An immunohistochemical and pharmacological study of tachykinins in the rat and guinea-pig prostate glands

Neuropeptide Profiles of Mammalian Male Genital Tract: Distribution and Functional Relevance in Reproduction

Neuropeptides are secretory peptides characterized by small chains of amino acids linked by peptide bonds. They are majorly found in some mammalian neurons and glial cells, where they modulate a variety of physiological homeostasis. In the male genital tract, they are mostly found in the neuronal fibers supplying the vasculature, smooth muscle layer, interstitium, and lamina propria of the tunica mucosa of the various reproductive organs. Functionally, neuropeptides are strongly implicated in vascular temperature regulations, spermatozoa extrusion, epididymal content transportation, and movement of accessory gland secretions. This review provides an overview of neuropeptides with respect to their synthesis, release, and mechanism of actions, with emphasis on the locally acting neuropeptides, such as substance P (SP), neuropeptide Y (NPY), vasoactive intestinal peptides (VIP), calcitonin gene-related peptide (CGRP), galanin (GAL), cholecystokinin (CCK), C-terminal flanking peptide of NPY (CPON), peptide histidine isoleucine (PHI), and met- and leu-enkephalins (M-ENK and L-ENK) along the male genital tract (i.e., the spermatic cord, testis, epididymis, ductus deferens, and accessory sex organs) of 14 species of mammals and their marked influence on reproduction. This review also revealed from documented reports that the vast majority of neuropeptides present in the autonomic nerve supply to the male genital tract probably coexist with other peptides or with various neurotransmitters (tyrosine hydroxylase, dopamine beta hydroxylase, and 5-hydroxytryptamine). In addition, documented evidence of variation in age, season, and intraspecies differences were identified as notable factors of influence in peptidergic nerve fiber distribution.

The role of prostate inflammation and fibrosis in lower urinary tract symptoms

Lower urinary tract symptoms (LUTS) in aging men are extremely common. They have historically been attributed to benign prostatic hyperplasia (BPH), enlargement of the prostate, and bladder outlet obstruction. However, recent studies have revealed acute and chronic inflammation to be highly associated with LUTS, correlated with prostatic enlargement, and implicated as a cause of prostatic fibrosis that contributes to bladder outlet obstruction. This review examines the evidence implicating inflammation and fibrosis in BPH/LUTS. It identifies potential mechanisms by which inflammation may drive nociceptive signaling as well as hyperplastic growth and fibrosis and identifies targets for pharmacological intervention. This is a promising area for research and development of novel therapies to prevent or more effectively treat LUTS in aging men.

Age-related changes in the innervation of the prostate gland: implications for prostate cancer initiation and progression

The adult prostate gland grows and develops under hormonal control while its physiological functions are controlled by the autonomic nervous system. The prostate gland receives sympathetic input via the hypogastric nerve and parasympathetic input via the pelvic nerve. In addition, the hypogastric and pelvic nerves also provide sensory inputs to the gland. This review provides a summary of the innervation of the adult prostate gland and describes the changes which occur with age and disease. Growth and development of the prostate gland is age dependent as is the occurrence of both benign prostate disease and prostate cancer. In parallel, the activity and influence of both the sympathetic and parasympathetic nervous system changes with age. The influence of the sympathetic nervous system on benign prostatic hyperplasia is well documented and this review considers the possibility of a link between changes in autonomic innervation and prostate cancer progression.

Novel drug targets for the pharmacotherapy of benign prostatic hyperplasia (BPH)

