Central galanin stimulates pituitary prolactin secretion in rats: possible involvement of hypothalamic vasoactive intestinal polypeptide

The effect of galanin, a newly identified neuropeptide, on pituitary prolactin (PRL) secretion was examined in the rat. Intracerebroventricular (i.c.v.) injection of all 5 doses of galanin (0.4, 1, 2, 5 and 10 micrograms/rat) raised plasma PRL levels in urethane-anesthetized rats. Galanin injection (2 micrograms/rat, i.c.v.) also increased plasma PRL levels in conscious rats. The intermediate dose of galanin (2 micrograms/rat, i.c.v.) produced a greater response in plasma PRL levels than either smaller or larger doses of galanin. Intravenous injection of galanin did not affect plasma PRL levels. Passive immunization with specific anti-vasoactive intestinal polypeptide (VIP) rabbit serum suppressed plasma PRL response to galanin (2 micrograms/rat, i.c.v.) in anesthetized rats. These findings indicate that central galanin has a stimulatory role in pituitary PRL secretion via the hypothalamus in the rat and that VIP may be involved in rat PRL release induced by galanin.     

The stimulatory effect of a non-opiate beta-endorphin fragment on arginine-vasopressin release in rats

The effect of the non-opiate beta-endorphin (beta E) fragment 2-9 and related peptides on immunoreactive (IR) arginine8 -vasopressin (AVP) levels was studied in the rat eye plexus plasma. Additionally, the effect of beta E 2-9 on AVP release from pituitary neurointermediate lobes ( NILs ), in vitro was studied. IR AVP levels in the eye plexus plasma increased after subcutaneous (s.c.) injection of beta E 2-9. In female rats peak values were observed 2 min after the administration of beta E 2-9 (10 micrograms/rat). Male rats were 100 times more sensitive than female rats. A dose-response study revealed a U-shaped relationship for this effect of beta E 2-9 in animals of both sexes. From structure-activity studies it appeared that beta E 2-9 was the most effective fragment. Intracerebroventricular (i.c.v.) administration of beta E 2-9 did not affect the IR-AVP levels in eye plexus plasma. Moreover, AVP release from the rat NILs cells in vitro was stimulated by perfusion with beta E 2-9, indicating a direct effect of the peptide on the pituitary. Therefore we suggest that beta E 2-9 increases AVP release by a direct action on the posterior pituitary.     

The role of vasopressin in the nicotine-induced stimulation of ACTH and cortisol in men

Summary Experimental evidence indicates that arginine vasopressin (AVP) contributes to the release of ACTH under certain conditions. The present study investigates the role of vasopressin as a secretagogue of ACTH during cigarette smoking or nicotine infusion with additional injection of corticotropin releasing hormone (CRH) and using the specific AVP antagonist d(CH₂)₅Tyr(Me)-AVP. We first tested the effect of the AVP antagonist (10 g/kg body weight i.v.) on ACTH and cortisol release following cigarette smoking in 15 healthy young male smokers. Smoking led to marked increments in plasma nicotine and to a small rise in plasma ACTH and cortisol. Mean plasma ACTH and cortisol levels were at no time significantly altered by the antagonist. This might be due to a slight agonistic effect of the AVP antagonist, to high interindividual variability of the ACTH and cortisol responses after smoking or to a neglegible role of AVP in smoking-induced ACTH release. In a second study we performed the following tests in six healthy male non-smokers: (1) nicotine infusion (1.0 g/kg body weight per min); (2) CRH i.v. (100 g); (3) AVP antagonist i.v. (5 g/ kg); (4) nicotine infusion plus CRH i.v.; (5) nicotine infusion plus AVP antagonist i.v. ; (6) nicotine infusion plus CRH and AVP antagonist i.v.; and (7) sham infusion. Nicotine infusion led to greater increments of AVP, ACTH and cortisol than smoking without causing nausea. Peak nicotine levels after nicotine infusion were lower than after smoking. The AVP antagonist in the reduced dosage given alone had no effect on hormone levels. However, it slightly attenuated the effect of nico tite on ACTH and cortisol (P<0.05, ANOVA). Nicotine and CRH given together stimulated AACH and cortisol in a less than additive manner. The combined effect of nicotine and CRH was not inhibited by the antagonist. Our results indicate that the effect of nicotine on ACTH and cortisol may be partly mediated by hypothalamic AVP. Nicotine may also enhance CRH release by stimulating acetylcholine receptors of hypothalamic CRH neurons.Abbreviations ACTH adrenocorticotropic hormone - ANOVA analysis of variance - AVP arginin vasopressin - CRH corticotropin releasing hormone - K⁺a potassium; d (CH₂)₅ Tyr(Me)- - AVP vasopressin (V₁)-antagonist Supported by a grant from Forschungsrat Rauchen und Gesundheit     

