The effects of age and streptozotocin diabetes on the sympathetic innervation in the rat penis

Effects of low-intensity shock wave therapy (LiST) on the erectile tissue of naturally aged rats

Low-intensity shock wave therapy (LiST) improves erectile function in patients with erectile dysfunction (ED), probably by promoting angiogenesis as suggested by studies on animals with comorbidities as disease associated ED models. We aim to investigate the effects of LiST on erectile tissue of healthy, naturally aged rats. Twelve naturally aged male rats were randomized into two groups: control group (n = 6) and LiST-treatment group (n = 6). Young rats (8 weeks) (n = 6) was also used as control. Each rat in treatment group received 300 shock waves with an energy flux density of 0.09 mJ/mm² at 2 Hz. Sessions were repeated three times/week for 2 weeks, followed by a 2-week washout period. Real-time RT-PCR for the expressions of vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), nerve growth factor (NGF), neuronal NOS (nNOS), as well as α1 and α2-adrenergic receptors (α1AR, α2AR) was performed, followed by immunohistochemical analysis (IHC) to evaluate protein expression. The expressions of VEGF, eNOS, and α2AR/α1AR ratio were increased after LiST (p = 0.039, p = 0.008, and p = 0.006 respectively). The increase of VEGF, eNOS, and α2AR was confirmed in IHC (p = 0.013, p = 0.092, and p = 0.096, respectively). The increase of VEGF and eNOS seem to play key role in the mechanism of action of LiST, apparently by inducing angiogenesis. The altered expression of α1/α2-adrenergic receptors could indicate a decrease in sympathetic activity. LiST showed to partially reverse changes associated with aging in erectile tissue of rats, which supports future research for ED prevention.

Sympathetic Hyperactivity, Increased Tyrosine Hydroxylase and Exaggerated Corpus Cavernosum Relaxations Associated with Oxidative Stress Plays a Major Role in the Penis Dysfunction in Townes Sickle Cell Mouse

Background

Sickle cell disease patients display priapism that may progress to erectile dysfunction. However, little is known about the pathophysiological alterations of corpus cavernosum in sickle cell disease.

Objective

Thus, this study aimed to evaluate the functional and molecular alterations of sympathetic machinery and nitric oxide—cyclic guanosine monophosphate signaling pathway in Townes transgenic sickle cell disease mice.

Methods

Concentration–response curves to contractile (phenylephrine) and relaxant agents (acetylcholine and sodium nitroprusside) were obtained in corpus cavernosum strips from sickle and C57BL/6 (control) mice. Neurogenic contractions and nitrergic relaxations were obtained using electrical-field stimulation. Measurements of endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), phosphodiesterase-5 (PDE5) and α_1A-, α_1B- and α_1D-adrenoceptor mRNA expressions and reactive-oxygen species were performed. Tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expressions in cavernosal tissues were also measured.

Results

The neurogenic contractions were higher in the sickle cell disease group, in association with elevated tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expression, as well as increased tyrosine hydroxylase mRNA expression. Likewise, phenylephrine-induced contractions were greater in the sickle mice, whereas α_1A-, α_1B- and α_1D-adrenoceptor mRNA expression remained unchanged. Cavernosal relaxations to acetylcholine, sodium nitroprusside and EFS were higher in sickle mice, accompanied by decreased eNOS and nNOS, along with lower PDE5 mRNA expression. An increase of about 40% in reactive-oxygen species generation in corpus cavernosum from sickle mice was also detected.

Conclusion

Our study shows that decreased nitric oxide bioavailability in erectile tissue due to increased oxidative stress leads to both sympathetic hyperactivity and dysregulation of nitric oxide signaling in corpus cavernosum from Townes sickle mice.

