Dual vasoconstrictor and vasodilator innervation of the uterine arterial supply in the guinea pig

Uterine Inflammation Changes the Expression of Cholinergic Neurotransmitters and Decreases the Population of AChE-Positive, Uterus-Innervating Neurons in the Paracervical Ganglion of Sexually Mature Gilts

Simple Summary

Endometritis, both with non-infectious and infectious backgrounds, is one of the most prevalent pathological states among domestic animals. In animals, it generates severe economic problems, including lowered reproductive indices and rising medical treatment costs, and in women, it might lead to severe fertility impairment. In order to determine how the autonomic nervous system responds to such a pathological state, an experimental group of pigs were treated with Escherichia coli injection into the uterine horns, and several ganglions responsible for innervation of this organ were examined, including the paracervical ganglion located on both sides of the broad ligament of the uterus. The results clearly showed a strong impact of the inflammation on the chemical coding of neurons, some even synthesizing neurotransmitters de novo such as the GAL-expressing perikarya. Additionally, applied injections decreased the number of parasympathetic, acetylcholinesterase-expressing neurons implying the importance of the cholinergic population to keep the inflammation under control. The obtained data serve as a basis for the future implementation of modern treatment and enhancements in animal breeding.

Abstract

The focus of this study was based on examining the impact of endometritis on the chemical coding of the paracervical ganglion (PCG) perikaryal populations supplying pig uterus. Four weeks after the injection of Fast Blue retrograde tracer into uterine horns, either the Escherichia coli (E. coli) suspension or saline solution was applied to both horns. Laparotomy treatment was performed for the control group. Uterine cervices containing PCG were extracted on the eighth day after previous treatments. Subsequent macroscopic and histopathologic examinations acknowledged the severe form of acute endometritis in the E. coli-treated gilts, whereas double-labeling immunofluorescence procedures allowed changes to be analyzed in the PCG perikaryal populations coded with vesicular acetylcholine transporter (VAChT) and/or somatostatin (SOM), vasoactive intestinal polypeptide (VIP), a neuronal isoform of nitric oxide synthase (nNOS), galanin (GAL). The acetylcholinesterase (AChE) detection method was used to check for the presence and changes in the expression of this enzyme and further confirm the presence of cholinergic perikarya in PCG. Treatment with E. coli resulted in an increase in VAChT+/VIP+, VAChT+/VIP−, VAChT+/SOM+, VAChT+/SOM−, VAChT+/GAL− and VAChT+/nNOS− PCG uterine perikarya. An additional increase was noted in the non-cholinergic VIP-, SOM- and nNOS-immunopositive populations, as well as a decrease in the number of cholinergic nNOS-positive perikarya. Moreover, the population of cholinergic GAL-expressing perikarya that appeared in the E. coli-injected gilts and E. coli injections lowered the number of AChE-positive perikarya. The neurochemical characteristics of the cholinergic uterine perikarya of the PCG were altered and influenced by the pathological state (inflammation of the uterus). These results may indicate the additional influence of such a state on the functioning of this organ.

Effect of partial hysterectomy on the neurons of the paracervical ganglion (PCG) of the pig

Autonomic neurons innervating uterine horn is probably the only nerve cell population capable of periodical physiological degeneration and regeneration. One of the main sources of innervation of the uterus is paracervical ganglion (PCG). PCG is a unique structure of the autonomic nervous system. It contains components of both the sympathetic and parasympathetic nervous system. The present study examines the response of neurons of PCG innervating uterine horn to axotomy caused by partial hysterectomy in the domestic pig animal model. The study was performed using a neuronal retrograde tracing and double immunofluorescent staining for tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DβH), choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), neuronal nictric oxide synthase (nNOS), galanin, neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), somatostatin and substance P (SP). Our study showed that virtually all neurons of the porcine PCG innervating uterine horn are adrenergic and we did not confirm that PCG is the source of cholinergic fibers innervating uterine horn of the pig. After axotomy there was a decrease in expression of catecholamine-synthesizing enzymes (TH, DβH) and a strong increase in the galanin expression. The increase of the number of NPY-IR neurons in the ganglia after axotomy was observed. There were no changes in the expression of other studied substances in the PCG neurons innervating the uterine horn, what was often found in rodents studies. This indicates that neurons can respond to damage in a species-specific way.

Cotransmission in the autonomic nervous system

After some early hints, cotransmission was proposed in 1976 and then "chemical coding" later established for sympathetic nerves (noradrenaline/norepinephrine, adenosine 5'-triphosphate (ATP), and neuropeptide Y), parasympathetic nerves (acetylcholine, ATP, and vasoactive intestinal polypeptide (VIP)), enteric nonadrenergic, noncholinergic inhibitory nerves (ATP, nitric oxide, and VIP), and sensory-motor nerves (calcitonin gene-related peptide, substance P, and ATP). ATP is a primitive signaling molecule that has been retained as a cotransmitter in most, if not all, nerve types in both the peripheral and central nervous systems. Neuropeptides coreleased with small molecule neurotransmitters in autonomic nerves do not usually act as cotransmitters but rather as prejunctional neuromodulators or trophic factors. Autonomic cotransmission offers subtle, local variation in physiological control mechanisms, rather than the dominance of inflexible central control mechanisms envisaged earlier. The variety of information imparted by a single neuron then greatly increases the sophistication and complexity of local control mechanisms. Cotransmitter composition shows considerable plasticity in development and aging, in pathophysiological conditions and following trauma or surgery. For example, ATP appears to become a more prominent cotransmitter in inflammatory and stress conditions.

Comparative study of the neuropeptide-Y sympathetic nerves in endometriotic involved and noninvolved sacrouterine ligaments in women with pelvic endometriosis

STUDY OBJECTIVE

To show the relationship between the neuropeptide-Y pelvic sympathetic nerves and neoangiogenesis in the development of endometriosis

DESIGN

Prospective study.

SETTING

Academic community teaching hospital.

PATIENTS

Fifteen consecutive women with unilateral endometriotic infiltration of the sacrouterine ligaments.

INTERVENTIONS

A laparoscopic excision/biopsy of involved and noninvolved parts of the sacrouterine ligaments were taken. The sections were incubated with the neuronal marker rabbit polyclonal anti-protein gene product 9.5 and rabbit polyclonal anti-neuropeptide-Y. We made a comparative study on the distribution of nerve fibers and their relationship to the vessels on intact and endometriotic involved tissue.

