BJU International (1999), 83, 327–333

EVects of androgens on the expression of nitric oxide synthasemRNAs in rat corpus cavernosumK.H. PARK*, S .W. KIM, K.D. KIM and J .-S. PAICKDepartments of Urology, *Sung Kyun Kwan University and Seoul National University, College of Medicine, Seoul, Korea

Objective To examine the eCects of androgens on erectile response and the ratio of maximal intracavernosalpressure (ICPmax) to systemic blood pressure (SBP),response and the expression of nitric oxide synthase

(NOS) isoform mRNAs in the penile corpus cav- although both testosterone and DHT eCectivelyrestored the response to normal. NOS activity and theernosum of castrated rats.

Materials and methods The study comprised 50 adult amount of nNOS mRNA were reduced in castratedrats but restored by androgen replacement. Althoughmale Sprague-Dawley rats in five groups: sham con-

trols; castrated; castrated and receiving testosterone; there was no significant diCerence in NOS activitybetween the androgens, nNOS mRNA expression wascastrated and receiving dihydrotestosterone (DHT);

castrated and receiving testosterone and 5a-reductase higher in rats treated with DHT. There were no eCectsof androgen in rats treated with finasteride, as theinhibitor (finasteride). Androgen replacements were

administered via implants of silicone tubing. After ICPmax/SBP ratio, NOS activity and amount of nNOSmRNA decreased. eNOS mRNA expression was inde-7 days, some animals underwent electrical stimulation

of the cavernosal nerves and the remainder were used pendent of androgen.Conclusions Androgens enhance nNOS gene expressionfor further analysis. NOS activity was measured in the

soluble fraction of the corpus cavernosum, using the in the penile corpus cavernosum of rats, suggestingthat they play an important role in maintaining NOSGriess reaction. Total RNA was isolated and nNOS

and eNOS mRNA expression examined using semi- activity. Of the two androgens, DHT was morepotent.quantitative reverse-transcriptase polymerase chain

reaction. Keywords Androgen, penile erection, corpuscavernosum, nitric oxide synthaseResults Castration caused a marked decrease in erectile

influenced by castration, which decreased NOS activityIntroduction

of penile tissue; activity was later restored by testosteronereplacement to normal levels [10]. Further studies haveAlthough it is generally accepted that erectile response

in mammals is regulated by androgens, and androgen confirmed that as the administration of l-arginine failedto augment erectile response while supplementation ofreceptors have been identified in cavernosal tissue [1,2],

the extent of the involvement and precise role of these testosterone in castrated rats resulted in increased nNOSmRNA synthesis, enzyme activity is dependent on thesteroids remains to be established. To date, a variety of

animal models, including man, has been used to eluci- availability of androgens rather than of substrates [11].It can therefore be postulated that androgens play andate the role of androgens in erectile response. It has

been shown that castration results in a diminished essential role in the production and maintenance oferectile response via modulation of NOS activity.frequency and duration of penile erection [3–5], a sig-

nificant decrease in the magnitude of intracavernosal However, there is no clear evidence of the extent towhich androgens control the NO-dependent erectilepressure [6] and a considerable reduction in the erectile

response to electrical field stimulation (ES) [7]. mechanism. It is still not clear whether androgens exerttheir eCects on a specific NO-production system byNitric oxide (NO), a potent vasodilator, has recently

been shown to be responsible for the relaxation of smooth activating a specific NOS isoform gene(s).Thus the purpose of this study was to investigate themuscle cells in the penile corpus cavernosum [8,9].

