Enhanced phosphoinositol hydrolysis in response to vasopressin in the septum of the homozygous Brattleboro rat

Vasopressin and angiotensin receptors of the medial septal area in the control of mean arterial pressure induced by vasopressin

Introduction. Brain arginine 8-vasopressin (AVP), through the V1a- and V2-receptors, is essential for the maintenance of mean arterial pressure (MAP). Central AVP interacts with the components of the renin-angiotensin system, which participate in MAP regulation. This study aimed to determine the effects of V1a-, V2- and V1a/V2-AVP selective antagonists and AT1- and AT2-angiotensin II (Ang II) selective antagonists on the MAP induced by AVP injected into the medial septal area (MSA) of the brain.

Materials and methods. Male Holtzman rats with stainless steel cannulae implanted into the MSA were used in experiments. Direct MAP was recorded in conscious rats.

Results. AVP administration into the MSA caused a prompt and potent pressor response in a dose-dependent fashion. Pretreatment with the V1a- and V2-antagonists reduced, whereas prior injection of the V1a/V2-antagonist induced a decrease in the MAP that remained below the baseline. Both AT 1- and AT2-antagonists elicited a decrease, while simultaneous injections of two antagonists were more effective in decreasing the MAP induced by AVP.

Conclusion. These results indicate there is a synergism between the V1a- and V2-AVP and AT1and AT2-Ang II receptors in the MSA in the regulation of MAP.

Interaction between arginine vasopressin and angiotensin II receptors in the central regulation of sodium balance

We speculated that the influence of lateral preoptic area (LPO) in sodium balance, involves arginine8-vasopressin (AVP) and angiotensin (ANG II) on Na+ uptake in LPO. Therefore, the present study investigated the effects of central administration of specific AVP and ANG II antagonists (d(CH2)5-Tyr (Me)-AVP (AAVP) and [Adamanteanacetyl1, 0-ET-d-Tyr2, Val4, Aminobutyryl6, Arg(8,9)]-AVP (ATAVP) antagonists of V1 and V2 receptors of AVP. Also the effects of losartan and CGP42112A (selective ligands of the AT1 and AT2 angiotensin receptors, respectively), was investigated on Na+ uptake and renal fluid and electrolyte excretion. After an acclimatization period of 7 days, the animals were maintained under tribromoethanol (200 mg/kg body weight, intraperitonial) anesthesia and placed in a Kopf stereotaxic instrument. Stainless guide cannula was implanted into the LPO. AAVP and ATAVP injected into the LPO prior to AVP produced a reduction in the NaCl intake. Both the AT1 and AT2 ligands administered into the LPO elicited a decrease in the NaCl intake induced by AVP injected into the LPO. AVP injection into the LPO increased sodium renal excretion, but this was reduced by prior AAVP administration. The ATAVP produced a decreased in the natriuretic effect of AVP. The losartan injected into LPO previous to AVP decreased the sodium excretion and the CGP 421122A also decreased the natriuretic effect of AVP. The AVP produced an antidiuresis effect that was inhibited by prior administration into LPO of the ATAVP. The AAVP produced no change in the antidiuretic effect of AVP. These results suggest that LPO are implicated in sodium balance that is mediated by V1, V2, AT1 and AT2 receptors.

Influence of arginine vasopressin receptors and angiotensin receptor subtypes on the water intake and arterial blood pressure induced by vasopressin injected into the lateral septal area of the rat

