Brain sodium channels and central sodium-induced increases in brain ouabain-like compound and blood pressure

OBJECTIVE: To assess the role of benzamil-sensitive sodium channels in the increases in brain ouabain-like compounds (OLC) and in blood pressure by cerebrospinal fluid (CSF) Na+. METHODS: Artificial CSF (aCSF) or Na+-rich (0.8 mol/l Na+) aCSF, either alone or combined with benzamil (at 1.2 and 4.0 microg/kg per h), were infused intracerebroventricularly (i.c.v.) at 5 microl/h to Wistar rats for 14 days and the effects on the brain and peripheral OLC and blood pressure were studied. OLC content was measured by enzyme-linked immunosorbent assay. RESULTS: In Wistar rats infused i.c.v. with aCSF, benzamil did not affect blood pressure or brain and peripheral OLC concentrations. I.c.v. infusion of Na+-rich aCSF increased systolic blood pressure (140 +/- 4 mmHg compared with 119 +/- 3 mmHg; P < 0.05). Benzamil fully blocked this increase. Na+-rich aCSF increased hypothalamic (23 +/- 3 ng/g tissue compared with 10 +/- 1 ng/g tissue; P < 0.05) and pituitary (233 +/- 35 ng/g tissue compared with 62 +/- 7 ng/g tissue; P < 0.05) contents of OLC. In contrast, Na+-rich aCSF decreased OLC in the adrenal gland (7 +/- 1 ng/g tissue compared with 21 +/- 3 ng/g tissue; P < 0.05) and plasma (0.5 +/- 0.04 ng/ml compared with 0.7 +/- 0.08 ng/ml; P < 0.05). Benzamil inhibited these responses of OLC to CSF sodium in a dose-related manner. CONCLUSIONS: These findings suggest that benzamil-sensitive brain sodium channels mediate the increase in brain OLC and the subsequent hypertension induced by increased CSF Na+.     

Role of the serotonergic nervous system in hemodynamic and vasopressin responses to centrally administrated angiotensin-II in spontaneously hypertensive rats

The purpose of the study is to investigate the role of the serotonergic nervous system in centrally administrated angiotensin II (A-II) mediated hemodynamic as well as vasopressin (AVP) responses. Eight-week-old male SHR and age-matched Wistar Kyoto rats (WKY) were used and the experiment was performed in the conscious state. In protocol 1, after resting observation of 30 minutes 10ng of A-II was given intracerebroventricularly (i.c.v.). This was followed by i.c.v. injection of 1 microgram of 5-HT2 receptor antagonist, xylamidine, 50 minutes later; then 10ng of i.c.v. A-II was repeated after 10 minutes (SHR: n = 7, WKY: n = 10). In protocol 2, plasma vasopressin (AVP) was measured in the following groups. In one group, 1.3ml of blood was sampled from the carotid cannula after resting observation, and the same amount of blood from an age-matched donor rat of the same strain was transfused immediately. Two hours later, 10ng of A-II was given i.c.v., and blood was sampled again after 1 minute (SHR: n = 7, WKY: n = 12). In another group, 1 microgram of xylamidine was given i.c.v. and was followed by 10ng of A-II 10 minutes later; then blood was collected after 1 minute (SHR: n = 8, WKY: n = 13). In protocol 1, resting MAP were 144 +/- 6mmHg in SHR and 99 +/- 2mmHg in WKY. I.c.v. A-II elicited a consistent pressor response in both SHR and WKY, but the response was significantly larger in SHR than that in WKY, +45 +/- 3 and +37 +/- 1mmHg, respectively. Xylamidine had no effect on MAP, and repeated A-II produced significant pressor responses. However, the responses were significantly smaller in both SHR (+36 +/- 3mmHg) and WKY (+25 +/- 1mmHg) as compared with those to initial A-II injection. In protocol 2, resting AVP were similar in SHR (1.5 +/- 0.2pg/ml) and in WKY (1.6 +/- 0.1pg/ml). However, after i.c.v. A-II injection, AVP became higher in SHR (131 +/- 14pg/ml) than in WKY (64 +/- 6pg/ml). AVP after A-II injection with xylamidine pretreatment were similar in SHR (48 +/- 6pg/ml) and in WKY (45 +/- 4pg/ml). Since the responses of both MAP and AVP to i.c.v. A-II were larger in SHR, and the responses were effectively suppressed by S2 receptor antagonists, the central serotonergic nervous system may play an important role in the hemodynamic as well as AVP responses to i.c.v. A-II administration.     

