By B. Luca. Westminster College, Fulton Missouri. 2018.
Many neurodegenerative diseases 100mg penegra sale, such as Alzheimer disease purchase 50 mg penegra overnight delivery, Parkin- calcium influx into nerve cells discount 50mg penegra. Once anandamide is released order penegra 100mg online, it acts as a retrograde son disease generic 50 mg penegra fast delivery, and Lou Gehrig disease, have in messenger, binding to receptors on the presynaptic membrane that alter ion fluxes common increased oxidative stress. Anandamide is degraded by the enzyme fatty acid amide hydrolase, which splits anandamide to arachidonic acid and ethanolamine. The hydro- lase enzyme is the target of drug research, because inhibiting the action of this enzyme will prolong the analgesic effects induced by anandamide. MECHANISM OF ACTION OF THE EICOSANOIDS The eicosanoids have a wide variety of physiologic effects, which are generally initiated through an interaction of the eicosanoid with a specific receptor on the plasma membrane of a target cell (Table 35. This eicosanoid-receptor binding either activates the adenylate cyclase-cAMP-protein kinase A system (PGE, PGD, 664 SECTION SIX / LIPID METABOLISM O O CH2 O C R1 CH2 O C R1 Membrane O Membrane O HC O C R2 HC O C R2 O– O + HC O P OX HC O P OCH2CH2NH3 H H O O– R2 = Arachidonic acid R2 = Arachidonic acid TAE O Free – radicals O O CH2 O C R1 O HC O H CH2 O C R1 O O O H HC O P OCH2CH2 N C HC O C R*2 H O– O HC O P OX N-acyl-phosphatidyl H ethanolamine O– selective phospholipase D Phospholipase A2 O CH2 O C R1 O Lysophosphatidic acid CH2 O C R1 HC OH O HC OH HC O P O– O H O– HC O P OX H O O– + C H OH Lysophospholipid N + Isoprostane OH OH O Anandamide C O – fatty acid amide hydrolase O OH C H O– + N CH CH OH 2 2 Fig. Rad- H ical damage to a phospholipid on the arachi- Arachidonic acid Ethanolamine donic acid residue at position 2 generates an isoprostane, which is then removed from the Fig. The example of an isoprostane shown in this figure is just one of many that can be produced. Prostaglandin and Thromboxane Receptors Receptor Type Ligand G-protein coupled cAMP response Calcium response DP PGD series Yes Increase None EP1 PGE series Yes None Increase EP2 PGE series Yes Increase None EP3 PGE series Yes Decrease None EP4 PGE series Yes Increase None FP PGF series Yes None Increase IP PGI series Yes Increase None TP Thromboxane A Yes None Increase CHAPTER 35 / METABOLISM OF THE EICOSANOIDS 665 and PGI series) or causes an increase in the level of calcium in the cytosol of tar- get cells (PGF2 , TXA2, the endoperoxides, and the leukotrienes). In some systems, the eicosanoids appear to modulate the degree of activation of adenylate cyclase in response to other stimuli. In these instances, the eicosanoid may bind to a regulatory subunit of the GTP-binding proteins (G proteins) within the plasma membrane of the target cell (see Chapter 11). If the eicosanoid binds to the stimulatory subunit, the effect of the stimulus is amplified. Conversely, if the eicosanoid binds to the inhibitory subunit, the cellular response to the stimulus is reduced. Through these influences on the activation of adenylate cyclase, eicosanoids contribute to the regulation of cell function. Some of the biologic effects of certain eicosanoids occur as a result of a paracrine or autocrine action. One paracrine action is the contraction of vascular smooth muscle cells caused by TXA2 released from circulating platelets (vasocon- striction). An autocrine action of eicosanoids is exemplified by platelet aggregation induced by TXA2 produced by the platelets themselves. The eicosanoids influence the cellular function of almost every tissue of the Although our knowledge of the body. Certain organ systems are affected to a greater degree than others. For exam- In the presence of aspirin, cyclooxygenase is irreversibly inactivated by ple, drugs that are analogs of PGE1 and PGE2 acetylation. New cyclooxygenase molecules are not produced in platelets, suppress gastric ulceration, in part by because these cells have no nuclei and, therefore, cannot synthesize new inhibiting secretion of hydrochloric acid in mRNA. Thus, the inhibition of cyclooxygenase by aspirin persists for the lifespan of the mucosal cells of the stomach. When aspirin is taken daily at doses between 81 and 325 mg, PGE1 are used in the treatment of sexual impotence. Men with certain forms of sexual new platelets are affected as they are generated. Higher doses do not improve efficacy impotence can self-inject this agent into the but do increase side effects, such as gastrointestinal bleeding and easy bruisability. The stimulatory action of PGE2 and PGF2 on This action of aspirin helps to prevent thrombus formation in the area of an athero- uterine muscle contraction has led to the use sclerotic plaque at critical sites in the vascular tree. PGE1 is also Corticosteroids reduce inflammation, in part, through their inhibitory effect used as palliative therapy in neonates with on phospholipase A2. In addition, suppression of COX-2 induction is now congenital heart defects to maintain patency thought to be a primary anti-inflammatory mechanism of action for gluco- of the ductus arteriosus until surgery can be performed. Despite the unquestionable value of glucocorticoid therapy in a variety of shown to be effective in the treatment of pri- diseases associated with acute inflammation of tissues, the suppression of the inflam- mary pulmonary hypertension. The sudden appearance of temporary glucose intolerance when Emma Wheezer was treated with large doses of dexamethasone, a gluconeogenic steroid (glucocorticoid), is just one of the many potential adverse effects of this class of drugs when given systemically in pharmacologic doses over an extended period. The inhaled steroids, conversely, have far fewer systemic side effects because their absorption across the bronchial mucosa into the circulation is very limited. This property allows them to be used over prolonged periods in the treatment of asthma.
