Central angiotensin receptor blockade impairs thermolytic and dipsogenic responses to heat exposure in rats

The effect of central angiotensin AT(1) receptor blockade on thermoregulation and water intake after heat exposure was investigated. Rats were placed in a chamber heated to 39 +/- 1 degrees C for 60 min and then returned to their normal cage (at 22 degrees C), and water intake was measured for 120 min. Artificial cerebrospinal fluid (5 microl) was injected intracerebroventricularly 60 min before heat exposure in five control rats. Colonic temperature increased from 37.22 +/- 0.21 to 40.68 +/- 0.31 degrees C after 60 min. In six rats injected intracerebroventricularly with 10 microg of the AT(1) antagonist losartan, colonic temperature increased from 37.41 +/- 0.27 to 41.72 +/- 0.28 degrees C after 60 min. This increase was significantly greater than controls (P < 0.03). Losartan-treated rats drank 1.1 +/- 0.4 ml of water compared with 5.9 +/- 0.77 ml (P < 0.002) drank by control animals, despite a similar body weight loss in the two groups. Central losartan did not inhibit the drinking response to intracerebroventricular carbachol in heated rats, suggesting that losartan treatment did not nonspecifically depress behavior. We conclude that central angiotensinergic mechanisms have a role in both thermoregulatory cooling in response to heat exposure and also the ensuing water intake.

Antisense oligonucleotide inhibition of angiotensinogen in the brains of rats and sheep

Phosphorothioated antisense oligodeoxynucleotides (ODNs) that were complementary to various parts of the rat or sheep mRNA encoding angiotensinogen were synthesized by conventional techniques. Their effectiveness as blockers of angiotensinogen synthesis in the brain was tested by bioassay. This involved measuring the effect of centrally administered antisense ODNs on water drinking that occurred in response to intracerebroventricular injection of hog renin. Renin-induced drinking requires brain angiotensinogen for the generation of angiotensin I and then angiotensin II to stimulate thirst. Intracerebroventricular injection of an 18-mer antisense ODN (0.5 microg twice in 24 h) complementary to the 5'-end start codon for rat angiotensinogen mRNA caused a pronounced inhibition of renin-induced drinking. This effect appeared to be specific for this region of the codon because antisense ODNs directed against other regions of rat angiotensinogen mRNA were ineffective, and renin-induced drinking was not inhibited by intracerebroventricular injection of scrambled or mismatched sequences of the effective ODN or by intraperitoneal injection of it. Intracerebroventricular injection of antisense ODN (0.5 microg twice in 24 h) did not inhibit appetite or affect water drinking in response to some other dipsogenic stimuli, thus demonstrating the specificity of its action against renin-induced drinking. By contrast, intracerebroventricular administration of 625 microg of an antisense ODN directed against the corresponding 5'-end start codon region of sheep angiotensinogen mRNA did not inhibit intracerebroventricular renin-induced drinking in sheep. These data show that while intracerebroventricularly administered antisense may be used effectively in rodents, the method is not necessarily applicable in larger mammals.

Renal nerve inhibition by central NaCl and ANG II is abolished by lesions of the lamina terminalis

The lamina terminalis is situated in the anterior wall of the third ventricle and plays a major role in fluid and electrolyte homeostasis and cardiovascular regulation. The present study examined whether the effects of intracerebroventricular infusion of hypertonic saline and ANG II on renal sympathetic nerve activity (RSNA) were mediated by the lamina terminalis. In control, conscious sheep (n = 5), intracerebroventricular infusions of 0.6 M NaCl (1 ml/h for 20 min) and ANG II (10 nmol/h for 30 min) increased mean arterial pressure (MAP) by 6 +/- 1 (P < 0.001) and 14 +/- 3 mmHg (P < 0.001) and inhibited RSNA by 80 +/- 6 (P < 0.001) and 89 +/- 7% (P < 0.001), respectively. Both treatments reduced plasma renin concentration (PRC). Intracerebroventricular infusion of artificial cerebrospinal fluid (1 ml/h for 30 min) had no effect. In conscious sheep with lesions of the lamina terminalis (n = 6), all of the responses to intracerebroventricular hypertonic saline and ANG II were abolished. In conclusion, the effects of intracerebroventricular hypertonic saline and ANG II on RSNA, PRC, and MAP depend on the integrity of the lamina terminalis, indicating that this site plays an essential role in coordinating the homeostatic responses to changes in brain Na(+) concentration.

