Shown are the various m em brane activation M LC— m yosin light chain; M LCK— m yosin light chain m echanism s and signal transduction events leading to kinase; PGE2— prostaglandin E2; PGI2— prostaglandin a change in cytosolic calcium ions (Ca2+) safe viagra super active 25mg impotence jelly, cyclic AM P I2; PKA— protein kinase A; PKC— protein kinase C; (cAM P) 25mg viagra super active amex erectile dysfunction vegan, and phosphorylation of m yosin light chain PLC— phospholipase C; PTH — parathyroid horm one; kinase. M any of the circulating hormones and paracrine R— receptor; SR— sarcoplasm ic reticulum ; TXA2 — factors that increase or decrease vascular smooth muscle throm boxane A2. The relative contributions of the activation pathways are different in afferent and efferent arterioles. Increases in cytosolic Ca2+ in afferent arterioles appear to be prim arily by calcium ion (Ca2+) entry by way of receptor- and voltage-dependent Ca2+ channels. The efferent arterioles are less dependent on voltage-dependent Ca2+ channels. These differential mechanisms in the renal vasculature are exem plified by com paring the afferent and efferent arteriolar responses to angiotensin II before and after treatm ent with Ca2+ channel blockers. A, These experim ents were done using the juxtamedullary nephron preparation that allows direct visualization of the renal m icrocirculation. AA— afferent arteriole; ArA— arcuate artery; PC— peritubular capillaries; V— vein; VR— vasa recta. Ca2+ channel blockers, dilate only the afferent arterioles and prevents the afferent vasoconstriction responses to 25 angiotensin II. In contrast, Ca2+ channel blockers do not signifi- cantly vasodilate efferent arterioles and do not block the vasocon- strictor effects of angiotensin II. Thus, afferent and efferent arteri- 20 oles can be differentially regulated by various horm ones and paracrine agents. N itric oxide is form ed by nitric oxide synthase, which cleaves nitric oxide from L-arginine. N itric oxide diffuses TXA2 EDCF from the endothelial cells to activate soluble EDHF NO PGF2α PGI2 Endothelin guanylate cyclase and increases cyclic Relaxing factors Constricting factors GM P (cGM P) levels in vascular sm ooth Angiotensin II m uscle cells, thus causing vasodilation. Agents that can stim ulate nitric oxide ACE are shown. The relative am ounts of the Endothelial cell various factors released by endothelial Angiotensin I cells depend on the physiologic circum - Thrombin Insulin stances and pathophysiologic status. Shear Bradykinin Thus, endothelial cells can exert vasodilator stress Platelet Histamine activating ATP-ADP Serotonin or vasoconstrictor effects. At least one Leukotrienes factor Acetylcholine m ajor influence participating in the norm al regulation of vascular tone is nitric oxide. EDCF— endothelial derived constrictor factor; EDH F— endothelial derived hyper- FIGURE 1-12 polarizing factor; PGF2 — prostaglandin Endothelial-derived factors. In addition to serving as a diffusion barrier, the endothelial F2 ; PGI2— prostaglandin I2; TXA2— cells lining the vasculature participate actively in the regulation of vascular function. Several recent studies arterial stress nitric oxide but counteracted have demonstrated that nitric oxide also directly affects tubular sodi- pressure release by autoregulation um transport and may be an important mediator of the changes induced by arterial pressure in sodium excretion, as described in Figure Diffusion to 1-5 [9,24]. Increases in arteriolar shear stress caused by increases in 3 tubules arterial pressure stimulate production of nitric oxide. Nitric oxide may 2 exert direct effects to inhibit tubule sodium reabsorptive mechanisms Control Epithelial and may elicit vasodilatory actions. Nitric oxide increases intracellular 1 NOS inhibition cGMP cyclic GM P (cGM P) in tubular cells, which leads to a reduced reab- sorption rate through cGM P-sensitive sodium entry pathways [24,25]. W hen formation of nitric oxide is blocked by agents that prevent nitric 50 75 100 125 150 Decreased sodium Sodium reabsorption excretion oxide synthase activity, sodium excretion is reduced and the pressure Renal arterial pressure, mm Hg natriuresis relationship is markedly suppressed. Thus, nitric oxide may exert a critical role in the regulation of arterial pressure by influencing vascular tone throughout the cardiovascular system and by serving as a mediator of the changes induced by the arterial pressure in tubular sodium reabsorption. Sodium excretion is the difference PCT between the very high filtered load and net tubular reabsorption 60% rate such that, under norm al conditions less than 1% of the filtered sodium load is excreted. The percentage of reabsorption of the filtered 7% load occurring in each nephron segm ent is shown. The end result is CCD that norm ally less than 1% of the filtered load is excreted; however, PST the exact excretion rate can be changed by many mechanisms.
