Inhibition Of Vasopressin Release Research Articles

Difelikefalin, a peripherally restricted KOR (kappa opioid receptor) agonist, produces diuresis through a central KOR pathway

Difelikefalin is a peripherally restricted kappa opioid receptor (KOR) agonist that was recently approved by the FDA to treat pruritis in dialysis patients. Here, we investigated the cardiovascular and renal responses to difelikefalin, and using the KOR antagonist norbinaltorphimine (norBNI), examined whether any difelikefalin-induced changes in the renal excretion of water and/or electrolytes were mediated through a central or peripheral KOR pathway. The effects of norBNI pretreatment on nalfurafine, a KOR agonist that crosses the blood-brain barrier, were also examined. We hypothesized that difelikefalin would alter urine output differently than nalfurafine, given that KOR agonists produce diuresis via activating central KORs to inhibit vasopressin release. Following catheterization, conscious Sprague-Dawley rats were infused i.v. with isotonic saline and pretreated with norBNI centrally via an intracerebroventricular (ICV) cannula or peripherally via an intravenous catheter. After stabilization, difelikefalin or nalfurafine was administered i.v. and urine output, heart rate and mean arterial pressure (MAP) were recorded for 90 min. Difelikefalin produced a significant increase in urine output, and significant decrease in urinary sodium and potassium excretion, urine osmolality, and MAP. ICV norBNI pretreatment markedly attenuated the increase in urine output caused by difelikefalin and nalfurafine but did not inhibit the electrolyte effects. However, IV norBNI pretreatment prevented all responses to difelikefalin and nalfurafine. Together, these findings demonstrate that difelikefalin and nalfurafine utilize central KOR pathways to elicit diuresis and a decrease in MAP but enhance renal tubular electrolyte reabsorption through a peripheral KOR pathway, providing important insight into two clinically useful KOR agonists.

TOLVAPTAN USE IN SEVERE NEONATAL AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE (ADPKD): THE PHARMACEUTICAL CHALLENGE

BackgroundUnlicensed medications are used all the time in the management of diseases in childhood. Tolvaptan (Jinarc®) is a vasopressin V2-receptor antagonist licensed for use to slow the progression of cyst...

Effects of hydration in rats and mice with polycystic kidney disease.

Vasopressin and V2 receptor signaling promote polycystic kidney disease (PKD) progression, raising the question whether suppression of vasopressin release through enhanced hydration can delay disease advancement. Enhanced hydration by adding 5% glucose to the drinking water has proven protective in a rat model orthologous to autosomal recessive PKD. We wanted to exclude a glucose effect and explore the influence of enhanced hydration in a mouse model orthologous to autosomal dominant PKD. PCK rats were assigned to normal water intake (NWI) or high water intake (HWI) groups achieved by feeding a hydrated agar diet (HWI-agar) or by adding 5% glucose to the drinking water (HWI-glucose), with the latter group used to recapitulate previously published results. Homozygous Pkd1 R3277C (Pkd1(RC/RC)) mice were assigned to NWI and HWI-agar groups. To evaluate the effectiveness of HWI, kidney weight and histomorphometry were assessed, and urine vasopressin, renal cAMP levels, and phosphodiesterase activities were measured. HWI-agar, like HWI-glucose, reduced urine vasopressin, renal cAMP levels, and PKD severity in PCK rats but not in Pkd1(RC/RC) mice. Compared with rat kidneys, mouse kidneys had higher phosphodiesterase activity and lower cAMP levels and were less sensitive to the cystogenic effect of 1-deamino-8-d-arginine vasopressin, as previously shown for Pkd1(RC/RC) mice and confirmed here in Pkd2(WS25/-) mice. We conclude that the effect of enhanced hydration in rat and mouse models of PKD differs. More powerful suppression of V2 receptor-mediated signaling than achievable by enhanced hydration alone may be necessary to affect the development of PKD in mouse models.

