Binding affinities of oxytocin, vasopressin and Manning compound at oxytocin and V1a receptors in male Syrian hamster brains

Oxytocin (OT) and arginine vasopressin (AVP), as well as synthetic ligands targeting their receptors (OTR, V1aR), are used in a wide variety of research contexts, although their pharmacological properties are determined in only a few species. Syrian hamsters (Mesocricetus auratus) have a long history of use as a behavioural and biomedical model for the study of OT and AVP and, more recently, hamsters have been used to investigate behavioural consequences of OT-mediated activation of V1aR. We aimed to determine the binding affinities of OT, AVP and the selective V1aR antagonist, Manning compound, for OTR and V1aR in hamster brains. We performed saturation binding assays to determine the Kd values for the selective OTR and V1aR radioligands, [125 I]ornithine vasotocin analogue and [125 I]linear vasopressin antagonist. We then performed competition binding assays to determine Ki values for OT, AVP and Manning compound at both the OTR and V1aR. We found that OT and AVP each had the highest affinity for their canonical receptors (OT-OTR Ki = 4.28 [95% confidence interval (CI) = 2.9-6.3] nmol L-1 ; AVP-V1ar Ki = 4.70 [95% CI = 1.5-14.1] nmol L-1 ) and had the lowest affinity for their non-canonical ligands (OT-V1aR = 495.2 [95% CI = 198.5-1276] nmol L-1 ; AVP-OTR Ki = 36.1 [95% CI = 12.4-97.0] nmol L-1 ). Manning compound had the highest affinity for the V1aR (MC-V1aR Ki = 6.87 [95% CI = 4.0-11.9] nmol L-1 ; MC-OTR Ki = 213.8 [95% CI = 117.3-392.7] nmol L-1 ), although Manning compound was not as selective for the V1aR in hamsters as has been reported for the receptor in rats. When comparing these data with previously published work, we found that the promiscuity of the V1aR in hamsters with respect to OT and AVP binding is more similar to the promiscuity of the human V1aR than to the rat V1aR receptor. Moreover, the selectivity of OT at hamster receptors is more similar to the selectivity of OT at human receptors than the selectivity of OT at rat receptors. These data highlight the importance of determining the pharmacological properties of behaviourally relevant compounds in diverse model species.

[Absorption of arginine-vasopressin and arginine-vasotocin in small intestine of the frog Rana temporaria]

Experiments in vitro demonstrated a partial absorption of arginine-vasopressin (AVP) in the frog small intestine. Dynamics and efficiency of the nonapeptide absorption are studied with use of hydroosmotic method of recording of the osmotic permeability of the frog urinary bladder epithelium and immunoenzyme analysis. In the process of absorption there were preserved intactness of the hormone cyclic structure and its physiological activity, like in the case of the arginine-vasotocin (AVT) absorption. The AVP absorption increased at its administration into the gut with inhibitor of proteases. By methods of immunoelectron and immunofluorescent microscopy with use of polyclonal antibody to AVP, location of the label to the hormone was shown in the enterocyte cytoplasm. Thus, there was obtained a morphological evidence for the AVP absorption and transepithelial transfer in the frog small intestine. These data enlarge the concept of the poorly studied properties of the absorbing epithelium of the vertebrate intestine with respect to absorption of intact molecules of polypeptides.

Effects of the Mucoadhesive Polymer Polycarbophil on the Intestinal Absorption of a Peptide Drug in the Rat

The absorption across rat intestinal tissue of the model peptide drug 9-desglycinamide, 8-arginine vasopressin from bioadhesive formulations was studied in-vitro, in a chronically isolated internal loop in-situ and after intraduodenal administration in-vivo. A controlled-release bioadhesive drug delivery system was tested, consisting of microspheres of poly(2-hydroxyethyl methacrylate) with a mucoadhesive Polycarbophil-coating, as well as a fast-release formulation consisting of an aqueous solution of the peptide in a suspension of Polycarbophil particles. Using the controlled-release system, a slight improvement of peptide absorption was found in-vitro in comparison with a non-adhesive control system, but not in-situ or in-vivo. In contrast, bioavailability was significantly increased in all three models from the Polycarbophil suspension in comparison with a solution of the drug in saline. The effect appeared to be dose-dependent, indicative of intrinsic penetration-enhancing properties of the mucoadhesive polymer. A prolongation of the absorption phase in-vitro and in the chronically isolated loop in-situ suggested that the polymer was able to protect the peptide from proteolytic degradation. This could be confirmed by degradation studies in-vitro. The duration of the penetration enhancing/enzyme inhibiting effect was diminished with increasing complexity of the test model, in the same way as was previously found for the bioadhesive effect. This interrelationship suggests that the observed improvement in peptide absorption and the mucoadhesive properties of this polymer are associated. The development of a fast-release oral dosage form for peptide drugs on the basis of Polycarbophil appears to be possible.

Osmotic and nonosmotic regulation of arginine vasopressin during prolonged endurance exercise

CONTEXT

Although the primary cause of exercise-associated hyponatremia (EAH) is relative overconsumption of fluids beyond the kidneys' ability to excrete excess fluid, the mechanisms limiting maximum renal excretory ability during exercise remain to be elucidated.

OBJECTIVE

The objective of the study was to: 1) perform a comprehensive evaluation of the endocrine secretion of pituitary, natriuretic and adrenal steroid hormones, and cytokines immediately before and after running an ultramarathon; and 2) evaluate the relationship between osmotic and nonosmotic stimuli to arginine vasopressin (AVP) secretion within the overall context of assessing the hormonal regulation of fluid balance during prolonged endurance exercise.

DESIGN

This was an observational study.

SETTING

The study setting was a 56-km ultramarathon.

PARTICIPANTS

Eighty-two runners participated in the study.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

Plasma sodium concentration [Na(+)] and plasma volume [(AVP)(p)] were measured.

RESULTS

Fluid homeostasis during exercise (356 +/- 4 min) was maintained with ad libitum fluid intakes. [Na(+)] was maintained from before the race (139.3 +/- 0.3 mmol/liter) to after the race (138.1 +/- 0.4 mmol/liter) with a significant decrease in plasma volume (-8.5 +/- 0.1%, P < 0.01). Increases in the plasma (AVP)(p) (3.9-fold), oxytocin (1.9-fold), brain natriuretic peptide (4.5-fold), and IL-6 (12.5-fold) were highly significant (P < 0.0001). Changes in brain natriuretic peptide, oxytocin, and corticosterone were associated with 47% of the variance noted in (AVP)(p) and 13% of the variance in plasma [Na(+)] in pathway analyses.

CONCLUSIONS

(AVP)(p) was markedly elevated after the ultramarathon despite unchanged plasma [Na(+)](.) Therefore, an inability to maximally suppress (AVP)(P) during exercise as a result of nonosmotic stimulation of AVP secretion may contribute to the pathogenesis of exercise-associated hyponatremia if voluntary fluid intake were to exceed fluid output.

Biological half-life and organ distribution of [3H]8-arginine vasopressin following administration of vasopressin receptor antagonist OPC-31260

The effects of the antidiuretic (V(2)) non-peptide receptor antagonist OPC-31260 on the plasma vasopressin level and the biological half-life and organ distribution of radiochemically pure, biologically active [(3)H]8-arginine vasopressin [spec. act.: 15.9 mCi/mmol (588 GBq/mmol)] were studied in Wistar rats. The plasma vasopressin level increased significantly throughout the whole experimental period (24 h). There was no change in the fast phase of the curves of total radioactivity disappearance from the plasma after the administration of [(3)H]arginine vasopressin (control: 1.51+/-0.17 min, OPC-31260-treated: 1.42+/-0.12 min, n=10). The fast phase of the disappearance curves of intact [(3)H]arginine vasopressin did not change either following the administration of OPC-31260 in a dose of 30 mg/kg p.o. (control: 1.06+/-0.19 min, OPC-31260-treated: 1.00+/-0.15 min, n=6). The slow phase of the biological half-life, which is characteristic for the examined compound, proved to be significantly longer (total radioactivity control: 9.29+/-0.61 min, OPC-31260-treated: 12.33+/-0.42 min, P<0.05, n=10; [(3)H]arginine vasopressin radioactivity: control: 5.96+/-0.58 min, OPC-31260-treated: 8.90+/-0.37 min, P<0.05, n=6). In the control rats, the radioactivity was accumulated to the greatest extent in the neurohypophysis, adenohypophysis and kidney. Following OPC-31260 administration, significantly more radioactive compounds accumulated in the kidney (control: 0.30+/-0.052 total radioactivity %/100 mg organ weight, OPC-31260-treated: 0.50+/-0.133 total radioactivity %/100 mg organ weight, P<0.05, n=10) and neurohypophysis (control: 0.37+/-0.053 total radioactivity %/100 mg organ weight, OPC-31260-treated: 0.52+/-0.076 total radioactivity %/100 mg organ weight, P<0.05, n=10). Our results permit the conclusion that the antidiuretic antagonist OPC-31260 not only blocks the V(2) receptors, but also increases the biological half-life of vasopressin. The longer biological half-life of vasopressin following OPC-31260 administration may play a role in the elevation of the plasma vasopressin level.

