Mouse Penis Research Articles

Hypercholesterolemia-Induced Erectile Dysfunction: Endothelial Nitric Oxide Synthase (eNOS) Uncoupling in the Mouse Penis by NAD(P)H Oxidase

Hypercholesterolemia induces erectile dysfunction (ED) mostly by increasing oxidative stress and impairing endothelial function in the penis, but the mechanisms regulating reactive oxygen species (ROS) production in the penis are not understood. We evaluated whether hypercholesterolemia activates nicotinamide adenine dinucleotide phosphate (NAD[P]H) oxidase in the penis, providing an initial source of ROS to induce endothelial nitric oxide synthase (eNOS) uncoupling and endothelial dysfunction resulting in ED. Low-density-lipoprotein receptor (LDLR)-null mice were fed Western diet for 4 weeks to induce early-stage hyperlipidemia. Wild type (WT) mice fed regular chow served as controls. Mice received NAD(P)H oxidase inhibitor apocynin (10 mM in drinking water) or vehicle. Erectile function was assessed in response to cavernous nerve electrical stimulation. Markers of endothelial function (phospho [P]-vasodilator-stimulated-protein [VASP]-Ser-239), oxidative stress (4-hydroxy-2-nonenal [HNE]), sources of ROS (eNOS uncoupling and NAD[P]H oxidase subunits p67(phox) , p47(phox) , and gp91(phox) ), P-eNOS-Ser-1177, and eNOS were measured by Western blot in penes. The main outcome measures are the molecular mechanisms of ROS generation and endothelial dysfunction in hypercholesterolemia-induced ED. Erectile response was significantly (P<0.05) reduced in hypercholesterolemic LDLR-null mice compared with WT mice. Relative to WT mice, hypercholesterolemia increased (P<0.05) protein expressions of NAD(P)H oxidase subunits p67(phox) , p47(phox) and gp91(phox) , eNOS uncoupling, and 4-HNE-modified proteins, and reduced (P<0.05) P-VASP-Ser-239 expression in the penis. Apocynin treatment of LDLR-null mice preserved (P<0.05) maximal intracavernosal pressure, and reversed (P<0.05) the abnormalities in protein expressions of gp67(phox) and gp47(phox) , 4-HNE, P-VASP-Ser-239, and eNOS uncoupling in the penis. Apocynin treatment of WT mice did not affect any of these parameters. Protein expressions of P-eNOS-Ser-1177 and total eNOS were unaffected by hypercholesterolemia. Activated NAD(P)H oxidase in the penis is an initial source of oxidative stress resulting in eNOS uncoupling, thus providing a mechanism of eNOS uncoupling and endothelial dysfunction in hypercholesterolemia-induced ED.

Expression of Luteinizing Hormone Receptors in the Mouse Penis

The role of luteinizing hormone (LH) in the regulation of normal reproductive functions in males and females is quite well established. Besides the expression of LH receptors in the target cells in gonads, it has been found in several extragonadal organs. There is no information about the expression of LH receptors in the penis up to now. The aim of the present study is to investigate the expression of the LH receptor in the mouse penis to see if LH effects are possible in the penis. BALB/c mice were used as donors of normal penis and testis tissue. Immunocytochemistry, Western blotting, and quantitative reverse transcriptase polymerase chain reactions (RT-PCRs) were used for the detection of the LH receptor. Positive immunoreaction for LH receptors was present in the nuclei of urethral epithelium and endothelial cells of cavernous spaces in the corpus cavernosum and corpus spongiosum penis. Western blotting experiments demonstrated the presence of LH antigen at M(r) = 97.4 and 78 kd. Quantitative RT-PCRs confirmed the expression of LH receptor in the penis. Our results show that LH receptor is expressed in the body of the mouse penis; thus, it may directly regulate functions of penile tissue.

Morphology of Mouse External Genitalia: Implications for a Role of Estrogen in Sexual Dimorphism of the Mouse Genital Tubercle

