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Keywords:

  • dopamine receptor;
  • corpus cavernosum;
  • rat penis

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Authors

Objective  To detect and locate anatomically peripheral dopamine D1 and D2 receptors in rat cavernosa, as dopamine is important in sexual drive and penile erection through receptors located in the central nervous system.

Materials and methods  Corpora cavernosa were obtained from Sprague-Dawley rats; total RNA and membrane proteins were extracted and cryostat sections prepared. The rat brain hypothalamus was used as a control for dopamine D1 and D2 receptors. The presence and expression of peripheral dopamine D1 and D2 receptor mRNAs in rat corpus cavernosa was assessed using reverse transcription and polymerase chain reaction (RT-PCR), and Northern blot hybridization using 32 P-UTP-labelled RNA probes. Concurrently, corresponding proteins from D1 and D2 receptors were assayed and detected by a Western blotting technique. The anatomical location of dopamine D1 and D2 receptor mRNAs in rat penile tissues was identified by in situ hybridization using 35 S-UTP-labelled RNA probes in cryostat sections. Immunohistochemical staining was used to locate peripheral dopamine D1 and D2 receptor proteins in rat corpora cavernosa.

Results  Dopamine D1 and D2 receptor gene expression was detected in rat corpora cavernosa. In situ hybridization signals for dopamine D1 and D2 receptor mRNAs were localized to corpus cavernosal tissues and dorsal vessels in the rat penis. Western blot analyses showed peripheral dopamine D1 and D2 receptor proteins in rat corpora cavernosa. Immunohistochemically, peripheral dopamine D1 and D2 receptor proteins were detected in dorsal nerves, dorsal vessels and corpus cavernosal smooth muscle of the rat penile tissues.

Conclusions  Peripheral dopamine D1 and D2 receptors are present in the corpora cavernosa of rats. The functional significance of these receptors and signal transduction pathways in modulating the vascular tone of the penis warrants further investigation.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Authors

Dopamine is a CNS neurotransmitter recognized to have many physiological activities; the actions of dopamine on target tissues are mediated by high-affinity cell surface receptors [1,2]. These receptors belong to a large family linked by guanine nucleotide-binding proteins to their signal-transduction pathways. Recent advances in molecular biology have identified at least five subtypes of dopamine receptors, which have been subdivided pharmacologically as D1-like (D1 and D5) or D2-like (D2, D3 and D4) on the basis of their ability to stimulate or inhibit adenylate cylase, respectively. Stimulation of peripheral D1-receptors in vascular smooth muscle leads to vasodilatation of the coronary and other vascular beds [3–9].

Dopamine is a recognized modulator of peripheral organ function, as shown by the ability of local tissues to synthesise dopamine. The peripheral location of dopamine receptors, and significant physiological effects of dopaminergic agents on renal, adrenal and cardiovascular function, have been documented [10–15]. The presence of dopamine receptor subtypes outside the CNS was shown by pharmacological and biochemical techniques. Recently, dopamine receptors have been identified in kidney, heart and lymphocytes [16–21].

Dopamine plays a critical role in promoting sexual drive and penile erection. Dopamine and apomorphine (a dopamine agonist) induce penile erection in humans and rats, and a stretching-yawning syndrome in normal rats. Hull et al.[22] reported that in male rats, low levels of dopaminergic stimulation (via the D1 receptor) increased erection, and higher levels or prolonged stimulation produced seminal emission (through D2 receptors). Although the mechanism of action of dopamine or dopamine agonists (apomorphine) in inducing erections has not been completely elucidated, a low concentration is postulated to centrally stimulate dopamine receptors in the brain, especially in the median pre-optic area and paraventricular nucleus of the hypothalamus. If peripheral dopamine receptors are similarly identified in the genital organs and their signalling pathways determined at the molecular level, penile erection may also be modulated by peripheral dopamine receptors. In an attempt to define the role of dopamine and its receptors in rat penile tissues, we investigated the presence and anatomical location of peripheral dopamine D1 and D2 receptor mRNAs and their corresponding proteins.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Authors

Male Sprague-Dawley rats (body weight 300–350 g) were anaesthetized by an intraperitoneal injection with pentobarbital sodium (30 mg/kg). The penises were excised and washed in an ice-cold 0.9% NaCl solution to remove blood traces. The extracted tissues were initially fixed by immersion in 4% paraformaldehyde (24 h) and cryoprotected in 20% sucrose-phosphate buffer (24 h). Sections were cut on a cryomicrotome (10 µm), thaw-mounted on prepared slides at room temperature and then stored at −70 °C until use.