Combined pleted but BASF buy viagra super active 100mg overnight delivery erectile dysfunction radiation treatment, who was jointly conducting the phase therapy was performed on nine patients and no intracerebral III trials order viagra super active 100mg online icd-9-cm code for erectile dysfunction, has decided not to continue the trials after an hemorrhages or significant systemic bleeding complications independent group looked at the interim results and failed occurred. Marked clinical improvement was noted in four to see any evidence of efficacy (19). From numerous combining rather than comparing these two delivery strate- trials, one thing is clear of all agents in this category: They gies (30). There is an NIH-approved trial (Interventional must be given early or serious hemorrhagic complications Management Study, IMS trial) comparing IV versus com- are likely (7). Urokinase (uPA) is an endogenous proteolytic bined IV and IA tPA therapy that will be underway by the enzyme, secreted as a proenzyme, which converts circulating time this is published. Intraarterial administration of pro-urokinase (the single chain precursor of urokinase) was evaluated in the Prolyse in NEUROPROTECTIVE AGENTS Acute Cerebral Thromboembolism Trial (PROACT) with high- or low-dose heparin (20) and in the PROACTII trial Once the excitotoxic cascade has begun, the first therapeutic with low-dose heparin (21). Although prourokinase and in- strategy, and the one that has raised the most hope in the travenous high-dose heparin resulted in an increased rate last decade, utilizes neuroprotective agents targeting media- of hemorrhage, intraarterial pro-urokinase with low-dose tors in the excitotoxic cascade (Fig. The cascade can heparin significantly improved the proportion of good out- be separated spatially and temporally. The cascade begins comes from 25% to 40% and hemorrhage was seen in 10% with an increase in presynaptic calcium influx, followed by of patients, consistent with other thrombolytic trials. More recently, a more aggressive trial (Very Early Ni- modipine Use in Stroke, VENUS) designed to treat with nimodipine within 6 hours of symptom onset was termi- nated before completion because the results indicated that there was no beneficial role of early administration of oral nimodipine at 3 months (40). Although nimodipine failed to demonstrate efficacy in treating acute stroke, it was ap- proved for the treatment of subarachnoid hemorrhage more than a decade ago. The results of a phase III trial of flunari- zine (Sibelium) for acute stroke suggested that it also did not improve neurologic or functional outcome at 3 months when administered early ( 6 hours) (41). The N-type calcium channel antagonist, SNX-111 (Zi- conotide), preferentially blocks presynaptic calcium chan- nels and inhibits neurotransmitter release. In both focal and global animal models of cerebral ischemia SNX-111 is highly neuroprotective, even when administered after a FIGURE 93. Thereapy utilizing neuroprotective agents target- delay of 24 hours following reperfusion (42). SNX-111 has ing mediators in the excitotoxic cascade. Although the stroke trials of SNX-111 were discontinued because of severe hypotension that exacerbated the ischemic damage (43), SNX-111 has progressed to phase III trials for head Voltage-gated sodium and potassium channels are targets trauma (44,45) and has just been approved by the FDA for that affect depolarization, whereas calcium channels me- the treatment of pain (46). Spider toxin antagonists of the diate calcium influx and affect depolarization. Most of the P/Q-type neuronal calcium channels are neuroprotective in neuroprotective agents tested in the clinic have targeted vitro but their in vivo toxicity in animals, primarily respira- either voltage-gated calcium channels or glutamate recep- tory depression causing death, has limited their clinical de- tors, particularly the NMDA receptor subtype. However, efforts to generate small peptide ana- GABA receptor agonists attenuate excitotoxicity (31) and logues of these spider toxins, which exhibit efficacy in vitro, free radical scavengers are neuroprotectants aimed at the are ongoing. After the excito- toxic cascade has progressed, an inflammatory response oc- curs in which there is infiltration of leukocytes and mono- cytes (33). Microglia and astrocytic glial cells are activated GLUTAMATE RECEPTOR ANTAGONISTS and