Water and sodium intake of wild and New Zealand Rabbits following angiotensin

Two rabbit strains, New Zealand (laboratory) rabbits and Australian wild rabbits, both members of the Oryctolagus cuniculus genus were studied. New Zealand rabbits under control conditions consumed 2-5 times more water and 8-30 times more 0.5 M NaCl/kg body weight than wild rabbits. Single injections of angiotensin II or III administered ICV did not induce water drinking in either strain. Acute ICV infusion of angiotensin II also did not influence water intake, but after several days of administration, induced increased sodium intake. Intravenous infusion of graded doses of angiotensin II induced diuresis only at the higher doses in both strains. In New Zealand rabbits, this was accompanied by a commensurate and concurrent increase in water intake. Intravenous infusion of angiotensin II also induced urinary sodium loss that was either accompanied or followed by increased sodium intake. The development of salt appetite in both strains was preceded by sodium loss.     

What makes wild rabbits drink?

Wild rabbits Oryctolagus cuniculus (L) introduced to Australia over a century ago successfully colonized diverse environments in a large part of the continent varying from arid desert, alps, to lush grasslands and coastline where water and salt may be either abundant or very scarce. Wild rabbits caught in Northern Victoria were studied under laboratory conditions, where they adapted to dry pelleted food and drank regularly water and a cafeteria of electrolyte solutions offered. Intracerebroventricular (IVT) infusion of angiotensin II (AII) in doses 10, 50 and 500 ng/h did not increase their water drinking, but increased salt appetite, although it was delayed one or more days after the beginning of AII infusion. IVT infusion of AII 500 ng/h for one day caused a halving in water intake and a tenfold increase in sodium excretion. These were followed by compensatory changes in water and 0.5 M NaCl intake on the consecutive days. IVT infusion of AII 50 ng/h for one day induced an increased urinary sodium excretion, a negative sodium balance which was not followed by an increased salt appetite. IVT infusion of AII 10 ng/h for five days caused a progressive increase in sodium excretion and salt appetite which were significant on the fourth day of infusion and both remained eight-ten times greater than control levels for three days after the cessation of infusion. Water intake was unchanged. IVT infusion of 0.3 M Na-CSF for two days reduced water and food intake, and caused a negative sodium balance on the second day of infusion which was not followed by increase in salt appetite.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of intracerebroventricular atrial natriuretic polypeptide on blood pressure and urine production in rats

In order to clarify the role of atrial natriuretic polypeptide (ANP) in the brain on regulation of blood pressure and urine output, we examined the effects of intracerebroventricular (i.c.v.) administration of synthetic alpha-human ANP (alpha-hANP) to both anesthetized and conscious rats. In anesthetized rats, i.c.v. injection of angiotension II (A II) caused increases of blood pressure, urine flow and sodium excretion in a dose dependent manner. alpha-HANP alone had no effect on these two parameters. The hypertensive effect of A II was apparently attenuated by concurrent injection of alpha-hANP, while, the diuretic response to A II was not changed by alpha-hANP. In conscious spontaneously hypertensive rats, i.c.v. injection of saralasin (an A II antagonist) produced a decrease in blood pressure. The i.c.v. pretreatment with alpha-hANP significantly potentiated the central depressor effect of saralasin. These findings suggest that brain ANP may be involved in controlling blood pressure in the central renin-angiotensin system.     

Salt Appetite Is Reduced by a Single Experience of Drinking Hypertonic Saline in the Adult Rat