MEASUREMENTS AND MAIN RESULTS

The results show that a large amount of nerves are present around the blood vessels in the endometriosis samples, and a large number of these nerves are neuropeptide-Y sympathetic nerves. Adrenergic fibers are also present in the intact control subjects, however, in significantly smaller amounts.

CONCLUSION

This finding shows a strong relationship between the neuropeptide-Y sympathetic pelvic nerves and the neoangiogenesis required for the development of endometriosis.

Vaso-active factors in pregnancy

Pregnancy results in profound physiological changes in the cardiovascular system, yet these changes are completely reversible. It is apparent that vaso-active factors, some as yet probably unidentified, which act as humoral or local autocrine or paracrine regulators of vasular resistance, play a major role in these cardio-vascular changes. This role may be heightened in pregnancy when there has to be a large increase in blood flow to the uterus and placenta while maintaining adequate flow to other vascular beds. Our knowledge of the mechanisms of action of these vaso-active factors and their interactions with each other still remains incomplete. Alterations in synthesis and action of these vaso-active factors may occur in pregnancies associated with pregnancy-induced hypertension, pre-eclampsia or intra-uterine growth retardation. Investigation of such alterations may help to elucidate the roles of vaso-active factors in both normal and pathological situations. The gestational hormones oestrogen and progesterone, are obviously prime candidates as overall regulators of the cardiovascular changes of pregnancy and as agents which alter the synthesis or action of other vaso-active factors. Currently, much attention is being focused on the role of local autocrine or paracrine vaso-active factors which may be produced by the endothelium or by the underlying vascular smooth muscle cells and alterations in their production or action in the hyptertensive disorders of pregnancy. The endothelium forms the largest endocrine organ within the body and so its importance in the mediation of vascular events should not be under-estimated. The principal objective of this review is to examine the roles of these many autocrine and paracrine vaso-active factors during pregnancy and their relation with the overall regulation of the vascular system. Changes which may occur and be involved in the aetiology of pre-eclampsia and growth retardation will also be examined.

Developmental influences on vascular structure and function

Blood vessels with apparently similar structures show remarkable functional heterogeneity. Differences exist in the nature and extent of their innervation, synaptic architecture, receptor characteristics, excitation coupling systems, capacity for intrinsic tone, contractility, elasticity and calcium-pool dependence, to mention only a few variables. The underlying basis of these differences is unknown. Similarity between the distribution of particular features in the vascular bed and the early patterns of embryological development suggest that some specific functional characteristics are determined during the process of gastrulation, if not before. Examples are given of receptor characteristics and tissue sensitivity that seem to reflect the different mesenchymal origins of particular vessels. Studies on vessels from immature fetal lambs confirm that individuality of specific vessels is established early. Interruption of sympathetic nerve traffic influences the function of vascular smooth muscle cells in a complex manner which is expressed differently at different ages. If the findings of experiments on the ear artery of the rabbit reveal a general principle seen in the circulation, then the level of sympathetic nerve traffic during growth would be expected to influence both qualitatively and quantitatively the structure and reactivity of the adult circulation. By this effect the sympathetic nervous system exerts a long-term influence on blood pressure. The characteristics of a particular blood vessel in the adult depend on many factors such as the level of blood pressure and the amplitude of the pulse wave which are not discussed in this chapter. These studies show that the character of the mature vessels also reflects influences that occur during early development and growth.

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.

Endothelium-dependent Relaxation of Canine Uterine Artery in Response to Acetylcholine: the Possible Involvement of Alternative Pathways

The effect of acetylcholine on the isolated, pre-contracted, uterine artery of non-pregnant dog was investigated. Acetylcholine-induced concentration-dependent relaxation of isolated canine uterine artery with endothelium (pEC50 = 6.48 +/-0.01, n = 37) and was without effect on arterial segments denuded of endothelium. Indomethacin, 4-aminopyridine (10-5 m) and pre-contraction with K+-rich Krebs-Ringer bicarbonate solution had no effect on acetylcholine-induced relaxation. NG-nitro-l-arginine (l-NOARG) (10-5 m) inhibited relaxation evoked by acetylcholine. Indomethacin applied with l-NOARG led to further inhibition of acetylcholine-induced relaxation. In the presence of both l-NOARG and indomethacin, 4-aminopiridine did not provoke further inhibition of acetylcholine-induced relaxation of canine uterine artery. It is concluded that the acetylcholine-induced relaxation of canine uterine artery is probably mediated by endothelial production of nitric oxide (NO). However, if NO-synthase is inhibited, acetylcholine-induced vasorelaxation may be, in part, mediated through activation of cyclooxygenase pathway.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Possible mechanisms underlying pregnancy-induced changes in uterine artery endothelial function

The last 10 years has seen a dramatic increase in our understanding of the mechanisms underlying the pregnancy-specific adaptation in cardiovascular function in general and the dramatic changes that occur in uterine artery endothelium in particular to support the growing fetus. The importance of these changes is clear from a number of studies linking restriction of uterine blood flow (UBF) and/or endothelial dysfunction and clinical conditions such as intrauterine growth retardation (IUGR) and/or preeclampsia in both humans and animal models; these topics are covered only briefly here. The recent developments that prompts this review are twofold. The first is advances in an understanding of the cell signaling processes that regulate endothelial nitric oxide synthase (eNOS) in particular (Govers R and Rabelink TJ. Am J Physiol Renal Physiol 280: F193-F206, 2001). The second is the emerging picture that uterine artery (UA) endothelial cell production of nitric oxide (NO) as well as prostacyclin (PGI2) may be as much a consequence of cellular reprogramming at the level of cell signaling as due to tonic stimuli inducing changes in the level of expression of eNOS or the enzymes of the PGI2 biosynthetic pathway (cPLA2, COX-1, PGIS). In reviewing just how we came to this conclusion and outlining the implications of such a finding, we draw mostly on data from ovine or human studies, with reference to other species only where directly relevant.