Oxidative stress associated with middle aging leads to sympathetic hyperactivity and downregulation of soluble guanylyl cyclase in corpus cavernosum

Impairment of nitric oxide (NO)-mediated cavernosal relaxations in middle age contributes to erectile dysfunction. However, little information is available about the alterations of sympathetic neurotransmission and contraction in erectile tissue at middle age. This study aimed to evaluate the alterations of the contractile machinery associated with tyrosine hydroxylase (TH) in rat corpus cavernosum (RCC) at middle age, focusing on the role of superoxide anion. Male Wistar young (3.5-mo) and middle-aged (10-mo) rats were used. Electrical-field stimulation (EFS)- and phenylephrine-induced contractions were obtained in RCC strips. Levels of reactive-oxygen species (ROS) and TH mRNA expression, as well as protein expressions for α1/β1-subunits of soluble guanylyl cyclase (sGC), in RCC were evaluated. The neurogenic contractile responses elicited by EFS (4–32 Hz) were greater in RCC from the middle-aged group that was accompanied by elevated TH mRNA expression ( P < 0.01). Phenylephrine-induced contractions were also greater in the middle-aged group. A 62% increase in ROS generation in RCC from middle-aged rats was observed. The mRNA expression for the α1A-adrenoceptor remained unchanged among groups. Protein levels of α1/β1-sGC subunits were decreased in RCC from the middle-aged compared with young group. The NADPH oxidase inhibitor apocynin (85 mg·rat−1·day−1, 4 wk) fully restored the enhanced ROS production, TH mRNA expressions, and α1/β1-subunit sGC expression, indicating that excess of superoxide anion plays a major role in the sympathetic hyperactivity and hypercontractility in erectile tissue at middle age. Reduction of oxidative stress by dietary antioxidants may be an interesting approach to treat erectile dysfunction in aging population.

Microglia are selectively activated in endocrine and cardiovascular control centres in streptozotocin-induced diabetic rats

Type 1 and 2 diabetes are associated with dysfunction in multiple hormone systems, as well as increased sympathetic nerve activity, which may contribute to the development of diabetic complications. In other pathologies, such as myocardial infarction, increased sympathetic drive is associated with neuroinflammation and microglial activation in the hypothalamic paraventricular nucleus (PVN), a brain region that regulates sympathetic drive and multiple endocrine responses. In the present study, we used immunohistochemistry to study microglial and neuronal activation in the PVN and related brain regions in streptozotocin (STZ)-induced diabetic rats. As expected, STZ treatment was associated with elevated blood glucose within 1 week. STZ injections also caused neuronal activation in the PVN and superoptic nucleus (SON) but not in the nucleus tractus solitarius (NTS), which was evident by 6 weeks. STZ-treated rats showed increased plasma osmolarity, which would be expected to activate PVN and SON neurones. There was no apparent increase in histochemical markers of microglial activation, including phospho-p38, phospho-extracellular signal regulated kinase, P2X4 receptor or interleukin 1-β even at 10 weeks after STZ-treatment. However, we did see a significant increase in the percentage of microglia with an activated morphology in the PVN, SON and NTS, although not in surrounding hypothalamic, brainstem or cortical regions. These morphological changes included a significant reduction in microglial process length and were evident by 8 weeks but not 6 weeks. The delayed onset of microglial changes compared to neuronal activation in the PVN and SON suggests the over-excitation of neurones as a mechanism of microglial activation. This delayed microglial activation may, in turn, contribute to the endocrine dysregulation and the elevated sympathetic nerve activity reported in STZ-treated rats.

