Corpus cavemosum

Schwell-korper, m. Anat.) corpus cavemosum. -kraft,/. Leather) plumping power, -mittel,... 

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... 

Ignarro, L. I, Bush, P. A., Buga, G. M., Wood, K. S., Fukuto, J. M., and Rajfer, J., 1990, Nitric oxide and cychc GMP formation upon electrical field stimulation cause relaxation of corpus cavemosum smooth muscle, Biochem. Biophys. Res. Commun. 170 843-850. 

More than a decade ago, it became clear that the human body makes NO. It is made in the brain, in the muscle cells which exist in the interior of the blood vessels, by macrophages (white cells that form an important part of the immune system), by the corpus cavemosum of the penis, and perhaps elsewhere. NO plays an important role in each of these tissues. The source of the atoms for the synthesis of NO is the common amino acid arginine (chapter 9). Under the influence of an enzyme termed NO synthase, arginine is converted to NO (and other products). The lifetime of NO in the tissues is quite short, a few seconds, but it lasts long enough to be effective. 

A further characteristic of this principle is that, if the activity of phosphodiesterase is decreased, the concentration of cyclic GMP will increase to an extent dependent upon the extent of the decrease in activity. This characteristic has been made use of by the pharmaceutical industry. Cyclic GMP has a vasodilatory effect and this is the case for the arterioles that supply blood to the corpus cavemosum in the penis, which controls the erection of the penis. Drugs were developed (e.g. sildenafil) that inhibits cyclic GMP phosphodiesterase and hence increases the cyclic GMP level which resnlts in vasodilation of the arterioles and an increase in the snpply of blood to the spongy tissue of the corpus cavemosum, which expands resulting in erection. This dmg has been found to be effective in some patients snffering from erectile dysfunction. This can be a particular problem in diabetic patients and more elderly men (Chapter 19). 

Matsumoto K, Yoshida M, Andersson K, Hedlund P. (2005) Effects in vitro and in vivo by apomorphine in the rat corpus cavemosum. Br J Pharmacol 146 259-267. 

Uses Viagra ED, Revatio Pulm artery HTN Action X PDE5 (responsible for cGMP breakdown) T cGMP activity to relax smooth muscles T flow to corpus cavemosum and pulm vasculature antiproliferative on pulm artery smooth muscle Dose ED 25-100 mg PO 1 h before sexual activity, max 1 X d if >65 y avoid... 

In a series of studies conducted in our laboratory (Ignarro et al., 1990b Rajfer et al., 1992), relaxation of corpus cavemosum smooth muscle from the penis of the rabbit and human caused by electrical stimulation of the NANG neuronal pathway was found to be inhibited by oxyhemoglobin, methylene blue, N°-nitro-... 

Campos de Carvalho AC, Moreno AP, Christ GJ, Melman A, Roy C, Hertzberg EL, Spray DC Gap junctions formed of connexin43 interconnect smooth muscle cells of the human corpus cavemosum. J Urol 1993 149 1568-1575. 

The effect of histamine on rabbit corpus cavemosum was apparently due to the activation of Hi receptors, whereas H3 receptors were absent. However, the effect on electrically-induced contractions was investigated only by the use of thioperamide, and the H3 agonist was tested on basal motility and noradrenaline-induced contractions (Kim et al., 1995). We think therefore that further studies are needed to definitely exclude the presence of prejunctional H3 receptors in this tissue. 

Erection occurs when adrenergic-induced sinusoid tone is antagonized by sacral parasympathetic stimulation that produces sinusoidal relaxation primarily by synthesis and release of the nonadrenergic-noncholinergic (NANC) neurotransmitter nitric oxide (NO). The contribution of acetylcholine-dependent release of NO from the vascular endothelium is uncertain. In vitro electrical stimulation of isolated corpus cavemosum strips (with or without endothelium) produces sinusoidal relaxation by release of neurotransmitters within nerve terminals that is resistant to adrenergic and cholinergic blockers. Inhibitors of the synthesis of NO or of guanosine monophosphate (GMP),... 