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

In oculo transplants of myometrium from postpartum guinea pigs fail to support sympathetic reinnervation

Sympathetic nerves to the enlarged fetus-containing region of the uterus undergo degenerative changes during late pregnancy and show slow regrowth after parturition. It is not known whether this unusual response of sympathetic nerves to smooth muscle hypertrophy is due to the sensitivity of short adrenergic neurons to hormonal changes, or whether the nerves respond to changes in the neurotrophic capacity of the target. We have investigated this question using in oculo transplantation. Small pieces of myometrium from the uterine horn of virgin guinea pigs, or from the region previously occupied by the placenta and fetus in postpartum guinea pigs, were transplanted into the anterior eye chamber. After 3 wk in oculo, the pattern of reinnervation of the transplants was assessed on whole mount stretch preparations stained for tyrosine hydroxylase. The histology of the transplants was examined in toluidine blue-stained semithin sections. Myometrial transplants from virgin donors and uterine artery transplants from both virgin and postpartum donors became organotypically reinnervated by sympathetic fibres from the host iris. In contrast, sympathetic nerves did not reinnervate myometrial transplants from postpartum donors, although they approached the transplants and became distributed in the surrounding connective tissue. All transplanted tissues showed a normal histological appearance. Both the myometrium and uterine artery from postpartum donors retained a hypertrophic appearance after 3 wk in oculo. We interpret these results to indicate that the degeneration of sympathetic nerves in late pregnancy, as well as their slow regrowth to the uterus after delivery, may be due to changes in uterine smooth muscle rather than a particular sensitivity of short adrenergic neurons to hormonal changes.

Neurochemical distinction between skeletal muscle vasodilator neurons and pelvic vasodilator neurons in guinea-pigs

This study sets out to compare the combinations of potential vasodilator transmitters expressed by sympathetic and pelvic vasodilator neurons of guinea-pigs. Triple-labelling fluorescence immunohistochemistry was used to examine immunoreactivity (IR) to vasoactive intestinal peptide (VIP), nitric oxide synthase (NOS) and calcitonin gene-related peptide (CGRP) in lumbar sympathetic ganglia, and in perivascular axons supplying hindlimb skeletal muscles or pelvic viscera. Only 0.2% of VIP-IR nerve cell bodies in lumbar sympathetic ganglia (n = 4632 VIP-IR nerve cell profiles) contained NOS-IR, and one VIP-IR neuron contained CGRP-IR. The VIP-IR perivascular axons along the common and external iliac arteries, femoral artery and arteries to hindlimb muscles lacked NOS-IR and CGRP-IR. In contrast, all VIP-IR perivascular axons projecting from pelvic ganglia to the main uterine artery, and half of the VIP-IR axons along the internal iliac artery, contained NOS-IR and CGRP-IR. Thus, the neurochemical content of sympathetic vasodilator neurons to skeletal muscle arteries was clearly distinguishable from that of pelvic vasodilator neurons to the uterine vasculature. Furthermore, the autonomic dilation in each vascular bed is likely to be qualitatively different, and matched to the functional requirements of each target organ.

Development and maturation of noradrenaline-containing nerves of the rat uterine artery. Effects of acute and chronic oestrogen treatment

The development and maturation of noradrenaline-containing nerves of the rat uterine artery was investigated, histochemically and biochemically, at seven different postnatal age-stages and following acute and chronic treatment with oestradiol. Morphological changes in the vessel were quantitatively evaluated on Toluidine Blue-stained semithin sections and low magnification electronmicrographs. In summary, the uterine artery is innervated at birth; the adult pattern of innervation is established at two weeks of age; the innervation density increases progressively between the infantile and prepubertal periods, accompanying proliferation and growth of smooth muscle cells in the tunica media; changes in the innervation are followed by an increase in the tissue concentration of noradrenaline and neither the endocrine changes characterizing puberty nor acute or chronic treatment with oestradiol have an effect on the pattern of development of the uterine artery and associated noradrenaline-containing nerves. Results are interpreted considering the differential susceptibility of urinogenital organs to sex hormones.

Sympathetic and parasympathetic regulation of the uterine blood flow and contraction in the rat

The effects of electrical stimulation of hypogastric sympathetic and pelvic parasympathetic nerves on uterine blood flow and contraction in anesthetized female non-pregnant normal cycling rats were examined. Electrical stimulation of the efferent pelvic nerve with supramaximal intensity induced marked increase of uterine blood flow accompanied by uterine contraction. On the other hand, the stimulation of efferent hypogastric nerve caused decrease of uterine blood flow accompanied by uterine contraction. These responses could only be elicited with stimulus intensity above the threshold for unmyelinated C fibers in both the hypogastric and pelvic nerves. Intravenous administration of atropine (0.5 mg/kg) totally blocked the response of uterine contraction elicited by pelvic and hypogastric nerve stimulation and also the increase of blood flow induced by pelvic nerve stimulation. Intravenous administration of phenoxybenzamine (0.5 mg/kg) blocked the decreased response of uterine blood flow induced by hypogastric nerve stimulation. It was concluded that uterine blood flow and contraction were regulated by both the parasympathetic and sympathetic nerves, but in different manners; blood flow is regulated reciprocally (1) by parasympathetic vasodilators mainly via activation of muscarinic cholinergic receptors, and (2) by sympathetic vasoconstrictors via activation of alpha-adrenergic receptors; contraction is produced by activation of both parasympathetic and sympathetic nerves via muscarinic cholinergic receptors.

Comparison of endothelium-derived relaxing factor activity between nonpregnant and pregnant rats

The tension of isolated ring preparation of aorta from nonpregnant and pregnant rats was measured isometrically to study the effect of pregnancy on endothelium-derived relaxing factor activity. Contraction in response to norepinephrine and potassium chloride was greater in aortae from nonpregnant rats than in those from pregnant rats. The endothelium-dependent relaxation that was caused by acetylcholine (10(-10)-3 x 10(-9) M) in aortae precontracted with norepinephrine was significantly enhanced in aortae from pregnant rats compared with the relaxation in those from nonpregnant rats. NG-nitro-L-arginine methyl ester (L-NAME) inhibited the endothelium-dependent relaxation in both aorta from pregnant and nonpregnant rats. L-Arginine reversed the inhibition of L-NAME. Those results suggest that the enhanced endothelium-derived relaxing factor activity in rats aortae is associated with pregnancy.