Galanin stimulates the release of vasoactive intestinal polypeptide from perifused hypothalamic fragments in vitro and from periventricular structures into the cerebrospinal fluid in vivo in the rat

Intracerebroventricular injection of galanin (2 micrograms/rat) raised plasma prolactin (PRL) levels in the rat, which was accompanied by an increase in immunoreactive vasoactive intestinal polypeptide (VIP) in the cerebrospinal fluid (CSF). Immunoreactive VIP release from superfused rat hypothalamic fragments in vitro was dose-relatedly stimulated by galanin (10(-7) and 10(-8) M). PRL release from superfused rat anterior pituitary cells was stimulated by TRH (10(-8) M) but not affected by galanin (10(-7) to 10(-5) M). These findings indicate that central galanin has a stimulating role in the release of hypothalamic VIP, which results in pituitary PRL secretion in the rat.     

Vasopressin release during endotoxaemic shock in mice lacking inducible nitric oxide synthase

We tested the hypothesis that nitric oxide (NO) arising from the action of inducible nitric oxide synthase (iNOS) is responsible for the deficiency in vasopressin (AVP) release and consequent hypotension during endotoxaemic shock. Wild-type (WT) and iNOS knockout mice (iNOS^–/–) were given either saline or Escherichia coli lipopolysaccharide (LPS, 1.0 mg/kg i.v., final volume 0.03 ml). Mean arterial blood pressure (MAP) was measured and plasma AVP levels determined before and after LPS or saline injection. In WT mice, MAP was significantly lower 2 h after LPS administration and remained low for the remainder of the 6-h observation period. AVP plasma levels were increased at the 2nd and 4th h of the experiment, returning thereafter to basal levels. Conversely, LPS injection in iNOS iNOS^–/– mice elicited a sustained increase in plasma AVP concentration and attenuated the fall in blood pressure. These data indicate that NO arising from the iNOS plays an important inhibitory role in AVP release during endotoxaemia and may be responsible for the hypotension occurring during this vasodilatory shock.     

Effect of M35, a neuropeptide galanin antagonist on glucose uptake translated by glucose transporter 4 in trained rat skeletal muscle

In this study, we used M35, a galanin antagonist to explore the effect of an increase in galanin release induced by exercise on glucose transporter 4 (GLUT4) content and function. The rats tested were divided into four groups: rats from sedentary and trained drug groups were injected by M35, 5 times per week during four weeks. Rats from sedentary and trained control groups by 0.1 mol/l citrate buffer. The rats from both exercise groups swam after each injection. The results showed that M35 significantly decreased glucose infusing speeds in euglycemic–hyperinsulinemic clamp tests. M35 treatment elevated plasma insulin levels in both drug groups. And the insulin levels in both drug groups were higher also than that after experiments in each control group respectively. The four weeks swimming enhanced the plasma galanin contents. The galanin levels after experiments in both exercise groups were higher than that in each sedentary control group respectively too. The GLUT4 densities were attenuated by M35 at plasma membranes and total cell membranes. The change ratios of GLUT4 immunoreaction at plasma membranes to total cell membranes were lower in both drug groups compared to each control group. Those results suggest that endogenous galanin has an important attribute to elevate the insulin sensitivity by increasing GLUT4 contents and promoting GLUT4 transportation from intracellular membranes to plasma membranes in muscle cells. Galanin is an important hormone to elevate insulin sensitivity in rest and exercise conditions.     