macrophages begin responding to chemoattractants. Still other therapeutic strategies have targeted leukocyte ad- Numerous clinical trials have been carried out for NMDA hesion (34,35) and nitric oxide production (36,37). Once receptor antagonists based on preclinical testing in animal much of the damage has occurred and neuroprotection is no models of cerebral ischemia (47). All the phase III trials to longer a viable strategy, neural regeneration and trophism date have failed. Optimism for the use of NMDA receptor becomes an option. This approach has been mounted with antagonists in the treatment of acute ischemia has waned infusion of growth factors but trials to date have been unsuc- and has even prompted some pharmaceutical companies to cessful (38). We now look at trials of compounds targeted abandon efforts to develop therapeutics for acute stroke.
Numerous clinical trials have now sponses to both noxious and innocuous pressure applied to been conducted with NK1 receptor antagonists to define their therapeutic potential in psychiatric and neurologic dis- orders best 100 mg viagra super active erectile dysfunction vascular disease. In all these studies viagra super active 100mg overnight delivery erectile dysfunction just before penetration, the compounds have been ex- tremely well tolerated, with no significant side effects. PRECLINICAL EVIDENCE OF AN ANALGESIC PROFILE OF NK1 RECEPTOR are as yet no reports of clinical trials with NK2 or NK3 ANTAGONISTS receptor antagonists in patients with CNS disorders. Assay Morphine Indomethacin NK1 Antagonist Tail flick/hot plate √ Pain Paw pressure √ Writhing Radioligand-binding studies confirm the expression of Formalin paw tachykinin NK1 and NK3 (but not NK2) receptors in the Carrageenan paw dorsal horn of the spinal cord (33–35). A role of spinal Nerve injury √ X √ CFA arthritis substance P and NKA in nociception is suggested by the Facilitated spinal reduction in response thresholds to noxious stimuli by cen- reflex tral administration of NK1 and NK2 (but not NK3) agonists 172 Neuropsychopharmacology: The Fifth Generation of Progress the knee joint (50). CP-122,721 was also effective in preventing Migraine postoperative nausea and vomiting after gynecologic surgery (68), a finding suggesting the utility of NK1 receptor antag- The vasculature of meningeal tissues such as the dura mater onists as broad-spectrum antiemetics in humans. There are is densely innervated by nociceptive sensory afferents that no published studies examining the effects of selective NK2 run in the trigeminal nerve and contain substance P and and NK3 receptor agonists and antagonists on emesis. The release of neuropeptides from these sensory fibers during a migraine attack is thought to cause neurogenic inflammation within the meninges and Schizophrenia activation of nociceptive afferents projecting to the trigemi- A rationale that NK1 receptor antagonists may be useful as nal nucleus caudalis (52). In rats, antidromic stimulation antipsychotic drugs has been built on evidence that sub- of the trigeminal nerve increases vascular permeability and stance P modulates the activity of the mesolimbic dopamine causes plasma protein extravasation in the meninges that is system through which established antipsychotic drugs are inhibited by NK1 receptor antagonists (53). Substance P–containing fibers have been suggest that if meningeal plasma extravasation and inflam- shown to make synaptic contact with tyrosine hydroxyl- mation of the meninges is involved in the pathogenesis of ase–positive neurons in the ventral tegmental area (VTA) migraine, then NK1 receptor antagonists should provide an from which the mesolimbic dopamine projection arises effective antimigraine therapy. Infusion of substance P agonists into the VTA stimu- potential analgesic activity, CNS-penetrant NK1antagonists lates locomotor activity in rats, an effect attributed to the may also be able to alleviate headache by preventing activa- activation of dopamine neurons because this is accompanied tion of sensory neurons in the trigeminal nucleus caudalis. Consistent with this in patients with migraine, in whom neither LY 303870 (54) interpretation, the locomotor hyperactivity and changes in nor GR205171 (55) gave headache relief. Emesis The ability of a monoclonal antibody to substance P, Substance P is present in the nucleus tractus solitarius and injected into the nucleus accumbens, to