Carbon monoxide and nitric oxide modulate hyperosmolality-induced oxytocin secretion by the hypothalamus in vitro

OT (oxytocin) is secreted from the posterior pituitary gland, and its secretion has been shown to be modulated by NO (nitric oxide). In rats, OT secretion is also stimulated by hyperosmolarity of the extracellular fluid. Furthermore, NOS (nitric oxide synthase) is located in hypothalamic areas involved in fluid balance control. In the present study, we evaluated the role of the NOS/NO and HO (haem oxygenase)/CO (carbon monoxide) systems in the osmotic regulation of OT release from rat hypothalamus in vitro. We conducted experiments on hypothalamic fragments to determine the following: (i) whether NO donors and NOS inhibitors modulate OT release and (ii) whether the changes in OT response occur concurrently with changes in NOS or HO activity in the hypothalamus. Hyperosmotic stimulation induced a significant increase in OT release that was associated with a reduction in nitrite production. Osmotic stimulation of OT release was inhibited by NO donors. NOS inhibitors did not affect either basal or osmotically stimulated OT release. Blockade of HO inhibited both basal and osmotically stimulated OT release, and induced a marked increase in NOS activity. These results indicate the involvement of CO in the regulation of NOS activity. The present data demonstrate that hypothalamic OT release induced by osmotic stimuli is modulated, at least in part, by interactions between NO and CO.

Central but not systemic inhibition of inducible nitric oxide synthase modulates oxytocin release during endotoxemic shock

Previous studies have shown that immunological challenges as lipopolysaccharide (LPS) administration increases plasma oxytocin (OT) concentration. Nitric oxide (NO), a free radical gas directly related to the immune system has been implicated in the central modulation of neuroendocrine adaptive responses to immunological stress. This study aimed to test the hypothesis that the NO pathway participates in the control of OT release induced by LPS injection. For this purpose, adult male Wistar rats received bolus intravenous (i.v.) injection of LPS, preceded or not by iv. or intracerebroventricular (i.c.v.) injections of aminoguanidine (AG), a selective inducible nitric oxide synthase (iNOS) inhibitor. Rats were decapitated after 2, 4 and 6 h of treatment, for measurement of OT by radioimmunoassay. In a separate set of experiments, mean arterial pressure (MAP) and heart rate (HR) were measured every 15 min over 6 h, using a polygraph. These studies revealed that LPS reduced MAP and increased HR at 4 and 6 h post-injection. LPS significantly increased plasma OT concentration at 2 and 4 h post-injection. Pre-treatment with i.c.v. AG further increased plasma OT concentration and attenuated the LPS-induced decrease in MAP, however, i.v. AG failed to show similar effects. Thus, iNOS pathway may activate a central inhibitory control mechanism that attenuates OT secretion during endotoxemic shock. (C) 2009 Elsevier Inc. All rights reserved.

Hypothalamic oxytocin neurons modulate hypophagic effect induced by adrenalectomy

Glucocorticoids have major effects on food intake, as demonstrated by the decrease of food intake following adrenalectomy (ADX); however, the mechanisms leading to these effects are not well understood. Oxytocin (OT) has been shown to reduce food intake. We evaluated the effects of glucocorticoids on OT neuron activation and OT mRNA expression in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei induced by feeding. We also evaluated the effect of pretreatment with OT-receptor antagonist ([d(CH2)5,Tyr(Me)2,Orn8]-vasotocin, OVT) on food intake in ADX rats. Fos/OT neurons in the posterior parvocellular subdivision of the PVN were increased after refeeding, with a higher number in the ADX group, compared with sham and ADX+corticosterone (B) groups, with no difference in the medial parvocellular and magnocellular subdivisions of the PVN. ADX increased OT mRNA expression in the PVN both in fasting and refeeding condition, compared with sham and ADX+B groups. In the SON, refeeding increased the number of Fos/OT neurons, with a higher number in the ADX+B group. In fasted condition, OT mRNA expression in the SON was increased in ADX and ADX+B, compared with sham group. Pretreatment with OVT reversed the ADX-induced hypophagia, with no difference between sham and ADX+B animals. The present results show that glucocorticoid withdrawal induces a higher activation of PVN OT neurons in response to feeding, and an increase of OT mRNA expression in the PVN and OT-receptor antagonist reverses the anorexigenic effect induced by ADX These data indicate that PVN OT neurons might mediate the hypophagic effect induced by adrenalectomy. (C) 2009 Elsevier Inc. All rights reserved.

