 minimum alveolar concentration end-tidal halothane. The neuromuscular function was recorded by adductor pollicis electromyogram evoked by a train-of-four ulnar nerve stimulation at 20 second intervals. An individual cumulative log-probit dose-response curve was established and maintenance requirement of pipecuronium determined. Between-group comparisons were made by analysis of variance and Scheffe F-test. Dose-response curves were parallel with a dose-requirement of pipecuronium similar in infants and adults (ED95 of 40-42 micrograms/kg) and greater in children (ED95 of 52 micrograms/kg). After 30 minutes of surgical neuromuscular block, pipecuronium was required in each age group at a rate of 0.6 to 0.7 individual ED95 doses per hour to maintain an 85% to 95% neuromuscular block. Bolus dose requirement of pipecuronium is greatest in children. Maintenance requirement is related to potency in each age group studied.

PROLONGED EXPOSURE TO 5′-N-ETHYLCARBOXAMIDOADENOSINE (NECA) DOES NOT AFFECT THE ADENOSINE A2A-MEDIATED VASODILATION IN PORCINE CORONARY ARTERIES

At present, four distinct adenosine receptors (A1, A2A, A2B, and A3) have been cloned and characterized in several species. It is known that prolonged exposure of tissues to receptor agonists induces A1receptor desensitization. However, controversial data are reported on whether or not prolonged stimulation of A2Aadenosine receptors induces tolerance. Using the porcine coronary artery, a sensitive vascular model, studies were designed, with the aim to clarify how prolonged exposure to the adenosine agonist 5′-N-ethylcarboxamidoadenosine (NECA) affects A2Areceptor responsiveness. The arteries were precontracted with PGF2α(3gmM) and cumulative dose-response curves to either NECA itself, or the selective A2Aagonists, 2-[4-2(2-carboxyethyl)phenethylamino]-5′-N-ethylcarboxamidoadenosine (CGS 21680) and 2-hexynyl-5′-N-ethylcarboxamidoadenosine (2HE-NECA) were obtained. In separate experiments, coronary rings were incubated with NECA (10gmM) for 30min or 2h. After 2h washout period, functional response was assessed.The arteries showed high sensitivity to adenosine agonist-induced vasorelaxation.EC50(nM) values were 71.8 (35.5–145), 20.0 (11.2–32.7) and 40.2 (20.4–79.1) for NECA, 2HE-NECA and CGS 21680, respectively. Vasorelaxant response of A2Aselective agonists 2HE-NECA and CGS 21680 was not influenced by preincubation with NECA for 30min or 2h. Conversely, dose-response curves to NECA were shifted toward the right by preincubation with NECA itself: ED50(nM) values were 114 (79.2–165), 211 (161–276) and 412 (132–1290) for 30min, 2h and 15h preincubation, respectively. These effects did not occur after 4h washout. The present results indicate that prolonged stimulation of A2Areceptors does not lead to loss of functional response, suggesting that this receptor subtype does not desensitize after prolonged stimulation by agonists.

Effect of radiographic contrast media on endothelium derived nitric oxide-dependent renal vasodilatation.

