Sympathetic regulation of fructose secretion in the seminal vesicle of the guinea-pig

Biological role of fructose in the male reproductive system: Potential implications for prostate cancer

BACKGROUND

Over the last 20 years, fructose has gradually emerged as a potential metabolic substrate capable of promoting the growth and progression of various cancers, including prostate cancer (PCa). The biological and molecular mechanisms that underlie the effects of fructose on cancer are beginning to be elucidated.

METHODS

This review summarizes the biological function of fructose as a potential carbon source for PCa cells and its role in the functionality of the male reproductive tract under normal conditions.

RESULTS

The most recent biological advances related to fructose transport and metabolism as well as their implications in PCa growth and progression suggest that fructose represent a potential carbon source for PCa cells. Consequently, fructose derivatives may represent efficient radiotracers for obtaining PCa images via positron emission tomography and fructose transporters/fructose-metabolizing enzymes could be utilized as potential diagnostic and/or predictive biomarkers for PCa.

CONCLUSION

The existing data suggest that restriction of fructose from the diet could be a useful therapeutic strategy for patients with PCa.

Physiology and Pharmacology of Ejaculation

Ejaculation is the final stage of coitus in mammalian male and is mandatory for natural procreation. Two synchronized phases, emission and expulsion, form the ejaculatory response and involve specific organs and anatomical structures. The peripheral events leading to ejaculation are commanded by autonomic (sympathetic and parasympathetic) and somatic divisions of the nervous system. The autonomic and somatic motor efferents originate in spinal nuclei located in thoracolumbar and lumbosacral segments. Co-ordinated activation of autonomic and somatic spinal nuclei is orchestrated by a group of lumbar spinal interneurons defined as the spinal generator of ejaculation. The generator of ejaculation together with the autonomic and somatic spinal nuclei constitutes a spinal network that is under the strong influence of stimulating or inhibiting genital sensory and supraspinal inputs. A brain circuitry dedicated to ejaculation has been delineated that is part of a more global network controlling other aspects of the sexual response. This circuitry includes discrete neuronal populations distributed in all divisions of the brain. The corollary to the expanded CNS network is the variety of neurotransmitter systems participating in the ejaculatory process. Among them, serotonin neurotransmission plays a key role and its targeting led to the development of the first registered pharmacological treatment of premature ejaculation in human beings. Critical gaps remain in the understanding of neurophysiopharmacology of ejaculation and management of ejaculatory disorders in human beings needs improvement. Because the ejaculatory response in laboratory animals and in human beings shares many similarities, the use of animal models will certainly provide further advances in the field.

Testosterone regulates levels of cystic fibrosis transmembrane regulator, adenylate cyclase, and cAMP in the seminal vesicles of orchidectomized rats

Secretions of chloride (Cl(-))- and bicarbonate (HCO3(-))-rich fluid by the seminal vesicles could involve cystic fibrosis transmembrane regulator (CFTR), which activity can be stimulated by cAMP generated from the reaction involving adenylate cyclase (AC). In this study, we investigated levels of CFTR, AC, and cAMP in the seminal vesicles under testosterone influence. Orchidectomized adult male rats received 7-day treatment with 125 or 250 μg/kg/day of testosterone with or without flutamide or finasteride. At the end of the treatment, animals were sacrificed and seminal vesicles were harvested for analyses of CFTR and AC protein expression level by Western blotting. Distribution of CFTR and AC in seminal vesicles was observed by immunohistochemistry. Levels of cAMP and dihydrotestosterone in seminal vesicle homogenates were measured by ELISA. Cystic fibrosis transmembrane regulator, AC, and cAMP levels increased with increasing doses of testosterone (P < 0.05 compared to nontreated orchidectomized rats). Cystic fibrosis transmembrane regulator and AC were expressed at the apical membrane of the epithelium lining the seminal vesicle lumen with higher expression levels observed in testosterone-treated rats than in non-treated orchidectomized rats (P < 0.05). The inhibitory effects of flutamide or finasteride on these parameters were greater in 250 μg/kg/day testosterone-treated rats than their effects in 125 μg/kg/day testosterone-treated rats. Higher dihydrotestosterone levels were observed in seminal vesicle homogenates after treatment with 250 μg/kg/day than with 125 μg/kg/day of testosterone (P < 0.05). Increased levels of CFTR, AC, and cAMP in seminal vesicles might contribute toward an increase in Cl(-) and HCO3(-) concentrations in the seminal fluid as reported under testosterone influence.