13,14-Dihydro-15-Keto Prostaglandin F(2)alpha Release in Response to Oxytocin Challenge Early Post-Partum in Anoestrous Nelore Cows Submitted to Temporary Calf Removal and Progesterone Priming

The study evaluated, in early post-partum anoestrous Nelore cows, if the increase in plasma oestradiol (E2) concentrations in the pre-ovulatory period and/or progesterone priming (P4 priming) preceding ovulation, induced by hormonal treatment, reduces the endogenous release of prostaglandin PGF(2)alpha and prevents premature lysis of the corpus luteum (CL). Nelore cows were subjected to temporary calf removal for 48 h and divided into two groups: GPE/eCG group (n = 10) and GPG/eCG group (n = 10). Animals of the GPE/eCG group were treated with a GnRH agonist. Seven days later, they received 400 ID of eCG, immediately after PGF(2)alpha treatment, and on day 0, 1.0 mg of oestradiol benzoate (EB). Cows of the GPG/eCG group were similarly treated as those of the GPE/eCG group, except that EB was replaced with a second dose of GnRH. All animals were challenged with oxytocin (OT) 9, 12, 15 and 18 days after EB or GnRH administration and blood samples were collected before and 30 min after OT. Irrespective of the treatments, a decline in P4 concentration on day 18 was observed for cows without P4 priming. However, animals exposed to P4 priming, treated with EB maintained high P4 concentrations (8.8 +/- 1.2 ng/ml), whereas there was a decline in P4 on day 18 (2.1 +/- 1.0 ng/ml) for cows that received GnRH to induce ovulation (p < 0.01). Production of 13,14-dihydro-15-keto prostaglandin F(2)alpha (PGFM) in response to OT increased between days 9 and 18 (p < 0.01), and this increase tended to be more evident in animals not exposed to P4 priming (p < 0.06). In conclusion, the increase in E2 during the pre-ovulatory period was not effective in inhibiting PGFM release, which was lower in P4-primed than in non-primed animals. Treatment with EB promoted the maintenance of elevated P4 concentrations 18 days after ovulation in P4-primed animals, indicating a possible beneficial effect of hormone protocols containing EB in animals with P4 priming.

Men perform comparably to women in a perspective taking task after administration of intranasal oxytocin but not after placebo

Oxytocin (OT) is thought to play an important role in human interpersonal information processing and behavior. By inference, OT should facilitate empathic responding, i.e. the ability to feel for others and to take their perspective. In two independent double-blind, placebo-controlled between-subjects studies, we assessed the effect of intranasally administered OT on affective empathy and perspective taking, whilst also examining potential sex differences (e.g., women being more empathic than men). In study 1, we provided 96 participants (48 men) with an empathy scenario and recorded self reports of empathic reactions to the scenario, while in study 2, a sample of 120 individuals (60 men) performed a computerized implicit perspective taking task. Whilst results from Study 1 showed no influence of OT on affective empathy, we found in Study 2 that OT exerted an effect on perspective taking ability in men. More specifically, men responded faster than women in the placebo group but they responded as slowly as women in the OT group. We conjecture that men in the OT group adopted a social perspective taking strategy, such as did women in both groups, but not men in the placebo group. On the basis of results across both studies, we suggest that self-report measures (such as used in Study 1) might be less sensitive to OT effects than more implicit measures of empathy such as that used in Study 2. If these assumptions are confirmed, one could infer that OT effects on empathic responses are more pronounced in men than women, and that any such effect is best studied using more implicit measures of empathy rather than explicit self-report measures.

Evoked axonal oxytocin release in the central amygdala attenuates fear response.

The hypothalamic neuropeptide oxytocin (OT), which controls childbirth and lactation, receives increasing attention for its effects on social behaviors, but how it reaches central brain regions is still unclear. Here we gained by recombinant viruses selective genetic access to hypothalamic OT neurons to study their connectivity and control their activity by optogenetic means. We found axons of hypothalamic OT neurons in the majority of forebrain regions, including the central amygdala (CeA), a structure critically involved in OT-mediated fear suppression. In vitro, exposure to blue light of channelrhodopsin-2-expressing OT axons activated a local GABAergic circuit that inhibited neurons in the output region of the CeA. Remarkably, in vivo, local blue-light-induced endogenous OT release robustly decreased freezing responses in fear-conditioned rats. Our results thus show widespread central projections of hypothalamic OT neurons and demonstrate that OT release from local axonal endings can specifically control region-associated behaviors.