Salt appetite, the primordial instinct to favorably ingest salty substances, represents a vital evolutionary important drive to successfully maintain body fluid and electrolyte homeostasis. This innate instinct was shown here in Sprague-Dawley rats by increased ingestion of isotonic saline (IS) over water in fluid intake tests. However, this appetitive stimulus was fundamentally transformed into a powerfully aversive one by increasing the salt content of drinking fluid from IS to hypertonic saline (2% w/v NaCl, HS) in intake tests. Rats ingested HS similar to IS when given no choice in one-bottle tests and previous studies have indicated that this may modify salt appetite. We thus investigated if a single 24 h experience of ingesting IS or HS, dehydration (DH) or 4% high salt food (HSD) altered salt preference. Here we show that 24 h of ingesting IS and HS solutions, but not DH or HSD, robustly transformed salt appetite in rats when tested 7 days and 35 days later. Using two-bottle tests rats previously exposed to IS preferred neither IS or water, whereas rats exposed to HS showed aversion to IS. Responses to sweet solutions (1% sucrose) were not different in two-bottle tests with water, suggesting that salt was the primary aversive taste pathway recruited in this model. Inducing thirst by subcutaneous administration of angiotensin II did not overcome this salt aversion. We hypothesised that this behavior results from altered gene expression in brain structures important in thirst and salt appetite. Thus we also report here lasting changes in mRNAs for markers of neuronal activity, peptide hormones and neuronal plasticity in supraoptic and paraventricular nuclei of the hypothalamus following rehydration after both DH and HS. These results indicate that a single experience of drinking HS is a memorable one, with long-term changes in gene expression accompanying this aversion to salty solutions.     

Neuroendocrine factors in salt appetite.

We dedicate this paper to Curt P. Richter, father of the study of salt appetite, who died recently at the age of 94. Richter first demonstrated that the adrenalectomized rat's voracious appetite for salt kept it alive (1936) and showed the same in humans (1940). Our first paper in 1955 demonstrated that salt appetite was an innate response to salt depletion. Since then, we have pursued the notion that the neuroendocrine consequences of sodium depletion create a brain state that raises salt appetite. In Epstein's laboratory, it was shown that angiotensin and aldosterone, the hormones of salt retention in the periphery, act synergistically in the brain to produce salt appetite in the rat. Block either hormone and the appetite is reduced by half; block both and the appetite is eliminated despite severe bodily need. With repeated depletions or treatments of the brain with angiotensin and aldosterone, salt ingestion increases, reaching an asymptote by the third depletion. Need-free intake of NaCl also increases, especially in female rats which ingest more NaCl than male rats. In Stellar's laboratory, running speed to salt solutions in a runway is used as a measure of salt appetite. When the appetite is raised with large doses of DOCA, a mimic of aldosterone, rats run rapidly for a taste of strong salt solutions as high as 24% (almost 4 molar). Using ingestion as a measure, the role of the atrial natriuretic peptide (ANP), an antagonist of angiotensin's physiological effect, was investigated as a modulator of salt appetite. When angiotensin is involved is producing salt appetite, following sodium depletion by a diuretic combined with a low-salt diet, ANP reduced salt intake by 40%. When salt appetite was raised by DOCA, however, ANP either had no effect or reduced salt ingestion by only 10%. The subfornical organ, the lateral preoptic area, and the central and medial nuclei of the amygdala are being investigated as major components of the limbic circuit underlying salt appetite produced by the actions of angiotensin, aldosterone and ANP in the brain.     

The renin-angiotensin system and sodium appetite

Intracranial renin is a potent stimulus to sodium appetite and thirst, the effects being mediated by local generation of angiotensin II. Intakes are persistent and lead to fluid retention during the first 24 h (Avrith and Fitzsimons, 1983). Increased circulating renin after captopril treatment in adrenalectomized rats (Elfont and Fitzsimons, 1981), or in renal hypertension following partial inter-renal aortic ligation (Costales et al., 1982), also leads to increased intakes of 2.7% NaCl and water. Fluid intakes after aortic ligation were independent of the severity of hypertension produced by this procedure. In both the examples given, additional stimulation resulting from the hypovolaemia itself is required for the full expression of increased sodium appetite, but in both cases angiotensin makes a significant contribution to sodium appetite as well as thirst. Therefore, as has been shown for thirst, angiotensin is one of a number of factors that act together to cause increased sodium appetite in hypovolaemia.     

