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

The role of the apelin/APJ system in water homeostasis regulation

Water balance in the body is achieved by balancing renal and non-renal water losses with corresponding water intake. It is under the control of both the central nervous system, which integrates many parameters of water and electrolyte balance in the body, including inducing important adaptive behavioral responses, and three hormonal systems: vasopressinergic, renin-angiotensin-aldosterone and apelinergic. A lot of research is devoted to the regulation of water-electrolyte metabolism. However, this process is still quite difficult to understand, especially since more and more of its regulators are being discovered over time. One of them is the hormone apelin, an endogenous ligand for the APJ receptor. As is known, the receptor is highly expressed in many organs, such as the brain, heart, liver and kidneys, lungs, and has multidirectional effects.

This literature review discusses the main characteristics and features of the regulation of these systems in relation to water-electrolyte metabolism, as well as issues of intersystem interaction and modulation of the effects of apelin.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Roles of arginine vasotocin receptors in the brain and pituitary of submammalian vertebrates

This chapter reviews the functions of arginine vasotocin (AVT) and its receptors in the central nervous system (CNS) of primarily submammalian vertebrates. The V1a-type receptor, which is widely distributed in the CNS of birds, amphibians, and fish, is one of the most important receptors involved in the expression of social and reproductive behaviors. In mammals, the V1b receptor of arginine vasopressin, an AVT ortholog, is assumed to be involved in aggression, social memory, and stress responses. The distribution of the V1b-type receptor in the brain of submammalian vertebrates has only been reported in an amphibian species, and its putative functions are discussed in this review. The functions of V2-type receptor in the CNS are still unclear. Recent phylogenetical and pharmacological analyses have revealed that the avian VT1 receptor can be categorized as a V2b-type receptor. The distribution of this newly categorized VT1 receptor in the brain of avian species should contribute to our knowledge of the possible roles of the V2b-type receptor in the CNS of other nonmammalian vertebrates. The functions of AVT in the amphibian and avian pituitaries are also discussed, focusing on the V1b- and V1a-type receptors.

Effects of hypertonic stimuli and arginine vasotocin (AVT) on water absorption response in Japanese treefrog, Hyla japonica

Anuran amphibians do not drink orally but absorb water osmotically through the highly permeable ventral skin. In this cutaneous water absorption, roles of the putative cerebral osmoreceptors and functions of arginine vasotocin (AVT) were examined in the central nervous system of the Japanese treefrog, Hyla japonica. Intracerebroventricular (ICV) or intralymphatic sac (ILS) administration of various hypertonic solutions (NaCl, mannitol and urea) significantly extended the residence time in water in a dose-dependent manner, suggesting facilitation of water absorption in frogs. ICV injection of AVT also increased significantly the residence time in a dose-dependent manner. The water absorption effect of AVT was significantly inhibited by pretreatment of ICV OPC-21268, a vasopressin V(1) receptor antagonist. But pre-ICV injection of OPC-31260, a vasopressin V(2) receptor antagonist, did not block the water absorption effect of AVT. Extension of the residence time induced by hyperosmotic NaCl (1000 mOsm) ICV injection was significantly inhibited by pretreatment of ICV OPC-21268. The present results showed that increases of osmotic pressure in plasma and/or cerebrospinal fluid stimulate water absorption response, suggesting that osmoreceptors are certainly present in the central nervous system and AVT may directly stimulate water absorption in the treefrog. It is also suggested that AVT activates cellular mechanisms via V(1)-like but not V(2)-like receptors in the central nervous system and facilitates water absorption response in the treefrog.

Vasopressin and angiotensin receptors of the medial septal area of the brain in the control of thirst and salt appetite induced by vasopressin in water-deprived and sodium-depleted rats

