Retinal changes in an experimental model of early type 2 diabetes in rats characterized by non-fasting hyperglycemia

Diabetic retinopathy is a leading cause of acquired blindness in young, but also in elder adults, mostly affected by type 2 diabetes mellitus (T2DM). The aim of this work was to develop an experimental model of early human T2DM in adult rats, and to analyze retinal functional, morphological, and biochemical changes arising during the early stages of the moderate metabolic derangement. For this purpose, animals were divided in four groups: adult male Wistar rats receiving: tap water and citrate buffer i.p. (group 1), tap water with 30% sucrose and citrate buffer i.p. (group 2), tap water and 25mg/kg i.p streptozotocin (STZ, group 3), or 30% sucrose and STZ (group 4). Fasting and postprandial glycemia, fructosamine and serum insulin levels were assessed. In addition, i.p. glucose and insulin tolerance tests were performed. Retinal function (electroretinogram, ERG) and morphology (optical microscopy), retinal nitric oxide synthase (NOS) activity (using (3)H-arginine), lipid peroxidation (thiobarbituric acid reactive substances, TBARS), and TNFα levels (ELISA) were evaluated. At 6 and 12 weeks of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in most metabolic tests, as compared with the other groups. At 12 weeks of treatment, a significant decrease in the ERG a- and b- wave and oscillatory potential amplitudes, and a significant increase in retinal NOS activity, TBARS, TNFα, glial fibrillary acidic protein in Müller cells, and vascular endothelial growth factor levels were observed. These results indicate that the combination of diet-induced insulin resistance and a slight secretory impairment resulting from a low-dose STZ treatment mimics some features of human T2DM at its initial stages, and provokes significant retinal alterations.

Anti-inflammatory effect of the endocannabinoid anandamide in experimental periodontitis and stress in the rat

OBJECTIVE

Periodontitis is an infectious disease leading to inflammation and destruction of tissue surrounding and supporting the tooth. The progress of the inflammatory response depends on the host's immune system and risk factors such as stress. The aim of the present study was to investigate the role of the endocannabinoid anandamide (AEA) in experimental periodontitis with restraint stress, since the endocannabinoid system is known to modulate the hypothalamo-pituitary-adrenal axis as well as immune functions and has been found in human gingival tissues.

METHODS

Experimental periodontitis was induced by ligature around first inferior molars and immobilization stress for 2 h twice daily for 7 days in a rat model.

RESULTS

Corticosterone plasma levels, locomotor activity, adrenal gland weight and bone loss were increased in periodontitis and stress groups, and there was also less weight gain. The inflammatory parameters such as prostaglandin E(2) (radioimmunoassay), nitric oxide (radioconversion of (14)C-arginine), tumor necrosis factor (TNF)-α (ELISA) and interleukin (IL)-1β (Western blot) measured in the gingival tissue were significantly increased in the periodontitis groups compared to the control group. Local injection of AEA (10(-8)M, 30 µl) decreased corticosterone plasma levels and the content of the cytokines TNF-α and IL-1β in gingival tissue in periodontitis-stress groups. These AEA-induced inhibitions were mediated by CB(1) and CB(2) cannabinoid receptors since the injection of both antagonists together, AM251 (10(-6)M) and AM630 (10(-6)M) in 30 µl, prevented these effects.

CONCLUSION

The endocannabinoid AEA diminishes the inflammatory response in periodontitis even during a stressful situation.

Allopregnanolone induces LHRH and glutamate release through NMDA receptor modulation

LHRH release from hypothalamus is influenced by the neurotransmitter glutamate that acts, among others, on NMDA receptors present in LHRH neurons. On the other hand, the neurosteroid allopregnanolone can modulate the activity of specific neurotransmitter receptors and affect neurotransmitter release. We examined the role of allopregnanolone on in vitro LHRH and glutamate release from mediobasal hypothalamus and anterior preoptic area of ovariectomized rats with estrogen and progesterone replacement. Moreover, we evaluated whether the neurosteroid might act through modulation of NMDA receptors. Allopregnanolone induced an increase in LHRH release. This effect was reversed when the NMDA receptors were blocked by the NMDA antagonist 2-amino-7-phosphonoheptanoic acid (AP-7) indicating that this neurosteroid would interact with NMDA receptors. Moreover allopregnanolone induced an augment in K(+) evoked [(3)H]-glutamate release from mediobasal hypothalamus-anterior preoptic area explants and this effect was also reversed when NMDA receptors were blocked with AP-7. These results suggest an important physiologic function of allopregnanolone on the regulation of neuroendocrine function in female adult rats. Not only appears to be involved in enhancing LHRH release through modulation of NMDA receptors but also in the release of glutamate which is critical in the control of LHRH release.

Adrenal gland responses to lipopolysaccharide after stress and ethanol administration in male rats

All forms of stress, including restraint stress (RS) and lipopolysaccharide (LPS) administration, activate the hypothalamic-pituitary-adrenal (HPA) axis. LPS binds to a recognition protein (CD14) and toll-like receptor 2/4 in different cells and tissues, including the adrenal gland, to induce the production of cytokines and cause upregulation of cyclooxygenase and nitric oxide synthase (NOS) enzymes. Acute ethanol exposure activates the HPA axis, but in some conditions prolonged administration can dampen this activation as well as decrease the inflammatory responses to LPS. Therefore, this study was designed to evaluate the adrenal response to a challenge dose of LPS (50 μg/kg) injected i.p., after submitting male rats to RS, twice a day (2 h each time) for 5 days and/or ethanol administration (3 g/kg) by gavage also for 5 days, twice daily. At the end of the experiment, plasma corticosterone concentrations and adrenal gland content of prostaglandin E (PGE) and NOS activity were measured as stress mediators. The results showed that repetitive ethanol administration attenuated the adrenal stress response to LPS challenge alone and after RS, by preventing the increase in plasma corticosterone concentrations and by decreasing the PGE content and NOS activity in the adrenal gland. Therefore, we conclude that moderate alcohol consumption could attenuate the effects of psychophysical stress and impair an inflammatory response.

Participation of the endocannabinoid system in lipopolysaccharide-induced inhibition of salivary secretion

OBJECTIVE

The aim of the present paper was to assess whether lipopolysaccharide (LPS)-induced inhibition of salivary secretion involves the activation of the endocannabinoid system and the participation of tumor necrosis factor (TNF)alpha in the submandibular gland.