AT(1) receptor blockade with losartan during gestation in Wistar rats leads to an increase in thirst and sodium appetite in their adult female offspring

We studied the effects of angiotensin II receptor blockade with losartan on thirst and sodium appetite in pregnant Wistar rats and on their adult female offspring. During maternal adaptation to pregnancy, average daily total water intake increased by 63% (P<0.01); NaCl intake by 214% (P<0.001). These changes were not blocked by daily s.c. injections of losartan (50 mg/kg bw i.p.) from gestation day (GD) 2 until GD 19 which implied that maternal AT(1) receptors were not involved in the up regulation of thirst and sodium appetite during pregnancy. Losartan blockade during gestation led to a significant and continued increase in thirst and sodium appetite in the adult female offspring. Daily water intakes were greater in the losartan (LO) group than in the vehicle-injected control group (CO), leading to a total water intake of 1114 +/- 80.6 ml/kg bw compared with 738 +/- 56.7 ml/kg bw (P<0.05) during the 8-day period of observation. Daily sodium intakes were usually 2-3 times greater in the LO group compared with the CO group, amounting to a final cumulative intake of 232 +/- 33 mmol/kg bw compared with 93.8 +/- 16.5 mmol/kg bw (P<0.05) in 8 days. These elevated sodium and water intakes were nearly counterbalanced by the increased renal excretion of water and sodium by fully functional kidneys that were not injured by the drug. Body weights were 10% lower in the LO group at the start but remained unchanged relative to the CO group during the entire 8-day period of observation. Plasma electrolytes, blood hematocrit and carotid MABP in the LO group did not differ from the CO group.     

Increased sodium intake is somehow induced in rats by intravenous angiotensin II

Adult male rats maintained on dry food, water, and 3% NaCl solution received continuous infusion of angiotensin II (A II) via right atrial catheters. A II was delivered in 0.315 ml/hr at doses of 15, 30, and 60 ng/min/rat for 3 to 5 days. At the higher doses mean daily salt solution intake rose from very low preinfusion levels to 18.7 and 19.6 ml, respectively. Daily water intakes increased in some animals and decreased in others on the first day of infusion but were double preinfusion levels by the second day. Persistence of the sodium appetite after the end of A II infusion was seen in most of the rats which received the highest dose. The mechanisms which might underlie the effect of blood-borne A II on sodium intake are discussed and three possibilities considered: (1) that A II may act on the brain to stimulate sodium appetite, (2) that A II may act via the adrenal cortex, and that the sodium appetite may arise as a result of increased plasma levels of adrenal steroids, and (3) that A II may act via the kidney, producing a natriuresis. According to this view, sodium appetite would arise as a result of loss of body sodium and/or blood volume.     

Angiotensin and other peptides in the control of water and sodium intake

Several neuroactive peptides have been implicated in thirst and sodium appetite in different species; three peptides are considered here. The best established of these is the octapeptide angiotensin II, which when administered systemically or intracranially causes completely normal drinking behaviour in all vertebrates tested, including many mammals, four or five birds, one reptile and one bony fish. In the rat, in which the original experiments were carried out, injection of a few femtomoles of angiotensin II caused a brisk drinking response within a minute or so of injection at a time of day when the animal would usually be resting. The response is usually completed within 10 min and after the larger doses the amounts of water taken may approach what the animal would normally drink in the course of 24 h. Another response to intracranial angiotensin, seen so far only in the rat, is an increase in sodium appetite. This is slower in onset than thirst, lasts for many hours and the response tends to become greater with repeated injections of hormone. Naturally occurring increases in sodium appetite may be caused by angiotensin generated by the action of cerebral isorenin. A second neuroactive peptide that affects thirst is the undecapeptide eledoisin, which is found in the salivary glands of certain Mediterranean cephalopods. Eledoisin and, to a lesser extent, substance P, with which it is related, are potent intracranial dipsogens in the pigeon, producing behaviour that is indistinguishable from that produced by angiotensin. However, in contrast to the stimulatory action of angiotensin on drinking behaviour in all other vertebrate species tested, these substances specifically depress drinking in the rat. A third peptide that has been implicated in thirst is antidiuretic hormone (ADH). This hormone has a profound but indirect effect on water intake in diabetes insipidus. In the dog, however, ADH in physiological amounts may influence thirst mechanisms by direct action on the central nervous system. In this species, but not in the rat, ADH lowers the threshold of thirst in response to osmotic stimulation and also to infusion of angiotensin. Of these three peptides, and others not mentioned here, angiotensin II has the best claim to be regarded as a neuroactive peptide. It alone is always dipsogenic when injected into the brain and it also stimulates sodium appetite. Whether the effects of angiotensin, on thirst and sodium appetite should be regarded as manifestations of the activity of a classical endocrine system, of a paracrine system, of a neurotransmitter system, or of all of these, cannot be decided at present. But these actions of angiotensin, when considered with its other actions on the distribution and conservation of body fluid, show that the hormone is intimately concerned in extracellular fluid volume control.     

