Vasopressin and oxytocin release as influenced by thyrotropin-releasing hormone in euhydrated and dehydrated rats.

Since the thyrotropin-releasing hormone (TRH) can modulate the processes of vasopressin (AVP) and oxytocin (OT) biosynthesis and release mainly at the hypothalamo-neurohypophysial level, the present experiments were undertaken to estimate whether TRH, administered intravenously in different doses, modifies these mechanisms under conditions of osmotic stimulation, brought about by dehydration. AVP and OT contents in the hypothalamus and neurohypophysis as well as plasma levels of AVP, OT, free thyroxine (FT4) and free triiodothyronine (FT3) were studied after intravenously TRH treatment in euhydrated and dehydrated for two days male rats. Under conditions of equilibrated water metabolism TRH diminished significantly the hypothalamic and neurohypophysial AVP and OT content but was without the effect on plasma oxytocin level; however, TRH in a dose of 100 ng/100 g b.w. raised plasma AVP level. TRH, injected i.v. to dehydrated animals, resulted in a diminution of AVP content in the hypothalamus but did not affect the hypothalamic OT stores. After osmotic stimulation, neurohypophysial AVP and OT release was significantly restricted in TRH-treated rats. Under the same conditions, injections of TRH were followed by a significant decrease of plasma OT level. I.v. injected TRH enhanced somewhat FT3 concentration in blood plasma of euhydrated animals but diminished FT4 plasma level during dehydration. Data from the present study suggest that TRH displays different character of action on vasopressin and oxytocin secretion in relation to the actual state of water metabolism.     

Immunocytochemical localization of substance P in the neurohypophysis and hypothalamus of the mouse compared with the distribution of other neuropeptides

Summary Substance-P immunoreactivity has been located in semithin sections of mouse hypothalami and pituitaries and compared with the distribution of other hypothalamic peptides. In the mouse, nerve fibres and terminals reacting with antibodies against substance P (SP) were detected both in the external zone of the median eminence (ME) and in the neural lobe of the pituitary. Immunoreactive SP (ISP) axons of the ME did not react with antibodies against other peptides, i.e. arginine-vasopressin (AVP), oxytocin (OT), somatostatin and enkephalin, and were also negative with an antibody to serotonin. In the neural lobe, SP immunostaining occurred in AVP but not in OT axons. In the hypothalamus, ISP axons were widespread but conspicuously lacking in areas containing AVP neurones, i. e. in the suprachiasmatic nucleus and the clusters of AVP cells in the SO and PV nuclei. In contrast, multiple ISP endings were seen in contact with OT neurones. Immunoreactive cell bodies, only detected after colchicine treatment, belonged to two distinct classes of neurones: 1) single AVP neurones of the SO and PV nuclei; 2) specific (staining only for SP) neurones, scattered or grouped in different areas of the hypothalamus, not showing relationship with any circumscribed nucleus. These results reinforce the opinion that SP can be released as a neurohormone into the vascular portal system and can directly affect the pars distalis. The presence of immunoreactive SP in the neural lobe, which has not been reported in species other than the mouse, may have a different physiological significance.     

Centrally administered galanin modifies vasopressin and oxytocin release from the hypothalamo-neurohypophysial system of euhydrated and dehydrated rats.

Galanin (Gal) as a neuropeptide with widespread distribution in the central nervous system may be involved in the mechanisms of vasopressin (AVP) and oxytocin (OT) release from the hypothalamo-neurohypophysial system. Vasopressin and oxytocin content in the hypothalamus and neurohypophysis as well as plasma level of both neurohormones were studied after galanin treatment in euhydrated and dehydrated rats. In not dehydrated rats intracerebroventricular (i.c.v.) injections of Gal did not affect the hypothalamic and neurohypophysial OT content, however, distinctly increased plasma OT concentration. In the same animals Gal diminished the hypothalamic AVP content but was without the effect on neurohypophysial AVP storage; plasma AVP level then raised. Galanin, administered i.c.v. to rats deprived of water, distinctly inhibited AVP and OT release from the hypothalamo-neurohypophysial system. Simultaneously, plasma AVP and OT level was significantly diminished after Gal treatment in dehydrated rats. These results suggest that modulatory effect of galanin on vasopressin and oxytocin release depends on the actual state of water metabolism. Gal acts as an inhibitory neuromodulator of AVP and OT secretion under conditions of the dehydration but stimulates this process in the state of equilibrated water metabolism.     