Function of the hypothalamo-neurohypophysial system in rats with myocardial infarction is modified by melatonin

BackgroundPineal and melatonin interactions with the hypothalamo-neurohypophysial system are well documented. In addition, vasopressin and oxytocin secretion are known to be part of the neuroendocrine response to chronic heart failure evoked by myocardial infarction. The present study was undertaken to evaluate the possible regulatory role of melatonin in the vasopressin and oxytocin release in rats with myocardial infarction. MethodsThe vasopressin and oxytocin content of the hypothalamus and neurohypophysis, as well as their plasma levels, were radioimmunoassayed in sham-operated or pinealectomized rats with left coronary artery ligation (CAL)-evoked myocardial infarction as well as under melatonin treatment. ResultsInfarcted rats demonstrated increased vasopressin and oxytocin plasma levels, but melatonin restricted the release of both neurohormones in these rats. Experimental myocardial infarction in pinealectomized rats caused a distinct inhibition of vasopressin release but intensified oxytocin secretion. In pinealectomized rats substituted with melatonin, pineal indole amine was seen to inhibit oxytocin release and stimulate vasopressin secretion. Conclusions(i) CAL-induced myocardial infarction is the reason for increased hypothalamo-neurohypophysial system activity in rats; melatonin plays the role of inhibitory neuromodulator of vasopressin and oxytocin release in this state. (ii) Myocardial infarction evoked in pinealectomized rats is characterized by the inversion of the neurohumoral response pattern in respect of inhibited vasopressin release. (iii) Melatonin stimulates vasopressin (but decreases oxytocin) release in pinealectomized rats with myocardial infarction.

Augmented central nitric oxide production inhibits vasopressin release during hemorrhage in acute alcohol-intoxicated rodents

Acute alcohol intoxication (AAI) attenuates the AVP response to hemorrhage, contributing to impaired hemodynamic counter-regulation. This can be restored by central cholinergic stimulation, implicating disrupted signaling regulating AVP release. AVP is released in response to hemorrhage and hyperosmolality. Studies have demonstrated nitric oxide (NO) to play an inhibitory role on AVP release. AAI has been shown to increase NO content in the paraventricular nucleus. We hypothesized that the attenuated AVP response to hemorrhage during AAI is the result of increased central NO inhibition. In addition, we predicted that the increased NO tone during AAI would impair the AVP response to hyperosmolality. Conscious male Sprague-Dawley rats (300-325 g) received a 15-h intragastric infusion of alcohol (2.5 g/kg + 300 mg·kg(-1)·h(-1)) or dextrose prior to a 60-min fixed-pressure hemorrhage (∼40 mmHg) or 5% hypertonic saline infusion (0.05 ml·kg(-1)·min(-1)). AAI attenuated the AVP response to hemorrhage, which was associated with increased paraventricular NO content. In contrast, AAI did not impair the AVP response to hyperosmolality. This was accompanied by decreased paraventricular NO content. To confirm the role of NO in the alcohol-induced inhibition of AVP release during hemorrhage, the nitric oxide synthase inhibitor, nitro-l-arginine methyl ester (l-NAME; 250 μg/5 μl), was administered centrally prior to hemorrhage. l-NAME did not further increase AVP levels during hemorrhage in dextrose-treated animals; however, it restored the AVP response during AAI. These results indicate that AAI impairs the AVP response to hemorrhage, while not affecting the response to hyperosmolality. Furthermore, these data demonstrate that the attenuated AVP response to hemorrhage is the result of augmented central NO inhibition.