Effect of atrial natriuretic peptide on ACTH, dibutyryl cAMP, angiotensin II and potassium-stimulated aldosterone secretion by rat adrenal glomerulosa cells

We examined the effect of rat atrial natriuretic peptide (ANP) on ACTH, dibutyryl cAMP, angiotensin II and potassium-stimulated aldosterone secretion by dispersed rat adrenal glomerulosa cells. ANP inhibited ACTH, angiotensin II and potassium-stimulated aldosterone secretion with IC50's between 0.15-0.20 nM. Inhibition by 10 nM ANP could not be overcome with higher concentrations of these stimuli. ANP shifted the dibutyryl cAMP dose-response curve slightly to the right but did not blunt the maximal aldosterone secretory response. The sites of ANP inhibition in the aldosterone biosynthetic pathway for these stimuli were also examined. ANP inhibited activation of the cholesterol desmolase (CD) enzyme complex by ACTH, angiotensin II and potassium. Activation of the corticosterone methyl oxidase (CMO) enzyme complex by potassium was inhibited by ANP, however, activation by ACTH was not blocked. We concluded that: 1) ANP is a potent inhibitor of ACTH, angiotensin II and potassium-stimulated aldosterone secretion; 2) inhibition of ACTH stimulation is primarily due to lower cAMP levels and; 3) inhibition of angiotensin II and potassium stimulation reflects a block in the activating mechanism of the CMO and/or CD enzyme complexes, whereas CD but not CMO activation by ACTH is inhibited by ANP.     

Enhanced water and salt intake in transgenic mice with brain-restricted overexpression of angiotensin (AT1) receptors

To address the relative contribution of central and peripheral angiotensin II (ANG II) type 1A receptors (AT(1A)) to blood pressure and volume homeostasis, we generated a transgenic mouse model [neuron-specific enolase (NSE)-AT(1A)] with brain-restricted overexpression of AT(1A) receptors. These mice are normotensive at baseline but have dramatically enhanced pressor and bradycardic responses to intracerebroventricular ANG II or activation of endogenous ANG II production. Here our goal was to examine the water and sodium intake in this model under basal conditions and in response to increased ANG II levels. Baseline water and NaCl (0.3 M) intakes were significantly elevated in NSE-AT(1A) compared with nontransgenic littermates, and bolus intracerebroventricular injections of ANG II (200 ng in 200 nl) caused further enhanced water intake in NSE-AT(1A). Activation of endogenous ANG II production by sodium depletion (10 days low-sodium diet followed by furosemide, 1 mg sc) enhanced NaCl intake in NSE-AT(1A) mice compared with wild types. Fos immunohistochemistry, used to assess neuronal activation, demonstrated sodium depletion-enhanced activity in the anteroventral third ventricle region of the brain in NSE-AT(1A) mice compared with control animals. The results show that brain-selective overexpression of AT(1A) receptors results in enhanced salt appetite and altered water intake. This model provides a new tool for studying the mechanisms of brain AT(1A)-dependent water and salt consumption.     

Hindbrain serotonin and the rapid induction of sodium appetite

Both systemically administered furosemide and isoproterenol produce water intake (i.e., thirst). Curiously, however, in light of the endocrine and hemodynamic effects produced by these treatments, they are remarkably ineffective in eliciting intake of hypertonic saline solutions (i.e., operationally defined as sodium appetite). Recent work indicates that bilateral injections of the serotonin receptor antagonist methysergide into the lateral parabrachial nuclei (LPBN) markedly enhance a preexisting sodium appetite. The present studies establish that a de novo sodium appetite can be induced with LPBN-methysergide treatment under experimental conditions in which only water is typically ingested. The effects of bilateral LPBN injections of methysergide were studied on the intake of water and 0. 3 M NaCl following acute (beginning 1 h after treatment) diuretic (furosemide)-induced sodium and water depletion and following subcutaneous isoproterenol treatment. With vehicle injected into the LPBN, furosemide treatment and isoproterenol injection both caused water drinking but essentially no intake of hypertonic saline. In contrast, bilateral treatment of the LPBN with methysergide induced the intake of 0.3 M NaCl after subcutaneous furosemide and isoproterenol. Water intake induced by subcutaneous furosemide or isoproterenol was not changed by LPBN-methysergide injections. The results indicate that blockade of LPBN-serotonin receptors produces a marked intake of hypertonic NaCl (i.e., a de novo sodium appetite) after furosemide treatment as well as subcutaneous isoproterenol.     