Changes in nerve- and endothelium-mediated contractile tone of the corpus cavernosum in a mouse model of pre-mature ageing

Erectile dysfunction (ED) is very prevalent in the older population, although the ageing-related mechanisms involved in the development of ED are poorly understood. We propose that age-induced differences in nerve- and endothelium-mediated smooth muscle contractility in the corpus cavernosum (CC) could be found between a senescent-accelerated mouse prone (SAMP8) and senescent-accelerated mouse resistant (SAMR1) strains. We analysed the changes in muscle tension induced by electrical field stimulation (EFS) or agonist addition 'in vitro', assessing nerve density (adrenergic, cholinergic and nitrergic), the expression of endothelial nitric oxide synthase (eNOS), cGMP accumulation and the distribution of interstitial cells (ICs) by immunofluorescence. We observed no change in both the nerve-dependent adrenergic excitatory contractility at physiological levels of stimulation and in the nitrergic inhibitory response in SAMP8 animals. Unlike cholinergic innervation, the density of adrenergic and nitrergic nerves increased in SAMP8 mice. In contrast, smooth muscle sensitivity to exogenous noradrenaline (NA) was slightly reduced, whereas cGMP accumulation in response to EFS and DEA/NO, and relaxations to DEA/NO and sildenafil, were not modified. No changes in the expression of eNOS and in the distribution of vimentin-positive ICs were detected in the aged animals. The ACh induced atropine-sensitive biphasic endothelium-dependent responses involved relaxation at low concentrations that turned into contractions at the highest doses. CC relaxation was mainly because of the production of NO together with some relaxant prostanoid, which did not change in SAMP8 animals. In contrast, the contractile component was considerably higher in the aged animals and it was completely inhibited by indomethacin. In conclusion, a clear imbalance towards enhanced production of contractile prostanoids from the endothelium may contribute to ED in the elderly. On the basis of these data, we propose the senescence-accelerated mouse model as a reliable tool to analyse the basic ageing mechanisms of the CC.

Autonomic neuropathy in experimental models of diabetes mellitus

Autonomic neuropathy complicates diabetes by increasing patient morbidity and mortality. Surprisingly, considering its importance, development and exploitation of animal models has lagged behind the wealth of information collected for somatic symmetrical sensory neuropathy. Nonetheless, animal studies have resulted in a variety of insights into the pathogenesis, neuropathology, and pathophysiology of diabetic autonomic neuropathy (DAN) with significant and, in some cases, remarkable correspondence between rodent models and human disease. Particularly in the study of alimentary dysfunction, findings in intrinsic intramural ganglia, interstitial cells of Cajal and the extrinsic parasympathetic and sympathetic ganglia serving the bowel vie for recognition as the chief mechanism. A body of work focused on neuropathologic findings in experimental animals and human subjects has demonstrated that axonal and dendritic pathology in sympathetic ganglia with relative neuron preservation represents one of the neuropathologic hallmarks of DAN but it is unlikely to represent the entire story. There is a surprising selectivity of the diabetic process for subpopulations of neurons and nerve terminals within intramural, parasympathetic, and sympathetic ganglia and innervation of end organs, afflicting some while sparing others, and differing between vascular and other targets within individual end organs. Rather than resulting from a simple deficit in one limb of an effector pathway, autonomic dysfunction may proceed from the inability to integrate portions of several complex pathways. The selectivity of the diabetic process appears to confound a simple global explanation (e.g., ischemia) of DAN. Although the search for a single unifying pathogenetic hypothesis continues, it is possible that autonomic neuropathy will have multiple pathogenetic mechanisms whose interplay may require therapies consisting of a cocktail of drugs. The role of multiple neurotrophic substances, antioxidants (general or pathway specific), inhibitors of formation of advanced glycosylation end products and drugs affecting the polyol pathway may be complex and therapeutic elements may have both salutary and untoward effects. This review has attempted to present the background and current findings and hypotheses, focusing on autonomic elements including and beyond the typical parasympathetic and sympathetic nervous systems to include visceral sensory and enteric nervous systems.