Sensory neuropeptide interactions in the production of plasma extravasation in the rat.

We used an experimental model of neurogenic inflammation to study the contribution of the primary afferent peptides substance P, calcitonin gene-related peptide, galanin and somatostatin to plasma extravasation in rat synovium. Perfusion of the C-fiber excitotoxin, capsaicin (1.6 mM), through the knee joint of the pentobarbital anesthetized rat, increased plasma extravasation transiently (< 30 min). Perfusion of substance P (1 microM) or calcitonin gene-related peptide (100 nM), two primary afferent neuropeptides that are released by acute capsaicin administration, had no significant effect on plasma extravasation. Co-perfusion of these two neuropeptides, however, evoked an increase in plasma extravasation that was greater than that produced by capsaicin remaining above 250% of the baseline level by the end of the perfusion period (55 min). Capsaicin co-perfused with either galanin (100 nM) or somatostatin (1 microM) failed to increase plasma extravasation. Neither galanin nor somatostatin significantly affected increase in plasma extravasation induced by co-perfusion of substance P plus calcitonin gene-related peptide. Therefore, we suggest that galanin and somatostatin inhibit, presynaptically, the release of substance P and calcitonin gene-related peptide from primary afferent terminals. The interactions among these four neuropeptides provide a novel mechanism for the regulation of primary afferent neurogenic inflammation.     

Involvement of substance P in hyperalgesia induced by intrathecal galanin.

Previously we have demonstrated that an intrathecal injection of galanin (GAL) decreases the nociceptive threshold for mechanical stimulation without effect on thermal nociceptive responses. The present experiments were conducted to determine whether substance P (SP) would be involved in such a decrease in the nociceptive threshold produced by GAL. An intrathecal injection of anti-SP monoclonal antibody inhibited the nociceptive threshold-decreasing effect of intrathecal GAL (0.1 nmol/rat). This antibody significantly suppressed the contractile action of SP (3 nM) on the longitudinal muscle and that of neurokinin A (3 nM) to a lesser degree. Binding of [125I]Tyr8-SP to this antibody was inhibited by SP in a concentration-dependent manner in the range 0.1-33 nM without suppression by GAL at a concentration of 3300 nM. In addition, an intrathecal injection of the anti-SP monoclonal antibody increased the nociceptive threshold for mechanical stimulation in carrageenin-inflamed rats without effect on thermal nociceptive behaviors. The capsaicin (0.5 microM)-evoked release of immunoreactive SP from dorsal-half slices of the spinal cord was increased by galanin (1 microM, but not 0.1 microM) without effects on basal release. An intrathecal injection of GAL did not produce aversive responses (biting, licking and scratching) at doses of 0.1 and 1 nmol/rat. GAL (0.1 nmol/rat) did not affect biting/licking behaviors evoked by SP (1 nmol/rat), but inhibited SP-evoked scratching behavior. These results suggest that the nociceptive threshold-decreasing action of intrathecal GAL is at least in part mediated by SP, and that GAL may act on primary afferent terminals to increase the release of SP evoked by stimulation.     

Central nitric oxide blocks vasopressin, oxytocin and atrial natriuretic peptide release and antidiuretic and natriuretic responses induced by central angiotensin II in conscious rats

The presence of nitric oxide synthase (NOS), the enzyme that catalyses the formation of nitric oxide (NO), in the circumventricular organs and magnocellular neurones suggests an important role of NO in the modulation of vasopressin (AVP) and oxytocin (OT) release. Intracerebroventricular (I.C.V.) injection of angiotensin II (Ang II) stimulates the release of AVP, OT and atrial natriuretic peptide (ANP), with the resultant antidiuretic and natriuretic effects. This study investigated the interaction between nitrergic and angiotensinergic pathways on the release of AVP, OT and ANP and on urinary volume and sodium excretion in water-loaded rats. Unanaesthetized, freely moving, male Wistar rats received two water loads followed by an injection into the lateral ventricle of an inhibitor of NOS (L-NAME), a NO donor [3-morpholinylsydnoneimine chloride (SIN-1) or S-nitroso-N-acetyl penicillamine (SNAP)] or vehicle (isotonic saline) and, 20 min after, they received a second I.C.V. injection of Ang II or vehicle. Injections of L-NAME or Ang II produced an increase in plasma levels of AVP, OT and ANP, a reduction in urinary volume and an increase in sodium excretion. Pretreatment with L-NAME enhanced the Ang II-induced increase in AVP, OT and ANP release, as well as the antidiuresis and natriuresis. Injection of SIN-1 or SNAP did not modify hormonal plasma levels and urinary parameters. In contrast SNAP blocked the AVP, OT and ANP release, as well as antidiuretic and natriuretic responses induced by ANG-II. Thus, the central nitrergic system can act to inhibit AVP, OT and ANP secretion and the antidiuretic and natriuretic effects in response to Ang II.     