In this study we investigated the influence of d(CH2)5-Tyr(Me)-[Arg8]vasopressin (AAVP) and [adamanteanacetyl1,0-ET-d-Tyr2,Val4,aminobutyryl6,Arg8,9]-[Arg8]vasopressin (ATAVP), which are antagonists of vasopressin V1 and V2 receptors, and the effects of losartan, a selective angiotensin AT1 receptor antagonist, and CGP42112A, a selective AT2 receptor antagonist, injected into the lateral septal area (LSA) on thirst and hypertension induced by [Arg8]vasopressin (AVP). AAVP and ATAVP injected into the LSA reduced the drinking responses elicited by injecting AVP into the LSA. Both the AT1 and AT2 ligands administered into the LSA elicited a concentration-dependent decrease in the water intake induced by AVP injected into the LSA, but losartan was more effective than CGP42112A. The increase in MAP, due to injection of AVP into the LSA, was reduced by prior injection of AAVP from 18 +/- 1 to 6 +/- 1 mm Hg. Losartan injected into the LSA prior to AVP reduced the increase in MAP to 7 +/- 0.8 mm Hg. ATAVP and CGP42112A produced no changes in the pressor effect of AVP. These results suggest that the dipsogenic effects induced by injecting AVP into the LSA were mediated primarily by AT1 receptors. However, doses of losartan were more effective when combined with CGP42112A than when given alone, suggesting that the thirst induced by AVP injections into LSA may involve activation of multiple AVP and angiotensin II receptor subtypes. The pressor response of AVP was reduced by losartan and by AAVP. CGP42112A and ATAVP did not change the AVP pressor response. These results suggest that facilitator effects of AVP on water intake are mediated through the activation of V1 receptors and that the inhibitory effect requires V2 receptors. The involvement of AT1 and AT2 receptors can be postulated. Based on the present findings, we suggest that the AVP in the LSA may play a role in the control of water and arterial blood pressure balance.

Effects of V1 and angiotensin receptor subtypes of the paraventricular nucleus on the water intake induced by vasopressin injected into the lateral septal area

In this study, we investigated the influence of d(CH(2))(5)-Tyr (Me)-AVP (AAVP) an antagonist of V(1) receptors of arginine(8)-vasopressin (AVP) and the effects of losartan and CGP42112A (selective ligands of the AT(1) and AT(2) angiotensin receptors, respectively) injections into the paraventricular nucleus (PVN) on the thirst effects of AVP stimulation of the lateral septal area (LSA). AVP injection into the LSA increased the water intake in a dose-dependent manner. AAVP injected into the PVN produced a dose-dependent reduction of the drinking responses elicited by LSA administration of AVP. Both the AT(1) and AT(2) ligands administered into the PVN elicited a concentration-dependent inhibition in the water intake induced by AVP injected into the LSA, but losartan was more effective than CGP42112A the increase in the AVP response. These results indicate that LSA dipsogenic effects induced by AVP are mediated primarily by PVN AT(1) receptors. However, doses of losartan were more effective when combined with CGP42112A than when given alone, suggesting that the thirst induced by AVP injections into LSA may involve activation of multiple angiotensin II (ANG II) receptor subtypes. These results also suggests that facilitatory effects of AVP on water intake into the LSA are mediated through the activation of V(1)-receptors and that the inhibitory effect requires V(2)-receptors. Based on the present findings, we suggest that the administration of AVP into the LSA may play a role in the PVN control of water control.

Differential expression of vasopressin V1a and V1b receptors mRNA in the brain of renin transgenic TGR(mRen2)27 and Sprague-Dawley rats

Recent evidence indicates that renin transgenic rats TGR(mRen2)27 (TGR) manifest increased activity of the central vasopressinergic system. Because one of the reasons for this finding could be an increased synthesis of vasopressin receptors, we determined in the present study expression of V1a and V1b vasopressin receptors (R) mRNA in the brain of TGR rats and of their parent Sprague-Dawley (SD) strain. Competitive PCR method was applied for quantitative analysis of V1a and V1b receptors mRNA in the preoptic, diencephalic, mesencephalopontine and medullary regions. V1aR mRNA expression was similar in SD and TGR rats in the preoptic, diencephalic and mesencephalopontine regions. In the medullary region expression of V1aR mRNA was significantly lower in TGR than in SD rats. V1bR mRNA did not differ in TGR and SD rats in the preoptic, diencephalic and medullary region whereas it was significantly elevated in the mesencephalopontine region. The results provide evidence for differential regulation of V1a and V1b receptors genes in the brain stem of TGR rats that is manifested by downregulation of V1aR mRNA in the medulla and upregulation of V1bR mRNA in the mesencephalopontine region.

Steroid hormone regulation of vasopressinergic neurotransmission in the central nervous system

Vasopressinergic neurotransmission is intimately linked to steroid hormone signaling. Both arginine vasopressin (VP) and the extrahypothalamic VP V1a receptors are regulated by steroid hormones. Here, we present work that has been done in our laboratory, investigating mechanisms underlying steroid hormone effects on the expression of both VP and its primary receptor in the brain, the VP V1a receptor. Data on VP receptors, their coupling to second messenger pathways, their localization in brain, and their regulation by peptide exposure are discussed. We also cover the regulation of the V1a receptor by adrenal hormones, and the molecular basis of this effect. Evidence for the existence of other receptors for VP in the brain is presented. Lastly, the regulation of the VP peptide by gonadal hormones is discussed at the transcriptional level in the rodent brain. Finally, the potential significance of the 'cross-talk' between the vasopressinergic system and the steroid hormone system is addressed.