DESIGN

Pharmacological approaches were performed by using CB1 and/or CB2 cannabinoid receptor antagonists, AM251 and AM630, respectively, injected into the submandibular gland, to study the participation of the endocannabinoid system in LPS inhibitory effects on metacholine-induced salivary secretion. To assess the participation of TNFalpha on LPS inhibitory effects, salivary secretion was studied in LPS treated rats after the intraglandular injection of etanercept, a soluble form of TNF receptor which blocks TNFalpha action. Finally, to evaluate the possible interplay between endocannabinoids and TNFalpha on the submandibular gland function reduced during LPS challenge, the salivary secretion was studied after the intraglandular injection of this cytokine alone or concomitantly with AM251 and AM630.

RESULTS

AM251 and AM630, injected separately or concomitantly, partially prevented LPS-induced inhibition of salivation. Also, anandamide synthase activity was increased in submandibular glands extracted from rats 3h after LPS injection, suggesting that the endocannabinoid system was activated in response to this challenge. On the other hand, etanercept, prevented the inhibitory effect of LPS on salivary secretion and moreover, TNFalpha injected intraglandularly inhibited salivary secretion, being this effect prevented by AM251 and AM630 injected concomitantly.

CONCLUSION

The present results demonstrate the participation of the endocannabinoid system and TNFalpha on salivary responses during systemic inflammation induced by LPS.

Anandamide injected into the lateral ventricle of the brain inhibits submandibular salivary secretion by attenuating parasympathetic neurotransmission

Our objective was to determine the effect of arachidonylethanolamide (anandamide, AEA) injected intracerebroventricularly (icv) into the lateral ventricle of the rat brain on submandibular gland (SMG) salivary secretion. Parasympathetic decentralization (PSD) produced by cutting the chorda tympani nerve strongly inhibited methacholine (MC)-induced salivary secretion while sympathetic denervation (SD) produced by removing the superior cervical ganglia reduced it slightly. Also, AEA (50 ng/5 microL, icv) significantly decreased MC-induced salivary secretion in intact rats (MC 1 microg/kg: control (C), 5.3 +/- 0.6 vs AEA, 2.7 +/- 0.6 mg; MC 3 microg/kg: C, 17.6 +/- 1.0 vs AEA, 8.7 +/- 0.9 mg; MC 10 microg/kg: C, 37.4 +/- 1.2 vs AEA, 22.9 +/- 2.6 mg). However, AEA did not alter the significantly reduced salivary secretion in rats with PSD, but decreased the slightly reduced salivary secretion in rats with SD (MC 1 microg/kg: C, 3.8 +/- 0.8 vs AEA, 1.4 +/- 0.6 mg; MC 3 microg/kg: C, 14.7 +/- 2.4 vs AEA, 6.9 +/- 1.2 mg; P < 0.05; MC 10 microg/kg: C, 39.5 +/- 1.0 vs AEA, 22.3 +/- 0.5 mg; P < 0.001). We showed that the inhibitory effect of AEA is mediated by cannabinoid type 1 CB1 receptors and involves GABAergic neurotransmission, since it was blocked by previous injection of the CB1 receptor antagonist AM251 (500 ng/5 microL, icv) or of the GABA A receptor antagonist, bicuculline (25 ng/5 microL, icv). Our results suggest that parasympathetic neurotransmission from the central nervous system to the SMG can be inhibited by endocannabinoid and GABAergic systems.

Expression and function of endocannabinoid receptors in the human adrenal cortex

Endogenous cannabinoids are important signaling molecules in neuroendocrine control of homeostatic and reproductive functions including stress response and energy metabolism. The hypothalamic paraventricular and supraoptic nuclei have been shown to release endocannabinoids, which act as retrograde messengers to modulate the synaptic release of glutamate during stress response. This study endeavors to elucidate possible interaction of the endocannabinoid system with the regulation of adrenocortical function at the adrenal level. Human adrenocortical NCI-H295R cells and normal human adrenal glands were used to study the possible effects of anandamide and cannabinoid receptor 1 (CB1) antagonist SR141716A on aldosterone and cortisol secretion. Our data indicate the expression of CB1 in human adrenal cortex and adrenocortical NCI-H295R cells; CB2 was not expressed. Furthermore, anandamide inhibited basal release and stimulated release of adrenocortical steroids (corticosterone and aldosterone); this effect was reversed by CB1 antagonist (SR141716A). Therefore, the endocannabinoid system at the level of the adrenal, can directly influence adrenocortical steroidogenesis.

Endocannabinoid system participates in neuroendocrine control of homeostasis

The hypothalamo-neurohypophyseal system plays a role in homeostasis under a variety of stress conditions, including endotoxemia. Oxytocin (OXT) and vasopressin (VP) are important hormones synthesized by neurons in the hypothalamic paraventricular and supraoptic nuclei and released into different brain regions and from the neurohypophyseal terminals into the blood in response to many patho-physiological stimuli. However, the mechanism that controls OXT and VP secretion has not been fully elucidated. Nitric oxide (NO) is a known mediator that regulates the release of these hormones. The endocannabinoid system is a new intercellular system that modulates several neuroendocrine actions. Endocannabinoids (eCB) are released as retrograde messengers by many neurons, including hypothalamic magnocellular neurons and cannabinoid receptors are localized within these neurons, as well as in the anterior and posterior pituitary lobes, suggesting an eCB role in the production and release of OXT and VP. Lipopolysaccharide (LPS) injection is a model used as immune challenge. LPS causes a neuroendocrine response that is mediated by cytokines, tumor necrosis factor-alpha being one of them. We focused on NO and endocannabinoid system participation on OXT and VP production and secretion during basal and stress conditions and found that eCB affect basal OXT and VP secretion by acting differently at each level of the hypothalamo-neurohypophyseal system. After LPS, there is an increase in eCB synthesis that enhances OXT secretion.

Role of the endocannabinoid system in ethanol-induced inhibition of salivary secretion

AIM

The aim of the present study was to determine whether the endocannabinoid system could be involved in the ethanol-induced inhibition of salivation in adult male Wistar rats.

METHODS

Salivary secretion induced by different concentrations of methacholine, a cholinergic agonist, and the endocannabinoid arachidonoyl ethanolamide (anandamide, AEA) production in the submandibular gland (SMG) were determined in rats after ethanol (3 g/kg) administration by gastric gavage. To study the participation of cannabinod receptors in ethanol action, we evaluated methacholine-induced salivary secretion after ethanol administration when CB1 or CB2 receptors were blocked by intra-SMG injections of their selective antagonists AM251 and AM630, respectively. Additionally, we evaluated the in vitro effect of ethanol (0.1 M) on SMG production of cAMP, alone or combined with AM251 or AM630.

