Relaxation of human female genital sphincters by the neuropeptide vasoactive intestinal polypeptide

Loss of nerve fibers in the oviduct isthmus in women with hydrosalpinx

Apart from the abnormalities of tubal anatomy, the main concern linked to infertility is impaired tubal motility associated with hydrosalpinx, which is thought to be controlled by hormones and nerves. The objective of this study was to determine the distribution of nerve fibers in the oviduct isthmus in women with and without hydrosalpinx. Histological sections of the oviduct isthmus tissue were obtained from 18 women undergoing salpingectomy for hydrosalpinx, and from 15 women undergoing hysterectomy and salpingectomy for benign gynecologic diseases. The tissues were immunohistochemically stained for protein gene product (PGP) 9.5, protein S100, neuropeptide tyrosine (NPY), and vasoactive intestinal peptide (VIP) to reveal all nerve fibers, as well as sympathetic and parasympathetic nerve fibers, in the oviduct isthmus. We detected the presence of PGP9.5, S100, VIP, and NPY-immunoreactive nerve fibers in the oviduct isthmus in all study subjects. However, the densities of PGP9.5, S100, VIP, and NPY-immunoreactive nerve fibers in the oviduct isthmus were all significantly decreased in women with hydrosalpinx compared with those in women without hydrosalpinx (P<0.01). Our results suggest that reduced nerve fibers in the oviduct isthmus in women with hydrosalpinx compared with women without hydrosalpinx may have an important function in the mechanism of hydrosalpinx-associated infertility.

Pregnancy induces degenerative and regenerative changes in the autonomic innervation of the female reproductive tract

The uterus is supplied with an extensive system of adrenergic nerves. The neurobiological properties of this innervation have been investigated in a series of studies primarily using the guinea-pig as model. The guinea-pig uterus is supplied from three different sources: the paracervical plexus, containing short adrenergic neurons; the inferior mesenteric ganglion; and a cranial source, probably the aorticorenal plexus, via nerves in the uterine suspensory ligaments. The nerve density is higher in the tubal end of the uterine horn and in the cervix than in the main part of the uterine horn. The turnover rate of transmitter is lower in the uterus than in a control organ, such as the heart. Noradrenaline levels in the uterus, but not the heart, are influenced by alterations in the endocrine milieu, e.g. during the oestrous cycle and after treatment with sex steroids. In the uterine tissue surrounding the conceptus during pregnancy, there is an early and drastic decay in various functional parameters related to the adrenergic nerve plexus and primarily reflecting a local, pregnancy-induced axonal degeneration. In the main part of the empty horn, in unilateral pregnancy, there is an extensive decay in various adrenergic functional parameters; these, however, reflect changes in a nerve plexus that has an essentially intact structure. No sign of functional impairment is seen in the adrenergic nerves of the uterine cervix. The increased turnover rate and reduced transmitter content in this region during late pregnancy may reflect increased frequency of firing of the adrenergic nerves. The tubal end of the uterine horn shows no signs of altered sympathetic function. This is the only part of the uterine horn that appears unaffected by pregnancy. The deficient recovery post partum of the changes in the uterine horn that previously contained the fetuses suggests permanent damage to the adrenergic nerve plexus after a pregnancy. The post partum recovery of changes seen in the previously empty horn, however, is more pronounced but still incomplete by comparison with the innervation before pregnancy. Studies on the adult human uterus indicate that similar events to those described for the guinea-pig model occur in human pregnancy.

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.

The bovine tubouterine junction: general innervation pattern and distribution of adrenergic, cholinergic, and peptidergic nerve fibers

The innervation of the bovine tubouterine junction was studied in sexually mature heifers using antisera against various neuronal markers and a modified acetylcholinesterase method. The vast majority of the nerve fibres in the bovine tubouterine junction belongs to the sympathetic nervous system; peptidergic and cholinergic fibers are restricted to characteristic locations. The endosalpinx in the adovarian portion of the terminal tubal segment is poorly innervated. The mucosa of the aduterine portion and of the tubouterine transitional region proper receives a strikingly dense innervation, which is observed mainly in combination with a strong vascularisation of specialised mucosal structures. In the endometrium, perivascular nerves accompany the ascending spiral arteries but sporadic contacts between nerve fibres and uterine glands are also observed. From the muscular coat the inner longitudinal layer of the terminal tubal segment is more richly supplied by nerve fibres than the intermediate circular and outer longitudinal layers of the tubouterine junction. No changes in the innervation pattern were seen during the different stages of the sexual cycle.