Intracerebroventricular administration of the beta(3)-adrenoceptor agonist CL 316243 causes Fos immunoreactivity in discrete regions of rat hypothalamus

Intracerebroventricular (i.c.v.) administration of the beta(3)-AR agonist BRL37344 causes dose dependent decreases in food intake in rats suggesting a role for beta(3)-AR in the central control of feeding. We have conducted experiments investigating the effects of i.c.v. administration of the selective beta(3)-AR agonist CL316243 on Fos expression to determine whether beta(3)-AR stimulation affects neurones within specific brain nuclei. Significantly higher numbers of Fos positive cells were found in the rats treated i.c.v. with CL316243 compared with control rats in the paraventricular hypothalamus, lateral hypothalamic area, ventromedial hypothalamic nucleus and dorsal hypothalamic area. Pre-treatment with the selective beta(3)-AR antagonist SR59230A resulted in a significant decrease in the number of Fos positive cells in all those areas compared with rats treated with CL316243 alone. These experiments demonstrate that i.c.v. administration of selective beta(3)-AR agonist causes neuronal activation in hypothalamic areas important in the central regulation of appetite via a beta(3)-AR mediated effect.

Fos immunoreactivity in the lamina terminalis of adrenalectomized rats and effects of angiotension II type 1 receptor blockade or deoxycorticosterone

Neural activity, as measured immunohistochemically by the presence of Fos protein, was determined in the lamina terminalis, a thin strip of tissue forming the anterior wall of the third brain ventricle, after adrenalectomy. Several weeks after surgery, the adrenalectomized rats were maintained with access to water and a low sodium diet for five days. In addition, hypertonic (0.5M) NaCl solution was available for the entire five-day period (sodium available) or only during the first four days (sodium unavailable). The number of neurons expressing Fos, determined at the end of the fifth day, was increased in the adrenalectomized rats with or without NaCl solution to drink. Fos activity in the median preoptic nucleus was increased only in adrenalectomized rats without access to NaCl solution. Treatment of adrenalectomized rats with the sodium-retaining mineralocorticoid hormone, deoxycorticosterone, at the end of the fourth day, decreased Fos expression in the subfornical organ and the organum vasculosum of the lamina terminalis when NaCl solution was available but not when the NaCl solution was unavailable. In the adrenalectomized rats with NaCl solution available, mineralocorticoid treatment decreased both urinary sodium excretion and daily sodium intake. Brain nuclei in the lamina terminalis also became activated in intact rats made sodium deplete by treatment with the diuretic, furosemide. Relative to sodium-deplete intact rats, however, sodium-deplete adrenalectomized rats had a greater number of neurons expressing Fos in the organum vasculosum. Treatment of sodium-deplete rats, adrenalectomized or intact, with the angiotensin II-type 1 receptor antagonist, ZD7155, decreased sodium intake and Fos expression in the subfornical organ but not in the organum vasculosum of the lamina terminalis or median preoptic nucleus. In conclusion, the results demonstrated that activation of the brain nuclei located in the lamina terminalis of adrenalectomized rats was primarily related to sodium deficit and not to the absence of the mineralocorticoid hormones, although the adrenal hormones may have a role in limiting the activation of organum vasculosum of the lamina terminalis during sodium depletion. Furthermore, the results obtained with the administration of the angiotensin receptor antagonist are consistent with the proposal that sodium appetite of the sodium-deplete rat, adrenalectomized or intact, is mediated by circulating angiotensin II acting in the subfornical organ.