Oxytocin response to an experimental psychosocial challenge in adults exposed to traumatic experiences during childhood or adolescence.

Long-term implications of the exposure to traumatizing experiences during childhood or adolescence, such as sexual abuse, or cancer, have been documented, namely the subjects' response to an acute stress in adulthood. Several indicators of the stress response have been considered (e.g. cortisol, heart rate). Oxytocin (OT) response to an acute stress of individuals exposed to trauma has not been documented. Eighty subjects (n=26 women who had experienced episodes of child abuse, n=25 men and women healthy survivors of cancer in childhood or adolescence, and 29 controls) have been submitted to a laboratory session involving an experimental stress challenge, the Trier social stress test. Overall, there was a clear OT response to the psychosocial challenge. Subjects having experienced a childhood/adolescence life-threatening illness had higher mean levels of OT than both abused and control subjects. There was a moderate negative relationship between OT and salivary cortisol. It is suggested that an acute stress stimulates OT secretion, and that the exposure to enduring life-threatening experiences in childhood/adolescence has long-lasting consequences regarding the stress system and connected functions, namely the activation of OT secretion. Better knowledge of such long-term implications is important so that to prevent dysregulations of the stress responses, which have been shown to be associated to the individual's mental health.

Neuromodulation by oxytocin and vasopressin.

Oxytocin (OT) and vasopressin (VP) are two closely related neuropeptides, widely known for their peripheral hormonal effects. Specific receptors have also been found in the brain, where their neuromodulatory actions have meanwhile been described in a large number of regions. Recently, it has become possible to study their endogenous neuropeptide release with the help of OT/VP promoter-driven expression of fluorescent proteins and light-activated ion channels. In this review, I summarize the neuromodulatory effects of OT and VP in different brain regions by grouping these into different behavioral systems, highlighting their concerted, and at times opposite, effects on different aspects of behavior.

Oxytocin response to an experimental psychosocial challenge in adults exposed to traumatic experiences during childhood or adolescence.

Long-term implications of the exposure to traumatizing experiences during childhood or adolescence, such as sexual abuse, or cancer, have been documented, namely the subjects' response to an acute stress in adulthood. Several indicators of the stress response have been considered (e.g. cortisol, heart rate). Oxytocin (OT) response to an acute stress of individuals exposed to trauma has not been documented. Eighty subjects (n=26 women who had experienced episodes of child abuse, n=25 men and women healthy survivors of cancer in childhood or adolescence, and 29 controls) have been submitted to a laboratory session involving an experimental stress challenge, the Trier social stress test. Overall, there was a clear OT response to the psychosocial challenge. Subjects having experienced a childhood/adolescence life-threatening illness had higher mean levels of OT than both abused and control subjects. There was a moderate negative relationship between OT and salivary cortisol. It is suggested that an acute stress stimulates OT secretion, and that the exposure to enduring life-threatening experiences in childhood/adolescence has long-lasting consequences regarding the stress system and connected functions, namely the activation of OT secretion. Better knowledge of such long-term implications is important so that to prevent dysregulations of the stress responses, which have been shown to be associated to the individual's mental health.

Oxytocin is a cardiovascular hormone

Oxytocin (OT), a nonapeptide, was the first hormone to have its biological activities established and chemical structure determined. It was believed that OT is released from hypothalamic nerve terminals of the posterior hypophysis into the circulation where it stimulates uterine contractions during parturition, and milk ejection during lactation. However, equivalent concentrations of OT were found in the male hypophysis, and similar stimuli of OT release were determined for both sexes, suggesting other physiological functions. Indeed, recent studies indicate that OT is involved in cognition, tolerance, adaptation and complex sexual and maternal behaviour, as well as in the regulation of cardiovascular functions. It has long been known that OT induces natriuresis and causes a fall in mean arterial pressure, both after acute and chronic treatment, but the mechanism was not clear. The discovery of the natriuretic family shed new light on this matter. Atrial natriuretic peptide (ANP), a potent natriuretic and vasorelaxant hormone, originally isolated from rat atria, has been found at other sites, including the brain. Blood volume expansion causes ANP release that is believed to be important in the induction of natriuresis and diuresis, which in turn act to reduce the increase in blood volume. Neurohypophysectomy totally abolishes the ANP response to volume expansion. This indicates that one of the major hypophyseal peptides is responsible for ANP release. The role of ANP in OT-induced natriuresis was evaluated, and we hypothesized that the cardio-renal effects of OT are mediated by the release of ANP from the heart. To support this hypothesis, we have demonstrated the presence and synthesis of OT receptors in all heart compartments and the vasculature. The functionality of these receptors has been established by the ability of OT to induce ANP release from perfused heart or atrial slices. Furthermore, we have shown that the heart and large vessels like the aorta and vena cava are sites of OT synthesis. Therefore, locally produced OT may have important regulatory functions within the heart and vascular beds. Such functions may include slowing down of the heart or the regulation of local vascular tone.