Galanin influences vasopressin and oxytocin release from the hypothalamo-neurohypophysial system of salt loaded rats.

Galanin is a peptide present in the nervous system and peripheral tissues which exerts a broad range of physiological functions. The influence of centrally administered galanin (Gal; 100 pM i.c.v.) on arginine vasopressin (AVP) and oxytocin (OT) content in the hypothalamus and neurohypophysis as well as on their blood plasma concentration was estimated in male Wistar rats drinking ad libitum 2% solution of natrium chloride per 48 hours. In euhydrated rats and subsequently applied i.c.v. with Gal a significant fall in the hypothalamic and neurohypophysial content of OT but not AVP was observed, however, without simultaneous changes in these neurohormones blood plasma concentration. On the contrary, i.c.v. injection of Gal to salt-loaded rats caused a marked raise in AVP and OT level in the hypothalamus and neurohypophysis with subsequent diminution of both neurohormones concentration in blood plasma. These results suggest that in euhydrated rats Gal has an inhibitory influence on the biosynthesis as well as axonal transport of OT, but not AVP. On the contrary, in salt-loaded rats galanin restricts secretion of both neurohormones into the systemic circulation.     

Demonstration of a different localization of perikarya immunoreactive to oxytocin and vasopressin in the cat hypothalamus

Using immunohistochemical techniques, we demonstrated oxytocin (OT) and vasopressin (AVP) neurons in the cat hypothalamus. The OT immunoreactive neurons were found mainly in the paraventricular nucleus, supraoptic nucleus and dorsal accessory group located lateral to the fornix. In addition to these hypothalamic structures, the AVP immunoreactive neurons were observed in the suprachiasmatic nucleus, ventral accessory group located in the retrochiasmatic area and lateral accessory group, dorsal to the supraoptic nucleus caudally, and ventral to the medial part of the internal capsule rostrally. We further demonstrated a different localization of the OT and AVP immunoreactive neurons in the paraventricular and supraoptic nuclei.     

Exposure to chronic isolation modulates receptors mRNAs for oxytocin and vasopressin in the hypothalamus and heart

The goal of our study was to explore the effect of social isolation stress of varying durations on the plasma oxytocin (OT), messenger ribonucleic acid (mRNA) for oxytocin receptor (OTR), plasma arginine vasopressin (AVP) and mRNA for V_1a receptor of AVP (V_1aR) expression in the hypothalamus and heart of socially monogamous female and male prairie voles (Microtus ochrogaster). Continuous isolation for 4 weeks (chronic isolation) increased plasma OT level in females, but not in males. One hour of isolation every day for 4 weeks (repeated isolation) was followed by a significant increase in plasma AVP level. Chronic isolation, but not repeated isolation, significantly decreased OTR mRNA in the hypothalamus and heart in both sexes. Chronic isolation significantly decreased cardiac V_1aR mRNA, but no effect on hypothalamic V_1aR mRNA expression. We did not find a gender difference within repeated social isolation groups. The results of the present study reveal that although chronic social isolation can down-regulate gene expression for the OTR in both sexes, the release of the OT peptide was increased after chronic isolation only in females, possibly somewhat protecting females from the negative consequences of isolation. In both sexes repeated, but not chronic, isolation increased plasma AVP, which could be permissive for mobilization and thus adaptive in response to a repeated stressor. The differential effects of isolation on OT and AVP systems may help in understanding mechanisms through social interactions can be protective against emotional and cardiovascular disorders.     

