A new extraction of arginine vasopressin from blood: the use of octadecasilyl-silica

Role of blood osmolality in the regulation of vasopressin secretion in man: application of a new radioimmunoassay method for vasopressin

A radioimmunoassay for plasma arginine vasopressin (AVP) has been developed based on R2 antibody of Thomas and Lee, synthetic standard (Ferring) and extraction on Sep-Pak column. High recovery of AVP (approximately 79%) was achieved with a detection limit of 0.25 pg/ml. By improving the technique of measurement of plasma osmolality an intraassay coefficient of variation less than 1% was obtained. Physiological studies performed with this method demonstrated that AVP becomes undetectable after water loading 20 ml per Kg of water po; (N = 6) and increases in response to hypertonic saline infusion (0.05 ml/kg/min; N = 15) with a linear relationship between plasma osmolality and AVP in individual subjects; this relationship is maintained when the test is repeated in the same subjects. However when pooling all data together, the relationship between plasma osmolality and AVP is best expressed by an exponential relationship. This implies that after AVP release is initiated, the concentration of the hormone increases more rapidly than plasma osmolality and the release is continuous possibly due to recruitment of increasing number of neuronal units whose osmotic threshold varies from individual to individual.

Lack of thirst, osmoreceptor dysfunction, early puberty and abnormally aggressive behaviour in two boys

Two unrelated boys (C.C. 13 years; J.W. 18 years) presenting with early puberty and episodes of aggressive behaviour were found to have hypernatraemia and hypodipsia. Plasma vasopressin (AVP) levels were inappropriately low in relation to plasma osmolality, but the patients did not have diabetes insipidus since 24 h urinary volumes were less than 1 litre and the maximal urinary osmolality was 1232 in C.C. and 950 in J.W. Plasma renin activity was elevated (greater than 2000 mg AI/1/h) although aldosterone concentrations were normal. Excretion of a water load (20 ml/kg) was delayed, but plasma renin and aldosterone fell with increased naturesis. An infusion of 0.85 mol/l saline produced a rise in AVP in C.C. but not in J.W. Insulin and hypotension resulted in the release of AVP in both boys suggesting a selective defect of osmoreceptor function. Hyperprolactinaemia and an exaggerated PRL response to TRH were also noted but no intracranial lesion was demonstrable on CT scan. These boys appear to have a hypothalamic syndrome with early puberty, hyperprolactinaemia, hypodipsia and osmoreceptor dysfunction which may be associated with aggressive behaviour.

Role of cardiopulmonary mechanoreceptors in ADH release in normal humans

Although animal studies have shown that cardiopulmonary receptors regulate the release of antidiuretic hormone (ADH), human studies have produced conflicting results. Consequently, we studied 17 normal healthy men to determine the ADH response to selective unloading (decreased stretch) of cardiopulmonary low-pressure receptors by thigh cuff inflation in the supine position. Thigh cuff inflation of 30 to 40 mm Hg decreased the central blood volume and right atrial pressure (cardiopulmonary receptor load), while mean arterial pressure and pulse pressure were unchanged (arterial baroreceptor load). Thigh cuff inflation to this level did not alter plasma osmolality or cardiac output. Plasma ADH increased an average of 67% (p less than 0.01) following thigh cuff inflation compared to the preceding supine baseline. After thigh cuff deflation (n = 6), the ADH decreased toward preinflation values. We conclude that selective unloading of the cardiopulmonary receptors in humans increases plasma ADH levels.

Proliferation of arterial smooth muscle cells incubated in serum from brain-stimulated rats

Platelet deficient serum prepared from rats subjected to acute electrical stimulation of the lateral hypothalamus demonstrated mitogenic activity when added to incubating media supporting growth of homologous arterial smooth muscle cells in vitro. This activity did not appear to be related to the presence of platelet-derived growth factor, hyperlipidemic lipoproteins or increased amounts of insulin. Plasma arginine vasopressin concentration was elevated in these animals, but further investigation is required to determine if this elevation is causally related. Since hypothalamic stimulation is also associated with severe endothelial injury in vivo, the mitogenic activity of the blood of such animals could induce proliferation of SMC which have migrated into the arterial intima. Such features have been observed in chronically stimulated animals and may be of relevance for the role of neural factors in atherogenesis.

Vasopressin response to hyperosmotic stimulus: blood pressure effect in normal subjects and patients with impaired sympathetic system

We have investigated the interaction of plasma vasopressin and plasma catecholamines in quadriplegic patients (with severed sympathetic tracts) and compared them to others with intact sympathetic system following I.V. administration of a hyperosmolar radiocontrast agent during a routine diagnostic pyelography. Baseline systolic and diastolic pressure as well as plasma norepinephrine were significantly lower in the quadriplegic subjects. At 5 minutes after administration of the hyperosmolar solution, systolic and diastolic pressure as well as plasma vasopressin rose in the quadriplegic subjects but not in normal subjects despite a significant and equal rise in serum osmolality occurring in both groups. These results demonstrate that an interaction between the two systems exists in humans: an intact sympathetic nervous system attenuates the vasopressin response to hyperosmolar stimuli and in its absence vasopressin may function as a pressor agent.

Acute asthma and antidiuretic hormone secretion

Plasma antidiuretic hormone concentrations were measured in a group of children with acute asthma and in a control group. Very high levels of antidiuretic hormone were found in the asthmatic group. There were no changes in other biochemical indices. If overproduction of antidiuretic hormone is sustained then fluid administration to children with severe acute asthma is potentially dangerous.