Improvement of cationic albumin conjugated pegylated nanoparticles holding NC-1900, a vasopressin fragment analog, in memory deficits induced by scopolamine in mice

NC-1900, an active fragment analog of arginine vasopressin [arginine vasopressin-(4-9)], has proved to be capable of improving the spatial memory deficits and the impairments in passive avoidance test. In this study, a novel drug carrier for brain delivery, cationic bovine serum albumin conjugated pegylated nanoparticles (CBSA-NPs) holding NC-1900, was developed and its improvement on scopolamine-induced memory deficits was investigated in mice using the platform-jumping avoidance test. CBSA-NPs loaded with NC-1900 in spherical shape and uniform size below 100 nm were prepared by the double emulsion/solvent evaporation procedure, and the zeta potential of CBSA-NPs was about -8mV with the loading capacity of NC-1900 around 0.46%. The in vitro study showed that approximately 10% NC-1900 was released from CBSA-NPs in pH 7.4 phosphate buffer saline (PBS) during 56 h incubation with about 15% NC-1900 released in pH 4.0 PBS during 7 days, indicating the sustained release of this carrier. Furthermore, the half-life of NC-1900 loaded in CBSA-NPs in plasma was about 78 h, which was 4-fold longer than that of free NC-1900 (19 h). The active avoidance behavioral results showed that the s.c. administration of NC-1900 tended to improve memory deficits, but the difference did not present any statistical significance, whereas this peptide failed to produce any positive effects by i.v. administration. However, the i.v. injection of CBSA-NPs loaded with NC-1900 greatly improved memory impairments to a normal level, but the efficacy was slight if the loaded nanoparticles (NPs) were exclusive of the conjugation of CBSA, indicating that CBSA-NP was a promising brain delivery carrier for NC-1900 with CBSA as a potent brain targetor. It was concluded that CBSA-NP loaded with NC-1900 was potentially efficacious in the treatment of memory deficits via i.v. administration.

Dopamine, oxytocin, and vasopressin receptor binding in the medial prefrontal cortex of monogamous and promiscuous voles

Comparisons between monogamous and promiscuous vole species have proven useful in examining neurobiological mechanisms underlying social attachment. Reward processing is important for social attachment, and the medial prefrontal cortex (mPFC) exerts a direct influence on reward pathways. Dopamine (DA), oxytocin (OT), and arginine vasopressin (AVP) all have been implicated in the regulation of social attachment in monogamous voles. Therefore, we used radiolabeled ligands to examine dopamine D(1)- and D(2)-like, OT, and AVP V(1a) receptor binding densities in the mPFC of monogamous and promiscuous voles. Species differences were found; monogamous voles had higher densities of D(2)-like and OT receptor binding and lower densities of D(1)-like and V(1a) receptor binding than did promiscuous voles. Sex differences also were found; females had higher densities of OT receptor binding but lower densities of V(1a) receptor binding than did males in both species. Further, the laminar distribution of receptor binding indicates the possibility of an interaction between DA and OT systems in the mPFC in the regulation of social attachment. Differences in D(1)- and D(2)-like receptor binding between species are discussed in terms of how they might modulate cortical activity and subsequent DA release in the nucleus accumbens (NAcc).

[The effect of glucose on antidiuretic hormone absorption in the rat and frog small intestine]

Administration of 5 ml/100 g body weight of 1% glucose solution to stomach produced the same diuretic kidney response in fasted Wistar rats as administration of the same amount of water. Intragastric administration of arginine vasopressin along with the water load evoked an antidiuretic response. Arginine vasopressin in the same volume of glucose induced no kidney response difference as compared with the hormone action in experiments with water load. 0.1 nmol of arginine vasotocin, having been itroduced into the rat isolated ileum, prevented the effect of glucose on the hormone absoption. 0.1 nmol of arginine vasotocin, having been introduced into the frog isolated ileum along with isotonic glucose solution, increased the hormone absorption; fructose did not affect this process whereas mannitol decreased absorption ofarginine vasotocin. This absorption was also reduced by intraileal introduction of arginine vasotocin with the hypotonic Ringer solution. The findings suggest that glucose in the rat gastrointestinal tract does not affect arginine vasopressin absorption in vivo, whereas in the frog ileum glucose increases arginine vasotocin absorption in vitro.

Phospholipid mediators and MgATPase modulation causes changes in the cardiovascular effects of vasopressin in lithium carbonate-induced polyuric rats

The effect of phospholipid and MgATPase modulation was evaluated on the cardiovascular actions of vasopressin in normal and lithium carbonate- (Li2CO3) induced polyuric rats. We examined the effects of the phospholipase inhibitor neomycin, the diacylglycerol kinase II inhibitor R59949 and the MgATPase activator sphingosine on heart rate (HR) and blood pressure (BP) responses to vasopressin analogues lysine vasopressin (LVP) and arginine vasopressin (AVP). R59949 (20 microg/kg) produced an increase while sphingosine (30 microg/kg) caused a decrease in HR responses in both control and polyuric rats. Pretreatment with sphingosine caused significant enhancement of LVP- (10 microg/kg) induced bradycardia in polyuria rats compared with control animals (p < 0.01). R59949 induced a potentiation of vasopressin-induced bradycardia in control animals compared with polyuria rats. Pretreatment with sphingosine and R59949 produced a significant increase in BP per se and potentiated the actions of LVP in control animals, while the response in the lithium-treated animals was attenuated. Neomycin caused a reduction in HR and BP in control and lithium-treated animals. To evaluate the central role of the MgATPase enzyme we used sphingosine, which significantly increased the locomotor activity of lithium-treated animals, suggesting a possible central interaction of lithium and MgATPase (p < 0.05). These results strongly suggest that phospholipid mediators and MgATPase modulation contribute to the alteration of the cardiovascular effects of vasopressin in lithium carbonate-induced polyuric rats.

Possible Absorption of Antidiuretic Hormone in Isolated Rat Intestine

Arginine-vasopressin or arginine-vasotocin hormones introduced into the small intestine are absorbed and exert a hydrosmotic effect. The amount of absorbed antidiuretic hormone increased when it is introduced with intestinal peptidase inhibitor aprotinin. These data attest to the possibility of absorption of pituitary hormones (vasotocin and vasopressin) in rat small intestine without losing their physiological activity.

Physicochemical considerations in the iontophoretic delivery of a small peptide: in vitro studies using arginine vasopressin as a model peptide

Transdermal iontophoresis (TI) is a physical enhancement technique to facilitate the delivery of primarily charged molecules across the skin. TI of peptides is influenced by a complex interplay of several factors and one of the main issues in optimizing iontophoretic delivery of peptides is to improve the transport efficiency. From this perspective, this study investigates the effect of the physicochemical parameters on the TI of a peptide arginine vasopressin (AVP). The permeation of AVP showed a linear dependence on the concentration of drug in the donor medium. The iontophoretic flux of AVP was strongly influenced by the pH of the donor solution. Increasing the pH from 5.16 to 7.4 resulted in a decrease in the enhancement ratio by 4.5 times. When the ionic strength was increased by varying the amount of NaCl from 0.05 to 0.25 M the flux was found to decrease by 3.2 times. Replacing normal saline in the receptor compartment by HEPES buffer showed a resultant four times increase in drug permeation. The physiochemical parameters of the donor medium play a significant role in the efficiency of drug delivery by iontophoresis for a small peptide like AVP. Though electrorepulsion would be expected to be the main mechanism involved in the movement of charged molecules across the skin by iontophoresis, for peptides in the molecular weight range of AVP, other associated secondary effects like osmosis, electroosmosis and counter ion flow may also play a significant role in transport across the skin.

Poloxamer gel as vehicle for transdermal iontophoretic delivery of arginine vasopressin: evaluation of in vivo performance in rats

The present study describes the formulation and evaluation for pharmacokinetic and pharmacodynamic activity of arginine vasopressin (AVP), a nanopeptide with antidiuretic activity on being delivered by transdermal iontophoresis. Poloxamer 407 was used to form stable gels that did not reduce the release of AVP. The release rate from the gel followed Higuchi kinetics indicating that the dominant mechanism of release is diffusion. Iontophoresis alone and in combination with chemical enhancers was used to augment the transdermal permeation of AVP. The results of both pharmacokinetic and pharmacodynamic studies emphasize the dimension of 'rapid onset' achieved by iontophoresis. The correlation between pharmacokinetic data and pharmacodynamic activity was only qualitative. Histopathological studies revealed that skin toxicity caused by either iontophoresis or chemical enhancers when used alone could be reduced by using a combination of both the techniques in tandem.

