Trigeminal nerve: the possible origin of substance p-nergic response in isolated rabbit iris sphincter muscle

We determined the effects of trigeminal nerve denervation on the noncholinergic, nonadrenergic response to electrical transmural stimulation of the isolated rabbit iris sphincter muscle. The left ophthalmic nerve (first branch of the trigeminal nerve) was cut at the intracranial, peripheral site of the trigeminal ganglion and five to ten days later, the iris sphincter muscle isolated from the left eye (operated side) was found to produce a fast cholinergic contraction in response to electrical transmural stimulation and there was no evidence of noncholinergic, nonadrenergic contractions. On the other hand, in the iris sphincter muscle isolated from the right eye (control side), electrical transmural stimulation produced both cholinergic and noncholinergic, nonadrenergic contractile responses. Capsaicin and bradykinin produced noncholinergic, nonadrenergic contractile responses in the muscle from the control side, while in the iris sphincter from the trigeminally denervated eye there was no such response to application of these drugs. Exogenous substance P (SP) and carbachol produced a strong contractile response in both the trigeminally innervated and denervated sphincter muscles. Somatostatin, vasoactive intestinal polypeptide (VIP) and enkephalin were without effects. These observations suggest that the noncholinergic, nonadrenergic responses to electrical transmural stimulation are derived from the trigeminal nerve and that the mediator involved is probably SP or a related peptide.     

Immunohistochemical demonstration of neurotensin and tyrosine hydroxylase in iris nerves of the rabbit eye

Summary In previous studies we have provided evidence that intracameral administration of neurotensin (NT), an endogenous tridecapeptide, produces strong miosis in the rabbit. The presence of NT immunoreactivity was investigated in rabbit iris whole mounts by light microscopic immunohistochemistry, and its distribution in the iris compared to that, of tyrosine hydroxylase (TH). A few scattered NT-positive cell bodies were localized in the dilator muscle. Both, the NT cell bodies and processes appeared parallel to the muscle cells. Extensive branching of NT-containing cell processes was observed in connection with the sphincter muscle. These NT-positive fibers formed a dense, randomly oriented network throughout the sphincter muscle cells. The distribution of TH immunoreactivity was similar to that of NT-positive cell processes, except that no TH-positive cell bodies were detected in any of the iris structures examined. Moderate branching of TH-positive fibers was observed in the dilator and sphincter iris muscles. These findings provide neuroanatomical support for an important role of NT in pupillary physiology. Its similar topographical distribution with TH suggests that NT and dopamine may be co-localized, as it has already been described in brain.     

Immunohistochemical demonstration of neurotensin and tyrosine hydroxylase in iris nerves of the rabbit eye

In previous studies we have provided evidence that intracameral administration of neurotensin (NT), an endogenous tridecapeptide, produces strong miosis in the rabbit. The presence of NT immunoreactivity was investigated in rabbit iris whole mounts by light microscopic immunohistochemistry, and its distribution in the iris compared to that, of tyrosine hydroxylase (TH). A few scattered NT-positive cell bodies were localized in the dilator muscle. Both, the NT cell bodies and processes appeared parallel to the muscle cells. Extensive branching of NT-containing cell processes was observed in connection with the sphincter muscle. These NT-positive fibers formed a dense, randomly oriented network throughout the sphincter muscle cells. The distribution of TH immunoreactivity was similar to that of NT-positive cell processes, except that no TH-positive cell bodies were detected in any of the iris structures examined. Moderate branching of TH-positive fibers was observed in the dilator and sphincter iris muscles. These findings provide neuroanatomical support for an important role of NT in pupillary physiology. Its similar topographical distribution with TH suggests that NT and dopamine may be co-localized, as it has already been described in brain.     

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.     