Benign prostatic hyperplasia (BPH) is the major cause of lower urinary tract symptoms in men aged 50 or older. Symptoms are not normally life threatening, but often drastically affect the quality of life. The number of men seeking treatment for BPH is expected to grow in the next few years as a result of the ageing male population. Estimates of annual pharmaceutical sales of BPH therapies range from $US 3 to 10 billion, yet this market is dominated by two drug classes. Current drugs are only effective in treating mild to moderate symptoms, yet despite this, no emerging contenders appear to be on the horizon. This is remarkable given the increasing number of patients with severe symptoms who are required to undergo invasive and unpleasant surgery. This review provides a brief background on prostate function and the pathophysiology of BPH, followed by a brief description of BPH epidemiology, the burden it places on society, and the current surgical and pharmaceutical therapies. The recent literature on emerging contenders to current therapies and novel drug targets is then reviewed, focusing on drug targets which are able to relax prostatic smooth muscle in a similar way to the α(1) -adrenoceptor antagonists, as this appears to be the most effective mechanism of action. Other mechanisms which may be of benefit are also discussed. It is concluded that recent basic research has revealed a number of novel drug targets such as muscarinic receptor or P2X-purinoceptor antagonists, which have the potential to produce more effective and safer drug treatments.

Current models of human prostate contractility

1. The human prostate is a compact gland contributing to seminal fluid. With increasing age, most humans will develop benign prostatic hyperplasia, a condition of prostatic enlargement and contractility that leads to occlusion of the urethra. Over many years, investigators have used a variety of animal and cell culture models to elucidate some of the contractile and proliferative mechanisms that may be associated with the development of this condition. 2. This review briefly assesses the current state of knowledge of the mechanisms underlying human prostatic contractility and compares it with that of animal and cell culture models. It is not intended as a comprehensive methodological review, nor is it intended to indicate our preferences for either model. Our aim is to correlate findings from animal and cell culture models with the current understanding of human prostate contractility. 3. We hope that the present review will increase awareness of the suitability of the current models in developing our understanding of benign prostatic hyperplasia.

Effect of neurokinins on canine prostate cell physiology

BACKGROUND

Sensory peptide neurotransmitters have been implicated as significant regulators of prostate growth. This study was designed to evaluate the role of neurokinins in proliferation, differentiation, and contraction of canine prostate cells in culture.

METHODS

NK1, NK2, and NK3 receptor subtypes were localized in canine prostate tissue by immunocytochemistry and ligand binding studies. Functional effects of neurokinin agonists were tested on cell differentiation (expression of smooth muscle actin (SMA)), proliferation (MTS assay), and contraction of canine prostate cells in culture.

RESULTS

Immunocytochemical staining of canine prostate sections revealed strong stromal staining for NK1 together with weak stromal staining for NK2 and even weaker staining for NK3. Furthermore, there was overlapping localization of NK1 receptors, substance P (SP), and calcitonin gene-regulated peptide (CGRP) in prostate tissue sections. SP caused concentration-dependent increase in SMA expression that was attenuated in a concentration-dependent manner by YM-44778, a non-selective antagonist for neurokinin receptors, but not by either the NK2 antagonist (SR-48968) nor by the NK3 antagonist (SB-223412). SP and neurokinin A (NKA) also caused a modest contraction of stromal cells in collagen gels. NKA stimulated proliferation of prostate epithelial cells without any apoptotic effect, which was attenuated by SR-48968. Surprisingly, in binding studies NK3 appeared to be the most abundant neurokinin receptor subtype, although functional studies failed to reveal significant coupling of this receptor.

CONCLUSIONS

Our results suggest that, at least in vitro, neurokinins have modest effects on canine prostate epithelial cell proliferation, stromal differentiation, and contraction.

Tachykinins and tachykinin receptors: effects in the genitourinary tract

Tachykinins (TKs) are a family of peptides involved in the central and peripheral regulation of urogenital functions through the stimulation of TK NK1, NK2 and NK3 receptors. At the urinary system level, TKs locally stimulate smooth muscle tone, ureteric peristalsis and bladder contractions, initiate neurogenic inflammation and trigger local and spinal reflexes aimed to maintain organ functions in emergency conditions. At the genital level, TKs are involved in smooth muscle contraction, in inflammation and in the modulation of steroid secretion by the testes and ovaries. TKs produce vasodilatation of maternal and fetal placental vascular beds and appear to be involved in reproductive function, stress-induced abortion, and pre-eclampsia. The current data suggest that the genitourinary tract is a primary site of action of the tachykininergic system.