Nitroxidergic nerve stimulation relaxes human uterine vein

The predominant action of nitroglycerin, a nitric oxide (NO) donor, on veins over arterioles is well recognized. This study was carried out to determine whether endogenous NO derived from vasodilator nerve regulates the tone of human uterine venous strips. The isolated vein partially contracted with prostaglandin F2 alpha responded to nicotine with a contraction or a relaxation; the contraction was reversed to a relaxation by prazosin, and the relaxation was potentiated by the alpha 1-adrenoceptor antagonist. In prazosin-treated strips, nicotine-induced relaxations were not affected by timolol, atropine and indomethacin but were abolished by oxyhemoglobin and NG-nitro-L-arginine (L-NA), a NO synthase inhibitor. The D-enantiomer was without effect. The inhibition by L-NA was reversed by L-arginine. The NO-induced relaxation was not influenced by L-NA but was abolished by oxyhemoglobin. It may be concluded that the human uterine vein is innervated by vasodilator nerves from which NO is liberated as a vasodilator neurotransmitter. Norepinephrine from adrenergic nerves contracts venous smooth muscle possibly via stimulation of alpha 1-adrenoceptors.

Peptides as neurotransmitters in vascular autonomic neurons

1. Neuropeptides are present in the majority of autonomic neurons projecting to blood vessels, where they are co-localized with non-peptide transmitters and sometimes with other peptides. 2. Neuropeptides are released from vasoconstrictor and vasodilator nerve terminals after high frequency stimulation ( > 2-5Hz) with trains of impulses. 3. Neuropeptides can have potent post-synaptic effects on vascular tone, but often these effects are restricted to selected regions of the vasculature. 4. Post-synaptic effects of neuropeptides tend to be more slowly-developing and more long-lasting than those of non-peptide transmitters. 5. Autonomic vasoconstrictor and vasodilator responses often have multiple phases, with the faster phases being mediated by non-peptide transmitters and the slower phases medicated predominantly by one or more neuropeptides. 6. Some neuropeptides do not seem to have post-synaptic effects in a particular vascular bed, but can have presynaptic actions on neurotransmitter release. 7. Neuropeptides form an important component of the repertoire of neurotransmitters used by vascular autonomic neurons to regulate regional blood flow in response to a range of physiological stimuli.

K+ channel blockers do not modify relaxation of guinea-pig uterine artery evoked by acetylcholine

The effect of K+ channel blockers on acetylcholine-induced relaxation in guinea-pig uterine arterial rings was investigated. Acetylcholine (0.1 nM-60 microM) induced endothelium-dependent relaxation of phenylephrine-precontracted guinea-pig uterine artery. Methylene blue (30 nM-1 microM) and NG-monomethyl-L-arginine (3-30 microM) antagonized the effect of acetylcholine, with suppression of the maximal acetylcholine-induced relaxation, in a concentration-dependent manner. The inhibition of relaxation by NG-monomethyl-L-arginine (10 microM) was significantly overcome by L-arginine (10 microM), but not by D-arginine (100 microM). In contrast, the administration of K+ channel blockers, tetraethylammonium (6 mM), glibenclamide (5 microM), apamin (1 microM) and 4-aminopyridine (1 mM), did not modify the relaxation of guinea-pig uterine artery induced by acetylcholine. The concomitant addition of K+ channel blockers in the same concentrations also did not alter the inhibition of acetylcholine-induced relaxation produced by NG-monomethyl-L-arginine (30 microM). Finally, the acetylcholine-evoked relaxations were unaltered when K(+)-rich Krebs-Ringer-bicarbonate solution was used to induce tone instead of phenylephrine. Indomethacin (10 microM) and diethylcarbamazine (100 microM) had no effects on acetylcholine-induced relaxation. These findings indicate that K+ channels are probably not involved in the endothelium-dependent guinea-pig uterine arterial relaxation elicited by acetylcholine.

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.

Effect of the vascular endothelium on noradrenaline-induced contractions in non-pregnant and pregnant guinea-pig uterine arteries

1. The effect of pregnancy on noradrenaline-mediated contraction of guinea-pig uterine artery rings with both intact and denuded endothelium was investigated. 2. Noradrenaline (25 nM-100 microM) induced concentration-dependent contraction of non-pregnant and pregnant guinea-pig uterine arterial rings with intact endothelium with similar pD2 and maximal response values (non-pregnant: pD2 = 5.85 +/- 0.02, maximal response = 121 +/- 8.2%; pregnant: pD2 = 5.81 +/- 0.04, maximal response = 122 +/- 9.1%). Removal of endothelium did not affect noradrenaline-induced contractions in non-pregnant guinea-pig uterine artery (pD2 = 5.97 +/- 0.02, maximal response = 119 +/- 8.6%). In contrast, in arteries from pregnant guinea-pigs, removal of endothelium shifted concentration-response curve for noradrenaline to the left, without affecting maximal response value (pD2 = 6.36 +/- 0.03, maximal response = 120 +/- 9.0%). 3. The pKA values for noradrenaline were: 5.76 +/- 0.09 and 5.82 +/- 0.10 for non-pregnant guinea-pig uterine artery with intact and denuded endothelium, respectively and 5.74 +/- 0.09 and 5.72 +/- 0.07 for pregnant guinea-pig uterine artery with intact and denuded endothelium, respectively. 4. The receptor occupancy-response relationship for noradrenaline was linear for all types of vessels, except for pregnant guinea-pig uterine artery with denuded endothelium, since half-maximal response to noradrenaline was obtained with 44.8 +/- 6.9% (non-pregnant guinea-pig uterine artery with intact endothelium), 43.3 +/- 6.1% (non-pregnant guinea-pig uterine artery with denuded endothelium) and 44.3 +/- 6.3% (pregnant guinea-pig uterine artery with intact endothelium) receptor occupancy. In pregnant guinea-pig uterine artery with denuded endothelium, occupancy-response relationship for noradrenaline was non-linear since half-maximal response to noradrenaline was obtained with 19.7 +/- 3.3% receptor occupancy. 5. NG-monomethyl-L-arginine (100 microM) and indomethacin (10 microM) did not affect concentration-response curve for noradrenaline in guinea-pig uterine arteries, regardless of pregnancy status or endothelial condition. 6. In quiescent preparations, the alpha-adrenoceptor antagonists, prazosin (5-50 nM) and yohimbine (1-10 microM) produced parallel rightward shifts of the curves for noradrenaline and the slopes of the Schild plots were not significantly different from unity. The plots constrained to a slope of unity gave the following - log Kb values: prazosin vs. yohimbine 8.78 +/- 0.03 vs. 6.41 +/- 0.02 for non-pregnant guinea pig uterine artery with intact endothelium, 8.95 +/- 0.03 vs. 6.34 +/- 0.02 for non-pregnant guinea-pig uterine artery with denuded endothelium, 8.91 +/- 0.01 vs. 6.44 +/- 0.03 for pregnant guinea-pig uterine artery with intact endothelium and 9.07 +/- 0.01 vs. 6.52 +/- 0.03 for pregnant guinea-pig uterine artery with denuded endothelium.7. It is concluded that initially there is no difference in noradrenaline action between uterine arteries from non-pregnant and pregnant guinea-pigs, but after removal of the endothelium the pregnant guinea-pig uterine artery is more sensitive to noradrenaline, which is related to increased receptor reserve for noradrenaline in this tissue. It is probable that relaxing factor derived from the endothelium mediates this effect, but it is unlikely to be nitric oxide or prostacyclin. Antagonist affinities and affinity of noradrenaline itself suggests that an identical subtype of alpha-adrenoceptor, probably the alpha 1 subtype, is involved in the noradrenaline-induced contraction of non-pregnant and pregnant guinea-pig uterine artery with or without endothelium.

