Intracerebroventricular administration of the angiotensin II receptor antagonist saralasin reduces respiratory rate and tidal volume variability in freely moving Wistar rats

Central ventilatory and cardiovascular actions of angiotensin peptides in trout

In the brains of teleosts, angiotensin II (ANG II), one of the main effector peptides of the renin-angiotensin system, is implicated in various physiological functions notably body fluid and electrolyte homeostasis and cardiovascular regulation, but nothing is known regarding the potential action of ANG II and other angiotensin derivatives on ventilation. Consequently, the goal of the present study was to determine possible ventilatory and cardiovascular effects of intracerebroventricular injection of picomole doses (5-100 pmol) of trout [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, ANG IV, and ANG 1-7 into the third ventricle of unanesthetized trout. The central actions of these peptides were also compared with their ventilatory and cardiovascular actions when injected peripherally. Finally, we examined the presence of [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, and ANG IV in the brain and plasma using radioimmunoassay coupled with high-performance liquid chromatography. After intracerebroventricular injection, [Asn(1)]-ANG II and [Asp(1)]-ANG II two ANG IIs, elevated the total ventilation through a selective stimulatory action on the ventilation amplitude. However, the hyperventilatory effect of [Asn(1)]-ANG II was threefold higher than the effect of [Asp(1)]-ANG II at the 50-pmol dose. ANG III, ANG IV, and ANG 1-7 were without effect. In addition, ANG IIs and ANG III increased dorsal aortic blood pressure (P(DA)) and heart rate (HR). After intra-arterial injections, none of the ANG II peptides affected the ventilation but [Asn(1)]-ANG II, [Asp(1)]-ANG II, and ANG III elevated P(DA) (50 pmol: +80%, +58% and +48%, respectively) without significant decrease in HR. In brain tissue, comparable amounts of [Asn(1)]-ANG II and [Asp(1)]-ANG II were detected (ca. 40 fmol/mg brain tissue), but ANG III was not detected, and the amount of ANG IV was about eightfold lower than the content of the ANG IIs. In plasma, ANG IIs were also the major angiotensins (ca. 110 fmol/ml plasma), while significant but lower amounts of ANG III and ANG IV were present in plasma. In conclusion, our study suggests that the two ANG II isoforms produced within the brain may act as a neurotransmitter and/or neuromodulator to regulate the cardioventilatory functions in trout. In the periphery, two ANG IIs and their COOH-terminal peptides may act as a circulating hormone preferentially involved in cardiovascular regulations.

Brain neuropeptides in central ventilatory and cardiovascular regulation in trout

Many neuropeptides and their G-protein coupled receptors (GPCRs) are present within the brain area involved in ventilatory and cardiovascular regulation but only a few mammalian studies have focused on the integrative physiological actions of neuropeptides on these vital cardio-respiratory regulations. Because both the central neuroanatomical substrates that govern motor ventilatory and cardiovascular output and the primary sequence of regulatory peptides and their receptors have been mostly conserved through evolution, we have developed a trout model to study the central action of native neuropeptides on cardio-ventilatory regulation. In the present review, we summarize the most recent results obtained using this non-mammalian model with a focus on PACAP, VIP, tachykinins, CRF, urotensin-1, CGRP, angiotensin-related peptides, urotensin-II, NPY, and PYY. We propose hypotheses regarding the physiological relevance of the results obtained.

In dystrophic hamsters losartan affects control of ventilation and dopamine D1 receptor density

The BIO 14.6 hamster (DV), an animal model of limb-girdle muscular dystrophy, has elevated angiotensin AT1 receptors that may affect ventilation. Moreover, AT1 receptors may modulate expression of dopamine D1 receptors. We investigated if chronic treatment of BIO 14.6 hamsters (DL) with losartan, an AT1 receptor blocker, affects D1 receptor density in the striatum and nucleus tractus solitarius (NTS) and normalizes ventilation during exposure to air, hypoxia, following hypoxia, and hypercapnia, Ventilation was evaluated using plethysmography. Compared to the golden Syrian hamsters (GS), DV hamsters exhibited lower hypercapnic and hypoxic responsiveness and ventilation during hypercapnic exposure. Relative to GS, DL hamsters increased breathing frequency in air and maintained ventilation during hypercapnia. Post-hypoxic minute ventilation decline occurred in DV but not in DL or GS hamsters. DL hamsters exhibited higher D1 receptor density in the striatum and NTS relative to DV hamsters. Thus, in dystrophic hamsters chronic losartan treatment stimulated frequency of breathing and increased the density of D1 receptors.