We examined the role of androgens and estrogens in mammalian sexual differentiation by morphological characterization of adult wt and mutant mouse external genitalia. We tested the hypothesis that external genitalia development depends on androgen and estrogen action. We studied serial sections of the external genitalia of the CD-1 and C57BL6 wt strains of adult mice (Charles River Laboratories, Wilmington, Massachusetts). We recorded linear measurements of key structures in each specimen, including the urethra, erectile tissue, bone and cartilage. We used similar methodology to analyze mice mutant for estrogen receptor α (αERKO) and androgen receptor (X(Tfm)/Y) (Jackson Laboratory, Bar Harbor, Maine). Morphology in X(Tfm)/Y adult murine external genitalia was remarkably similar to that in wt females. Bone and clitoral length was similar in wt females and X(Tfm)/Y mice. Conversely the αERKO clitoris was 59% longer and bone length in αERKO females was many-fold longer than that in female wt mice or X(Tfm)/Y mutants. The αERKO clitoris contained cartilage, which is typical of the wt penis but never observed in the wt clitoris. Serum testosterone was not increased in female αERKO mice 10 days postnatally when sex differentiation occurs, suggesting that masculinization of the αERKO clitoris is not a function of androgen. Masculinization of the αERKO clitoris suggests a role for estrogen in the development of female external genitalia. We propose that normal external genital development requires androgen and estrogen action.

Attenuated RhoA/Rho-kinase Signaling in Penis of Transgenic Sickle Cell Mice

The Ras homolog gene family, member A (RhoA) and its main downstream effector, Rho-kinase (ROCK) are important in maintaining the penis in the flaccid state. The pathophysiology of sickle cell disease-associated priapism is not well defined. We hypothesized that the RhoA/ROCK vasoconstrictive pathways might be involved in the development of priapism. Therefore, the objective of the present study was to evaluate the molecular changes in RhoA and ROCK in an established transgenic sickle cell mouse model of priapism. Two groups of mice were used: wild type (WT; C57BL/6) mice and transgenic sickle cell mice. We evaluated RhoA guanosine triphosphatase and total ROCK activities, as well as ROCK1 and ROCK2 protein expression, in WT and sickle mice penises. We also evaluated the in vivo erectile responses to cavernous nerve stimulation and the frequency and duration of spontaneous erections before and after cavernous nerve stimulation. Sickle mice demonstrated significantly (P <.05) enhanced erectile responses to cavernous nerve stimulation and frequency of spontaneous erections both before and after cavernous nerve stimulation compared with the WT mice. The sickle mice penises had a significant decline in RhoA guanosine triphosphatase (P <.01) and total ROCK activities (P <.05) compared with the WT mice. A significant (P <.05) reduction in ROCK2 protein expression in sickle mice penises compared with WT mice protein expression. No change in ROCK1 protein expression was observed in either cohort of mice penises. These data suggest that sickle cell disease associated-priapism might be contributed by a lack of RhoA/ROCK-mediated vasoconstriction and highlight a novel molecular mechanism in the pathophysiology of priapism.

Derangements in Endothelial Cell-to-Cell Junctions Involved in the Pathogenesis of Hypercholesterolemia-Induced Erectile Dysfunction

Endothelial cell-to-cell junctions are crucial for vascular formation, networking, and remodeling of blood vessels as well as for inducing and integrating intracellular signals. We investigated the differential expression and distribution of endothelial cell-to-cell junction proteins in the penis of mice with hypercholesterolemia-induced erectile dysfunction. Two-month-old C57BL/6J mice were fed a diet containing 4% cholesterol and 1% cholic acid, and age-matched control animals were fed a normal diet, for 3 months. We performed dual priming oligonucleotide (DPO)-based multiplex polymerase chain reaction (PCR) (Seegene, Seoul, Korea) to screen the differential gene expression of 21 endothelial cell-to-cell junctions. At 5 months, erectile function was measured by electrical stimulation of the cavernous nerve, and the penis was harvested and stained with antibody to claudin-5, vascular endothelial (VE)-cadherin, and platelet/endothelial cell adhesion molecule (PECAM)-1 (N = 8 per group). Cavernous specimens from a separate group of animals were used for claudin-5, VE-cadherin, and PECAM-1 reverse transcriptase-PCR and Western blot analysis. Erectile function was significantly lower in hypercholesterolemic mice than in controls. DPO-based multiplex PCR revealed a profound decrease in the gene expression of endothelium-specific cell-to-cell junction proteins, including claudin-5, VE-cadherin, and PECAM-1, in hypercholesterolemic mice compared with that in controls. The expression of claudin-5, VE-cadherin, and PECAM-1 protein evaluated by Western blot or immunohistochemistry was significantly lower in hypercholesterolemic mice than in controls. These endothelial cell-to-cell junction proteins were more sparsely distributed in the endothelium of cavernous sinusoids than in the endothelium of cavernous artery and dorsal blood vessels. Down-regulation of the endothelial cell-to-cell junctions and decreased endothelial content in the corpus cavernosum might play a major role in the deterioration of erectile function in hypercholesterolemic mice.