Effect of iontophoresis and fatty acids on permeation of arginine vasopressin through rat skin

The aim of this study was to assess the effects of fatty acids and iontophoretic mode of penetration enhancement on transdermal delivery of Arginine Vasopressin (AVP). Sprague-Dawley (SD) rat skin was pretreated with fatty acids (e.g. 5% w/v, lauric acid, oleic acid, and linoleic acid in ethanol:water (EtOH:W, 2:1 system) for 2h and iontophoresis in vitro, separately or together. The results indicate that all fatty acids studied increased (P<0.05) the flux of AVP in comparison to control (not pretreated with enhancer) and their effectiveness in flux enhancement was comparable. Further, oleic acid in combination with iontophoresis significantly increased the permeation of AVP both in comparison to pretreatment with fatty acids and iontophoresis alone. However, iontophoresis did not further increase the permeation of AVP through linoleic acid pretreated skin. Fourier transform infrared (FT-IR) spectroscopic studies revealed that EtOH:W (2:1) system is not effective in lipid extraction. The shift to higher wavenumbers of the symmetric and asymmetric stretching peaks at 2850 and 2920cm(-1) revealed that at the concentration used, oleic acid and linoleic acid caused fluidization of stratum corneum (SC) lipids. This study provides direct evidence that oleic acid in EtOH:W (2:1) system causes disruption of the SC lipid lamellae and that a combination of oleic acid with iontophoresis further enhances the effects of oleic acid in a synergistic manner.

Management of vasodilatory shock: defining the role of arginine vasopressin

The rationale for an arginine vasopressin (argipressin) infusion was put forward after it was discovered that patients in shock states might have an endogenous arginine vasopressin deficiency. Subsequently, several investigations impressively demonstrated that arginine vasopressin can successfully stabilise haemodynamics even in advanced vasodilatory shock. We report on physiological and pharmacological aspects of arginine vasopressin, and summarise current clinical knowledge on employing a continuous arginine vasopressin infusion in critically ill patients with catecholamine-resistant vasodilatory shock of different aetiologies. In view of presented experimental evidence and current clinical experience, a continuous arginine vasopressin infusion of approximately 2 to approximately 6 IU/h can be considered as a supplemental strategy to vasopressor catecholamines in order to preserve cardiocirculatory homeostasis in patients with advanced vasodilatory shock. Because data on adverse effects are still limited, arginine vasopressin should be reserved for patients in whom adequate haemodynamic stabilisation cannot be achieved with conventional vasopressor therapy or who have obvious adverse effects of catecholamines that result in further significant haemodynamic deterioration. For the same reasons, arginine vasopressin should not be used as a single, alternative vasopressor agent instead of catecholamine vasopressors. Future prospective studies will be necessary to define the exact role of arginine vasopressin in the therapy of vasodilatory shock.

[Antidiuretic reaction of the human and rat kidney to peroral administration of arginine-vasopressin and desmopressin]

Water in amount of 5 ml/100 g body weight was administered through a gastric probe into the stomach in alert rats; subjects-volunteers drank 20 ml of water per 1 kg of body weight. This resulted in diuresis at the peak of which the excreted water fraction reached 23% in rats and 12.4% in human subjects, whereas excretion of the osmotically free water amounted to 0.103 +/- 0.018 ml/min/100 g body weight and 10.0 +/- 1.8 ml/min/1.73 m2 of the body surface, respectively. These data indicate a practically complete inhibition of the arginine vasopressin secretion. On intragastric administration of 10 micrograms of arginine vasopressin or 0.2 microgram of desmopressin, with water in rats, a prolonged and quite obvious antidiuretic response occurred, with a marked increase of reabsorption of the osmotically free water in kidneys. A direct correlation has been found between the dose of the intragastrically administered vasopressin in the dose range from 0.1 to 10 micrograms/100 g body weight and a decrease of clearance of the osmotically free water. In subjects volunteers, an antidiuretic reaction to administration of 0.2 mg of desmopressin with water, was found. The data obtained provide a direct proof of intestinal absorption of nanopeptides without loss of their physiological activity. Significance of the data obtained for physiology of digestion and for clinical medicine, is discussed.

Bioavailability assessment of arginine-vasopressin (AVP) using pharmacokinetic-pharmacodynamic (PK-PD) modeling in the rat

A novel method of assessing the extent of oral bioavailability of arginine-vasopressin (AVP) from pharmacological data was presented. After intravascular administration (i.v. bolus or short-term infusion) of AVP to rats, the relationship between blood concentrations and its effect on both mean arterial pressure (hemodynamic effect) and urinary sodium concentration (anti-diuretic effect) was described on the basis of an integrated pharmacokinetic-pharmacodynamic (PK-PD) model. A direct model was used for the hemodynamic response, while an indirect response model, rather than a hypothetical link model was used for the anti-diuretic response. A sigmoid Emax model was applied to describe the drug-receptor interaction. Pharmacological responses after intravascular administration of AVP were reasonably described by the PK-PD model. However, PD parameters estimated by the PK-PD analysis suggested that apparent receptor affinity rather than efficacy in i.v. bolus study was significantly higher than that in the short-term infusion study. This fact indicated that PK-PD relationship was influenced by the intravascular input rate of AVP. We then investigated the relationship between plasma concentration and amount of AVP bound to the V2 receptors in the kidney. The result indicated that the amount of AVP bound to the receptors after i.v. bolus injection was always greater than that after short-term infusion. Since the PK-PD relationship after oral administration was almost identical with that after short-term infusion, the PK-PD model obtained in the short-term infusion study was used to assess the extent of oral bioavailability (EBAPp.o.). The EBAp.o. values, estimated from pharmacological effects (hemodynamic effect and anti-diuretic effect) after oral administration of 5 microg/kg of AVP were 0.68% to 0.93% and were almost identical with the actual EBAPp.o. value (0.81%). From these results, we concluded that oral bioavailability of AVP was reasonably predicted by the PK-PD model, provided that appropriate pharmacological effects and appropriate intravascular dosing rate as a reference formulation are available. The method may be an alternative to methods based on plasma concentrations, when drug concentration cannot be measured and when appropriate pharmacological data are available.

In vivo and in vitro evidence of blood-brain barrier transport of a novel cationic arginine-vasopressin fragment 4-9 analog

The blood-brain barrier (BBB) transport and metabolism of a novel arginine-vasopressin fragment 4-9 [AVP(4-9), isoelectric point; (pI) = 9.2] analog, that is, cationic AVP(4-9) (C-AVP(4-9), PI = 9.8), were examined in vivo and in vitro. At 45 min after an i.v. administration to mice, the cerebrum-to-plasma concentration ratios of (35)S-labeled AVP(4-9) and (125)I-labeled C-AVP(4-9) were 0.103 and 0.330 ml/g cerebrum, respectively, and the BBB permeation clearances were 1.47 x 10(-4) and 3.10 x 10(-4) ml/min/g cerebrum, respectively. In the in vitro study using mouse brain capillary endothelial cells immortalized by SV40 infection (MBEC4), the acid-resistant binding values of (35)S-labeled AVP(4-9) and (125)I-labeled C-AVP(4-9) to MBEC4 at 120 min were 0.93 and 1.95 microliter/mg protein (as the cell/medium ratios), respectively. (35)S-labeled AVP(4-9) showed two-phase saturable acid-resistant binding, and its half-saturation constants (K(D)) were 3.8 nM (high affinity) and 45.7 microM (low affinity). (125)I-labeled C-AVP(4-9) showed single-phase saturable acid-resistant binding, with a K(D) value of 16.4 microM. The acid-resistant binding of (125)I-labeled C-AVP(4-9) was significantly dependent on temperature and medium osmolarity. The acid-resistant binding of (125)I-labeled C-AVP(4-9) was inhibited by dancylcadaverine, phenylarsine oxide (endocytosis inhibitors), 2,4-dinitrophenol (a metabolic inhibitor), and AVP(4-9), poly(L-lysine), and protamine (cationic substances), but not by poly(L-glutamic acid) (an anionic peptide) and the V(1) and V(2) vasopressin receptor antagonists. In addition, the conversion of C-AVP(4-9) to AVP(4-9) in the cerebral homogenate was confirmed by HPLC and mass spectrometry. The present results demonstrate that C-AVP(4-9) is transported through the BBB more effectively than AVP(4-9), via absorptive-mediated endocytosis, and that C-AVP(4-9) is converted to the neuroactive parent peptide, AVP(4-9), in the cerebrum.