Total RNAs were isolated by the method of Chomczynski and Sacchi [23,24] from rat corpus cavernosal tissue and rat cerebral striatum, the latter serving as the control. RNA concentrations and quality were quantified spectrophotometrically and by gel analyses. Only RNA samples that yielded intact 18S and 28S bands with the expected band ratio were included in subsequent experiments. A total RNA of 2 µg was reverse-transcribed using RT-PCR (GeneAmp PCR system, Model 2400 Perkin-Elmer Corp). The RT reaction was performed in a reaction mixture of 20 µL total volume containing Moloney murine leukaemia virus reverse transcriptase, 1 mmol/L each of the dNTPs (dATP, dCTP, dGTP and dGTP), 20 U of ribonuclease inhibitor, oligo(dT) primer, and 10× standard reaction buffer, giving the following final composition when diluted 1 : 10; 50 mmol/L Tris-HCl (pH 8.3), 75 mmol/L KCL, 10 mmol/L dithiothreitol and 3 mmol/L MgCl2. The RT mix was incubated in a thermal cycler at 42 °C for 15 min, 99 °C for 5 min and 5 °C for 5 min, sequentially. Subsequent PCRs were carried out in the presence of 20 µmol/L sense and antisense primer, 2.5 µL MgCl2 (25 mmol/L), 0.4 µL Taq DNA polymerase, 1 µL of each dNTP (10 mmol/L), 2.5 µL of 10 × buffer and 5 µL of template cDNA, in a total volume of 25 µL. The primer sequences used for PCR amplification are shown in Table 1. Oligonucleotide primers for rat α-actin were used as a positive control in each sample. PCR was performed initially after the denaturation step at 95 °C (2 min) for either 25 cycles (rat α-actin) or 30 cycles (rat dopamine receptors D1 and D2). Each cycle consisted of denaturation at 94 °C (45 s), annealing at 57 °C (30 s) and extension at 72 °C (2 min) for rat dopamine receptor D1; 94 °C (45 s), 66 °C (30 s) and 72 °C (30 s) for rat dopamine receptor D2; and 94 °C (45 s), 61 °C (30 s), and 72 °C (30 s) for rat α-actin. The PCR products were analysed on a 2.0% agarose gel, which was subsequently stained with ethidium bromide and visualized under ultraviolet light.

Table 1.  Primer sequences and sizes of RT–PCR product
PrimerSequenceSize, bp
Rat D1
 Sense5′-TGACATCATGTGCTCTACGGC-3′
 Antisense5′-GAAATGGCATACGTCCTGCTC-3′288
Rat D2
 Sense5′-TGAACCTGTGTGCCATCAGCA-3′
 Antisense5′-TTGGCTCTGAAAGCTCGACTG-3′338
Rat α-actin
 Sense5′-AAGAGAGGCATCCTCACCCT-3′
 Antisense5′-TACATGGCTGGGGTGTTGAA-3′218

Full-length cDNA clones of the rat dopamine D1 and D2 receptors were kindly provided by Dr Choi (Gyeongsang National University, Korea). The partial dopamine D1 receptor (500 bp, 1564–2063) and D2 receptor (309, 2009–2317) cDNA fragments were subcloned into the RNA synthesizing vector pGEM3Z (Promega, Madison, Wisconsin, USA); there was no sequence homology between them. To verify correct fragment and orientation, these clones were sequenced and confirmed for further use in generating riboprobes (Sequenase 2.0; USB).