Cardiovascular effects of long-term central and peripheral administration of urocortin, corticotropin-releasing factor, and adrenocorticotropin in sheep

The neuroendocrine hormones ACTH and corticotropin- releasing factor (CRF), which are involved in the stress response, have acute effects on arterial pressure. New evidence indicates that urocortin (UCN), the putative agonist for the CRF type 2 receptor, has selective cardiovascular actions. The responses to long-term infusions of these hormones, both peripherally and centrally, in conscious animals have not been studied. Knowledge of the long-term effects is important because they may differ considerably from their acute actions, and stress is frequently a chronic stimulus. The present experiments investigated the cardiovascular effects of CRF, UCN, and ACTH in conscious sheep. Infusions were made either into the lateral cerebral ventricles (i.c.v.) or i.v. over 4 d at 5 microg/h. UCN infused i.c.v. or i.v. caused a prolonged increase in heart rate (HR) (P < 0.01) and a small increase in mean arterial pressure (MAP) (P < 0.05). CRF infused i.c.v. or i.v. progressively increased MAP (P < 0.05) but had no effect on HR. Central administration of ACTH had no effect, whereas systemic infusion increased MAP and HR (P < 0.001). In conclusion, long-term administration of these three peptides associated with the stress response had prolonged, selective cardiovascular actions. The striking finding was the large and sustained increase in HR with i.c.v. and i.v. infusions of UCN. These responses are probably mediated by CRF type 2 receptors because they were not reproduced by infusions of CRF.     

Stimulation of renal prostaglandins by pressor hormones in man: comparison of prostaglandin E2 and prostacyclin (6 keto prostaglandin F1 alpha)

The effect of vasoconstrictive agonists and their nonpressor analogs on renal prostaglandin production was investigated in normal subjects maintained on constant diets. Arginine vasopressin (AVP), 10 U, desamino-d arginine vasopressin (dDAVP), 4 micrograms, angiotensin II (AII), 5 ng/kg . min, des-Asp angiotensin II (AIII), 5 ng/kg . min, norepinephrine (NE), 0.1 microgram/kg . min, and NE plus phenoxybenzamine (PHB), 0.8 mg/kg, were administered on separate days. Prostaglandin E2 (PGE2) and the stable prostacyclin metabolite, 6 keto prostaglandin F1 alpha were measured in 4-h urine collections by procedures with high resolution chromatography and RIA using highly specific antisera. AVP and dDAVP similarly reduced urine volume and increased urine osmolality. AII, AIII, NE, and NE + PHB did not alter basal urine volume, osmolality, creatinine, or electrolyte excretion. Blood pressure was similarly increased by AII and NE infusions (23 +/- 3 vs. 19 +/- 2 (SE) mm Hg). AVP and AII increased only PGE2 excretion (61 +/- 8 to 151 +/- 34 ng/4 h for AVP, and 38.7 +/- 7 to 75 +/- 19 ng/4 h for AII, P less than 0.05). The nonpressor analogs, dDAVP and AIII, had no effect on urinary prostaglandin excretion. In contrast, NE increased both PGE2 (from 38.7 +/- 7 to 74.5 +/- 12 ng/4 h, P less than 0.02) and 6 keto prostaglandin F1 alpha (from 34.6 +/- 8 to 56.1 +/- 9 ng/4 h, P less than 0.02). alpha-Blockade with PHB totally abolished the NE-induced systemic pressor and prostaglandin stimulatory effect. These data suggest that renal PGE2 and prostacyclin are not altered in parallel by vasoactive stimuli. PGE2 appears to be released in response to agents that induce renal vasoconstriction and reduced renal blood flow whereas renal prostacyclin excretion is stimulated by an adrenergic agonist via alpha-receptor activation and not vasoconstriction per se.     

Central administration of corticotrophin releasing hormone but not arginine vasopressin stimulates the secretion of luteinizing hormone in rams in the presence and absence of testosterone.

