Substance P-immunoreactive nerve fibres in the anterior segment of the rabbit eye

Summary Substance P-immunoreactive nerve terminals were found in several locations in the anterior segment of the rabbit eye. In the iris they occurred in the sphincter muscle and were randomly distributed in the iris stroma with some fibres running close to the dilator muscle. In the ciliary body these immunoreactive elements were few and occurred within bundles of nerve fibres, while in the ciliary processes they were more numerous with a predominantly subepithelial location. Blood vessels in the anterior uvea were often surrounded by substance P-immunoreactive fibres. No substance P-fibres were found in the cornea, while the sclera contained very few such elements.Using conventional in vitro techniques it was found that the sphincter pupillae muscle of the iris responded to electrical stimulation with a contraction that was resistant to cholinergic and adrenergic blockade, but was inhibited by the neuronal blocker tetrodotoxin. This indicates the existence of a non-cholinergic, non-adrenergic neuronal mediator of the contractile response. Exogenously applied substance P produced a long-lasting contraction of the spincter muscle, an observation compatible with the view that substance P is the noncholinergic, non-adrenergic neurotransmitter involved.     

Different modes of action of substance P in the motor control of the feline stomach and pylorus

In an experimental in vivo model to study gastropyloric motility in the cat a contraction of the stomach and the pyloric sphincter was regularly obtained in animals subjected to electrical vagal nerve stimulation or local intraarterial (i.a.) injection of substance P (SP). Much more infrequently contractile motor responses were recorded at splanchnic nerve stimulation. The contractile effects of SP were sensitive to atropine or local infusion of a SP analogue, (d-Pro²,d-Trp^7,9)-SP, indicating that SP activated a final common cholinergic neuron in both stomach and pylorus. However, there seemed to be separate transmission mechanisms in these two regions based on the results of the physiological studies. The vagally induced pyloric contraction was noncholinergic, nonadrenergic, but sensitive to ganglionic blockade (hexamethonium) or the SP analogue, indicating involvement of SP in a peptidergic pathway to the sphincter. The infrequent splanchnically induced pyloric contraction was sensitive to atropine, the SP analogue or ganglionic blockade (hexamethonium) in favour of SP acting on a final cholinergic neuron in this system. On the other hand the gastric contraction, obtained at either extrinsic nerve stimulations or local i.a. injection of SP, was sensitive to atropine or the SP analogue but hexamethonium resistant. These findings suggest antidromic activation of SP-containing axon collaterals of the extrinsic nerves terminating on cholinergic neurons of the gastric wall. When afferent C-fibres of the vagal nerve were selectively activated by local heating, pyloric contraction and gastric relaxation were obtained via vago-vagal reflexes. After cervical vagotomy heating of the distal end of the vagal nerve elicited a gastric contraction, previously demonstrated to be atropine sensitive and hexamethonium resistant, but no pyloric motor response. This suggests that the antidromic activation mechanism was present only in the stomach, not in the pylorus.     

Response of the isolated rat iris sphincter to cholinergic and adrenergic agents and electrical stimulation

In isolated rat iris sphincter muscle, there has been no attempt to measure mechanical tension changes, because of the small size of the preparation. In this study, responses of the isolated rat iris sphincter to some agents and electrical stimulation were examined. Acetylcholine and electrical stimulation produced powerful contractions of the iris sphincter. These contractile responses were suppressed by atropine and enhanced by physostigmine. 10 μM norepinephrine induced a weak contraction of the sphincter muscle and 1 mM isoproterenol induced a very weak relaxation. These responses were antagonized by phentolamine and propranolol, respectively. In the presence of 0.1 μM atropine, electrical stimulation produced a weak alpha-adrenergic contraction and a very weak beta-adrenergic relaxation. Electrically induced responses were abolished by tetrodotoxin. In conclusion, in the rat iris sphincter, powerful contraction is due to the activation of muscarinic receptors, and that there are weak alpha-adrenergic contraction and weak beta-adrenergic relaxation. Thus in rats, muscarinic contraction of the sphincter muscle plays major role in the regulation of pupil diameter.     