Renal Na excretion in dehydrated and rehydrated adrenalectomized sheep maintained with aldosterone

The effect of water deprivation for 19 h on renal Na excretion of conscious adrenalectomized (ADX) sheep maintained on a constant intravenous infusion of aldosterone and cortisol (ADX-constant steroid sheep) was investigated. Both ADX and normal sheep showed large increases in renal Na excretion when they were deprived of water. ADX-constant steroid sheep also exhibited a normal postprandial natriuresis 3-6 h after feeding, whether or not water was available to drink. In another experiment, sheep deprived of water for 41 h were then allowed to drink water. Both normal and ADX-constant steroid sheep exhibited a large reduction of renal Na excretion in the 6 h after rehydration. Changes in plasma Na and K concentration and osmolality were similar in normal and ADX-constant steroid sheep during periods of dehydration and rehydration. These results show that change in aldosterone secretion is not a major factor in causing either dehydration-induced or postprandial natriuresis. Neither is it a major cause of rehydration-induced renal Na retention.

A preliminary study of growth hormone therapy for Crohn's disease

BACKGROUND

Crohn's disease is a chronic inflammatory disorder of the bowel. In a preliminary study, we evaluated whether the administration of growth hormone (somatropin) as well as a high-protein diet would ameliorate the symptoms of the disease.

METHODS

We randomly assigned 37 adults with moderate-to-severe active Crohn's disease to four months of self-administered injections of growth hormone (loading dose, 5 mg per day subcutaneously for one week, followed by a maintenance dose of 1.5 mg per day) or placebo. We instructed all patients to increase their protein intake to at least 2 g per kilogram of body weight per day. Patients continued to be treated by their usual physicians and to receive other medications for Crohn's disease. The primary end point was the change in scores on the Crohn's Disease Activity Index from base line to month 4. Scores can range from 0 to 600, with higher scores indicating more disease activity.

RESULTS

At base line, the mean (+/-SD) score on the Crohn's Disease Activity Index was somewhat higher among the 19 patients in the growth hormone group than among the 18 patients in the placebo group (287+/-134 vs. 213+/-120, P=0.09). Three patients in the placebo group withdrew before their first follow-up visit and were not included in the data analysis. At four months, the Crohn's Disease Activity Index score had decreased by a mean of 143+/-144 points in the growth hormone group, as compared with a decrease of 19+/-63 points in the placebo group (P=0.004). Side effects in the growth hormone group included edema (in 10 patients) and headache (in 5) and usually resolved within the first month of treatment.

CONCLUSIONS

Our preliminary study suggests that growth hormone may be a beneficial treatment for patients with Crohn's disease.

The inhibitory effect of hormones associated with stress on Na appetite of sheep

Stress is a large stimulus of Na appetite in rabbits, rats, and mice. This study investigated the influence of some peptides implicated in stress, i.e., adrenocorticotropin (ACTH), corticotropin-releasing factor (CRF), and the recently discovered member of the CRF family, urocortin, on the ingestive behavior of sheep. Intracerebroventricular infusion of these peptides over 4 days decreased the need-free Na intake of Na-repleted sheep. Intracerebroventricular infusion of urocortin, however, did not alter Na intake of Na-depleted sheep. Systemic infusion of ACTH increased, whereas systemic infusion of either urocortin or CRF decreased, Na intake of Na-repleted sheep. The increase in Na intake caused by the peripheral infusion of ACTH was blocked by concurrent i.v. infusion of urocortin, substantiating the inhibitory role of this peptide on Na appetite. Central administration of all peptides and i.v. administration of urocortin or urocortin and ACTH combined decreased food intake. Water intake was not directly influenced by the peptides. Rather, decreased water intake, when observed, was secondary to decreased food intake, as determined by pair-feeding experiments. Whereas systemic infusion of ACTH mimics the increase in Na intake observed in several different stressful situations, CRF and urocortin actually inhibit Na intake, indicating a direct central action overriding any effect of these peptides on ACTH release. Indeed, the inhibition of Na intake by urocortin occurred despite its stimulation of ACTH release and the subsequent increase in peripheral level of cortisol. Thus it would appear that hormones associated with stress have both excitatory and inhibitory influences on Na intake. Presumably, other physiological processes entrained by stress also will be important in determining the quantitative outcome on Na appetite.