Plasma vasopressin in ethanol intoxication and hangover.

The effect of ethanol intoxication and hangover on immunoreactive plasma arginine vasopressin (AVP) concentration was studied in 7 healthy supine men in controlled clinical conditions. In 6 subjects plasma AVP increased above control values at the time of maximal blood ethanol concentration. The highest AVP values were observed in the subjects having nausea and vomiting and the worst hangover symptoms. During hangover plasma AVP values were higher than the controls and the response of plasma AVP to upright posture was exaggerated. The dissociation of plasma AVP concentration and ethanol diuresis suggested that the suppression of AVP release is not the sole determinant of ethanol diuresis. The study may indicate that the toxic effects of ethanol and the severity of hangover symptoms are associated with the state of hydration and individual sensitivity of AVP triggering mechanisms.     

Plasma vasopressin in ethanol intoxication and hangover

The effect of ethanol intoxication and hangover on immunoreactive plasma arginine vasopressin (AVP) concentration was studied in 7 healthy supine men in controlled clinical conditions. In 6 subjects plasma AVP increased above control values at the time of maximal blood ethanol Concentration. The highest AVP values were observed in the subjects having nausea and vomiting and the worst hangover symptoms. During hangover plasma AVP values were higher than the controls and the response of plasma AVP to upright posture was exaggerated. The dissociation of plasma AVP concentration and ethanol diuresis suggested that the suppression of AVP release is not the sole determinant of ethanol diuresis. The study may indicate that the toxic effects of ethanol and the severity of hangover symptoms are associated with the state of hydration and individual sensitivity of AVP triggering mechanisms.     

Synergistic interaction of corticotropin releasing factor and arginine vasopressin on adrenocorticotropin and cortisol secretion in Macaca fuscata

Plasma immunoreactive CRF measured by radioimmunoassay decreased rapidly after intravenous injection of synthetic ovine corticotropin releasing factor (CRF) and showed a bi-exponential decay curve in five macaca fuscatas. Half lives of plasma immunoreactive CRF were 5.8 +/- 1.4 (Mean +/- SEM) min for the fast component and 38.3 +/- 2.4 min for the slow component. A bolus injection of 5 micrograms/kg CRF significantly increased the plasma cortisol level. CRF at 5 micrograms/kg induced a delayed response of ACTH and cortisol. Arginine vasopressin (AVP) at 0.5 micrograms/kg induced a slight increase in plasma ACTH and cortisol, but AVP at 0.1 micrograms/kg evoked no significant increase. When 0.5 micrograms/kg CRF and 0.1 micrograms/kg AVP were administered simultaneously, significant ACTH and cortisol responses occurred. The results indicate that CRF and AVP act synergistically to stimulate ACTH secretion in vivo.     

Inhibition of vasopressin and aldosterone release by atrial natriuretic peptide in conscious rabbits.

