Distribution of vasoactive intestinal polypeptide binding sites in guinea pig genital tissues

Endogenous vasoactive peptides and the human vagina--a molecular biology and functional study

INTRODUCTION

Endogenous peptides, such as vasoactive intestinal polypeptide (VIP), C-type natriuretic peptide (CNP), and bradykinin (BK), have been proposed to play a role in the female sexual arousal response by exerting relaxation of clitoral, labial, and vaginal smooth muscle. While the effects of endogenous peptides on the human male erectile tissue have already been described, only very few studies have been conducted to investigate the peptidergic control of female genital tissues, including the vagina.

AIMS

To elucidate the expression of mRNA specifically encoding for peptide receptors in the human vagina and the effects of VIP, CNP, and BK on the tension induced by endothelin-1 (ET-1) of isolated human vaginal wall smooth muscle. The production of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in response to exposure of the tissue to the peptides was also measured.

METHODS

The expression of mRNA encoding for receptor proteins specific for VIP, CNP, and BK were investigated by means of molecular biology (reverse transcriptase polymerase chain reaction [RT-PCR] analysis). Using the organ bath technique, the effects of VIP, CNP, and BK (0.1 nM to 1 µM) on the tension induced by 0.1 µM ET-1 of human vaginal strips were investigated. The tissue was also exposed to three different concentrations of VIP, CNP, and BK (0.01 µM, 0.1 µM, 1 µM) and the production of cAMP and cGMP determined by means of radioimmunoassays.

MAIN OUTCOME MEASURES

Characterize the expression of peptide receptors in the human vagina and measure the relaxation exerted by BK, CNP, and VIP on the contraction induced by ET-1 of isolated human vaginal tissue. In addition, the effects of the peptides on the production of cAMP and cGMP were also elucidated.

RESULTS

RT-PCR analysis revealed the expression of mRNA transcripts encoding for the VIP receptors VIP1R/vasoactive intestinal polypeptide receptor type 1 (VPAC1) and VIP2R/VPAC2, CNP receptors natriuretic peptide receptor type A (NPRA), natriuretic peptide receptor type B (NPRB) and natriuretic peptide receptor type C (NPRC), and BK receptor B2R. The tension induced by ET-1 was reversed by the peptides with the following rank order of efficacy: BK (21.7%) > VIP (20.9%) > CNP (13.3%). The relaxing effects of VIP and BK were paralleled by a 4.8-fold and fivefold increase in cAMP, while the production of cGMP was stimulated 38-fold and 119-fold in the presence of CNP or BK, respectively.

CONCLUSION

Our results are in support of the hypothesis that endogenous peptides may contribute to the control of human vaginal smooth muscle tone through the involvement of the cyclic nucleotide-dependent pathways.

Neuropeptide receptor transcripts are expressed in the rat clitoris and oscillate during the estrus cycle in the rat vagina

Vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and angiotensin 2 are key neuropeptides that innervate the sexual organs. For further understanding of neuropeptide involvement in female sexual function, we investigated peptide receptor mRNA expression using reverse transcription-polymerase chain reaction (RT-PCR) in the rat vagina and clitoris, and alteration during the shift from the proestrus to the estrus phase. VIP, angiotensin 2 and CGRP receptor subtypes transcripts were found to be expressed in the vagina and the clitoris. Significantly increased levels of angiotensin 2 and CGRP receptor subtypes transcripts were observed in the vagina as compared to the clitoris. Significant increases in the expression of the VIP receptor type 2 (VPAC2) mRNA and parallel increases in a novel VIP responsive gene, activity-dependent neuroprotective protein (ADNP) mRNA were detected in the rat vagina during the estrus phase. The expression pattern of neuropeptide receptors in the female sexual organs suggest an intimate involvement of the corresponding neuropeptides in female sexual function.

The distribution and co-localization of immunoreactivity to nitric oxide synthase, vasoactive intestinal polypeptide and substance P within nerve fibres supplying bovine and porcine female genital organs

The distribution of nitric oxide synthase-immunoreactive (NOS-IR) axons and their relationship to structures immunoreactive to vasoactive intestinal polypeptide (VIP), substance P (SP) and tyrosine hydroxylase (TH) were studied by means of the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) technique or double-labelling immunofluorescence in the genital organs of cow and pig. Relevant neurons were also investigated in the pig. NOS-containing neural structures were TH-immunonegative in bovine or porcine genital organs, or in the studied ganglia. In the bovine ovary, NOS-IR nerves were neither VIP-IR nor SP-IR, whereas in the pig, most NOS-containing axons were also VIP-IR. The oviduct was supplied by single NOS/VIP- or NOS/SP-containing nerves, whereas in the uterus, NOS-IR axons were moderate in number, often being immunoreactive for VIP or SP. Numerous NOS/VIP-IR and NOS/SP-IR nerves were found in the vagina of both species. In all tissues studied, NOS-IR axons were mainly related to vascular smooth muscle. Most of the neurons of the paracervical ganglia and some neurons in dorsal root ganglia exhibited strong NOS activity. Only single neurons in sympathetic ganglia were NADPH-d-positive. Most nitrergic neurons in the autonomic ganglia were VIP-IR but SP-immunonegative. The sensory neurons were mostly NOS/SP-IR, whereas only single neurons co-expressed NOS and VIP immunoreactivity.