Diabetes Increases the Expression of Hypothalamic Neuropeptides in a Spontaneous Model of Type I Diabetes, the Nonobese Diabetic (NOD) Mouse

1. Synthesis of oxytocin (OT) and arginine-vasopressin(AVP) is increased in induced models of Type I diabetes, such as thestreptozotocin model. However, these parameters have not yet been evaluated inspontaneous models, such as the nonobese diabetic mouse (NOD). Therefore, we studied in the magnocellular cells of the paraventricular nucleus (PVN)of nondiabetic and diabetic 16-week-old female NOD mice and control C57Bl/6mice, the immunocytochemistry of OT and AVP peptides and their mRNA expression, using nonisotopic in situ hybridization (ISH).2. In nondiabetic and diabetic NOD female mice, the number of OT- and AVP-immunoreactive cells were similar to those of the controls, whereas immunoreaction intensity was significantly higher for both peptides in diabetic NOD as compared with nondiabetic NOD and control C57Bl/6 mice.3. ISH analysis showed that the number of OT mRNA-containing cells was in the same range in the three groups, whereas higher number of AVP mRNA expressing cells was found in diabetic NOD mice. However, the intensity of hybridization signal was also higher for both OT and AVP mRNA in the diabetic group as compared with nondiabetic NOD and control mice.4. Blood chemistry demonstrated that haematrocrit, total plasma proteins, urea, sodium, and potassium were within normal limits in diabetic mice. Thus, NODmice were neither hypernatremic nor dehydrated.5. We suggest that upregulation of OT and AVP reflects a high-stress condition in the NOD mice. Diabetes may affect neuropeptide-producing cells of the PVN, with the increased AVP and OT playing a deleterious role on the outcome of the disease.     

Different signaling molecules responsible for IL-1beta-induced oxytocinergic and vasopressinergic neuron activation in the hypothalamic paraventricular nucleus of the rat

It has been well known that oxytocin (OT)-ergic and arginine vasopressin (AVP)-ergic neurons located in the hypothalamic paraventricular nucleus (PVN) and super optic nucleus (SON) are two kinds of neuroendocrine cells with diverse functions. It has also been demonstrated that immune stimuli can activate these neurons to secret OT and AVP. However, the intracellular signal transduction molecules responsible for the activation of these OT-ergic and AVP-ergic neurons in PVN by immune stimuli are still unclear. In this experiment, the roles of Fos, a protein product of immediate early gene c-fos, and extracellular signal-regulated protein kinase (ERK) 1/2, a signal transduction molecule of mitogen-activated protein kinase (MAPK) family, in these processes were studied in the PVN of the rat following IL-1beta stimulation. The Sprague-Dawley rats were received either 750 ng/kg IL-1beta or equal volume normal saline (NS) injection intravenously (i.v.), and perfused transcardially by 4% paraformaldehyde 3h later. Fos and phosphorylated ERK1/2 (pERK1/2)-immunoreactivity (-ir) was observed in PVN by ABC immunohistochemical staining. Meanwhile, the double staining for OT/Fos, AVP/Fos, OT/pERK1/2 and AVP/pERK1/2 were also processed. The ABC immunohistochemical staining results showed that after an i.v. injection of IL-1beta, the expressions of Fos and pERK1/2 increased evidently in the PVN. Double-staining results showed that a large number of OT-ir cells contained strong Fos-ir products in their nuclei, while only a few of OT cells were double labeled with pERK1/2. As to AVP neurons, great quantities of AVP cells were strongly double labeled with pERK1/2 while there were nearly no Fos-ir nuclei in AVP-ir cells. We conclude from these results that the intracellular IL-1beta-induced events in OT and AVP neurons in PVN are quite different. The OT neurons are mainly activated via Fos without involvement of ERK1/2 pathway, while the latter, but not Fos, involves the intracellular event in AVP neurons activated by IL-1beta.     

The interrelationships between nonapeptide and steroid hormones secretion by bovine granulosa cells in vitro.

The effects of adding oxytocin (OT) and arginine-vasopressin (AVP) on progesterone and estradiol-17 beta secretion by bovine granulosa cells in culture were studied. The influence of these steroids on OT and AVP release was also evaluated. OT (1, 10, 100 or 1000 mIU/ml) stimulates both progesterone and estradiol output. Small doses (10 pM/ml) of exogenous progesterone or estradiol stimulated a surge in OT, while the intermediate doses (100 or 1000 pM/ml) had no influence, and large doses (10,000 pM/ml) inhibited OT secretion by granulosa cells. Thus, a potential regulatory loop between OT and steroid hormone release by granulosa cells was demonstrated. Stimulation of a surge in steroids by OT, activation of OT release by small doses of steroids and inhibition of OT secretion by excess steroids may suggest the existence of a feedback mechanism regulating these hormones production. Addition of AVP (1, 10, 100 or 1000 pM/ml) inhibited progesterone and stimulated a surge in estradiol, while steroid hormones did not induce AVP release. These data suggest the regulation of ovarian steroidogenesis by AVP, feedback influences are less likely.     