Distribution of androgen and oestrogen receptors-α in the seminal vesicle-related spinal neurones in male rats

The seminal vesicles are male accessory sex glands that contribute much of the seminal fluid volume. Previous studies have suggested that the majority of autonomic innervations to the rat seminal vesicles originate from the bilateral major pelvic ganglia. Many preganglionic autonomic neurones innervating the pelvic ganglion were expressed androgen receptors (AR) or oestrogen receptor (ER)-α immunoreactivity. However, direct neuroanatomic data regarding the distribution of AR and ER-α in seminal vesicle related-spinal neurones are lacking. In the present study, a nonvirulent pseudorabies virus (PRV-152 strain) was used in a retrograde tracing experiment. Four days after PRV injection into the seminal vesicles of male rats, spinal cord sections were prepared. Double- and triple-fluorescence techniques using AR and ER-α with choline acetyltransferase (ChAT) and PRV were used to investigate the AR and ER-α distribution in the seminal vesicles related spinal neurones in male rats. In lamina X, 14% of the PRV-labelled neurones in the L1-L4 segments and 43% in the L5-S1 segments were double-labelled with AR. In the L1-L4 segments, 6% of PRV-labelled neurones and 26% in the L5-S1 segments were double-labelled with ER-α. In the intermedial cell column area, 10% of PRV-labelled neurones in the L1-L4 segments and 47% of PRV-labelled neurones in the L5-S1 segments were double-labelled with AR. Up to 16% of PRV-labelled neurones in the L5-S1 segments were double-labelled with ER-α. No PRV-labelled neurones in the L1-L4 segments were double-labelled with ER-α. However, for the AR and ER-α/PRV/ChAT triple-fluorescence experiments, very few seminal vesicle preganglionic neurones expressed AR or ER-α. Our data suggests that many spinal interneurones but not preganglionic neurones involved in the seminal vesicle control in male rats were double-labelled with AR or ER-α, and they were mainly located at the parasympathetic level in the spinal cord.

The effect of streptozotocin-induced diabetes on the rat seminal vesicle: A possible pathophysiological basis for disorders of ejaculation

In the streptozotocin (STZ)-diabetic rat major increases in noradrenaline concentration and content of the seminal vesicles were evident as early as 7 weeks following induction of hyperglycemia and returned toward normal after 34 weeks of hyperglycemia. There were significant reductions in the concentration and content of dopamine at 19-42 weeks of diabetes, and small occasionally significant reductions in the content of serotonin and adrenaline, particularly around 19-26 weeks after STZ treatment. The uptake of tritiated noradrenaline in the diabetics was increased at 12 weeks compared to the controls, and decreased to control levels with increasing age. Release of tritiated noradrenline was increased in response to electrical field stimulation and high potassium solutions, and raising calcium concentration caused increased release at rest and during electrical stimulation. Immunohistochemical demonstration of tyrosine hydroxylase was increased during the period when the noradrenaline concentration and content were elevated. It is concluded that there are significant changes in the sympathetic innervation of the seminal vesicle during the course of STZ diabetes, and that alterations in the reuptake, release, and synthesis of the neurotransmitter noradrenaline may contribute to changes in the concentration of the amine in the tissue. It is possible that the changes observed are related to the remodeling and regrowth of sympathetic nerve endings damaged in the early stages of hyperglycemia. These changes may also contribute to disorders of ejaculation in diabetes.

Muscarinic acetylcholine receptor subtypes in the rat seminal vesicle

The aim of the present study was to identify the muscarinic acetylcholine receptor (mAChR) mRNA subtypes in the rat seminal vesicle. Furthermore, the mAChR subtypes involved in the contraction of the seminal vesicle were also explored. Reverse transcriptase-polymerase chain reaction (PCR) was performed and five PCR products corresponding to M1-M5 mAChR mRNA subtypes were detected in this tissue. Functional pharmacological studies indicated that the rank order of mAChR antagonists in blocking the contractile effects of carbachol was p-fluoro-hexahydro-sila-difenidol (pF-HHSiD) >> tropicamide > methoctramine = pirenzepine. This antagonist profile indicates that M3 mAChR subtype is predominantly involved in the seminal vesicle contraction. Furthermore, immunohistochemical studies confirmed the presence of the M3 mAChR subtype in the smooth muscle layers. M2 mAChR subtype was also immunolocalized in smooth muscle cells and may be involved in the contraction of this tissue. The presence of M2 and M3 mAChR subtypes in the epithelial cells suggests that these receptors could be involved in the protein secretion. Taken together, the cholinergic neurotransmitter may be a factor controlling contractility and protein secretion in this tissue.

Immunocytochemical distribution of nitric oxide synthase in the human seminal vesicle: a light and electron microscopical study