Contractile responses to adrenergic nerve stimulation are enhanced with removal of endothelium in rat caudal artery

Removal of the endothelium from isolated perfused rat caudal arteries produced a two fold increase in the contractile response to transmural nerve stimulation. Pretreatment with 6-hydroxydopamine eliminated the contractile response to adrenergic nerve stimulation but failed to uncover any vasodilatory effect of electrical stimulation, either directly on smooth muscle or via non-adrenergic nerves. Endothelial removal also produced two and four fold enhancement of the contractile responses to the selective alpha 1- and alpha 2-adrenoceptor agonists methoxamine and B-HT 920. However, pKB values for prazosin and yohimbine versus both agonists indicate that both methoxamine and B-HT 920 are acting primarily at alpha 1-adrenoceptors in this tissue. These results provide evidence that endothelial factors released either at basal levels or by the stimulation of agonists play a significant physiological role in modifying the contractile responses of blood vessels.     

Presence and actions of vasopressin-like peptides in the rabbit anterior uvea

The presence of vasopressin-like immunoreactivity (VP-IR) in the rabbit eye was demonstrated by radioimmunoassay. Trigeminal nerve denervation resulted in a significant and selective decrease in the levels of VP-IR in the iris sphincter muscle and the cornea. The isolated iris sphincter muscle contracted in response to low concentrations of [Arg8]vasopressin (AVP) and related peptides. The V1 vasopressin receptor antagonist, d(CH2)5Tyr(Me)AVP, potently inhibited the contractile responses to AVP. AVP was found to induce an increase in the accumulation of inositol phosphates in the iris sphincter muscle but not in the dilator/ciliary body preparation in vitro. The present investigation demonstrates the presence of VP-IR in the rabbit eye and that this substance may be another sensory nerve-derived mediator acting on specific target sites in the anterior uvea.     

Nerves containing substance P,vasoactive intestinal polypeptide,enkephalin or somatostatin in the guinea-pig taenia coli

Summary The guinea-pig taenia coli is rich in peptide-containing nerves. Nerve fibres containing substance P (SP), vasoactive intestinal peptide (VIP), or enkephalin, were numerous in the smooth muscle while somatostatin fibres were very few. Nerve fibres displaying SP or VIP immunoreactivity were numerous in the myenteric plexus. Enkephalin nerve fibres were fairly numerous in the plexus while somatostatin nerve fibres were sparse. Nerve cell bodies containing immunoreactive SP or VIP were regularly seen in the plexus. Delicate varicose elements of the different types of nerve fibres were found to ramify around nerve cell bodies in a manner suggestive of innervation.In the electron microscope the various peptide-storing nerve fibres (i.e., elements containing SP, VIP or enkephalin) were found to contain a varying number of fairly large, electron-opaque vesicles in the varicose swellings. These vesicles represent the storage site of the neuropeptides.The isolated taenia coli responded to electrical nerve stimulation with a contraction. After cholinergic and adrenergic blockade the contractile response was replaced by a relaxation followed by a contraction upon cessation of stimulation. SP contracted the taenia while VIP caused a relaxation. The enkephalins raised the resting tension slightly while somatostatin had no effect. These observations are compatible with a role for SP as an excitatory neurotransmitter and for VIP as an inhibitory one, and with the view that both SP neurones and VIP neurones act as motor neurones. In preparations contracted by SP the electrically induced contractions were reduced in amplitude while the electrically induced relaxations seen after adrenergic and cholinergic blockade were enhanced in amplitude. In preparations relaxed by VIP there was an increased contractile response to electrical stimulation, while in the atropine + guanethidine-treated preparation the electrically induce relaxations were reduced in amplitude. The enkephalins reduced the contractile response to electrical stimulation, while somatostatin induced a very small reduction in the amplitude of such responses. These observations suggest that SP neurones and VIP neurones may play additional roles as interneurones. Somatostatin neurones probably act as interneurones. Enkephalin-containing fibres may serve to modify the release of transmitter from other nerves in the smooth muscle, perhaps through axo-axonal arrangements. Alternatively, the enkephalin nerve fibres in the smooth muscle are afferent elements involved in mediating sensory impulses to the myenteric plexus.     