Vasopressin and sympathetic systems mediate the cardiovascular effects of the GABAergic system in the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BST) is an important part of the limbic system. It has been shown that chemical stimulation of the BST elicited cardiovascular depressive and bradycardic responses. It was also demonstrated that GABA is present in the BST, though its role in cardiovascular control is not yet understood. This study was performed to find the effects of GABA receptor subtypes in the BST on cardiovascular responses and to find the possible mechanisms that mediate these responses in urethane-anesthetized rats. Microinjection of muscimol (500 pmol/100 nl), a GABA A agonist, into the BST produced a weak unsignificant decrease in the mean arterial pressure (MAP) and heart rate (HR). Injection of bicuculline methiodide (BMI, 100 pmol/100 nl), a GABA A antagonist, caused a significant increase in the MAP (41.3 ± 5.1 mmHg) as well as in the HR (33.2 ± 5.6 beats/min). Injection of two doses (500 and 1000 pmol/100 nl) of phaclofen, a GABA B antagonist, produced no significant change in either MAP or HR. Administration (i.v.) of the muscarinic receptor blocker, homatropine methyl bromide had no effect on the magnitude of mean arterial pressure or heart rate responses to BMI. This suggests that the parasympathetic system is not involved in these responses. However, administration (i.v.) of the nicotinic receptor blocker, hexamethonium bromide had no effect on the magnitude of mean arterial pressure response but abolished heart rate response to BMI. This suggests that the sympathetic system is involved in the bradycardic effect of GABA. On the other hand, administration (i.v.) of a selective vasopressin V 1 receptor antagonist abolished the pressor effect of BMI, which indicates that the GABAergic system of the BST decreases the arterial pressure via tonic inhibition of vasopressin release. In summary, we demonstrated, for the first time, that GABA exerts its influence in the BST through the activation of GABA A, but not GABA B, receptors that, in turn, tonically inhibit vasopressin release and sympathetic outflow to the heart.

The Angiotensin Converting Enzyme 2/Ang-(1-7) Axis in the Heart

For decades, the literature has been inundated with evidence of the important role of the renin–angiotensin system (RAS) in cardiac remodeling and function with most in the field familiar with this classic, dogmatic story. The protease renin is synthesized and released from the kidney and acts on a circulating inactive peptide, angiotensinogen, produced by the liver, giving rise to angiotensin (Ang) I. Ang I is then transformed into the biologically active octapeptide, Ang II, through enzymatic cleavage by angiotensin-converting enzyme (ACE).1 Ang II is the main effector molecule of the RAS, acting in an endocrine, autocrine/paracrine, and intracrine hormone pathway on cardiac cells. Ang II binds and activates G protein–coupled receptors, the angiotensin type 1 (AT1R) and angiotensin type 2 (AT2R) receptors, to mediate its actions. Activation of AT1R mediates most of the cardiovascular responses attributed to Ang II (ie, vasoconstriction, mitogenic and hypertrophic effects, fibrosis, inflammation, and fluid retention). In contrast, AT2R activation may cause opposing physiological responses that are increased in several disease processes.2 Nearly 50 years after the discovery of ACE, a genomic based screening resulted in a characterization of ACE2, thus adding an unexpected twist into the well-known tale of the RAS.3,4 ACE2 is a carboxypeptidase that cleaves a single residue from Ang I to form Ang-(1-9), which is then converted to Ang-(1-7) by either ACE or neutral endopeptidases.3 This process is less efficient because of the requirement of 2 enzymatic processes. ACE2 …

Use of Vasopressin Bolus and Infusion to Treat Catecholamine-resistant Hypotension during Pheochromocytoma Resection