Fine structure of the photosensitive iris of the toad, Bufo marinus

The iris of the toad Bufo marinus is directly photosensitive and will constrict in response to light striking only the iris. This is true even when the iris is isolated from the rest of the eye, and therefore from reflex neuronal influences initiated in the retina. This autonomous response is probably mediated by the sphincter pupillae muscle, since no specialized photoreceptors are present in the iris, nor does the sphincter exhibit any specializations likely to subserve a purely photoreceptive function. The photosensitive sphincter appears typical of smooth muscle and, like mammalian sphincters, possesses many intercellular junctions. The iris possesses a well-developed neuronal plexus with fibers projecting into the sphincter muscle layer. Nerve terminals contain small, agranular (30-70nm) and large, dense-cored (80-120nm) vesicles. No consistent postsynaptic specializations are seen on any cells of the iris, including the cells of the sphincter muscle. The anterior pigment epithelial cells of the iris appear specialized and resemble the myoepithelial dilator muscle described by Kelly and Arnold ('72) for the iris of rats.     

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.     

Immunoreactivity for substance P in the gasserian ganglion, ophthalmic nerve and anterior segment of the rabbit eye

Summary The distribution of substance P (SP) immunofluorescence was investigated in the Gasserian ganglion, ophthalmic nerve and in the anterior segment of the rabbit eye. About one third of the nerve cell bodies in the Gasserian ganglion exhibited SP immunofluorescence, which was also observed in some nerve fibres of the ophthalmic nerve. In the cornea, some SP-positive iris contained numerous nerve fibres with SP immunofluorescence. In the sphincter area such fibres were circular, while the orientation of the SP fibres was radial in the dilator muscle. Both in the iris and in the ciliary body, the largest vessels were surrounded by nerves exhibiting SP immunofluorescence. A few nerve fibres also appeared in the stroma of the ciliary processes.     

Species differences in the effects of leukotriene D4 on inositol trisphosphate accumulation, cyclic AMP formation and contraction in iris sphincter of the mammalian eye

The effects of leukotriene (LT) D4 on inositol trisphosphate (IP3) accumulation, cAMP formation, and contraction in the iris sphincter smooth muscle of different mammalian species were investigated and functional and biochemical reciprocal interactions between the IP3-Ca2+ and cAMP second messenger systems were demonstrated. The effects of the LT on the biochemical and pharmacological responses are dose- and time-dependent, and are not mediated through the release of acetylcholine or prostaglandins. Addition of LTD4 (0.1-1 microM) to cat and bovine iris sphincters increased IP3 accumulation by 60% of that of the control and induced muscle contraction (the EC50 value for the contractile response in the cat sphincter was 4.8 x 10(-9) M), but had no effect on cAMP formation in these species. In contrast, addition of LTD4 to dog, human, pig, and rabbit sphincters increased cAMP formation by 53-61% of their respective controls, but had no effect on IP3 accumulation and on the contractile state. The rates of formation of LTs in iris sphincters of the different species were found to increase in the following order: bovine less than cat less than human less than dog less than pig less than rabbit. This could suggest that desensitization of LT receptors may in part underlie the species differences observed in the effects of LTD4. We suggest that LTD4 may be involved in regulation of contraction and relaxation in the iris sphincter by increasing IP3 accumulation and consequently Ca2+ mobilization and muscle contraction, and by elevating the level of cAMP which in turn may be involved in the regulation of muscle tension.     

Effects of Surgical Sympathetic Denervation on myo-Inositol Trisphosphate Production and Contraction in the Dilator and Sphincter Smooth Muscles of the Rabbit Iris: Evidence for Interaction Between the Cyclic AMP and Calcium Signaling Systems

