Karl G. Hofbauer

Acute hemodynamic effect of a vascular antagonist of vasopressin in patients with congestive heart failure

To assess the role of arginine vasopressin (AVP) in congestive heart failure (CHF), 10 patients with CHF refractory to conventional treatment were studied before and 60 minutes after intravenous administration of 5 micrograms/kg of d(CH2)5Tyr(Me)AVP, a specific antagonist of AVP at the vascular receptor level. Heart rate, systemic arterial pressure, pulmonary arterial pressure, pulmonary capillary wedge pressure, cardiac index by thermodilution and cutaneous blood flow by laser-Doppler technique were measured. In 9 patients with no significant hemodynamic and cutaneous blood flow response to the AVP antagonist, baseline values (mean +/- standard deviation) were: heart rate, 77 +/- 14 beats/min; systemic arterial pressure, 120/79 +/- 18/8 mm Hg; pulmonary arterial pressure, 42/21 +/- 12/8 mm Hg; pulmonary capillary wedge pressure, 19 +/- 7 mm Hg; cardiac index, 2.2 +/- 0.6 liters/min/m2; plasma AVP, 2.3 +/- 0.8 pg/ml; and plasma osmolality, 284 +/- 14 mosm/kg H2O. The tenth patient had the most severe CHF. His plasma AVP level was 55 pg/ml and plasma osmolality was 290 mosm/kg. He responded to the AVP antagonist with a decrease in systemic arterial pressure from 115/61 to 79/41 mm Hg, in pulmonary arterial pressure from 58/31 to 33/13 mm Hg and in pulmonary capillary wedge pressure from 28 to 15 mm Hg. Simultaneously, cardiac index increased from 1.1 to 2.2 liters/min/m2 and heart rate from 113 to 120 beats/min; cutaneous blood flow increased 5-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal Antibodies to Human Renin: Properties and Applications

A series of 11 different monoclonal antibodies generated against human kidney renin have been characterised. Their binding affinity, inhibition of renin activity, epitope distribution, crossreactivity with related enzymes and finally in vivo pharmacological effects were analysed. All antibodies were found to be specific for primate renin recognising 6 independent antigenic structures on the renin molecule. They expressed different effects on renin activity namely (1) no inhibition, (2) only partial, or (3) complete inhibition. Partially inhibiting antibodies demonstrated specific degrees of inhibition (30, 60 or 80%). One antibody, R-36-16, demonstrated an IC 50 of 1.3 X 10(-11) M/L and, when injected into marmosets, induced complete inhibition of plasma renin activity and reduction of blood pressure. Using a selected pair of antibodies a radioimmunoassay has been established providing a fast and highly reproducible determination of human and marmoset immunoreactive renin, detecting both active and inactive renin down to concentrations of 10 pg/ml (1.25 X 10(-17) moles of renin per 50 microliter sample).

The significance of vasopressin as a pressor agent

The antidiuretic hormone, arginine-vasopressin (AVP), may participate in the regulation of blood pressure (BP) through its vasoconstrictor effects. In anesthetized rats, exogenous AVP induced stronger vasoconstriction in the mesenteric than in the renal vascular bed. Conversely, mesenteric but not renal vascular resistance was reduced by a vascular antagonist of AVP, d(CH2)5 VDAVP, in rats with increased endogenous AVP after anesthesia, dehydration, or injection of glycerol. Another vascular AVP-antagonist, d(CH2)5 Tyr (Me) AVP, induced a transient fall in BP in conscious primates (marmosets) after diuretic-induced volume depletion. In conscious rats with established deoxycorticosterone acetate (DOCA)/salt hypertension, d(CH2)5 Tyr (Me) AVP decreased systolic BP after acute administration. After chronic administration of this antagonist during 6 weeks after the beginning of DOCA/salt treatment, the severity of hypertension was reduced. When another, AVP-antagonist, d(CH2)5-D-Tyr (Et) VAVP, which blocks vascular and renal tubular AVP-receptors, was administered chronically, the development of DOCA/salt hypertension was prevented at the expense of severe and persistent hypernatremia. These results demonstrate that under certain conditions the vascular effects of AVP may contribute to the maintenance of BP, AVP appears to participate in the pathogenesis of DOCA/salt hypertension through both its vasoconstrictor and its antidiuretic effects.