attenuate the loco- the area postrema (56), regions implicated in the control of motor response to amphetamine (72) was consistent with emesis. Local application of substance P in the area postrema the proposal that endogenous substance P modulates the causes retching in ferrets (57), a finding suggesting that NK1 release of dopamine in the mesolimbic system. A subsequent receptor antagonists may be antiemetic. Consistent with this study appeared to support this interpretation because the proposal, these compounds have emerged as an important NK1 receptor antagonist CP-96,345 reduced the firing of new class of antiemetics in preclinical studies using ferrets. However, other studies with CP-99,994 completely abolished cisplatin-induced retching NK1 receptor antagonists are not consistent with these find- and vomiting and exhibited broad-spectrum activity against ings. Surprisingly, intra-VTA coinfusion of CP-96,345 was peripheral and centrally acting emetogens (58–60). Impor- unable to block substance P agonist–induced locomotor tantly, CP-99,994 markedly attenuated both acute and de- activation in rats (71), and amphetamine-induced hyperac- layed emesis induced by cisplatin, a profile that distinguishes tivity in guinea pigs was not selectively inhibited by CP- NK1 receptor antagonists from established antiemetics (61, 99,994. The ability of CP-99,994 to block both peripherally A possible explanation for the lack of effect of NK1 recep- and centrally acting emetogens and the demonstration that tor antagonists in these studies is that the effects of substance direct injection of CP-99,994 into the region of the nucleus P in the rodent VTA may be mediated by stimulation of tractus solitarius inhibited cisplatin-induced emesis in fer- NK3, rather than NK1, receptors, as is suggested by ana- rets (63) suggest that the antiemetic activity of NK1antago- tomic (19), electrophysiologic (74), and behavioral (75) evi- nists is centrally mediated. Intra-VTA application of the NK3 receptor agonist the use of a poorly brain-penetrant quaternary NK1 receptor senktide was shown to enhance markedly the extracellular antagonist, L-743,310, which prevented cisplatin-induced concentration of dopamine in the nucleus accumbens and Chapter 13: Substance P and Related Tachykinins 173 prefrontal cortex of anesthetized guinea pigs, and this was blocked by the selective NK3 receptor antagonist SR142801 (76). SR142801 (but not the NK1 receptor antagonist GR205171 or the NK2 antagonist SR144190) was able to antagonize the increase in neuronal activity caused by acute administration of haloperidol in guinea pigs (77), a finding suggesting that NK3 receptors play a key role in regulating midbrain dopamine neurons in this species. Preliminary findings from an exploratory trial with MK-869 in patients with schizophrenia indicated that this compound did not ameliorate the core symptoms of acute psychosis (46). Anxiety and Depression Substance P and its preferred NK1 receptor are highly ex- pressed in brain regions that are critical for the regulation of emotion and neurochemical responses to stress (14,15, 24). Direct central injection of substance P agonists pro- duces a range of fear-related behaviors and defensive cardio- FIGURE 13. Activity of L-760,735 in the hamster resident- intruder test. The subjects were individually housed adult male vascular changes in animals (78–81). On test days, both resident and intruder hamsters were ies have revealed rapid reductions in substance P content dosed with the same drug and were returned to their own cages for 30 minutes before testing. Pretreatment with either fluoxe- in the mesolimbic system, hippocampus, septum, periaque- tine (0. These caused a dose-dependent increase in the latency to initiate an aggressive encounter. CGP 49823 has been reported to be Substance P antagonists are capable of attenuating psy- active in the rat social interaction test for anxiolytic activity chological stress responses in paradigms using neurochemi- (89,90) and the forced swim test for antidepressant drugs cal and behavioral endpoints. In guinea pig pups, the vocalization response elicited demonstration that intra-VTA injection of a monoclonal by maternal separation is inhibited by brain-penetrant NK1 antibody to substance P prevented stress-induced activation receptor antagonists (L-773,060, L-760,735, GR205171), of mesocortical dopamine neurons (85).