Nitrergic modulation of vasopressin, oxytocin and atrial natriuretic peptide secretion in response to sodium intake and hypertonic blood volume expansion

The central nervous system plays an important role in the control of renal sodium excretion. We present here a brief review of physiologic regulation of hydromineral balance and discuss recent results from our laboratory that focus on the participation of nitrergic, vasopressinergic, and oxytocinergic systems in the regulation of water and sodium excretion under different salt intake and hypertonic blood volume expansion (BVE) conditions. High sodium intake induced a significant increase in nitric oxide synthase (NOS) activity in the medial basal hypothalamus and neural lobe, while a low sodium diet decreased NOS activity in the neural lobe, suggesting that central NOS is involved in the control of sodium balance. An increase in plasma concentrations in vasopressin (AVP), oxytocin (OT), atrial natriuretic peptide (ANP), and nitrate after hypertonic BVE was also demonstrated. The central inhibition of NOS by L-NAME caused a decrease in plasma AVP and no change in plasma OT or ANP levels after BVE. These data indicate that the increase in AVP release after hypertonic BVE depends on nitric oxide production. In contrast, the pattern of OT secretion was similar to that of ANP secretion, supporting the view that OT is a neuromodulator of ANP secretion during hypertonic BVE. Thus, neurohypophyseal hormones and ANP are secreted under hypertonic BVE in order to correct the changes induced in blood volume and osmolality, and the secretion of AVP in this particular situation depends on NOS activity.

The role of oxytocin in cardiovascular regulation

Studies of body volume expansion have indicated that lesions of the anteroventral third ventricle and median eminence block the release of atrial natriuretic peptide (ANP) into the circulation. Detailed analysis of the lesions showed that activation of oxytocin (OT)-ergic neurons is responsible for ANP release, and it has become clear that activation of neuronal circuitry elicits OT secretion into the circulation, activating atrial OT receptors and ANP release from the heart. Subsequently, we have uncovered the entire functional OT system in the rat and the human heart. An abundance of OT has been observed in the early development of the fetal heart, and the capacity of OT to generate cardiomyocytes (CMs) has been demonstrated in various types of stem cells. OT treatment of mesenchymal stem cells stimulates paracrine factors beneficial for cardioprotection. Cardiovascular actions of OT include: i) lowering blood pressure, ii) negative inotropic and chronotropic effects, iii) parasympathetic neuromodulation, iv) vasodilatation, v) anti-inflammatory activity, vi) antioxidant activity, and vii) metabolic effects. OT actions are mediated by nitric oxide and ANP. The beneficial actions of OT may include the increase in glucose uptake by CMs and stem cells, reduction in CM hypertrophy, oxidative stress, and mitochondrial protection of several cell types. In experimentally induced myocardial infarction in rats, continuous in vivo OT delivery improves cardiac healing and cardiac work, reduces inflammation, and stimulates angiogenesis. Because OT plays anti-inflammatory and cardioprotective roles and improves vascular and metabolic functions, it demonstrates potential for therapeutic use in various pathologic conditions.

Evaluation of oxytocin pharmacokinetic : pharmacodynamic profile and establishment of its cardiomyogenic potential in swine