Water drinking in rats resulting from intravenous relaxin and its modification by other dipsogenic factors

The purpose of the study was to determine whether iv infusion of relaxin would acutely stimulate water drinking in rats and, if it did, whether such drinking is affected by other dipsogenic stimuli or is blocked by centrally administered losartan. iv infusions of human gene 2 relaxin at doses of 25, 40, 55, or 80 microg/kg x h for 1 h induced dose-dependent water drinking in both male and female rats within 15-30 min of commencement of infusions. iv infusion of a nondipsogenic dose of angiotensin II (0.5 microg/h), combined with relaxin (40 microg/kg x h), almost tripled the relaxin-induced water intake. iv infusion of hypertonic (1 M) NaCl did not potentiate relaxin-induced drinking. Intracerebroventricular injection of the angiotensin AT1 antagonist losartan (10 microg) reduced water drinking induced by iv infusion of relaxin. The water drinking induced by iv infusion of relaxin in the rat suggests that blood-borne relaxin may be a dipsogenic hormone. Potentiation of this relaxin-induced drinking by moderate levels of circulating angiotensin II is additional evidence in support of this view. The results also indicate that a central angiotensinergic neural pathway, utilizing AT1 receptors, subserves relaxin-induced drinking.

Identification of neural projections from the forebrain to the kidney, using the virus pseudorabies

These data demonstrate a chain of synaptically connected neurons extending to the rat kidney through several levels of the neuraxis from the forebrain, and the lamina terminalis -- an area known to be involved in the regulation of body fluid homeostasis. The Bartha strain of pseudorabies virus was injected into the kidney of male Sprague-Dawley rats, resulting in retrograde infections in spinal cord segments (T1-T8), and successive infection in five autonomic 'premotor' areas of the brain, the rostroventrolateral medulla, rostroventromedial medulla, raphe nuclei, A5 region of the pons, and the paraventricular nucleus of the hypothalamus, as well as the nucleus of the solitary tract, locus coeruleus, and subcoeruleus nuclei. Higher order labelling was found in regions of the forebrain, including the organum vasculosum of the lamina terminalis, median preoptic nucleus, subfornical organ, medial preoptic area, bed nucleus of the stria terminalis, anteroventral periventricular nucleus, lateral preoptic area, suprachiasmatic nucleus, retrochiasmatic nucleus, primary motor cortex, and visceral cortex. This polysynaptic pathway to the kidney may form the substrate underlying the impact of forebrain structures on renal function.

Characterization of a specific antibody to the rat angiotensin II AT1 receptor

We raised a polyclonal antibody against a decapeptide corresponding to the carboxyl terminus of the rat angiotensin II AT1 receptor. This antibody was demonstrated to be specific for the rat receptor according to a number of approaches. These included (a) the ultrastructural localization of immunogold-labeled receptor on the surfaces of zona glomerulosa cells in the adrenal cortex, (b) the specific labeling of Chinese hamster ovarian (CHO) cells transfected with AT1 receptors, (c) the identification of a specific band on Western blots, (d) the immunocytochemical co-localization of angiotensin receptors on neurons in the lamina terminalis of the brain shown to be responsive to circulating angiotensin II, as shown by the expression of c-fos, and (e) the correlation between the expression of the mRNA of the AT1 receptor and AT1 receptor immunoreactivity.(J Histochem Cytochem 47:507-515, 1999)

Effect of individual or combined ablation of the nuclear groups of the lamina terminalis on water drinking in sheep

