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where to buy viagra safely canadian pharmacy viagra The expression pattern of PDE11 has become the source of some controversy recently because of the drug tadalafil. Of the three major PDE5 inhibitors commonly used to treat erectile dysfunction (tadalafil, sildenafil, and vardenafil), only tadalafil has been found to have a relatively high affinity for PDE11 with a reported IC50 of ?73 nM (Tables 4 and 5) (Card et al., 2004; Weeks et al., 2005). Therefore, some scientists speculate that tadalafil will be more likely to have nonspecific side effects than sildenafil or vardenafil because of inhibitory effects on PDE11. Given that tadalafil inhibits PDE5 with substantially higher affinity (IC50 ?10 nM), our lack of information about physiological roles for PDE11, and the very similar safety profiles for all three drugs, it will probably take long-term trials to determine the validity of these speculations. This work has been supported by grants from the MIUR-PRIN (project no. 2005069853), Cariverona, Bando 2004 "Integrazione tra tecnologia e sviluppo di settore - Bando per progetti di ricerca a indirizzo biomedico," and the Italian Association for Cancer Research. Almost all antihypertensive medications have been implicated in erectile dysfunction.23 The mechanisms vary from central-acting sympatholytics, depression of libido as well as higher blood pressure requirement to achieve erection in atherosclerotic patients taking diuretics and vasodilators. The role of smoking in causing erectile dysfunction remains a source of controversy. A recent consensus group analysis failed to document a direct link to erectile dysfunction. However, smoking seems to amplify other risk factors, such as hypertension and coronary artery disease.24 Martin-Morales and colleagues25 have shown an increased risk of erectile dysfunction among smokers (odds ratio [OR] 2.5). Systemic diseases are also associated with erectile dysfunction. This is often multifactorial, as in diabetes and renal failure.26 Given the role of androgens in the physiology of erections, it is not surprising that many hypogonadal men do not experience erectile dysfunction per se. Low serum testosterone levels may be primary or secondary to another condition, such as hyperprolactinemia or hypothyroidism. Regardless of the mechanism, the result is primarily a loss of libido, although many hypogonadal men retain their ability to obtain erections.27 searching for cheap viagra? 150mg viagra online without prescription