Specific renal delivery of sugar-modified low-molecular-weight peptides

To develop a novel delivery system for peptides involving sugar modification, Arg-vasopressin (AVP) was modified by linking it to a variety of sugars via an octamethylene group and the subsequent tissue uptake by rats was then monitored after administration by i.v. injection. The glucosyl, mannosyl, and 2-deoxyglucosyl derivatives of AVP exhibited selective renal uptake. These derivatives were found to be distributed in the proximal tubules of the renal cortex. In addition, they exhibited specific binding to the kidney microsomal fraction in vitro (Kd = approximately 60 nM), suggesting that they are taken up by a specific recognition mechanism located in the kidneys. From the results of the uptake study of glucosyl derivatives, the following points are clear: 1) renal uptake in vivo becomes saturated with increasing dose, and the Km from the uptake study is almost the same as the Kd obtained in the binding assay in vitro and 2) because the renal first-pass uptake extraction is about 70% at a low dose (10 nmol/kg), there is an effective mechanism for uptake from blood. Furthermore, glucosyl and mannosyl derivatives of oxytocin, a neutral peptide, unlike AVP that is basic, also have high renal uptake clearances. Thus, the renal uptake may not be dependent on derivatives having a cationic nature. We conclude that there is a novel transport mechanism in the kidneys that can be used for the specific renal delivery of glycosylated peptides.

Arginine vasopressin transport and metabolism in the pigmented rabbit conjunctiva

The purpose of this study was to evaluate the transepithelial transport and metabolism of arginine vasopressin (AVP) in the pigmented rabbit conjunctiva, both in the absence and presence of protease inhibitors. The apparent permeability coefficient, P(app), for 3H-AVP was determined in the modified Ussing chamber, and AVP metabolites were monitored by reversed phase HPLC using a C18 column. At 50 nM donor 3H-AVP, the P(app) in the mucosal-to-serosal (ms) direction was about five times higher than that in the opposite direction. Excess (0.1 mM) AVP decreased the P(app) for labelled AVP in the mucosal-to-serosal (ms) direction by about 50%. However, intact AVP transport showed neither concentration nor direction dependence. HPLC analysis revealed two subspecies of 3H-AVP in the receiver fluid and virtually no degradation products in the donor fluid following 3 h flux experiments. 3H-AVP transported in the ms direction underwent extensive hydrolysis (73%), which was decreased by 33% with mucosal application of 2 mM camostat mesylate (an aminopeptidase inhibitor) or by 27% with 0.5 mM leupeptin (a serine protease inhibitor). By contrast, 3H-AVP transported in the serosal-to-mucosal (sm) direction resulted in only 37% hydrolysis, and mucosal application of either inhibitor did not significantly affect the P(app) for intact AVP. These data suggest that intact AVP transport in the conjunctiva may be mediated mostly by passive diffusion and enzymatic degradation of AVP may be mediated by proteolytic enzymes present on the mucosal side of the conjunctiva.

Effects of protease inhibitors on vasopressin transport across rat alveolar epithelial cell monolayers

The transepithelial transport of arginine vasopressin (AVP) across cultured rat alveolar epithelial cell monolayers was studied. At 0.1 nM donor [125I]AVP, the radiolabel flux measured in the apical-to-basolateral (AB) direction was about 10 times greater than that in the reverse (BA) direction. HPLC analyses of the basolateral receiver fluid collected at the end of these flux measurements showed that about 97% of the total [125I]label represented subspecies of AVP, whereas the apical receiver fluid contained largely intact AVP (approximately 85% of total [125I]label). Both donor fluids contained virtually no degradation products of AVP (> 99%). In the presence of an excess 0.1 mM unlabeled AVP in the apical donor fluid, the Papp for radiolabeled AVP in the AB direction was decreased by approximately 68%, while the fraction of intact AVP in the basolateral receiver fluid was increased six-fold as compared to that observed at 0.1 nM [125I]AVP alone. Under this condition, the flux of intact AVP was approximately the same in both directions. When the concentration of apical camostat mesylate, an aminopeptidase inhibitor, was varied from 0 to 2 mM, the radiolabeled flux in the AB direction (with 0.1 nM [125I]AVP in the donor fluid) was significantly decreased in a dose-dependent manner, yielding commensurably elevated concentrations of intact AVP in the basolateral receiver fluid. In contrast, leupeptin (0.5 mM), a serine protease inhibitor, was without effect. These data, taken together, suggest that apically-presented AVP undergoes proteolysis (most likely by peptidases localized at apical cell membranes of alveolar epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Iontophoresis of a model peptide across human skin in vitro: effects of iontophoresis protocol, pH, and ionic strength on peptide flux and skin impedance

This study deals with effects of electrical (current density, frequency and duty cycle) and chemical (buffer pH and ionic strength) conditions on the flux of the octapeptide, 9-desglycinamide, 8-arginine-vasopressin (DGAVP), through dermatomed human skin. A pulsed constant current was applied during iontophoresis. The anode faced the anatomical surface of the skin samples inside the diffusion cells. The resistive and capacitative components of the equivalent electrical circuit of human skin could be calculated by fitting the voltage response to a bi-exponential equation. The skin resistance prior to iontophoresis varied between 20 and 60 k omega.cm2. During iontophoresis a decrease of skin resistance and an increase of the series capacitances was observed, which were most pronounced during the first hour of iontophoresis; thereafter both quantities gradually levelled off to an apparent steady state value. The reduction of the resistance during iontophoresis increased non-linearly with increasing current density between 0.013-0.64 mA.cm-2. The steady state resistance and capacitances did not vary significantly with frequency and duty cycle of the current pulse. There was no pH dependence of skin resistance at steady state. Between pH 4 and 10, the steady state peptide flux had a bell-shaped pH-dependence with a maximum of 0.17 nmol.cm-2.h-1 at pH 7.4, which is close to the I.E.P. of the peptide. Lowering the ionic strength from 0.15 to 0.015 M NaCl increased the steady state flux at pH 5 and pH 8 by a factor 5 to 0.28 +/- 0.21 and 0.48 +/- 0.37 nmol.cm-2.h-1, respectively. Together these observations suggested that DGAVP is transported predominantly by volume flow.(ABSTRACT TRUNCATED AT 250 WORDS)

V1-like [Arg8]vasopressin binding sites occur in rat hepatocyte nuclei

Arginine vasopressin binding site characterisation was performed on purified nuclei and plasma membranes from livers of Sprague-Dawley rats. [125I][d(CH2)5,Sarc7,Arg8]vasopressin, a selective V1 vasopressin receptor antagonist radioligand, bound to the nuclei in a protein concentration and time dependent manner. Scatchard analysis of nuclear binding sites revealed a single binding site with maximal binding site density (Bmax) of 115 +/- 13 fmol/mg protein and affinity (KD) of 5.2 +/- 0.7 nM. Plasma membrane binding demonstrated a Bmax of 529 +/- 25 fmol/mg protein and KD of 1.9 +/- 0.1 nM. The displacement profile for nuclear binding sites using vasopressin analogues was similar to that for plasma membrane binding sites and was typical of a V1 vasopressin receptor type. There was no evidence of V2-like vasopressin receptor binding using [3H]des-Gly-NH9(2)[d(CH2)5,D-Ile2,Ile4,Arg8]vasopressi n, a selective V2 vasopressin receptor radioligand, in the nuclear or membrane fractions. These results suggest the existence of nuclear V1-like vasopressin binding sites.

Pharmacokinetics of DGAVP in plasma following intranasal and oral administration to healthy subjects

A pharmacokinetic study was carried out to assess the bioavailability of desglycinamide-[Arg8]vasopressin (DGAVP, Org 5667). DGAVP (2 mg) was administered both intranasally and orally to healthy subjects with a treatment interval of 1 week. Blood samples were taken regularly between 15 min before and 210 min after administration and were assayed for DGAVP by radioimmunoassay. In all subjects endogenous vasopressin (AVP) levels were detectable. Peak levels of DGAVP occurred at 15 min after both treatments. The mean absorption half-life was 8.7 and 7.3 min and the mean elimination half-life was 38 and 34.6 min for the intranasal and oral route of administration, respectively. The bioavailability of orally administered DGAVP was low compared with the intranasally administered drug; the relative bioavailability of oral/nasal administration was 0.7%. The results indicate that DGAVP is absorbed rapidly after both oral and intranasal administration, but the intranasal route of administration of DGAVP is 100 times more effective in increasing plasma DGAVP levels.

Intracerebroventricular infusion of glycine stimulates vasopressin release in conscious sheep

We have previously observed that elevation of the plasma glycine concentration stimulates vasopressin (AVP) release in man and sheep. In the present study we show that this effect of glycine can be elicited directly via a cerebral site of action in conscious sheep. Intracerebroventricular infusions of 0.05 and 0.15 M glycine solutions increased the plasma AVP concentration by 6 and 50 times, respectively, while no effect on water intake was observed. Hyperhydration did not block the stimulation of AVP release. No behavioural side effects, or changes in blood pressure, were observed in response to the infusions.