Adenosine 5'-triphosphate and noradrenaline are excitatory cotransmitters to the fibromuscular stroma of the guinea pig prostate gland

Immunohistochemical studies demonstrated abundant P2X(1)-receptor immunoreactivity colocalized with alpha-actin within the fibromuscular stroma of the guinea pig prostate. P2X(2)-, P2X(3)- and P2X(4)-receptor immunoreactivity was absent. alphabetamethylene Adenosine 5'-triphosphate (ATP) attenuated contractile responses to electrical field stimulation (50 V, 0.5 ms, 5-20 Hz) in the absence and presence of prazosin (0.3 microM). Responses to 1-2 Hz were unaffected. ARL 67156 (6-N, N-diethyl-beta-gamma-dibromomethylene-D-adenosine-5-triphosphate; 100 microM) enhanced contractile responses to electrical field stimulation (50 V, 0.5 ms, 10-20 Hz). Concentration-response curves to exogenously applied ATP analogues on unstimulated preparations elicited concentration-dependent suramin (100 microM)-sensitive contractions. The rank order of potency was: alphabetamethylene ATP>2methylthio ATP=betagammamethylene ATP>adenosine 5'-diphosphate (ADP)=ATP. Adenosine and adenosine 5'-monophosphate (AMP) did not produce contractile responses. These results demonstrate the presence of functional P2X(1)-receptors within the fibromuscular stroma of the guinea pig prostate and suggest a cotransmitter role for ATP with noradrenaline during high-frequency stimulation.

Evaluation of the mouse prostate as a suitable model for the study of human prostate function

INTRODUCTION

Research into prostate development and function is mainly carried out in rats and guinea pigs. While these animals have proven to be good models of human prostate function, their use is limited when compared with what could be achieved using the various currently available gene knockout mice. This study aimed to ascertain whether the mouse prostate was a viable model for studying human prostate function.

METHODS

Sections from mouse prostate glands were histochemically processed to visualise the neurotransmitters and receptors present. Isolated organ bath studies were conducted in Krebs-Henseleit solution at 37 degrees C to delineate the physiological mechanisms involved in contractility.

RESULTS

Positive histochemical staining for noradrenaline and acetylcholinesterase (AChE) was observed in the fibromuscular stroma. AChE-positive staining was also observed in epithelial cells lining prostatic acini. Immunoreactivity to P2X(1) and P2X(7) purinoceptors was observed in the fibromuscular stroma and immunoreactivity to P2X(4) purinoceptors in the glandular epithelium. Positive immunostaining for neuropeptide Y, big endothelin, calcitonin gene-related peptide (CGRP), substance P, and neurokinin A was observed in the fibromuscular stroma. Frequency-response curves (1.0 ms pulse duration, 60 V, 0.1-20 Hz) to electrical field stimulation yielded frequency-dependent contractions that were attenuated by tetrodotoxin (P < .001), guanethidine (P < .001), and prazosin (P = .01). Suramin (P = .21), alpha,beta-methylene ATP (P = .84), and atropine (P = .76) caused no significant effects. Concentration-response curves to endogenously administered phenylephrine yielded concentration-dependent contractions (pEC(50) = 6.1 +/- 0.3, maximum response 0.20 +/- 0.03 g), which were attenuated by prazosin (P < .001).

DISCUSSION

Histochemistry suggests that mouse prostates have a similar innervation to that of humans and other laboratory animals. Furthermore, responses to nerve stimulation are noradrenergic and mediated by alpha(1)-adrenoceptors. Therefore, the mouse prostate is a suitable model for human prostate function and a viable isolated preparation for contractility studies.