Tetrodotoxin-resistant relaxation to transmural nerve stimulation in canine saphenous veins: a possible neural origin

Transmural nerve stimulation following sympathetic (guanethidine 10(-4) mol/L, phenoxybenzamine 2 X 10(-5) mol/L, propanolol 2 X 10(-6) mol/L) and muscarinic blockade (atropine 5 X 10(-5) mol/L) produces a relaxatory response in canine saphenous veins contracted with prostaglandin F2 alpha. This relaxatory response was shown previously to be resistant to tetrodotoxin. Transmural nerve stimulation (10 V, 1.0 ms) was applied as intermittent trains of stimuli of 30 s duration at frequencies of 1-32 Hz. The veins showed a frequency dependent relaxation (maximum 2.65 +/- 0.20 g). The stimulations were repeated in the presence of lignocaine (10(-3) mol/L), apamin (10(-8) mol/L), ascorbic acid (10(-4) mol/L), or catalase (50 micrograms/mL). The relaxatory response was unaffected by apamin, scorpion toxin, superoxide dismutase, ascorbic acid, and catalase (p greater than 0.05). However, lignocaine (10(-3) mol/L) reduced significantly the relaxatory response to transmural nerve stimulation in this preparation (p less than 0.05). In a separate group of veins, lignocaine (10(-3) mol/L)l abolished the contractile response to transmural nerve stimulation with little effect upon the contractile response to exogenous noradrenaline and the relaxatory responses to isoprenaline and sodium nitrite. These findings support the proposition that the nonadrenergic, noncholinergic tetrodotoxin-resistant relaxatory response observed with transmural nerve stimulation in the canine saphenous vein is mediated by a neural mechanism.     

Prostaglandin involvement in contractions evoked in rabbit detrusor by field stimulation and by adenosine 5'-triphosphate

Previous reports suggest that in rabbit urinary bladder both noncholinergic nonadrenergic excitatory responses and the contraction produced by adenosine 5'-triphosphate (ATP) are antagonized by indomethacin. We have attempted by further indirect testing on isolated detrusor strips to determine what role prostaglandins (PGs) might play in these processes. The second part of the biphasic contractile response to ATP was reduced to about 30% of control by PG synthesis inhibitors but the initial phase of the ATP response and te contraction produced by the beta, gamma-methylene analogue of ATP were unaffected. At concentrations that did not affect the response to acetylcholine but greatly suppressed the response to arachidonic acid, indomethacin antagonized the contraction evoked by field stimulation by about 30% at 1-2 Hz (largely noncholinergic and nonadrenergic). SC 19220, a putative PG receptor blocker, also produced about 25% reduction in the response to field stimulation but with only about 50% reduction in the response to arachidonic acid, PGE2, or PGF2alpha, SC 19220 also antagonized the frequency-response curve in atropine-treated strips. These findings lead us to suggest that beside maintaining tone and spontaneous activity in the bladder PGs mediate the slow tonic phase of the ATP response and may contribute to facilitatory modulation of noncholinergic nonadrenergic excitatory transmission.     

Effect of streptozotocin diabetes on motor and inhibitory transmission in rat anococcygeus.

The effect of streptozotocin diabetes of 4-week duration on the adrenergic motor transmission and on the nonadrenergic, noncholinergic, inhibitory transmission in the rat anococcygeus was investigated by recording contractile and relaxant activity of isolated muscle preparations taken from diabetic and age-matched control animals. The neurogenic contractile responses to electrical field stimulation were significantly reduced in the preparations from diabetic rats. The inhibitory transmission remained unaffected in the diabetic rats. Concentration--response curves showed no change in sensitivity of the diabetic anococcygei to noradrenaline. The maximum tension generated was also similar in preparations from diabetic and nondiabetic animals. The contractile responses to electrical field stimulation were significantly greater in preparations from diabetic rats treated for 4 weeks with either sorbinil (20 mg.kg-1.day-1 orally) or myo-inositol (667 mg.kg-1.day-1 orally) when compared with the untreated diabetic controls; the sensitivity to noradrenaline was identical in all three groups. It is concluded that streptozotocin diabetes causes a significant reduction of adrenergic contractile responses of the anococcygeus to electrical field stimulation by a prejunctional mechanism, and the reduction can be prevented by treating the animals with the aldose reductase inhibitor sorbinil or with myo-inositol.     

The mechanism of action of bombesin on cat lower esophageal sphincter

The effect of bombesin on the tone and the responses of strips from the lower esophageal sphincter (LES) to field electrical stimulation (FES) (2 Hz, 0.2 ms, supramaximal current intensity, 20 s duration) was studied. Bombesin dose-dependently increased the LES tone. The threshold for this effect was 10(-14) M and was particularly pronounced with a concentration of 10(-8) M. The response reached maximum between the 3rd and the 5th min after application, persisted for 15-20 min, and was followed by a slight time-dependent decrease. Bombesin increased FES-produced relaxation of LES by 39% as compared to the control. The potentiating effect of bombesin on the LES relaxation was also observed after cholinergic and adrenergic receptor blockade. It is concluded that bombesin may modulate the release of cholinergic, adrenergic and noncholinergic, nonadrenergic inhibitory neurotransmitters.     

