Oxytocin deficiency at delivery with epidural analgesia.

The effect of epidural analgesia on oxytocin release during the second stage of normal labour was studied by comparing 10 primigravidae who had epidurals with 10 control subjects who did not have epidurals. A significant increment in oxytocin between paired peripheral blood samples taken at the onset of full cervical dilatation and crowning of the fetal head was found in the control subjects but not in those with epidurals. Forceps delivery was required more often in the group with epidural analgesia and was associated with lower oxytocin levels at crowning. Since distension of the lower birth canal and stimulation of pelvic autonomic nerves leads to oxytocin release, and the need for forceps associated with epidurals can be reduced by oxytocin, these differences are attributed to the lumbar epidural block.

The vasotocin-like biological activity present in the bovine pineal is due to a compound different from vasotocin.

The vasotocin-like biological activity detected in an extract (E5 fraction) of bovine pineal gland was found not to be due to the presence of vasotocin, vasopressin or oxytocin. The data obtained by means of bio- and radioimmunoassays suggest that the peptide responsible for this biological activity, however, possess the same Pro-Arg-Gly(NH2) tripeptidic carboxy-terminal end as vasotocin.

Studies on the mechanism of polyuria induced by cortisol excess in the dog.

Water balance studies were performed in 7 experimental dogs before and during a period of cortisol-induced polyuria and in one dog with spontaneous hyperadrenocorticism before and after removal of an adrenocortical carcinoma. Measurements of urine and plasma osmolality and plasma arginine vasopressin concentration were made at regular intervals during the water deprivation studies. The results indicate that cortisol does not block the release of vasopressin but interferes with its action in the kidney.

Pituitary content of oxytocin, vasopressin and alpha-melanocyte-stimulating hormone in the fetus of the rat during labour.

The pituitary contents of oxytocin, vasopressin and alpha-MSH were measured in fetal and newborn rats to assess possible changes in their release during the process of labour. In the 24 h period during which delivery is likely to occur in the Wistar rat, both the oxytocin and vasopressin content of the fetal pituitary gland increased, whereas alpha-MSH content remained the same. During and/or just before labour, the oxytocin content was found to decrease by 30%, indicating an enhanced fetal release of the hormone at this stage. It was concluded that the expulsion of each fetus did not provide an extra stimulus for release of oxytocin by the fetus. In addition, if the fetus remained in the uterus after decapitation of the mother, the oxytocin content of the fetal pituitary gland decreased a further 30%. Neither vasopressin nor alpha-MSH content was altered by the process of labour or by the fetus remaining in the uterus after decapitation of the mother. The levels of vasopressin and alpha-MSH were, however, 20 times higher than the oxytocin content in the fetus and the newborn, which might have obscured the demonstration of a relatively small change in levels of these two hormones.

Effect of low-frequency stimulation of the pituitary stalk on neurohypophysial hormone release in vivo.

Because of the usually low spontaneous activity of oxytocin producing cells, the effect of low frequency (6 Hz) electrical stimulation of the pituitary stalk in vivo upon plasma oxytocin concentration, uterine contractions and intramammary pressure was studied. 30 min of stimulation increased plasma oxytocin concentration. The same type of stimulation elicited both uterine contractions in early post partum rats and milk ejection in the lactating rat, but the latter phenomenon was not considered to mimic physiological events as contrasted with the former. It was concluded that in contrast to previous data, below 10 Hz stimulation of the pituitary stalk in vivo is also effective in producing hormone release and, furthermore, that it may have physiological consequences.

Neurophysins, vasopressin and oxytocin in the bovine pineal gland.

Vasopressin, oxytocin, neurophysin I and neurophysin II have been detected and quantitatively determined in the bovine pineal gland. The neurohormones and the neurophysins are present in all parts of the gland. The oxytocin concentration, however, is higher in the anterior part than in the posterior one. The ratio of oxytocin to vasopressin appears to be similar to that of neurophysin I to neurophysin II. This similarity suggests that the neurophysins present in the pineal are the carrier proteins of the neurohormones vasopressin and oxytocin, rather than or arginine vasotocin.

Studies on the presence of vasopressin, oxytocin and vasotocin in the pineal gland, subcommissural organ and fetal pituitary gland: failure to demonstrate vasotocin in mammals.