This study tested the hypothesis that central administration of corticotrophin-releasing hormone (CRH) and/or arginine vasopressin (AVP) will affect the secretion of LH in rams and that testosterone is necessary for these actions to occur. Plasma LH levels were measured in castrated rams during 1 h infusion of either 100 microliter vehicle/mock cerebrospinal fluid (CSF) or mock CSF containing 25 microgram CRH, 25 microgram AVP or 25 microgram of each peptide through guide cannulae into the third cerebral ventricle. These intracerebroventricular (i.c.v.) infusions were given to the castrated rams following injections (i.m.) each 12 h of oil or 8 mg testosterone propionate for 7 days. Blood samples were collected every 10 min for 4 h before i.c.v. infusion, during infusion and for 4 h following the infusion. Infusion of vehicle did not affect any endocrine parameters. In contrast, the plasma concentrations of LH and the amplitude of LH pulses were increased significantly during and following infusion of CRH, and this effect was not influenced by whether the castrated rams were treated with testosterone propionate or whether the CRH was administered in combination with AVP. Infusion of AVP alone did not affect LH secretion. The frequency of LH pulses and the plasma concentrations of FSH did not change with any of the i.c.v. treatments. The plasma concentrations of cortisol were significantly increased by CRH and AVP infusions. The plasma concentrations of cortisol achieved during and following i.c.v. infusion of CRH and AVP combined were greater than the concentrations achieved as a result of treatment with AVP alone but were similar to those with CRH. There was no effect of testosterone propionate on cortisol levels. These results show that CRH, but not AVP, is capable of acting either centrally or at the pituitary level to increase the secretion of LH in rams and these actions are not affected by testosterone. The stimulatory effects of CRH on LH secretion are to increase the amplitude of GnRH pulses and/or the responsiveness of the pituitary to the actions of GnRH with no effect on the frequency of GnRH pulses. The secretion of FSH in rams is not influenced by either CRH or AVP. The effect of CRH to increase LH pulse amplitude occurs in the face of increased cortisol levels, further reinforcing our belief that this adrenal steroid does not affect the reproductive axis in this species.     

Involvement of vasopressin in the cardiovascular effects of intracerebroventricularly administered alpha 1-adrenoceptor agonists in the conscious rat

To determine the interaction between central adrenergic and vasopressinergic mechanisms in the regulation of cardiovascular function, the effects of intracerebroventricular (i.c.v.) administration of the alpha 1-agonists, methoxamine and phenylephrine, in conscious Long-Evans (LE) rats were compared with those in Brattleboro rats with hereditary hypothalamic diabetes insipidus (DI). In LE rats, both i.c.v. methoxamine and phenylephrine increased mean arterial pressure (MAP) and decreased heart rate (HR) in a dose-related manner, while they had no effect on MAP and HR in DI rats within the dose range of 3-30 micrograms/kg. Both i.c.v. methoxamine (10 micrograms/kg) and phenylephrine (30 micrograms/kg) also increased plasma levels of arginine vasopressin (AVP) in LE rats from 2.6 +/- 0.4 (n = 9) to 22.4 +/- 3.5 (n = 6, P less than 0.01) and 37.0 +/- 4.0 pg/ml (n = 6, P less than 0.01), respectively, without affecting plasma renin activity (PRA) and plasma angiotensin II (ANG II) levels. Central alpha 1-adrenoceptor stimulation increases vasopressin release from the posterior pituitary, which in part is responsible for the hypertensive and bradycardic responses. However, central vasopressinergic pathways have also been shown to be involved in these cardiovascular effects. Neither i.c.v. nor intravenous (i.v.) infusion of AVP restored the cardiovascular response to i.c.v. alpha 1-agonists in DI rats. In LE rats, however, i.v. pretreatment with the specific vascular antagonist to the pressor effect of AVP, d(CH2)5Tyr(Me)AVP (VP-ANT; 10 micrograms/kg), significantly attenuated, but did not completely block the hypertensive and bradycardic effects of i.c.v. methoxamine and phenylephrine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Central interaction between endothelin and brain natriuretic peptide on vasopressin secretion.