RESULTS

Acute ethanol administration increased AEA production in SMG and also inhibited the methacholine-induced saliva secretion that was partially restored by intraglandular injection of AM251 or AM630. In addition, ethanol significantly reduced the forskolin-induced increase in cAMP content in SMG in vitro while treatment with AM251 blocked this response.

CONCLUSION

We conclude that the inhibitory effect produced by ethanol on submandibular gland salivary secretion is mediated, at least in part, by the endocannabinoid system.

Acute effect of manganese on hypothalamic luteinizing hormone releasing hormone secretion in adult male rats: involvement of specific neurotransmitter systems

Manganese chloride (MnCl2) is capable of stimulating luteinizing hormone releasing hormone (LHRH) secretion in adult male Sprague-Dawley rats through the activation of the hypothalamic nitric oxide/cyclic guanosine monophosphate (cGMP)/protein kinase G pathway. The present study aimed to determine the involvement of specific neurotransmitters involved in this action. Our results indicate that dopamine, but not glutamic acid and prostaglandins, mediates the MnCl2 stimulated secretion of LHRH from medial basal hypothalami in vitro, as well as increases the activity of nitric oxide synthase. Furthermore, a biphasic response was observed in that gamma aminobutyric acid (GABA) release was also increased, which acts to attenuate the MnCl2 action to stimulate LHRH secretion. Although it is clear that manganese (Mn+2) can acutely induce LHRH secretion in adult males, we suggest that the additional action of MnCl2 to release GABA, a LHRH inhibitor, may ultimately contribute to suppressed reproductive function observed in adult animals following exposure to high chromic levels of Mn+2.

Cannabinoid receptors in conjunctival epithelium: identification and functional properties

PURPOSE

Preservation of the ocular surface barrier requires complex control of epithelial cell proliferation and inflammation mechanisms. The endocannabinoid system may be regulating these processes. Therefore, the authors explored the presence and properties of cannabinoid receptors (CB1 and CB2) in conjunctival epithelial cells.

METHODS

The authors used immunohistochemistry to detect CB1 and CB2 in normal mouse conjunctiva, human conjunctival cryosections and impression samples, and IOBA-NHC cells, a human conjunctiva-derived cell line. The presence of CB1 and CB2 proteins and transcripts was studied in IOBA-NHC cells by Western blot and RT-PCR, respectively. The authors also used this cell line to assay cannabinoid ligand-induced changes in cAMP levels, cell growth, and tumor necrosis factor-alpha (TNF-alpha)-induced activation of c-jun N-terminal kinase (JNK) and nuclear factor-kappaB (NF-kappaB).

RESULTS

Mouse and human conjunctival epithelial cells displayed CB1 and CB2 proteins and transcripts. Cannabinoid receptor activation decreased cAMP levels in IOBA-NHC cells, and specific CB1 and CB2 antagonists canceled this effect. Cannabinoid ligands also increased cell growth and blocked stress pathways activated by TNF-alpha in vitro.

CONCLUSIONS

Cannabinoid receptors are present in mouse and human conjunctival cells. Functional responses, such as decreased cAMP levels, proliferation, and modulation of stress signaling pathways, were mediated by CB1 and CB2 stimulation. Thus, these receptors might be involved in the regulation of epithelial renewal and inflammatory processes at the ocular surface.

Nitric oxide mediates prostaglandins' deleterious effect on lipopolysaccharide-triggered murine fetal resorption

Genital tract bacterial infections could induce abortion and are some of the most common complications of pregnancy; however, the mechanisms remain unclear. We investigated the role of prostaglandins (PGs) in the mechanism of bacterial lipopolysaccharide (LPS)-induced pregnancy loss in a mouse model, and we hypothesized that PGs might play a central role in this action. LPS increased PG production in the uterus and decidua from early pregnant mice and stimulated cyclooxygenase (COX)-II mRNA and protein expression in the decidua but not in the uterus. We also observed that COX inhibitors prevented embryonic resorption (ER). To study the possible interaction between nitric oxide (NO) and PGs, we administered aminoguanidine, an inducible NO synthase inhibitor. NO inhibited basal PGE and PGF(2alpha) production in the decidua but activated their uterine synthesis and COX-II mRNA expression under septic conditions. A NO donor (S-nitroso-N-acetylpenicillamine) produced 100% ER and increased PG levels in the uterus and decidua. LPS-stimulated protein nitration was higher in the uterus than in the decidua. Quercetin, a peroxynitrite scavenger, did not reverse LPS-induced ER. Our results suggest that in a model of septic abortion characterized by increased PG levels, NO might nitrate and thus inhibit COX catalytic activity. ER prevention by COX inhibitors adds a possible clinical application to early pregnancy complications due to infections.

Participation of the endocannabinoid system in the effect of TNF-alpha on hypothalamic release of gonadotropin-releasing hormone

It is known that Delta(9)-tetrahydrocannabinol (THC), the major active ingredient of marijuana, can suppress reproductive function. Also, we reported previously that the endocannabinoid, anandamide (AEA), inhibited gonadotropin-releasing hormone (LHRH) release from medial basal hypothalamus (MBH) of male rats incubated in vitro as well as reduced plasma LH levels after i.c.v. AEA injections into the cerebral lateral ventricle. On the other hand, it is known that during endotoxemia the hypothalamic gonadotropin axis is inhibited. Therefore, the aim of the present study was to determine whether the effect of TNF-alpha, a proinflammatory cytokine induced by lipopolysaccharide (LPS) that inhibits LHRH release, is mediated by the activation of the endocannabinoid system. The intraperitoneal injection of LPS (5 mg/kg) as well as the i.c.v. injection of tumor necrosis factor-alpha (TNF-alpha) (100 ng/rat) increased significantly the AEA synthesis measured ex vivo in MBHs removed 3 h after the treatments. To examine the possibility that TNF-alpha also acted by increasing the synthesis of AEA that was released and activated the CB1-r followed by inhibition of LHRH release, we measured the effect of TNF-alpha on the AEA synthase activity in MBHs incubated in vitro. As expected, we found that TNF-alpha (2.9 x 10(-9) M) increased the AEA synthesis. Second, we showed that TNF-alpha reduced significantly the forskolin-stimulated LHRH release and that the CB1-r antagonist AM251 (10(-5) M) blocked that inhibition, supporting the hypothesis that TNF-alpha inhibits LHRH release, acting at least in part by activating the endocannabinoid system. Therefore, our data demonstrate a key role for the endocannabinoid system in the response of the reproductive system to inflammatory signals.