Hydrogel-based iontotherapeutic delivery devices for transdermal delivery of peptide/protein drugs

Hydrogels were synthesized as the drug reservoir matrix for peptide-based pharmaceuticals, and the iontophoretic release and transdermal delivery of three model peptides, insulin, calcitonin, and vasopressin, from these hydrogel-based iontotherapeutic devices were investigated. The swelling behavior of polyacrylamide-type hydrogel as a function of its monomer and cross-linker concentration was studied, and a hydrogel with minimal swelling was synthesized. The release of peptides from the hydrogel matrix was found to follow a Q vs t1/2 relationship under passive diffusion conditions, which shifted to a Q vs t relationship under iontophoresis-facilitated transport. The release flux (dQ/dt) of peptides was observed to decline when the electric current was turned off and was resumed when the current was turned on, thus allowing for modulation of drug release by varying the application parameters of iontophoresis-facilitated transport. The permeability coefficients for these peptides across the hairless rat skin were evaluated using the hydrogel formulations prepared from polyacrylamide, p-HEMA, and carbopol. A rank order of vasopressin > calcitonin > insulin was obtained in accordance with the order of molecular size.

Water and sodium homeostasis in conscious rabbits: role of arginine-vasopressin

The aim of this study was to assess the role of arginine-vasopressin (AVP) on extracellular water distribution (VE) and on the urinary excretion of sodium in conscious rabbits with or without water deprivation. The study included two groups of animals. The first group involved two subgroups, both receiving an infusion of 0.9% NaCl-5% glucose (50-50, v:v) at the rate of 24 ml/hr to adequately hydrate the rabbits, but one received 2.5 ng/min/kg of AVP with the infusion; 120 min later, a bolus of inulin was injected to assess the distribution in the extracellular water. The rabbits of the second group were divided into 3 subgroups, receiving a 0.9% NaCl-5% glucose (50-50, v:v) infusion, at the rate of 6 ml/min; two subgroups received AVP, at the rate of 2.5 or 5 ng/min/kg; 40 minutes later, all animals received a bolus of inulin. In adequately hydrated rabbits, the infusion of AVP generated plasma levels of 35 +/- 7 pg/ml; the VE decreased from 204 +/- 23 to 111 +/- 10 ml/kg (p < 0.01) because of a decrease in plasma (VP) and interstitial volumes (VI). In the same group, natriuresis and osmolal clearance increased and free water clearance decreased. In rabbits deficiently hydrated, AVP reached plasma levels of 47 +/- 18 and 86 +/- 12 pg/ml following the 2.5 and 5 ng/min/kg infusions, respectively. In these animals, high plasma levels of AVP did not diminish VE but decreased the diuresis and osmolal clearance. It is concluded that in adequately hydrated rabbits, pathophysiological plasma levels of AVP shift the water from the VE to the intracellular space and increase the natriuresis, but in partially hydrated rabbits, the infusion of AVP maintains plasma volume constant because of an antidiuretic effect.

Pharmacokinetic and pharmacologic properties of antiuterotonic oxytocin analogs in the rat

The pharmacologic and pharmacokinetic properties were evaluated in a series of antiuterotonic oxytocin analogs, modified at positions 1, 2, 4, 8 and, in one case, position 9 of the oxytocin (OT) molecule. [Mpa1,D-Tyr2(Et),Val4,Orn8,desGly9]-OT, [Mpa1,Tyr2(Et),Val4,Orn8]-OT and [Mpa1,D-Tyr2,Val4,Orn8]-OT displayed similar plasma clearance rates (Clps) using the constant infusion method in rats. Two analogs, [Mpa1,D-Tyr2(Et),Val4,Orn8]-OT and, particularly, [Mpa1,D-Tyr2(Et),Thr4,Orn8]-OT, were cleared at significantly higher rates compared with the others. [Mpa1, D-Tyr2(Et), Val4, Orn8]-OT and [Mpa1, D-Tyr2(Et), Thr4, Orn8, desGly9]-OT were most potent in eliciting a short-term in vivo antiuterotonic effect, whereas the duration of effect was longest for [Mpa1, D-Tyr2, Val4, Orn8]-OT and [Mpa1, D-Tyr2(Et), Thr4, Orn8, desGly9]-OT. The Clp of [Mpa1, D-Tyr2, Val4, Orn8]-OT was similar regardless of the infusion rate. No relationship between antiuterotonic effect and Clp of the five peptides could be demonstrated, and no significant linear correlation between Clp and effect duration was found. The apparent volumes of distribution for the present analogs were 10-fold larger than the blood volume, a finding to be considered when measuring in vivo antagonistic activity. The 24-h urinary excretion ranged from 14.3 to 25.6% of the i.v. dose and was negatively correlated with peptide lipophilicity. It is concluded that, in addition to diverging pharmacologic properties, peptide analogs may differ markedly in kinetic parameters like Clp, volumes of distribution and urinary excretion despite minor molecular modifications.

Metabolic clearance rate of arginine vasopressin in severe chronic renal failure

1. The metabolic clearance rate of arginine vasopressin was determined using a constant infusion technique in normal subjects and patients with chronic renal failure immediately before commencing dialysis. Endogenous arginine vasopressin was suppressed in all subjects before the infusion with a water load. 2. Plasma arginine vasopressin concentrations were determined using a sensitive and specific radioimmunoassay after Florisil extraction. The detection limit of the assay was 0.3 pmol/l, and intra- and inter-assay coefficients of variation at 2 pmol/l were 9.7% and 15.3%, respectively. 3. In normal subjects, the metabolic clearance rate was determined at two infusion rates producing steady-state concentrations of arginine vasopressin of 1.3 and 4.4 pmol/l. In the patients with renal failure, a single infusion rate was used, producing a steady-state concentration of 1.5 pmol/l. 4. At comparable plasma arginine vasopressin concentrations, metabolic clearance rate was significantly reduced in patients with renal failure (normal 1168 +/- 235 ml/min versus renal failure 584 +/- 169 ml/min; means +/- SD; P < 0.001). 5. Free water clearance was significantly reduced in normal subjects during the arginine vasopressin infusion from 8.19 +/- 2.61 to -1.41 +/- 0.51 ml/min (P < 0.001), but was unchanged in the patients with renal failure after attaining comparable plasma arginine vasopressin concentrations. 6. In normal subjects there was a small but significant fall in metabolic clearance rate at the higher steady-state arginine vasopressin concentration (1168 +/- 235 ml/min at 1.3 pmol/l versus 1059 +/- 269 ml/min at 4.4 pmol/l; P = 0.016).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic clearance rate of arginine vasopressin in patients with cirrhosis

Metabolic clearance rate and half-time of arginine vasopressin were measured in 43 cirrhotic patients and 10 control subjects. Synthetic arginine vasopressin was infused intravenously at a rate of 500 pg/min/kg of body weight for 75 min. The metabolic clearance rate was significantly reduced, and the half-time of arginine vasopressin after stopping the infusion was significantly increased in patients with cirrhosis, particularly in those with ascites and in those with moderate or severe liver dysfunction. Changes in metabolic clearance rate and half-time of arginine vasopressin correlated with the score of the liver dysfunction, prothrombin activity and levels of serum albumin and bilirubin but not with parameters of kidney function (serum creatinine levels and clearance of creatinine). We conclude that reduced metabolic clearance rate and prolonged half-time of vasopressin in plasma are frequent findings in cirrhotic patients with poor liver function. This impaired catabolism of antidiuretic hormone may contribute to maintaining elevated plasma levels of this hormone in these patients and may be an additional factor leading to fluid retention and to dilutional hyponatremia.

Transport, uptake, and metabolism of blood-borne vasopressin by the blood-brain barrier

Transport, binding, and metabolism of [phenylalanyl-3,4,5,-3H(N)]arginine vasopressin (AVP) by the blood-brain barrier (BBB) was studied in adult guinea-pigs by means of a novel vascular brain perfusion (VBP)/capillary depletion technique and HPLC. A time-dependent, progressive brain uptake of 3H-radioactivity was measured over the 10 min period of VBP both in brain homogenates and in brain tissue depleted of cerebral microvessels. The unidirectional blood-to-brain transport constant, K(IN), estimated by multiple-time tissue uptake analysis of the homogenate and postcapillary supernatant, indicated that the BBB transfer rate for [3H]AVP (K(IN) = 2.37 +/- 0.25 microliters min-1 per gram brain homogenate) was almost 10 times higher than for simultaneously perfused [14C]sucrose, a cerebrovascular space marker. In contrast to homogenate and postcapillary supernatant, the [3H]radioactivity determined in the vascular pellet after dextran density centrifugation of the brain homogenate was very low and only somewhat higher than for [14C]sucrose. HPLC analysis of the perfused brain tissue revealed time-dependent degradation of the blood-borne neuropeptide. The percentage of intact [3H]AVP as determined in the postcapillary supernatant progressively declined during brain perfusion, from 49% at 1 min to 11.9% at 10 min. The major detectable labeled metabolite was [3H]phenylalanine, the labeled amino acid residue of [3H]AVP. The aminopeptidase inhibitor bestatin (0.5 mM), perfused simultaneously with [3H]AVP by the VBP technique, did not alter tissue uptake of [3H]AVP, indicating that there was no significant hydrolysis of peptide by the luminal BBB surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged systemic delivery of peptide drugs by long-circulating liposomes: illustration with vasopressin in the Brattleboro rat

The value of novel systemically long-circulating liposomes to prolong the duration of an antidiuretic hormone, arg8-vasopressin (VP), was investigated as a representative of low molecular weight peptides with rapid clearance. Cholesterol content was found to have a controlling effect on VP release in serum. Three types of liposomes were selected for urine production measurements in VP deficient Brattleboro rats. One contained phosphatidylserine (PS), which was rapidly cleared from the circulation. In the other two liposomes, the PS component was replaced by either phosphatidylglycerol or a novel phospholipid derivatized with polyethylene glycol (PEG); both showing prolonged circulation. Free VP (up to 8 micrograms/kg) gave reduced urine production for less than 24 hr. The PG formulation exhibited a dose-dependent prolonged duration of bioactivity of up to 4 days. Substitution of PEG-PE resulted in a 2-day delay followed by a prolonged duration of bioactivity for over 4 days. The duration of the prolonged bioactivity was not dose dependent but the amplitude was. This is attributed to VP release from liposomes which have distributed intact to another compartment without having been taken up by the RES. By balancing liposome circulation time, release rate, and dose, long-circulating liposomes can be applied to prolong the biological activity of a therapeutic peptide.