The effect of diatrizoate (Urografin325) on the cumulative dose-response curve of the vasodilatory response to acetylcholine was studied in the isolated perfused rat kidney (IPRK). The effect of 1-nitroarginine methyl ester (L-NAME) (10 mumol l-1) on the cumulative concentration-response curve of the vasodilatory response to acetylcholine and sodium nitroprusside was also studied. Acetylcholine is a vasodilator dependent on nitric oxide (NO) synthesis by the endothelium; sodium nitroprusside is a vasodilator not dependent on endogenous NO synthesis and L-NAME is an inhibitor of endogenous NO synthesis. The effect of L-NAME (10 mumol l-1) on the vasodilatory effect of diatrizoate which is observed in the presence of endothelin A receptor antagonist (BQ123, 10 mumol l-1) was also studied. In all experiments an infusion of angiotensin II (5 ng min-1) was maintained to increase the vascular tone of the preparation. Acetylcholine induced vasodilatation and the maximum increase in renal perfusate flow (RPF) was 17.0 +/- 1.7%, (p < 0.05). Diatrizoate (20 mgl ml-1 perfusate concentration) which induced a sustained fall in the RPF (-31.0 +/- 1.7%, p < 0.05) had no effect on the vasodilatory response to acetylcholine, and a similar increase in the RPF (17.8 +/- 2.2%, p < 0.05) was observed. In contrast, L-NAME (10 mumol l-1) completely abolished the vasodilatory effect of acetylcholine and produced instead a modest decrease in RPF by -5.0 +/- 1.7% (p < 0.05). The vasodilatory effect of sodium nitroprusside was not affected by L-NAME, confirming its selectivity as an inhibitor of endogenous NO synthesis in the IPRK. The maximum increase in the RPF induced by sodium nitroprusside was 23.1 +/- 2.0% (p < 0.05) in the absence of L-NAME and 21.2 +/- 2.2% (p < 0.05) in its presence. L-NAME did not interfere with the vasodilatation induced by diatrizoate in the presence of BQ123. In the presence of BQ123 alone the RPF increased from 23.3 +/- 1.4 ml min-1 g-1 to 26.5 +/- 1.0 ml min-1 g-1 (p < 0.05). In the presence of L-NAME and BQ123 the RPF increased from 24.4 +/- 3.0 ml min-1 g-1 to 27.2 +/- 2.7 ml min-1 g-1 (p < 0.05). There was no difference between the two groups (p > 0.05). In conclusion, diatrizoate did not interfere with endothelium derived NO-dependent vasodilatation in the kidney. A reduced production of NO in the vascular endothelium induced by contrast media is unlikely to play any role in the pathophysiology of the increase in renal vascular resistance produced by these agents. The renal vasodilatation induced by diatrizoate is not dependent on endogenous production of NO.

The role of oxytocin receptors and vasopressin V 1a receptors in uterine contractions in rats: Implications for tocolytic therapy with oxytocin antagonists

OBJECTIVE: The objective of the study was to determine in the rat model whether the uterotonic action of vasopressin is mediated by the vasopressin V 1a receptor in the uterus, by the oxytocin receptor, or by both. The purpose is to assess whether the anti-V 1a activity of oxytocin antagonists is a desirable pharmacologic property in tocolytic therapy for preterm labor. STUDY DESIGN: Dose-response characteristics of the uterotonic action of oxytocin and arginine vasopressin were compared and analyzed by the in vitro cumulative dose-response curve technique. A nonselective oxytocin-V 1a receptor antagonist, a selective oxytocin receptor antagonist, and a selective V 1a receptor antagonist were selected for this study. Their relative effectiveness in inhibiting the uterine contractile responses induced by oxytocin and by arginine vasopressin in the isolated rat uterus was examined. RESULTS: The uterotonic dose-response curves for oxytocin and arginine vasopressin were parallel and had the same maximal response. The nonselective oxytocin/V 1a receptor antagonist and the selective oxytocin receptor antagonist were equally potent in inhibiting the uterine contractions induced by either oxytocin or arginine vasopressin, whereas the selective V 1a receptor antagonist had no antiuterotonic activity. Inhibition by the selective oxytocin antagonist caused a similar parallel shift to the right of the dose-response curves for oxytocin and arginine vasopressin. CONCLUSIONS: The parallel dose-response curves for oxytocin and arginine vasopressin suggest that the uterotonic action of vasopressin is also mediated by the oxytocin receptor. Arginine vasopressin binds to both oxytocin and V 1a receptors in the uterus, but the activation of V 1a receptors appears not to be a mechanism involved in the uterine-stimulating action of vasopressin. The anti-V 1a activity of oxytocin antagonists does not contribute to tocolytic efficacy and may represent an undesirable side effect. By blocking the vascular V 1a receptors, it may compromise the patient's ability to maintain arterial blood pressure during hemorrhage. (Am J Obstet Gynecol 1996;175:1331-5.)