OBJECTIVE: To examine the interaction between i.c.v. administration of endothelin and brain natriuretic peptide (BNP) on vasopressin (AVP) secretion in unanesthetized, freely moving rats. METHODS: I.c.v. cannulation and femoral artery catheterization were performed 7-8 days and 2 days before the experiment, respectively. Endothelin and BNP were injected into the third ventricle through the guide cannula. One millilitre of blood was collected for AVP measurement 30 min before and 10 min after i.c.v. injection. RESULTS: Central administration of endothelin (20 or 40 pmol/2 microliters) dose-dependently evoked the elevation of plasma AVP levels. Preinjection of BNP (0.2 or 1 nmol/3 microliters, i.c.v.) dose-dependently attenuated central endothelin (40 pmol/2 microliters)-induced plasma AVP secretion. CONCLUSIONS: We have already reported that BNP attenuated central endothelin-induced pressor response and plasma catecholamine secretion. Taken together, the results indicate that BNP attenuated central endothelin-induced pressor response, at least partially, by suppressing sympathetic nervous system activation and plasma AVP secretion.     

Role of endogenous nociceptin in the regulation of arginine vasopressin release in conscious rats

The effects of central administration of the opioid-like peptide nociceptin (also known as orphanin FQ) were investigated on the secretion of arginine vasopressin (AVP) in response to dehydration and hyperosmolar or hypovolemic stimulation in conscious rats. Intracerebroventricular (i.c.v.) administration of nociceptin suppressed plasma AVP concentration in a dose-dependent manner (0.1-10 microg/rat) in dehydrated rats, and the maximum effect was obtained 10 min after the administration (dehydration with 10 microg/rat nociceptin, 3.11 +/- 0.27 pg/ml vs. control, 10.32 +/- 0.96 pg/ml). The plasma AVP increase in response to either hyperosmolality [i.p. injection of hypertonic saline (HS) (600 mosml/kg)] or hypovolemia [i.p. injection of polyethylene glycol (PEG)] was also significantly blunted when nociceptin was injected i.c.v. (HS with 10 microg/rat nociceptin, 1.16 +/- 0.09 pg/ml vs. control, 1.82 +/- 0.30 pg/ml; PEG with 10 microg/rat nociceptin, 0.91 +/- 0.16 pg/ml vs. control, 2.41 +/- 0.26 pg/ml). Pretreatment with a selective opioid kappa-receptor antagonist, nor-binaltorphimine (1 microg/ rat, i.c.v.) or naloxone (2.5 mg/rat, s.c. injection) did not reverse the inhibitory effects of nociceptin on AVP release. Moreover, when plasma AVP was suppressed by acute water loading, immunoneutralization of endogenous nociceptin by antinociceptin-antiserum i.c.v. significantly reversed the suppression (0.57 +/- 0.12 pg/ml vs. control, 0.25 +/- 0.04 pg/ml). These results suggest that central nociceptin is physiologically involved in the control of AVP release through an inhibitory action.     

Similar baroreflex bradycardic actions of atrial natriuretic peptide and B and C types of natriuretic peptides in conscious rats.

OBJECTIVE: We have previously shown that atrial natriuretic peptide (ANP) modulates cardiac barosensitive afferent pathways to enhance reflex bradycardia in rats. The present study examined whether B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) also modulate heart rate reflex function. DESIGN: Baroreflex bradycardia was evoked by rapid (over 4-6 s) intravenous (i.v.) infusions of methoxamine (100 microg/kg; 'ramp' baroreflex technique) in the presence of infused i.v. natriuretic peptide and of vehicle (0.9% saline, 270 microl/h) in conscious adult Munich-Wistar rats. Initially a dose-response study to ANP (infused at 25, 50 and 100 pmol/kg per min i.v.) was performed in 10 rats to determine an appropriate dose for subsequent experiments with the other peptides. In a separate group of 11 animals, rat BNP-32 and rat CNP-22 were infused at 50 pmol/kg per min i.v. RESULTS: Reflex responses to ANP were dose-related, with a significant increase in baroreflex sensitivity of 50+/-15% at the 25 pmol dose, 102+/-10% at the 50 pmol dose and 117+/-11% at 100 pmol dose (all P<0.05). BNP and CNP (50 pmol/kg/min i.v.) substantially increased baroreflex bradycardia (by 115+/-17% and 62+/-15%, respectively; P<0.05) compared to vehicle infusion. CONCLUSIONS: Both BNP and CNP augmented baroreflex slowing of heart rate in response to rapid increases in blood pressure in rats. Whereas other reports have shown marked differences in cardiovascular responses between the natriuretic peptides, particularly with CNP, our findings demonstrate an important common action of ANP, BNP and CNP to facilitate vagal heart rate baroreflexes.     