Replacement therapy with arginine vasopressin in homozygous Brattleboro rats

We studied the replacement therapy of different doses of AVP in DI rats. It is surprising that relatively high levels of plasma AVP were needed to achieve significant antidiuretic effects. Measured plasma AVP concentrations are less than those predicted from the release rates of AVP by the minipumps. This difference may be due to the subcutaneous mode of release of AVP. The study also provides evidence that urinary excretion of AVP is a good indicator of the plasma AVP level.

Hemodynamic and hormonal responses to 8-arginine-vasopressin in healthy man: effects of indomethacin

Previous investigations suggest that in a normotensive organism the vasopressor effect of 8-arginine-vasopressin (AVP) is very effectively buffered by cardiovascular reflex mechanisms. Exogenous AVP administration shows only small, transient increases in blood pressure in spite of continued AVP-infusion and high plasma AVP concentrations. The present study aims to clarify the mechanism of the observed transient blood pressure elevations which are often referred to as "tachyphylaxis". Our results in healthy subjects show a two phase response to exogenous AVP: an initial phase which is characterized by cardiac reflex mechanisms and a second phase during which a normalisation of the elevated total peripheral resistance occurs. Inhibition of prostaglandin synthesis with indomethacin almost completely attenuates this vascular counterregulation to exogenous AVP, thus providing evidence that a prostaglandin mediated vasodilation in response to AVP may be the underlying mechanism for "vasopressin tachyphylaxis". The role of the renin-angiotensin-system and the importance of different regional hemodynamic effects of AVP are discussed.

Interaction of the sympathetic nervous system with vasopressin and renin in the maintenance of blood pressure

To evaluate the partial contributions and interaction of three vasopressor systems in blood pressure maintenance, nephrectomized rats and rats with intact kidneys were submitted sequentially to catecholamine depletion, elimination of vasopressin's vasoconstrictor action, and (for those with kidneys in situ) angiotensin blockade. Catecholamine depletion decreased blood pressure and stimulated vasopressin levels in all rats, but significantly more so in the anephric ones. Subsequent injection of an antagonist to the vasopressor effect of vasopressin produced a lasting fall of blood pressure in anephric rats, but only transient fall in those with intact kidneys. Infusion of teprotide--an angiotensin converting enzyme inhibitor--in the latter animals also produced transient blood pressure fall, but if this were followed by injection of the vasopressin antagonist, the pressure remained low for several hours. Blood pressure levels were closely correlated with those of plasma catecholamines throughout these maneuvers. Catecholamine levels were inversely correlated with those of plasma vasopressin, which were far greater in anephric rats through both stimulation and accumulation. Plasma renin activity was increasingly stimulated by falling blood pressure after each maneuver in rats with intact kidneys. Thus, it appears that in the resting state the sympathetic nervous system is more involved in the maintenance of blood pressure, whereas vasopressin and renin are important backup mechanisms.

Vasopressin and renin response to dehydration in aged rats

Abnormalities in neurohypophyseal function have been postulated to contribute to the alterations in fluid and electrolyte balance observed during aging. In this study, parameters of fluid and electrolyte balance were evaluated during chronic water deprivation in old (30 months) and young (3 months) Fischer 344 rats. The increase in serum vasopressin (VP) and renin concentrations observed in the 3 month animals following chronic water deprivation were absent in the aged rats (p less than 0.05 and p less than 0.02, respectively). This occurred in spite of apparently comparable alterations in fluid volume and osmolality (assessed by changes in body weight, hematocrit and plasma osmolality). Relative to body weight, VP content of the neural lobe was significantly reduced and was more severely depleted by dehydration in aged rats than in young rats. Thus, inadequate neurohypophyseal hormone stores may contribute to the inability of the aged animals to attain elevated serum VP concentrations during chronic stimulation. Several parameters of renal function were examined in the aged rats. Although none of the old rats were in renal failure, they all showed some indication of reduced renal function. In spite of renal abnormalities including reduced concentrating capabilities, the old rats did demonstrate a significant antidiuretic response to dehydration. However, with prolonged fluid deprivation, they were unable to attain serum VP or renin concentrations comparable to that achieved by the young rats.

Effect of intracerebroventricular captopril on vasopressin and blood pressure in spontaneously hypertensive rats

In conscious, unrestrained spontaneously hypertensive rats (SHR), mean arterial blood pressure (MAP) increased from a pretreatment value of 150 +/- 4 to 179 +/- 7mm Hg within 10 min (p less than 0.01) following an intracerebroventricular (i.c.v.) injection of captopril (2 mg/kg body weight), and the plasma vasopressin concentration was increased eightfold (p less than 0.01). MAP than fell to 131 +/- 5 mm Hg at 120 minutes (p less than 0.01), and plasma vasopressin concentration returned to pretreatment levels. The initial increase in MAP was due in large part to increased plasma vasopressin levels since this increase was reduced 50% by pre-treatment with a specific antagonist of the pressor action of vasopressin. The reduction in MAP at 120 minutes in captopril-treated rats may been nonspecific, since a similar effect was observed in SHR given an i.c.v. injection of a control solution. In (Wistar-Kyoto) WKY rats, i.c.v. captopril was without a statistically significant effect on MAP, but the plasma vasopressin concentration increased three-fold (p less than 0.01). These findings may reflect an increased sensitivity of the control system for vasopressin release in the SHR.