Activities of NO-producing enzymes, NO synthases eCects of androgens on NOS activity of the penile corpuscavernosum in castrated rats under varying androgenic(NOSs), have been identified in the rat penile cytosol

fraction. Penile NOS activity has been shown to be hormone status. To verify the androgenic eCect on NOSgene activation, transcriptional changes in NOS isoformswere also examined. A further goal was to determineAccepted for publication 2 September 1998

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328 K.H. PARK et al.

whether these eCects of testosterone are mediated via its Each penis was weighed and homogenates prepared insix volumes of cold medium containing 0.32 mol/Lconversion into DHT.sucrose, 20 mmol/L HEPES (pH 7.2), 0.5 mmol/L EDTA,1 mmol/L dithiothreitol and protease inhibitors

Materials and methods(3 mmol/L leupeptin and 1 mmol/L phenylmethylsulpho-nylfluoride), using a Polytron homogenizer. The cyto-The study comprised 50 adult male Sprague-Dawley rats

(250–300 g body weight), maintained under controlled solic and particulate fractions were separated bycentrifugation at 12 500 g for 60 min. To the cytosollighting and treated according to local regulations. The

rats were castrated under ketamine anaesthesia fraction (200 mL), 10 mL each of 2 mmol/L arginine and2 mmol/L NADPH were added. After incubating the(35 mg/kg intraperitoneal). The animals were divided

into five experimental groups of five each: group 1, intact mixture for 1 h at 37°C, 200 mL of Griess reagent (1%sulphanylamide, 0.1% naphthylethylene diamine and(sham-operated) controls; group 2, castrated; group 3,

castrated with testosterone supplementation via 2.2-cm 2.5% H3PO

4) was added and incubated further for

10 min at room temperature. The nitrate concentrationSilastic@ tubing (Dow Corning, Midland, MI, USA; out-side diameter 3.17 mm; inside diameter 1.57 mm); group was measured by comparison with a standard curve,

using linear gradient concentrations of sodium nitrate.4, castrated, with DHT supplementation via 1-cm tubing;and group 5, castrated with testosterone supplemen- To normalize interassay variations of enzyme specific

activity against the control value for each series, atation and daily administration of finasteride (40 mg/kgbody weight) orally. Animals in groups 1 and 2 were complete set of penile cytosol samples per selected group

was used for each determination of citrulline synthesis.implanted with empty tubing. After treatment for 7 days,the rats were assessed to determine circulating androgen Specific activity was calculated as mmol/10 min per

gram of tissue.levels by radioimmunoassay, using blood collected fromthe heart.

Measurement of nNOS and eNOS gene expressionsMeasurement of erectile response to ES

To measure the expression of NOS genes, total RNA wasisolated using TRIzol (Gibco BRL, Gathisberg, MD, USA).Rats were anaesthetized as described and the erectile

response measured as previously described [3]. Briefly, The reverse transcription reaction was carried out usinga commercially available kit (Promega, Madison, WI,after surgical exposure of the hypogastric and pelvic

nerve, the major pelvic ganglion and the cavernosal USA). Briefly, 1.0 mg of total RNA was primed with0.5 mg of the oligo (dT)

15and incubated for 30 min atnerves, the last were stimulated with a glass electric

stimulator and a bipolar platinum electrode (1–3 V, 42°C. For each sample, 1×RT buCer (10 mmol/L Tris-HCl, pH 8.8, 50 mmol/L KCl, and 0.1% Triton X-100),20 Hz for 5 ms). During stimulation, erections were

evaluated on the basis of maximal intracavernosal press- 1.0 mmol/L dNTPs, 5 mmol/L MgCl2

, and 300 units ofM-MLV RT in a volume of 20 mL were combined.ure (ICPmax). After the ischiocavernosal muscle was

divided, the silver-white tunica albuginea of the penile Oligonucleotide primers for nNOS had the followingsequences: sense primer, 5∞-ACCTGAAGAGCACACT-crus was exposed. A 22 G butterfly needle was inserted

into the penile crus and connected to the monitor. For GGAAAC-3∞ and antisense primer, 5∞-GATGGCCGAC-CTGAGATTC-3∞; these amplified a 428 bp fragment forthe duration of the experiments, the animals were

re-injected every 45 min with 35 mg/kg ketamine. the nNOS sequence [11]. Nucleotide sequences of primersfor eNOS were: sense primer, 5∞-CAGGCTGCCTG-Systemic blood pressure (SBP) was simultaneously moni-

tored by inserting a polyethylene tube (PE-50) into the TGAAACTTT-3∞ and antisense primer, 5∞-TTGCTGCTC-TGTAGGTTCTC-3∞ [13]. For an internal standard, cyclo-right femoral artery.philin mRNA was also amplified. The primers used forcyclophilin were 5∞-TGTTCTTCGACATCACGGC-3∞