Localization and quantification of nonapeptide binding sites in the kidney of Xenopus laevis: evidence for the existence of two different nonapeptide receptors

The distribution and properties of nonapeptide binding sites in the kidney of the anuran Xenopus laevis were investigated using quantitative in vitro autoradiography. The binding studies were performed with [3H]arginine vasopressin (AVP) as ligand because [125I]arginine vasotocin (AVT) lacks biological activity. Specific binding sites for [3H]AVP are located in the glomeruli of the kidney. [3H]AVP binding results in a steady state of association and dissociation between ligand and binding sites. Scatchard and Hill analyses of saturation experiments showed that [3H]AVP binds to a single class of binding sites with a dissociation constant (Kd) of 430 +/- 109 pM and a maximum binding capacity (Bmax) of 5.306 +/- 1.379 fmol/mm2 (n = 8). Displacement studies demonstrated the same affinity of these [3H]AVP binding sites to [3H]AVP, unlabeled AVP, and AVT, whereas mesotocin possesses only weak affinity. Further nonapeptides like oxytocin and isotocin or the mammalian-specific V1 receptor antagonist [1-beta-mercapto-beta,beta-cyclopentamethylene propionic acid)-2-(O-methyl)-tyrosine)-AVP or the V2 receptor agonist (1-deamino-8-D-arginine)-vasopressin or unrelated peptides did not alter the binding of [3H]AVP. The localization of nonapeptide binding sites in the glomeruli with the same affinity to AVP as to AVT agrees with the finding that AVT causes antidiuresis in Xenopus laevis. An earlier study demonstrated Xenopus laevis interrenal tissue to possess a higher sensitivity for AVT than AVP which points to a nonapeptide receptor with a higher affinity for AVT than AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral-nasal membranes are not the major route for fetal absorption of amniotic fluid arginine vasopressin

Intraamniotically injected substances such as arginine vasopressin and digoxin have been found to rapidly appear in the ovine fetal circulation, irrespective of whether the fetal esophagus has been ligated or occluded. To determine if the ovine fetal oral-nasal membrane plays a significant role in this fetal absorption of amniotic substances, we used two groups of chronically catheterized fetal sheep with a surgical glove sewed over the fetal head to prevent access of the head to amniotic fluid. In the first group 22.5 micrograms of arginine vasopressin was injected into the amniotic cavity; in the second group 22.5 micrograms was injected into the glove over the fetal head. We found that, after injection into the amniotic cavity, there were rapid and highly significant increases in amniotic fluid arginine vasopressin concentrations, from 6.1 +/- 1.3 to 51,249 +/- 18,182 pg/ml (mean +/- SE) (p less than 0.00001). Concurrently there was a rapid increase in fetal plasma arginine vasopressin concentrations from 4.5 +/- 1.3 to 93.8 +/- 18.9 pg/ml (p less than 0.00001). The increase was significant within 15 minutes and reached a maximum at 60 minutes after the injection. Fetal arterial pressure increased by 10 +/- 2 mm Hg, whereas heart rate decreased by 30 +/- 5 beats/min (p less than 0.00001). In contrast, after the injection into the glove covering the fetal head, there were no significant changes in any of the measured parameters. This suggests that the ovine fetal oral-nasal membrane is not a significant route of absorption of amniotic fluid arginine vasopressin and that the most likely route of absorption is the vascularized fetal surface of the placenta and vascularized fetal membranes, i.e., the intramembranous pathway.

Effect of V2 antagonist on clearance of arginine vasopressin by isolated perfused rat kidneys

Isolated rat kidneys were perfused with Krebs-Henseleit-bovine serum albumin solution at a mean pressure of 99 +/- 2.6 mmHg. After control periods, arginine vasopressin (AVP) was added to the perfusate at a final calculated concentration of 25 pg/ml (2.5 x 10(-11) M). Urine and perfusate samples were collected at 15-min intervals for the following 60 min to measure kidney function and the renal clearance of immunoreactive AVP (irAVP). At 15-30 min after the addition of AVP, total renal clearance of irAVP was 1,623 +/- 190 microliters.min-1.g kidney wt-1. Glomerular filtration accounted for 35 +/- 3.0% of the total clearance, and 65 +/- 10.3% was cleared by peritubular pathways. Of the filtered irAVP, 48 +/- 4.8% was recovered in the urine. To investigate the importance of V2 receptors in the metabolism of AVP, clearance measurements were made in the presence of the V2 antagonist [d(CH2)5,D-Ile2,Ile4,Arg8]AVP (5 x 10(-9) M). Total renal clearance of irAVP was reduced by 48% to 848 +/- 79 microliters.min-1.g-1. This reduction was entirely accounted for by the complete inhibition of peritubular clearance of irAVP. In the presence of the V2 antagonist, irAVP was cleared only by filtration. The proportion of filtered AVP recovered in the urine (53 +/- 8.7%) was not significantly altered by the presence of the V2 antagonist. We conclude that a major component of the renal clearance of AVP depends on receptor-mediated uptake of AVP in the kidney cells.

Rapid intramembranous absorption into the fetal circulation of arginine vasopressin injected intraamniotically

Recently an intramembranous pathway was reported in the ovine fetus as a route for the movement of a significant volume of water from the amniotic cavity directly into the fetal blood, which perfuses the fetal membranes and fetal surface of the placenta. To test whether this pathway could be an avenue for the movement of arginine vasopressin from the amniotic cavity into the fetal circulation, we injected 1 to 25 micrograms of arginine vasopressin into the amniotic cavity of two groups of chronically catheterized fetal sheep: a control group of seven animals and a group of seven animals with surgical ligation of the fetal esophagus. We found similar and highly significant increases of arginine vasopressin concentrations in both control and surgically ligated fetuses in amniotic fluid (p less than 0.00001), fetal plasma (p less than 0.0001), and fetal urine (p less than 0.0001). Both groups had similar increases in arterial (p less than 0.0001) and venous (p less than 0.003) pressures with simultaneous decreases in urine flow (p less than 0.001) and heart rate (p less than 0.0001) after the intraamniotic injection of arginine vasopressin. We conclude that amniotic arginine vasopressin can be rapidly absorbed in its biologically active form directly into the fetal circulation through the intramembranous pathway. Furthermore, the observation that esophageal ligation did not alter this absorption suggests that the intramembranous pathway may be important in the regulation of amniotic fluid volume and composition.

Kinetics of arginine-vasopressin uptake at the blood-brain barrier

Uptake of arginine-vasopressin, VP, at the luminal side of the blood-brain barrier (BBB) was studied by means of an in situ brain perfusion technique in the guinea-pig. Kinetic experiments revealed a saturable peptide influx into the parietal cortex, caudate nucleus and hippocampus with Km between 2.1 and 2.7 microM, and Vmax ranging from 4.9 to 5.6 pmol.min-1.g-1. The non-saturable component, Kd, was not significantly different from zero. Influx of VP into the brain was not altered by the presence of the peptide fragments: VP-(1-8), pressinoic acid and [pGlu4,Cyt6]VP-(4-9) at 4.5 microM, nor yet by the aminopeptidase inhibitor, bestatin (0.5 mM) and the L-amino acid transport system substrates, L-tyrosine and L-phenylalanine at 5 mM. At a perfusate concentration of 4.5 microM, the V1-vasopressinergic receptor antagonist, d(CH2)5[Tyr(Me)2]VP, reduced VP influx; regional Ki values, assuming that the observed inhibitions were purely competitive, ranged between 4.7 and 8.5 microM. It is concluded that there is an apparent cerebrovascular permeability to circulating VP due to the presence of a carrier-mediated transport system for the peptide located at the luminal side. The mechanism for VP BBB uptake exhibits no affinity for peptide fragments and large neutral amino acids, but requires reception of the intact molecule, which may be the same initial step for both the BBB VP transporter and the V1-receptor.