Endocrine control of salt and water excretion : the role of vasopressin in DOCA-salt hypertension

Arginine-vasopressin (AVP), the antidiuretic hormone, not only regulates water balance but may also exert direct and indirect effects on blood pressure by influencing systemic vascular resistance and body fluid volumes. Recently, specific competitive antagonists of AVP at its vascular and tubular receptors have been described. We used d(CH2)5 Tyr(Me) AVP, a vascular (V), antagonist, and d(CH2)5-D-Tyr(Et) VAVP, a vascular and tubular (V1V2) antagonist, for studies on the role of AVP in deoxycorticosterone acetate (DOCA)-salt hypertension. The antagonists were infused intravenously via osmotic minipumps in unilaterally nephrectomized rats for 6 weeks after the beginning of the DOCA-salt treatment. At the end of the experiment, blood pressure was 15 mm Hg lower in the rats receiving the V1 antagonist than in those in which the vehicle was infused. In the rats receiving the V1V2 antagonist, blood pressure was reduced by 38 mm Hg. However, these rats were in poor general condition and gained no body weight. Their plasma sodium concentration was markedly increased throughout the duration of the experiment. These results suggest that AVP contributes to the development of DOCA-salt hypertension not only through its vascular but also through its renal tubular effects. Thus AVP may act as an impormediator of volume changes associated with alterations in sodium intake or excretion and thereby affect blood pressure.

Neuropeptide Y Y1 receptor antisense oligodeoxynucleotides enhance food intake in energy-deprived rats

In the literature, conflicting data on the effect of NPY Y1 antisense oligodeoxynucleotides (ODNs) on food intake have been reported, describing either an increase or a decrease in feeding in antisense-treated animals. In the present studies antisense oligodeoxynucleotides targeted to the Y1 receptor (Y1 antisense ODNs) were used to re-investigate the functional importance of this receptor subtype in vivo in the regulation of feeding in rats. We used phosphothioate-terminal protected derivatives of two ODN sequences used in previous reports. In addition, as one of these sequences was not tested in vitro, we demonstrated its efficacy in LMTK-cells transfected with the Y1 receptor subtype. In vivo, repeated intracerebroventricular (i.c.v.) injections of Y1 antisense ODNs did not affect basal food intake or the increase in food intake after i.c.v. injection of neuropeptide Y (NPY, 300 pmol). Y1 antisense ODNs given intracerebroventricularly enhanced food intake in energy-deprived rats (+175% and +60% vs. control scrambled and sense sequences, respectively after 2 h of refeeding). Analysis of the structure of feeding behaviour revealed that Y1 antisense ODNs enhanced fasting-induced food intake during the first hour of refeeding by inducing increases in meal size (+143% and +155% vs. sense and scrambled ODNs) but not meal duration. These data suggest that the NPY Y1 receptor is not directly implicated in feeding in the rat when calorie intake is normal but might be specifically activated during energy deprivation.

Two-kidney, one clip renal hypertension in the marmoset.

The purpose of this study was to assess whether two-kidney, one clip (2K1C) renal hypertension can be induced in the marmoset. During the first 3-5 weeks after renal arterial clipping, blood pressure (BP) and plasma renin activity (PRA) increased in approximately one-third of the operated marmosets. However, within 10 weeks after clipping, BP and PRA had returned to control values. There was a significant positive correlation between BP and log PRA 3 and 5 weeks after the operation, but no correlation was observed at 10 weeks. In a selected group of marmosets with the highest values of BP (greater than 140 mmHg; n = 4), the converting enzyme inhibitor, enalapril (2 mg/kg s.c.) lowered BP by 58 +/- 7 (s.e.m.) mmHg when given 3 weeks after clipping. At 18 weeks the response to enalapril was only -17 +/- 6 mmHg. These results demonstrate that unilateral renal arterial clipping in marmosets results in a transient renin-dependent hypertension. Marmosets in this initial hypertensive phase could be useful for investigating the antihypertensive effects of inhibitors of human renin.

Monoclonal antibodies against human renin. Blood pressure effects in the marmoset.

The in vivo effects of two anti-human renin monoclonal antibodies with a high binding affinity for primate renin were studied in conscious, volume-depleted marmosets. These antibodies, R-3-17-7 and R-3-36-16, both have high binding activity for renin, but only R-3-36-16 inhibits the enzymatic activity of renin in vitro. In vivo, R-3-17-7 did not affect blood pressure after intravenous injection of doses up to 100 micrograms/kg, although plasma renin activity was partially reduced. In contrast, R-3-36-16 induced a reduction in blood pressure and an inhibition of plasma renin activity at a threshold dose of 3 micrograms/kg. The maximum fall in blood pressure and complete inhibition of plasma renin activity were observed after R-3-36-16, 10 micrograms/kg; these effects persisted for up to 2 hours. Pretreatment with a converting enzyme inhibitor or nephrectomy prevented the hypotensive effects of R-3-36-16. Conversely, pretreatment with R-3-36-16 prevented the hypotensive effects of a converting enzyme inhibitor. These findings indicate that the hypotensive response induced by R-3-36-16 is due entirely to blockade of the renin-angiotensin system. Thus, R-3-36-16 appears to be a specific, potent, and long-acting inhibitor of primate renin. Such monoclonal antibodies provide interesting tools for studying the effects of acute and chronic renin blockade.