The demonstration of vasotocin in the mammalian pineal gland, subcommissural organ and fetal pituitary gland by bioassay has led to hypotheses regarding the function of this hormone in various reproductive processes. Preliminary examinations of the pineal gland and subcommissural organ with a specific radioimmunoassay failed to show vasotocin immunoreactivity. The presence of vasotocin, vasopressin and oxytocin in the pineal gland, subcommissural organ and fetal neurohypophysis was therefore investigated, using three specific radioimmunoassays. Frog and chicken pituitary glands were used to validate the vasotocin radioimmunoassay. Direct measurements in diluted homogenates of pituitary glands from frogs, chickens, mid-term fetal sheep and near-term fetal seals revealed the presence of vasotocin only in the frog and chicken pituitary glands, while vasopressin and oxytocin were found in the two fetal pituitary homogenates. Vasopressin and ocytocin were measured in homogenates of rat and bovine pineal glands and in preparations of the subcommissural organ of rats and rabbits after extraction with Vycor glass powder, but no specific vasotocin immunoreactivity was observed. These results indicate a discrepancy between the reported biological activity of vasotocin in the pineal gland, subcommissural organ and fetal pituitary gland and the immunoreactivity of this material, which can at present only be explained by the presence of a peptide which is structurally closely related to, but not identical with, vasotocin.

Studies on the mechanism of polyuria induced by cortisol excess in the dog.

Summary Water balance studies were performed in 7 experimental dogs before and during a period of cortisol-induced polyuria and in one dog with spontaneous hyperadrenocorticism before and after removal of an adrenocortical carcinoma. Measurements of urine and plasma osmolality and plasma arginine vasopressin concentration were made at regular intervals during the water deprivation studies. The results indicate that cortisol does not block the release of vasopressin but interferes with its action in the kidney.

Vasopressin in cerebrospinal fluid and plasma of man, dog, and rat.

Arginine-8-vasopressin (AVP) levels were measured by a sensitive and specific radioimmunoassay (RIA) in plasma and cerebrospinal fluid (CSF) of three species man, dog, and rat (Wistar and the Brattleboro strain). Basal plasma values were 1.7 pg/ml in Wistar rat, and 2.4 pg/ml in dog. Pentobarbitone, used as anesthetic during collection of CSF from dog and rat, caused a significant rise of plasma AVP values in Wistar rats, but not in dogs. After withdrawal of CSF, the plasma AVP levels of Wistar rats were increased to 29.5 +/- 9.5 pg/ml, whereas the CSF levels from the same animals were 11.5 +/- 3.9 pg/ml. The response to the various stimuli was similar in Brattleboro rats, heterozygous for hereditary hypothalamic diabetes insipidus, and in Wistar rats. In Brattleboro rats, homozygous for hereditary hypothalamic diabetes insipidus, AVP was neither detectable in plasma nor in CSF. In dog and man, AVP levels in CSF samples were higher than in simultaneously obtained plasma samples. The possibility that AVP present in CSF, might be released directly from the synthetizing hypothalamic nuclei into the ventricular system is discussed.

Intra- and extrahypothalamic vasopressin and oxytocin pathways in the rat.

Perfusion of rat brain followed by immersion fixation with 2.5% glutaraldehyde-1% paraformaldehyde, purification of the first antisera and application of the unlabelled antibody enzyme method were used to specifically identify vasopressin and oxytocin containing cells and fibres. The conventional sites of production of these hormones were confirmed as follows: supraoptic and paraventricular nuclei, suprachiasmatic nucleus (only vasopressin), and other cells and cell groups of the hypothalamus. Fibres from the suprachiasmatic nucleus spread out in various direction, and probably project to the nucleus praeopticus periventricularis, organum vasculosum laminae terminalis and in the direction of the supraoptic nucleus. Oxytocin and vasopressin containing pathways could be traced from the paraventricular nucleus to the lateral ventricle, the stria terminalis and the stria medullaris. Some of the oxytocin and vasopressin containing tracts appear to continue onto ther septum. The possible importance of these morphological findings for the behavioural effects of vasopressin and oxytocin is discussed.

The distribution of vasopressin and oxytocin in the rat brain.

Since vasopressin and oxytocin might be involved in processes of storage and retrieval of information in rats, the distribution of these hormones within the central nervous system was measured employing sensitive and specific radioimmunoassays in combination with an extraction method using Vycor glass powder. Vasopressin was detected in hypothalamus, amygdala, septum, hippocampus, nucleus parafascicularis and medulla oblongata of Wistar and Brattleboro rats, heterozygous for diabetes insipidus. It was not detectable in samples of Brattleboro rats, homozygous for diabetes insipidus. Oxytocin was found in hypothalamus, septum and nucleus parafascicularis of Wistar rats in lower amounts than vasopressin while it was present in higher amounts in the medulla oblongata. The extensive distribution of these hormones in the rat brain suggests a possible role in a variety of central nervous system processes rather than solely in the expression of acquired behavior.

Histamine as an extremely potent releaser of vasopressin in the rat.

Intraperitoneal and intraventricualr injection of histamine induces a very fast and high elevation of vasopressin in rat plasma as determined by radioimmunoassay. The effects are dose and time related. The intraventricular injection is more effective with regard to time and dose than the intraperitoneal injection.