Transport of desglycinamide-arginine vasopressin across the blood-brain barrier in rats as evaluated by the unit impulse response methodology

The pharmacokinetic characteristics of desglycinamide-arginine vasopressin (DGAVP) with respect to its transport across the blood-brain barrier (BBB) were studied with the use of serial CSF sampling in an individual animal and the unit impulse response methodology. Transport rate is determined as BBB clearance, the volume of plasma per unit time cleared of the peptide by BBB transport, and the extent of transport as the percentage of the administered dose transported into the central nervous system. Plasma kinetics of DGAVP were shown to be linear within the dose range studied (50-150 micrograms), plasma mean residence time (MRT) being 18 +/- 4 min (mean +/- SE; n = 9). Elimination of DGAVP from CSF after icv administration was linear, with an MRT of 10 +/- 1 min (n = 9). After iv administration of 100 micrograms DGAVP, CSF concentrations were detectable for 90 min. Transport from plasma to the central nervous system was linear. The BBB transport clearance value was 1.0 +/- 0.3 microliters/min, and 0.026 +/- 0.007% of the administered dose was transported into the central nervous system. Results demonstrate that, within the concentration range studied, DGAVP is transported across the BBB by passive diffusion, although to a very low extent.

Effects of sodium intake, furosemide, and infusion of atrial natriuretic peptide on the urinary and metabolic clearances of arginine vasopressin in normal subjects

Arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) have important influences on water and electrolyte metabolism, and studies on the interactions between these hormones may have important implications. We have investigated the effects of sodium intake, furosemide, and infusion of ANP on the urinary and metabolic (nonurinary) clearances of AVP in hydrated normal subjects. On a high sodium diet there was an increase in urine volume, sodium excretion, osmolal clearance, plasma ANP concentration, and urinary clearance and fractional excretion of AVP, with a decrease in PRA. The infusion of furosemide increased urine volume, sodium excretion, osmolal clearance, and PRA, but decreased circulating ANP levels and urinary clearance and fractional excretion of AVP. Since there was a positive correlation between circulating ANP and urinary clearance of AVP in these experiments, we infused human alpha ANP in physiological amounts and found increases in the urinary and metabolic (nonurinary) clearances of AVP. The changes in urinary clearance of AVP in all three experiments occurred even in relation to creatinine clearance. These observations demonstrate that urinary clearance of AVP does not correlate with urine volume, sodium or solute excretion, or PRA. The observations support a physiological role for ANP in modulating the renal action of AVP, probably at the level of the renal tubules, and indicate a need for caution when using plasma or urinary AVP as an indicator of AVP release from the neurohypophysis.

Rectal absorption enhancement of cefoxitin and desglycinamide arginine vasopressin by sodium tauro-24,25-dihydrofusidate in conscious rats

The effects of sodium tauro-24,25-dihydrofusidate (STDHF), an enhancer of nasal insulin absorption, on the rectal absorption of cefoxitin and desglycinamide arginine vasopressin (DGAVP) were evaluated in the rat. Cefoxitin and DGAVP proved to be poorly absorbed rectally without STDHF, but their bioavailability was considerably increased by STDHF in concentrations of 0.15 to 8% w/v. Both rectal infusion and rectal bolus delivery resulted in complete cefoxitin absorption at 4% w/v of STDHF. Delivery rate appeared to be an important factor in the effect of 4% w/v of STDHF on DGAVP bioavailability; on infusion a mean DGAVP bioavailability (+/- S.D.) of 47 +/- 12% was obtained, whereas after bolus delivery it amounted to 27 +/- 6%. For both compounds the effect of STDHF was significant at 0.5% w/v. It is concluded that STDHF is capable of actively enhancing the rectal absorption of poorly absorbed drugs, including small peptides.

Habenular nuclei specifically bind synthetic arginine vasotocin

The antidiuretic activity of an arginine vasotocin (AVT) solution (10 microU/ml) was studied in comparison with an arginine vasopressin (AVP) solution (10 microU/ml) after their incubation for 1 h at 37 degrees C with the supernatants (S) or the pellets (P) of the habenular nuclei (HN) or frontal cortex (FC) fragments homogenized in saline solution, removed from adult or newborn rats. Both SHN and SFC from adults inactivated about 5 microU/ml AVT and 10 microU/ml AVP, PHN and not PFC inactivated only about 7 microU/ml. In newborns the phenomena were in the same direction, but the specific inactivation of AVT by the PHN was of about twice greater than in adults. The results are interpreted as suggesting that, in contrast to an unspecific inactivation from S, probably of an enzymatic nature, the PHN specifically bind AVT and that this activity is greater in newborn than in adult rats.

Responses of vasopressin release in patients with cardiopulmonary bypass anesthetized with enflurane and morphine

Changes in plasma level of arginine vasopressin (AVP), arterial pressure, and urine flow were studied before, during and after cardiopulmonary bypass (CPB) in 11 patients with congenital heart disease. Anesthesia was induced with thiopental sodium (3-5 mg/kg) and was maintained with enflurane (1.0-1.5%), 50% N2O in O2 and morphine (0.5 mg/kg). Concentration of plasma AVP increased slightly from 3.8 +/- 1.5 pg/ml after induction and increased 3-fold after sternotomy. Plasma AVP level increased to 132 +/- 26 pg/ml and 218 +/- 54 pg/ml after 5 and 60 min on CPB, respectively. When the circulation returned to normal, plasma AVP level decreased gradually but was still significantly higher at 24 hr (13.4 +/- 2.5 pg/ml). Marked osmolar diuresis was induced with mannitol in the priming solution used during the CPB: increases in urine flow, Na excretion and osmolar clearance. Possible mechanisms of marked increase in AVP release and differences of AVP responses during CPB reported by other investigators are discussed.

Transport of vasopressin fragments across the blood-brain barrier: in vitro studies using monolayer cultures of bovine brain endothelial cells

A well established in vitro blood-brain barrier (BBB) model, consisting of bovine cerebrovascular endothelial monolayers from primary cultures, was used to study the transport profile of vasopressin and its fragments across the BBB and to assess the metabolic properties of the BBB for the behaviorally active vasopressin fragment arginine vasopressin (AVP)1-8 (desglycinamide-AVP). All vasopressin fragments crossed the in vitro BBB to a measurable extent. Endothelial permeabilities were (in 10(-3) cm/min): AVP1-6, 3.0 +/- 0.2; AVP1-7, 4.6 +/- 0.4; AVP1-8, 2.0 +/- 0.5 and AVP1-9, 2.4 +/- 0.4. A significant effect of molecular size on endothelial permeability was seen. Transport rate of AVP1-8, expressed as BBB-clearance, was not affected by luminal concentration change and proved to be symmetrical. These findings suggest that, in the concentration range studied, vasopressin-like peptides can cross the BBB mainly by paracellular transport and that no relevant carrier mediation is involved. AVP1-8 was metabolized slowly (half-life, 6.5 hr) by a 60 cm2 confluent monolayer to AVP1-7, which was not broken down further, suggesting that carboxypeptidases are responsible for AVP1-8 metabolism in the BBB.

Mechanisms underlying the cardiovascular responses to intrathecal vasopressin administration in rats

Vasopressinergic pathways within the spinal cord have been implicated in the control of cardiovascular function. This study was undertaken to determine the mechanisms whereby intrathecally administered arginine vasopressin (AVP) increases blood pressure and heart rate in anesthetized rats. The cardiovascular responses to intrathecal AVP administration were significantly attenuated after intravenous administration of the ganglionic blocking agent, chlorisondamine chloride, as were the pressor responses following alpha-adrenergic receptor blockade with phentolamine and the heart rate responses following beta-receptor blockade with propranolol. Intrathecal administration of the V1 vasopressin receptor antagonist d(CH2)5Tyr(Me)AVP completely blocked the cardiovascular responses to intrathecal AVP injections, but did not significantly alter the responses to intrathecal substance P injections. There was no evidence for the involvement of the renin-angiotensin system in the pressor responses to intrathecal AVP, as (i) an angiotensin II receptor blocking agent, [Sar1, Val5, Ala8]angiotensin, failed to significantly alter the responses to intrathecal AVP, and (ii) plasma renin levels did not change following administration of the peptide. Intrathecal injections of [3H]AVP suggest that only small amounts of the peptide may cross into the plasma during the time in which the cardiovascular variables are changing. These data provide evidence that intrathecally administered AVP discretely activates the sympathetic outflow to the heart and vasculature, and confirm the neurally mediated nature of the response.