Substance P in the control of extrahepatic biliary motility in the cat

The effects of regional intra-arterial injections of substance P (SP) or efferent electrical stimulation of the vagal nerves on feline extrahepatic biliary motility were studied in anesthetized cats using a constant perfusion model. Each of these procedures elicited contractile motor responses of the gallbladder and the sphincter of Oddi. Since SP is present in feline vagal axons, these findings may indicate a role of SP in the vagal motor control of biliary motility. Immunocytochemically neurons with SP-like immunoreactivity were found in the smooth muscle layers of the biliary tree as well as adjacent to acetylcholinesterase-positive ganglion cells indicating either direct activation of smooth muscle cells and/or indirect activation via cholinergic neurons. Depending on the type of stimulation different SP mechanisms were demonstrated; exogenous SP induced contraction of both the sphincter and the gallbladder which were probably direct (resistant to atropine but sensitive to a SP analogue), while vagal stimulation elicited contraction of both regions via a mechanism sensitive to atropine and to a SP analogue.     

Prokinetic effect of black tea on gastrointestinal motility

The gastrokinetic effects of hot water extract of black tea [Camellia sinensis, (L) O. Kuntze (Theaceae)] on gastrointestinal motility were studied both in vivo and in vitro. The extract significantly accelerated the gastrointestinal transit (GIT) in vivo in mice. These facilitatory effect was reduced after pretreatment with atropine, hemicholinium-3, morphine, indomethacin, McN-A-343 and L-arginine. In guinea pig ileum, the extract facilitated the peristaltic reflex in response to pressures in normal preparation. The black tea extract and L-NMMA (nitric oxide synthase inhibitor) significantly reduced the electrical field stimulated nonadrenergic, noncholinergic (NANC) relaxation of isolated rat fundal strips. The extract markedly enhanced the tonic ('hump') responses to transmural stimulation in longitudinal muscle of guinea pig ileum which was unaltered in the presence of atropine. These findings suggest a cholinergic involvement and a partial role of prostaglandin and nitric oxide in the mechanism of action of black tea extract on gastrointestinal motility. To determine the effective constituents in black tea responsible for this activity, the effect of black tea polyphenols on GIT were also studied. Thearubigin fraction (but not theaflavin) accelerated GIT significantly which suggests its involvement in the prokinetic effect of black tea.     

Substance P contracts the human iris sphincter: possible modulation by endogenous enkephalinase.

Substance P-immunoreactive neurons have been found in the irides of many species including humans. In several species, substance P has been shown to induce contraction of the sphincter muscle but this action of substance P has not been previously demonstrated in the human eye. Using an eye cup model in which the sensitivity of the iris muscle to substance P is increased compared to the isolated sphincter muscle, we have observed that nanomolar amounts of substance P induced contraction of the sphincter in the human iris. This contractile response was enhanced in eyes pretreated with thiorphan, an enkephalinase inhibitor, suggesting that endogenous enkephalinase (E.C. 3.4.24.11) may modulate the substance P contraction in the human iris. Further support for this hypothesis was the finding of enkephalinase-like immunoreactivity and enzyme activity in the human iris sphincter muscle.     

Enkephalinase inhibitor potentiates substance P- and electrically induced contraction in ferret trachea

To determine the role of endogenous enkephalinase (EC 3.4.24.11) in regulating peptide-induced contraction of airway smooth muscle, we studied the effect of the enkephalinase inhibitor, leucine-thiorphan (Leu-thiorphan), on responses of isolated ferret tracheal smooth muscle segments to substance P (SP) and to electrical field stimulation (EFS). Leu-thiorphan shifted the dose-response curve to SP to lower concentrations. Atropine or the SP antagonist [D-Pro2,D-Trp7,9]SP significantly inhibited SP-induced contractions in the presence of Leu-thiorphan. Leu-thiorphan increased the contractile responses to EFS dose dependently, an effect that was significantly inhibited by the SP antagonist [D-Pro2,D-Trp7,9]SP. SP, in a concentration that did not cause contraction, increased the contractile responses to EFS. This effect was augmented by Leu-thiorphan dose dependently and was not inhibited by hexamethonium or by phentolamine but was inhibited by atropine. Because contractile responses to acetylcholine were not significantly affected by SP or by Leu-thiorphan, the potentiating effects of SP were probably on presynaptic-postganglionic cholinergic neurotransmission. Captopril, bestatin, or leupeptin did not augment contractions, suggesting that enkephalinase was responsible for the effects. These results suggest that endogenous tachykinins modulate smooth muscle contraction and endogenous enkephalinase modulates contractions produced by endogenous or exogenous tachykinins and tachykinin-induced facilitation of cholinergic neurotransmission.     