Vasoactive intestinal polypeptide and other preprovasoactive intestinal polypeptide-derived peptides in the female and male genital tract: localization, biosynthesis, and functional and clinical significance

Vasoactive intestinal polypeptide, a neuropeptide with wide distribution in the central and peripheral nervous system, has a broad spectrum of biologic actions. The demonstration of vasoactive intestinal polypeptide containing nerve fibers within the female and male genital tract 17 years ago indicated a putative role for this peptide in the local nervous control of reproductive functions. The genes encoding the preprovasoactive intestinal polypeptide precursor molecule and the vasoactive intestinal polypeptide receptor have been identified. The gene expression has been studied by the use of specific antibodies against the functional domains of the vasoactive intestinal polypeptide precursor and the biologic action elucidated by both in vivo and in vitro methods. Evidence has been provided to support vasoactive intestinal polypeptide as a neurotransmitter in several physiologic events in the genital tracts (i.e., blood flow and nonvascular smooth muscle relaxation). In the ovary vasoactive intestinal polypeptide seems to play an important role as regulator and/or modulator of folliculogenesis and steroidogenesis. In the male genital tract vasoactive intestinal polypeptide seems to participate in the control of erection. Vasoactive intestinal polypeptide has been suggested as a causative factor in some diseases of the genital organs (e.g., it may play a pathophysiologic role in male impotence and the peptide is currently used in the treatment of this condition). Vasoactive intestinal polypeptide may be important for control of the low resistance in the fetomaternal vascular bed and is therefore a putative factor involved in the development of preeclampsia. The therapeutic potential of vasoactive intestinal polypeptide and future agonists and antagonists will be revealed by ongoing and forthcoming studies.

Vasoactive intestinal peptide in the hamster seminal vesicle: distribution, binding sites and possible functions

The presence and functional role of vasoactive intestinal peptide in the hamster seminal vesicle were studied by a combination of structural and functional approaches. The use of an immunofluorescence staining technique in both cryostat sections and whole-mount preparations revealed that vasoactive intestinal peptide-immunoreactive nerve fibres were mainly localized in the lamina propria of the mucosal layer. In double-stained preparations, vasoactive intestinal peptide immunoreactivity was found to be localized in nerves also containing acetylcholinesterase activity. At the ultrastructural level, the use of an immunogold staining method showed that vasoactive intestinal peptide immunoreactivity occurred in large granular vesicles (80-150 nm in diameter) in nerve varicosities which also contained small pleomorphic agranular vesicles. In order to evaluate the anatomical distribution of vasoactive intestinal peptide binding sites in the seminal vesicle, we have utilized an in vitro receptor autoradiographic technique. Vasoactive intestinal peptide binding sites were localized in the basal region of the secretory epithelium, in the muscle layer and in the wall of blood vessels. In vitro incorporation of [3H]L-leucine into protein by tissue slices revealed that vasoactive intestinal peptide (1 microM) significantly increases the amount of released protein. Vasoactive intestinal peptide (0.1-1 microM) did not affect the resting tension of the muscle but significantly inhibited the increase in muscle tension induced by carbachol. Atropine prevented the effect of carbachol, indicating that the latter is mediated by muscarinic receptors. Our results suggest that in the hamster seminal vesicle, vasoactive intestinal peptide is involved in the modulation of muscarinic function and in the control of secretion.

Postnatal development and distribution of peptide-containing nerves in the genital system of the male rat. An immunohistochemical study

The distribution and relative density of peptide-containing nerves was studied in the rat in order to assess the progression of neuronal changes during the postnatal development of the male genital system from the prepubertal age to adulthood. Testis, caput and cauda epididymis, ductus deferens, seminal vesicles, prostate and penis from 8-, 20-, 38-, and 70-day-old rats were sectioned and were immunostained with antisera to the neuropeptides calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), and to a general neuronal marker, protein gene product 9.5 (PGP 9.5). The testicular parenchyma and caput epididymis did not show any immunoreactivity. Very scattered CGRP-containing nerves were present in 8-day-old rats; numerous VIP-, CGRP-, and NPY-peptide-containing nerves were observed in the cauda epididymis, ductus deferens, accessory glands and penis of 20-day-old rats. The number of nerves increased in 35-day-old rats while no changes were observed in more adult rats. A parallel increase was seen for the immunostain for PGP 9.5. These data suggest that peptide-containing nerves appear in the genital system after birth and reach a full development before the completion of puberty. Peptide-containing nerves were visible first in the interstitial area and then spread in the muscular coat of the ducts, glands and of the blood vessels. While CGRP- and NPY-containing nerves were distributed in the vicinity of the muscle cells, VIP-containing nerves were also observed in the subepithelial regions, suggesting a possible role of this neuropeptide in the control of epithelial functions.

Gut endocrine and neural peptides

The once exponential growth in the number of new gut endocrine peptides being discovered has become slightly slower in recent years, and expansion of the field of gut hormones has involved mainly the application of new investigative methods. Some new peptides have been described and major inroads have been made into establishing the ontogeny of gut endocrine cells, the origins and pathways of the enteric innervation, and the involvement of the diffuse neuroendocrine system as a whole in disease states. Further insight is being gained into the functional activity of the peptide cell system by studying the control, sites and rates of peptide gene expression, and the localization and characterization of peptide binding sites on target cells.

Regulatory peptides in the mammalian urogenital system

By immunocytochemistry a number of the gut/brain peptides have been demonstrated in nerve fibers of the mammalian urogenital tract. These peptides are localized to large vesicles in nerve terminals of afferent fibers or efferent nerves innervating blood vessels, non-vascular smooth muscle, lining epithelium and glands. There is evidence that some neuropeptides (VIP, NPY) participate in the local non-cholinergic, non-adrenergic nervous control of smooth muscle activity and blood flow, while other peptides (substance P, CGRP) seem to be sensory transmitters. It is likely that impaired function of the peptidergic nerves is involved in sexual dysfunction such as male impotence.