Measurement of NOS activity(sense) and 5∞-TTATGGCGTGTGAAGTCACC-3∞ (anti-sense), amplifying a transcript of 216 bp. Semi-To determine whether androgens modulate the ability

of the penis to synthesize NO, NOS activity was quantitative RT-PCR of nNOS gene involved the ‘primerdropping’ method [14]; 4 mL of the cDNA product wasmeasured in the corpus cavernosal tissues. The activity

in tissue homogenates was determined in penises used and the reaction was carried out in a final volumeof 20 mL containing 2.5 mmol/L MgCl

2, 1×PCR buCerremoved from animals not subjected to other experi-

ments, as previously described [10,12]. Briefly, rats (20 mmol/L Tris-Cl, 50 mmol/L KCl, pH 8.4, TritonX-100), 2.5 units of Taq DNA polymerase, 0.2 mmol/Lwere anaesthetized and the penile shaft and bulb

(excluding skin and glans) excised and stored at −80°C. dNTPs and 25 pmol/L of each primer. A PTC-200

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ANDROGENS AND ERECTILE RES PONSE 329

thermal cycler (MJ Research, Inc, Watertown, MA, USA) was administered to animals on completion of treat-ment. The eCects of castration and androgen sup-completed eight cycles consisting of heat denaturation

at 94°C for 45 s, annealing at 54.5°C for 45 s and plementation on the erectile response to ES wereexpressed as the mean (sem) of the ratio of ICPmax toextension at 72°C for 1 min. After eight cycles the primer

for cyclophilin (25 pmol/L concentration of sense and SBP. Table 1 shows that the erectile response wassignificantly less in groups 2 and 4 than that in groupantisense) was added and the thermal cycler completed

24 additional cycles under the same conditions. Because 1. Castration reduced the ICPmax/SBP ratio by 40%(P<0.005), although both testosterone and DHTthere were large diCerences in the values of the melting

temperatures of the primers, it was not possible to replacement restored the magnitude of response tocontrol levels. The response of group 5 determinedco-amplify eNOS and cyclophilin cDNAs. After adding

4 mL of cDNA products to each tube, separate PCR whether testosterone alone induced a normal erectileresponse; because there was a 29% decrease in groupreactions were therefore carried out. The PCR condition

of eNOS was: 94°C for 45 s, 51°C for 45 s and 72°C for 5 (P=0.012), it is clear that the eCect of testosteronewas attenuated by finasteride treatment.1 min, total 30 cycles. Amplification of cyclophilin was

completed during 24 cycles under the same conditions. The NOS activity results are presented in Table 1,expressed as a percentage of the normal controls; thereIn preliminary experiments of up to 30 and 24 cycles,

the PCR and product amplification of eNOS and cyclophi- was a close relationship between ES response and NOSactivity for each of the groups assayed. Castration causedlin, respectively, was linear. Using a 2% agarose gel, a

10 mL aliquot of each reaction product was subjected to a significant decrease in penile NOS activity, althoughthis was restored by androgen treatment to levels whichelectrophoresis followed by staining with ethidium bro-

mide. The intensities of ethidium bromide fluorescence were not significantly diCerent from the control value.Although both testosterone and DHT did not completelywere determined using a CCD-camera (Fujifilm, Japan).

The density of nNOS and eNOS were normalized to that restore NOS activity, the levels reached did not diCersignificantly, although they were significantly higherof cyclophilin and the values expressed as arbitrary

units. than that of group 2. However, the administration offinasteride to rats receiving testosterone resulted in areduction of NOS activity by 55%.