It is believed the incidence has increased over the last half century (Bulik et al generic viagra super active 50 mg without prescription erectile dysfunction cures over the counter, 2006; Hoek viagra super active 100mg mastercard impotence jokes, 2006). Dieting reduces anxiety in the short term, but begins a destructive cycle of increasing anxiety, depression and obsessionality, and further dieting. Evidence suggests a genetic predisposition, and important contributions from culture, early life experience (including neglect and abuse), personality type, the neurological and hormonal changes associated maturation, and the stressors of adolescence (including increasing autonomy). The “hunger hormones” may play a role – but details are unclear. Leptin – an appetite suppressing hormone, is secreted by fat cells. Ghrelin – an appetite increasing hormone, is release by the stomach. The lifetime risk of AN is 7-12 times greater for individuals with a first degree relative with the disorder. Twin studies support high heritability (46-70%, Kendler et al, 1991; 33-84%, Bulik & Tozzi, 2004). Recent twin studies found heritability due to genetics 56%, shared environment 5% and unique environment 38% (Bulik et al, 2006). Nevertheless, significant genome-wide findings are yet to be reported (Hinney & Volckmar, 2013). Epigenetics is expected to become an area of active research (Pjetri et al, 2012). Others argue that genetic factors could be “switched on” by the hormonal changes and the particular stressors of puberty (Herpertz-Dahlman et al, 2011). Pregnancy and perinatal complications, especially preterm birth, are risk factors. The evidence for childhood sexual abuse as an aetiological factor in AN is inconclusive (Wonderlich et al, 1997). Severe life events are found in a minority of those with onset before 25 years ant the majority of patients with onset after 25 years. Personality disorder is found in at least 70% of those with AN; obsessive- compulsive personality disorder is the most common. Personality traits are characteristic, and may represent risk factors, or an underpinning pathological process. Herpertz-Dahlmann et al (2011) describe patients as “usually good and successful”, however, often with “some peculiarities”. They describe rigidity and perfectionism, depression, anxiety. Interpersonal function may be reduced with non-assertive, submissive interpersonal style, poor theory of mind, and autistic traits, while Ahren et al (2011) found that these patients characteristically evaluate themselves by comparison with others. Patients with AN also appear to demonstrate diminished “interoceptive awareness”. Interoception includes a range of sensations beyond taste, including the perception of pain, temperature, itch, tickle, sensual touch, muscle tension, air hunger, stomach pH and intestinal tension. Integration of these provides a sense of the entire body and the self – provides a link between cognitive and affective processes and the current body state. Altered interoceptive awareness might be a precipitating and reinforcing factor in AN (Guardia et al, 2013). Alexithymia is the term applied to an impaired ability to identify and communicate emotions. A recent review indicated that when alexithymia is present in AN, the prognosis is less favourable (Pinna et al, 2015). Many such personality features improve with remission of the condition. However, tendency to negative emotional states, harm avoidance, perfectionism, desire for thinness and mild dietary preoccupation persist – suggesting these are underlying traits which contribute to the pathogenesis of AN (Kaye et al, 2009). At the same time, it must be remembered that such features are exaggerated by starvation (Keys et al, 1950). Evidence suggests that individuals with AN experience anxiety, that dietary restraint reduces this unpleasant state, and that eating stimulates dysphoric mood (Kaye et al, 2009). Others state that dieting counteracts feeling of worthlessness (Herpertz-Dahlmann et al, 2011). Socio-cultural factors have shaped “the modern cult of thinness” in Western societies.
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