Cumulative and noncumulative dose-response curves to noradrenaline on the dorsal hand vein

Cumulative and noncumulative dose-response curves to noradrenaline were compared in the human dorsal hand vein (DHV), using the DHV compliance technique. This technique involves recording changes in the diameter of a superficial hand vein at a constant congestion pressure. Twelve healthy male volunteers (20–45 years) participated in one experimental session. Five incremental doses of noradrenaline acid tartrate (0.33–33.33 ng min −1) were infused twice in each subject: first with 5-min washout (5% dextrose saline) periods in between (“noncumulative dose-response curve”), then without interspersed washout periods (“cumulative dose-response curve”). Two-factor analysis of variance (dose of noradrenaline × method of infusion) showed a significant effect of dose ( F = 101.53, df = 4,44, p < 0.0001); however, there was no significant effect of method of infusion ( F = 0.21, df = 1,11, p > 0.1), indicating that cumulative and noncumulative applications of noradrenaline resulted in similar dose-response curves. Neither method of noradrenaline application had any effect on systemic blood pressure and heart rate. Construction of cumulative dose-response curves allows the study of the interactions of noradrenaline with a systemically taken antagonist during a narrow time window and the construction of more than one dose-response curve within the same experimental session.

Subconstrictor doses of neuropeptide Y potentiate alpha 1-adrenergic venoconstriction in vivo.

The 36-amino acid human neuropeptide Y is a vasoactive compound released after stimulation of the sympathetic nervous system. In addition to its direct and long-lasting vasopressor effects, it may potentiate the constrictor action of catecholamines and other vasoconstrictors at doses that do not per se exert vascular effects. Using the hand vein compliance technique, we have previously shown that neuropeptide Y also constricts superficial hand veins and that its effects may last for several hours. In this study, we investigated the local effect of neuropeptide Y on alpha 1-adrenergic venoconstriction in nine healthy volunteers at dose rates that did not affect venous compliance. On separate days, cumulative dose-response curves to phenylephrine alone and with coadministration of 1 or 30 pmol neuropeptide Y per minute were constructed, and the responses were fitted to a four-parameter logistic equation. Neuropeptide Y dose dependently shifted the phenylephrine curves toward lower dose rates without affecting maximal effects. ED50 values for phenylephrine alone and with 1 or 30 pmol/min neuropeptide Y were 4.0, 4.9 (P = NS versus control), and 1.2 (P < .005) nmol/min, respectively. Comparison with neuropeptide Y dose-response curves revealed that the interaction was synergistic. These are the first data in humans to show that small dose rates of neuropeptide Y may potentiate alpha-adrenergic effects in vivo. Because this interaction occurs at estimated local concentrations nearly achieved in humans, these studies suggest that neuropeptide Y might modulate the filling of this capacitance system in vivo.

Experimental Aortocoronary Saphenous Vein Graft Function After Mechanical Cardiac Massage With the Anstadt Cup

Direct mechanical ventricular actuation (DMVA) using the Anstadt Cup can achieve total circulatory support by massaging the fibrillating, asystolic, or failing heart. The device does not contact the blood or cause significant myocardial trauma. The purpose of this study was to assess the functional integrity of saphenous vein grafts (SVGs) subjected to DMVA vs cardiopulmonary bypass (CPB). Human SVGs were used to bypass the ligated left anterior descending coronary artery in 11 dogs. Animals then received 2 hrs of either DMVA (n = 5) or CPB (n = 6) during sustained ventricular fibrillation. Grafted and non grafted (control) SVG segments were then studied in vitro. SVG patency was confirmed by radiolabeled microspheres and pathologic evaluation. Matched SVG specimens (control) were not exposed to circulatory support. All SVGs were subjected to isometric tension studies. SVG contractile responses to norepinephrine, bradykinin, serotonin, and histamine were assessed. Maximal response to all agonists were similar between control SVG segments compared to either CPB or DMVA support (p = NS, ANOVA). All cumulative dose response curves were similar after DMVA vs CPB support. In conclusion, the smooth muscle function of SVGs in this study was not significantly altered by DMVA support. Therefore, short-term DMVA support does not impair patency or adversely effect the functional integrity of smooth muscle within SVGs.