The subfornical organ (SFO), organum vasculosum of the lamina terminalis (OVLT), and median preoptic nucleus (MnPO) were ablated either individually or in various combinations, and the effects on drinking induced by either intravenous infusion of hypertonic 4 M NaCl (1.3 ml/min for 30 min) or water deprivation for 48 h were studied. Ablation of either the OVLT or SFO alone did not affect drinking in response to intravenous 4 M NaCl, although combined ablation of these two circumventricular organs substantially reduced but did not abolish such drinking. Ablation of the MnPO or MnPO and SFO together also substantially reduced, but did not abolish, drinking in response to intravenous hypertonic NaCl. Only near-total destruction of the lamina terminalis (OVLT, MnPO, and part or all of the SFO) abolished acute osmotically induced drinking. The large lesions also reduced drinking after water deprivation, whereas none of the other lesions significantly affected such drinking. None of these lesions altered feeding. The results show that all parts of the lamina terminalis play a role in the drinking induced by acute increases in plasma tonicity. The lamina terminalis appears to play a less crucial role in the drinking response after water deprivation than for the drinking response to acute intravenous infusion of hypertonic saline.

Angiotensin II receptors in the human brain

The distribution of angiotensin AT1 and AT2 receptors in the human central nervous system has been mapped and is reviewed here. The results discussed provide the anatomical basis for inferences regarding the physiological role of angiotensin in the human brain. The distribution of the AT2 receptor is very restricted in the human brain and shows a high degree of variability across species. The physiological role of this receptor in the adult central nervous system is not clear. In contrast, a high correlation exists between the distributions of AT1 receptors in the human and other mammalian brains studied. This pattern of distribution suggests that angiotensin, acting through the AT1 receptor, would act as a neuromodulator or neurotransmitter in the human central nervous system to influence fluid and electrolyte homeostasis, pituitary hormone release and autonomic control of cardiovascular function.

Interaction of circulating hormones with the brain: the roles of the subfornical organ and the organum vasculosum of the lamina terminalis

1. Most circulating peptide hormones are excluded from much of the brain by the blood-brain barrier. However, they do have access to the circumventricular organs (CVO), which lack the blood-brain barrier. Three of the CVO, the subfornical organ (SFO), organum vasculosum of the lamina terminalis (OVLT) and area postrema, contain neurons responsive to peptides such as angiotensin II (AngII), atrial natriuretic peptide and relaxin. 2. We have studied the patterns of neuronal activation, as shown by Fos expression, in the SFO and OVLT in response to systemically infused AngII, relaxin or hypertonic saline and have found subgroups of neurons activated by the different stimuli. 3. Systemic infusion of relaxin or hypertonic saline activated neurons almost exclusively in the outer regions of the SFO and in the dorsal cap of the OVLT. Many of these neurons send axonal projections to regions of the brain subserving vasopressin secretion and thirst, such as the median preoptic, supraoptic and hypothalamic paraventricular nuclei. 4. At moderate blood concentrations, AngII only stimulates neurons in the inner core of the SFO and lateral regions of the OVLT. Higher levels of AngII in the bloodstream activate additional neurons in the outer parts of the SFO that connect to the supraoptic, paraventricular and median preoptic nuclei and these probably mediate water drinking and vasopressin secretion induced by blood-borne AngII. The efferent connections and the functions mediated by angiotensin-sensitive neurons in the inner core of the SFO and lateral part of the OVLT are unknown.

The brain as an endocrine target for Peptide hormones

Unlike circulating steroid hormones, which have a relatively unhindered passage into the central nervous system, blood-borne peptides are usually restricted by the blood-brain barrier. Some circulating peptides, such as angiotensin II, atrial natriuretic peptide and relaxin, influence central neural pathways subserving cardiovascular and body fluid homeostasis by acting on neurons in the subfornical organ, organum vasculosum of the lamina terminalis and area postrema, all of which lack a blood-brain barrier. There are some circulating peptides such as insulin and leptin that are transported from the bloodstream across cerebral blood vessel walls into sites in the hypothalamus that have appropriate neural connections to influence food intake and sympathetic control of brown fat.