To elucidate the regulatory role of atrial natriuretic factor (ANF) on vasopressin (AVP) and aldosterone release in conscious rabbits, ANF was administered systematically at a rate of 15 pmol min-1 (kg body wt)-1 for 15 min in two series of experimental animals in which AVP and/or aldosterone production was stimulated. In euhydrated rabbits (series I), systemic administration of angiotensin II (Ang II) (10 pmol min-1 (kg body wt)-1, 15 min) stimulated aldosterone release threefold from basal plasma concentrations (140 pg ml-1). The co-application of ANF inhibited the Ang II-induced release of aldosterone without influencing the non-stimulated AVP system. In dehydrated rabbits (series II) with elevated plasma osmolality and AVP concentration, exogenously applied ANF increased plasma ANF fourfold at marginally reduced arterial pressure. Plasma AVP concentrations were reduced by 3.4 pg ml-1 (25%) on average, and plasma aldosterone concentrations were lowered by 34 pg ml-1 (23%) at unchanged levels of plasma corticosterone. Receptor binding studies using [125I]ANF as radioligand revealed Ang II-independent high-affinity receptors for ANF in the zona glomerulosa of the adrenal gland. With regard to the hypothalamo-neurohypophyseal AVP system, ANF binding sites were localized to the median eminence and neurohypophysis, but not to the magnocellular nuclei. ANF receptors were also labelled in structures lacking a blood-brain barrier such as the subfornical organ and the choroid plexus.     

Vasopressin-mediated blood pressure response to intraventricular injection of angiotensin II in the rat

1. The role of stimulation of argininevasopressin (AVP) release in the blood pressure (BP) response to intracerebroventricular (ivt) injection of angiotensin II (AII) was investigated.
2. Ivt injection of AII to normal Long-Evans (LE) rats, which were conscious and unrestrained, induced a dose-related increase of BP in close correlation with the rise of plasma AVP concentrations (r=0.93;y=34.0 log X-14.4). This regression line crossed the X-axis at plasma AVP concentrations found under control conditions.
3. In comparison with the correlation obtained after intravenous injection of AVP (r=0.99;y=35.6 log X-46.9), the correlation between BP increase and plasma AVP after ivt AII exhibited a parallel shift to the left by a factor of 7.5.
4. When 0.5 ml of a specific AVP antiserum was injected intravenously, the BP response to subsequent ivt injection of AII was completely blocked in 2 of 7 rats tested and reduced by 50% or more in the other 5 rats.
5. In Brattleboro rats homozygous for hereditary hypothalamic diabetes insipidus (DI), in which plasma AVP remained undetectable after ivt AII, BP response was reduced by 50–80% in comparison with the response in LE rats. Drinking response, however, was not altered. During spontaneous drinking, DI rats showed a BP increase of similar magnitude as that after the highest dose of ivt AII.
6. We conclude that a close relationship exists in normal LE rats between the rise of BP and of plasma AVP after ivt AII; this correlation represents a cause-effect relationship, since after the intravenous injection of AVP antiserum the BP response to ivt AII is markedly or completely blocked; and sensitization to the vasopressor effect of AVP occurs after ivt AII. The BP increase observed in unrestrained DI rats after ivt AII as well as during spontaneous drinking might be related to a general arousal reaction which would be insignificant in normal LE rats.

     

Negligible role of catecholaminergic receptors in the anteroventral third ventricular region in mediating vasopressin-releasing and cardiovascular actions of prostaglandin E2

The aim of this study was to pursue the roles of the catecholamine receptors in the anteroventral third ventricular region (AV3V), a cerebral site engaged in various stress responses, in prostaglandin (PG) E₂-evoked vasopressin (AVP) release and cardiovascular action. Experiments were conducted in conscious rats in which cerebral and vascular cannulae had been implanted chronically. Local infusion (0.5 μl, 1 min) of dopamine (150 nmol), a D₁-dopaminergic agonist SKF 38393 (17 nmol) and an α-adrenergic agonist phenylephrine (150 nmol), as well as PGE₂ (7 nmol), into the AV3V enhanced plasma AVP 5 min later, without affecting plasma osmolality and electrolytes. In contrast to the increases in both arterial pressure and heart rate observed when PGE₂ was applied, dopamine and SKF 38393 did not affect these variables, and phenylephrine elevated only arterial pressure. The AV3V infusion of a β-agonist isoproterenol (100 nmol) did not change plasma AVP, although it decreased arterial pressure and increased heart rate. The increase in plasma AVP by dopamine was not blocked by the preinfusion of the D₂-antagonist sulpiride (13 nmol) into the AV3V 10 min before, but was abolished by that of the D₁-antagonist SCH-23390 (8 nmol). The effects of phenylephrine on both plasma AVP and the blood pressure were prevented by the preadministration of the α-antagonist phenoxybenzamine (13 nmol). However, the pretreatments with phenoxybenzamine, sulpiride or SCH 23390 did not inhibit the responses of AVP, arterial pressure and heart rate caused by PGE₂. These antagonists were without significant effect on AVP and other variables when given alone. The infusion sites of PGE₂ and the other drugs identified histologically included the AV3V structures such as the organum vasculosum laminae terminalis or its vicinity, median preoptic nucleus, medial preoptic nucleus and periventricular hypothalamic nucleus. Dopamine or phenylephrine administered into the cerebral ventricle at the same dose as used in the AV3V application did not exert a significant effect on plasma AVP, arterial pressure and heart rate. These results suggest that catecholamine receptors in the AV3V may not be involved in the AVP-secreting, tachycardiac and pressor responses evoked by topical action of PGE₂ on this area, despite their ability to influence hormone release and cardiovascular function. Received: 3 November 1998 / Accepted: 7 July 1999     