New insights into the local regulation of blood flow by perivascular nerves and endothelium

Blood flow, particularly in the skin, is essential for the success of plastic surgical operations. This review describes recent studies of the perivascular nerves and vascular endothelial cells which regulate blood flow. Perivascular nerves, once considered simply adrenergic or cholinergic, release many types of neurotransmitters, including peptides, purines and nitric oxide. Cotransmission (synthesis, storage and release of more than one transmitter by a single nerve) commonly takes place. Some afferent nerves have an efferent (motor) function and axon reflex control of vascular tone by these "sensory-motor" nerves is more widespread than once thought. Endothelial cells mediate both vasodilatation and vasoconstriction. The endothelial cells can store and release vasoactive substances such as acetylcholine (vasodilator) and endothelin (vasoconstrictor). The origins and functions of such vasoactive substances are discussed. Endothelial vasoactive substances may be of greater significance in the response of blood vessels to local changes while perivascular nerves may be concerned with integration of blood flow in the whole organism. The dual regulation of vascular tone by perivascular nerves and endothelial cells is altered by aging and conditions such as hypertension, as well as by trauma and surgery. Studies of vascular tone in disease and after denervation or mechanical injury suggest possible trophic interactions between perivascular nerves and endothelial cells. Such trophic interactions may be important for growth and development of the two control systems, particularly in the microvasculature where neural-endothelial separation is small.

Muscarinic receptor function in the guinea-pig uterine artery is not altered during pregnancy

The effects of acetylcholine on isolated uterine artery rings of non-pregnant and pregnant guinea-pigs were investigated. Acetylcholine induced a concentration- and endothelium-dependent relaxation of both types of vessels, with similar pD2 (non-pregnant: pD2 = 7.66; pregnant: pD2 = 7.59) and maximal response values. The pKA values (non-pregnant vs. pregnant) of acetylcholine were 6.17 vs. 6.09. The occupancy response relationship was non-linear since the half-maximal response to acetylcholine (non-pregnant vs. pregnant) was obtained with 2.86 vs. 2.91% receptor occupancy. In quiescent preparations, the muscarinic receptor antagonists, atropine, pirenzepine, N,N'-bis[6-[(2-methoxybenzyl)amino]hexyl]-1,8-octane-diamine tetrahydrochloride (methoctramine) and para-fluoro-hexahydro-sila-difenidol (pFHHSiD), produced parallel rightward shifts of the curves for acetylcholine and the slopes of the Schild plots were not significantly different from unity. The plots constrained to a slope of unity gave the following -log KB values (non-pregnant vs. pregnant): atropine (9.68 vs. 9.75), pirenzepine (6.75 vs. 6.53), methoctramine (6.13 vs. 6.23) and pFHHSiD (7.88 vs. 7.96). It is concluded that, in guinea-pig uterine arteries, acetylcholine induces endothelium-dependent relaxation and acts as a full agonist, regardless of pregnancy status. We suggest that the relaxation induced by acetylcholine, in either non-pregnant or pregnant guinea-pig uterine artery, is mediated via the M3 subtype of muscarinic receptors.

Endothelium-dependent relaxation in response to acetylcholine in the human uterine artery

The effect of acetylcholine on isolated human uterine artery rings was investigated. Acetylcholine induced concentration and endothelium-dependent relaxation (pD2 = 7.29 +/- 0.03) of the precontracted arterial segments. The dissociation constant (KA) for acetylcholine was 1.35 (0.92-1.77) mumol/l. The occupancy-response relationship was non-linear. Half-maximal response to acetylcholine was obtained with 5.25% receptor occupancy. Muscarinic receptor antagonists: atropine, pirenzepine, methoctramine, p-fluoro-hexahydro-sila-diphenidol (pFHHSiD) and 4-diphenyl-acetoxy-N-methyl-piperidine (4-DAMP) competitively antagonized the response to acetylcholine. The constrained pA2 values were 9.32 +/- 0.03, 7.13 +/- 0.01, 6.26 +/- 0.01, 8.17 +/- 0.01 and 9.13 +/- 0.02, respectively. A selective muscarinic M2 receptor antagonist, gallamine, had no effect on acetylcholine-induced relaxation. It is concluded that in human uterine arteries acetylcholine induces endothelium-dependent relaxation and acts as a full agonist. We suggest that the muscarinic receptors involved in the acetylcholine-induced relaxation of the isolated human uterine artery are predominantly of the M3 subtype.