Effect of manganese on luteinizing hormone-releasing hormone secretion in adult male rats

Recently studies have demonstrated that low doses of (Mn(+2)) in the form of manganese chloride can stimulate specific puberty-related hormones and advance signs of pubertal development in immature female and male rats. In the present study, we used an in vitro system to evaluate the ability of 0, 50, 250, and 500 microM doses of Mn(+2) to stimulate luteinizing hormone-releasing hormone (LHRH) secretion and to assess the hypothalamic mechanism of this action in adult male Sprague-Dawley rats. We demonstrated that Mn(+2) at 500 microM, but not the lower doses, increased LHRH release, nitric oxide (NO) synthase (NOS) activity, and the content of cyclic cGMP in the medial basal hypothalamus. Inhibition of NOS with a competitive inhibitor (Nomega-nitro-L-arginine methyl ester hydrochloride) prevented the Mn-induced increase in LHRH release. Additionally, methylene blue and KT5823, specific inhibitors of guanylyl cyclase and protein kinase G (PKG), respectively, also blocked the stimulatory effect of Mn(+2) on LHRH release. These in vitro studies demonstrated that the hypothalamic mechanism of Mn(+2) action in adult males is by activation of the NOS/NO system, resulting in increases in cGMP and PKG and thus the secretion of LHRH from the nerve terminals. These results indicate Mn(+2) can cause LHRH release in adult males, and this action is discussed in relation to age, gender, as well as mechanistic and functional differences between adult and immature animals.

Age-dependent regulation of chromaffin cell proliferation by growth factors, dehydroepiandrosterone (DHEA), and DHEA sulfate

The adrenal gland comprises two endocrine tissues of distinct origin, the catecholamine-producing medulla and the steroid-producing cortex. The inner adrenocortical zone, which is in direct contact with the adrenomedullary chromaffin cells, produces dehydroepiandrostendione (DHEA) and DHEA sulfate (DHEAS). These two androgens exhibit potential effects on neurogenesis, neuronal survival, and neuronal stem cell proliferation. Unlike the closely related sympathetic neurons, chromaffin cells are able to proliferate throughout life. The aim of this study was to investigate the effect of DHEA and DHEAS on proliferation of bovine chromaffin cells from young and adult animals. We demonstrated that graded concentrations of leukemia inhibitory factor induced proliferation of chromaffin cells from young animals, whereas EGF had no effect. On the contrary, EGF increased the cell proliferation in cells from adult animals, whereas leukemia inhibitory factor was inactive. In both cases, DHEA decreased the proliferative effect induced by the growth factors. Surprisingly, DHEAS enhanced, in a dose-dependent-manner, the effect of growth factors on proliferation in cells from adult animals but not from young animals. Flutamide, ICI 182,780, and RU 486 had no effect on the action of DHEA or DHEAS on chromaffin cell proliferation. These data show that DHEA and its sulfated form, DHEAS, differentially regulate growth-factor-induced proliferation of bovine chromaffin cells. In addition, the sensitivity of chromaffin cells to different growth factors is age-dependent. Furthermore, these two androgens may act through a receptor other than the classical steroid receptors.

Endocannabinoids in TNF-alpha and ethanol actions

During marijuana and alcohol consumption as well as during inflammation the reproductive axis is inhibited, mainly through the inhibition of luteinizing hormone-releasing hormone release. In male rats, this inhibitory effect is mediated, at least in part, by the activation of hypothalamic cannabinoid type 1 receptors (CB1). During inflammation, this activation of the endocannabinoid system seems to be mediated by an increase in TNF-alpha production followed by anandamide augmentations, similarly the effect of intragastric administration of ethanol (3 g/kg) seems to be due to an increase in anandamide. On the other hand, a number of different actions mediated by the endocannabinoid system in various organs and tissues have been described. Both cannabinoid receptors, CB1 and CB2, are localized in the submandibular gland where they mediate the inhibitory effect of intrasubmandibular injections of the endocannabinoid anandamide (6 x 10(-5)M) on salivary secretion. Lipopolysaccharide (5 mg/kg/3 h) injected intraperitoneally and ethanol (3 g/kg/1 h) injected intragastrically inhibited the salivary secretion induced by the sialogogue metacholine; this inhibitory effect was blocked by CB1 and/or CB2 receptor antagonists. Similar to the hypothalamus, these effects seem to be mediated by increased anandamide. In summary, similar mechanisms mediate the inhibitory actions of endocannabinoids and cannabinoids in both hypothalamus and submandibular gland during drug consumption and inflammation.

Manganese acts centrally to activate reproductive hormone secretion and pubertal development in male rats

Manganese (Mn) is an important element for normal growth and reproduction. Because Mn accumulates in the hypothalamus and is capable of stimulating puberty-related hormones in female rats, we assessed whether this metal could cause similar effects in male rats. We have demonstrated that MnCl2, when administered acutely into the third ventricle of the brain, acts dose dependently to stimulate luteinizing hormone (LH) release. Furthermore, there was a dose dependent stimulation in the secretion of LH-releasing hormone (LHRH) from the medial basal hypothalamus in vitro, and administration of an LHRH receptor antagonist in vivo blocks Mn-induced LH release. To assess potential chronic effects of the metal, male pups were supplemented with 10 or 25 mg MnCl2 per kg by gastric gavage from day 15 until days 48 or 55, at which times developmental signs of spermatogenesis were assessed. Results demonstrate that while significant effects were not observed with the 10 mg/kg dose, the animals receiving the 25 mg/kg dose showed increased LH (p<0.05), FSH (p<0.01) and testosterone (p<0.01) levels at 55 days of age. Furthermore, there was a concomitant increase in both daily sperm production (p<0.05) and efficiency of spermatogenesis (p<0.05), demonstrating a Mn-induced acceleration in spermatogenesis. Our results suggest Mn is a stimulator of prepubertal LHRH/LH secretion and may facilitate the normal onset of male puberty. These data also suggest that the metal may contribute to male precocious pubertal development should an individual be exposed to low but elevated levels of Mn too early in life.