Mechanism of the serotonin effect on motility of the duodenum,ileum, and jejunum in awake rabbits

I. v. administration of serotonin to alert rabbits produced a phasic change of contractile activity of duodenum, ileum, and jejunum including excitatory and inhibitory components. It is shown that stimulation of the small bowel motility is caused by serotonin activation of non-cholinergic excitatory mechanism with participation of effector cholinergic neurones. The initial suppression of the motility is caused by participation of nonadrenergic noncholinergic inhibitory mechanism, and the secondary inhibition of contractile activity of a small bowel with serotonin has an adrenergic nature.     

Spantide II, a novel tachykinin antagonist having high potency and low histamine-releasing effect.

Two undecapeptide substance P (SP) analogues, Spantide I and Spantide II, were tested for their capacity to block the contractile effect of SP on the guinea pig isolated taenia coli and the contractile effect of electrical stimulation of the rabbit isolated (and atropinized) iris sphincter, and for their capacity to mobilize histamine from rat isolated peritoneal mast cells. Spantide I and Spantide II have one feature in common, namely D-tryptophan in positions 7 and 9. Spantide I: D-Arg, Pro2, Lys3, Pro4, Gln5, Gln6, D-Trp7, Phe8, D-Trp9, Leu10, Leu11-NH2. Spantide II: D-NicLys1, Pro2, 3-Pal3, Pro4, D-Cl2Phe5, Asn6, D-Trp7, Phe8, D-Trp9, Leu10, Nle11-NH2. Both Spantide I and II were found to be competitive antagonists to SP on the taenia coli and to be capable of blocking the electrically induced non-cholinergic contraction of the iris sphincter. Spantide II had higher pA2 value (taenia coli) than Spantide I, 7.7 versus 7.0, and higher pIC50 value (blockade of tachykinin-mediated neurotransmission in iris sphincter), 6.0 versus 5.1. Both Spantide I and II mobilized histamine from rat peritoneal mast cells but Spantide II was less effective. Spantide I and II were tested for antagonistic specificity. Both blocked contractions of the taenia induced by SP and neurokinin A. In the concentration used, Spantide II in addition blocked the response to neurokinin B. The contractions induced by carbachol, 5-hydroxytryptamine, histamine and prostaglandins (F2 alpha and E1) were not affected; the contractile response to bombesin was inhibited by Spantide I but not by Spantide II.     

Response of isolated rat iris dilator to adrenergic and cholinergic agents and electrical stimulation

Responses of isolated rat iris dilator to some agents and to electrical stimulation were examined. Norepinephrine and epinephrine produced contraction, which was antagonized by 0.03 μM phentolamine. Acetylcholine produced relaxation at low concentrations (1 nM ? 1 μM) as great as 80 % of the resting tone while contraction at high concentrations (≥1 μM). Both responses were suppressed by 0.02 μM atropine and enhanced by 0.03 μM physostigmine. Electrical stimulation at low voltage or low frequency (up to 10 Hz) elicited relaxation while stimulation at high voltage or high frequency (30 Hz) produced contraction. Stimulation with intermediate strength elicited biphasic response. The contraction and relaxation induced by electrical stimulation were abolished by 3 μM phentolamine or by 0.05 μM atropine, respectively. Both phases were abolished by tetrodotoxin (0.3 μM). It is suggested that in the rat the cholinergic relaxation of the dilator may assist the cholinergic contraction of the sphincter (1). The pronounced cholinergic relaxation of nonvascular tissue is to be noted.     