Streptozotocin-induced diabetes differentially affects sympathetic innervation and control of plantar metatarsal and mesenteric arteries in the rat

In humans neural control of arterial vessels supplying skin in the extremities is particularly vulnerable to the effects of diabetes. Here the streptozotocin (STZ) rat model of type 1 diabetes was used to compare effects on neurovascular function in plantar metatarsal arteries (PMAs), which supply blood to skin of hind paw digits, with those in mesenteric arteries (MAs). Twelve weeks after STZ (60 mg/kg ip), wire myography was used to assess vascular function. In PMAs, lumen dimensions were unchanged but both nerve-evoked contractions and sensitivity to α(1) (phenylephrine, methoxamine)- and α(2) (clonidine)-adrenoceptor agonists were reduced. The density of perivascular nerve fibers was also reduced by ~25%. These changes were not observed in PMAs from STZ-treated rats receiving either a low dose of insulin that did not greatly reduce blood glucose levels or a high dose of insulin that markedly reduced blood glucose levels. In MAs from STZ-treated rats, nerve-evoked increases in force did not differ from control but, because lumen dimensions were ~20% larger, nerve-evoked increases in effective transmural pressure were smaller. Increases in effective transmural pressure produced by phenylephrine or α,β-methylene ATP in MAs from STZ-treated rats were not smaller than control, but the density of perivascular nerve fibers was reduced by ~10%. In MAs, the increase in vascular dimensions is primarily responsible for reducing effectiveness of nerve-evoked constrictions. By contrast, in PMAs decreases in both the density of perivascular nerve fibers and the reactivity of the vascular muscle appear to explain impairment of neurovascular transmission.

The promise of inhibition of smooth muscle tone as a treatment for erectile dysfunction: where are we now?

Ten years ago, the inhibition of Rho kinase by intracavernosal injection of Y-27632 was found to induce an erectile response. This effect did not require activation of nitric oxide-mediated signaling, introducing a novel target pathway for the treatment of erectile dysfunction (ED), with potential added benefit in cases where nitric oxide bioavailability is attenuated (and thus phosphodiesterase type 5 (PDE5) inhibitors are less efficacious). Rho-kinase antagonists are currently being developed and tested for a wide range of potential uses. The inhibition of this calcium-sensitizing pathway results in blood vessel relaxation. It is also possible that blockade of additional smooth muscle contractile signaling mechanisms may have the same effect. In this review, we conducted an extensive search of pertinent literature using PUBMED. We have outlined the various pathways involved in the maintenance of penile smooth muscle tone and discussed the current potential benefit for the pharmacological inhibition of these targets for the treatment of ED.

Tyrosine hydroxylase immunoreactivity as indicator of sympathetic activity: simultaneous evaluation in different tissues of hypertensive rats

Vasomotor control by the sympathetic nervous system presents substantial heterogeneity within different tissues, providing appropriate homeostatic responses to maintain basal/stimulated cardiovascular function both at normal and pathological conditions. The availability of a reproducible technique for simultaneous measurement of sympathetic drive to different tissues is of great interest to uncover regional patterns of sympathetic nerve activity (SNA). We propose the association of tyrosine hydroxylase immunoreactivity (THir) with image analysis to quantify norepinephrine (NE) content within nerve terminals in arteries/arterioles as a good index for regional sympathetic outflow. THir was measured in fixed arterioles of kidney, heart, and skeletal muscle of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (123 ± 2 and 181 ± 4 mmHg, 300 ± 8 and 352 ± 8 beats/min, respectively). There was a differential THir distribution in both groups: higher THir was observed in the kidney and skeletal muscle (∼3-4-fold vs. heart arterioles) of WKY; in SHR, THir was increased in the kidney and heart (2.4- and 5.3-fold vs. WKY, respectively) with no change in the skeletal muscle arterioles. Observed THir changes were confirmed by either: 1) determination of NE content (high-performance liquid chromatography) in fresh tissues (SHR vs. WKY): +34% and +17% in kidney and heart, respectively, with no change in the skeletal muscle; 2) direct recording of renal (RSNA) and lumbar SNA (LSNA) in anesthetized rats, showing increased RSNA but unchanged LSNA in SHR vs. WKY. THir in skeletal muscle arterioles, NE content in femoral artery, and LSNA were simultaneously reduced by exercise training in the WKY group. Results indicate that THir is a valuable technique to simultaneously evaluate regional patterns of sympathetic activity.