The Role of Toll-like Receptors in the Immune-Adrenal Crosstalk

Sepsis and septic shock remain major health concerns worldwide, and rapid activation of adrenal steroid release is a key event in the organism's first line of defense during this form of severe illness. Toll-like receptors (TLRs) are critical in the early immune response upon bacterial infection, and recent data from our lab demonstrate a novel link between the innate immune system and the adrenal stress response mediated by TLRs. Glucocorticoids and TLRs regulate each other in a bidirectional way. Bacterial toxins acting through TLRs directly activate adrenocortical steroid release. TLR-2 and TLR-4 are expressed in human and mice adrenals and TLR-2 deficiency is associated with an impaired glucocorticoid response. Furthermore, TLR-2 deficiency in mice is associated with marked cellular alterations in adrenocortical tissue. TLR-2-deficient mice have an impaired adrenal corticosterone release following inflammatory stress induced by bacterial cell wall compounds. This defect appears to be associated with a decrease in systemic and intraadrenal cytokine expression. In conclusion, TLRs play a crucial role in the immune-adrenal crosstalk. This close functional relationship needs to be considered in the treatment of inflammatory diseases requiring an intact adrenal stress response.

Chronology of Advances in Neuroendocrine Immunomodulation

This review documents the remarkable progress over the last 50 years of our knowledge of the control of anterior pituitary hormone release and synthesis by a family of peptidic releasing and inhibiting hormones, synthesized in hypothalamic neurons and released into the hypophysial portal vessels. These vessels transport them to the anterior pituitary, where they stimulate release and synthesis of pituitary hormones or inhibit these processes. In general, there are at least two hypothalamic hormones for each pituitary hormone-vasopressin and corticotrophin-releasing hormone (CRH) for adrenocorticotropin hormone (ACTH) and growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GIH) for growth hormone (GH). Some of these hormones have extrapituitary action: for example, luteinizing hormone-releasing hormone (LHRH) stimulates mating behavior. High doses of LHRH have an inhibitory action on the growth of prostate cancer. Proinflammatory and anti-inflammatory cytokines act not only in the brain, but also on the pituitary and peripheral tissues. All of these transmitters are controlled by neuronal transmitters. We anticipate further rapid progress and clinical application of these transmitters and the discovery of new ones.

Inhibition of salivary secretion by activation of cannabinoid receptors

It is known that marijuana use decreases saliva secretion. Therefore, we hypothesized that cannabinoid receptors (CBs) are located in salivary glands to mediate that effect. In these experiments, we used the submandibular gland (SMG) of male rats, which is one of the major salivary glands. Mammalian tissues contain at least two types of CBs, CB1 and CB2, mainly located in the nervous system and peripheral tissues, respectively. Both receptors are coupled to Gi protein and respond by inhibiting the activity of adenylyl cyclase. We demonstrated that both CB1 and CB2 are present in the SMG, each showing specific localizations. The best-known endocannabinoid is anandamide (AEA), which binds with high affinity to CB1 and CB2. We showed that AEA markedly reduced forskolin-induced increase of cAMP content in vitro. This effect was blocked by AM251 and AM630 (CB1 and CB2 antagonists, respectively), indicating that both receptors are implicated in SMG physiology. In addition, we showed that AEA injected intraglandularly to anesthetized rats inhibited norepinephrine (NE)- and methacholine (MC)-stimulated saliva secretion in vivo and that both AM251 or AM630 prevented the inhibitory action of AEA. Also, the intraglandular injection of AM251 increased saliva secretion induced by lower doses of NE or MC. This increase was synergized after coinjection with AM630. Therefore, we concluded that AEA decreases saliva secretion in the SMG acting through CB1 and CB2 receptors.

IL-1 resets glucose homeostasis at central levels

Administration of IL-1beta results in a profound and long-lasting hypoglycemia. Here, we show that this effect can be elicited by endogenous IL-1 and is related to not only the capacity of the cytokine to increase glucose uptake in peripheral tissues but also to mechanisms integrated in the brain. We show that (i) blockade of IL-1 receptors in the brain partially counteracted IL-1-induced hypoglycemia; (ii) peripheral administration or induction of IL-1 production resulted in IL-1beta gene expression in the hypothalamus of normal and insulin-resistant, leptin receptor-deficient, diabetic db/db mice; (iii) IL-1-treated normal and db/db mice challenged with glucose did not return to their initial glucose levels but remained hypoglycemic for several hours. This effect was largely antagonized by blockade of IL-1 receptors in the brain; and (iv) when animals with an advanced Type II diabetes were treated with IL-1 and challenged with glucose, they died in hypoglycemia. However, when IL-1 receptors in the brains of these diabetic mice were blocked, they survived, and glucose blood levels approached those that these mice had before IL-1 administration. The prolonged hypoglycemic effect of IL-1 is insulin-independent and develops against increased levels of glucocorticoids, catecholamines, and glucagon. These findings, together with the present demonstration that this effect is integrated in the brain and is paralleled by IL-1beta expression in the hypothalamus, indicate that this cytokine can reset glucose homeostasis at central levels. Such reset, along with the peripheral actions of the cytokine, would favor glucose uptake by immune cells during inflammatory/immune processes.

The nitric oxide theory of aging revisited

Bacterial and viral products, such as bacterial lipopolysaccharide (LPS), cause inducible (i) NO synthase (NOS) synthesis, which in turn produces massive amounts of nitric oxide (NO). NO, by inactivating enzymes and leading to cell death, is toxic not only to invading viruses and bacteria, but also to host cells. Injection of LPS induces interleukin (IL)-1beta, IL-1alpha, and iNOS synthesis in the anterior pituitary and pineal glands, meninges, and choroid plexus, regions outside the blood-brain barrier. Thereafter, this induction occurs in the hypothalamic regions (such as the temperature-regulating centers), paraventricular nucleus (releasing and inhibiting hormone neurons), and the arcuate nucleus (a region containing these neurons and axons bound for the median eminence). Aging of the anterior pituitary and pineal with resultant decreased secretion of pituitary hormones and the pineal hormone melatonin, respectively, may be caused by NO. The induction of iNOS in the temperature-regulating centers by infections may cause the decreased febrile response in the aged by loss of thermosensitive neurons. NO may play a role in the progression of Alzheimer's disease and parkinsonism. LPS similarly activates cytokine and iNOS production in the cardiovascular system leading to coronary heart disease. Fat is a major source of NO stimulated by leptin. As fat stores increase, leptin and NO release increases in parallel in a circadian rhythm with maxima at night. NO could be responsible for increased coronary heart disease as obesity supervenes. Antioxidants, such as melatonin, vitamin C, and vitamin E, probably play important roles in reducing or eliminating the oxidant damage produced by NO.