Osmoregulatory fluid intake but not hypovolemic thirst is intact in mice lacking angiotensin

Water intakes in response to hypertonic, hypovolemic, and dehydrational stimuli were investigated in mice lacking angiotensin II as a result of deletion of the angiotensinogen gene (Agt-/- mice), and in C57BL6 wild-type (WT) mice. Baseline daily water intake in Agt-/- mice was approximately threefold that of WT mice because of a renal developmental disorder of the urinary concentrating mechanisms in Agt-/- mice. Intraperitoneal injection of hypertonic saline (0.4 and 0.8 mol/l NaCl) caused a similar dose-dependent increase in water intake in both Agt-/- and WT mice during the hour following injection. As well, Agt-/- mice drank appropriate volumes of water following water deprivation for 7 h. However, Agt-/- mice did not increase water or 0.3 mol/l NaCl intake in the 8 h following administration of a hypovolemic stimulus (30% polyethylene glycol sc), whereas WT mice increased intakes of both solutions during this time. Osmoregulatory regions of the brain [hypothalamic paraventricular and supraoptic nuclei, median preoptic nucleus, organum vasculosum of the lamina terminalis (OVLT), and subfornical organ] showed an increased number of neurons exhibiting Fos-immunoreactivity in response to intraperitoneal hypertonic NaCl in both Agt-/- mice and WT mice. Polyethylene glycol treatment increased Fos-immunoreactivity in the subfornical organ, OVLT, and supraoptic nuclei in WT mice but only increased Fos-immunoreactivity in the supraoptic nucleus in Agt-/- mice. These data show that brain angiotensin is not essential for the adequate functioning of neural pathways mediating osmoregulatory thirst. However, angiotensin II of either peripheral or central origin is probably necessary for thirst and salt appetite that results from hypovolemia.     

Effects of hypotension and fluid depletion on central angiotensin-induced thirst and salt appetite

We examined the effects of hypotension and fluid depletion on water and sodium ingestion in rats in response to intracerebroventricular infusions of ANG II. Hypotension was produced by intravenous infusion of the vasodilator drug minoxidil (25 microg x kg(-1) x min(-1)) concurrently with the angiotensin-converting enzyme inhibitor captopril (0.33 mg/min) to prevent endogenous ANG II formation. Hypotension increased water intake in response to intracerebroventricular ANG II (30 ng/h) but not intake of 0.3 M NaCl solution and caused significant urinary retention of water and sodium. Acute fluid depletion was produced by subcutaneous injections of furosemide (10 mg/kg body wt) either alone or with captopril (100 mg/kg body wt sc) before intracerebroventricular ANG II (15 or 30 ng/h) administration. Fluid depletion increased water intake in response to the highest dose of intracerebroventricular ANG II but did not affect saline intake. In the presence of captopril, fluid depletion increased intakes of both water and saline in response to both doses of intracerebroventricular ANG II. Because captopril administration causes hypotension in fluid-depleted animals, the results of the two experiments suggest that hypotension in fluid-replete animals preferentially increases water intake in response to intracerebroventricular ANG II and in fluid-depleted animals increases both salt and water intake in response to intracerebroventricular ANG II.     

Vascular, renal, and endocrine responses to low-dose atrial natriuretic peptide in the fluid-balanced New Zealand genetically hypertensive rats with and without endogenous arginine vasopressin.