Effects of hyperglycemia on rat cavernous nerve axons: a functional and ultrastructural study

The present study explored parallel changes in the physiology and structure of myelinated (Adelta) and unmyelinated (C) small diameter axons in the cavernous nerve of rats associated with streptozotocin-induced hyperglycemia. Damage to these axons is thought to play a key role in diabetic autonomic neuropathy and erectile dysfunction, but their pathophysiology has been poorly studied. Velocities in slow conducting fibers were measured by applying multiple unit procedures; histopathology was evaluated with both light and electron microscopy. To our knowledge, these are the initial studies of slow nerve conduction velocities in the distal segments of the cavernous nerve. We report that hyperglycemia is associated with a substantial reduction in the amplitude of the slow conducting response, as well as a slowing of velocities within this very slow range (< 2.5 m/s). Even with prolonged hyperglycemia (> 4 months), histopathological abnormalities were mild and limited to the distal segments of the cavernous nerve. Structural findings included dystrophic changes in nerve terminals, abnormal accumulations of glycogen granules in unmyelinated and preterminal axons, and necrosis of scattered smooth muscle fibers. The onset of slowing of velocity in the distal cavernous nerve occurred subsequent to slowing in somatic nerves in the same rats. The functional changes in the cavernous nerve anticipated and exceeded the axonal degeneration detected by morphology. The physiologic techniques outlined in these studies are feasible in most electrophysiologic laboratories and could substantially enhance our sensitivity to the onset and progression of small fiber diabetic neuropathy.

Adenosine actions are preserved in corpus cavernosum from obese and type II diabetic db/db mouse

INTRODUCTION

Erectile dysfunction (ED) in diabetes is associated with autonomic neuropathy and endothelial dysfunction. Whereas the nonadrenergic-noncholinergic (NANC)/neurogenic nitric oxide pathway has received great attention in diabetes-associated ED, few studies have addressed sympathetic overactivity.

AIM

To test the hypothesis that adenosine-induced inhibition of adrenergic-mediated contractile responses in mouse corpus cavernosum is impaired in the presence of diabetes.

METHODS

The db/db (obesity and type II diabetes caused by a leptin receptor mutation) mouse strain was used as a model of obesity and type II diabetes, and standard procedures were performed to evaluate functional cavernosal responses.

MAIN OUTCOME MEASURES

Increased cavernosal responses to sympathetic stimulation in db/db mice are not associated with impaired prejunctional actions of adenosine.

RESULTS

Electrical field stimulation (EFS)-, but not phenylephrine (PE)-, induced contractions are enhanced in cavernosal strips from db/db mice in comparison with those from lean littermates. Direct effects of adenosine, 2-chloro-adenosine, A(1) receptor agonist C-8031 (N6 cyclopentyladenosine), and sodium nitroprusside are similar between the strips from lean and db/db mice, whereas relaxant responses to acetylcholine and NANC stimulation are significantly impaired in the cavernosal strips from db/db mice. 5'-Iodotubercidin (adenosine kinase inhibitor) and dipyridamole (inhibitor of adenosine transport), as well as the A(1) agonist C-8031, significantly and similarly inhibit contractions induced by stimulation of adrenergic nerves in the cavernosal strips from lean and db/db mice.

CONCLUSIONS

Results from this study suggest that corpora cavernosa from obese and diabetic db/db mice display altered neural-mediated responses that would favor penile detumescence, i.e., increased contractile response to adrenergic nerve stimulation and decreased relaxant responses upon activation of NANC nerves. However, increased cavernosal responses to adrenergic nerve stimulation are not due to impaired negative modulation of sympathetic neurotransmission by adenosine in this diabetic model.