Sildenafil increases the release of nitric oxide and increases the levels of cyclic guanosine monophosphate (cGMP), a smooth muscle relaxant. Sildenafil enhances the effects of nitric oxide by inhibiting phosphodiesterase 5, an enzyme found primarily in the penis that degrades cGMP. As a result, increased levels of cGMP in the corpus cavemosum enhance smooth muscle relaxation, the inflow of blood, and erection. Sildenafil has no effect in the absence of sexual stimulation (see Figure 60.1). 

A. Chemical mediators leading to erection. B. Effect of sildenafil on cGMP levels in the smooth muscle of the corpus cavemosum. 

SMC smooth muscle cells Corp. cav. corpus cavemosum... 

The mechanism of action of tadalafil is similar to the other PDE5 inhibitors, sildenafil and vardenafil. Through the inhibition on PDE5, tadalafil increases the concentrations of cGMP, producing smooth muscle relaxation and increased blood flow to the corpus cavemosum, thereby enhancing erectile response following appropriate sexual stimulation [52-55]. 

PGE alprostadil (used to maintain the patency of the ductus arteriosus in neonates with congenital heart defects, and for erectile dysfunction by injection into the corpus cavemosum of the penis) misoprostol (used for prophylaxis of peptic ulcer associated with NSAIDs) gemeprost (used as pessaries to soften the uterine cervix and dilate the cervical canal prior to vacuum aspiration for termination of pregnancy). 

Brindley G S 1986 Pilot experiments on the actions of drugs injected into the human corpus cavemosum penis. British Journal of Pharmacology 87 495 — an account of selfexperimentation with 17 drugs. 

Goepel M, Krege S, Price DT, Michelotti GA, Schwinn DA, Michel MC. Characterization of a-adrenoceptor subtypes in the corpus cavemosum of patients undergoing sex change surgery. J Urol 1999 162 1793-1799. 

Cirino G, Sorrentino R, d Emmanuele di Villa Bianca R, et al. Involvement of P3-adrenergic receptor activation via cyclic GMP- but not NO-dependent mechanisms in human corpus cavemosum function. Proc Natl Acad Sci USA 2003 100 5531-5536. 

The stem bark of P. yohimbe (= P. johimbe Corynanthe yohimbe), "yohimbe as it is known in Cameroon, Gabon and Congo is used traditionally as an aphrodisiac and stimulant to prevent sleep (41). The bark contains 1-6% of indole alkaloids, most of which are yohimbane-type alkaloids, the main one being yohimbine [7], which is structurally related to reserpine [8] (89). Yohimbine is a selective inhibitor of a-2- adrenergic receptors and, while at low dose it has hypertensive activity, at high dose it is hypotensive (vasodilation of peripheral vessels). It is the vasodilation of peripheral vessels, and especially vasodilation of the corpus cavemosum, which is the cause of the reputation of yohimbine as an aphrodisiac (90). Tests have shown, indeed, that increased... 

Erection occurs as a result of increased pressure in the corpora cavernosa, which translates into penile rigidity. The pressure increase is caused by three synergistic processes (i) relaxation of the smooth muscles of the corpora cavernosa (2)increase in arterial blood flow to the penis and (5) restriction of the venous blood flow out of the penis. Both central and peripheral mechanisms contribute to the process of penile erection. At the central level, the psychological component of penile erection is controlled by the hypothalamic and limbic systems (140). At the peripheral level, both sympathetic and parasympathetic pathways as well as several mediators are involved. Psychogenic and local stimulation results in the release of neurotransmitters from the cavemosal nerve terminals and smooth muscle endothelium. Factors that mediate the corpus cavemosum relaxation include nitric oxide (NO), vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), and prostaglandin. 

It is now believed that yohimbine exerts its erectogenic action by blocking post-S3oiap-tic a2 receptors in the corpus cavemosum and thus inhibits the contractility of the cavernosal tissue (128). In addition to its a-adren-ergic effects, yohimbine exerts a stimulatory action on the mood and may increase anxiety. This effect is at least partially attributed to yohimbine s central serotonergic activity... 

Gogmen C, Kumcu EK, Segilmis A, et al. 2000. Restorative effects of zinc and selenium on nitrergic relaxations impaired by cadmium in the mouse corpus cavemosum. Toxicol Lett 111 229-234. 

---