Albert Einstein Medical Center, Philadelphia, Pennsylvania. rothj@einstein.eduIn a recent review of vasopressin, it was stated that there were only two reported cases using bolus vasopressin (10–20 U) to restore blood pressure after pheochromocytoma resection.1This letter documents another rare case, using a lower dose of bolus vasopressin, for treatment of catecholamine-resistant hypotension after pheochromocytoma resection.A 54-yr-old man (height, 180 cm; weight, 84 kg) underwent laparoscopic right adrenalectomy for treatment of pheochromocytoma. Preoperative medications included phenoxybenzamine, metoprolol, ramipril, and atorvastatin. Preinduction blood pressure was 129/74 mmHg, and heart rate was 57 beats/min. During manipulation of the adrenal gland, the patient developed hypertension, which was treated with sodium nitroprusside (up to 10 ml/h of 200 μg/ml) and esmolol (up to 5 ml/h of 10 mg/ml) infusions. After resection and discontinuation of the nitroprusside and esmolol, the patient developed hypotension. A norepinephrine infusion of 24 μg/min was only able to increase the patient's systolic blood pressure to the low to mid 80s. Two 0.4-U vasopressin boluses were administered, which increased the systolic blood pressure to 120 mmHg. The patient was started on a 4-U/h infusion of vasopressin resulting in maintenance of a systolic blood pressure at 110 mmHg while permitting a decrease in the norepinephrine infusion rate. Both infusions were continued throughout the rest of the surgery and were weaned several hours postoperatively. The patient did well and was discharged home on postoperative day 2.There are now three previous reports of bolus vasopressin being used to treat hypotension after adrenal resection for pheochromocytoma.2–4Repeated bolus doses of 10–20 U followed by an infusion were required to treat hypotension after pheochromocytoma resection.2In another adult patient, an infusion of vasopressin required 20 min to achieve improvement in blood pressure during pheochromocytoma resection complicated by a large blood loss.3In an 11-yr-old patient, a 5-U bolus followed by an infusion was successful in treating postresection hypotension.4Although vasopressin infusions have been used in a variety of other situations, there are limited data to guide bolus dosing. Others report lower doses of vasopressin bolus. A 2-U bolus dose was used to treat anaphylactic shock.5As in this case, two 0.4-U boluses successfully treated hypotension secondary to both bowel retraction in patients having abdominal aortic resection repair and postreperfusion syndrome during liver transplantation.6,7Terlipressin (a vasopressin precursor) in doses of 1 or 2 mg successfully treated hypotension secondary to induction of anesthesia in patients chronically treated with renin–angiotensin system inhibitors.8Additional well-controlled studies must be conducted to establish the indications, safety, and efficacy of bolus vasopressin for rapid correction of hypotension, particularly catecholamine-resistant hypotension.This patient adds to the small number of reported cases that suggest vasopressin can be safely and effectively used to treat postadrenalectomy catecholamine-resistant hypotension in patients with pheochromocytoma. Although vasopressin is a vasoconstrictor and it is not surprising that it can treat hypotension, there may be a specific need for vasopressin in some pheochromocytoma patients. First, vasopressin is effective in the presence of residual α-adrenergic blockade and down-regulation of those receptors. Second, in some patients with pheochromocytoma, there is an oversecretion of vasopressin, which may contribute to the induced hypertension.9,10It is possible that chronic oversecretion of vasopressin leads to a down-regulation of vasopressin receptors, thus contributing to the postresection hypotension. Whether preoperative determination of vasopressin over secretion will affect management is an open question. Catecholamines are also known to inhibit vasopressin release.11It has been proposed that chronic inhibition by catecholamines may down-regulate neurohypophyseal vasopressin synthesis, thereby preventing the acute high release of vasopressin during a hypotensive episode.2Last, the use of vasopressin can reduce the catecholamine dose, thus allowing one to avoid their undesirable side effects such as increased myocardial oxygen consumption and ventricular arrhythmias.Albert Einstein Medical Center, Philadelphia, Pennsylvania. rothj@einstein.edu

Impaired ability to increase water excretion in mice lacking the taurine transporter gene TAUT

Cellular taurine uptake or release counteracts alterations of cell volume. Na+-coupled taurine transporter TAUT mediates concentrative cellular uptake of taurine. Inhibition of vasopressin secretion by hypotonicity may involve taurine release from glial cells of supraoptic nucleus. We compared renal function of mice lacking TAUT (taut-/-) and wild-type littermates (taut+/+). We observed renal taurine loss and subsequent hypotaurinemia in taut-/- mice. With free access to water, plasma and urine osmolality, urinary flow rate as well as urinary excretion and plasma concentrations of Na+ and K+ were similar in taut-/- and taut+/+ mice, whereas plasma concentrations of urea were enhanced in taut-/- mice. An oral water load (1 ml/16 g body weight) induced a similar diuresis in both genotypes. Repeating the oral water load immediately after normalization of urine flow rate, however, resulted in delayed diuresis and higher urinary vasopressin/creatinine ratios in taut-/- mice. In comparison, the repeated diuretic response to vasopressin V2 receptor blockade was not different between genotypes. Water deprivation for 36 h led to similar antidiuresis and increases of urinary osmolality in both genotypes. Upon free access to water after deprivation, taut-/- mice continued to concentrate urine up to 6 days, while taut+/+ mice rapidly returned to normal urinary osmolality. Urinary vasopressin/creatinine ratios and plasma aldosterone concentrations were not different under basal conditions but were significantly higher in taut-/- mice than in taut+/+ mice at 6 days after water deprivation. In conclusion, taut-/- mice suffer from renal taurine loss and impaired ability to lower urine osmolality and to increase urinary water excretion. The latter defect could reside extrarenally and result from a role of taurine in the suppression of vasopressin release which may be attenuated in taut-/- mice.