Intravenous hypertonic NaCl acts via cerebral sodium-sensitive and angiotensinergic mechanisms to improve cardiac function in haemorrhaged conscious sheep

Acute NaCl loading as resuscitation in haemorrhagic hypovolaemia is known to induce rapid cardiovascular recovery. Besides an osmotically induced increase in plasma volume the physiological mechanisms of action are unknown. We hypothesized that a CNS mechanism, elicited by increased periventricular [Na(+)] and mediated by angiotensin II type 1 receptors (AT(1)), is obligatory for the full effect of hypertonic NaCl. To test this we investigated the cardiovascular responses to haemorrhage and subsequent hypertonic NaCl infusion (7.5% NaCl, 4 ml (kg BW)(-1)) in six conscious sheep subjected to intracerebroventricular (i.c.v.) infusion of artificial cerebrospinal fluid (aCSF; control), mannitol solution (Man; 75 mmol l(-1) [Na(+)], total osmolality 295 mosmol kg(-1)) or losartan (Los; 1 mg ml(-1), AT(1) receptor antagonist) at three different occasions. Man normalized (144 +/- 6 mmol l(-1), mean +/- s.d.) the increase in i.c.v. [Na(+)] seen after aCSF (161 +/- 2 mmol l(-1)). Compared with control, both Man and Los significantly (P < 0.05) attenuated the improvement in mean arterial blood pressure (MAP), cardiac index and mesenteric blood flow (SMBF) in response to intravenous hypertonic NaCl: MAP, rapid response +45 mmHg versus +38 mmHg (Man) and +35 mmHg (Los); after 180 min, +32 mmHg versus +21 mmHg (Man) and +19 mmHg (Los); cardiac index after 180 min, +1.9 l min(-1) (m(2))(-1) versus +0.9 l min(-1) (m(2))(-1) (Man) and +0.9 l min(-1) (m(2))(-1) (Los); SMBF rapid response, +981 ml min(-1) versus +719 ml min(-1) (Man) and +744 ml min(-1) (Los); after 180 min, +602 ml min(-1) versus +372 ml min(-1) (Man) and +314 ml min(-1) (Los). The results suggest that increased periventricular [Na(+)] and cerebral AT(1) receptors contribute, together with plasma volume expansion, to improve systemic haemodynamics after treatment with hypertonic NaCl in haemorrhagic hypovolaemia.

Lack of association between angiotensin I-converting enzyme insertion/deletion gene functional polymorphism and panic disorder in humans

Family and twin studies have indicated that genes influence susceptibility to panic disorder, but the genes involved remain unknown. The neuropeptide angiotensin II has been found to be involved in anxiety and regulation of respiration which are important in the pathophysiology of panic attacks. Assuming that angiotensins may be candidate genes in panic disorder, we analyzed the association between panic disorder and angiotensin I-converting enzyme (ACE) insertion (I)/deletion (D) gene functional polymorphism. We recruited 101 patients with panic disorder diagnosed according to DSM-IV criteria, and 184 control subjects in the study. No significant differences in the frequency of the genotype or allele in the polymorphism between patient and control groups were found (genotype, chi(2)=0.56, d.f.=2, P=0.77; allele, chi(2)=0.074, d.f.=1, P=0.78). This study suggests that the ACE I/D gene polymorphism is not directly associated with panic disorder in our Japanese patient group.

Angiotensin-related genes in patients with panic disorder

Enhanced respiratory variability and decreased heart rate variability have repeatedly been observed in patients with panic disorder. Prompted by the notion that angiotensin may be involved in the control of respiration, heart rate variability, and anxiety-like behavior, we investigated the putative association between polymorphisms in three angiotensin-related genes and panic disorder-angiotensinogen (AGT), angiotensin converting enzyme (ACE), and angiotensin II (ANG II) receptor type 1 (ATr1) in 72 patients with panic disorder and 504 controls. Allele and genotype distribution of the ATr1 A1166C allele and the AGT M235T did not differ between patients and controls. With respect to the ACE I/D polymorphism, the I allele was found to be more frequent in male (chi(2) = 8.042, df = 1, P = 0.005), but not female, panic disorder patients than in controls. The results of this investigation provide preliminary evidence for the suggestion that angiotensin-related genes may be associated with panic disorder in men.