Changes in the metabolic clearance of vasopressin and in plasma vasopressinase throughout human pregnancy

Metabolic clearance rates (MCR) of arginine vasopressin (AVP) were measured serially in five women starting before conception, during gestational weeks 7-8 (early), 22-24 (middle), and 36-38 (late pregnancy), and again 10-12 wk postpartum. Hormonal disposal rates were determined after water loading to suppress endogenous AVP release using a constant infusion method designed to achieve three different steady-state concentrations of plasma AVP (PAVP) on each test occasion. Dose schedules were altered in mid- and late pregnancy to obtain comparable AVP levels at each stage of the protocol. Prehydration decreased plasma osmolality sufficiently to suppress AVP release, as circulating AVP-neurophysin measured serially in three of the women was undetectable. The MCR of AVP was similar before conception (0.75 +/- 0.31, 0.79 +/- 0.34, and 0.76 +/- 0.28 liters/min at PAVP of 2.6 +/- 1.9, 4.7 +/- 2.4, and 8.3 +/- 3.9 pg/ml), in early pregnancy (0.89 +/- 0.34, 0.97 +/- 0.04, and 0.95 +/- 0.40 liters/min at PAVP of 2.2 +/- 2.1, 3.9 +/- 3.2, and 7.9 +/- 3.4 pg/ml), and postpartum (0.70 +/- 0.21, 0.69 +/- 0.24, and 0.75 +/- 0.20 liters/min at PAVP 3.5 +/- 1.8, 5.1 +/- 3.7, and 9.1 +/- 4.2 pg/ml). Values at mid-pregnancy (2.8 +/- 1.3, 3.0 +/- 1.2, and 2.7 +/- 1.2 liters/min at PAVP 2.3 +/- 2.2, 4.0 +/- 3.6, and 7.7 +/- 3.9 pg/ml) and late pregnancy (3.2 +/- 1.4, 3.3 +/- 1.4, and 2.9 +/- 1.2 liters/min at PAVP 1.9 +/- 2.0, 3.8 +/- 2.6, and 7.4 +/- 4.1 pg/ml) increased 3-4-fold (all P less than 0.01). Plasma vasopressinase, undetectable at 7-8 gestational wk, increased markedly by mid- and slightly more by late gestation. Finally, relationships between PAVP and urine osmolality were similar before, during, and after pregnancy. We conclude that marked increments in the MCR of AVP occur between gestational weeks 7 and 8 and mid-pregnancy, which parallel the period of greatest rise in both trophoblastic mass and plasma vasopressinase. There was no evidence of a renal resistance to AVP during gestation.

Clearance and urinary excretion of vasopressin in conscious dogs

The purpose of this study was to determine the relationship between plasma arginine vasopressin (PAVP) levels and the urinary clearance rate, the nonurinary plasma clearance rate, and the urinary excretion rate of AVP. Female conscious dogs were given an intravenous infusion of p-aminohippuric acid and inulin, and, after a 90-min control period, the infusion was either continued or AVP was added to the infusate to produce doses of 0, 40, 100, and 200 microU.kg-1.min-1 for the last 90 min of the experiment. The resulting PAVP levels were 1.2, 8.2, 11.4, and 21.6 microU/ml, respectively. The urinary clearance rate of AVP nearly doubled between the infusion rates of 0 and 100 microU.kg-1.min-1. Likewise, the nonurinary plasma clearance rate of AVP also nearly doubled between the infusion rates of 40 and 100 microU.kg-1.min-1. However, at the rate of infusion of 200 microU.kg-1.min-1, both the urinary and nonurinary clearance rates were unchanged compared with the 100-microU.kg-1.min-1 rate. The largest incremental rise in PAVP was observed between the doses of 100 and 200 microU.kg-1.min-1, when the clearance rates were apparently plateaued. The urinary excretion rate of AVP was linearly correlated with PAVP (R = 0.91) under the conditions of this study. The results suggest that the measurement of the urinary excretion rate of AVP is a reliable method of assessing PAVP and that the clearance of AVP increases when PAVP is elevated.

Chlorpropamide alters AVP-receptor binding of rat renal tubular membranes

The effects of chlorpropamide on AVP-receptor binding in rat renal tubular basolateral membranes were investigated utilizing [3H][Arg8]vasopressin (AVP). Our data indicate that chlorpropamide alters AVP-receptor binding in a competitive manner.

Radioimmunoassay of desglycinamide-arginine vasopressin and its application in a pharmacokinetic study in the rat

The purpose of this investigation was to develop a sensitive and selective radioimmunoassay for Desglycinamide-Arginine Vasopressin (DGAVP). DGAVP was extracted from rat plasma after protein precipitation, using Sep-Pak C18 cartridges and 50 mM glycine buffer/methanol (10:90) solution. Extraction recovery was 73 +/- 14% (mean +/- S.D.; n = 11) and good linearity was achieved in the concentration range of 0.25-128 pg/tube. Instantaneous tracer addition resulted in a detection limit of 250 fg/tube, whereas 24 hours preincubation and delayed tracer addition resulted in a detection limit of 100 fg/tube. Intra-assay variation ranged between 7.4% and 10.0% depending on the peptide concentration and inter-assay variation was 13.2%. Using this procedure, plasma pharmacokinetics of DGAVP in the rat were determined after IV administration. DGAVP plasma concentration showed a rapid distribution phase (t1/2 = 1.0 +/- 0.2 min) and a somewhat slower elimination phase (t1/2 = 7.2 +/- 2.1 min). High clearance values (CLss = 97 +/- 30 ml.min-1) suggest rapid metabolism by amino- and carboxy-peptidases.

Nasal delivery of a vasopressin antagonist in dogs

The dosage form (drop or spray) and site of administration (dorsal or ventral surface of the nostril) profoundly affect the distribution and clearance of a gamma-emitting 99mTc-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) solution in dogs. The slowest nasal clearance was observed for dorsally administered drops. Administration of drops to the ventral surface or sprays to either dorsal or ventral surface results in rapid clearance and little deposition in the turbinates. The octapeptide vasopressin antagonist, SKF 101926, was administered intravenously (0.3, 1.0, 3.0, and 10 micrograms/kg) and then on separate occasions intranasally (10, 25, and 50 micrograms/kg as a drop to the ventral surface) to four conscious, trained, female, water-loaded, vasopressin-infused dogs. SKF 101926 reversed the antidiuretic response to vasopressin after administration by either the intravenous or intranasal route in a dose-dependent fashion. Peak dilution of urine occurred within 50- to 60-min postdosing by both routes. Estimated doses to reduce vasopressin antidiuresis by 50% were 1.4 micrograms/kg intravenously and 23 micrograms/kg intranasally. After recovery to at least 70% of antidiuretic base line, and then administration of a second dose of SKF 101926 (3 micrograms/kg), subsequent dilution of urine osmolality was inversely related to the magnitude of the previously administered dose. It is concluded that the estimated relative effectiveness of intranasally administered SKF 101926 is 3-21%, compared with intravenous administration. Acute tachyphylaxis to repeated dosing was observed. The mechanism of the apparent tachyphylaxic response was not elucidated. No tachyphylaxis to less frequent (weekly) dosing was observed.

Calcium-mobilizing hormones and phorbol myristate acetate mediate heterologous desensitization of the hormone-sensitive hepatic Na+/K+ pump

The Na+/K+ pump in rat hepatocytes is stimulated in response to Ca2+-mobilizing hormones such as [arginine]vasopressin (AVP), angiotensin II and adrenaline, as well as tumour promoters such as 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). The ability of these agents to increase cellular contents of diacylglycerol and activate protein kinase C may be necessary to observe this response. In the present work, ouabain-sensitive 86Rb+ uptake was studied in isolated rat hepatocytes to help to explain why stimulation of the Na+/K+ pump by Ca2+-mobilizing hormones and tumour promoters is not temporally sustained relative to other hormone responses. A transient stimulation (3-4 min) of the Na+/K+ pump was observed in hepatocytes exposed to high (10 nM), but not low (0.1 nM), concentrations of AVP. Experiments with the Ca2+ chelator EGTA and the Na+ ionophore monensin indicate that the rapid secondary decrease in Na+/K+-pump activity which occurs after AVP stimulation is not due to changes in cytosolic Ca2+ and Na+ concentrations. When added after the stimulation and rapid decrease in Na+/K+-pump activity induced in hepatocytes by a high concentration of AVP, a second challenge with AVP or PMA failed to stimulate the pump. Similarly, previous exposure of hepatocytes to angiotensin, adrenaline or PMA attenuated the subsequent Na+/K+-pump responses to AVP and PMA. In contrast, previous exposure to AVP had no significant effect on subsequent stimulation of the Na+/K+-pump by monensin, glucagon, forskolin or 8-p-chlorophenylthio cyclic AMP. In addition, exposure to monensin had no effect on subsequent responses to AVP and PMA. These data indicate that high concentrations of Ca2+-mobilizing hormones and PMA result in heterologous desensitization of the hepatic Na+/K+ pump to subsequent stimulation by Ca2+-mobilizing hormones and PMA, but not by cyclic-AMP-dependent agonists or monensin.