Sildenafil Inhibits Superoxide Formation and Prevents Endothelial Dysfunction in a Mouse Model of Secondhand Smoke Induced Erectile Dysfunction

We determined the effect of passive secondhand cigarette smoke on 1) erectile function in vivo, 2) molecular mechanisms involved in penile vascular function, and 3) erectile function and penile molecular signaling in the presence of phosphodiesterase type 5 inhibitor therapy. Four groups of mice were used, including group 1--controls, group 2--mice exposed to 3 weeks of secondhand smoke (5 hours per day for 5 days per week), group 3--control plus sildenafil (100 mg/kg per day) and group 4--smoke exposed plus sildenafil (100 mg/kg per day). Cavernous nerve electrical stimulation and intracavernous injection of acetylcholine were done to assess erectile function. Constitutive and inducible nitric oxide synthase activity, reactive oxygen species generation, nitrotyrosine formation and superoxide anion levels were assessed. Decreased erectile responses to cavernous nerve electrical stimulation and impaired endothelium dependent erectile responses to ACh in mice exposed to secondhand smoke were observed. Superoxide anion was increased in endothelial and corporeal smooth muscle cells of smoking mouse penises. In mice exposed to secondhand smoke constitutive nitric oxide synthase activity was decreased, and inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation increased. Sildenafil therapy restored constitutive nitric oxide synthase activity in the penis of smoking mice, decreased inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation, and improved erectile responses to cavernous nerve electrical stimulation and acetylcholine. Short-term exposure to secondhand smoke impairs erectile function through excessive penile reactive oxygen species signaling and inducible nitric oxide synthase activity. Decreased penile constitutive nitric oxide synthase activity may be attributable to the decreased endothelial nitric oxide synthase activity resulting from increased oxidative stress. Sildenafil therapy restored nitric oxide synthase activity and decreased reactive oxygen species signaling, resulting in improved erectile function.

Survey of Literature

Mesenchymal stem cells alone or ex vivo gene modified with endothelial nitric oxide synthase reverse age-associated erectile dysfunction. TJ Bivalacqua, W Deng, M Kendirci, MF Usta, C Robinson, BKTaylor, SNMurthy, HCChampion, WJG Hellstrom, PJ Kadowitz. Am J Physiol 2007; 292:H1278–90. Overexpression of arginase in the aged mouse penis impairs erectile function and decreases eNOS activity: Influence of in vivo gene therapy of anti-arginase. TJ Bivalacqua, AL Burnett, WJG Hellstrom, HC Champion. Am J Physiol 2007;292:H1340–51. Editorial Comment: Investigations into the molecular mechanisms responsible for ageassociated erectile dysfunction in the absence of overt disease have been undertaken only within the past decade. These two studies illustrate different, but effective, approaches in ameliorating erectile dysfunction in aged animals. In the first study, investigators isolated mesenchymal stem cells (MSCs) from bone marrow and injected them directly into the penile corpus cavernosum. Consistent with earlier studies by the same investigators, MSCs initially expressed markers for both smooth muscle (smooth muscle actin) and endothelial cells (von Willebrand factor) and survived within the corpus cavernosum for up to 21 days after injection with no signs of tissue inflammation. After 21 days,MSCs exhibited an alteration in phenotype, expressing additional proteins characteristic of smoothmuscle and endothelial cells that were not present at the time of isolation. Most importantly, aged rats injected with MSCs exhibited increases in endothelial nitric oxide synthase (eNOS) protein, enzyme activity, and cyclic guanosine monophosphate (cGMP) accumulation with enhanced erectile function at 21 days. Intracavernosal injection of modified MSCs, infected with adenovirus containing the eNOS gene, improved erectile function in aged rats as early as 7 days.While further studies are required to determine the feasibility of adult stem cell therapy in humans, these findings provide more evidence for the utility of MSCs in regenerative medicine and highlight the remarkable plasticity of stem cells and their ability to adapt to their local tissue environment. In the second study, investigators characterized changes in arginase and eNOS in aged mice. Erectile function in response to nerve stimulation or endothelium-dependent vasodilator was decreased as a function of age, whereas dietary intake of L-arginine for 2 weeks reversed this trend. Interestingly, mRNA and protein for both arginase I and eNOS were upregulated in endothelial cells isolated from penile tissue of aged mice. However, while arginase enzyme activity was also increased, NOS enzyme activity and baseline cGMP production was lower in penile tissue from aged mice. Because L-arginine serves as a common substrate for arginase and eNOS, the increased arginase activitymay decrease the available substrate pool to inhibit nitric oxide production. Indeed, cGMPproduction was increased to a greater extent in tissue extracts from aged rats when the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) was included. Further, intracavernosal administration of ABH normalized or enhanced erectile responses in aged mice. Intracavernosal injection of adenovirus containing an antisense sequence for the arginase-I gene decreased arginase-I expression and increased erectile function, NOS activity, and cGMP production in aged mice 1 month after infection. While it is likely that multiple factors contribute to the decline in erectile function with age, these data demonstrate that upregulation of arginase I contributes to endothelial dysfunction in penile corpus cavernosum of aged animals. This thorough study enhances our appreciation for perturbations in arginine metabolism that are increasingly being related to different pathological processes in a wide variety of organ systems. Noel N. Kim, PhD