Toll-like receptor 4 plays a crucial role in the immune-adrenal response to systemic inflammatory response syndrome

Sepsis and septic shock are leading killers in the noncoronary intensive care unit, and they remain worldwide health concerns. The initial host defense against bacterial infections involves Toll-like receptors (TLRs), which detect and respond to microbial ligands. In addition, a coordinated response of the adrenal and immune systems is crucial for survival during severe inflammation. Previously, we demonstrated a link between the innate immune system and the endocrine stress response involving TLR-2. Like TLR-2, TLR-4 is also expressed in human and mouse adrenals. In the present work, by using a low dose of LPS to mimic systemic inflammatory response syndrome, we have revealed marked cellular alterations in adrenocortical tissue and an impaired adrenal corticosterone response in TLR-4-/- mice. Our findings demonstrate that TLR-4 is a key mediator in the crosstalks between the innate immune system and the endocrine stress response. Furthermore, TLR polymorphisms could contribute to the underlying mechanisms of impaired adrenal stress response in patients with bacterial sepsis.

Role of ammonia and nitric oxide in the decrease in plasma prolactin levels in prehepatic portal hypertensive male rats

OBJECTIVES

Since very little is known about neuroendocrine changes that occur in portal-systemic hepatic encephalopathy, we studied plasma prolactin (PRL) levels and the involvement of hyperammonemia, nitric oxide (NO) and dopaminergic and adrenergic systems in the control of this hormone secretion in a male rat model of prehepatic portal hypertension (PH).

METHODS

We conducted in vivo studies to determine plasma ammonia and PRL levels. Dopamine (DA), dihydroxyphenylacetic acid (DOPAC), epinephrine and norepinephrine content in medial basal hypothalamus (MBH) and anterior pituitary (AP) were measured. In addition, NO synthase (NOS) activity and protein expression were evaluated in APs. In in vitro studies, the APs from intact rats were incubated with different doses of ammonia and PRL secretion was determined. In ex vivo studies, the APs from normal and PH rats were incubated in the presence of ammonia and/or a NOS inhibitor, NG-nitro-L-arginine-methyl ester (L-NAME) and PRL secretion was determined.

RESULTS

PH rats had a significant increase in plasma ammonia levels (p < 0.001) and a decrease in plasma PRL levels (p < 0.05). Neither DA nor DOPAC content or DOPAC/DA ratios were modified in both MBH and APs; however, we observed a significant increase in norepinephrine content in both MBH and AP (p < 0.001 and p < 0.05, respectively) and a significant increase in epinephrine in APs (p < 0.001). Moreover, PH produced an increase in NOS activity (p < 0.01) and NOS protein expression (p < 0.0001) in APs. The ammonia (100 microM) significantly reduced PRL secretion from APs in vitro (p < 0.05). The presence of L-NAME, an inhibitor of NOS, abrogated the inhibitory effect of ammonia on PRL secretion from APs from control and PH rats.

CONCLUSIONS

We found that plasma PRL levels were decreased in PH rats probably due to the high ammonia levels. The central noradrenergic system could also mediate this decrease. Also, the increase in NOS activity and/or content in AP induced NO production that directly inhibited PRL secretion from the AP, without the participation of the dopaminergic system.

Decrease in salivary secretion by radiation mediated by nitric oxide and prostaglandins

OBJECTIVE

In the present work, we evaluated the effect of exposing the submandibular glands (SMG) to radiation, studying different functional parameters such as salivary secretion, nitric oxide (NO) production, reactive oxygen species formation, prostaglandin (PGE) content and apoptosis.

METHODS

We irradiated rats in the head and neck region with a single dose of gamma-ray radiation of 15 Gy. Two hours after radiation, we measured norepinephrine-induced salivary secretion. After that, the SMG were dissected, and in this tissue, we measured the activity of NO synthase (NOS), the PGE content, the amount of reactive oxygen species, apoptotic cells and mitochondrial inducible NOS (iNOS) expression.

RESULTS

We found that radiation decreased salivary secretion when 10 and 30 microg/kg of norepinephrine was administered via the right femoral vein. We observed that iNOS activity was reduced and PGE content increased after radiation in SMG, indicating that NO and PGEs may participate in salivary secretion. The expression of mitochondrial NOS was increased after radiation leading to the formation of large amounts of NO that acts as a proapoptotic signal. In fact, we observed an augmentation in apoptotic cells. In this study, we also observed an increase in lipid peroxidation induced by radiation that may contribute to tissue damage.

CONCLUSIONS

Our results indicate that radiation induced a decrease in salivary secretion and SMG iNOS activity, meanwhile the PGE content, the lipid peroxidation and apoptosis increased in the tissue. These modifications decrease salivary secretion.

Epidermal growth factor prevents prepartum luteolysis in the rat

We have previously reported that intrauterine (i/u) administration of epidermal growth factor (EGF 500 ng) on day (d) 21 of pregnancy delayed 19.0 +/- 0.6 h the onset of labor. Progesterone (P) is secreted by ovarian corpora lutea (CL) throughout gestation in the rat. Prepartum CL regression due to increased uterine cyclooxygenase I and prostaglandin F(2alpha) results in P withdrawal followed by labor. The aims of the present work were (i) to study whether EGF delayed-onset of labor was mediated by a mechanism that prevented CL regression; (ii) to determine amniotic fluid (AF) EGF in pregnant rats. Rats on d21 of pregnancy received i/u EGF (500 ng) and were killed 0, 4, 8, 12, 24, and 48 h later. Control AF from rats on d13 and 18-22 of pregnancy was obtained. EGF decreased uterine prostaglandin F(2alpha) synthesis 8 h after treatment. Twelve hours after EGF injection, P reached its highest serum level and uterine cyclooxygenase I expression was undetectable. CL from rats killed 8 and 12 h after EGF were similar to those from rats on d13 of pregnancy, when serum P is maximum. EGF in AF increased throughout gestation, reached a maximum on d21, and decreased before the onset of labor. We suggest that the effect of EGF on the onset of labor was mediated by an early effect on the uterus that prevented prepartum CL regression.