Existence and coexistence of peptides in nerves of the mammalian ovary and oviduct demonstrated by immunocytochemistry

The immunocytochemical distribution of substance P (SP), gastrin releasing peptide (GRP), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), and neuropeptide Y (NPY) was studied in the ovary and the Fallopian tube (oviduct) of rats, guinea-pigs, cows, pigs and humans. Generally, the nerve supply was better developed in the oviduct than in the ovary. GRP fibers were most scarce in all tissues. Nerves containing SP were particularly numerous in the oviduct of rat and guinea-pig, supplying the muscular wall and blood vessels. VIP and PHI coexisted in dense plexuses of nerves, not only around blood vessels but also in the follicular wall and the interstitial gland of the ovary, as well as within the smooth muscle layers and subepithelially in the oviduct. The general distribution of NPY was similar, but these immunoreactive nerves were even more numerous. Sequential staining for dopamine-beta-hydroxylase and NPY together with results of chemical sympathectomy with 6-hydroxydopamine suggested that NPY was stored in the noradrenergic sympathetic nerves.

Vasoactive intestinal polypeptide influence on lower urinary tract smooth muscle from human and pig

The influence of vasoactive intestinal polypeptide on detrusor, trigone, bladder neck and urethral smooth muscle from human and pig was investigated in vitro. Vasoactive intestinal polypeptide reduced the tension and amplitude of the spontaneous contractions of strips from all regions studied. Human detrusor and pig trigone, bladder neck and urethral strips were more sensitive to vasoactive intestinal polypeptide than pig detrusor. The response was reversible, reproducible and dose-dependent from 10(-9) to 10(-6) mol. per liter. The time to onset of the response was within 1/2 minute and the time to maximal relaxation was 2 to 10 minutes. The response was not affected by selective nerve poisoning with tetrodotoxin, beta-adrenergic blockade with propanolol or prostaglandin synthesis blockade with ketoprofen. Vasoactive intestinal polypeptide did not prevent prostaglandin E2 activity on the musculature. Contractions evoked by transmural electric field stimulation or pharmacologically with carbachol, noradrenaline, substance P and prostaglandin F2 alpha were equally reduced by VIP 10(-7) mol. per liter.

Vasoactive intestinal polypeptide (VIP) inhibits neurally evoked smooth muscle activity of rat uterine cervix in vitro

VIP inhibits the spontaneous motor activity (including tone) in isolated preparations of uterine cervix from oophorectomized rats, but has no direct effect on preparations from estrogen-treated animals. Electrical field stimulation of nerves in the tissue evokes a contractile response that is inhibited by VIP in a concentration-dependent manner. The neuronal link probably involves a cholinergic mechanism, since the contraction is blocked by atropine. The results suggest the presence of VIP receptors both in cholinergic nerves and in smooth muscle cells of the rat uterine cervix.

Electron microscopic and pharmacologic evidence for a functional adrenergic innervation of the smooth musculature in the human fallopian tube

Triple fixation for electron microscopy of the isthmic region of the human Fallopian tube distinguished adrenergic nerve terminals through their content of synaptic vesicles with a diameter of 50-60 nm. Non-vascular adrenergic nerves were found both outside and within smooth muscle bundles. Adrenergic varicosities, partly devoid of their Schwann cell ensheathing, frequently approached the smooth muscle cells within a distance of about 200 nm, and sometimes as close as 60-100 nm. These close contacts often occupied a considerable area of the naked varicosity. Electrical field stimulation of adrenergic nerves in the isthmic smooth muscle preparations in vitro induced an alpha-receptor mediated, frequency-dependent contractile response. The results show that the sympathetic nerves in the human Fallopian tube are able to exert a motor control of its smooth musculature, and may thus be involved in local functions essential for the normal fertilization process.

