vasopressin (AVP; Yokoi et al . 1996 ). Central administration of AM activated oxytocin (OXT)-secreting neurones in the supraoptic (SON) and the paraventricular nuclei (PVN; Serino et al . 1999 , Ueta et al . 2000 ), and markedly increased plasma OXT
Hiroki Otsubo, Susumu Hyodo, Hirofumi Hashimoto, Makoto Kawasaki, Hitoshi Suzuki, Takeshi Saito, Toyoaki Ohbuchi, Toru Yokoyama, Hiroaki Fujihara, Tetsuro Matsumoto, Yoshio Takei, and Yoichi Ueta
M. R. Luck
The physiological role of ovarian oxytocin has been much debated since its (re)discovery at the beginning of the decade (Wathes, 1984). As a neuropeptide secreted in abundance from a non-neural tissue, ovarian oxytocin has been a good example of the 'ectopic' endocrinology discussed by Henderson (1987). As pointed out recently (Auletta, Jones & Flint, 1988), we are still only certain of its secretion in major quantities in domestic ruminants. For these species, much experimental evidence has accumulated at both the animal and tissue levels regarding the circumstances and mechanism of its secretion. The problem has been to define exactly what role it may play in the endocrinology of the reproductive cycle. Neither of the two main hypotheses put forward to account for the presence of oxytocin in the ovary has proved to be entirely satisfactory.
The first hypothesis proposes a paracrine role for oxytocin in the regulation of ovarian steroidogenesis.
M. P. EMBREY
The effects of desamino-oxytocin and oxytocin on the human pregnant uterus were compared by means of tocographic measurements. Desamino-oxytocin was found to be twice as potent as oxytocin.
G. K. BENSON, S. J. FOLLEY, and J. S. TINDAL
Synthetic oxytocin ('Syntocinon') and valyl oxytocin have been assayed for oxytocic and milk-ejection activities. In agreement with the previous results of others, valyl oxytocin exhibited about five times as much milk-ejection activity, per unit of oxytocic activity, as that shown by oxytocin. However, valyl oxytocin was no more active than synthetic oxytocin in retarding mammary involution in rats whose young were removed on the 4th day of lactation. This experiment, therefore, provided no evidence that the involution-retarding action of oxytocin is mediated by a direct effect on the myoepithelium of the mammary gland.
C. Meyer, M. J. Freund-Mercier, Y. Guerné, and Ph. Richard
Plasma concentrations of oxytocin and vasopressin were measured in relationship to oxytocin cell firing during suckling in urethane-anaesthetized rats.
Preliminary experiments showed that plasma concentrations of oxytocin and vasopressin, which were increased immediately after anaesthesia, reverted to basal concentrations 3 h later. Moreover, it was found that exogenous oxytocin had entirely disappeared 5 min after i.v. bolus injections of known doses of oxytocin.
Suckling did not modify the basal plasma concentration of oxytocin (14·6 ± 2·9 compared with 14·±61·5 pmol/l before suckling) except during a brief period immediately after neurosecretory bursts on oxytocin cells (37·8 ± 5·2 pmol/l; P < 0·001, n = 11). The plasma concentration of oxytocin did not differ significantly from the basal concentration 1·5 min later. The plasma concentration of vasopressin never varied.
After two neurosecretory bursts of similar amplitude (total number of spikes during the burst) recorded on the same oxytocin cell, the variations in plasma concentration of oxytocin were also similar. When, for a given cell, the amplitude of neurosecretory bursts increased or decreased, the amount of oxytocin released changed in the same way.
These data demonstrate (1) that suckling induces pulsatile release of oxytocin without vasopressin, and (2) a direct relationship between the amounts of oxytocin released and the amplitude of oxytocin cell neurosecretory bursts which argue in favour of simultaneous increases or decreases in the neurosecretory burst amplitudes on all oxytocin cells.
J. Endocr. (1987) 114, 263–270
O. ALTHABE Jr., I. C. ARNT, L. A. BRANDA, and R. CALDEYRO-BARCIA
The milk-ejecting potencies of deamino-oxytocin and oxytocin were compared by means of recordings of intramammary pressure in lactating women.
No difference in milk-ejecting potency was found between the two peptides in one woman 16 months after delivery; at this time her blood did not inactivate either of the peptides.
In other women on the third day post partum, deamino-oxytocin was found to be 1·5 times as potent as oxytocin (w/w). At this stage, the blood of the patients inactivated oxytocin (half life: 10 min.) but not deamino-oxytocin; this effect accounts only in part for the difference in potency between the two peptides.
J. R. Seckl and S. L. Lightman
The release of oxytocin into the cerebrospinal fluid (CSF) and plasma of lactating goats was studied following implantation of cisternal and lateral ventricular cannulae. Hand milking was associated with a significant increase in plasma concentrations of oxytocin, but no change in plasma concentrations of vasopressin or CSF concentrations of oxytocin. Intracerebroventricular (i.c.v.) infusion of oxytocin itself (1 pmol/min for 60 min) had no effect on basal plasma levels of oxytocin. It did, however, markedly potentiate the milking-induced increase in plasma oxytocin above the levels achieved during i.c.v. infusion of artificial CSF alone. In the goat, therefore, milking results in a selective release of oxytocin into the plasma, and this release can be potentiated by the presence of increased concentrations of oxytocin in the CSF.
J. Endocr. (1988) 116, 273–277
Meghan M White and Willis K Samson
and SON contain neurons that produce arginine vasopressin (AVP) and/or oxytocin (OT) and project not only to the posterior pituitary gland, but also elsewhere within the central nervous system (CNS). While AVP is well known to control fluid balance by
Greisa Vila, Michaela Riedl, Michael Resl, Aart Jan van der Lely, Leo J Hofland, Martin Clodi, and Anton Luger
expenditure ( van der Lely et al . 2004 ). A recent study has showed that intraventricular administration of ghrelin increases the c-fos activity of oxytocin (OXT)-secreting neurons ( Olszewski et al . 2007 ). OXT is involved in social bonding, has important
X H Zhang, S Filippi, L Vignozzi, A Morelli, R Mancina, M Luconi, S Donati, M Marini, G B Vannelli, G Forti, and M Maggi
oxytocin receptor (OTR) gene and protein in rabbit and human cavernous tissue in a similar concentration to that found in other portions of the male genital tract ( Vignozzi et al. 2004 ), classically considered the main male target of oxytocin (OT), such