Efferent connections of the lamina terminalis, the preoptic area and the insular cortex to submandibular and sublingual gland of the rat traced with pseudorabies virus

Neurones situated in the lamina terminalis (organum vasculosum of the lamina terminalis, median preoptic nucleus and subfornical organ) as well as within medial and lateral parts of the preoptic area and in the insular cortex become transneuronally labelled following pseudorabies virus injections into the submandibular or the sublingual gland. These neurones are efferently connected to a chain of central neurones directed to secretory or vascular tissue of the submandibular or the sublingual gland. By varying the postinoculation time a stepwise infection of different forebrain nuclei was registered, with the hypothalamic paraventricular nucleus and the lateral hypothalamic area being the first forebrain structures labelled. Such early infected neurones within these hypothalamic nuclei are in all likelihood third order neurones regulating salivary secretion and might have functioned as relays transmitting virus to other forebrain structures. The above mentioned forebrain areas together with several other hypothalamic nuclei as well as the bed nucleus of the stria terminalis, the central nucleus of the amygdala and the substantia innominata, seem to be the widespread anatomical basis for the central regulation of salivary gland function.

Cerebrospinal fluid formation and absorption in dehydrated sheep

Cerebrospinal fluid (CSF) plays an important role in the brain's adaptive response to acute osmotic disturbances. In the present experiments, the effect of 48-h dehydration on CSF formation and absorption rates was studied in conscious adult sheep. Animals had cannulas chronically implanted into the lateral cerebral ventricles and cisterna magna to enable the ventriculocisternal perfusion. A 48-h water deprivation altered neither CSF production nor resistance to CSF absorption. However, in the water-depleted sheep, intraventricular pressure tended to be lower than that found under control conditions. This likely resulted from decreased extracellular fluid volume and a subsequent drop in central venous pressure occurring in dehydrated animals. In conclusion, our findings provide evidence for the maintenance of CSF production during mild dehydration, which may play a role in the regulation of fluid balance in the brain during chronic hyperosmotic stress.

Central losartan blocks natriuretic, vasopressin, and pressor responses to central hypertonic NaCl in sheep

This study investigated the effect of intracerebroventricular administration of the angiotensin AT1 receptor antagonist losartan on the natriuresis, pressor effect, and arginine vasopressin (AVP) secretion caused by intracerebroventricular infusion of either ANG II, hypertonic saline, or carbachol. Losartan (1 mg/h) or artificial cerebrospinal fluid (CSF) was infused into the lateral ventricle before, during, and after infusions of either ANG II at 10 microg/h for 1 h, 0.75 mol/l NaCl at 50 microl/min for 20 min, or carbachol at 1.66 microg/min for 15 min. Intracerebroventricular infusions of ANG II, 0.75 mol/l NaCl, or carbachol caused increases in renal Na+ and K+ excretion, arterial pressure, and plasma AVP levels. Increases in arterial pressure, Na+ excretion, and plasma AVP concentration ([AVP]) in response to intracerebroventricular ANG II or intracerebroventricular 0.75 mol/l NaCl were either abolished or attenuated by intracerebroventricular infusion of losartan but not by intracerebroventricular infusion of artificial CSF or intravenous losartan. Intracerebroventricular losartan did not reduce the increase in plasma [AVP] or arterial pressure in response to intracerebroventricular carbachol, but it did attenuate the natriuretic response to intracerebroventricular carbachol. We conclude that an intracerebroventricular dose of losartan (1 mg/h) that inhibits responses to intracerebroventricular ANG II also inhibits vasopressin secretion, natriuresis, and the pressor response to intracerebroventricular hypertonic saline. These results suggest that common neural pathways are involved in the responses induced by intracerebroventricular administration of ANG II and intracerebroventricular hypertonic NaCl. We propose that intracerebroventricular infusion of hypertonic saline activates angiotensinergic pathways in the central nervous system subserving the regulation of fluid and electrolyte balance and arterial pressure in sheep.