Dopamine D1 and D2 receptor cRNA probes were generated from the pGEM3Z recombinant subclones. The antisense dopamine D1 receptor cRNA probe was transcribed with SP6 RNA polymerase from the dopamine D1 receptor construct, which was linearized with SacI restriction enzyme. For the sense probe, which served as a control, the D1 receptor cRNA probe was generated with T7 RNA polymerase. The antisense dopamine D2 receptor cRNA probe was synthesized by using SP6 RNA polymerase from the dopamine D2 receptor clone construct, which was linearized with ApaI restriction enzyme, while the sense RNA was used as a control for the D2 receptor and it was transcribed with SP6 RNA polymerase. 35S-UTP-labelled probes were prepared for in-situ hybridization (ISH) while a 32P-UTP-labelled probe was used for Northern blot hybridization, which was made by using an in vitro transcription kit (Promega) with a specific activity of 6 GBq/µg. Briefly, 4 µL of 5 × transcription buffer (200 mmol/L Tri-HCl, pH 7.5, 30 mmol/L MgCl2, 10 mmol/L serpmidine and 50 mmol/L NaCl); 2 µL of 100 µmol/L dithiothreitol; 20 unit of RNase inhibitor; 1 µL of ATP, CTP, and GTP (2.5 mmol/L each); 2.4 µL of 100 µmol/L UTP, linearized template DNA (500 ng); 5 µL of 35S or 32P-UTP (1.85 MBq at 370 MBq/mL); and 15–20 U of RNA polymerase were mixed to a final volume of 20 µL and incubated for 60 min at 37–40 °C. After incubation, RNase free DNase-I were added and incubated for 30 min. Antisense and sense cRNA probes were purified by Sephadex G-50 DNA grade column (Amersham Pharmacia Biotech, USA) and diluted with buffer (0.1% SDA, 1 mmol/L EDTA, 10 mmol/L Tris, 10 mmol/L dithiothreitol). PAGE of purified probes showed that > 90% of the probes had the expected fragment size. The activity of the cRNA probes was approximately 6 MBq/µg.

For Northern blot hybridization, male Sprague-Dawley rats (300–350 g) were killed, and penile and brain (used as a control) tissues excised. Total RNA was isolated from these tissues as described earlier [23,24]. The quality and yield of the RNA were assessed spectrophotometrically and by gel analyses of the samples before use. A 30-mg RNA sample was size fractionated on a 1.2% agarose/formaldehyde gel and transferred to Hybond XL nylon membranes (Amersham Pharmacia Biotech) by the capillary blot method. RNA was fixed to the membrane by ultraviolet cross linking. The blots were prehybridized in a freshly prepared solution containing 50% molecular grade de-ionized formamide, 5 × Denhardt's solution (50 × = 1 g Ficoll, 1 g polyvinylpyorolidone and 1 g BSA/100 mL), 0.5% SDS, 6 ×  buffer (0.9 mol/L NaCl, 60 mL NaH2PO7 and 6 mol/L EDTA) and 100 mg/mL sheared herring sperm DNA, at 42 °C overnight. This was followed by hybridization in the fresh solution with 32P-UTP-labelled probe for geqslant R: gt-or-equal, slanted 16 h at 42 °C. Blots were first washed three times for 10 min at room temperature in a solution containing 2 × saline-citrate buffer (0.30 mol/L NaCl, 0.33 mol/L sodium citrate) and 0.1% SDS, and this was followed by a second wash three times each for 15 min each in a solution of 0.15 mol/L NaCl, 0.165 mol/L sodium citrate and 0.1% SDS. The membranes were exposed to X-ray film for 24 h at −70 °C and developed to examine the hybridization signals.

For ISH, all solutions were made with diethylpyrocarbonate-treated sterile water and glassware baked to prevent contamination by RNases. After rehydration, the tissue slices were treated in 0.2 mol/L HCl for 30 min at room temperature, followed by a rinse and wash in water at 65 °C for 30 min. In the next step, tissues were treated with proteinase K treatment and acetylated to remove formaldehyde crosslinks that usually stabilize the protein, and to eliminate some protein from the cellular network to make the target mRNA accessible to the probe. The optimal conditions for proteinase K treatment were established, as this treatment can disintegrate the tissue when too much proteinase K is used for too long, but mRNA may not be detected when too little is used. Moreover, the requirement for proteinase K treatment for paraformaldehyde- and gentaraldehyde-fixed tissue is different. In the present experiment 10–15 mg/mL of proteinase K was used for paraformaldehyde-fixed tissue, for 15–20 min. Samples were pre-hybridized at 37 °C for geqslant R: gt-or-equal, slanted 2 h in a solution containing 50% formamide, 0.3 mol/L sodium chloride, 20 mmol/L Tris-HCl, pH 8.0, 1 mmol/L EDTA disodium salt, 10 × Denhardt's solution, 50 µg/mL denatured salmon sperm DNA, and 50 µg/mL polyadenylic acid.