Although nitric oxide (NO) has been proven to be one of the most important non-adrenergic, non-cholinergic mediators in the control of human reproductive tract organs, to date information on the significance of NO-mediated signal transduction in the control of human seminal vesicle (SV) function is still sparse.()Recent investigations have underlined the significance of NO in the maintenance of sperm capacitation and viscosity of the seminal plasma as well as in the control of mammalian seminal vesicle smooth muscle tone. In order to further investigate the functional impact of NO on the regulation of normal SV function, we examined the distribution of NADPH-diaphorase (NADPH-d), endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in the cellular anatomy of human SV by means of light and electron microscopical immunocytochemistry (LM, EM) in combination with the tyramide signal amplification technique. Human SV were obtained from 15 patients who had undergone surgery for pelvic malignancies (carcinoma of the prostate or urinary bladder). SV specimens were fixed, sectioned and examined by LM and EM for the presence of NAPDH-d, eNOS and nNOS using specific antibodies and advanced staining procedures. LM revealed a dense NADPH-d reaction in glandular epithelial structures, whereas no substantial labeling was detected in the fibromuscular stroma. EM showed that the NADPH-d reaction product was abundantly detectable attached to membranes of the endoplasmic reticulum, mitochondria and the nuclei of glandular epithelial cells. nNOS staining was found in nerve fibers branching within the SV tissue. eNOS staining was present in small vessels but was only observed to a minor degree in glandular and subglandular structures and the smooth muscle stroma. Our results support the hypothesis that human SV is a site of NO production. The distribution of NADPH-d may give rise to the speculation that NO is mainly involved in the regulation of SV secretory activity. The sparse correlation between NADPH-d-, eNOS- and nNOS-staining might hint at the existence of a previously unidentified NOS isoform in human SV.

Does nitric oxide act as a cellular messenger in muscarinic endometrial secretion in the guinea-pig?

Uterine secretory cells receive a sympathetic cholinergic secremotor innervation. Nitric oxide (NO) has been suggested to be a second messenger of neurogenic modulated glandular secretion of the seminal vesicle. Thus a similar pattern for nervous induced carbohydrate secretion of the endometrium was assumed. The nitric oxide synthase (NOS) activity was estimated via formation of L-citrulline from L-arginine and histochemically with the nicotinamide-adenine dinucleotide phosphate diaphorase (NADPH-d) nitro blue technique. The carbohydrate secretion from everted uterine horns placed in organ baths was estimated. A calcium dependent formation of citrulline was found in the uterine horn suggesting an NOS activity. Strong NADPH staining cells were found in the glandular ducts of the endometrium and in the epithelial linings of the oviduct. Carbachol induced carbohydrate secretion of the endometrium while N-nitro L-arginin (L-NNA) and N-nitro L-arginin methyl ester (L-NAME) inhibited the carbachol induced secretion. The isomer D-NAME had no effect on carbachol induced secretion. When L-arginine was administered together with L-NNA no inhibitory effect on carbachol induced secretion was seen. L-arginine only had no effect on carbohydrate secretion. The NO donor glyceryl tritrate increased carbohydrate secretion but no synergistic effect was seen in combination with carbachol. The results suggest that glandular NO production is a prerequisite for muscarinic carbohydrate secretion of the endometrium.

Is glandular formation of nitric oxide a prerequisite for muscarinic secretion of fructose in the guinea-pig seminal vesicle?

The significance of nitric oxide (NO) formation in seminal secretion was studied in guinea-pig seminal vesicles. The nitric oxide synthase (NOS) activity was estimated and reduced nicotinamide-adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry was performed. Furthermore, cyclic guanosine 3,5-monophosphate (cGMP) concentration as well as fructose secretion from isolated vesicles was estimated. High Ca2+-dependent NOS activity as well as prominent glandular NADPH-diaphorase staining was found in the secretory epithelium. The NOS inhibitors N(G)-nitro L-arginine methyl ester (L-NAME) and N(G)-nitro L-arginine (L-NNA) inhibited carbachol-induced fructose secretion but the D-isomer to L-NAME had no effect. When L-arginine was administered together with L-NAME, no inhibitory effect on the carbachol-induced fructose secretion could be seen. Nerve-induced fructose secretion was also inhibited by L-NAME. The NO donor glyceryl trinitrate (GTN) increased the fructose secretion. Carbachol or GTN did not increase cGMP levels, nor was fructose secretion inhibited by a guanylate cyclase inhibitor (ODQ). Our results suggests that glandular NO production is a prerequisite for muscarinic fructose secretion in the seminal vesicle via a cGMP-independent pathway.

Calcitonin gene-related peptide in the hamster seminal vesicle and coagulating gland: an immunohistochemical, autoradiographical, and pharmacological study

The distribution of calcitonin gene-related peptide (CGRP)-immunoreactive nerves and CGRP binding sites, as well as the effect of CGRP on the muscle tension, was studied in the hamster seminal vesicle and coagulating gland. The use of an immunofluorescence staining technique on cryostat sections revealed that in the hamster seminal vesicle and coagulating gland, CGRP-positive nerve fibers are found in the connective interstitium and in the muscular and mucosal layers. Using an in vitro receptor autoradiographic technique, CGRP binding sites were found associated with the muscular coat. CGRP (10 pM to 1 microM) relaxed the seminal vesicle and the coagulating gland precontracted by either noradrenaline (10-30 microM) or the alpha 1-agonist, phenylephrine (10 microM). In preparations contracted by carbachol (10 microM), CGRP relaxed the seminal vesicle but not the coagulating gland. In both preparations, CGRP (1 microM) did not affect the muscle resting tension. These results suggest that CGRP may act as an inhibitory modulator of the autonomic control of contractility in the male accessory sex glands of the hamster.