Experimental Aortocoronary Saphenous Vein Graft Function After Mechanical Cardiac Massage With the Anstadt Cup

Direct mechanical ventricular actuation (DMVA) using the Anstadt Cup can achieve total circulatory support by massaging the fibrillating, asystolic, or failing heart. The device does not contact the blood or cause significant myocardial trauma. The purpose of this study was to assess the functional integrity of saphenous vein grafts (SVGs) subjected to DMVA vs cardiopulmonary bypass (CPB). Human SVGs were used to bypass the ligated left anterior descending coronary artery in 11 dogs. Animals then received 2 hrs of either DMVA (n = 5) or CPB (n = 6) during sustained ventricular fibrillation. Grafted and non grafted (control) SVG segments were then studied in vitro. SVG patency was confirmed by radiolabeled microspheres and pathologic evaluation. Matched SVG specimens (control) were not exposed to circulatory support. All SVGs were subjected to isometric tension studies. SVG contractile responses to norepinephrine, bradykinin, serotonin, and histamine were assessed. Maximal response to all agonists were similar between control SVG segments compared to either CPB or DMVA support (p = NS, ANOVA). All cumulative dose response curves were similar after DMVA vs CPB support. In conclusion, the smooth muscle function of SVGs in this study was not significantly altered by DMVA support. Therefore, short-term DMVA support does not impair patency or adversely effect the functional integrity of smooth muscle within SVGs.

Rocuronium in infants, children and adults during balanced anaesthesia.

We studied 20 infants, 20 children and 20 adults during balanced anaesthesia to compare the neuromuscular blocking effects of rocuronium in these age groups. Neuromuscular function was recorded by adductor pollicis emg and a cumulative log-probit dose-response curve of rocuronium was established. Thereafter, full spontaneous recovery of the neuromuscular function was recorded. Onset time of the first dose of rocuronium was shorter in children than in infants or adults. The potency of rocuronium was greatest in infants and least in children; the ED50 doses (mean +/- SD) being 149 +/- 36 micrograms.kg-1 in infants, 205 +/- 52 micrograms.kg-1 in children and 169 +/- 47 micrograms.kg-1 in adults (P < 0.05 between infants and children) and the ED95 doses being 251 +/- 73 micrograms.kg-1, 409 +/- 71 micrograms.kg-1 and 350 +/- 77 micrograms.kg-1, respectively (P < 0.05 between all groups). The emg recovery following an average 94.5 +/- 4.8% neuromuscular blockade established by rocuronium was roughly similar in all study groups. Thus, one ED95 dose of rocuronium, unlike vecuronium, acts as an intermediate-acting agent in all age groups.

Adrenergic and cholinergic response of ventricular muscle from the turtle, Trachemys ( Pseudemys) scripta

Muscle strips were dissected from the ventricle of the turtle, Trachemys ( Pseudemys) scripta. Individual strips were placed in a muscle bath, set at a resting tension of three grams and electrically paced at 24 min −1 for a control period of 1 hr. Cumulative dose-response curves were constructed using the adrenergic agonist, epinephrine (Epi) and the cholinergic agonist, metacholine (MCh). The administration of Epi to the muscle bath resulted in a dose-dependent increase in active tension development. The maximum tension developed was 40% above the control values and the concentration producing a half-maximal response (EC 50) was 7.5 × 10 −7 M. The positive inotropic effect of Epi was diminished following the administration 1 × 10 −7 M propranolol. This reduced the maximum active tension by over 80% at the highest dose of Epi. In addition, the EC 50 was increased to 8.9 × 10 −6 M. The administration of MCh resulted in a dose-dependent decrease in active tension development. The maximum decrease in active tension was 35% below the control values and the EC 50 was 2.5 × 10 −6 M. The negative inotropic effect of MCh was diminished by the application of 1 × 10 −6 M atropine, with the EC 50 increasing to 2.5 × 10 −4 M. These findings show that the isolated, in vitro turtle ventricle responds to adrenergic and cholinergic agonist. The results of this study support the hypothesis that the ventricular function, in reptiles, is controlled by both subdivisions of the autonomic nervous system.