Overexpression of arginase in the aged mouse penis impairs erectile function and decreases eNOS activity: influence of in vivo gene therapy of anti-arginase

Since both increased nitric oxide (NO) synthase (NOS) abundance and diminished NO signaling have been reported in the aging penis, the role of NO in the adaptations of aging remains controversial. Here we tested the hypothesis that arginase, an enzyme that competes with NOS for the substrate l-arginine, contributes to erectile dysfunction with advanced age in the B6/129 mouse strain. Arginase protein abundance, mRNA expression, and enzyme activity were elevated in aged compared with young penile endothelial cells. In addition, endothelial NOS (NOS3) protein abundance was greater in aged versus young penile endothelial cells, whereas NOS activity and cGMP levels were reduced. Calcium-dependent l-arginine-to-l-citrulline conversion and cGMP formation increased significantly in aged mouse penes in the presence of the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH). However, there was no effect on l-arginine-to-l-citrulline conversion or cGMP accumulation in the endothelium from young mouse penes. To assess the functional role of arginase in the inhibition of NOS pathway responsiveness in the penis, we evaluated the effects of ABH and an adeno-associated virus encoding an antisense sequence to arginase I (AAVanti-arginase) on erectile function in vivo. ABH and AAVanti-arginase enhanced endothelium-dependent erectile responses in the aged mice without altering endothelium-independent responses. Paralleling our in vitro observations, ABH or AAVanti-arginase did not affect vascular responses in the young mice. Inhibition of the arginase pathway improves endothelial function in the aging penile circulation, suggesting that the arginase pathway may be exploited to improve erectile dysfunction associated with aging.

Differential expression of E- and P-selectin in the microvasculature of sickle cell transgenic mice.

There is a growing body of evidence that endothelial cells assume an inflammatory phenotype in sickle cell disease. The authors determined whether (1) the expression of E- and P-selectin differs between sickle cell transgenic (beta(S)) mice and their wild-type counterparts, and (2) blood platelets and/or neutrophils contribute to the altered selectin expression. Expression of E- and P-selectin was measured in different regional vascular beds of wild-type and beta(S) mice (with or without thrombocytopenia or neutropenia) using the dual radiolabeled monoclonal antibody technique. Constitutive expression of P-selectin was significantly increased in the heart, lungs, small bowel, large bowel, and penis of beta(S) versus WT mice. While thrombocytopenia reduced P-selectin expression in the small bowel and penis of beta(S) mice, neutropenia was associated with a reduction in P-selectin expression only in the penis. E-selectin expression was not significantly elevated in any vascular bed except the penis of beta(S) mice. Sickle cell disease promotes an increased P-selectin expression in several vascular beds. An accumulation of platelets may explain the increased P-selectin expression observed in some vascular beds.

A castrated mouse model of erectile dysfunction.