A baclofen trial tion demonstrated Ashworth grade 1 and 2 spasticity was given proven 100mg penegra, but he could not stand with the decreased throughout most muscles in the lower extremity and the spasticity after the baclofen injection purchase penegra 50mg with amex, and his parents felt upper extremity discount 100 mg penegra free shipping. He had no ability to do individually the benefit of the decreased spasticity during custodial isolated joint movement in the lower extremity discount penegra 50mg amex. The hip care would not make up for his functional loss of not be- demonstrated a symmetric 30° of abduction order penegra 100mg without prescription, popliteal ing able to stand. In children with CP, this inequality can be a physically short limb, but is more commonly a functional limb shortening due to asymmetric hip, knee, or ankle flexion. Treatment of the limb length inequality will treat the hip adduction. Asymmetric adduction on one hip and abduction on the op- posite hip may also be caused by fixed pelvic obliquity emanating from spinal deformities. Increased hip abduction leads to a wide-based gait, which is cosmetically unappealing and is very functionally disabling if the children are functional ambulators. The wide-base position forces excessive side-to-side movement of the body to keep the center of mass over the weightbearing limb. If chil- dren have increased abduction with a wide-based gait but have no abduc- tion contracture on physical examination, the cause of the wide-based gait is weakness of the adductor muscles. Usually, the cause is incompetent ad- ductors secondary to excessive adductor lengthening, or the addition of an obturator neurectomy to an adductor lengthening (Case 7. The best treatment of this problem is to prevent it from happening by not doing this type of surgery on a functional ambulator. However, if presented with the problem, working on strengthening the remaining adductor strength and allowing the children to grow often slowly corrects the problems. The wide-based gait may also be due to an abduction contracture, usually of the gluteus medius or fascia latae. The eti- ology of wide-based gait due to a contracture requires identifying the source of the contracture, and the kinematic measure should show increased ab- duction, especially in midstance phase. Once the specific source of the abduction contracture is identified, the treatment is surgical lengthening of the contracted muscle. Fixed contractures of the hip joint may also cause the same effect as muscle contractures. His hip radiographs were spastic hip disease at age 3 years. His gait was characterized by a wide- efficiently with a walker; however, his parents were con- based gait with foot drag and knee stiffness in swing cerned about his wide-based gait and foot drag. Based on these data, Sean had bilateral rectus ical examination, he was not able to get into the walker transfers because the knee stiffness was believed to be without assistance, but had functional gait once he was adding to the tendency to have a wide-based gait. His hip abduction was 50° on each side, initiating a circumduction maneuver because of adductor full hip flexion and extension was present, the popliteal weakness to assist with foot clearance. After the rectus angle was 40°, and he had grade 2 spasticity in the rec- transfers, his base of support narrowed and knee flexion tus, with a positive Ely test at 40°. Transverse Plane Deformity Transverse plane deformity in children is common and is often confused with coronal plane deformity. The difference between scissoring, which is excessive hip adduction, and hip internal rotation gait is often missed. Scis- soring is a completely different motion requiring a different treatment (Fig- ure 7. Hip rotation is defined as a rotation of the knee joint axis relative to the center of hip motion in the pelvis. In normal gait, this rotation around the mechanical axis of the femur allows the feet to stay in the midline and allows the pelvis to turn on top of the femur, which are both motions that work to decrease movement of the HAT segment and therefore conserve energy. At initial contact, the normal hip has slight external rotation of ap- proximately 10°, then it slowly internally rotates, reaching a maximum at terminal stance or initial swing phase. If the hip is positioned in internal ro- tation at initial contact, then during stance phase as the knee flexes, there is an obligatory hip adduction and the knee may impact the opposite limb (Case 7. If the internal rotation is present during midstance, such as in a crouched gait pattern, the knees often rub during swing phase of the con- tralateral limb. Internal rotation positioning in terminal swing also causes the knee to cross the midline, a problem that continues into initial swing. Another primary effect of this internal rotation is placing the knee axis out of line with the forward line of motion.