Does conversion of ATP to adenosine terminate ATP-stimulated vasopressin release from hypothalamo-neurohypophyseal explants?

ATP stimulates vasopressin (VP) release from explants of the hypothalamo-neurohypophyseal system (HNS), but the response is not sustained for the duration of exposure to ATP. Since adenosine, a metabolite of ATP, inhibits VP release from neurohypophysial terminals and adenosine receptors (AR) are expressed in supraoptic nucleus (SON) neurons, we postulated that conversion of ATP to adenosine contributed to termination of ATP-stimulated VP release from HNS explants. This was tested using a non-selective AR antagonist, 5-amino-9-chloro-2-(2-furyl)-1, 2, 4-triazolo [1, 5- c] quinazoline (CGS-15943). CGS-15943 did not affect basal VP release and did not alter the initial response to ATP. A selective A 1R antagonist, 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX), increased basal VP release at 1 μM, without altering the response to ATP. However, at a higher concentration of DPCPX (10 μM), VP release was enhanced by ATP for an extended period of time. Inhibition of the enzymatic conversion of ATP to adenosine using a combination of a potent ecto-5′-nucleotidase inhibitor, α,β-methylene adenosine 5′-diphosphate (AMP-CP), and a competitive substrate for ecto-5′-nucleotidase (guanosine monophosphate, GMP) did not affect basal VP release. Enzymatic inhibition did slightly prolong the response to ATP, but it was not sustained for the duration of exposure to ATP. We conclude that an endogenous inhibitory influence of adenosine decreases basal VP release from HNS explants and that conversion of exogenously applied ATP to adenosine contributes to termination of ATP-induced stimulation of VP release, but additional mechanisms such as receptor desensitization also limit the response to extended exposure to ATP.

Intermittent footshock facilitates dendritic vasopressin release but suppresses vasopressin synthesis within the rat supraoptic nucleus.

Emotional stress inhibits vasopressin release from the pituitary but may facilitate its release from the dendrites in the hypothalamus. We examined effects of intermittently applied footshock upon the amount of vasopressin heteronuclear RNA in the hypothalamus. The footshock decreased plasma vasopressin concentration but increased its extracellular concentration within the supraoptic nucleus. The contents of the vasopressin heteronuclear RNA in the supraoptic nucleus were significantly decreased after the shock. These data suggest that intermittent footshock decreases not only vasopressin release from the axon terminals in the pituitary, but also vasopressin synthesis in the cell bodies in the hypothalamus while the stimulus facilitates vasopressin release from the dendrites in the hypothalamus. The data also suggest differential control of dendritic vasopressin release and synthesis in the hypothalamus.

Vasopresin and human hypertension.

1. Two clinical studies are reported which investigate: (1) the regulation of vasopressin release in moderate hypertensive subjects not under treatment compared to normotensives and, (2) the effects of antihypertensive treatment on vasopressin and on its osmoregulation in moderate hypertensives. 2. In the first study two stimuli facilitating vasopressin release (active upright position and hypertonic saline infusion) and a stimulus inhibiting vasopressin release (hypotonic saline infusion) have been applied to 13 moderate essential hypertensives and 8 control normotensives. In the second study, limited to hypertensives, the effects on plasma vasopressin and other plasma and urine variables, of either acute (by clonidine, n = 6 or by sodium nitroprusside, n = 6) or chronic (antihypertensive treatment for 1 month, n = 8) blood pressure lowering, before and after the i.v. administration of a hypertonic NaCl solution, were investigated. 3. Baseline plasma vasopressin was not different in hypertensive and in normotensive subjects. Upright posture and hypertonic challenge augmented, while hypotonic saline reduced plasma vasopressin levels with no difference between the two groups. Acute, but not chronic, lowering of blood pressure increased plasma vasopressin from 1.6 +/- 0.63 to 3.4 +/- 0.7 pg/mL (p < 0.05); administration of hypertonic saline further increased vasopressin to 10.8 +/- 2.22 (p < 0.01) in the acute and to 6.0 +/- 1.03 pg/mL (p < 0.01) in the chronic study. 4. No significant alterations of the regulation of vasopressin have been found in moderate, uncomplicated hypertension. Moreover, acute lowering of blood pressure facilitated the release of vasopressin and its osmoregulation while a chronic antihypertensive treatment did not interfere with a normal control of vasopressin secretion.