Both oxytocin and vasopressin may influence alloparental behavior in male prairie voles

Neuropeptides, especially oxytocin (OT) and arginine vasopressin (AVP), have been implicated in several features of monogamy including alloparenting. The purpose of the present study was to examine the role of OT and AVP in alloparental behavior in reproductively na?ve male prairie voles. Males received intracerebroventricular (ICV) injections of artificial cerebrospinal fluid (aCSF), OT, an OT receptor antagonist (OTA), AVP, an AVP receptor antagonist (AVPA), or combinations of OTA and AVPA and were subsequently tested for parental behavior. Approximately 45 min after treatment, animals were tested for behavioral responses to stimulus pups. In a 10-min test, spontaneous alloparental behavior was high in control animals. OT and AVP did not significantly increase the number of males that showed parental behavior, although more subtle behavioral changes were observed. Combined treatment with AVPA and OTA (10 ng each) significantly reduced male parental behavior and increased attacks; following a lower dose (1 ng OTA/1 ng AVPA), males were less likely to display kyphosis and tended to be slower to approach pups than controls. Since treatment with only one antagonist did not interfere with the expression of alloparenting, these results suggest that access to either OT or AVP receptors may be sufficient for the expression of alloparenting.     

Locus Coeruleus Lesions Decrease Oxytocin and Vasopressin Release Induced by Hemorrhage

The role of the noradrenergic nucleus Locus Coeruleus (LC) on hemorrhage-induced vasopressin (AVP) and oxytocin (OT) secretion was examined. Rats with LC lesion were submitted to three 1-min hemorrhage sessions at 5-min intervals; 15% of the total blood volume was withdrawn in each session. OT and AVP were measured in plasma, paraventricular (PVN) and supraoptic (SON) nuclei and in posterior pituitary (PP). LC Lesion did not affect basal plasma AVP or OT levels, but partly blocked the increase in plasma AVP and OT induced by hemorrhage. Hemorrhage produced decreases in content of AVP and OT in the PVN and SON and increased levels in the PP. These responses were attenuated in the lesioned group, but only in the PVN and PP. Data suggest a stimulatory role of the inputs from LC to PVN neurons on hemorrhage-induced OT and AVP secretion and that, this pathway is critical in the hypo-volemic neuroendocrine reflex.Special Issue Dedicated to Miklós Palkovits.     

Variations in concentration of oxytocin and vasopressin in the paraventricular nucleus of the hypothalamus during the estrous cycle in rats

Oxytocin (OT) and arginine-8-vasopressin (AVP) were measured by radioimmunoassay in micropunched hypothalamic neurosecretory nuclei of estrous cycling female Sprague-Dawley rats. In the paraventricular nucleus (PVN): the concentration (pg/microgram protein) of OT was significantly higher in rats in diestrus than during proestrus, estrus, or metestrus, while the concentration during metestrus was significantly greater than in proestrus and estrus; the concentration of AVP was significantly lower in animals in estrus than during the other three stages; because the paraventricular OT levels dropped before proestrus, the AVP/OT ratio was significantly greater in animals in proestrus than in diestrus, metestrus, and estrus. In the supraoptic nucleus (SON) a similar trend was noted: the concentration of OT was highest during diestrus, and AVP was lowest during estrus, though neither was significantly different from other stages. Because the OT and AVP cycles in the SON were asynchronous, the ratio of AVP to OT was significantly higher in proestrus than in metestrus or diestrus and significantly greater in estrus than during diestrus. In contrast to these two areas, peptide concentrations did not vary significantly across the estrous cycle in other sites of nonapeptide synthesis, i.e. the anterior commissural nucleus (ACN) and the suprachiasmatic nuclei (SCN).     