Co-transmission from autonomic vasodilator neurons supplying the guinea pig uterine artery

This study set out to identify the neurotransmitters involved in autonomic vasodilatation of the guinea pig uterine artery. Non-noradrenergic, paracervical neurons supplying this artery contain at least four neuropeptides: vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), dynorphin A (1-17) and somatostatin, probably in addition to acetylcholine. Transmural nerve stimulation of arterial segments precontracted with phenylephrine (3 x 10(-7) mol l-1 and treated with guanethidine (10(-6) mol l-1), produced relaxations which varied in form with the frequency of stimulation and the length of the pulse train. The relaxations were monophasic at low frequencies (< 2 Hz), and were biphasic at higher frequencies (> 5 Hz) and with longer pulse trains (> 50 pulses). Neither phase of the relaxations was reduced by hyoscine (10(-6) mol l-1), or by removal of the endothelium. The faster phase of the relaxations was selectively reduced (by 61%) during treatment with L-nitro-arginine methyl ester (L-NAME; up to 3 x 10(-5) mol l-1). This reduction was reversed by an excess of L-arginine, indicating that the fast relaxation was mediated by nitric oxide, possibly acting as a neurotransmitter. The slower phase of the neurogenic relaxation was preferentially reduced (by 43%) by the endopeptidase, trypsin (1-3 micrograms.ml-1). As VIP is the only currently identified peptide present in the paracervical neurons which causes vasodilatation, it is likely that VIP, or a closely-related peptide, is the transmitter responsible for the slow relaxation. Acetylcholine and an opioid peptide also seem to be released from the vasodilator neurons, but their effects were small, and may have been restricted to pre-synaptic sites. The slower neurogenic relaxations were inhibited by exogenous neuropeptide Y (68% reduction in amplitude), and were slightly potentiated by somatostatin (21% increase in amplitude). Therefore, endogenous stores of these peptides may also contribute to the sum effect of stimulating the paracervical vasodilator neurons. In conclusion, many different substances may act as autonomic co-transmitters from these pelvic vasodilator neurons.

Properties of sympathetic neuromuscular transmission and smooth muscle cell membranes in vascular beds

In vascular smooth muscle tissues, the cycle of contraction-relaxation is mainly regulated by the cytosolic Ca, and many other factors, such as substances released from endothelial cells and perivascular nerve terminals (mainly sympathetic nerves). In this article, we introduce regional differences in specific features of ionic channels in vascular smooth muscle membranes (mainly on features of Ca, Na and K channels) in relation to mobilization of the cytosolic Ca. In many vascular tissues, neurotransmitters released from sympathetic nerve terminals activate post-junctional receptors, and subsequently modify ion channels (receptor-activated cation channel and voltage-dependent Ca channel), whereas in some tissues, ionic channels are not modified by receptor activations (pharmaco-mechanical coupling). However, activation of receptors, with or without modulation of ionic channels, regulates the cytosolic Ca through synthesis of second messengers. In addition, receptors distributed on prejunctional nerve terminals positively or negatively regulate the release of transmitters. Roles of neurotransmitters (mainly ATP and noradrenaline) are also discussed in relation to the generation of excitatory junction potentials.

Changes in expression of autonomic nerves in aging and disease

Mechanisms of autonomic neuroeffector transmission are summarised, including evidence for a multiplicity of transmitters, co-transmission, neuromodulation and 'chemical coding' of individual autonomic neurons, where the combination of transmitters they contain is known, as well as their projections and central connections. Changes in expression of autonomic nerves and co-transmitters that occur during development and aging, following trauma, surgery, after chronic exposure to drugs, and in a number of disease situations are described. It is suggested that in neuropathological analysis, compensatory increases in innervation should be considered as well as loss or damage to nerves. Studies of the molecular mechanisms involved in the control of co-transmitter and receptor expression are now needed.

Pregnancy reduces noradrenaline but not neuropeptide levels in the uterine artery of the guinea-pig

Using histochemical, immunohistochemical and biochemical techniques, noradrenaline-, neuropeptide Y-, vasoactive intestinal polypeptide-, substance P- and calcitonin gene-related peptide-containing nerve fibres were studied in the uterine artery of virgin, progesterone-treated and pregnant guinea-pigs. Morphological changes following hormone treatment or in pregnancy were also evaluated in a quantitative study on semithin sections of the uterine artery. In late pregnancy, the number of noradrenaline-containing nerve fibres, which formed the densest plexus in virgin animals, was significantly decreased, a finding supported by a significant reduction in noradrenaline levels. This reduction was not mimicked by systemic progesterone treatment. In contrast, the innervation of the uterine artery by neuropeptide Y-containing nerve fibres was increased in pregnancy, while the other peptidergic nerves and peptide levels were unchanged after progesterone treatment and in pregnancy. These changes led to a predominance of innervation by neuropeptide Y- rather than noradrenaline-containing nerve fibres in late pregnancy. No morphological changes were detected following progesterone treatment, but pregnancy led to a marked increase in the cross-sectional area of the vessel accompanied by an increase in the thickness of the media.

In vitro release of endothelium-derived relaxing factor by acetylcholine is increased during the guinea pig pregnancy

The relaxation of isolated blood vessels by acetylcholine is dependent on the presence of intact endothelium and its release of a smooth muscle relaxing nitroso-like compound. Pregnancy is associated with altered vascular responsiveness to a variety of agents. Because many of these agents stimulate the release of endothelium-derived relaxing factor, we investigated in vitro the effect of pregnancy on acetylcholine-mediated relaxation of guinea pig uterine and carotid artery rings. The presence of intact and functional endothelium was confirmed both by examination under the scanning electron microscope and by vessel relaxation after the addition of acetylcholine. The addition of acetylcholine to the vessel bath produced dose-dependent relaxation of both carotid and uterine artery segments obtained from pregnant and nonpregnant animals after they had been submaximally preconstricted with phenylephrine. There was a significant increase in both response and efficacy to acetylcholine during pregnancy for both uterine and carotid arteries (p less than 0.0001 for each). The concentrations of endothelial cells (cells per square micrometer) were similar in uterine arteries from pregnant and nonpregnant animals. We conclude that the most likely explanation for these findings is a pregnancy-mediated enhancement of endothelium-derived relaxing factor activity.