The neuromuscular blocking effects of vecuronium during sevoflurane, halothane and balanced anaesthesia in children

Forty-five children aged 5-12 years were randomly allocated to receive 1.0 MAC of sevoflurane or halothane, or balanced anaesthesia with propofol and alfentanil. The ulnar nerve was stimulated every 20 s supramaximally with a train-of-four pattern and adductor pollicis electromyography was recorded. A cumulative log-probit dose-response curve of vecuronium was established. Thereafter, spontaneous recovery of neuromuscular function was monitored until complete. Effective doses of vecuronium were lowest in the sevoflurane group and greatest during balanced anaesthesia; for 50% neuromuscular blockade these were 13.3% micrograms.kg-1, 21.8 micrograms.kg-1 and 36.6 micrograms.kg-1 during sevoflurane, halothane and balanced anaesthesia, respectively, p < 0.05. Recovery of neuromuscular function was slower during sevoflurane than during halothane or balanced anaesthesia. Sevoflurane potentiated vecuronium more than halothane; when compared to balanced anaesthesia the dose requirements of vecuronium were reduced by approximately 60% and 40%, respectively.

Control of Accelerated Vein Graft Atheroma with the Nitric Oxide Precursor: l-Arginine

Hyperlipidemia contributes to the development of intimal hyperplasia and subsequent accelerated atherosclerosis in vein bypass grafts. This study examines the effect of dietary supplementation with l-arginine on the development of intimal hyperplasia and the vasomotor function of vein grafts in hypercholesterolemic animals. Thirty male New Zealand White rabbits had a right carotid vein bypass graft and were sacrificed at 28 days postoperatively. Twenty animals received a 1% cholesterol diet for 4 weeks prior to surgery and this diet was continued until harvest. Of these, 10 also received l -arginine (2.25%, 2 g/kg, p.o.) 7 days preoperatively and thereafter until harvest. The last 10 animals were controls. Vein grafts were harvested either for morphology or for in vitro isometric tension studies. Cumulative dose-response curves to norepinephrine, serotonin, and bradykinin were recorded, and following norepinephrine precontraction, relaxation to acetylcholine and sodium nitroprusside were determined. After in situ pressure fixation, intimal thicknesses of the vein grafts were measured by videomorphometry. The addition of l-arginine doubled the serum arginine concentrations. Intimal hyperplasia of both groups of hypercholesterolemic vein grafts contained foam cells and lipid-laden endothelial and smooth muscle cells. There was a 24% reduction in the intimal thickness of vein graft intimal hyperplasia in the l-arginine group compared to that in the hypercholesterolemia group (P < 0.05). All hypercholesterolemic vein grafts were twofold thicker than in the control group. l-arginine supplementation resulted in the preservation of acetylcholine-mediated relaxation but did not change hypercholesterolemia-induced contractile agonist supersensitivity. Therefore, l-arginine supplementation can slow the formation of atheromatous intimal hyperplasia in vein grafts; it can improve endothelial cell function but it does not prevent the persistence of the hypercholesterolemia-associated smooth muscle phenotype.

Discrimination by benextramine between the NPY‐Y1 receptor subtypes present in rabbit isolated vas deferens and saphenous vein

1. In order to characterize the neuropeptide Y (NPY) Y1 receptors known to be present in rabbit isolated vas deferens and saphenous vein, the pharmacological activity of the selective NPY Y1 receptor agonists, [Leu31,Pro34] NPY and various other peptide agonists, together with the putative NPY antagonist, benextramine, were compared in the two tissues. 2. In rabbit isolated saphenous vein, cumulative dose-response curves to various NPY agonists were obtained. All the peptides tested caused contractions which developed quite slowly. The rank order of potency obtained was: PYY > NPY > [Leu31,Pro34] NPY = NPY2-36 > hPP >> NPY13-36 = NPY18-36. Incubation with benextramine (BXT) at 100 microM for 30 min irreversibly abolished the contractile response to [Leu31,Pro34] NPY but was ineffective against NPY18-36-induced contractions. 3. Cumulative dose-response curves to [Leu31,Pro34] NPY were performed in the same preparation before and after incubation with 100 microM BXT for 20 min in order to inactivate NPY Y1 receptors. The pKA (-logKA) estimation for [Leu31,Pro34] NPY was 7.60 +/- 0.30 using the operational model and 7.20 +/- 0.33 using the null method; the difference between the two methods was not statistically significant (P = 0.36). 4. Prostatic segments of rabbit vas deferens were electrically stimulated with single pulses. Immediately after stabilization of the contractile response, a cumulative dose-response curve to various NPY agonists was obtained in each tissue. The rank order of potency for twitch inhibition was: PYY> [Leu31,Pro34]NPY > NPY > hPP>NPY2- 36 >>NPY13-36>> NPY 18-36 which indicates the presence of a prejunctional NPY Y1 receptor. BXT at 100 microM incubated for 10 or 60 min did not antagonize the response to[Leu31,Pro34] NPY.5. We conclude that rabbit isolated saphenous vein contains a population of post-junctional NPY Y1 receptors irreversibly blocked by BXT, as well as a population of post-junctional NPY Y2 receptors,which are insensitive to BXT. In contrast, the rabbit isolated vas deferens express a pre-junctional NPYY1 receptor subtype which is not blocked by BXT. Tetramine disulphides such as BXT could be useful tools in classifying NPY receptors.