Cardiovascular Regulation of Vasopressin Neurons in the Supraoptic Nucleus

This paper reviews the regulation of hypothalamic vasopressin and oxytocin neurosecretory cells in the neural response to plasma volume expansion. Many questions remain unanswered regarding how an increase in volume affects neurohypophysial hormone secretion, what receptors are important in mediating this response, and which neural pathways are responsible for conveying the signal from those receptors to the hypothalamus. Plasma volume expansion activates regions of the central nervous system associated with inhibition of vasopressin release, oxytocin secretion, and inhibition of sympathetic nerve activity. Cardiac receptors, not arterial baroreceptors, are primarily responsible for activation of the regions associated with regulation of vasopressin secretion and sympathetic outflow. Other stimuli that as yet are undefined account for activation of oxytocin-secreting neurons. Electrophysiology experiments have measured the inhibition of vasopressin-secreting magnocellular neurons in the supraoptic nucleus by select stimulation of cardiac receptors in the caval–atrial junction. Further experiments suggest that the perinuclear zone, a population of neurons surrounding the supraoptic nucleus, is a necessary part of the pathway by which caval–atrial stretch decreases the excitability of vasopressin neurons. The perinuclear zone is also a necessary synapse for arterial baroreceptor-mediated inhibition of vasopressin neurons. This suggests that the neural pathways that inhibit vasopressin release in response to an increase in blood pressure and an increase in blood volume may overlap at the perinuclear zone of the supraoptic nucleus. Finally, the integration of various neural pathways activated by multiple receptors to ultimately determine the activity of magnocellular neurons and vasopressin secretion is discussed.

Melatonin inhibits spontaneous and VIP-induced vasopressin release from suprachiasmatic neurons

We have studied melatonin effects on vasopressin release from dispersed cells of the rat suprachiasmatic nuclei (SCN). The release follows a circadian rhythm peaking during the day and decreasing at night. Melatonin inhibits the spontaneous increase and accelerates the decrease of vasopressin release. Melatonin also inhibits vasopressin release induced by vasoactive intestinal peptide (EC 50=0.4 nM). The inhibition of vasopressin release correlates with the known inhibitory effect of melatonin on spontaneous neuronal activity in SCN.

Central administration of urocortin inhibits vasopressin release in conscious rats

Urocortin (UCN) is a new mammalian member of the corticotropin releasing factor (CRF) family and supposed to be an endogenous ligand for type 2 CRF receptors. Previous studies have revealed that UCN mRNA exists in the supraoptic nucleus (SON), and that water deprivation increases UCN immunoreactivity in SON. In this study, we examined the effect of centrally-administered UCN on arginine vasopressin (AVP) release in conscious rats. Intracerebroventricular (i.c.v.) injection of UCN (5.0 μg/rat) significantly attenuated AVP release induced by hyperosmolality at 30 min after the injection. In contrast, CRF (5.0 μg/rat) injected i.c.v. had no significant effect on AVP release. These results suggest that central UCN play an inhibitory role in osmoregulation of AVP release.

Gaseous neurotransmitter modulation of vasopressin and oxytocin release.