Chronic blockade of vasopressin receptors in rats.

Chronic i.v. administration of a competitive antagonist of arginine-vasopressin (AVP), d(CH2)5-D-Tyr(Et)-VAVP, in Sprague-Dawley rats induced only a transient diabetes insipidus (DI)-like state. Water excretion and intake were markedly increased on the first day of administration but subsequently reverted to normal. A similar response to the antagonist was observed upon continuous i.v. infusion in Brattleboro rats, homozygous for hereditary hypothalamic DI, which had been substituted with exogenous AVP. This excludes the possibility that increased secretion of endogenous AVP had overcome the blocking effect of the competitive antagonist in Sprague-Dawley rats. However, when AVP was withdrawn from chronically AVP-treated DI rats, water intake increased to values higher than those observed after the antagonist. Subsequently, water intake also decreased but remained elevated compared to that of AVP-substituted rats receiving the antagonist. This suggests that the antagonist might have AVP-like agonistic properties that limit its efficacy and allow compensatory mechanisms to restore normal water balance despite continuous blockade of AVP receptors. The agonistic properties of d(CH2)5-D-Tyr(Et)VAVP were verified upon chronic i.v. administration in nonpretreated DI rats. Thus, the normalization of water balance in Sprague-Dawley rats chronically receiving d(CH2)s-D-Tyr(Et)VAVP is probably due to the activation of compensatory mechanisms and to the agonistic effects of d(CH2)5-D-Tyr(Et)VAVP.

Renal vascular effects of angiotensin II, arginine-vasopressin and bradykinin in rats: Interactions with prostaglandins

1. The renal vascular responses to the peptide hormones angiotensin II (ANG II), arginine-vasopressin (AVP) and bradykinin (BK) were studied in anaesthetized rats with flow-meter techniques. The contribution of prostaglandins (PG) to their renal vascular effects was assessed with the aid of the PG-synthesis inhibitor indomethacin. 2. ANG II and AVP induced a dose-dependent increase in renal vascular resistance (RVR). The renal vasoconstrictor effects of both peptides were significantly augmented in rats pretreated with indomethacin. Indomethacin alone induced an increase in RVR, but not in mesenteric vascular resistance (MVR). 3. BK in low doses (1 micrograms/kg . min) tended to decrease RVR but increased RVR in high doses (20 micrograms/kg . min). MVR was reduced after all doses. The renal vasoconstrictor effect of BK was not affected by the ANG II-antagonist saralasin but almost completely blocked by indomethacin. 4. These results suggest that in the rat, as in other animal species and in man, renal PGs attenuate the renal effects of vasoconstrictor hormones such as ANG II and AVP. Although it has no such effect in other species. BK in high doses induces renal vasoconstriction in the rat, which appears also to be mediated by PGs. This response might be peculiar to the rat, since PGs act as renal vasodilators in other species.

Mechanism of interaction between neuropeptide Y and angiotensin II in the rabbit femoral artery

Neuropeptide Y has direct vasoconstrictor actions and potentiates the effects of other vasoconstrictor agents. To find out whether both effects of neuropeptide Y are mediated via the same receptor and intracellular mechanism, the interaction between neuropeptide Y and angiotensin II was studied in rabbit femoral arteries. In this preparation, neuropeptide Y, but not its 13-36 fragment, induced constriction. Only neuropeptide Y potentiated the vasoconstrictor response to angiotensin II and the associated rise in inositol-1-phosphate. These potentiating effects of neuropeptide Y were totally prevented by removal of extracellular Ca2+, partially prevented by a Ca(2+)-channel blocker and mimicked by a Ca(2+)-channel activator. Pharmacological modulation of adenylate cyclase had no effect. These results suggest that the direct and indirect vascular effects of neuropeptide Y are mediated via Y1 receptors and depend on the influx of extracellular Ca2+. The rise in inositol-1-phosphate seems to be secondary to an increase in intracellular Ca2+, while modulation of adenylate cyclase is apparently not involved.