Vascular reactivity in sepsis: importance of controls and role of nitric oxide.

We have previously reported differential impairment of pulmonary and systemic vascular contractility in hyperdynamic sepsis. The objectives of this study were (1) to determine whether the magnitude of this phenomenon depends on the control group chosen for comparison, and (2) to examine the role of nitric oxide (NO) in this altered vascular contractility. Rats were randomized to sepsis induced by cecal ligation and perforation (CLP) or to one of two control procedures. The Sepsis group had a jugular venous line for fluid administration, laparotomy, and CLP. Control group 1 (Control) had only a jugular venous line inserted, while group 2 (Sham) had a jugular venous line inserted and an abdominal incision. All rats were killed 24 h after surgery. Vascular contractility of small pulmonary arterial and thoracic aortic rings was assessed in vitro by obtaining cumulative dose-response curves to the contractile agonists potassium chloride (KCl), phenylephrine (PE), and prostaglandin F2 alpha (PGF2 alpha). Pulmonary vessels from animals in the Sepsis and Sham groups exhibited significant attenuation of the contractile responses to KCl, PE, and PGF2 alpha compared with the Control group. In contrast, contractility of the aortic rings to KCl, PE, and PGF2 alpha was not significantly different in the three groups studied. Incubation of pulmonary and aortic vessels with NG-nitro-L-argine methyl ester (L-NAME, 10 microM) caused an increase in the response to KCl, PE, and PGF2 alpha in pulmonary vessels in Sepsis and Sham rats but not in Control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative 5-HT2A-receptor and alpha1-adrenoceptor antagonistic activity of an ergoline LEK-8829 and its degradation product LEK-1814 in rabbit isolated aorta

Endothelium derived relaxing factor (EDRF) is a local modulator of vasomotor tone in most blood vessels. Reversed vein grafts in several animal models do not produce EDRF when stimulated, and have been shown to have altered responses to several vasoconstrictors. The preservation of EDRF production and vasomotor function in in situ vein grafts was examined in this study. In situ vein grafts of the right carotid artery were performed in five mongrel dogs using external jugular vein. The contralateral jugular vein was used as a control. The vessels were harvested after 6 weeks and rings from the central portion of each vessel studied in vitro in an organ bath. Following cumulative dose response curves to noradrenaline, the rings were precontracted with the estimated ED50 (50% effective dose) dose of noradrenaline, and cumulative doses of acetylcholine added to induce EDRF release. The vein grafts were hypersensitive to noradrenaline, the ED50 being reduced from 8.7 ± 2.7 × 10−7m in the jugular veins to 1.7 ± 0.7 × 10−7m in the vein grafts (p < 0.05). All of the jugular vein segments relaxed in response to acetylcholine with a mean maximal relaxation of 42 ± 6% of precontraction. None of the vein graft segments relaxed in response to acetylcholine despite the presence of an intact endothelium on scanning electron microscopy, but did relax in response to calcium ionophore. The results indicate that in situ vein grafts, like reversed grafts, fail to produce EDRF in response to acetylcholine. The grafts are also hypersensitive to noradrenaline. It is concluded that the in situ technique confers no benefits to the graft in terms of preservation of endothelial or vasomotor function.