Following microbial invasion, inflammatory mediators are released which bring about vascular and many other changes. In previous studies we have demonstrated that neurohypophysial hormone release can be stimulated by cytokines, particularly interleukin-1 and interleukin-61. This has suggested that inflammatory modulators can directly regulate vasopressin and oxytocin, and vasopressin may in turn have circulatory effects as well as possibly modulating the hypothalamo-pituitary adrenal (HPA) axis. More recently we have begun exploring the role of gaseous neurotransmitters in the hypothalamus in terms of the regulatory control of these two hormones. Specifically we have demonstrated that the synthetic enzyme for nitric oxide, NOS, is present within the hypothalamus, particularly in the supraoptic and paraventricular nuclei2. Donors of nitric oxide (NO) are able to inhibit the stimulated release of vasopressin from acute hypothalamic explants3, while the inducible isoform of NOS can be induced in vivo in rats in response to endotoxin.4,5. Carbon monoxide (CO) is another possible gaseous neuromodulator and is formed from haeme under the influence of heme oxygenase (HO), biliverdin and bilirubin being formed. Carbon monoxide has now been shown to inhibit the stimulated release of the neurohypophjysial hormones in vitro6,7, but by contrast the synthetic enzyme HO is not induced in response to endotoxin. Recent studies have demonstrated that explants acutely exposed to endotoxin show inhibition of vasopressin release, which reverses to stimulation in the presence of an HO inhibitor such as zinc protoporphyrin-IX or tin mesoporphyrin-IX; no marked effect was shown in the presence of NOS antagonists.

Inter-relationships between nonapeptide hormones and cyclic nucleotides within cultured porcine granulosa cells

The reciprocal control of nonapeptide hormone (oxytocin, vasopressin) and cyclic nucleotide (cAMP, cGMP) release by porcine granulosa cells was studied. In particular, the influence of vasopressin and oxytocin treatment (10-10 000 ng/ml) on basal and LH-induced cAMP and cGMP output, as well as the effects of dibutyryl cAMP (dbcAMP; cAMP analogue) and forskolin (a stimulator of cAMP formation; 0.1-1000 ng/ml) on vasopressin and oxytocin secretion by cultured porcine granulosa cells were examined. It was observed that the addition of arginine-8-vasopressin or oxytocin stimulated both cAMP and cGMP output from granulosa cells. Moreover, both vasopressin and oxytocin also increased LH-stimulated cAMP and cGMP release. On the other hand, both dbcAMP and forskolin decreased vasopressin secretion. Oxytocin release was stimulated under the influence of dbcAMP. The same stimulating effect occurred with forskolin given at a low dose (1 ng/ml), whilst higher doses of forskolin (10 or 1000 ng/ml) were inhibitory. The present observations demonstrate the reciprocal influence of nonapeptide hormones and cyclic nucleotides in porcine ovarian cells. Oxytocin and vasopressin, like LH, exert their action on the ovary via the activation of cAMP- and cGMP-dependent intracellular mechanisms. cAMP in turn inhibits vasopressin release through a negative feedback mechanism. On the other hand, a reciprocal stimulation of oxytocin and cAMP output in granulosa cells is suggested. Thus, cyclic nucleotides can be both regulators of nonapeptide hormone secretion and mediators of their action within porcine ovaries.

The CCK A receptor antagonist devazepide inhibits the effect of apomorphine on vasopressin release in pigs

1. 1. A transient increase in plasma vasopressin concentrations represents a physiological correlate of nausea in animals that vomit. 2. 2. The CCK A receptor antagonist devazepide has previously been shown to inhibit vasopressin release induced in pigs by intravenous (i.v.) CCK. 3. 3. This study investigated whether devazepide (70 μg/kg i.v.) would affect vasopressin secretion induced in pigs ( n = 6) by the emetic drug apomorphine (25 μg/kg i.v.). 4. 4. Apomorphine stimulated vasopressin release in the 30 min period following injection; this effect was prevented by prior administration of devazepide. 5. 5. The results suggest that CCK A receptor antagonists may have the ability to prevent nausea and/or emesis.