La thérapie cellulaire est une avenue pleine de promesses pour la régénération myocardique, par le remplacement du tissu nécrosé, ou en prévenant l'apoptose du myocarde survivant, ou encore par l'amélioration de la néovascularisation. Les cellules souches de la moelle osseuse (CSMO) expriment des marqueurs cardiaques in vitro quand elles sont exposées à des inducteurs. Pour cette raison, elles ont été utilisées dans la thérapie cellulaire de l'infarctus au myocarde dans des études pre-cliniques et cliniques. Récemment, il a été soulevé de possibles effets bénéfiques de l'ocytocine (OT) lors d’infarctus. Ainsi, l’OT est un inducteur de différenciation cardiaque des cellules souches embryonnaires, et cette différenciation est véhiculée par la voie de signalisation du monoxyde d’azote (NO)-guanylyl cyclase soluble. Toutefois, des données pharmacocinétiques de l’OT lui attribue un profil non linéaire et celui-ci pourrait expliquer les effets pharmacodynamiques controversés, rapportés dans la lttérature. Les objectifs de ce programme doctoral étaient les suivants : 1) Caractériser le profil pharmacocinétique de différents schémas posologiques d'OT chez le porc, en développant une modélisation pharmacocinétique / pharmacodynamique plus adaptée à intégrer les effets biologiques (rénaux, cardiovasculaires) observés. 2) Isoler, différencier et trouver le temps optimal d’induction de la différenciation pour les CSMO porcines (CSMOp), sur la base de l'expression des facteurs de transcription et des protéines structurales cardiaques retrouvées aux différents passages. 3) Induire et quantifier la différenciation cardiaque par l’OT sur les CSMOp. 4) Vérifier le rôle du NO dans cette différenciation cardiaque sur les CSMOp. Nous avons constaté que le profil pharmacocinétique de l’OT est mieux expliqué par le modèle connu comme target-mediated drug disposition (TMDD), parce que la durée du séjour de l’OT dans l’organisme dépend de sa capacité de liaison à son récepteur, ainsi que de son élimination (métabolisme). D'ailleurs, nous avons constaté que la différenciation cardiomyogénique des CSMOp médiée par l’OT devrait être induite pendant les premiers passages, parce que le nombre de passages modifie le profile phénotypique des CSMOp, ainsi que leur potentiel de différenciation. Nous avons observé que l’OT est un inducteur de la différenciation cardiomyogénique des CSMOp, parce que les cellules induites par l’OT expriment des marqueurs cardiaques, et l'expression de protéines cardiaques spécifiques a été plus abondante dans les cellules traitées à l’OT en comparaison aux cellules traitées avec la 5-azacytidine, qui a été largement utilisée comme inducteur de différenciation cardiaque des cellules souches adultes. Aussi, l’OT a causé la prolifération des CMSOp. Finalement, nous avons observé que l'inhibition de la voie de signalisation du NO affecte de manière significative l'expression des protéines cardiaques spécifiques. En conclusion, ces études précisent un potentiel certain de l’OT dans le cadre de la thérapie cellulaire cardiomyogénique à base de cellules souches adultes, mais soulignent que son utilisation requerra de la prudence et un approfondissement des connaissances.

Oxytocin promotes bone formation during the alveolar healing process in old acyclic female rats

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13,14-Dihydro-15-Keto Prostaglandin F-2 alpha Release in Response to Oxytocin Challenge Early Post-Partum in Anoestrous Nelore Cows Submitted to Temporary Calf Removal and Progesterone Priming

The study evaluated, in early post-partum anoestrous Nelore cows, if the increase in plasma oestradiol (E2) concentrations in the pre-ovulatory period and/or progesterone priming (P4 priming) preceding ovulation, induced by hormonal treatment, reduces the endogenous release of prostaglandin PGF(2)alpha and prevents premature lysis of the corpus luteum (CL). Nelore cows were subjected to temporary calf removal for 48 h and divided into two groups: GPE/eCG group (n = 10) and GPG/eCG group (n = 10). Animals of the GPE/eCG group were treated with a GnRH agonist. Seven days later, they received 400 ID of eCG, immediately after PGF(2)alpha treatment, and on day 0, 1.0 mg of oestradiol benzoate (EB). Cows of the GPG/eCG group were similarly treated as those of the GPE/eCG group, except that EB was replaced with a second dose of GnRH. All animals were challenged with oxytocin (OT) 9, 12, 15 and 18 days after EB or GnRH administration and blood samples were collected before and 30 min after OT. Irrespective of the treatments, a decline in P4 concentration on day 18 was observed for cows without P4 priming. However, animals exposed to P4 priming, treated with EB maintained high P4 concentrations (8.8 +/- 1.2 ng/ml), whereas there was a decline in P4 on day 18 (2.1 +/- 1.0 ng/ml) for cows that received GnRH to induce ovulation (p < 0.01). Production of 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM) in response to OT increased between days 9 and 18 (p < 0.01), and this increase tended to be more evident in animals not exposed to P4 priming (p < 0.06). In conclusion, the increase in E2 during the pre-ovulatory period was not effective in inhibiting PGFM release, which was lower in P4-primed than in non-primed animals. Treatment with EB promoted the maintenance of elevated P4 concentrations 18 days after ovulation in P4-primed animals, indicating a possible beneficial effect of hormone protocols containing EB in animals with P4 priming.