Neural control of relaxation in cat airways smooth muscle

Functional innervation of cat airways smooth muscle was examined in isolated segments of trachea and bronchi using electrical field stimulation (EFS) techniques. Field stimulation caused contraction in tissues at resting tone and biphasic responses (contraction followed by relaxation) in tissues precontracted with 5-hydroxytryptamine (5-HT). Contractions were abolished by 10(-6) M atropine. Inhibitory responses were dependent on impulse voltage, duration, and frequency. At low voltages (less than or equal to 10 V) and pulse durations (less than or equal to 0.3 ms), EFS induced relaxations were abolished by 3 X 10(-6) M tetrodotoxin (TTX). Greater stimulus parameters elicited TTX-resistant relaxations. Pretreatment of the tissues with 10(-6) M propranolol and 10(-5) M guanethidine caused rightward shifts in relaxation frequency-response curves. These findings indicate that cat airways are innervated by excitatory cholinergic, inhibitory adrenergic, and inhibitory nonadrenergic noncholinergic (NANC) nerves. Pretreatment of the tissues with hexamethonium, cimetidine, indomethacin, or nordihydroguaiaretic acid did not affect NANC relaxation responses. It is concluded that NANC inhibitory responses in cat airway smooth muscle are mediated through intrinsic postganglionic nerve fibers and occur independently of histamine H2-receptor activation and without involvement of cyclooxygenase or lipoxygenase products of arachidonic acid metabolism.     

Locus coeruleus fibre growth in oculo induced by trigeminotomy

Locus coeruleus from fetal donors was homologously grafted to the anterior eye chambers of adult rats whose eyes were sympathetically denervated. After intraocular maturation, outgrowth of noradrenaline-containing fibres from the locus coeruleus neurons on the host iris was studied by Falck--Hillarp fluorescence histochemistry.In control animals locus coeruleus grafts produce a halo of noradrenaline-containing nerve fibres around the graft, covering approximately one third of the surface of the host iris. Sensory denervation of host eyes carrying maturated locus coeruleus grafts was produced by intracranial lesions of the trigeminal nerve. Such lesions induced a rapid growth response in the grafted locus coeruleus neurons, leading within three weeks to complete innervation of the host iris. It was concluded that removal of non-sympathetic, non-parasympathetic nerve fibres on the host iris elicits a strong fibre-growth response in the grafted locus coeruleus.     

Immunohistochemical localization of substance P, vasoactive intestinal polypeptide and gastrin-releasing peptide in vas deferens and seminal vesicle, and the effect of these and eight other neuropeptides on resting tension and neurally evoked contractile activity

Immunohistochemical studies of the vas deferens and seminal vesicle of mouse, guinea-pig, and rabbit showed the presence of nerve fibres containing vasoactive intestinal polypeptide (VIP), substance P (SP), and gastrin-releasing peptide (GRP) supplying the smooth muscle layers as well as blood vessels. The nerve supply was better developed in the seminal vesicle than in the vas deferens. The motor activity of the vas deferens and seminal vesicle of the guinea-pig was studied in vitro. The vas deferens responded to transmural electrical stimulation with a twitch followed by a slow contraction. The twitch was blocked by guanethidine and tetrodotoxin, but not by atropine, propranolol, phenoxybenzamine, or fluphenazine. The slow contraction exhibited features of an alpha-receptor-mediated response. SP, physalaemin and eledoisin contracted the smooth muscle and also potentiated the twitch response to electrical nerve stimulation in a concentration-dependent manner. The SP blocking agent, (D-Pro2,D-Trp7,9)-SP, affected neither the resting tension nor the response to electrical stimulation. It is therefore suggested that the SP fibres act mainly prejunctionally. VIP, Leu-enkephalin, cholecystokinin octapeptide (CCK-8), angiotensin II, vasopressin, neurotensin, bombesin, and GRP had no effect on either the resting tension or the response to electrical nerve stimulation. The seminal vesicle responded to electrical stimulation with a contraction which was unimpaired by atropine, propranolol, phenoxybenzamine, and guanethidine, but abolished by tetrodotoxin. Hence, this contraction is mediated by a non-adrenergic, non-cholinergic neurotransmitter. Bombesin, GRP, SP, physalaemin and eledoisin contracted the smooth muscle and potentiated the response to electrical stimulation. VIP, Leu-enkephalin, CCK-8, angiotensin II, vasopressin, and neurotensin had no effect on the resting tension or on the response to transmural electrical stimulation. The SP antagonist abolished the contraction elicited by SP but did not influence the response to nerve stimulation. The results suggest that the SP and GRP nerves may have prejunctional and facilitating postjunctional effects in the seminal vesicle.