Vasopressin-independent alterations in renal water excretion in quadriplegia

Postural effects on water excretion are known to be increased in patients with cervical spinal cord injury and may result in marked impairment of the ability to excrete a water load, especially in erect posture. Both vasopressin-dependent and vasopressin-independent mechanisms have been implicated. To assess the roles of these mechanisms and further identify the factors involved in the renal response to erect posture, sustained water loading studies were performed on 11 quadriplegic subjects and 9 healthy control subjects, supine and erect (sitting). Renal blood flow was assessed by p-aminohippurate clearance (CPAH) measurements in 7 quadriplegic and 5 control subjects. During maximal water diuresis, plasma vasopressin concentrations were reduced to unquantifiable levels in all subjects. Osmolar clearance, free water clearance (CH2O), and distal delivery of filtrate (DDF) were all lower in quadriplegic than in control subjects, supine and erect. The relationship between CH2O and DDF was the same in quadriplegic as in control subjects and was not altered by change in posture in either group. Creatinine clearance and CPAH were lower in erect than in supine posture in quadriplegic subjects but not in control subjects. We conclude that impairment of water excretion in stable normonatremic quadriplegic subjects can be attributed primarily to vasopressin-independent mechanisms involving reduced filtrate delivery to diluting segments of the renal tubules rather than to resistance to normal suppression of vasopressin release.

The role of endogenous atrial natriuretic peptide in resting and stress-induced release of corticotropin, prolactin, growth hormone, and thyroid-stimulating hormone.

Our previous studies have shown that stimulation of the anteroventral third ventricle region increases atrial natriuretic peptide (ANP) release, whereas lesions of the anteroventral third ventricle or median eminence block the release of ANP from blood volume expansion, suggesting a critical central nervous system participation in this response. ANP is also produced within neurons that have cell bodies in the rostral hypothalamus and axons that extend to the median eminence and neural lobe. In addition to its natriuretic effect, the peptide can inhibit the release of corticotropin (ACTH) and prolactin, anterior pituitary hormones that are released during stress. To determine the physiologic significance of ANP in the control of basal and stress-induced release of anterior pituitary hormones, highly specific antiserum against the peptide (AB-ANP) was microinjected into the third cerebral ventricle of conscious freely moving male rats to immunoneutralize hypothalamic ANP. In the initial experiment, the antiserum or control normal rabbit serum (NRS) was injected into the third cerebral ventricle to determine the effect of the antiserum on basal release of pituitary hormones. The antiserum had no effect on the concentrations of plasma ACTH, prolactin, or thyroid-stimulating hormone for 3 hr after the injection; however, plasma growth hormone concentration, although unchanged for 2 hr, was markedly elevated at 3 hr. These results indicate that although ANP appears to have no effect on the basal release of the other hormones, it has a physiologically significant inhibitory effect on growth hormone release. The delay of the effect is probably related to the time required for the antiserum to diffuse to the site of action of the peptide, presumably at some distance from the ventricle. Since this effect was demonstrable only after 3 hr, in the stress experiment, the antiserum or NRS was microinjected into the third ventricle 3 hr prior to application of ether stress. The rapid elevation of plasma ACTH in NRS-injected rats was markedly augmented by AB-ANP. Ether also induced a rapid increase in plasma prolactin in the NRS-injected animals, as expected. Contrary to the ACTH response, the maximal increase in plasma prolactin after ether was attenuated in animals preinjected with AB-ANP. In the NRS-injected animals, there was a significant decline in plasma growth hormone after the application of ether that was significantly accentuated by AB-ANP, but this was probably the result of the higher initial levels of plasma growth hormone in the ANP-AB group followed by its disappearance with a half-time similar to that of the NRS-injected group. The decline in plasma thyroid-stimulating hormone after ether stress was unaltered in the animals injected with AB-ANP. The results of these immunoneutralization studies suggest that endogenous ANP does not play a role in thyroid-stimulating hormone release. On the other hand, the endogenous peptide appears to have a physiologically significant inhibitory role in suppressing ACTH release during stress, mediated at least partly by suppression of vasopressin release. Endogenous ANP has a pathophysiologic role in augmenting the prolactin release in stress either by inhibiting release of prolactin-inhibiting factors or, alternatively, by enhancing release of prolactin-releasing factors. Endogenous ANP appears to inhibit resting, without altering stress-induced inhibition of growth hormone release by stimulating somatostatin release and/or inhibiting growth hormone-releasing hormone release or by both actions.