This pathway is feedback regulated cheap penegra 50mg amex, so that as her muscles use ATP 100mg penegra for sale, the rate of glycolysis will increase to generate more ATP buy generic penegra 100mg line. Glycogen Glycogen Glycogenolysis synthesis Glucose Glucose-6-P hexokinase glucokinase Glycolysis Energy discount penegra 100 mg free shipping, ATP When she is resting 100mg penegra otc, her muscles and liver will convert glucose 6-phosphate to glycogen (a fuel storage pathway, shown in blue). Glyco- gen synthesis is feed-forward regulated by the supply of glucose and by insulin and other hormones that signal glucose availability. Glycogenolysis (glycogen degradation) is activated during exercise to supply additional glucose 6-P for glycolysis. Unless Ann consumes sufficient calories, her glycogen stores will not be replenished after exercise, and she will tire easily. REGULATION BY SUBSTRATE AND PRODUCT CONCENTRATION A. Velocity and Substrate Concentration The velocity of all enzymes is dependent on the concentration of substrate. This dependence is reflected in conditions such as starvation, in which a number of pathways are deprived of substrate. In the following sections, relates the initial velocity of the we use the Michaelis-Menten equation to describe the response of an enzyme to reaction (v ) to the concentration ofi changes in substrate concentration and use glucokinase to illustrate the role of sub- enzyme substrate complexes (ES). This strate supply in regulation of enzyme activity. MICHAELIS-MENTEN EQUATION to form ES with the rate constant of k1. The The equations of enzyme kinetics provide a quantitative way of describing the depend- complex dissociates with the rate constant ence of enzyme rate on substrate concentration. The simplest of these equations, the of k2, or is converted to P with the rate con- Michaelis-Menten equation, relates the initial velocity (v ) to the concentration of sub-i stant k3. Under conditions in which [S] >> strate [S] and the two parameters Km and Vmax (Equation 9. The concentration of and the Km of the enzyme for a substrate is the concentration of substrate required to i 3 reach 1⁄2 V. The Michaelis-Menten model of enzyme kinetics applies to a simple ES is a fraction of ET, the total amount of max enzyme present as ES and E. The initial velocity of prod- uct formation, v , is proportionate to the concentration of enzyme–substrate complexesi k3[ET][S] [ES]. As substrate concentration is increased, the concentration of enzyme–substrate vi k3[ES] Km [S] complexes increases, and the reaction rate increases proportionately. Substitution of Vmax The graph of the Michaelis-Menten equation (vi as a function of substrate con- for k3 [ET] gives the Michaelis-Menten equa- centration) is a rectangular hyperbola that approaches a finite limit, Vmax, as the tion (see Equation 9. The Michaelis-Menten equation: V max For the reaction Vmax k1 k3 E S ESS S P d k2 Vmax [S] the Michaelis-Menten equation is given by Vmax/2 vi = Km + [S] Vmax[S] vi Km [S] Km where Km (k2 k3)/k1 Substrate concentration [S] and Vmax k3 [ET] Fig. Vmax (solid blue line) is the initial velocity extrapolated to infinite [S]. Km (dashed blue At a hypothetical infinitely high substrate concentration, all of the enzyme mole- line) is the concentration of S at which vi cules contain bound substrate, and the reaction rate is at Vmax. Saturation kinetics is a charac- teristic property of all rate processes dependent on the binding of a compound to a protein. The Km of the enzyme for a substrate is defined as the concentration of sub- MODY. Patients with maturity onset strate at which v equals 1⁄2 V. The velocity of an enzyme is most sensitive to diabetes of the young (MODY) have i max changes in substrate concentration over a concentration range below its K (see a rare genetic form of diabetes mel- m 1 litus in which the amount of insulin being Fig. At substrate concentrations less than ⁄10th of the Km, a doubling of sub- secreted from the pancreas is too low, result- strate concentration nearly doubles the velocity of the reaction; at substrate con- ing in hyperglycemia. The disease is caused centrations 10 times the Km, doubling the substrate concentration has little effect by mutations in the gene for pancreatic glu- on the velocity. Glucokinase is part of the mech- example, a genetic mutation that decreases the rate of substrate binding to the anism controlling release of insulin from the enzyme decreases the affinity of the enzyme for the substrate and increases the Kd pancreas. A decreased activity of glucokinase and Km of the enzyme for that substrate. The higher the Km, the higher is the sub- results in lower insulin secretion for a given strate concentration required to reach 1⁄2 V. HEXOKINASE ISOZYMES HAVE DIFFERENT Km VALUES FOR GLUCOSE A comparison between the isozymes of hexokinase found in red blood cells and in As Ann O’Rexia eats a high carbo- the liver illustrates the significance of the K of an enzyme for its substrate.