In hypertension, the relationship between atrial natriuretic peptide (ANP) and vasopressin (AVP) is not yet clear, although their renal actions are effectively autoregulation. To examine the possible interaction further, the responses to ANP infusion (75 ng x min (-1), i.v.) have been investigated in both hypertensive and normotensive AVP-replete (HT and NT) and AVP-deficient (HTDI and NTDI) rats. This study aimed to assess the renal function and the plasma hormone concentrations of AVP, angiotensin II (AII), ANP, aldosterone, and corticosterone in the conscious, chronically catheterized, fluid-balanced rats, and to examine the cardiovascular, renal, and endocrine responses to a constant infusion of a low-dose ANP. Data gained from the present study showed, for the first time, the hormone profile, plasma electrolyte composition, and detailed renal function of the servo-controlled, fluid-balanced rats. The similarities of plasma electrolyte composition between servo-controlled and untreated rats indicated that the servo-controlled fluid replacement technique maintained the differences between the strains and maintained body fluid balance during the experimental periods. Following ANP administration, there were no changes in glomerular filtration rate (GFR) in all groups, but an enduring diuresis and natriuresis were observed in HT and NT, which were milder in HTDI rats. However, the hypotensive effect of ANP was of a similar magnitude in all rat strains. HTDI rats exhibited an inhibition of the renin-angiotensin system (RAS), which may have participated in the reduced mean arterial blood pressure (MAP) and natriuresis observed in these rats. The renal actions of ANP appear to rely upon renal tubular events, as indicated by increased fractional electrolyte excretions in the AVP-replete rats. This study highlights the importance of AVP to the profile of the renal actions of ANP in normal rats.     

Physiological role of brain angiotensin III in drinking behavior in the rat

We examined the physiologic role of endogenous brain angiotensin III (AIII), an active degradative product of angiotensin II, in drinking behavior. Adult, male spontaneously hypertensive (SH) and Wistar-Kyoto normotensive (WKY) rats that were instrumented with an intracerebroventricular (i.c.v.) cannula connected to an osmotic minipump for chronic infusion were used. 7-day i.c.v. infusion of the specific AIII antagonist, Ile⁷-AIII (10 or 100 pmol/min), resulted in no significant alteration in daily (24 h), diurnal (8:00 a.m.-8:00 p.m.) or nocturnal (8:00 p.m.-8:00 a.m.) basal water intake in both SH and WKY rats. Similar results were obtained with i.c.v. infusion of the aminopeptidase inhibitor, bestatin (150 or 300 pmol/min), given alone or simultaneously with Ile⁷-AIII (10 pmol/min). Rats that were water-deprived for the first 3 days of 7-day infusion of Ile⁷-AIII consumed significantly less water during the first 2 h after water became available. Furthermore, the accumulated water intake during the first 24 h was appreciably greater in SH than WKY rats. We interpret these results to suggest that the endogenous brain AIII may not be tonically involved in fluid homeostasis. Instead, it must be activated under conditions of dehydration, such as water deprivation, particularly in the SHRs, to initiate drinking behavior.     

Circulating angiotensin II mediates sodium appetite in adrenalectomized rats

We investigated the role of circulating ANG II in sodium appetite after adrenalectomy. Adrenalectomized rats deprived of their main access to sodium (0.3 M NaCl) for 9 h drank 14.1 +/- 1.5 ml of the concentrated saline solution in 2 h of access. Intravenous infusion of captopril (2.5 mg/h) during the last 5 h of sodium restriction reduced sodium intake by 77 +/- 12% (n = 5) without affecting the degree of sodium depletion and hypovolemia incurred during deprivation. Functional evidence indicates that this dose of captopril blocked production of ANG II in the peripheral circulation, but not in the brain; that is, injection of ANG I into the lateral brain ventricle stimulated intake of both water and 0.3 M NaCl. Intravenous infusion of ANG II (starting 10-15 min before 0.3 M NaCl became available) in adrenalectomized, captopril-treated rats restored both sodium intake and blood pressure to values seen in rats not treated with captopril. Longer (20 h) infusions of captopril in 22-h sodium-restricted rats also blocked sodium appetite, but reduced or prevented sodium depletion. Intravenous infusion of ANG II after these long captopril infusions stimulated sodium intake, but intake was less than in controls not treated with captopril. These results indicate that most or all of the sodium appetite of adrenalectomized rats is mediated by circulating ANG II.     