Arginine vasopressin metabolism in dogs. I. Evidence for a receptor-mediated mechanism.

The plasma clearance rates (PCR) of arginine vasopressin (AVP), and iodinated AVP (125I-AVP) were determined after pulse injection in conscious water-loaded dogs. Both the PCR and the apparent initial volume of distribution were significantly greater for AVP than for the biologically inactive iodinated AVP 37.4 +/- 4.8 ml/kg per min vs. 6.7 +/- 0.8 ml/kg per min (P less than 0.001) and 12.7 +/- 0.9% body wt vs. 7.1 +/- 0.4% body wt (P less than 0.001). AVP clearance was then determined by the constant-infusion technique at doses that produced equilibrium AVP concentrations within and above the physiological range. AVP-PCR was 37.4 +/- 7.1 ml/kg per min at 34 microU/kg per min, which was comparable to that after pulse injection (P less than 0.9). AVP clearance fell progressively, and urine osmolality progressively increased with increasing AVP infusion rates to plateau values at 136 microU/kg per min; a strong negative correlation was observed between mean AVP-PCR and urine osmolality (r = -0.993). The data suggest a relationship between the biological activity of AVP and its clearance. It is proposed that plasma membrane receptors may mediate a portion of the metabolic clearance of AVP.     

Effects of steady-state plasma vasopressin levels on the distribution of intrarenal blood flow on electrolyte excretion.

1. In order to evaluate the effects of arginine vasopressin (AVP) on the distribution of intrarenal blood flow and on electrolyte excretion, steady-state plasma AVP levels (4-8, 19-1, 44-3, and 100-6 micro u./ml.) were produced in anaesthetized dogs, which were hydrated to minimize endogenous anti-diuretic hormone (ADH) release. 2. The urinary excretion of sodium and potassium increased without change in their filtered loads during AVP infusion. 3. Measurement by the 133xenon washout method revealed diphasic blood flow shifts, as a function of the plasma AVP level, between compartment 1 (outer cortex) and compartment 2 (inner cortex and outer medulla) without change in compartment 3 (inner medulla). 4. In a separate study, the radioactive microsphere (15 micronm) method was used with a plasma AVP levels of 19-8 micronu./ml. Blood flow (expressed as % flow/g tissue) decreased in the outer cortex and increased in the inner cortex. 5. Total renal blood flow did not change during infusion of AVP. However, the values measured by 133xenon were lower than those measured by the microsphere method. 6. There was agreement between these two independent methods that blood flow shifted from outer to inner cortex, with no change in total renal flow, at similar plasma AVP levels (19-1 and 19-8 micronu./ml.). The relationship of these intrarenal circulatory changes to the increased electrolyte excretion is discussed.     