The effects of norepinephrine (NE), carbachol (CCh), NaF, 3-isobutyl-1-methylxanthine (IBMX), and high K+ concentration (80 mM) depolarization on inositol trisphosphate (IP3) accumulation, cyclic AMP (cAMP) formation, and contraction were investigated in the dilator and sphincter smooth muscles of the sympathetically denervated as well as the normal rabbit eye. (a) In the denervated dilator muscle, NE-stimulated IP3 production and contraction are enhanced. (b) In the sphincter muscle of rabbits that have undergone sympathetic denervation. CCh-stimulated IP3 production and contraction are attenuated. (c) The increase in tension by a maximal effective dose of NaF (209 mM) in the dilator was 12.5 and 18 mg of tension/mg wet weight in normal and denervated tissue, respectively, and in the sphincter was 33.8 and 15.2 mg of tension/mg wet weight in normal and denervated tissue, respectively. NaF had no effect on cAMP formation. (d) Addition of NE had no effect on cAMP formation in both the normal and denervated dilator, whereas basal and IBMX-induced cAMP formation increased. in the denervated sphincter over that of the normal tissue by 15 and 60%, respectively. (e) Isoproterenol (5 microM) increased cAMP formation in the normal and denervated sphincter by 47 and 91%, respectively. (f) Whereas CCh inhibits cAMP formation in the normal sphincter, it lost its inhibitory effect in the sphincter with denervation. (g) IBMX (0.1 mM) attenuated the CCh-stimulated IP3 production and contraction of the sphincter by approximately 30% of their respective controls. (h) High K+ concentration depolarization attenuated contraction in both dilator and sphincter muscles with denervation. These observations suggest that an increase in the level of cAMP in the iris sphincter due to sympathetic denervation could lead to inhibition of phospholipase C (or other target sites, such as phosphorylation of the muscarinic receptor, Gp protein itself, myosin light chain kinase, or the IP3 receptor), IP3 production, and contraction. In conclusion, we suggest that the supersensitivity and subsensitivity observed after surgical sympathetic denervation of the iris dilator and sphincter muscles, respectively, are caused by alterations in the efficiency of coupling, probably through the Gp proteins, between their respective receptors and the breakdown of polyphosphoinositides by phospholipase C. In addition, we propose that the sympathetic nervous system can regulate, through alterations in cAMP levels, the muscarinic stimulation of IP3 accumulation and contraction in the iris sphincter. These findings add further support to the hypothesis that there are reciprocal interactions between the cAMP and IP3-Ca2+ signaling systems and the contractile response in the iris smooth muscle.     

Blockade of sensory nerve mediated contraction of the rabbit iris sphincter by a series of novel tachykinin antagonists

Electrical stimulation of the isolated rabbit iris sphincter muscle in the presence of atropine gives rise to a contraction that can be blocked by tachykinin antagonists. The ability of a series of novel tachykinin antagonists to inhibit the contractile effect of SP on the guinea-pig taenia coli and to suppress the electrically evoked contraction of the atropinized rabbit iris sphincter was tested. Several of the novel antagonists were found to be more potent in terms of pA₂ and pIC₅₀ values than the two previously described analogs, [d-Pro², d-Trp^7,9]SP-(1–11) and [d-Arg¹, d-Trp^7,9, Leu¹¹]SP-(1–11) (Spantide). Apart from d-Trp in positions 7 and 9 the characteristic features of the potent novel antagonists were d-Cl₂Phe (or d-Cys(Bzl)) in position 5, Asn in position 6 and Nle in position 11. In addition Pal in position 3 seemed to offer an enhanced potency.     

Purification and characterization of protein kinase C from rabbit iris smooth muscle. Myosin light-chain phosphorylation in vitro and in intact muscle.