Kappa-opioid modulation of vasopressin secretion in conscious rats.

A series of studies has been performed in the conscious rat to investigate the effect of the intracerebroventricular (i.c.v.) administration of the selective kappa-opioid receptor agonist, U50 488H, on arginine vasopressin (AVP) secretion stimulated by i.c.v. administration of hypertonic NaCl. Similarly, the effect of the i.c.v. administration of morphine and the i.v. administration of naloxone on AVP secretion was investigated. The response of AVP to an i.c.v. injection of hypertonic NaCl was potentiated by naloxone at a dose of 0.4 mg/kg, but a higher dose (1.2 mg/kg) was required to increase the basal plasma concentration of AVP. Prior treatment with U50 488H or morphine attenuated the increase in plasma concentrations of AVP stimulated by i.c.v. injection of hypertonic NaCl from 13.92 +/- 4.44 to 1.22 +/- 0.34 and 1.78 +/- 0.74 pmol/l respectively (n = 7; P less than 0.05). Prior administration of U50 488H also attenuated the potentiating effect of naloxone on AVP secretion stimulated by i.c.v. injection of hypertonic NaCl. These results indicate that basal AVP secretion is under tonic inhibitory control by dynorphin, and that mu- and kappa-opioid receptors mediate an inhibitory influence of endogenous opioids on osmoreceptor-mediated AVP secretion.     

Studies of the factors modulating antidiuretic hormone excretion in man in response to the osmolar stimulus: effects of oestrogen and angiotensin II

The aim of this study was to assess the influence of hormones known to regulate fluid and electrolyte balance on the release of antidiuretic hormone induced by raising serum osmolality. The stimulus provoked by the infusion of a 2.5% NaCl solution induces an increase of urinary [arginine-8]-vasopressin from 1.12 to 2.64 ng/h in men and from 1.65 to 7.27 ng/h in women as has been previously reported. These results were compared to those obtained in males infused with angiotensin II (AII) before and during a hypertonic sodium load and in males infused with hypertonic saline on the fourth day of administration of ethinyl-oestradiol. During the combined infusion of AII and then hypertonic saline, the mean hourly urinary excretion of AVP increased from 2.8 to 5.67 ng/h. Within each group the increase of urinary AVP was highly significant. The rise of urinary AVP during AII infusion was significantly different from the rise observed both in untreated males and untreated females, lying in between. The mean hourly excretion rate of AVP increased before and after hypertonic saline loading from 2.65 to 5.3 ng/h in males pre-treated with ethinyl-oestradiol. The significant difference observed between males and females is reduced when males treated with oestrogen were compared to female subjects. In each group plasma renin activity decreased to low values during the salt-loading test. During oestrogen treatment PRA and plasma renin substrate rose, while urinary aldosterone remained almost unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aldosterone acts on the kidney,not the brain,to cause mineralocorticoid hypertension in sheep

OBJECTIVE : To determine the extent to which mineralocortioid hypertension depends on a direct action of aldosterone on the kidney or on the brain. METHODS : Studies were performed in conscious sheep that were previously uninephrectomized, implanted with silastic cannulae in the renal artery of the remaining kidney, and had guide tubes implanted over the lateral cerebral ventricles. The effect of aldosterone, infused either intrarenally (i.r.; 2 microg/h) or intravenously (i.v.; 2 and 10 microg/h) for 10 days (n = 5), on arterial pressure and fluid and electrolyte balance was determined. The i.r. (2 microg/h) and i.v. (10 microg/h) doses were calculated to give similar intrarenal concentrations of aldosterone. In a further study, the effect of intracerebroventricular (i.c.v.) infusion of aldosterone (2 microg/h for 21 days) on arterial pressure was examined (n = 5). RESULTS : Infusion of aldosterone caused a progressive increase in mean arterial pressure from 83 +/- 3 mmHg to a maximum of 100 +/- 4 mmHg (P < 0.001) with 2 microg/h i.r. and from 84 +/- 3 mmHg to a maximum of 104 +/- 4 mmHg (P < 0.001) with 10 microg/h i.v., both by day 7. With both infusions there were similar increases in plasma [Na+] and decreases in plasma [K+] and total protein concentration (P < 0.05) between days 3 and 5; these were maintained throughout the infusion. There were no significant changes with i.v. aldosterone (2 microg/h). Long-term i.c.v. infusion of aldosterone (2 microg/h for 21 days) caused no change in arterial pressure. CONCLUSIONS : In conscious sheep the hypertensive response to aldosterone resulted from an action on the kidney, with no evidence for a direct action on the brain.     