The rapid release of corticosterone from the adrenal induced by ACTH is mediated by nitric oxide acting by prostaglandin E2

The adrenal cortex is a major stress organ in mammals that reacts rapidly to a multitude of external and internal stressors. Adrenocorticotropin (ACTH) is the main stimulator of the adrenal cortex, activating corticosteroid synthesis and secretion. We evaluated the mechanism of action of ACTH on adrenals of male rats, preserving the architecture of the gland in vitro. We demonstrated that both sodium nitroprusside (NP), a nitric oxide (NO) donor, and ACTH stimulate corticosterone release. NO mediated the acute response to ACTH because Nomega-nitro-l-arginine methyl ester, a NO synthase inhibitor, and hemoglobin, a NO scavenger, blocked the stimulation of corticosterone release induced by ACTH. NP stimulated prostaglandin E release, which in turn stimulated corticosterone release from the adrenal. Additionally, indomethacin, which inhibits cyclooxygenase, and thereby, prostaglandin release, prevented corticosterone release from the adrenal induced by both NP and ACTH, demonstrating that prostaglandins mediate acute corticosterone release. Corticosterone content in adrenals after incubation with ACTH or NP was lower than in control glands, indicating that any de novo synthesis of corticosterone during this period was not sufficient to keep up with the release of the stored hormone. The release induced by ACTH or NP depleted the corticosterone content in the adrenal by approximately 40% compared with the content of glands incubated in buffer. The mechanism of rapid release is as follows: NO produced by NO synthase activation by ACTH activates cyclooxygenase, which generates PGE(2), which in turn releases corticosterone stored in microvesicles and other organelles.

Impaired adrenal stress response in Toll-like receptor 2-deficient mice

Septicemia is one of the major health concerns worldwide, and rapid activation of adrenal steroid release is a key event in the organism's first line of defense during this form of severe illness. The family of Toll-like receptors (TLRs) is critical in the early immune response upon bacterial infection, and TLR polymorphisms are frequent in humans. Here, we demonstrate that TLR-2 deficiency in mice is associated with reduced plasma corticosterone levels and marked cellular alterations in adrenocortical tissue. TLR-2-deficient mice have an impaired adrenal corticosterone release after inflammatory stress induced by bacterial cell wall compounds. This defect appears to be mediated by a decrease in systemic and intraadrenal cytokine expression, including IL-1, tumor necrosis factor alpha, and IL-6. Our data demonstrate a link between the innate immune system and the endocrine stress response. The critical role of TLR-2 in adrenal glucocorticoid regulation needs to be considered in patients with inflammatory disease.

The inhibitory effect of anandamide on luteinizing hormone-releasing hormone secretion is reversed by estrogen

Because Delta-9-tetrahydrocannabinol (THC) inhibited luteinizing hormone-releasing hormone (LHRH) in male rats, we hypothesized that the endocannabinoid, anandamide (AEA), would act similarly. AEA microinjected intracerebroventricularly (i.c.v.) decreased plasma luteinizing hormone (LH) at 30 min in comparison to values in controls (P < 0.001). The cannabinoid receptor 1 (CB1-r)-specific antagonist, [N-(piperidin-1-yl)-1-(2,4-dichlorophenyl)-5-(4-chlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] (AM251), produced a significant elevation in plasma LH (P < 0.01). AEA (10(-9) M) decreased LHRH release from medial basal hypothalami incubated in vitro. These results support the concept that endogenous AEA inhibits LHRH followed by decreased LH release in male rats. In ovariectomized (OVX) female rats, AEA i.c.v. also inhibited LH release, but in this case AM251 had an even greater inhibitory effect than AEA. In vitro, AEA had no effect on LHRH in OVX rats. It seems that endogenous AEA inhibits LHRH followed by decreased LH release in OVX rats but that AM251 has an inhibitory action in this case. In striking contrast, in OVX, estrogen-primed (OVX-E) rats, AEA i.c.v. instead of decreasing LH, increased its release. This effect was completely blocked by previous injection of AM251. When medial basal hypothalami of OVX-E rats were incubated, AEA increased LHRH release. The synthesized AEA was higher in OVX-E rats than in OVX and males, indicating that estrogen modifies endocannabinoid levels and effects. The results are interpreted to mean that sex steroids have profound effects to modify the response to AEA. It inhibits LHRH and consequently diminishes LH release in males and OVX females, but stimulates LHRH followed by increased LH release in OVX-E-primed rats.

Toll-like receptor 2 and Toll-like receptor 4 expression in human adrenals

Toll-like receptors (TLRs) are key elements in the innate immune response, functioning as pattern-recognition receptors for the detection and response to endotoxins and other microbial ligands. Inflammatory cytokines play an important role in the activation of the hypothalamic-pituitary-adrenal HPA axis during inflammation and sepsis. The newly recognized major role of TLR2 and TLR4 and the adrenal stress response during critical illnesses such as inflammation and sepsis demand comprehensive analysis of their interactions. Therefore, we analyzed TLR2 and TLR4 expression in human adrenal glands. Western blot analysis demonstrated the expression of TLR2 and TLR4 in the human adrenocortical cell line NCI-H295. Immunohistochemical analysis of normal human adrenal glands revealed TLR2 and TLR4 expression in the adrenal cortex, but not in the adrenal medulla. Considering the crucial role of the HPA axis and the innate immune response during acute sepsis or septic shock, elucidating the functional interaction of these systems should be of great clinical relevance.

Actions of ethanol on epidermal growth factor receptor activated luteinizing hormone secretion

OBJECTIVE

Activation of the epidermal growth factor receptor (EGF-R) stimulates prepubertal luteinizing hormone-releasing hormone (LHRH) release, which in turn induces luteinizing hormone (LH) secretion. Although ethanol (ETOH) diminishes LHRH secretion and delays the onset of female puberty, its actions following EGF-R activation are unknown. We therefore investigated the effects of ETOH on EGF-induced LHRH and LH release, both in vivo and in vitro.

METHOD

Basal blood samples were taken every 15 minutes from immature female rats, which then received ETOH (3 g/kg) or saline by gastric gavage. After a 90-minute ETOH absorption period, a single blood sample was drawn from each rat. Finally, EGF (200 ng/3 microl) was injected into the third ventricle of all animals and postinjection samples were drawn every 15 minutes. A similar experimental design was performed except no blood samples were taken. After ETOH exposure, EGF was administered, and 45 minutes later the animals were killed and their medial basal hypothalamus and pituitary were removed and analyzed for EGF-R and cyclooxygenase (COX) 1 and 2 by western blot analysis. For in vitro experiment, median eminence fragments from immature female rats were exposed to ETOH in a static incubation system, and prostaglandin-E, (PGE2) and LHRH were measured.

RESULTS

EGF stimulated LH release, and this release was blunted (p < .05) by ETOH. Western blot analysis revealed that ETOH did not alter the EGF-R protein levels in the hypothalamus. ETOH blocked EGF-induced PGE2 and LHRH released from isolated median eminences. EGF administration increased both COX-1 (p < .001) and COX-2 (p < .01), but both enzymes were blocked by ETOH.