Vasoactive intestinal polypeptide and the female genital tract: relationship to reproductive phase and delivery

Recently, vasoactive intestinal polypeptide (VIP) has been localized in nerve fibers in the human female genital tract. In the present investigation, the effect and concentration of VIP was studied in uterine tissue from pregnant and nonpregnant women, and the plasma concentration of VIP was measured in relationship to diurnal rhythm, intake of food, menstrual cycle, pregnancy, labor, age, and sexual arousal. In vitro VIP inhibited the contractions of the nonpregnant but not of the pregnant uterus. The median concentration of VIP in myometrium from pregnant women (less than 0.1 pmole/gm) was significantly lower than that in myometrium from nonpregnant women (1.6 pmoles/gm). The venous plasma concentrations of VIP during labor (10.5 to 13.0 pmoles/L) were significantly higher than those during pregnancy (2.0 to 5.0 pmoles/L) and the menstrual cycle of VIP increased significantly during sexual arousal, from 4.0 to 8.5 pmoles/L. The median arterial and venous concentrations in the umbilical cord (12.5 and 14.5 pmoles/L, respectively) were significantly higher than the concentration in maternal peripheral venous blood (5.2 pmoles/L). The plasma concentrations of VIP were not related to intake of food, diurnal rhythm, menstrual cycle, or age. The conclusion is that the function of VIP may be related to pregnancy, delivery, and sexual stimulation.

Effect of vasoactive intestinal polypeptide (VIP) on the in vitro and in vivo motility of the rabbit reproductive tract

Isolated segments of rabbit ampulla and isthmus and strips of uterus and cervix were spontaneously mechanically active in vitro, and this activity was inhibited in a dose-dependent manner by 2 to 200 ng/ml vasoactive intestinal polypeptide (VIP). The oviductal segments were the most inhibited, the uterine strips the least inhibited. These tissues were stimulated to contract in a dose-dependent manner by epinephrine (EPI), with the uterus and cervix being the more responsive. VIP (200 ng/ml) produced only a slight noncompetitive antagonism of this stimulation. Recordings made with miniature force transducers showed the isthmus, uterus, and cervix also to be spontaneously active in vivo. This activity was inhibited by injections (1, 10, and 20 micrograms) and infusions (1.0 and 2.5 micrograms/min) of VIP. The isthmus was the most inhibited, the cervix the least inhibited. Possible physiologic implications of these pharmacologic effects are discussed.

Neurogenic relaxation mediated by vasoactive intestinal polypeptide (VIP) in the isthmus of the human fallopian tube

The smooth musculature of the Fallopian tube is important for normal ovum transport, fertilization and implantation. Little is known about the factors controlling the motor activity of the isthmic sphincter. Studies were performed on smooth muscle preparations from the human tube in vitro. Electrical field stimulation of the nerves in the isthmic region reduced the motor activity, particularly in the circular muscle. The response was unaffected by adrenergic and cholinergic antagonists, but blocked by tetrodotoxin, suggesting a neural involvement. Vasoactive intestinal polypeptide (VIP) was considered a likely candidate for the neural mediation of this response in view of the high density of VIP-containing nerve fibres in this region, and in view of the fact that exogenous VIP causes a marked reduction of the tubal motor activity. To test whether VIP might be the endogenous mediator of this effect, nerve stimulation was carried out in the presence of large amounts of exogenous VIP in order to occupy all VIP receptors; the motor inhibitory action of VIP was counteracted by vasopressin. Under these conditions, nerve stimulation failed to reduce isthmic motor activity. This was not due to vasopressin since reduction occurred in the presence of this peptide alone. The results suggest that VIP is responsible for the neurogenic inhibition of motor activity in the isthmus region of the human Fallopian tube.

Vasoactive intestinal polypeptide (VIP): effect on rabbit uterine smooth muscle in vivo and in vitro

The effect of vasoactive intestinal polypeptide (VIP) on uterine smooth muscle electrical and mechanical activity in non-pregnant estradiol-treated rabbits was investigated using in vivo and in vitro methods. The studies were performed on spontaneous, oxytocin-, carbachol-, and prostaglandin-42 alpha-induced activity. VIP had a dose-related inhibitory effect on both myoelectrical and mechanical activity. The concentration needed for 50% inhibition (ID50) was 2 x 10(-10) mol VIP . 1(-1) (in vivo), an 6 x 10(-8) mol VIP . 1(-1) (in vitro). This inhibition was unaffected by the presence of atropine (10(-5) mol . 1(-1)), propranolol (10(-5)), phentolamine (10(-5)), naloxone (10(-5)), apamin (10(-5)), and tetrodotoxin (10(-5)). These findings indicate that VIP may act via a specific receptor on the smooth muscle and supports the hypothesis that VIP may be a neurotransmitter involved in the local nervous control of uterine smooth muscle activity.