Hybridization with the antisense and sense probes was carried out in this same solution by adding 500 µg/mL yeast tRNA, 20 mmol/L mercaptoethanol, 10% dextran sulphate, and 0.1 ng of RNA probe per 1 µL of solution. After placing a cover slip, the slides were incubated at 60 °C for ≈ 24 h. Cover slips were removed and tissue sections dehydrated by immersion in ethanol containing 300 mmol/L ammonium acetate. Sections were then incubated at 65 °C for 10 min in a hybridization buffer, rinsed, and treated for 30 min at 37 °C with 20 µg/mL RNase T1. Final washes were in 2 × saline-citrate buffer at room temperature for 30 min and 0.1 × buffer at 65 °C for 15 min.

After dehydration in a solution containing 0.3 mol/L NaCl and 0.33 mol/L sodium citrate and molecular graded ethanols containing 300 mmol/L ammonium acetate, the slides were dipped in Kodak NTB-2 emulsion which had been diluted in sterile water. Slides were stored at 4 °C in light-tight cassettes for 2 weeks. After developing, the tissue slides were counter-stained with methyl green to visualize the tissue. Sections were assessed under dark-field and direct light microscopy, and photographed.

For the Western blot analysis, rat penile tissues were homogenized separately in a buffer containing 0.32 mol/L sucrose, 10 mmol/L Tris-HCl, pH 7.4, 2 mmol/L EDTA and 10 µL/mL protease inhibitor. The homogenate was centrifuged at 900 g for 10 min, and the resulting supernatant centrifuged at 100 000 g for 1 h. The final pellet was re-suspended in a buffer containing 50 mmol/L Tris-HCl, 10 mmol/L EDTA, 100 mmol/L NaCl and 8 mmol/L MgCl2, pH 7.4. After denaturing extracted membrane protein at 95 °C for 3 min, membrane proteins (150 µg protein/lane) were separated using 10% discontinuous SDS-PAGE. The resolved membrane proteins were transferred onto a 0.2-µm Hybond-P nitrocellulose (Amersham Pharmacia Biotech) and then soaked in 5% non-fat dried milk in Tris-buffered saline containing Tween 20 (TBS-T; 10 mmol/L Tris-HCl, pH 7.2, 250 mmol/L NaCl, 0.05% Tween 20) at 4 °C overnight. The membrane was incubated with rabbit anti-rat D1 and D2 receptor polyclonal primary antibody (1 : 5000 dilution in TBS-T) at room temperature for 1 h, then incubated with a biotinylated secondary antibody (1 : 5000 dilution in TBS-T) at room temperature for 1 h, and reacted with peroxidase-conjugated streptavidin at room temperature for 1 h. Specific bands were visualized with chemiluminescence (ECL Western Blotting Kit, Amersham). The rat dopamine D1 receptor primary antibody consists of 13 amino acids and shows no significant sequence homology with the other dopamine receptor (D2-5) [25]. The rat dopamine D2 receptor primary antibody consists of 27 amino acids and shows no significant sequence homology with other dopamine receptors (D1 and D3-5) [26].

The slides of rat penile tissues were stored at −70 °C and subsequently used for immunohistochemical staining. To detect D1 and D2 receptors, endogenous peroxidase was blocked with 0.3% H2O2 in methanol for 30 min. The sections were washed in TBS-T and then blocked for 1 h with normal horse serum in TBS-T and incubated overnight at 4 °C with rabbit anti-rat D1 or D2 receptor polyclonal primary antibody (1 : 50 dilution in TBS-T; control study, only TBS-T). After washes in TBS-T, immunostaining was detected with an avidin-biotin immunoperoxidase reaction and visualized by diaminobenzidine. Tissue sections were counterstained with haematoxylin.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Authors

To investigate the presence of dopamine D1 and D2 receptor mRNA in rat penile tissues, total RNA from rat brain (control) and corpus cavernosa were first isolated and then analysed by RT-PCR and Northern blot hybridization. The results of PCR amplification for the dopamine D1 and D2 receptor are depicted in Fig. 1. Amplification products at predicted sizes were clearly detected (rat D1 288 bp; rat D2 338 bp; rat α-actin 218 bp) for the dopamine D1 and D2 receptors in rat penile and brain tissue (Fig. 1). Northern blot hybridization showed dopamine D1 and D2 receptor mRNA expression in rat penile and brain (used as a control) tissue (Fig. 2).

image

Figure 1. Analysis of PCR products resolved on 2% agarose gel and subsequently stained with ethidium bromide. Amplification products of the predicted size for the dopamine D1 and D2 receptors were detected in the RT–PCR reaction, where extracted rat penile tissue RNA samples were used as shown in a , rat dopamine D1 receptor, 288 bp. b Rat dopamine D2 receptor, 338 bp. c rat β-actin, 218 bp. Rb; rat brain, Rp; rat penis.