Protein kinase C of rabbit iris smooth muscle was purified by the sequential use of three chromatographic steps, i.e. anion-exchange (DEAE-cellulose), gel filtration (Sephadex G-150) and substrate affinity (protamine-agarose), and its properties were investigated by using as substrate myosin light-chain protein (MLC) isolated from the same tissue. The enzyme appeared as a single band on SDS/polyacrylamide-gel electrophoresis, with a molecular mass of approx. 80 kDa. Histone H-1 and iris muscle MLC, but not rabbit skeletal-muscle MLC, were effective substrates for the enzyme, with apparent Km values of 3.0 and 16.6 microM respectively. The enzyme, with MLC as substrate, had the following characteristics. (a) Its activity was dependent on Ca2+ and phosphatidylserine (PS). In the presence of Ca2+ and PS, diolein and phorbol dibutyrate (PDBu) increased its activity by 61 and 65% respectively. Half-maximal activation of the enzyme (Ka) occurred at 10 microM free Ca2+, and in the presence of diolein and PDBu the apparent Ka for Ca2+ was decreased to 3 microM and 2 microM respectively. (b) Studies on the relative potency of various cofactors in activating the enzyme revealed that PS, phorbol myristate acetate and 1-stearoyl-2-arachidonylglycerol were the most potent of the phospholipids, phorbol esters and diacylglycerols respectively. (c) H-7, a protein kinase C inhibitor, inhibited MLC phosphorylation in a dose-dependent manner, with 50% inhibition at 10 microM. (d) Addition of carbamoylcholine (for 1 min) or PDBu (for 25 min) to iris sphincter muscle prelabelled with [32P]Pi specifically increased MLC phosphorylation, and only the stimulatory effect of the muscarinic agonist was blocked by atropine. The data provide additional support for a role for protein kinase C in the contractile response of the iris smooth muscle.     

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.     

Induction of c-fos protein by activation of vasopressin receptors in smooth muscle cells

Stimulation of vasopressin (V1) receptors of rat aortic smooth muscle cells (A-10, ATCC CRL 1476) results in the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) to inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) with the mobilization of intracellular calcium. When A-10 cells are exposed to arginine vasopressin (AVP), there is an increase in the level of c-fos oncoprotein. The extent of induction of c-fos oncoprotein depends on both the time of exposure of the cells to AVP, reaching a maximum at 60 min after which there is a slow decline, and the concentration of AVP used, with an approximate EC50 of 1 nM which corresponds well with the Kd of vasopressin binding to these receptors. This vasopressin-mediated increase in c-fos protein level is inhibited by a V1/V2 antagonist (SKF 101498) suggesting that this is a receptor-mediated event. In addition dDAVP, a V2 selective agonist, is much less effective than AVP in inducing c-fos protein suggesting that AVP mediates its effect via V1 receptors. Desensitization of vasopressin receptors by prolonged exposure to AVP resulted in no additional induction of c-fos protein level in response to second challenge of AVP. In addition to AVP, phorbol dibutyrate (PDBu), an activator of protein kinase C (PKC), also stimulates the accumulation of c-fos protein although to a lesser extent than AVP. The above data suggest that c-fos protein levels in smooth muscle cells are regulated by AVP and the hormonal effect may be mediated through PI turnover and DAG, IP3 and Ca2+ signals.     

Direct Action of Light in Naturally Pigmented Muscle Fibers : I. Action spectrum for contraction in eel iris sphincter

Contraction due to light in excised eel irises appears to follow a simple first order law. The action spectrum for contraction has a maximum which agrees with the eel rhodopsin absorption maximum. Inasmuch as rhodopsin is the rod pigment-opsin complex and the iris sphincter pupillae evolves from the pigment epithelium of the retina in the region of the iris, the muscle pigment might be the same as the visual pigment. In the human eye the contraction of the iris sphincter is activated only by light incident on the retina and the pupil diameter varies inversely with the square root of the light intensity. The inverse first power relation observed in the present experiments suggests a more primitive origin for the light reaction in eel irises. Relaxation is a much slower process and can be approximated as the sum of two first order processes.     