Statistical analysis The eCect of androgens on NOS activity was assessedby determining the regulation of NOS mRNA expression

Experimental values were expressed as the mean (sem);in the penis using the RT-PCR method with isoform-

Student’s t-test and the Wilcoxon rank-sum test werespecific primers, measuring the availability of nNOS and

used to calculate probabilities when comparing twoeNOS mRNAs. Figure 1 shows the results of electrophor-

groups independently from the others, and P<0.05etic analysis of the RT-PCR products of nNOS mRNA.

considered to indicate significance. For comparing allThe expected size of the PCR products of nNOS (428 bp)

groups with the controls, a one-way anova wasand cyclophilin (216 bp) were obtained and the results

computed.analysed further by computing the ratio of nNOS tocyclophilin peak areas for each sample (Table 1).Castration caused an 80% reduction in the amount of

ResultsnNOS mRNA, compared with that in control rats. Theamount of nNOS mRNA in cavernosal tissue wasCastration caused a marked decrease in the circulating

plasma levels of androgens; in control rats (group 1) the significantly greater in rats in group 1 and 5 than inthose that were castrated. While DHT replacementtestosterone level was 1.58 (0.50) ng/mL and the DHT

level was 61.7 (16.0) pg/mL. Castrated rats (group 2) restored levels to control values, testosterone was lesseCective, as nNOS mRNA expression was only 38% ofhad an undetectable level of testosterone and a lower

DHT level, at 15.8 (6.6) pg/mL, but levels were higher, the control value. The administration of finasteride torats receiving testosterone significantly decreased nNOSat 1.43 (0.36) ng/mL and 58.1 (26.9) pg/mL of testoster-

one and DHT respectively, in rats in group 3. The DHT mRNA expression. Figure 1B shows the RT-PCR prod-ucts of eNOS mRNA, with an expected size of 310 bp.level in rats in group 5, at 17.9 (5.7) pg/mL, was not

significantly diCerent from those of rats in group 2 The results also show that there was no significantdiCerence in relative expression levels between castratedand finasteride thus eCectively inhibited 5a-reductase

activity. and androgen-replaced rats (Table 1). As there was nosignificant diCerence between castrated and controlTo confirm the previously reported eCects of andro-

gens on erectile response, ES of the major pelvic animals, it is also evident that castration did not altereNOS mRNA expression.ganglion, at the voltage producing maximum pressure,

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330 K.H. PARK et al.

Table 1 The relative ratio of ICPmax/SBP during ES-induced erection, total NOS activity of rat penile corpus cavernosum and NOS RNAexpression (as relative optical densities) after orchidectomy and androgen replacement in the rat

Group

Mean (SEM) variable 1 2 3 4 5

ICPmax/SBP 0.69 (0.07) 0.38 (0.02)† 0.71 (0.21) 0.49 (0.12)* 0.74 (0.04)Total NOS activity (mmol/g) 9.06 (1.53) 2.94 (1.15)† 8.18 (1.45) 4.08 (1.36)† 8.80 (1.26)nNOS* 1.81 (0.75) 0.33 (0.21)† 0.63 (0.2)*‡ 0.37 (0.11)† 1.53 (0.75)eNOS* 1.36 (0.58) 1.45 (0.51) 1.03 (0.31) 1.08 (0.66) 1.23 (0.31)

†P<0.01 and *P<0.05; Wilcoxon rank-sum test, compared with group 1; ‡P<0.05, higher than group 3.

nNOS (428 bp)

Group

Group

nNOS (310 bp)

Cyclophilin (216 bp)

Cyclophilin (216 bp)

M 1 2 3 4 5

M 1 2 3 4 5 1 2 3 4 5

a

b

Fig. 1. a, nNOS and b, eNOS expression, as shown by semiquantitative RT-PCR in rat penile corpus cavernosum after orchidectomy andandrogen replacement in the rat. M, 100 bp DNA ladder.

vations by others [3,9,16] showing that castration inDiscussion

rats decreases erectile function and androgens restore it.These results showed that androgens modulate smoothDespite androgen receptor levels decreasing rapidly in

the penis after puberty [15], the eCect of androgen on muscle relaxation in the penile corporal cavernosum;the ICPmax/SBP ratio was reduced in castrated ratsnormal penile erection is supported by several lines of

experimental results. The present results confirm obser- but restored to normal levels by androgen treatment