Plasma hormone levels and central c-Fos expression in ferrets after systemic administration of cholecystokinin

Posterior pituitary hormone secretion and central neural expression of the immediate-early gene product c-Fos was examined in adult ferrets after intravenous administration of CCK octapeptide. Pharmacological doses of CCK (1, 5, 10, or 50 microg/kg) did not induce emesis, but elicited behavioral signs of nausea and dose-related increases in plasma vasopressin (AVP) levels without significant increases in plasma oxytocin (OT) levels. CCK activated neuronal c-Fos expression in several brain stem viscerosensory regions, including a dose-related activation of neurons in the dorsal vagal complex (DVC). Activated brain stem neurons included catecholaminergic and glucagon-like peptide-1-positive cells in the DVC and ventrolateral medulla. In the forebrain, activated neurons were prevalent in the paraventricular and supraoptic nuclei of the hypothalamus and also were observed in the central nucleus of the amygdala and bed nucleus of the stria terminalis. Activated hypothalamic neurons included cells that were immunoreactive for AVP, OT, and corticotropin-releasing factor. Comparable patterns of brain stem and forebrain c-Fos activation were observed in ferrets after intraperitoneal injection of lithium chloride (LiCl; 86 mg/kg), a classic emetic agent. However, LiCl activated more neurons in the area postrema and fewer neurons in the nucleus of the solitary tract compared with CCK. Together with results from previous studies in rodents, our findings support the view that nauseogenic treatments activate similar central neural circuits in emetic and nonemetic species, despite differences in treatment-induced emesis and pituitary hormone secretion.     

Social environment regulates corticotropin releasing factor, corticosterone and vasopressin in juvenile prairie voles

Stressful social conditions, such as isolation, that occur during sensitive developmental periods may alter present and future social behavior. Changes in the neuroendocrine mechanisms closely associated with affiliative behaviors and stress reactivity are likely to underlie these changes in behavior. In the present study, we assessed the effects of post-weaning social housing conditions on the neuropeptides arginine vasopressin (AVP) and oxytocin (OT), and components of the hypothalamic-pituitary-adrenal axis (corticotropin releasing factor: [CRF], and corticosterone: [CORT]) in the prairie vole (Microtus ochrogaster), a socially monogamous bi-parental rodent. Following weaning at 21 days of age, prairie voles were maintained in one of three housing conditions: social isolation (isolate), paired with a same sex sibling (sibling) or paired with a stranger (stranger) of the same sex and age. Housing conditions were maintained for either 4 or 21 days. Central CRF, AVP and OT immunoreactivity (ir) were quantified and circulating plasma CORT, AVP and OT were assayed. Isolated voles had higher CRF-ir in the paraventricular nucleus of the hypothalamus (PVN) compared with sibling and stranger housed voles. Plasma CORT was significantly higher in isolates. AVP-ir was significantly lower in the PVN of isolate females compared to either sibling females or stranger females. However, AVP-ir was significantly higher in the supraoptic nucleus (SON) of isolates compared to siblings. There were no differences in central OT-ir or plasma OT. These results identify neuroendocrine mechanisms which respond to isolation and potentially modulate behavior.     

Functional relations of crab molt-inhibiting hormone and neurohypophysial peptides

Biological and immunological relationships between molt-inhibiting hormone (MIH) activity in eyestalk ganglia extracts of the crab, Cancer antennarius Stimpson, and peptides of the vasopressin-oxytocin family were assessed. Lysine vasopressin (LVP), arginine vasopressin (AVP), vasotocin (VT), and oxytocin (OT) mimicked MIH action by inhibiting ecdysteroid production of Y-organ segments in vitro with the relative potencies LVP greater than AVP greater than VT much much greater than OT. The inhibitory effect was reversible and specific (6 other peptides did not alter Y-organ activity). MIH and LVP increased Y-organ cyclic adenosine 3',5' monophosphate (cAMP) levels dose-dependently and with identical time course in which the rise in cAMP preceded inhibition of ecdysteroid production. The synthetic vasopressin antidiuretic agonist 1-deamino-8-D-AVP (dDAVP) inhibited Y-organ steroidogenesis dose-dependently; the vasopressin analog ([1(B-mercapto-beta, beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine[AVP) (d(CH2)5Tyr(Me)AVP), a vasopressor antagonist, had no effect on basal or MIH-suppressed steroidogenesis. AVP antiserum abolished the inhibitory action of MIH, LVP, and AVP. Competitive binding curves for MIH, LVP, AVP, VT, and OT with the AVP antiserum suggested that MIH is most closely related to LVP. MIH may be structurally related to the vasopressins and act on Y-organ cells via type V2 (cAMP-linked) receptors.     