Origin and Chemical Coding of Primary Afferent Neurones Supplying the Prostate of the Dog

Retrograde tracing technique combined with the double-fluorescent immunohistochemistry were used to investigate the distribution and chemical coding of primary afferent neurones supplying the canine prostate. After the injection of Fast Blue (FB) into the prostatic tissue retrogradely-labelled (FB(+)) primary afferent neurones were localized in bilateral L(1)-Ca(1) dorsal root ganglia (DRG). Statistical analysis using anova test showed that there are two major sources of afferent prostate innervation. The vast majority of prostate-supplying primary afferent neurones were located in bilateral L(2)-L(4) DRG (56.9 +/- 0.6%). The second source of the afferent innervation of canine prostate were bilateral S(1)-Ca(1) DRG (40.6 +/- 1.0%). No statistically significant differences were found between average number of FB(+) neurones localized in the left and right DRG (49.5 +/- 1.7 and 50.5 +/- 1.7%, respectively). Immunohistochemistry revealed that FB(+) primary afferent neurones contain several neuropeptides in various combinations. In the prostate-supplying neurones of lumbar and sacro-caudal DRG the immunoreactivity to substance P (SP) and calcitonin gene-related peptide (CGRP) was found most frequently (50 +/- 3.7 and 37.3 +/- 1.9%, respectively). Both in the lumbar and sacro-caudal DRG, considerable population of FB(+) neurones immunoreactive neither to SP nor CGRP were also found (23 +/- 2.6 and 32.8 +/- 2.3%, respectively). In the lumbar DRG 10.7 +/- 1.1% of SP-immunoreactive FB(+) neurones also contained galanin (GAL). In 9.2 +/- 2.2% of the prostate-supplying primary afferent neurones located in the sacro-caudal DRG the co-localization of SP and GAL was also reported. Results of the retrograde tracing experiment demonstrated for the first time sources of afferent innervation of the canine prostate. Double immunohistochemistry revealed that many of the prostate-supplying primary afferent neurones express some of sensory neuropeptides which presumably may be involved in nociception and some pathological processes like inflammation or nerve injury.

Distribution of calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) immunoreactive nerve fibers in the seminal vesicle and prostate of the male sheep

Double immunohistochemistry was used to determine the occurrence and distribution pattern of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) in seminal vesicles and prostate of the male sheep. Numerous CGRP- and SP-immunoreactive (IR) nerve fibres were found in the mucosal layer and smooth musculature of the seminal vesicles and prostate. In both glands nerve terminals immunoreactive to CGRP were more numerous than SP-IR ones. The majority of CGRP-IR nerve fibers showed colocalization of this peptide and SP. In both layers of the seminal vesicle and prostate, rare nerve terminals immunoreactive to GAL were also found. Immunoreactivity to SP was also found in all GAL-IR nerve fibers. The presence of numerous CGRP- and SP-IR nerve fibers in the seminal vesicle and prostate of the male sheep suggests that these neuropeptides may be involved in the sensory transmission and/or control of smooth muscle contractility. On the other hand, a relatively low number of GAL-IR nerve fibers of the seminal vesicle and prostate suggest that this peptide may act as an anti-nociceptive agent. It cannot be excluded that, in the seminal vesicle, GAL may also be involved in the control of the smooth muscle fiber activity. The possible role of CGRP, SP and GAL in the regulation of functions of the accessory sexual glands needs to be determined in further physiological studies.

Species differences in the actions of sensory neuropeptides on contractility of the smooth muscle of the rat and guinea-pig prostate

1. The present review describes the actions of sensory neuropeptides on the contractility of the rat and guinea-pig prostate gland and discusses the differences in sensitivity of the smooth muscle of the prostates taken from these species to these neuropeptides. 2. Nerve fibres immunoreactive for the tachykinins substance P and neurokinin A, as well as for the sensory neuropeptide calcitonin gene-related peptide (CGRP), are sparsely distributed throughout the fibromuscular stroma of the prostate gland in both the rat and guinea-pig. 3. In functional experiments, tachykinin agonists potentiate electrical field stimulation-induced contractile responses of prostates taken from guinea-pigs, but have no effect on those taken from rats. This potentiation is through stimulation of tachykinin NK1-receptors. 4. Conversely, CGRP inhibits electrical field stimulation-induced contractile responses of prostates taken from rats, but has no effect on those taken from guinea-pigs. 5. It is concluded that although the sensory innervation to the prostate glands of the rat and guinea-pig appears similar, the nature and sensitivity of the contractile response of the prostatic smooth muscle to applied sensory neuropeptides is vastly different in the two species.