To establish a mouse model for the study of venoocclusive erectile dysfunction, we investigated erectile function in wild-type (WT), castrated (CAST), and castrated mice receiving immediate testosterone replacement (TEST). Adult C57BL6 mice ( approximately 30 g) underwent electrical stimulation of the cavernous nerve in vivo (parameters: 16 Hz frequency, 5 ms duration, 4V stimulatory voltage) with intracavernosal pressure (ICP) monitoring. A total of 55 mice (5 WT, 25 CAST, and 25 TEST) were evaluated. CAST and TEST (5.0 mg/pellet, 60-day release) mice were divided into groups of 5 and evaluated at 24 hours, 72 hours, 1 week, 2 weeks, and 4 weeks. Penile tissue was immunohistochemically stained for alpha-actin (marker for smooth muscle cells) and CD-31 (marker for endothelial cells). Stained slides were analyzed using Image Pro-plus software. In secondary studies, a Doppler flow meter was employed to evaluate penile blood flow. ICP measurements (mm Hg) were significantly decreased in CAST mice at 24 hour-, 72 hour-, 1 week-, 2 week-, and 4-week time points compared with WT mice (41.9 +/- 14.9, 19.1 +/- 4.2, 17.5 +/- 8.2, 14.2 +/- 4.4, and 10.0 +/- 3.8, respectively, vs 50.2 +/- 2.8), but TEST animals maintained or had an increase in ICP in comparison with WT mice (48.0 +/- 1.4, 52.3 +/- 1.3, 60.8 +/- 7.6, 80.5 +/- 2.1, and 81.5 +/- 1.2, respectively). Mean systemic arterial pressure remained approximately 80 mm Hg irrespective of treatment. CAST mouse penis specimens revealed decreased alpha-actin and CD-31 immunoreactivity only at the 4-week interval, compared with WT and TEST specimens. Doppler ultrasound flow rates (centimeter per second), taken before, during, and immediately after cavernous nerve stimulation, were WT 45.4 +/- 7.3, 30.6 +/- 5.2, 55.3 +/- 8.2 vs CAST (2 weeks) 22.2 +/- 2.5, 25.0 +/- 1.5, 23.1 +/- 2.0 vs TEST (2 weeks) 30.5 +/- 6.5, 25.7 +/- 2.0, 45.2 +/- 4.5. This prominently showed that intrapenile flow was not reduced normally during erectile stimulation in CAST mice. This is the first described mouse model of castration-induced veno-occlusive erectile dysfunction. Erectile response abnormalities as measured by ICP and Doppler ultrasound studies in CAST mice may be attributed to hypogonadal effects on erectile tissue function. Morphologic changes in the cavernosal tissue of CAST mice coincide with these abnormalities to some extent. This study defines an androgen-dependent mechanism of veno-occlusive erectile function in the mouse. The castrated mouse model can be applied in future studies of veno-occlusive erectile dysfunction.

Epithelial-Mesenchymal Interactions in Development of the Mouse Fetal Genital Tubercle

Epithelial-mesenchymal interactions play a central role in the development of urogenital organs. We hypothesized that normal development of the external genitalia depends upon proper mesenchymal-epithelial signaling. The mesenchyme of the adult mouse penis consists of a corpus cavernosum and proximal and distal bones. The differentiation of penile mesenchyme into bone and cartilage begins after birth and can be accelerated by androgens. After determining the sex, genital tubercles of fetal mice at gestational day 15 were removed. The genital tubercles were trypsinized and microdissected to remove the epidermis and urethra from the mesenchyme. Recombinant specimens were created by combining genital tubercle mesenchyme with genital tubercle epithelium, bladder epithelium or tail epidermis. Tissues were grafted under the renal capsule of male athymic mice. After 3 weeks of growth, grafts were removed from the kidney, weighed and stained with hematoxylin and eosin, Alcian blue and peanut agglutinin. Male and female grafts showed no difference in growth or differentiation. Intact grafts and recombinant grafts, irrespective of the epithelial source, grew significantly more than grafts of the mesenchyme only. Recombinant grafts demonstrated a significantly higher prevalence of cartilage formation and mesenchymal differentiation compared to grafts of the mesenchyme without epithelium. Since heterologous epithelium is able to induce equivalent growth and differentiation of phallic mesenchyme, epithelium carries a permissive, but critical, role in genital mesenchyme development.

Distribution of immunoreactive 2',5'-oligoadenylate synthetase in mouse reproductive organs.

Although 2', 5'-oligoadenylate synthetase (2-5AS) is an enzyme induced by inferferon (IFN) or viral infections and mediates one of the principal antiviral pathways turned on by IFN, low constitutive levels of the enzyme can be detected in various "normal" animals that have not been treated with IFN or virus. The distribution of this enzyme in the female and male reproductive organs of normal healthy mice was studied by Western blotting and by an immunohistochemical method, using a specific monoclonal antibody. On Western blotting, an antibody to 42-kD 2-5AS reacted with extracts from the ovary, oviduct, uterus, vagina, and placenta among the female reproductive organs, and testis, epididymis, and ductus deferens in the male. Immunohistochemically, the 2-5AS was localized on the following cells in the female reproductive organs: oocytes in the ovary; epithelium in the oviduct, uterus, and vagina; and trophoblasts in the placenta. Furthermore, the 2-5AS was localized on the epithelium and muscular layer in the ductus deferens and epithelium in the penis of the male mice, whereas the epithelium of the testis, epididymis, and seminal vesicle were stained faintly. It is well known that IFN is produced continuously in normal mice, so the 2-5AS in the tissues of normal mice is considered to be induced by such IFN produced under physiological conditions. Expression of the 2-5AS on the epithelium and trophoblasts in the reproductive organs may be responsible for the prevention of viral infections. However, the enzyme in oocytes may have some functions other than as an antiviral agent, since the enzyme was not detectable in embryos during early development.