杏仁内侧核注射AVP和AVPMcAb对家兔ET性发热效应的影响

目的和方法：在大脑杏仁内侧核微量注射精氨酸加压素（ＡＶＰ）和精氨酸加压素单克隆抗体（ＡＶＰＭｃＡｂ）,观察其对家兔内毒素（ＥＴ）性发热效应以及视前区一下丘脑前部（ＰＯＡＨ）温敏神经元放电活动的影响。结果：①杏仁内侧核微量注射ＡＶＰ能明显抑制家兔ＥＴ性发热效应,注射ＡＶＰＭｃＡｂ能明显易化家兔ＥＴ性发热效应;②杏仁外侧核分别注射ＡＶＰ和ＡＶＰＭｃＡｂ则对家兔ＥＴ性发热效应无明显影响;③杏仁内侧核分别注射ＡＶＰ和ＡＶＰＭｃＡｂ后ＰＯＡＨ热敏神经元和冷敏神经元放电活动均无明显变化。结论：家兔杏仁内侧核也是ＡＶＰ抗热效应的一个重要的作用部位,杏仁内侧核注射ＡＶＰ的抗热作用途径与隔区注射ＡＶＰ的抗热途径可能不同     

Ca2+ influx stimulated by vasopressin is mediated by phosphoinositide hydrolysis in rat smooth muscle cells

The mechanism of Ca2+ influx stimulated by arginine vasopressin (AVP) was studied in cultured rat smooth muscle cells. AVP stimulated 45Ca2+ influx even in the presence of nifedipine, a Ca2+ antagonist that inhibits voltage-dependent Ca2+ channel. NaF, a GTP-binding protein activator, mimicked the AVP-stimulated 45Ca2+ influx. The 45Ca2+ influx stimulated by a combination of AVP and NaF was not additive. The affinity of AVP receptor was decreased by guanosine 5'-O-(3-thiotriphosphate). Pertussis toxin failed to affect the AVP-stimulated 45Ca2+ influx. AVP did not stimulate cAMP production, but increased inositol trisphosphate generation. Both AVP-stimulated 45Ca2+ influx and inositol trisphosphate generation were inhibited by neomycin, a phospholipase C inhibitor, in a dose-dependent manner, and the patterns of both inhibitions were similar. These results suggest that, in rat smooth muscle cells, AVP-stimulated Ca2+ influx is mediated exclusively through phosphoinositide hydrolysis.     

Arginine vasotocin mRNA revealed by in situ hybridization in bovine pineal gland cells

Arginine vasopressin (AVP) is the main antidiuretic hormone in mammals and arginine vasotocin (AVT) in submammalian vertebrates. The possibility that the genetic material encoding AVT is maintained in mammals is controversial. In this study, we investigated by radioactive in situ hybridization the possible presence of the mRNA encoding AVP and AVT, and using immunocytochemistry the presence of structures immunoreactive for AVP and AVT in the bovine pineal gland. In situ hybridization was performed by use of ³⁵S-labelled oligoprobes. Immunocytochemistry was performed using specific polyclonal rabbit antibodies and the avidin-biotin-complex method. In situ hybridization revealed positive signals for both AVP mRNA and AVT mRNA in a few cells scattered throughout the pineal body. Immunocytochemistry revealed thin AVP-immunoreactive fibres in the pineal stalk and the pineal gland. It also revealed staining of several AVT-immunoreactive nerve fibres in both the pineal stalk and the gland. In addition, polyhedral, neuron-like cell bodies from which two to three processes emerged were also AVT-immunoreactive. Thus, our investigation shows the presence of AVP/AVT-immunoreactive cellular structures in the bovine pineal gland. Our data further show the presence of mRNAs encoding both AVT and AVP. We therefore suggest that AVT mRNA is translated into an AVT-like peptide in the bovine pineal.     

垂体后叶素和加压素对离体心肌的直接作用

本实验采用大鼠离体右心房和右心室肌条模型,观察了垂体后叶素和加压素对右心房和右心室肌的直接作用。结果表明:垂体后叶素对右心房的自主性收缩频率和幅度及右心室肌的收缩幅度均有剂量依赖性抑制作用;加压素对右心房和右心室肌收缩幅度也有剂量依赖性抑制作用,但对右心房自主节律无影响;催产素对右心房的收缩频率和幅度则均无影响。加压素V_1、V_2受体拮抗剂d(CH_2)_5Tyr(Me)AVP和d(CH_2)_5(D-Ile~2,Ile~4,Ala(NH_2)~9)AVP对垂体后叶素的负性变力作用具有不同程度的阻断作用,但对垂体后叶素的负性变时作用无阻断作用。以上结果提示,垂体后叶素的负性变力作用主要是由加压素产生的,加压素对心肌有直接的负性变力作用;垂体后叶素的负性变时作用可能是非加压素和催产素成分的作用结果。     