The autonomic and sensory innervation of the smooth muscle of the prostate gland: a review of pharmacological and histological studies

1. We review literature demonstrating (a) the presence and (b) the actions of substances that mediate or modify neuroeffector transmission to the smooth muscle of the prostrate stroma of a number of species including man. 2. In all species studied prostatic stroma, but not secretory acini, receives rich noradrenergic innervation. Stimulation of these nerves causes contractions of prostate smooth muscle that are inhibited by guanethidine and by alpha1-adrenoceptor antagonists that probably act at the alpha1L-adrenoceptor. Such actions underlie the clinical use of alpha1-adrenoceptor antagonists in benign prostatic hyperplasia (BPH). 3. Acetylcholinesterase-positive nerves innervate prostatic stroma as well as epithelium. Atropine reduces nerve-mediated contractions of stromal muscle in the rat, guinea-pig and rabbit. M1, M2 and M3 muscarinic receptors have been implicated in eliciting or facilitating contraction in the prostate from guinea-pig, dog and rat, respectively. 4. Adenine nucleotides and nucleosides, nitric oxide (NO), opioids, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) may act as co-transmitters or modulators in autonomic effector nerves supplying prostate stroma. Adenosine inhibits neurotransmission to the rat prostate, and NO is inhibitory in prostate from human, rat, rabbit, pig and dog. The activity of peptides present in the relatively sparse sensory innervation of the prostate exhibits species variation, but, when effective, calcitonin gene-related peptide is inhibitory while tachykinins are stimulant. The roles of NPY and VIP in modulating stromal contractility remain unclear. 5. Taken together the current literature indicates that, in addition to noradrenaline, other neurotransmitters and neuromodulators may regulate the tone of prostatic smooth muscle. Whether drugs that mimic or modify their actions might be useful in providing symptomatic relief of the urinary symptoms associated with BPH remains to be established.

Calcitonin gene-related peptide (CGRP) inhibits contractions of the prostatic stroma of the rat but not the guinea-pig

This study investigated the presence and effects of calcitonin gene-related peptide (CGRP) within the rat and guinea-pig prostate glands. Immunohistochemical studies demonstrated that CGRP immunoreactive nerve fibres are sparsely distributed throughout the prostatic fibromuscular stroma in both species. These CGRP immunopositive nerve fibres shared a similar distribution profile but were not colocalized with tyrosine hydroxylase immunopositive nerve fibres which also innervate the prostatic stroma of these species. Nerve terminals within rat and guinea-pig prostatic tissues were electrically field stimulated (60 V, 0.5 ms, 10 Hz, 20 pulses every 60 s). In guinea-pig preparations, application of human alpha-CGRP, rat adrenomedullin or rat amylin (0.1 nM-1 microM) had no effect on responses to field stimulation. In contrast, both rat and human alpha-CGRP (10 pM-300 nM), rat adrenomedullin (0.3 nM-1 microM) and rat amylin (3 nM-1 microM) concentration-dependently inhibited electrically evoked contractile responses in the rat prostate. The relative order of potency was rat alpha-CGRP=human alpha-CGRP>rat adrenomedullin>rat amylin. The inhibition by rat alpha-CGRP of field stimulation-induced contractions in the rat prostate was competitively antagonized by human CGRP((8-37)) (1, 3 and 10 microM) with a pA(2) of 6.20+/-0.13. Rat alpha-CGRP (10 nM) attenuated contractile responses of the rat prostate to exogenously added noradrenaline (1-100 microM). Inhibitory concentration-response curves to rat alpha-CGRP in rat prostates were unaffected by preincubation in either glibenclamide (10-100 microM), N-nitro-L-arginine methyl ester (L-NAME) (10 microM), bestatin (10 microM), captopril (10 microM) or phosphoramidon (3 microM). Our results indicate that CGRP-induced inhibition of electrically evoked contractions in the rat prostate occurs through activation of postjunctional CGRP(2) receptors which act independently of a K(ATP) channel or nitrergic mechanisms. Degradation of rat alpha-CGRP via peptidases does not appear to occur in the rat prostate.