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image

Figure 2. Northern blot hybridization of rat dopamine D1 ( a ) and D2 ( b ) receptor mRNA in rat brain (Rb) and penis (Rp). Northern blot hybridization used 32 P-UTP-labelled dopamine D1 and D2 receptor cRNA probes.

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To locate the mRNA expression of dopamine D1 and D2 receptors in penile tissues, cryostat tissues sections were prepared and analysed by ISH. Dark-field images of rat penile tissue showed hybridization signals produced by antisense cRNA probes, which were generated in vitro for dopamine D1 and D2 receptors to detect corpus cavernosal and dorsal vessels, and they were compared with hybridization signals produced by sense cRNA probes used as a control (Fig. 3). It was not clear whether the hybridization signals corresponded to expressed signals in the dorsal nerves of the rat penis, as hybridization signals were not sufficiently strong to distinguish the antisense and sense probes. However, these results indicate clearly that mRNAs of dopamine D1 and D2 receptors are present in the corpus cavernosal tissues and dorsal vessels of the rat penis.

image

Figure 3. ISH of rat dopamine receptor mRNAs using 35 S-UTP-labelled dopamine D1 and D2 receptor antisense cRNA probe in a coronal section of rat penis. Hybridization signals (dark-field× 20) are present in the corpus cavernosal tissues (arrowhead) and dorsal vessels (arrow) using the antisense probe, as shown in a (D1 receptor) and c (D2 receptor). The antisense signals were also compared with the hybridization signals using sense probe ( b , D1 receptor; d , D2 receptor). The results of the control study ( b and d ) reflect homogeneous background hybridization signals, which may result from nonspecific binding by the sense probe.

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The corresponding proteins of dopamine D1 and D2 receptors in rat corpus cavernosa were assessed using Western blotting. Bands of the predicted size (≈ 50 kDa) for rat dopamine D1 and D2 receptors were detected in rat penile tissues, and in rat brain tissues, which were included as a control (Fig. 4). Non-specific bands (≈ 75 kDa) were also detected, which might be attributed to glycosylation and phosphorylation or dimerization of dopamine receptor proteins, as previously noted [20,27,28].

image

Figure 4. Western blot analysis of dopamine D1 ( a ) and D2 ( b ) receptor in rat penis. Bands of the predicted size (≈ 50 kDa) for D1 and D2 receptor were detected in rat brain (Rb, control), rat penis (Rp). M, protein size marker.

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Immunohistochemical staining was used to locate the peripheral dopamine D1 and D2 receptor proteins, with a polyclonal rabbit antibody in the corpora cavernosa. Immunoreactive staining showed that these receptors were located in the corpus cavernosal smooth muscle, dorsal nerves and vessels of the rat (Fig. 5).

image

Figure 5. Immunoreactivity located the peripheral dopamine D1 and D2 receptors in rat penis. The staining signals corresponding to D1 receptors are shown a , d and g ; brain tissue (control) immunohistochemical staining is shown in b , e and f . The D2 receptor staining is highlighted in c , f and i . a , b , c , g , h and i are × 40, and d , e and f are × 100. The immunoreactivity shows the presence of dopamine D1 and D2 receptors in rat penis, in corpus cavernosal smooth muscle ( h and i ) dorsal nerve (arrowheads) and dorsal vessel (arrows).

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Authors

Dopamine is an endogenous catecholamine that influences many cellular activities, including behaviour, hormone synthesis/release, blood pressure and intracellular ion transport. The actions of dopamine on target tissues are mediated by cell surface receptors. There are at least five genes encoding functional dopamine receptors that have been characterized on the human genome. Moreover, two additional pseudogenes, which were found to be highly homologous to dopamine receptor 5, have been identified [1,2]. These dopamine receptors have been subdivided into two subclasses referred to as D1 and D2 on the basis of various biophysical and pharmacological characteristics [9]. D1 receptors are coupled to adenylate cyclase stimulation to generate cAMP formation. The D1-like receptors consist of D1 and D5 [7,29]. Activation of D1 receptors was also implicated in promotion of vasodilatation. However, D2 receptor activation has many effects, e.g. inhibition of adenylate cyclase activation, inhibition of phosphatidyl inositol turnover, inhibition of Ca2+ mobilization and increase in K+ channel activity. The D2-like receptors are exemplified by the D2, D3 and D4 subtypes [1,30,31].