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ANDROGENS AND ERECTILE RES PONSE 331

(Table 1). Similar results have previously been reported conflicting reports as to whether this reduction is alsoaccompanied by a decrease in nNOS content, as deter-by others; maximal cavernosal pressure is markedly

reduced after castration but returns to normal levels mined by immunoblot detection [22]. On the other hand,it has been proposed that castration inhibits penile NOSafter treatment with testosterone [3]. It has also been

shown that androgens act to maintain both the inflow activity without aCecting NOS levels [25].The eCects of androgens on penile NOS mRNA inand outflow of blood from cavernosal spaces during

erection [4]. In castrated rats with spinal-cord tran- castrated rats appear to be NOS-isoform specific. Thepresent results showed that castration decreased nNOSsection, erectile response (ex copula) declines but is

restored by testosterone replacement [17]. In the same mRNA expression, whereas androgens reversed it(Table 1). Similar results, that testosterone treatment ofanimals, oestrogen fails to restore penile responsiveness

[18] but restores copulatory behaviour [19]. As reports castrated animals results in a marked increase of nNOSgene expression, have been reported previously [11]. Itfrom this and other laboratories have shown, the extent

to which intracavernosal pressure rises during erection is therefore assumed that androgens increase nNOSmRNA levels by enhancing nNOS gene expression or bydepends on the availability of functional androgens.

Convincing evidence has shown that erection in the decreasing mRNA degradation, resulting in more avail-able enzyme for the production of NO in rat penis. Therat is androgen-dependent and mediated by NO

[10,20,21]; androgens may act primarily to stimulate or present finding that nNOS mRNA expression is lessinfluenced by testosterone than is DHT also confirms themaintain the activity of NOS for the production of erectile

response [3,7,22,23]. NOS activity has been measured previous suggestion that DHT induces a greater erectileresponse [10].as the conversion of arginine to citrulline and was shown

to be lower in castrated rats than in those which were The present results showed a discrepancy betweenNOS activity and the amount of nNOS mRNA in ratsintact or supplemented with testosterone [7]. When

adult rats are infused with an inhibitor of NO synthesis, which received testosterone; the possibility that nNOSexpression is regulated at the translational level, ascavernosal pressure decreases in both castrated and

testosterone-replaced animals [3]. In the present study, postulated previously by Chamness et al. [22], mayaccount for this finding. It is also likely that activity oftotal NOS activity decreased in castrated rats, while

androgens restored enzyme activity to control levels the translational machinery may be limited to the useof only a small portion of nNOS transcripts. Another(Table 1). These results correlate with those relating

with the responsiveness to ES (the ICPmax/SBP ratio; possibility is that androgenic eCects are not of primaryimportance for the expression of NOS mRNAs. However,Table 1). Both responses indicate that with reconstitution

of the androgen milieu, erectile response returns to near- these eCects on erectile response appear to be species-dependent. It has been postulated that for the mainten-normal values and NOS activity is restored. From an

overall perspective it may be suggested that the role of ance of the erectile mechanism, only a minute level ofandrogens might be required, and that in men, this levelandrogens in the production of penile erection is modu-

lated through NOS activity. Modulation of NOS by is not aCected by physiological reductions in serumandrogens [26]. In fact, the administration of finasterideandrogens has also been shown by histological examin-

ation showing that the density of NOS-positive nerve to normal men does not significantly impair erectilefunction [27]. On the other hand, the blockage offibres decreased in castrated animals but recovered to

normal levels when rats were treated with androgens testosterone action by a 5a-reductase inhibitor in cas-trated rats markedly reduces both erectile response and[24].