The effect of angiotensin AT1 receptor blockade in the brain on the maintenance of blood pressure during haemorrhage in sheep

The effect of systemic or intracerebroventricular (ICV) infusion of the angiotensin AT1 receptor antagonist losartan on blood pressure during hypotensive haemorrhage was investigated in five conscious sheep. Mean arterial pressure (MAP) was measured during haemorrhage (15 mL kg-1 body wt). Losartan (1 or 0.33 mg h-1) was given to sheep by ICV, intravenous or intracarotid administration, beginning 60 min before and continuing during the haemorrhage. During control infusion of ICV artificial cerebrospinal fluid, MAP was maintained until 13.16 +/- 0.84 mL kg-1 blood loss, when a rapid reduction of at least 15 mmHg in arterial pressure occurred (the decompensation phase). ICV infusion of losartan at 1 mg h-1 caused an early onset of the decompensation phase after only 9.8 +/- 0.8 mL kg-1 of blood loss compared with control. Intravenous infusion of losartan (1 mg h-1) also caused an early onset (P < 0.05) of the decompensation phase at 10.2 +/- 1.0 mL kg-1 blood loss. This dose of losartan inhibited the pressor response to ICV angiotensin II, but not to intravenously administered angiotensin II, indicating that only central AT1 receptors were blocked. Bilateral carotid arterial administration of losartan at 0.33 mg h-1 caused an early onset of the decompensation phase during haemorrhage at 11.06 +/- 0.91 mL kg-1 blood loss (P < 0.05), which did not occur when infused by intravenous or ICV routes. The results indicate that an angiotensin AT1-receptor-mediated mechanism is involved in the maintenance of MAP during haemorrhage in sheep. The locus of this mechanism appears to be the brain.

Effects of angiotensinogen antisense oligonucleotides on fluid intake in response to different dipsogenic stimuli in the rat

The role of centrally synthesised angiotensinogen in neural mechanisms subserving water drinking in rats was investigated by injecting antisense oligonucleotides complementary to rat angiotensinogen mRNA into the brain with the aim of inhibiting cerebral angiotensinogen synthesis. Phosphorothioate antisense oligonucleotides (18 mer) encompassing the translation start codon were injected into the lateral ventricle of rats and their responses to a number of dipsogenic stimuli tested. These were: intracerebroventricular (i.c.v.) renin, i.c.v. angiotensin II, i.c.v. carbachol, subcutaneous isoproterenol, intravenous hypertonic saline, water deprivation for 24 h or subcutaneous injection of polyethylene glycol. Antisense treatment significantly reduced (by approximately 50%) the volume of water drunk in response to i.c.v. injection of renin or subcutaneous isoproterenol, but did not reduce water intake elicited by the other dipsogenic stimuli. The i.c.v. administration of mismatch, scrambled or sense oligonucleotides did not inhibit water intake. These data suggest that centrally produced angiotensinogen may have a role in neural pathways subserving isoproterenol-induced drinking.

Angiotensinogen antisense oligonucleotides and fluid intake

The effectiveness of antisense oligonucleotides (ODNs) to angiotensinogen on intracerebrovenricularly injected renin induced thirst was investigated. As a corollary, information would be gained about the role of centrally synthesised angiotensinogen in the neural mechanisms subserving water drinking in rats. Stable, easily synthesised phosphorothioate antisense oligonucleotides (18 mer), one of which included the sequence encompassing the translation start site, were injected into the lateral ventricle of rats. The drinking response to a number of dipsogenic stimuli was tested. Antisense significantly reduced (by about 50%) the volume of water drunk in response to intracerebroventricular (icv) renin or isoproterenol but did not reduce drinking in response to the physiological challenge of icv angiotensin II, icv carbachol, intravenous hypertonic saline, water deprivation or subcutaneous injection of polyethylene glycol. Only one out of four antisense probes gave positive results, while mismatch or scrambled oligonucleotides did not inhibit water intake. This finding reduces the probability that the results observed are non-specific. In these experiments, an ODN specific for angiotensinogen was discovered and was produced easily in large enough amounts and stabilised against intracellular nucleases without floss of cellular access or biological effect.