Adrenergic and cholinergic nerve supply in the porcine myometrium and cervix. A histochemical investigation during pregnancy and parturition

The distribution of adrenergic and acetylcholinesterase-containing (cholinergic) nerves in the porcine myometrium and cervix was investigated neurohistochemically. In early and mid-pregnancy the number of adrenergic nerves increased from the adtubal part of the horns to corpus uteri, being more abundant in non-placental than in placental regions. No obvious difference in the distribution of cholinergic nerves was observed among the regions examined. The cervix was richest innervated by both types of nerves throughout gestation. The diameter of the adrenergic nerves decreased during pregnancy, while cholinergic nerves showed no such a decrease. In late pregnancy and at parturition the adrenergic innervation was richest at the adtubal part of the horns and in the cervix and scanty in the rest of the uterus. Adrenergic nerves were seen both in vascular and in non-vascular smooth muscle, while cholinergic nerves were mostly associated to blood vessels.

Co-existence of neuropeptides and differential inhibition of vasodilator responses by neuropeptide Y in guinea pig uterine arteries

The co-localization of substance P (SP) with calcitonin gene-related peptide (CGRP), and vasoactive intestinal peptide (VIP) with neuropeptide Y (NPY) of the guinea pig uterine artery were investigated with immunocytochemistry. The SP/CGRP fibre population was distinct from the VIP/NPY fibre population. Both types of fibres ran in the medial-adventitial border, and appeared as coarsed and fine varicosed. Uterine arterial dilatation was evoked by acetylcholine (ACh), SP, CGRP, and VIP in precontracted arteries as examined by a sensitive in vitro method. Strong relaxations were seen by ACh, CGRP and VIP. NPY had no relaxant effect per se but was found to be a potent inhibitor of vasodilation induced by ACh and SP, while relaxations induced by VIP and CGRP were unaffected. The functional significance of NPY in the uterine artery may to a large extent be to increase tension not only by potentiation of contraction but additionally by inhibiting vasodilator responses.

Involvement of perivascular neuropeptide Y nerve fibres in uterine arterial vasoconstriction in conjunction with pregnancy

The perivascular neuropeptide Y (NPY) innervation and its relation to adrenergic nerves of uterine arteries from non-pregnant and pregnant guinea pigs was analyzed immunocytochemically. The NPY content of the uterine artery was, in addition, measured radioimmunologically (RIA). Vasomotor effects of NPY per se and in combination with other vasoconstrictors were examined using a sensitive in vitro method. Pregnancy did not visibly affect density and distribution of NPY-immunoreactive fibres. The NPY fibres contained in addition immunoreactivity to dopamine-beta-hydroxylase (marker for noradrenergic neurons). RIA revealed a slight decrease of NPY content during pregnancy, probably due to the increased smooth muscle volume of uterine arteries. The contractile effect of NPY on uterine arteries was weak, while vasoconstriction induced by various agonists was potentiated by NPY, particularly during pregnancy. It is concluded that perivascular NPY-containing nerve fibres may be involved in the dramatic blood flow alterations that occur in the uterine circulation in connection with pregnancy and partus.

VIP and autonomic neurotransmission

A variety of peptides have been proposed as transmitter candidates in non-cholinergic, non-adrenergic nerves. The nerves containing vasoactive intestinal polypeptide (VIP), which innervate blood vessels, non-vascular smooth muscle, mucosal epithelium and glands comprise a major and wide-spread population of the peptide-containing systems. There is now experimental data supporting the view that VIP is a transmitter in non-adrenergic, non-cholinergic nerves in the digestive tract, respiratory tract and urogenital tract, controlling smooth muscle tone and motility, blood flow and secretion. It is possible that impairment of VIP-containing nerves is involved in a number of autonomic dysfunctions.

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.

Evidence that neuropeptide Y released from noradrenergic axons causes prolonged contraction of the guinea-pig uterine artery

The participation of neuropeptide Y (NPY) in transmission from sympathetic vasoconstrictor neurons was investigated in the guinea-pig uterine artery, where NPY has been demonstrated immunohistochemically in noradrenergic axons. Exogenous NPY produced long-lasting contractions of isolated arterial segments at low resting tone. Low concentrations of NPY (10(-8)-3 X 10(-7) mol.l-1) were more potent than equimolar concentrations of noradrenaline (NA). NPY produced concentration-dependent desensitization to further application of NPY, but did not affect the magnitude of NA contractions. Trypsin (1.4-2 micrograms.ml-1) reduced NPY-induced contractions by 80-100%, but did not alter NA-induced contractions. Transmural electrical stimulation of arterial segments, after surgical removal of vasodilator axons, produced biphasic contractions which were abolished by guanethidine. Prazosin abolished the fast phase of the neurogenic contraction, leaving a slow contraction with a time course similar to that produced by a low concentration of NPY. The slow contraction was more pronounced at higher frequencies of stimulation (15-20 Hz) than at lower frequencies, and was selectively reduced after desensitization produced by NPY (10(-5) mol.l-1), or after exposure to trypsin. These results suggest that sympathetic vasoconstriction of the guinea-pig uterine artery is produced by release of both NA and NPY from noradrenergic axons.

Increased dopamine-beta-hydroxylase-like immunoreactivity in non-noradrenergic axons supplying the guinea-pig uterine artery after 6-hydroxydopamine treatment

We have reinvestigated the immunohistochemistry of autonomic axons supplying the guinea-pig uterine artery to determine whether non-noradrenergic paracervical ganglion neurons projecting to the artery contain immunoreactivity to dopamine-beta-hydroxylase (DBH) or somatostatin (SOM) in addition to neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). In untreated arteries no VIP axons had immunoreactivity to tyrosine hydroxylase (TH), although 9% had immunoreactivity to DBH. Somatostatin immunoreactivity was detected in 25% of non-noradrenergic axons containing NPY and VIP. After in vivo treatment with 6-hydroxydopamine (6-OHDA), noradrenergic axons containing immunoreactivity to NPY, DBH and TH were absent from the adventitia-medial junction. However, 65-70% of the non-noradrenergic axons with NPY and VIP showed DBH immunoreactivity after 6-OHDA. These axons did not show catecholamine fluorescence after incubation with pargyline together with noradrenaline, dopamine or L-DOPA. The number of axons with SOM immunoreactivity increased by 44% after 6-OHDA treatment, but only 24% of SOM axons had DBH immunoreactivity. Surgical destruction of the non-noradrenergic autonomic axons in 6-OHDA-treated animals led to the loss of all DBH immunoreactivity. These results demonstrate that DBH immunoreactivity can be detected in a small proportion of non-noradrenergic axons supplying uterine arteries from untreated animals. After chemical sympathectomy with 6-OHDA, the levels of DBH immunoreactivity in axons of non-noradrenergic neurons increased, and more axons with DBH immunoreactivity were detected. DBH immunoreactivity seemed to increase preferentially in axons with NPY and VIP, but not SOM. The number of NPY, VIP axons containing SOM also increased after 6-OHDA. These findings demonstrate that peripheral neurons containing several different potential neurotransmitters can change their levels of neuropeptides and transmitter-synthesizing enzymes in response to local environmental changes.