There were no differences between the two formulations with regard to efﬁcacy or frequency of motor ﬂuctuations buy penegra 100 mg with mastercard. Despite low doses there was a signiﬁcant improvement of the UPDRS motor score that gradually diminished over time but was still better than the baseline score as seen in the earlier studies buy discount penegra 50mg line. However order 50mg penegra, only about 20% of patients in each group developed wearing off and dyskinesias generic penegra 50 mg line, far lower than prior numbers discount penegra 50mg otc. The CALM-PD study (36,37), a parallel-group, double-blind, randomized trial consisting of both clinical and imaging substudies, compared the rates of dopaminergic motor complications and dopamine neuron degeneration (primary endpoints), respectively, after initial treatment of early PD with pramipexole versus LD. The clinical 2-year data reported that 28% of patients assigned to pramipexole developed motor complications compared with 51% of patients assigned to LD (p < 0. However, the mean improvement in UPDRS score was signiﬁcantly greater in the LD group compared with pramipexole (9. When extended to 4 years, slightly Copyright 2003 by Marcel Dekker, Inc. The mean improvement in UPDRS scores from baseline through 48 months was signiﬁcantly greater in the LD group (3. The imaging portion of the study (38,39) included 82 patients who underwent four sequential I B-CIT single photon emission computed tomography (SPECT) scans over a 46-month period to compare the rate of nigrostriatal dopaminergic degeneration between the treatment groups. It is assumed that a reduction in striatal I B-CIT uptake is a marker of dopamine neuron degeneration. The authors report a 40% relative reduction in the rate of loss of uptake when comparing pramipexole to LD. Whether this suggests a protective effect of the dopamine agonist with respect to LD or that LD may accelerate the rate of loss of uptake or that this is a pharmacological effect is not clear given the limits of the study design. A similar 5-year comparison of ropinirole and LD in 268 patients was reported in 2001 (40). Approximately half of the patients withdrew by the end of 5 years. The primary endpoint was the appearance of dyskinesias as measured by item 32 on the UPDRS. They were shown to occur earlier and more frequently in patients treated with LD than ropinirole. Regardless of LD supplementation, 20% of ropinirole subjects experienced dyskinesias by the end of 5 years versus 45% of LD subjects. Prior to the addition of LD, 5% of the ropinirole group and 36% of the LD group developed dyskinesias. The change from baseline of the UPDRS activities of daily living (ADL) score was similar between the two groups, but there was a signiﬁcant difference in favor of the LD group for the change from baseline of the UPDRS motor score, which improved by approximately four times compared to the ropinirole group. This difference in efﬁcacy was reported in the 6-month interim report published earlier (41). LD treatment is associated with greater therapeutic beneﬁt (both early in the course of disease as well as later), and at least half of the patients developed motor complications after several years regardless of initial treatment. Thirty years of experience and literature have led to several conclusions regarding LD therapy in PD. It is currently the most potent symptomatic therapy for PD. We have learned quite a bit about the nuances of treatment such that our goals have changed. We now treat with the lowest effective dose, not the highest tolerated one, we avoid frequent small doses, which only add to the unpredictable responses seen, and we have developed adjunctive therapies that complement LD. In short, we have become better Copyright 2003 by Marcel Dekker, Inc. The outcome is fewer late complications, though we do not state that these are no longer a problem. It has been well known since the early days of LD that motor ﬂuctuations and dyskinesias relate to therapy (2). Barbeau referred to it as the long-term levodopa syndrome (42). At that time, with no alternative treatments available, he indicated that its existence did not counterbalance the great usefulness of the drug. The debate addresses whether it is disease progression or primarily LD itself or both. The answer is not totally clear but this question has been examined extensively in two ways: (1) evaluating patient populations and examining which of the two factors correlates with the onset of ﬂuctuations and dyskinesias; (2) examining the actual response ﬂuctuations in a controlled setting to determine possible etiological explanations. The conclusion to this debate is now more important than ever since alternative therapies are becoming available and the choice of which drug to use ﬁrst is in question.
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