Central Infusion of Aldosterone Increases Blood Pressure by Mechanisms Independent of Na Retention

Experiments were performed to test the hypothesis that Na retention and Na in the diet are not required to initiate central aldosterone induced hypertension. Rats were fed either standard rat chow or Na-deficient diet and infused intracerebroventricularly (i.c.v.) with aldosterone (28 ng/h) dissolved in artificial cerebrospinal fluid (vehicle) or vehicle alone. In Na-replete rats the central infusion of aldosterone did not promote Na or water retention, prior to increases in systolic blood pressure (SBP). Infusion of aldosterone in Na-deficient rats also initiated a rise in SBP, although the response was delayed. In neither group of rats did aldosterone infusion significantly change plasma Na, K, renin, norepinephrine (NE) or vasopressin (AVP) concentrations. There was no significant increase in plasma aldosterone concentration in Na replete rats centrally infused with aldosterone. Infusion of vehicle had no effect on SBP. We conclude that central aldosterone infusion initiates an increase in blood pressure by a mechanism independent of Na retention. Furthermore, increased concentrations of systemic renin, vasopressin, and activation of the sympathetic nervous system do not appear to be involved in maintaining hypertension.     

Involvement of hypothalamic somatostatin in the suppression of growth hormone secretion by central corticotropin-releasing factor in conscious male rats

The role of central corticotropin-releasing factor (CRF) in the regulation growth hormone (GH) secretion was studied in freely moving conscious male rats with indwelling intra-atrial and intracerebroventricular (i.c.v.) cannulae. GH measurements in blood samples obtained every 20 min from 10.00 to 14.00 h in control animals injected with saline either intravenously (i.v.) or into the lateral cerebral ventricle revealed that spontaneous GH secretion was pulsatile, and occurred regularly at around 12.00 h. When ovine CRF (10 micrograms) was injected i.c.v., spontaneous GH secretion was inhibited (mean plasma GH [11.20-13.00 h]: 20 +/- 7 ng/ml vs. control: 126 +/- 22 ng/ml, p less than 0.01). In contrast, the intravenous injection of CRF (10 micrograms) did not affect spontaneous GH secretion (mean plasma GH [11.20-13.00 h]: 162 +/- 25 ng/ml vs. control: 193 +/- 31 ng/ml). This GH suppressive action of central CRF was blocked by the i.v. injection (0.5 ml) of antisomatostatin serum (AS), but not of normal sheep serum (NS), (mean plasma GH [11.20-13.00 h]: NS + CRF: 15 +/- 2 ng/ml vs. AS + CRF: 202 +/- 30 ng/ml, p less than 0.01). The mean plasma GH value [11.20-13.00 h] in animals receiving AS and CRF was not significantly different from those in animals receiving saline (i.v.) together with AS. These results suggest a potential inhibitory role of central CRF in the regulation of spontaneous GH secretion in the rat which is mediated by the stimulation of hypothalamic somatostatin.     

ENDOGENOUS OPIOIDS INHIBIT OXYTOCIN RELEASE DURING NICOTINE-STIMULATED SECRETION OF VASOPRESSIN IN MAN

The effects of the opioid antagonist naloxone on the vasopressin (AVP) and oxytocin (OT) responses to nicotine were studied in male non-smokers (21-30 years old). Either saline (n = 6) or naloxone (4 mg bolus + 6 mg/h, n = 6) was infused i.v. during the study. After 60 min infusion the subjects smoked one high-nicotine content cigarette. Naloxone infusion for 60 min did not alter basal plasma AVP or OT levels. Smoking led to a significant rise in plasma vasopressin in both saline and naloxone-infused subjects (P less than 0.05). There was no significant difference in the plasma AVP response to smoking between the two groups. Saline-infused subjects did not show any change in plasma OT in response to smoking. Naloxone infusion was associated with a significant rise in OT from 1.3 +/- 0.1 pmol/l to 4.3 +/- 2.4 pmol/l 5 min after smoking (P less than 0.05). We conclude that there is endogenous opioid-mediated inhibition of OT which prevents its release when AVP is secreted in response to nicotine in man.     