In this study we investigated the influence of d(CH(2))(5)-Tyr (Me)-AVP (A(1)AVP) and [Adamanteanacatyl(1),D-ET-D-Tyr(2), Val(4), aminobutyril(6),A(8,9)]-AVP (A(2)AVP), antagonists of V(1) and V(2) arginine(8)-vasopressin (AVP) receptors, respectively, as well as the effects of losartan and CGP42112A, antagonists of angiotensin II (ANGII) AT(1) and AT(2,) receptors, respectively, on water and 0.3 M sodium intake induced by water deprivation or sodium depletion (furosemide treatment) and enhanced by AVP injected into the medial septal area (MSA). A stainless steel cannula was implanted into the medial septal area (MSA) of male Holtzman rats AVP injection enhanced water and sodium intake in a dose-dependent manner. Pretreatment with V(1) antagonist injected into the MSA produced a dose-dependent reduction, whereas prior injection of V(2) antagonist increased, in a dose-dependent manner, the water and sodium responses elicited by the administration of AVP. Both AT(1) and AT(2) antagonists administered into the MSA elicited a concentration-dependent decrease in water and sodium intake induced by AVP, while simultaneous injection of the two antagonists was more effective in decreasing AVP responses. These results also indicate that the increase in water and sodium intake induced by AVP was mediated primarily by MSA AT(1) receptors.

Effects of acute heat exposure on prosencephalic c-Fos expression in normohydrated, water-deprived and salt-loaded rats

In the present study, the distribution pattern of c-Fos protein immunoreactivity (Fos-IR) in prosencephalic areas of the brain involved in thermoregulatory and osmoregulatory responses was investigated, in rats exposed or not exposed to a hyperthermic environment, under three different conditions: normohydration, dehydration induced by water deprivation and hyperosmolarity induced by an acute intragastric salt load. Normohydrated, water-deprived or salt-loaded male Wistar rats (270+/-30 g) were submitted or not to acute heat exposure (33 degrees C for 45 min). A separate group of animals was submitted to the same experimental protocol and had blood samples collected before and after the heating period to measure serum osmolarity and sodium. The brains were processed for c-Fos immunohistochemistry using the avidin-biotin peroxidase method. After analyzing Fos-IR in the brains of animals in the present study, three different types of prosencephalic areas were identified: (1) those that respond to hydrational and to heat conditions, with an interaction between these two factors (PaMP and SON); (2) those that respond to hydrational and to heat conditions, but with no interaction between these factors (MnPO, LSV and OVLT); and (3) those that respond only to hydrational status (SFO and PaLM).

Interaction between supraoptic nucleus and septal area in the control of water, sodium intake and arterial blood pressure induced by injection of angiotensin II

We investigated the effects of injection into the supraoptic nucleus (SON) of losartanand PD 123319 (nonpeptide AT(1) and AT(2)-angiotensin II [ANG II] receptor antagonists, respectively); d(CH(2))(5)-Tyr(Me)-AVP (AVPA; an arginine-vasopressin [AVP] V(1) receptor antagonist), FK 409 (a nitric oxide [NO] donor), and N(W)-nitro-l-arginine methyl ester (l-NAME; an NO synthase inhibitor) on water intake, sodium chloride 3% (NaCl) intake and arterial blood pressure induced by injection of ANG II into the lateral septal area (LSA). Male Holtzman rats (250-300 g) were implanted with cannulae into SON and LSA unilaterally. The drugs were injected in 0.5 microl over 30-60 s. Controls were injected with a similar volume of 0.15 M NaCl. ANG II was injected at a dose of 10 pmol. ANG II antagonists and AVPA were injected at doses of 80 nmol. FK 409 and l-NAME were injected at doses of 20 and 40 microg, respectively. Water and NaCl intake was measured over a 2-h period. Prior administration of losartan into the SON decreased water and NaCl intake induced by injection of ANG II. While there was a decrease in water intake, ANG II-induced NaCl intake was significantly increased following injection of AVPA. FK 409 injection decreased water intake and sodium intake induced by ANG II. l-NAME alone increased water and sodium intake and induced a pressor effect. l-NAME-potentiated water and sodium intake induced by ANG II. PD 123319 produced no changes in water or sodium intake induced by ANG II. The prior administration of losartan or AVPA decreased mean arterial pressure (MAP) induced by ANG II. PD 123319 decreased the pressor effect of ANG II to a lesser degree than losartan. FK 409 decreased the pressor effect of ANG II while l-NAME potentiated it. These results suggest that both ANG II AT(1) and AVP V(1) receptors and NO within the SON may be involved in water intake, NaCl intake and the pressor response were induced by activation of ANG II receptors within the LSA. These results do not support the involvement of LSA AT(2) receptors in the mediation of water and NaCl intake responses induced by ANG II, but influence the pressor response.