The development of a radioimmunoassay for arginine-vasopressin: production of antisera and labelled hormone; separation techniques; specificity and sensitivity of the assay in aqueous solution

The fetal hypothalamus and pituitary in the initiation of labour

Evidence is presented for a number of events in the fetal hypothalamic-pituitary axis which may play a key role in the onset of labour: (1) In the sheep fetus a progressive rise in the fetal circulating concentrations of corticotropin in the days preceding delivery; (2) In the human fetus a switch from the production of corticotropin-like fragments (melanotropin and corticotropin-like intermediate lobe peptide) to authentic corticotropin in the last weeks of gestation; there is evidence also for a placental origin of corticotropin; (3) In the human fetus, a release of oxytocin and vasopressin associated with the process of spontaneous labour.

Autoimmune alterations in the neurohypophysis of rabbits immunized against vasopressin

Rabbits immunized against vasopressin developed clinical signs of diabetes insipidus persisting for up to two months after the last boost. Ultrastructural and immunocytochemical studies of the neurohypophysis demonstrated autoimmune alterations: infiltration by immune cells and extracellular deposits of immunoglobulins. No alterations were observed in the hypothalamic nuclei synthesizing vasopressin nor in hormone-target cells of the kidney. Immunization against vasopressin may provide the first example of an autoimmune disease in the hypothalamo-neurohypophysial system.

A practical proposal for arginine-vasopressin radioimmunoassay

This work proposes the use of (a) a commercially available homologous system AVP antibody-AVP (Arginine Vasopressin) standard and (b) new acquisitions for the improvement of sensitivity for AVP radioimmunoassay by separate or simultaneous use of two-phase sequential incubation and epsilon-aminocaproic acid (EACA). The antiserum used in the system described is very specific since none even cross-reacted with lysine vasopressin (LVP) and has an apparent affinity constant (K) of 0.909 +/- 0.047 X 10(12) l/mol. This is sufficiently high to detect 0.5 +/- 0.2 pg/tube, which is theoretically expected of biological AVP. The total assay time is less than 48 h.

Effect of adrenocorticotropic hormone on plasma glucocorticoids and antidiuretic hormone of cattle exposed to 20 and 33 C

Four open, dry Holstein cows in the University of Missouri Climatic Laboratory were used to study the effect of adrenocorticotropic hormone administration on glucocorticoids and antidiuretic hormone of plasma in two reversal trials at thermoneutral (20 C, 50% relative humidity) and heat (33 C, 50% relative humidity) conditions. Average glucocorticoids (saline versus adrenocorticotropic hormone) at thermoneutral were 8.3 and 41.2 ng/ml while values for heat were 6.2 and 40.4 ng/ml. The effect of heat on glucocorticoids of plasma was not significant. Injection of adrenocorticotropic hormone under thermoneutrality and heat caused a marked increase in antidiuretic hormone within 5 min which lasted to 120 min. At thermoneutral average antidiuretic hormone levels (saline versus adrenocorticotropic hormone) were .5 and 1.9 pg/ml while values for heat were 1.8 and 3.6 pg/ml. Antidiuretic hormone concentrations under heat were higher than thermoneutral in cows injected with saline and andrenocorticotropic hormone. The fast response of antidiuretic hormone of plasma to exogenous adrenocorticotropic hormone suggests that adrenocorticotropic hormone might act directly at higher levels of the central nervous system causing release of antidiuretic hormone.

The development of a radioimmunoassay for the measurement of human plasma arginine vasopressin

A radioimmunoassay for AVP capable of measuring human plasma AVP is described. Iodination was performed by the chloramine T method and purified by chromatography on Sephadex G-25. Specific activity of 125I-AVP was 1710 +/- 155 Ci/mmol. Antiserum of high affinity (Keq = 2.7 X 10(11) 1/mol) has been raised in rabbits, which shows slight cross-reactivity with LVP and negligible reactivity with oxytocin. The aqueous assay is capable of detecting 0.4 fmol of AVP/tube and it is highly reproducible. A F lorisil extraction technique is described in detail and gives recovery of 70% of synthetic AVP added to plasma over a wide physiological range. The lowest detectable concentration of plasma AVP is 0.3 pmol/l. The method has been validated by studying changes in plasma AVP concentration following overnight dehydration (plasma AVP =3.46 +/- 1.89 (SD) pmol/l), and water loading (plasma AVP = 1.54 +/- 0.59 pmol/l), P less than 0.005, in normal subjects. A highly significant positive correlation has been found between plasma AVP and plasma osmolality (r =+0.75). Plasma AVP concentration has also been determined in patients with DI and the syndrome of inappropriate ADH secretion. No effect was found on the level of plasma AVP in normally hydrated volunteers undergoing postural change but levels rose following strenuous exercise from basal concentrations of 1.57 +/- 0.59 pmol/l to 4.77 +/- 3.43 pmol/l, P less than 0.01.

The effects of halothane on plasma vasopressin during cardio-pulmonary bypass

Plasma vasopressin concentrations were estimated in twelve patients undergoing cardio-pulmonary bypass for open heart surgery. In six patients anaesthesia was maintained with 66% nitrous oxide in oxygen, whilst the remaining six additionally received halothan as a vasodilator during the bypass period. Induction of anaesthesia had little effect on plasma vasopressin concentrations, whilst marked increases were seen during surgery and bypass in both groups of patients. However, in those patients receiving halothane, significantly higher concentrations were reached, a maximun b36.1 +/- 8.9 (SEM) muu/ml being seen in contrase to 15.4 +/- 2.2 muu/ml in the group receiving nitrous oxide in oxygen alone.

Vasopressin analogue DDAVP in diabetes insipidus: clinical and laboratory studies

In seven patients with cranial diabetes insipidus an analogue of vasopressin, DDAVP, produced an antidiuresis lasting up to 20 hours after a single intranasal dose. Lysine vasopressin (LVP) in the same dose produced a less potent antidiuresis which lasted for only three to four hours. The plasma half life of DDAVP was 7.8 and 75.5 min for the fast and slow phases, compared with 2.5 and 14.5 min for LVP. Radioiodine-labelled DDAVP was not destroyed by incubation with late pregnancy plasma, which contains an enzyme that inactivates vasopressin. The slow metabolic clearance of DDAVP, its absorption through the nasal mucosa, and its lack of side effects make this the ideal drug for the treatment of vasopressin-sensitive diabetes insipidus. Patients usually require 10 to 20 mug DDAVP given intranasally twice daily for good clinical control of their diabetes insipidus.