Influence of acute intracerebroventricular (i.c.v.) administration of adrenocorticotrophin (ACTH) on LH secretion in male rats: effect of pretreatment (i.c.v.) with ACTH antiserum on the serum LH response to an acute ether stress

Adult male rats with chronic indwelling intracerebroventricular (i.c.v.) and jugular catheters were given an i.c.v. injection (over 1 min) of 1, 10, 100 ng or 1 microgram ACTH(1-24), or 300 ng ACTH(4-10) or saline, and blood samples were taken 0, 5, 15, 30 and 60 min later. Increasing dosages of ACTH(1-24) caused a dose-related rise in serum LH levels. Peak levels of serum LH (ranging from 157 to 473% of pretreatment levels) were reached 5-15 min after treatment, and then serum LH values returned to pretreatment levels by 60 min. The serum LH response to 1 microgram ACTH(1-24) did not differ from the response to 100 ng ACTH(1-24). Administration (i.c.v.) of 300 ng ACTH(4-10) was also effective in increasing serum LH values. Repeated withdrawal of blood during the experiment increased serum corticosterone values in all groups (including saline-treated), but i.c.v. administration of ACTH(1-24) or ACTH(4-10) did not further increase serum corticosterone levels. Two additional groups of rats were injected i.p. with either saline or pentobarbital (30 mg/kg body weight) 1 h before i.c.v. administration of 10 ng ACTH(1-24) and blood samples were taken as in the other groups. The animals in these groups did not show a rise in serum LH concentrations in response to ACTH(1-24). In a third experiment, rats were pretreated (i.c.v.) with either ACTH antiserum (ACTH-Ab) or normal rabbit serum 15 min before a 2-min ether stress. The ether stress evoked a significant rise in serum LH concentrations within 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Centrally bradykinin B2-receptor-induced hypertensive and positive chronotropic effects are mediated via activation of the sympathetic nervous system.

OBJECTIVE: The presence of bradykinin B2 receptors in the cardiovascular regulatory centres of the brain indicates that increase in mean arterial pressure (MAP) and heart rate after intracerebroventricular (i.c.v.) injections of bradykinin is mediated via stimulation of sympathetic nervous system. METHODS: Adult Wistar- Kyoto (WKY) rats were instrumented chronically with an i.c.v. cannula, and the catheters were placed into the femoral artery and vein. Increasing doses of bradykinin (1 -300 pmol) were given i.c.v. and (i) MAP and heart rate, (ii) plasma dopamine, noradrenaline and adrenaline, and (iii) plasma arginine vasopressin (AVP) levels were determined. In addition, following blockade of peripheral alpha1 -adrenoceptors with prazosin (50 and 250 microg/kg i.v.) beta1-adrenoceptors with atenolol (10 mg/kg i.v.) or V1 -receptors with TMe-AVP (Manning compound) (10 microg/kg i.c.v. and 100 microg/kg i.v.) the effects of bradykinin (100 pmol i.c.v.) on MAP and heart rate were determined. RESULTS: Bradykinin increased MAP and heart rate dose-dependently. The pressor effects of 100 pmol bradykinin i.c.v. were completely blocked by pretreatment with the specific B2 receptor antagonist Hoe 140 (3 pmol, i.c.v.). There was no change in plasma dopamine, noradrenaline, adrenaline or AVP levels after increasing doses of bradykinin. However, peripheral blockade of alpha1- and beta1-adrenoceptors reduced the bradykinin-induced increase in MAP and heart rate, whereas central and peripheral V1 receptor blockade did not alter the cardiovascular responses to i.c.v. bradykinin. CONCLUSION: Our data suggest that the hypertensive and positive chronotropic effects induced by i.c.v. bradykinin are due to stimulation of sympathoneuronal rather than sympathoadrenal pathway in vivo.     