Behavioral consequences of intracerebral vasopressin and oxytocin: focus on learning and memory

Since the pioneering work of David de Wied and his colleagues, the neuropeptides arginine vasopressin and oxytocin have been thought to play a pivotal role in behavioral regulation in general, and in learning and memory in particular. The present review focuses on the behavioral effects of intracerebral arginine vasopressin and oxytocin, with particular emphasis on the role of these neuropeptides as signals in interneuronal communication. We also discuss several methodological approaches that have been used to reveal the importance of these intracerebral neuropeptides as signals within signaling cascades. The literature suggests that arginine vasopressin improves, and oxytocin impairs, learning and memory. However, a critical analysis of the subject indicates the necessity for a revision of this generalized concept. We suggest that, depending on the behavioral test and the brain area under study, these endogenous neuropeptides are differentially involved in behavioral regulation; thus, generalizations derived from a single behavioral task should be avoided. In particular, recent studies on rodents indicate that socially relevant behaviors triggered by olfactory stimuli and paradigms in which the animals have to cope with an intense stressor (e.g., foot-shock motivated active or passive avoidance) are controlled by both arginine vasopressin and oxytocin released intracerebrally.

Microdialysis administration of vasopressin into the septum improves social recognition in Brattleboro rats

The role of septal arginine vasopressin (AVP) in a social recognition test was investigated in both homozygous Brattleboro (HO-DI) and normal Long-Evans rats. To do this, the duration of investigation of conspecific juveniles by untreated adult males of both rat strains was measured before and after inter exposure intervals of 30 and 120 min. Additionally, a microdialysis administration technique was used to administer synthetic AVP (0.2 or 2.0 ng) or its V1 receptor antagonist d(CH2)5Tyr(Me)AVP (5.0 ng) into the mediolateral septum concomitantly with the behavioral test. Untreated HO-DI rats showed an impaired social recognition compared with untreated Long-Evans rats. A similarly impaired performance was observed after V1 receptor antagonist treatment of Long-Evans rats. Microdialysis administration of synthetic AVP, on the other hand, significantly improved social recognition in both rat strains. The data suggest that endogenous AVP in the septal brain area is critically involved in the acquisition, storage, and/or recall of olfactory cues in rats.

Arginine vasopressin V1-antagonist and atrial natriuretic peptide reduce hemorrhagic brain edema in rats

BACKGROUND AND PURPOSE

Injection of arginine vasopressin into the cerebral ventricles in animals with brain injury increased brain water, whereas injection of atrial natriuretic peptide reduced water content. Therefore, to determine the role of endogenous arginine vasopressin in brain edema, we attempted to inhibit edema from a hemorrhagic lesion with an arginine vasopressin V1 receptor antagonist or atrial natriuretic peptide.

METHODS

Adult Sprague-Dawley rats with hemorrhages induced by 0.4 IU bacterial collagenase were treated with 75 ng (n = 9) or 8 micrograms (n = 9) of the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)Arg, 3.2 micrograms (n = 4) atrial natriuretic peptide injected intracerebrally, or 5 micrograms/kg per hour (n = 7) atrial natriuretic peptide intraperitoneally. They were compared with control groups injected with 0.4 IU collagenase only. Brain water and electrolytes were measured 24 hours later. Brain uptake of [14C]sucrose was measured 30 minutes after lesions were induced by 0.4 IU collagenase alone (n = 5) or after collagenase injection and 50 micrograms/kg per hour (n = 5) atrial natriuretic peptide injected intravenously.

RESULTS

The arginine vasopressin V1 receptor antagonist and atrial natriuretic peptide significantly (p < 0.05) reduced water and sodium contents in the posterior edematous regions. Brain uptake of [14C]sucrose was significantly reduced by intravenous atrial natriuretic peptide.

CONCLUSIONS

Antagonists to arginine vasopressin V1 receptors and atrial natriuretic peptide both significantly reduce hemorrhagic brain edema, and atrial natriuretic peptide appears to protect the blood-brain barrier.