Recently, there has been interest in peripheral dopamine receptors. Using molecular biology techniques peripheral dopamine receptors have been identified outside the CNS, e.g. in the heart, basilar artery, portal vein, cornea of the eye, and in lymphocytes [9,20,21,32–34]. Dopamine receptor subtypes have also been detected in the kidney, ureter and urinary bladder [16–19,35]. The presence of peripheral dopamine receptors outside the CNS suggests a possible role for dopamine receptors in the penis, and might indicate an intriguing interaction between the nervous and reproductive systems [22].

Dopamine and dopamine agonists (e.g. apomorphine) are known to cause penile erection in rats and humans [36]. In the medial pre-optic area of the rat, dopamine is released during male copulatory behaviour [37,38]. Subcutaneous injection with low-dose apomorphine in rats and sublingual application of low-dose apomorphine in humans causes penile erection. The erectile responses to dopamine also occur with other dopamine agonists, e.g. flupenthiol and l-dopa [39,40]. Because the mechanism of action of dopamine and apomorphine has not been completely elucidated, several theories have been proposed. Low-dose apomorphine stimulates the yawning and erection reflexes centrally, by its action on the dopamine autoreceptor [41]. Hull et al.[22] reported that low levels of dopaminergic stimulation via the D1 receptor augment erection, but higher levels or prolonged stimulation cause seminal emission through a D2 receptor pathway. Melis et al.[42] suggested that the hypothalamic-hippocampal oxytocinergic pathway mediates the apomorphine-induced penile erection and yawning, and that oxytocin is involved at different levels in the CNS for the control of these behavioural responses. An unanswered question about the mechanism of penile erection induced by dopamine or dopamine agonists is whether it is mediated in the CNS by: (i) direct stimulation of the central dopamine receptor subtypes; (ii) indirect stimulation of other intermediary substances, e.g. oxytocin; or (iii) by a direct dopaminergic effect within the penis. The present results suggest that dopamine exerts its pro-erectile effects via both central and peripheral dopamine receptors.

Evidence for the existence of peripheral dopamine receptor subtypes include activity on vascular smooth muscle causing vasodilatation or contraction of the coronary and other vascular beds [43,44]. Han et al.[45] postulated that dopamine-induced vasodilatation occurs by activation of vascular dopamine D1 receptors opening calcium-voltage-activated K+ (Bkca) channels via the cyclic AMP-dependent stimulation of protein kinase. The opening of these channels leads to K+ efflux, membrane repolarization, and relaxation of blood vessels. When dopamine or dopamine agonists are injected subcutaneously in the rat, one of the more reproducible responses is penile erection. If peripheral dopamine receptors participating in signalling or physiological processes are present in the penis, then the current hypothesis on penile erection will need to be expanded to include these other local pathways.

In the present study, dopamine D1 and D2 receptor mRNAs and their corresponding proteins were detected in rat corpora cavernosa; this is the first such report. The gene expressions of dopamine D1 and D2 receptors were clearly detected in both rat corpus cavernosa and rat brain tissue. Gene expression in rat corpus cavernosa was similar to rat brain, even though quantitatively not assessed. The protein size of dopamine D1 and D2 receptors is ≈ 50 kDa; there were nonspecific bands of 75 kDa acetylate, possibly caused by other effects discussed above. Although the present study anatomically located peripheral dopamine D1 and D2 receptors in rat corpus cavernosa, the role and mechanism of peripheral dopamine receptors in the penis has not been established. Future studies will need to focus on the function of these peripheral dopamine receptors in penile erectile tissues, which may in turn lead to further pharmacological manipulation of their actions.

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Authors

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Authors

J.-S. Hyun, MD, PhD, Andrology Fellow.

T.J. Bivalacqua, BS, Medical Student.

M.R. Baig, MS, MPhil, PhD, Post-doctoral Fellow.

D.-Y. Yang, MD, Andrology Fellow.

S. Leungwattanakij, MD, Andrology Fellow.

A. Abdel-Mageed, DVM, MS, PhD, Assistant Professor of Urology.

K.-D. Kim, Professor of Urology.

W.J.G. Hellstrom, MD, FACS, Professor of Urology.

Abbreviations
ISH

in-situ hybridization

TBS-T

Tris-buffered saline+Tween.

W.J.G. Hellstrom, Tulane University Health Sciences Center, 1430 Tulane Ave., SL-42 New Orleans, Louisiana 70112, USA. e-mail: whellst@tulane.edu