Erection, penile

MISCELLANEOUS ANTIDEPRESSANTS. An uncommon but potentially serious adverse reaction of trazodone is priapism (a persistent erection of die penis). If not treated within a few hours, priapism can result in impotence The nurse instructs the patient to report any prolonged or inappropriate penile erection. Use of the drug is discontinued immediately and the primary care provider notified. Injection of a-adrenergic stimulants (eg, norepinephrine) may be helpful in treating priapism. In some cases, surgical intervention may be required. Venlafaxine may cause an increase in die blood pressure. A sustained increase in die blood pressure may indicate that die dosage of venlafaxine needs to be decreased. 

Involved in penile erection sildenafil citrate (Viagra) affects this process by inhibiting a cGMP phosphodiesterase... 

Identify the structures of the male reproductive system and describe the physiology of a penile erection. 

Yohimbine is an indole alkaloid produced in the bark of yohimbe trees. It selectively inhibits a2-adrenergic receptors in the brain that are associated with libido and penile erection. Since there is only limited data supporting its efficacy, yohimbine is not a recommended treatment for any form of ED.22 Adverse effects of the drug include nausea, irritability, headaches, anxiety, tachycardia, and hypertension. 

The Mas group recently published results on the measurement of NO release from the corpus cavemosum of the penis and its relation to penile erection [101], For this... 

Erectile dysfunction (ED) is the failure to achieve a penile erection suitable for sexual intercourse. Patients often refer to it as impotence. 

ED can result from an abnormality in one of the four systems necessary for a normal penile erection or from a combination of abnormalities. Vascular, nervous, or hormonal etiologies of ED are referred to as organic ED. Abnormality of the fourth system (i.e., patient s psychological receptivity to sexual stimuli) is referred to as psychogenic ED. 

The goal of treatment is to improve the quantity and quality of penile erections suitable for intercourse. 

At clinical trials, sildenafil did not work well as a treatment for angina. Instead, it was observed that it overcomes erectile dysfunction. Later, it was found that cyclic GMP also increases the level of nitric oxide, which is needed in penile erections. 

Penile erection occurs by relaxation of the smooth muscle of the corpus cavernosum, increasing blood flow into the penis and producing erection and rigidity. In a parallel fashion, vaginal pressure stimulation increases blood velocity and flow into clitoral arteries (Lavoisier et al. 1995). Cavernosal vasodilation is accomplished by neurotransmitters released from the cavernosal nerve and endothelial cells. One of the most important transmitters in this cascade is nitric oxide (NO), which induces synthesis of cyclic GMP from guanylate cyclase (Rajfer et al. 1992). Thus, ginkgo s vascular mechanisms could be responsible for some of the putative sexual effects. 

But not everything that norepinephrine and acetylcholine do is opposed. In one case, they cooperate. Acetylcholine stimulates penile erection by increasing blood flow to that organ. Norepinephrine controls ejaculation. In still other cases, the pharmacology of these neurotransmitters is unique. For example, acetylcholine induces urination by causing the bladder to constrict. Acetylcholine also induces secretion of saliva and tears. Norepinephrine has nothing to do with these functions. 

Penile erection is essential for insertion of the penis into the vagina and therefore is essential for reproduction. This process depends upon relaxation of smooth muscle in the... 

Figure 19.15 The hydraulic mechanism for penile erection. Erection begins when the penile arterioles dilate, under the influence of nitric oxide, allowing more blood to enter the corpora cavernosa of the penis. These contain a spongy tissue which now expands but at the same time compresses the veins so that the pressure within the cavernosa increases further, producing more expansion of the cavernosa and maintaining the erection.

Figure 19.16 Role of nitric oxide synthase in control of penile erection. Nitric oxide synthase catalyses conversion of arginine to nitric oxide, which then acts to acb vate guanyl cyclase which results in an increase in the concentrab on of cyclic GMP. The latter relaxes smooth muscle in the arterioles that supply blood to the corpora cavernosa in the penis so that blood flow increases and erection results.

Figure 19.17 The biochemistiy and physiology responsible for penile erection. Sexual activity itself begins with a state of arousal that leads to erection. Arousal results in part from stimulation of the sense organs. The hypothalamus coordinates the sensations and activates the autonomic nervous system. Sensory nerves from the skin of the penis and other erogenous zones stimulate the parasympathetic system. This activates nitric oxide synthase and the resultant nitric oxide, via cyclic GMP, causes vasodilation of the arterioles. This increases blood flow through the corpora cavernosa which then expands producing an erection. Pheromones secreted by the female can stimulate the odour detecting system in the nasal cavity of the male (Chapter 12 and see above). Stress, however, activates the sympathetic system releases cyclic AMP which can result in vasoconstriction of the arterioles. Other factors that can interfere with an erection are physical fatigue and alcohol.

Hsieh GC, Hollingsworth PR, Martino B, Chang R, TerranovaMA, O Neill AB, Lynch JJ, Moreland RB, Donnelly-Roberts DL, Kolasa T, Mikusa JP, McVey JM, Marsh KC, Sullivan JP, Brioni JD. (2004) Central mechanisms regulating penile erection in conscious rats The dopaminergic systems related to the proerectile effect of apomorphine. J Pharmacol Exp Ther 308 330-338. 

Priapism Patients with prolonged or inappropriate penile erection should discontinue use immediately and consult a physician or go to an emergency room. Priapism of the clitoris has also occurred. 

The wide-spread and diverse functions of NO in biology can be mediated through metallonitrosyl complexes. This opens the way for the coordination chemist to design new agents as 1) cytotoxic drugs that are activated by reduction in vivo to release NO 2) more versatile hypotensive drugs 3) facilitators of penile erection that might be applied topically, possibly in... 

The physiology of penile erection involves an interplay of anatomical, hemodynamic, neurophysiological, and sex hormone interaction. Penile erection is the result of a complex interaction between the central nervous system and other local factors. This physical event also can be influenced by psychological factors. 

Hydroxytryptamine (5-HT), dopamine, and norepinephrine play important roles as central neurotrans-mitters in the process of erection. Still other substances or hormones, such as endorphins, oxytocin, vasopressin, adrenocorticotropic hormone (ACTH) and related peptides, and prolactin, appear to participate in the complex and coordinated process of penile erection. Central nonadrenergic neurons also may influence male sexual behavior. 

I Central initiator Compounds that have the main site of action in the CNS to activate neural events that result in coordinated signaling that results in the initiation of a penile erection (e.g. apomorphine)... 

III Central conditioner Compounds that act mainly to improve the internal milieu of the CNS so that penile erection is enabled or enhanced, they do not on their own initiate an erection (e.g. trazodone)... 

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