Effect of vasopressin administration and deficiency upon 3H-AVP binding sites in the CNS and periphery during development

Arginine8-vasopressin (AVP, 40 micrograms/100 g b.wt., SC) was administered to male Long-Evans (LE) pups from day 1 to 7 of life and the pups were sacrificed on day 8 or 60. 3H-AVP binding was performed on membranes prepared from the liver, kidney, and septum. No significant changes were observed in the kidney or septum of animals 8 or 60 days old. However, the chronic AVP treatment did result in a significant increase in the density of 3H-AVP binding sites in the liver when compared to control day 8 pups (control 44 +/- 2 vs. AVP 56 +/- 3 fmol/mg protein), with no change in affinity. This effect was maintained into adulthood, as the day 60 AVP-treated LE rats also showed a significant increase in liver 3H-AVP binding sites compared to control (control 186 +/- 9 vs. AVP 239 +/- 14 fmol/mg protein), with no change in affinity. A comparison of 3H-AVP binding sites in 8-day-old LE, heterozygous Brattleboro (HET-BB), and homozygous Brattleboro rats (HOM-BB) was performed to assess the effect of complete (HOM-BB) and partial (HET-BB) VP deficiency on binding sites in the CNS and periphery. The liver again was the only tissue in which a change in 3H-AVP binding characteristics was noted. The HOM-BB rat (Bmax 144 +/- 6 fmol/mg protein) displayed a significant increase in AVP binding sites from the LE rat (Bmax 100 +/- 7 fmol/mg protein), while the 3H-AVP binding sites in the HET-BB rat liver (Bmax 69.8 +/- 9 fmol/mg protein) were significantly lower than LE rats. Thus hepatic AVP receptors appear most sensitive to the presence or absence of vasopressin during the early postnatal period.

Chronic treatment with vasopressin analogues alters affinity of vasopressin receptors in the septum and amygdala of the rat brain

Accurel devices were used to administer AVP or AVP-antagonist into the lateral ventricle of the rat brain for 7 days. Neither AVP nor antagonist altered total binding site concentration in either septum or amygdala. However, treatment with antagonist caused a marked decrease in the affinity of the receptor for agonist in both the septum and amygdala.

Central vasopressin pretreatment sensitizes phosphoinositol hydrolysis in the rat septum

Previous in vivo and in vitro studies have demonstrated that exposure of the brain to arginine vasopressin (AVP) can potentiate various responses to a second central challenge with AVP. To determine whether this sensitization is mediated by changes at the receptor level, we investigated the effects of AVP on the phosphoinositide metabolism in septal slices prepared from rats centrally pretreated with saline or AVP. Addition of vasopressin (10(-7) M, 10(-6) M) to septal slices from saline-pretreated rats failed to elicit a significant stimulation of inositol-1-phosphate (IP1). In contrast, AVP (10(-7) M) significantly stimulated IP1 release in septal slices prepared from rats pretreated intracerebroventricularly (i.c.v.) 24 h earlier with 10 or 100 ng AVP. Pretreatment with the same i.c.v. doses of AVP also induced a significant enhancement of the carbachol-induced stimulation of IP1 release, but i.e.v. pretreatment with carbachol did not stimulate the IP1 release in response to AVP. Our results suggest that a novel facilitation of phosphoinositide metabolism can be induced by central AVP pretreatment.

Positive Feedback of Vasopressin on its Own Release in the Central Nervous System: in vitro Studies

Abstract In this paper evidence is shown that synthetic arginine vasopressin (AVP) can evoke marked in vitro release of endogenous immunoreactive AVP (I-AVP) from male rat septal and hypothalamic tissue superfused in vitro. The stimulatory action was dosedependent with a maximal amplification factor of 2.3 when using 14 pg of synthetic AVP as the stimulus. It was highly specific since only AVP was effective and not three closely related substances such as lysine vasopressin, oxytocin and a 4-9 C fragment of AVP. This reproducible effect of AVP required, however, effective concentrations of bacitracin (10(-4) to 10(-5) M) in the superfusion medium to inhibit aminopeptidase(s) capable of inactivating AVP. Lastly, the stimulatory action of AVP on its own release was not blocked by a V(1)-receptor antagonist of AVP but was blocked by a V(2)-antagonist. It is proposed that this novel and robust positive feedback of AVP on its own release may be involved in the mechanism of memory consolidation of certain behavioral tasks known to be affected by AVP.