Role of arginine vasopressin in control of ACTH and LH release during stress

To determine the role of arginine vasopressin (AVP) in stress-induced release of anterior pituitary hormones, AVP antiserum or normal rabbit serum (NRS) was micro-injected into the 3rd ventricle of freely-moving, ovariectomized (OVX) female rats. A single 3 microliter injection was given, and 24 hours later, the injection was repeated 30 min prior to application of ether stress for 1 min. Although AVP antiserum had no effect on basal plasma ACTH concentrations, the elevation of plasma ACTH induced by ether stress was lowered significantly. Plasma LH tended to increase following ether stress but not significantly so; however, plasma LH following stress was significantly lower in the AVP antiserum-treated group than in the group pre-treated with NRS. Ether stress lowered plasma growth hormone (GH) levels and this lowering was slightly but significantly antagonized by AVP antiserum. Ether stress also elevated plasma prolactin (Prl) levels but these changes were not significantly modified by the antiserum. To evaluate any direct action of AVP on pituitary hormone secretion, the peptide was incubated with dispersed anterior pituitary cells for 2 hours. A dose-related release of ACTH occurred in doses ranging from 10 ng (10 p mole)-10 micrograms/tube, but there was no effect of AVP on release of LH. The release of other anterior pituitary hormones was also not affected except for a significant stimulation of TSH release at a high dose of AVP. The results indicate that AVP is involved in induction of ACTH and LH release during stress. The inhibitory action of the AVP antiserum on ACTH release may be mediated intrahypothalamically by blocking the stimulatory action of AVP on corticotropin-releasing factor (CRF) neurons and/or also in part by direct blockade of the stimulatory action of vasopressin on the pituitary. The effects of vasopressin on LH release are presumably brought about by blockade of a stimulatory action of AVP on the LHRH neuronal terminals.     

Arginine-vasopressin immunoreactive material in the gastrointestinal tract

Like many other neuropeptides, vasopressin is not confined to the hypothalamic neurohypophysial system. Furthermore, vasopressin was found to be a potent vasoconstrictor in the rat jejunum, reducing myenteric artery flow. These associations were the basis of this investigation on the presence of vasopressin in the gastrointestinal (GI) tract by both RIA and immunohistochemistry. Portions of the gastrointestinal tract and pancreatic islets of the rat were extracted with 0.1 N HCl for RIA measurements of AVP content. Similar portions from the male cat GI tract were used for immunohistochemistry studies. Acid extracts of the GI tract were found to contain immunoreactive AVP with the highest concentration (pg/mg protein) in the fundus portion of the stomach (15.0 +/- 1.6) and slightly lower values down along the antrum-pylorus portion (6.7 +/- 0.6), proximal jejunum (8.6 +/- 0.2), distal ileum (9.7 +/- 0.3) and colon (11.9 +/- 0.5). In the pancreatic islets the concentration was much higher (72.0 pg/mg protein). The extract inhibition curves showed parallelism with the appropriate standard preparation of AVP in the specific RIA. Immunohistochemical localization showed IR-AVP in the nerve fibers around the myenteric plexus of the second portion of the duodenum. It was also found in fibers starting from where the myenteric plexus goes through the layer of muscle fibers, penetrating the submucosa and duodenal mucosa, ending near the capillaries situated along the basal side of the villous epithelium cells. Similar IR-AVP activity was found in cells located in the mucosal epithelium of the duodenum, jejunum, ileum, colon and rectum.(ABSTRACT TRUNCATED AT 250 WORDS)