Intracerebroventricular injections of cholecystokinin octapeptide suppress feeding in rats--pharmacological characterization of this action

Cholecystokinin octapeptide (CCK-8), administered intracerebroventricularly (i.c.v.), will suppress feeding. The aim of the present study was to determine the pharmacological characteristics of this satiety inducing effect in rats. For this purpose, we employed a feeding bioassay model in 24 h fasted rats and examined the effects of CCK-8 and a variety of structurally related analogs on latency to feed after i.c.v. injection and on the amount of food and water consumed as measured after the initiation of feeding in sequential 20-min epochs for 1 h. CCK-8, given in doses of 0.1, 1 and 10 nmol, produced a dose-dependent increase in feeding latency and a reduction of food intake during the first 20 min after initiation of feeding. Food intake during the next 40 min and water consumption were not altered. Plasma levels of CCK-like immunoreactivity after an i.c.v. injection of a dose of CCK-8 which blocked feeding (10 nmol) rose insignificantly from 117 to 125 pg/ml. In contrast, at the minimally effective dose of CCK-8 after i.v. administration (10 nmol), which also produced an inhibition of feeding, the plasma level was 1430 pg/ml. This difference indicates that plasma levels of CCK after i.c.v. CCK-8 are not adequate to produce the observed feeding suppression and suggests that the effects of i.c.v. CCK-8 are not mediated by a peripheral redistribution. Systematic dose response studies revealed the following rank order of potencies: CCK-8 greater than or equal to G-17 II much greater than CCK-8 NS = G-17 I greater than or equal to CCK-4 = CCK 26-29 = 0. Only gastrin-17 II (sulfated) produced an effect comparably significant to CCK-8. I.c.v. proglumide at 2500 nmol failed to modify the effects of CCK-8 at 10 nmol after i.c.v. injection. These data demonstrate that the structural requirements for feeding suppressive activity in rat brain are the carboxyterminus with a sulfated tyrosine residue, located 6 to 7 residues from the carboxyterminus, as present in CCK-8 and gastrin-17 II.     

Hypothalamic alpha-adrenergic blockade modifies drinking and blood pressure responses to central angiotensin II in conscious rats

These experiments investigated in the awake rat the involvement of noradrenergic projections to the rostral hypothalamus in the drinking and pressor responses elicited by intracerebroventricular (i.c.v.) injections of 25 ng of angiotensin II. Phentolamine mesylate in doses of 2.5-125 micrograms injected into the rostral hypothalamus produced a dose-dependent depression of both the drinking and pressor responses elicited by i.c.v. administration of angiotensin II. A paradoxical increase in heart rate was associated with a decrease in pressor responses with increasing doses of phentolamine. This response was due to tissue injections, since pretreatment by injecting 12.5 micrograms of phentolamine into the ventricle did not block either the cardiovascular or drinking responses to i.c.v. injections of angiotensin II. Yohimbine (0.33-3.3 micrograms), DL-propranolol (25 micrograms), and atenolol (25 micrograms) did not, but prazosin (0.7 microgram) did significantly alter the pressor responses. Although yohimbine also was without effect on drinking, prazosin reduced the drinking responses. These results suggest that alpha 1-adrenergic receptors in the rostral hypothalamus are involved in the control of both the drinking and pressor responses elicited by i.c.v. injections of angiotensin II. In the case of propranolol and atenolol, beta-adrenergic receptors altered only the drinking response in a nonspecific manner by eliciting competing behaviors. Whether they are involved in modifying the drinking response only remains to be demonstrated.     

Angiotensin, thirst, and sodium appetite: retrospect and prospect.

The fact that drinking in response to some hypovolemic stimuli was attenuated by nephrectomy but not by ureteric ligation led to the suggestion that the renal renin-angiotensin system may play a role in hypovolemic thirst. The isolation of a thirst factor from the kidney and the demonstration that this substance was renin supported the hypothesis. Subsequently, it was shown that the effects of renin on drinking were mediated through angiotensin II, which proved to be a potent dipsogenic substance when administered systemically or injected directly into the brain. Recently, it has been shown that angiotensin II, infused intravenously or through the carotid artery at rates that produce increases in plasma angiotensin II levels similar to those that occur in mild sodium depletion, causes the water-replete animal to drink. This discovery establishes that angiotensin is a physiological stimulus to drinking but it leaves open the question of the extent of the involvement of renal renin in normal thirst. Other unsolved problems are the role of cerebral isorenin in angiotensin thirst and its relationship with renal renin, and in view of its stimulating action on sodium intake when infused into the brain, whether angiotensin plays a significant role in sodium appetite.