The hemodynamic response of the conscious pregnant guinea pig to nicotine

The hemodynamic response to continuous intravenous infusion of nicotine, at 4.5 and 18 micrograms/min, was measured using radiolabeled microspheres in nine chronically catheterized pregnant guinea pigs. These gave serum nicotine levels of 72.3 +/- 6.6 ng/ml and 315 +/- 32 ng/ml (mean +/- SEM), respectively. During low-dose nicotine infusion there was no significant change in cardiac output, its distribution, or uteroplacental blood flow. During high-dose nicotine infusion, cardiac output fell from 257.8 +/- 30.9 ml/min to 212.7 +/- 19.3 ml/min (p less than 0.05) and uteroplacental blood flow fell from 31.2 +/- 3.1 ml/min to 22.3 +/- 2.4 ml/min (p less than 0.05). During control, low-dose, and high-dose periods, serum epinephrine levels rose from control value of 60.2 +/- 2.6 to 98.9 +/- 35 and 1200 +/- 295 pg/ml (p less than 0.05 low dose versus high dose) and serum norepinephrine levels did not change significantly during nicotine infusion. Hence at nicotine levels 20 times but not at two to five times those seen in smokers, modest reductions in cardiac output and uteroplacental blood flow were observed.

Characterization of adrenoceptor mechanisms in isolated guinea-pig uterine arteries

The adrenoceptors of the guinea-pig uterine artery were characterized pharmacologically. Circular segments of the artery, approximately 2 mm long, and with an external diameter of 250 micron, were mounted in miniaturized tissue baths. Noradrenaline, methoxamine and phenylephrine (concentrations ranging from 10 nM to 1 mM), in the presence of propranolol (0.1 microM) and cocaine (1 microM), induced concentration-dependent contractions of the arterial segments. Clonidine (10 nM to 0.1 mM) was less effective in producing contraction of the vessel. Prazosin (10 nM to 1 microM) antagonized noradrenaline-induced contractions; its pA2 was 7.68. Rauwolscine (10 nM to 1 microM) had no effect on noradrenaline-induced contractions. Isoprenaline (10 nM to 0.1 mM) in the presence of prazosin (1 microM) and cocaine (1 microM) had no relaxant effect on arteries contracted submaximally by prostaglandin F2 alpha (5 microM). Cocaine or normetanephrine treatment did not influence the noradrenaline-induced contractions. It is concluded that in guinea-pig uterine arteries, amine-induced contractions are mediated predominantly by alpha 1-adrenoceptors and that in this arterial preparation, relaxant beta-adrenoceptor effects and neuronal or extraneuronal uptake are of minor if any importance.

Electrophysiological analysis of neurogenic vasodilatation in the isolated lingual artery of the rabbit

The nature of neurogenic vasodilatation was investigated in isolated segments of rabbit lingual artery. In separate experiments membrane responses to nerve stimulation were studied by use of microelectrodes. In the presence of guanethidine to block constrictor responses and noradrenaline to induce tone, field stimulation with trains of pulses (8 Hz for 0.5 to 4 s) produced vasodilatation. Atropine (10(-6) M) reduced the relaxations to about 50% of the control values while the induced vasodilatations were potentiated by physostigmine. Tetrodotoxin (TTX, 10(-7) M) blocked all nerve-evoked responses. These data suggest that there is a cholinergic and a non-cholinergic component of the vasodilatation produced by nerve stimulation in the rabbit lingual artery. Single stimuli did not evoke electrophysiological responses. With parameters similar to those used in the mechanical studies, periarterial stimulation in the presence of guanethidine evoked membrane hyperpolarizations which achieved amplitudes of up to 11 mV. The ionophoretic application of acetylcholine (ACh) produced hyperpolarization. The inhibitory junction potentials (i.j.ps) but not the ionophoretic-induced responses were blocked by TTX. The nerve-evoked and the ACh-induced hyperpolarizations were potentiated by physostigmine (5 X 10(-7) M) and totally blocked by atropine (10(-7) M). I.j.ps and hyperpolarization to ionophoresis of ACh were recorded from arteries in which the endothelium had been removed by mechanical rubbing. Mechanical relaxation to field stimulation and ACh was observed in preparations without endothelium. These data suggest that the cholinergic component of the neurogenic vasodilatation in the rabbit lingual artery is accompanied by hyperpolarization. The non-cholinergic component does not appear to possess an electrophysiological correlate. In addition, it seems that the action of nerve-released ACh is mediated by muscarinic receptors which are situated directly on the vascular smooth muscle cells.

Co-localization of neuropeptide Y, vasoactive intestinal polypeptide and dynorphin in non-noradrenergic axons of the guinea pig uterine artery

Two major populations of perivascular axons containing immunoreactivity to neuropeptide Y (NPY) have been revealed in the main uterine artery of the guinea pig by immunohistochemical procedures which allow the simultaneous visualization of two antigens. One population contained immunoreactivity to dopamine-beta-hydroxylase (D beta H) and was presumably noradrenergic. The other main population of axons with NPY-like immunoreactivity (NPY-LI) did not have D beta H-like immunoreactivity (D beta H-LI) and was presumably non-noradrenergic. These non-noradrenergic axons also contained immunoreactivity to vasoactive intestinal polypeptide (VIP) and dynorphin (DYN). Indeed, nearly all axons with VIP-LI also contained NPY-LI and DYN-like immunoreactivity (DYN-LI). NPY constricted the uterine artery perfused in vitro, whilst VIP dilated uterine arteries preconstricted with noradrenaline or NPY. Thus, we have evidence for the coexistence of a vasoconstrictor peptide and a vasodilator peptide in the same non-noradrenergic perivascular axons, which also contain an opioid peptide, dynorphin.