Non-invasive measurement of small peptides in the common marmoset (Callithrix jacchus): a radiolabeled clearance study and endogenous excretion under varying social conditions

A non-invasive assay for measurement of oxytocin (OT) and vasopressin (AVP) in primates would enable researchers to study the relationship between the endocrine system and behavior without disturbing potentially endangered animals in their natural habitats. In order to test whether or not OT specifically would be measurable in the urine of a primate, 10 microCi of tritium-labeled OT were injected into the peripheral blood supply of four adult male common marmosets (Callithrix jacchus), with continuous urinary collection over 48 h. When urine was processed by HPLC separation and beta counting for radioactive clearance, the label was present in all samples in the fraction where OT elutes. Large amounts of OT were also seen in a fraction other than that containing the OT standard, indicating that OT is measurable but that it also undergoes substantial metabolic breakdown. In a second experiment, we isolated six common marmosets for 48 h and then exposed them to social contact to evaluate the effect of changing social stimuli on endogenous urinary measurement of both OT and AVP. Both were measured after HPLC separation to isolate the intact molecule and also to control for cross-reactivity with metabolites in subsequent RIA. Cortisol was also measured to objectively evaluate the stress response. A priori assumptions were that urinary OT and AVP would be lower during a period of isolation and higher during periods of social contact. These assumptions were met, leading us to conclude that peripheral OT and AVP are measurable via urinary assay and that such an assay is a valid means of evaluating social condition in this species.     

Rhythmic activities of hypothalamic magnocellular neurons: Autocontrol mechanisms

Electrophysiological recordings in lactating rats show that oxytocin (OT) and vasopressin (AVP) neurons exhibit specific patterns of activities in relation to peripheral stimuli: periodic bursting firing for OT neurons during suckling, phasic firing for AVP neurons during hyperosmolarity (systemic injection of hypertonic saline). These activities are autocontrolled by OT and AVP released somato-dentritically within the hypothalamic magnocellular nuclei. In vivo, OT enhances the amplitude and frequency of bursts, an effect accompanied with an increase in basal firing rate. However, the characteristics of firing change as facilitation proceeds: the spike patterns become very irregular with clusters of spikes spaced by long silences; the firing rate is highly variable and clearly oscillates before facilitated bursts. This unstable behaviour dramatically decreases during intense tonic activation which temporarily interrupts bursting, and could therefore be a prerequisite for bursting. In vivo, the effects of AVP depend on the initial firing pattern of AVP neurons: AVP excites weakly active neurons (increasing duration of active periods and decreasing silences), inhibits highly active neurons, and does not affect neurons with intermediate phasic activity. AVP brings the entire population of AVP neurons to discharge with a medium phasic activity characterised by periods of firing and silence lasting 20–40 s, a pattern shown to optimise the release of AVP from the neurohypophysis. Each of the peptides (OT or AVP) induces an increase in intracellular Ca²⁺ concentration, specifically in the neurons containing either OT or AVP respectively. OT evokes the release of Ca²⁺ from IP3-sensitive intracellular stores. AVP induces an influx of Ca²⁺ through voltage-dependent Ca²⁺ channels of T-, L- and N-types. We postulate that the facilitatory autocontrol of OT and AVP neurons could be mediated by Ca²⁺ known to play a key role in the control of the patterns of phasic neurons.     