Central infusion of the AT1 receptor antagonist losartan inhibits thirst but not sodium appetite in cattle

Experiments in cattle compared the effects of intracerebroventricular (i.c.v.) infusions of losartan and PD-123319 on water intake caused by water restriction, i.c.v. infusion of hypertonic NaCl, or i.c.v. infusion of angiotensin II (ANG II). The effects of these receptor antagonists on sodium intake caused by sodium depletion were also examined. Losartan infusion caused dose-dependent inhibition of the high water intake caused by the physiological stimulus of water restriction or by ANG II infusion but did not affect salt appetite. PD-123319 infused at equimolar or greater (in ANG II experiments) doses did not affect water intake or salt intake due to sodium depletion. The results of these i.c.v. infusion experiments confirm our earlier proposal that the physiological regulation of water intake in cattle may be mediated by ANG II acting centrally via AT1 receptors. The dose of losartan that inhibited thirst in cattle did not inhibit sodium appetite, nor did an equimolar dose of PD-123319.

Distribution of Fos immunoreactivity in the lamina terminalis and hypothalamus induced by centrally administered relaxin in conscious rats

The effect of intracerebroventricular (ICV) injections of synthetic human or rat relaxin (25 or 250 ng) on the distribution of Fos detected immunohistochemically in the rat forebrain was investigated. Following ICV relaxin, many Fos-positive neurons were observed in the periphery of the subfornical organ, dorsal part of the organum vasculosum of the lamina terminalis, throughout the median preoptic nucleus, supraoptic nucleus and hypothalamic paraventricular nucleus. Such effects did not occur following ICV injection of artificial cerebrospinal fluid or the separated A and B chains of relaxin, nor following the intravenous injection of 250 ng of relaxin. Both vasopressin and oxytocin containing neurons identified immunohistochemically in the supraoptic and paraventricular nuclei exhibited Fos following ICV relaxin, and many neurons in the medial parvocellular part of the paraventricular nucleus contained Fos. The results indicate that centrally administered relaxin may increase neuronal activity in regions of the hypothalamus and lamina terminalis which are associated with cardiovascular and body fluid regulation and oxytocin secretion.

Distribution of bradykinin B2 receptors in sheep brain and spinal cord visualized by in vitro autoradiography

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Intracerebroventricular losartan inhibits postprandial drinking in sheep

We investigated the contribution of brain angiotensinergic mechanisms to postprandial drinking in sheep. Sheep in fluid balance were given 0.8 kg chaff for 30 min, and water intake was measured for the next hour. Intracerebroventricular infusion of the AT1 type angiotensin II (ANG II) receptor blocker losartan (1 mg/h) reduced postprandial drinking by approximately 70% (n = 7, P < 0.01) but did not affect food intake. The same losartan dose given intravenously had little or no effect on prandial drinking. Feeding increased Na+ concentrations in plasma and cerebrospinal fluid (CSF; n = 5, P < 0.05). Intracerebroventricular losartan (1 mg/h) inhibited the drinking responses to intracarotid infusion of ANG II (0.8 microg/min for 30 min, n = 4, P < 0.01) and to intracerebroventricular infusion of 0.5 M NaCl (1 ml/h for 1 h, n = 5, P < 0.05) but had no effect on drinking responses to intravenous infusion of 4 M NaCl (1.3 ml/min for 30 min). These findings indicate that a brain ANG II-dependent mechanism is involved in postprandial drinking in sheep. They suggest also that the mechanism by which increasing CSF Na+ causes thirst involves brain ANG II and is different from the mechanism subserving the drinking response to changes in blood Na+.