It has previously been suggested that in the production nNOS expression to castrate levels.There has been no attempt to identify a specific NOSof erectile response in castrated animals, DHT is a more

potent androgen [10]. The present results also showed isoform in penile cytosolic fraction; in fact, cytosolicenzyme activity represents most of the penile NOS [7,15].that as the 5a-reductase inhibitor (finasteride) adminis-

tered to rats receiving testosterone resulted in decreased The present results show that the amount of eNOSmRNA was not significantly aCected by androgens. AnNOS activity, the conversion of testosterone to DHT may

be required to exert their eCects. oestrogen response element has previously been foundwithin the promoter region of bovine eNOS gene [28],Although cDNA probes for NOS isozymes are currently

available, few reports have described the detection of suggesting that oestrogen may be a physiological regu-lator of eNOS expression. However, as there was noNOS mRNA in the penis. Furthermore, it is still unclear

whether the eCect of androgens on NOS expression is significant diCerence between finasteride-and androgen-treated rats, oestrogenic eCects were not apparent in theisoform-specific. As penile erection is dependent on NO

[7,15,21], it is not surprising that castration has been present model. Although oestrogen can be produced incastrated rats by androgen supplementation, the amountshown to decrease NOS activity. However, there are

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332 K.H. PARK et al.

control of erectile function and nitric oxide synthase in themay be negligible and insuBcient to induce eNOS generat penis. Endocrinology 1997; 138: 3925–32activation.

13 Morales-Ruiz M, Jimenez W, Perez-Sala D et al. IncreasedIn conclusion, it is apparent that androgens are indis-nitric oxide synthase expression in arterial vessels ofpensable to normal erectile response in rats, althoughcirrhotic rats with ascites. Hepatology 1996; 24: 1481–6their eCects seem to depend partly on the NOS-mediated

14 Wong H, Anderson WD, Cheng T, Riabowol KT. Monitoringerectile mechanism. In humans, the most common

mRNA expression by polymerase chain reaction: thecauses of impotence are ageing and diabetes, which are ‘primer dropping’ method. Anal Biochem 1994; 223: 251–8frequently accompanied by a moderate reduction of free 15 Gonzalez-Cadavid NF, Rajfer J. Nitric oxide and otherserum testosterone [3,10]. A reduction in erectile neurotransmitters of the corpus cavernosum. In Hellstromcapacity and penile NOS activity has been found in both WJG, ed. Textbook of Andrology: Relevant Issues in Male

Infertility and Sexual Dysfunction, New York: Springer Verlag,senescent [23] and congenitally diabetic rats [29]. Both1997: 425–39clinical situations therefore suggest an essential role for

16 Heaton JP, Varrin SJ. ECects of castration and exogenousandrogens in the production of normal erection,testosterone supplementation in an animal model of penilealthough it is possible that other hormones also contrib-erection. J Urol 1994; 151: 797–800ute to maintenance of the erectile mechanism and may

17 Hart BL, Wallach SJ, Melese-d’Hospital PY. DiCerences inaCect nNOS content in the penis. This is supported byresponsiveness to testosterone of penile reflexes and

recent findings showing a significant relationshipcopulatory behavior of male rats. Horm Behav 1983;

between the adrenal gland and penile erection [25]. 17: 274–8318 Hart BL. Sexual behavior and penile reflexes of neonatally

castrated male rats treated in infancy with estrogen andReferences dihydrotestosterone. Horm Behav 1979; 13: 256–68

1 Horwitz KB, Horwitz LD. Canine vascular tissues are targets 19 Meisel RL, O’Hanlon JK, Sachs BD. DiCerential maintenancefor androgens, estrogens, progentins, and glucocorticoids. of penile responses and copulatory behavior by gonadalJ Clin Invest 1982; 69: 750–8 hormones in castrated male rats. Horm Behav 1984;

2 Takane KK, Wilson JD, McPhaul MJ. Decreased levels of 18: 56–64the androgen receptor in the mature rat phallus are 20 Andersson KE, Holmquist F. Regulation of tone in penileassociated with decreased levels of androgen receptor cavernous smooth muscle. Established concepts and newmessenger ribonucleic acid. Endocrinology 1991; 129: findings. World J Urol 1994; 12: 249–611093–100 21 Burnett AL. Nitric oxide in the penis: physiology and