Effect of histamine on microvascular endothelial junctional permeability, structure and adhesion molecules

Endothelial cell-to-cell junctions are crucial for vascular formation, networking, and remodeling of blood vessels as well as for inducing and integrating intracellular signals.We investigated the differential expression and distribution of endothelial cell-to-cell junction proteins in the penis of mice with hypercholesterolemia-induced erectile dysfunction.Two-month-old C57BL/6J mice were fed a diet containing 4% cholesterol and 1% cholic acid, and age-matched control animals were fed a normal diet, for 3 months. We performed dual priming oligonucleotide (DPO)-based multiplex polymerase chain reaction (PCR) (Seegene, Seoul, Korea) to screen the differential gene expression of 21 endothelial cell-to-cell junctions.At 5 months, erectile function was measured by electrical stimulation of the cavernous nerve, and the penis was harvested and stained with antibody to claudin-5, vascular endothelial (VE)-cadherin, and platelet/endothelial cell adhesion molecule (PECAM)-1 (N = 8 per group). Cavernous specimens from a separate group of animals were used for claudin-5, VE-cadherin, and PECAM-1 reverse transcriptase-PCR and Western blot analysis.Erectile function was significantly lower in hypercholesterolemic mice than in controls. DPO-based multiplex PCR revealed a profound decrease in the gene expression of endothelium-specific cell-to-cell junction proteins, including claudin-5, VE-cadherin, and PECAM-1, in hypercholesterolemic mice compared with that in controls. The expression of claudin-5, VE-cadherin, and PECAM-1 protein evaluated by Western blot or immunohistochemistry was significantly lower in hypercholesterolemic mice than in controls. These endothelial cell-to-cell junction proteins were more sparsely distributed in the endothelium of cavernous sinusoids than in the endothelium of cavernous artery and dorsal blood vessels.Down-regulation of the endothelial cell-to-cell junctions and decreased endothelial content in the corpus cavernosum might play a major role in the deterioration of erectile function in hypercholesterolemic mice. Ryu J-K, Zhang LW, Jin H-R, Piao S, Choi MJ, Tuvshintur B, Tumurbaatar M, Shin SH, Han J-Y, Kim WJ, and Suh J-K. Derangements in endothelial cell-to-cell junctions involved in the pathogenesis of hypercholesterolemia-induced erectile dysfunction. J Sex Med 2009;6:1893–1907.

Morphology and histochemistry of helicine arteries in the corpora cavernosa penis of mice.

The epitheloid modified walls of helicine arteries are built of tightly arranged specialized smooth muscle cells (epitheloid cells). They are polygonal in shape, but do not branch out. The number of myofilaments is markedly reduced, whereas cell organelles are well developed (mitochondria, Golgi regions, rough endoplasmic reticulum). Myofilaments are gathered to bundles with no orientation as to their direction. Regular dense patches and attachment zones do occur. The cell surface is provided with caveolae (surface vesicles) and a basal lamina. Where epitheloid cells are joined together, they share a single basal lamina in common. In circumscribed regions basal lamina material is completely absent, and the cell membranes approach to form a 150 A gap (paired cells). Endothelial cells are rich in cytoplasmic filaments and show only a few transport vesicles. In particular areas a basal lamina is absent, and epitheloid cells and endothelial cells are joined together leaving a 200 A wide cleft. Fluorescence histochemistry shows that helicine arteries are provided with an extremely dense network of adrenergic nerves located at the medio-adventitial border. Epitheloid cells, like ordinary vascular smooth muscle cells, show a postive ATPase reaction, but lack any histochemically demonstrable 5'-nucleotidase activity. Endothelial cells in helicine arteries react on unspecific alkaline phosphatase, while the endothelium of deep arteries and of the cavernous spaces does not.