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Changes in the neurohypophysial content of arginine vasopressin (AVP) and neurosecretory material in different states of hydration have been reported by many authors (see Jones & Pickering, 1969; Vilhardt, 1970). The present paper reports the effect of hydration on pituitary and plasma levels of AVP and neurophysin in the rat, and on the release of these two peptides in response to haemorrhage.
Four groups of male Wistar rats were studied over a period of 1 week. One group was maintained on an unrestricted water intake (control), another on a restricted water intake, the third on 1·8% sodium chloride solution and a fourth group was hydrated (water intake equivalent to 25% body weight/24 h). The rats used weighed 200 g and at least six animals were included in each group. After 1 week the animals were anaesthetized with sodium pentobarbitone (3 mg/100 g) and 0·8 ml blood removed for the determination
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SUMMARY
Pregnancy was sustained to term (>63 days) in 15 out of a total of 46 guinea-pigs, hypophysectomized within 4 days after mating. The majority (22/29) of complete or partial abortions occurred between 20 and 35 days post coitum. Analysis of plasma samples showed that the pregnant hypophysectomized animals with live foetuses had high progesterone and progesterone-binding protein concentrations, equivalent to those found in intact pregnant guinea-pigs. Animals that received daily injections of cortisone acetate from day 55 (7/15) gave birth to live young at the normal time (67–68 days). Plasma samples from one animal taken during parturition showed no measurable oxytocin in maternal plasma, but oxytocin was present in foetal plasma at the moment of birth.
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SUMMARY
Circulating levels of neurophysin, oxytocin and vasopressin were determined in rats under various physiological conditions using bovine neurophysin as the reference standard. Under resting conditions the mean plasma concentration of immunoreactive neurophysin was 6·2 ± 2·4 ng/ml while oxytocin and vasopressin were undetectable.
Neurophysin and vasopressin were released in response to haemorrhage in Wistar and heterozygous Brattleboro rats; in the homozygous strain haemorrhage resulted in a release of oxytocin and neurophysin. Infusion of 0·1 M-calcium chloride into Wistar rats caused a rise in plasma neurophysin, oxytocin and vasopressin. The half-times for the disappearance from the plasma of arginine-vasopressin and neurophysin in the circulation were 1·6 ± 0·8 (S.D.) and 3·4 ± 0·9 min respectively.