Paradoxical effects of oxytocin and vasopressin on basal prolactin secretion and the estrogen-induced prolactin surge

The roles of oxytocin (OT) and vasopressin (AVP) on both basal and estrogen-induced prolactin (PRL) secretion were examined. Adult female Sprague-Dawley rats that were ovariectomized for 3 weeks and received estrogen treatment for 1 week were used. Intravenous administration of hormones and serial blood sampling were accomplished through indwelling intraatrial catheters which were implanted two days before. Plasma PRL levels were measured by radioimmunoassay. Oxytocin at a dose of 20 micrograms/rat stimulated a moderate PRL release in the morning and lower doses (5 and 10 micrograms) were without effect. Vasopressin was most effective at a dose of 5 micrograms/rat in stimulating PRL release, while consecutive injections of higher doses (10 and 20 micrograms) were less effective. In contrast, TRH, ranging from 1 to 8 micrograms/rat, induced a dose-dependent increases in PRL secretion. Using the effective dosages determined from the morning studies, repeated injections of either OT, AVP or their specific antagonists MPOMeOVT [( 1-(beta-mercapto-beta, beta-cyclopentamethylene propanoic acid), 2-(O-methyl)tyrosine, 8-ornithine]-vasotocin) and d (CH2)5Tyr(Me)AVP ([1-(beta-mercapto-beta, beta-cyclo-pentamethylene propionic acid), 2-(O-methyl)tyrosine, 8-arginine]-vasopressin), were given hourly between 1300 to 1800 h and blood samples were obtained hourly from 1100 to 1900 h. It was found that either OT or AVP significantly reduced the afternoon PRL surge, while their antagonists were not as effective. When OT or AVP were administered together with their specific antagonists, the inhibitory effects of either hormone on PRL surge were reversed. Thus it is concluded that both OT and AVP assume a non-specific stress-like effect on PRL release, in which basal secretion is stimulated and surge secretion is inhibited.     

Urinary oxytocin as a non-invasive biomarker for neurohypophyseal hormone secretion

The objective was to characterize the urinary oxytocin (OT) system with the goal of using it as a biomarker for neurohypophyseal peptide secretion. We studied urinary OT secretion in mice under three conditions: (1) in OT gene deletion mice (OT -/-) which lack the ability to produce the peptide; (2) after arterial vascular infusion of OT and (3) after physiological stimulation with consumption of 2% sodium chloride. OT was measured by radioimmunoassay (RIA) and Surface-Enhanced Laser Desorption Ionization Time of Flight Mass Spectroscopy (SELDI TOF MS). In OT -/- mice (n=25), urinary OT levels were not detectable, while in OT +/+ mice (n=23) levels were 250.2+/-35.3 pg/ml. To evaluate blood/urine transfer, mice with chronic carotid arterial catheters were infused with saline or OT (5 or 20 pmol/min). Peak urine OT levels were 89+/-11.5 and 844+/-181 ng/ml in the low and high OT groups, respectively. Proteomic evaluation showed MS peaks, corresponding to OT ( approximately 1009 Da) and a related peptide ( approximately 1030 Da) with highest levels in mice infused with OT. Salt loading (5 days of 2% NaCl as drinking water) increased plasma osmolality (3.3%), increased plasma and urinary vasopressin (AVP), but caused no changes in OT. Thus, using non-invasive urine samples, we document that urinary OT and AVP can be used to monitor changes in peptide secretion. Urinary OT and AVP, as well as other urinary peptides, may provide a viable biomarker for peptide secretion and may be useful in clinical studies.     

Central cholinergic signal-mediated neuroendocrine regulation of vasopressin and oxytocin in ovine fetuses

Background  

The hypothalamic-neurohypophysial system plays a fundamental role in the maintenance of body fluid homeostasis by secreting arginine vasopressin (AVP) and oxytocin (OT) in response to a variety of signals, including osmotic and nonosmotic stimuli. It is well established that central cholinergic mechanisms are critical in the regulation of cardiovascular responses and maintenance of body fluid homeostasis in adults. Our recent study demonstrated that intracerebroventricular (i.c.v.) injection of carbachol elicited an increase of blood pressure in the near-term ovine fetuses. However, in utero development of brain cholinergic mechanisms in the regulation of the hypothalamic neuropeptides is largely unknown. This study investigated AVP and OT neural activation in the fetal hypothalamus induced by central carbachol.