Alpha relaxation effects

LLDPE Storage modulus (alpha relaxation) Effects of beta irradiation 112... 

Alfuzosin is a selective alpha-blocker, which relaxes smooth muscle, thereby increasing urinary flow rate. Because of its alpha-blockade effect, alfuzosin tends to lower the blood pressure and the first dose of the drug may lead to a hypotensive effect. 

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

In this study, both the normal mode relaxation of the siloxane network and the MWS processes arising from the interaction of the dispersed nanoclay platelets within the polymer network have been observed. Although it is routine practice to observe the primary alpha relaxation of a polymeric system at temperatures below Tg, in this work it is the MWS processes associated with the clay particles within the polymer matrix that are of interest. Therefore, all BDS analyses were conducted at 40°C over a frequency range of 10 to 6.5x10 Hz. At these temperatures, interfacial polarization effects dominate the dielectric response of the filled systems and although it is possible to resolve a normal mode relaxation of the polymer in the unfilled system (see Figure 2), MWS processes arising from the presence of the nanoclay mask this comparatively weak process. 

The assignment of the alpha relaxation was additionally confirmed by AC-calorimetric measurements on thin films of POHOAc [31], The effect of confinement on the overall dynamics of POHOAc is given in Fig. 24, showing the dielectric spectra for different film thicknesses, ranging from 310 nm down to 17 nm. While the beta and the gamma relaxations, as local processes, are not affected with decreasing film thickness (except a decrease of the dielectric... 

Much more pronounced effects are observed at higher temperatures The alpha relaxation peak of a thin PS film of 75 nm (measured at 122°C) is shifted to higher frequencies after keeping the sample at 180°C in ambient air (Fig. 33). Consequently, the average relaxation rate of the alpha relaxation process increases in time by more than one order of magnitude during this thermal treatment (inset, Fig. 33). 

Hall DB, Hooker JC, Torkelson JM (1997) Ultrathin polymer films near the glass transition effect on the distribution of alpha-relaxation times as measured by second harmonic generation. Macromolecules 30 667-669... 

Several polymers combine excellent ultraviolet resistance with good tensile and elongation at break properties (Table 11.3). The storage modulus, alpha relaxation, and creep in polymers are influenced by electron irradiation. Thus, the creep of some polymers increased upon exposure to electron beam irradiation below 4 Mrad. Neutron/gamma irradiation also had an adverse effect on some polymer properties. Thus, some glass fiber-reinforced plastics lose 20%-40% of their flexural strength after exposure to neutron/gamma irradiation doses above 1 x 10 Gy [3]. 

Mechanism of Action An antihypertensive that selectively blocks alpha -adrenerglc receptors, decreasing peripheral vascular resistance. Therapeutic Effect Causes peripheral vasodilation and lowers BP. Also relaxes smooth muscle of bladder and prostate. 

Mechanism of Action An antihypertensive that produces long-lasting noncompetitive alpha-adrenergic blockade of postganglionic synapses in exocrine glands and smooth muscles. Relaxes urethra and increases opening of the bladder. Therapeutic Effect Controls hypertension. 

Caution [C, ] CrCl <30 Contra Component sensitivity, asthma, severe COPD, sinus bradycardia Disp Soln SE Irritation, bitter taste, superficial keratitis, ocular allergic Rxn EMS Drug is absorbed systemically OD May cause electrolyte disturbances (K), acidosis and bradycardia monitor ECG Doxazosin (Cardura, Cardura XL) [Antihypertensive/Alpha Blocker] Uses HTN symptomatic BPH Action < [-Adrenergic blocker relaxes bladder neck smooth muscle Dose HTN Initial 1 mg/d PO may be T to 16 mg/d PO BPH Initial 1 mg/d PO, may T to 8 mg/d XR 2-8mg qAM Caution [B, ] Use w/ PDE5 inhibitor (eg, sildenafil) can cause 1 BP Contra Component sensitivity Disp Tabs SE Dizziness, HA, drowsiness, sexual dysfxn, doses >4 mg T postural BP risk Interactions T Effects W/ nitrates, antihypertensives, EtOH i effects W/ NSAEDs, butcher s broom -t effects OF clonidine EMS Concurrent EtOH use can T drowsiness syncope may occur w/in 90 min of initial dose OD May cause profound hypotension place pt in supine position, give IV fluids, use pressors if needed... 

It is not clear, however, exactly how these drugs inhibit neurons involved in the polysynaptic pathways. There is preliminary evidence that one of these compounds (cyclobenzaprine) might block serotonin receptors on spinal interneurons, thereby decreasing the excitatory influence of serotonin on alpha motor neuron activity.50,55 Although this effect has been attributed to cyclobenzaprine in animals (rats), the effect of this drug and other muscle relaxants in humans remains to be determined. 

Vascular smooth muscle tone is regulated by adrenoceptors consequently, catecholamines are important in controlling peripheral vascular resistance and venous capacitance. Alpha receptors increase arterial resistance, whereas 2 receptors promote smooth muscle relaxation. There are major differences in receptor types in the various vascular beds (Table 9-4). The skin vessels have predominantly receptors and constrict in the presence of epinephrine and norepinephrine, as do the splanchnic vessels. Vessels in skeletal muscle may constrict or dilate depending on whether ffor 13 receptors are activated. Consequently, the overall effects of a sympathomimetic drug on blood vessels depend on the relative activities of that drug at and 8receptors and the anatomic sites of the vessels affected. In addition, Di receptors promote vasodilation of renal, splanchnic, coronary, cerebral, and perhaps other resistance vessels. Activation of the Di receptors in the renal vasculature may play a major role in the natriuresis induced by pharmacologic administration of dopamine. 

The human uterus contains and B2 receptors. The fact that the Breceptors mediate relaxation may be clinically useful in pregnancy (see Clinical Pharmacology). The bladder base, urethral sphincter, and prostate contain receptors that mediate contraction and therefore promote urinary continence. The specific subtype of ai receptor involved in mediating constriction of the bladder base and prostate is uncertain, but uia receptors probably play an important role. The B2 receptors of the bladder wall mediate relaxation. Ejaculation depends upon normal a-receptor (and possibly purinergic receptor) activation in the ductus deferens, seminal vesicles, and prostate. The detumescence of erectile tissue that normally follows ejaculation is also brought about by norepinephrine (and possibly neuropeptide Y) released from sympathetic nerves. Alpha activation appears to have a similar detumescent effect on erectile tissue in female animals. 

These mediators can produce a number of effects including bronchiolar constriction, capillary dilatation, or urticaria (i.e., hives). In severe episodes of type I reactions a life-threatening anaphylaxis can develop in humans due to extreme bronchoconstriction and precipitate hypotension. Epinephrine is the principal drug used in the acute management of these critical effects since it achieves (1) an elevated blood pressure via activation of alpha receptors in peripheral resistance blood vessels and (2) relaxation of bronchiolar smooth muscle via activation of (32 receptors in the lung. Relief from the dermatological problem (i.e., hives) is also achieved via vasoconstriction of capillaries in the skin that reduce permeability, and, hence, fluid accumulation. Penicillin is a classic example of a drug that can cause a type I reaction. 

Q9 Myometrial contractile activity is modified by both endocrine and autonomic factors. The increase in oestrogens during pregnancy gradually increases both the excitability of uterine smooth muscle and its sensitivity to agonists, particularly oxytocin. The uterus receives sympathetic innervation, which exerts excitatory effects via alpha-1-receptors (a i-receptors). Uterine smooth muscle also possesses beta-2-receptors (/d2-recept°rs)> which mediate relaxation. 

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