Activation of the hypothalamo-pituitary-adrenocortical axis in the conscious rabbit by the pyrogen polyinosinic:polycytidylic acid is dependent on corticotrophin-releasing factor-41.

The pyrogenic interferon inducer polyinosinic:polycytidylic acid (Poly I:C) was shown to activate the rabbit hypothalamo-pituitary-adrenocortical (HPA) axis in vivo. The immunoreactive cortisol response to Poly I:C (2.5 micrograms/kg) was shown to have a corticotrophin-releasing factor-41 (CRF-41)-dependent component which was abolished by peripheral immunoneutralization using an anti-CRF-41 monoclonal antibody (KCHMB001; 2.5 mg/kg i.v.). Peripheral administration of the arginine vasopressin (AVP) V1 receptor antagonist ([deamino-Pen1, O-Me-Tyr2, Arg8]-vasopressin; 225 nmol/kg i.v.) had no effect on the response of immunoreactive cortisol to Poly I:C, suggesting that AVP was not involved in activation of the HPA axis. Poly I:C increased both body temperature and circulating immunoreactive prostaglandin E2; these responses were abolished by the cyclo-oxygenase inhibitor ketoprofen (3 mg/kg s.c.). The immunoreactive cortisol response to Poly I:C, however, remained after the administration of ketoprofen, indicating a prostaglandin (PG)-independent component. The immunoreactive cortisol levels in control, saline vehicle-treated, animals were reduced by both the CRF-41 receptor antagonist (alpha-helical CRF (9-41); 6.25 nmol/kg i.v.) and ketoprofen (3 mg/kg s.c.) indicating that this basal state is dependent on both CRF-41 and PGs.     

Radioimmunoassay of (8-arginine)-vasopressin. II. Application to determination of antidiuretic hormone in urine.

A radioimmunoassay for [8-arginine]-vasopressin (AVP), previously described (Czernichow et al. 1975) has been used for the determination of antidiuretic hormone in a 4 ml urine sample. AVP is extracted from acidified urine with a cation exchanger (Amberlite CG 50) with an overall recovery of 72%. The blank value measured in extracted samples of urine was 0.29 pg/ml +/- 0.21 (SEM) and calculated by extrapolation of the regression line of the recovery experiment was 0.49 pg/ml. The coefficient of variation within-assay was 13% and between-assay 18%. Addition of the amounts of AVP found in each specimen of urine voided gave results nearly identical to those of the amounts found in 24 h pool of urine, indicating that the assay was not affected by changes in concentration of the other urinary components during the day. The daily urinary excretion of AVP measured in 34 subjects was found to be 34 ng in 17 women and 70 ng in 17 men, a significant difference. Urinary concentration and excretion rate of AVP rose during thirst test and during Carter-Robbins test performed in 13 healthy subjects. In the latter test it was observed that the women displayed a strikingly more pronounced AVP elevation after the osmolar stimulus than the men. In both sexes a significant correlation was found between AVP excretion rate and plasma osmolality as well as free water clearance. Three cases of complete or incomplete diabetes insipidus and potomania could be clearly differentiated according to the total output of AVP during the thirst test. Extremely high values of AVP were found in the urine of 5 subjects with Schwartz-Bartter syndrome associated with bronchogenic tumours.     

Chronic Cardiovascular Effects of Central Vasopressin in Conscious Rats

To clarify the cardiovascular effects of central vasopressin (AVP), a chronic intracerebroventricular (ICV) infusion of AVP was performed in conscious Wistar normotensive rats. Animals were divided into 3 groups: 1) AVP 1 ng/hr (Low), 2) AVP 100 ng/hr (High), and 3) saline (control) ICV infusion. After a 6 day control period, AVP or saline was continuously infused into the lateral cerebroventricle at a rate of 1 μ/hr using osmotic minipump for 7 days. As a result, a dose-related elevation of AVP concentration in CSF was achieved. Systolic blood pressure in both Low and High AVP infusion was slightly (7-12 mmHg) but significantly higher than that in control. ICV infusion of AVP did not alter urine volume, electrolytes excretion or osmolality, and AVP vascular antagonist injected intravenously failed to affect mean arterial pressure. Furthermore, plasma catecholamines and renin activity did not differ significantly among the groups. Thus, chronic ICV infusion of AVP induced the elevation of blood pressure, which is due to centrally mediated effect of AVP.