3 Mills TM, Wiedmeier VT, Stopper VS. Androgen mainten- pathology. J Urol 1997; 157: 320–4ance of erectile function in the rat penis. Biol Reprod 1992; 22 Chamness SL, Ricker DD, Crone JK et al. The eCect of46: 342–8 androgen on nitric oxide synthase in the male reproductive

4 Mills TM, Stopper VS, Wiedmeier VT. ECects of castration tract of the rat. Fertil Steril 1995; 63: 1101–7and androgen replacement on the hemodynamics of penile 23 Garban H, Marquez D, Cai L, Rajfer J, Gonzalez-Cadaviderection in the rat. Biol Reprod 1994; 51: 234–8 NF. Restoration of normal adult penile erectile response in

5 Mills TM, Stopper VS, Reilly CM. Sites of androgenic aged rats by long-term treatment with androgens. Biolregulation of cavernosal blood pressure during penile Reprod 1995; 53: 1365–72erection in the rat. Int J Impotence Res 1996; 18: 56–64 24 Zvara P, Sioufi R, Schipper HM, Begin LR, Brock GB. Nitric

6 Muller SC, Hsieh JT, Lue TF, Tanagho EA. Castration and oxide mediated erectile activity is a testosterone dependenterection. An animal study. Eur Urol 1988; 15: 118–24 event: a rat erection model. Int J Impot Res 1995; 7: 209–19

7 Lugg JA, Gonzalez-Cadavid NF, Rajfer J. The role of nitric 25 Penson DF, Ng C, Cai L, Rajfer J, Gonzalez-Cadavid NF.oxide in erectile function. J Androl 1995; 16: 2–4 Androgen and pituitary control of penile nitric oxide

8 Kim N, Azadzoi KM, Goldstein I, Saenz de Tejada I. A nitric synthase and erectile function in the rat. Biol Reprod 1996;oxide-like factor mediates nonadrenergic-noncholinergic 55: 567–74neurogenic relaxation of penile corpus cavernosum smooth 26 Buena F, SwerdloC RS, Steiner BS et al. Sexual functionmuscle. J Clin Invest 1991; 88: 112–8 does not change when serum testosterone levels are

9 Bush PA, Aronson WJ, Buga GM, Rajfer J, Ignarro LJ. Nitric pharmacologically varied within the normal male range.oxide is a potent relaxant of human and rabbit corpus Fertil Steril 1993; 59: 1118–23cavernosum. J Urol 1992; 147: 1650–5 27 Gormley GJ, Stoner E, Bruskewitz RC et al. The eCect of

10 Lugg JA, Rajfer J, Gonzalez-Cadavid NF. Dihydrotestosterone finasteride in men with benign prostatic hyperplasia. Theis the active androgen in the maintenance of nitric oxide- Finasteride Study Group. N Engl J Med 1992; 327: 1185–91mediated penile erection in the rat. Endocrinology 1995; 28 Venema RC, Sayegh HS, Inoue N, Murphy TJ, Harrison136: 1495–501 DG. Functional characterization of the 5∞-regulatory region

11 Reilly CM, Zamorano P, Stopper VS, Mills TM. Androgenic of the bovine endothelial nitric oxide synthase gene.regulation of NO availability in rat penile erection. J Androl Program of the First International Conference on the1997; 18: 110–5 Biochemistry and Molecular Biology of Nitric Oxide. Los

Angeles CA. 1994 (Abstract C26: 88)12 Penson DF, Ng C, Rajfer J, Gonzalez-Cadavid NF. Adrenal

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29 Vernet D, Cai L, Garban H et al. Reduction of penile nitric K.D. Kim, PhD, Consultant Biologist.J.-S. Paick, MD, Associate Professor.oxide synthase in diabetic BB/WORdp (type I) and

BBZ/WORdp (type II) rats with erectile dysfunction. Correspondence: Dr J.-S. Paick, Seoul National UniversityHospital, Department of Urology 28, Yunkeun-Dong,Endocrinology 1995; 136: 5709–17Chongno-Ku, Seoul, Korea.

Authors

K.H. Park, MD, Assistant Professor.S.W. Kim, MD, Lecturer.

© 1999 BJU International 83, 327–333