Role of cytochrome P450 metabolites of arachidonic acid in regulation of corporal smooth muscle tone in diabetic and older rats

This study examined the role of cytochrome P450 (CYP) metabolites of arachidonic acid (AA) to rat corporal smooth muscle tone. 11, 12-Epoxyeicosatrienoic acid (EET) (10(-11)-10(-6 )M) produced dose-dependent relaxation of rat (control; 10 weeks old) corpus cavernosum with a pD(2) value of 8.8+/-0.2 and a maximal relaxation of 80+/-9%, whereas 20-hydroxyeicosatetraenoic (20-HETE) did not have an effect. EET-mediated relaxation of corpus cavernosum was attenuated by 71+/-3%, 55+/-2%, 53+/-5% and 84+/-3% in the presence of nitro-L-arginine methyl ester (L-NAME) (10(-4) M), an inhibitor of nitric oxide (NO) synthase, iberiotoxin (5 x 10(-8) M), an inhibitor of calcium-activated potassium (BK) channels, glibenclamide (10(-5) M), an inhibitor of ATP-sensitive K(+) channels or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10(-5) M), an inhibitor of soluble guanylyl cyclase, respectively. EET-mediated relaxation of rat corpus cavernosum was significantly less in the streptozotocin (STZ)-treated (diabetic) and 30 weeks old (older) animals compared to control. Carbachol (10(-9)-10(-4) M)-induced relaxation was significantly reduced whereas phenylephrine (PE) (10(-9)-5 x 10(-3) M)-induced contraction was significantly increased in the cavernosum strips from old and diabetic rats compared to the control. Pre-incubation of the cavernosum strips obtained from control, older or diabetic rats with N-hydroxy-N'-(4-butyl-2-methyl-phenyl)-formamidine (HET0016), a selective inhibitor of 20-HETE synthesis, or 1-cyclohexyl-3-dodecyl urea (CDU), a specific inhibitor of soluble epoxide hydrolase (sEH) resulted in a significant attenuation of PE-induced contraction and improvement in carbachol-induced relaxation. We conclude that 11, 12-EET-induced relaxation of the rat corpus cavernosum involves activation of cGMP/NO pathway as well as activation of ATP-sensitive K(+) channels and BK channels. These results also suggest that inhibition of 20-HETE production or reduction of EET inactivation may have therapeutic potential to prevent erectile dysfunction associated with diabetes and aging.

Long-term changes in sympathetic innervation in the corpus cavernosum of the STZ-diabetic rat

The noradrenaline (NA) concentration in the rat corpus cavernosum (CC) increased to approximately 350% of control values after about 8 weeks of hyperglycaemia induced by the intraperitoneal injection of streptozotocin (STZ) at 10 weeks of age. These changes were maintained for at least a further 32 weeks of hyperglycaemia and occurred without any significant change in the weight in the tissue. Smaller but significant increases in NA concentration occurred in the glans penis (GP) reaching 150-175% of the control levels during the period of prolonged hyperglycaemia. In contrast, there was no significant change in the NA concentration in the penile urethra. Measurements have also been made that relate to changes in the synthesis and reuptake of NA in the CC during the period during which high NA concentration is maintained. Immunohistochemical studies for the synthetic enzyme tyrosine hydroxylase in the CC indicate that the intensity of staining in the tissue had increased after 10, 20 and 32 weeks of hyperglycaemia, relative to the tissues from control animals. Dilated nerve fibres and engorged endings were present in the CC of the diabetic animals at these times. Reuptake of tritiated NA by the terminal axonal membranes in the CC was raised to 181% of control values after 12 weeks of hyperglycaemia (P<0.05), but later declined to values that are not significantly different from the control levels (after 26 and 64 weeks of hyperglycaemia). There are few studies of the effects of prolonged diabetes on functional aspects of sympathetic postganglionic neurones in the CC, and this paper suggests that the changes described represent remodelling of noradrenergic axonal terminals starting about after 8-10 weeks of hyperglycaemia; this delay in onset of the neuropathic changes is also a feature of type I diabetes in humans.