精氨酸加压素在内毒素热限形成中的作用

本文观察了家兔静脉注射不同剂量ＥＴ后中隔区，下丘脑组织及血浆中ＡＶＰ含量的变化。结果显示：在ＥＴ发热过程中，中隔区，下丘脑及血浆ＡＶＰ含量均显著增多（Ｐ＜０．０１）；ＥＴ发热达热限时，体温不再升高，中隔区与血浆ＡＶＰ含量也不再增多，且中隔区及血浆ＡＶＰ含量变化与体温变化呈明显正相关（ｒ＝０．９８４，０．０５＜Ｐ＜０．０１；ｒ＝０．９９４，Ｐ＜０．０１）；此时，下丘脑升高的ＡＶＰ含量开始下降（Ｐ０。     

Glucocorticoid modulation of atrial natriuretic peptide, oxytocin, vasopressin and Fos expression in response to osmotic, angiotensinergic and cholinergic stimulation

The regulation of fluid and electrolyte homeostasis involves the participation of several neuropeptides and hormones that utilize hypothalamic cholinergic, alpha-adrenergic and angiotensinergic neurotransmitters and pathways. Additionally, it has been suggested that hypothalamus-pituitary-adrenal axis activity modulates hormonal responses to blood volume expansion. In the present study, we evaluated the effect of dexamethasone on atrial natriuretic peptide (ANP), oxytocin (OT) and vasopressin (AVP) responses to i.c.v. microinjections of 0.15 M and 0.30 M NaCl, angiotensin-II (ANG-II) and carbachol. We also evaluated the Fos protein immunoreactivity in the median preoptic (MnPO), paraventricular (PVN) and supraoptic (SON) nuclei. Male Wistar rats received an i.p. injection of dexamethasone (1 mg/kg) or vehicle (0.15 M NaCl) 2 h before the i.c.v. microinjections. Blood samples for plasma ANP, OT, AVP and corticosterone determinations were collected at 5 and 20 min after stimulus. Another set of rats was perfused 120 min after stimulation. A significant increase in plasma ANP, OT, AVP and corticosterone levels was observed at 5 and 20 min after each central stimulation compared with isotonic saline-injected group. Pre-treatment with dexamethasone decreased plasma corticosterone and OT levels, with no changes in the AVP secretion. On the other hand, dexamethasone induced a significant increase in plasma ANP levels. A significant increase in the number of Fos immunoreactive neurons was observed in the MnPO, PVN and SON after i.c.v. stimulations. Pre-treatment with dexamethasone induced a significant decrease in Fos immunoreactivity in these nuclei compared with the vehicle. These results indicate that central osmotic, cholinergic, and angiotensinergic stimuli activate MnPO, PVN and SON, with a subsequent OT, AVP, and ANP release. The present data also suggest that these responses are modulated by glucocorticoids.     

Spantide II, a novel tachykinin antagonist, and galanin inhibit plasma extravasation induced by antidromic C-fiber stimulation in rat hindpaw.

The effect of intradermal injection of Spantide II, a novel tachykinin antagonist, and the neuropeptide galanin on neurogenic plasma extravasation induced by antidromic stimulation of C-fibers in the sciatic nerve was examined in the hindpaws of rats. Activation of C-fibers by antidromic sciatic nerve stimulation (2 Hz, 5 min) consistently evoked a localized plasma extravasation of Evans Blue in the skin area of the hindpaw innervated by the sciatic nerve. Intradermal injection of 3 nmol Spantide II significantly inhibited this response. The plasma extravasation was nearly totally abolished when the concentration of Spantide II was increased to 9 nmol. Intradermal injection of 1.5 and 15 nmol galanin also inhibited plasma extravasation. Intradermal injection of 9 nmol Spantide II effectively blocked the plasma extravasion in the hindpaw induced by 8 nmol intravenous substance P. Plasma extravasation induced by intravenous substance P was also inhibited by the higher, but not by the lower, dose of galanin injected intradermally. The present results indicate that Spantide II, a potent non-toxic tachykinin antagonist, effectively blocks the neurogenic plasma extravasation induced by antidromic C-fiber stimulation, thus supporting the view that tachykinins play an important role in this neurogenic inflammatory process. It is further shown that galanin, a naturally occurring neuropeptide present in primary afferents, also inhibits C-fiber activation-evoked plasma extravasation, indicating an interaction between galanin and tachykinins in the peripheral terminals of primary afferents, possibly through both pre- and postsynaptic mechanisms.