CONCLUSIONS

The ETOH-induced decrease in EGF-stimulated LH release is due to a reduction in the formation of hypothalamic PGE2 and, subsequently, suppressed LHRH release.

Alcohol inhibits luteinizing hormone-releasing hormone release by activating the endocannabinoid system

We hypothesized that ethanol (EtOH) might act through the endocannabinoid system to inhibit luteinizing hormone-releasing hormone (LHRH) release. Therefore, we examined the mechanism by which EtOH and anandamide (AEA), an endogenous cannabinoid, inhibit LHRH release from incubated medial basal hypothalamic explants. In previous work, we demonstrated that EtOH inhibits the N-methyl-D-aspartic acid-stimulated release of LHRH by increasing the release of two neurotransmitters: beta-endorphin and gamma-aminobutyric acid (GABA). In the present work, bicuculline, a GABAergic antagonist, completely prevented the inhibition of AEA (10(-9)M) on N-methyl-D-aspartic acid-induced LHRH release, but naltrexone, a micro-opioid receptor antagonist, had no effect. AEA also significantly increased GABA release but had no effect on beta-endorphin release. Therefore, AEA could inhibit LHRH release by increasing GABA but not beta-endorphin release. Because EtOH and AEA acted similarly to inhibit LHRH release, we investigated whether both substances would affect the adenylate cyclase activity acting through the same GTP-coupled receptors, the cannabinoid receptors 1 (CB1-rs). AEA and EtOH (10(-1)M) reduced the forskolin-stimulated accumulation of cAMP, but AM251, a specific antagonist of CB1-r, significantly blocked that inhibition. Additionally we investigated whether CB1-r is involved in the inhibition of LHRH by EtOH and AEA. AEA and EtOH reduced forskolin-stimulated LHRH release, but AM251 significantly blocked that inhibition. Also, we demonstrated that EtOH did not act by increasing AEA synthase activity to inhibit LHRH release in our experimental conditions. Therefore, our results indicate that EtOH inhibits the release of LHRH acting through the endocannabinoid system.

Alpha-melanocyte-stimulating hormone through melanocortin-4 receptor inhibits nitric oxide synthase and cyclooxygenase expression in the hypothalamus of male rats

There is evidence that alpha-melanocyte-stimulating hormone (alpha-MSH) has immunomodulatory and anti-inflammatory actions within the brain. In this study, we tested whether these actions are due to inhibition of the synthesis of nitric oxide (NO) and prostaglandins induced by lipopolysaccharide (LPS). Since melanocortin subtype MC4 receptor has been detected in the hypothalamus, we investigated the effect of central administration of alpha-MSH and HS024 (a selective MC4 receptor antagonist) on the gene expression of inducible, neuronal and endothelial NO synthase (iNOS, nNOS and eNOS) and on cyclooxygenase (COX-1 and COX-2) expression in the mediobasal hypothalamus (MBH) of LPS-treated male Wistar rats. Peripheral administration of LPS (250 microg/rat, 3 h) induced iNOS and COX-2 gene expression in the MBH. This stimulatory effect was reduced by alpha-MSH (3 nmol/rat) injected 30 min before LPS. alpha-MSH and HS024 (1 nmol/rat) alone had no effect on iNOS and COX-2 expression. The action of alpha-MSH on LPS-induced iNOS and COX-2 mRNA levels was not observed in the presence of HS024, suggesting that MC4-R may be involved in the modulatory effect of alpha-MSH. None of these treatments produced any modifications in nNOS, eNOS and COX-1 expression in MBH. The increase in serum corticosterone levels induced by LPS was attenuated by alpha-MSH. Both LPS and alpha-MSH decreased serum LH and prolactin levels. HS024 failed to modify the inhibitory effects of LPS and alpha-MSH on prolactin release but reverted the effect of LPS on LH secretion, indicating that MC4-R activation may be involved in the effects of alpha-MSH on LH secretion in male rats. When we examined the in vitro effect of LPS (10 microg/ml) and LPS plus interferon-gamma (IFN-gamma, 100 ng/ml) on iNOS expression in MBH, an increase in iNOS mRNA levels was observed only in the presence of LPS + IFN-gamma. This stimulatory effect was attenuated in the presence of alpha-MSH (5 microM), which by itself had no effect. No changes were found in nNOS, eNOS, COX-1 or COX-2 expression. These results indicate that alpha-MSH reduces the induction of iNOS and COX-2 gene expression at the hypothalamic level during endotoxemia and suggest that endogenous alpha-MSH may exert an inhibitory tone on iNOS and COX-2 transcription via MC4 receptors acting as a local anti-inflammatory agent within the hypothalamus.

The role of nitric oxide (NO) in control of LHRH release that mediates gonadotropin release and sexual behavior

Nitric oxide (NO) plays a crucial role in reproduction at every level in the organism. In the brain, it activates the release of luteinizing hormone-releasing hormone (LHRH). The axons of the LHRH neurons project to the mating centers in the brain stem and by efferent pathways, evoke the lordosis reflex in female rats. In males, there is activation of NOergic terminals that release NO in the corpora cavernosa penis to induce erection by generation of cyclic guanosine monophosphate (cGMP). NO also activates the release of LHRH which reaches the pituitary and activates the release of gonadotropins by activating neural NO synthase (NOS) in the pituitary gland. Follicle stimulating hormone (FSH)RH selectively releases FSH also by activating NOS. Leptin releases LHRH by activating NOS to release FSH and LH with the same potency as LHRH. These actions are mediated by specific receptors on the gonadotropes for LHRH, FSHRH and leptin. The responsiveness of the pituitary is controlled by gonadal steroids. In the gonad, NO plays an important role inducing ovulation and in causing luteolysis; whereas in the reproductive tract, it relaxes uterine muscle via cGMP and constricts it by prostaglandins.

Effect of neurogenic stress and ethanol on nitric oxide synthase and cyclooxygenase activities in rat adrenals

Repeated restraint stress (RRS) in male rats activated the pituitary adrenal system, as indicated by increases in adrenal weight and plasma corticosterone concentration that were accompanied by a decrease in constitutive nitric oxide synthase (cNOS), but not inducible NOS (iNOS). iNOS activated cyclooxgenase, causing elevated prostaglandin E(2) (PGE(2)) and F(2 alpha) in the adrenals, but had no effect on lipoxygenase. Administration of ethanol (ETOH) was also associated with elevated adrenal weight and a slight increase in corticosterone coupled with a decrease in both cNOS and iNOS and PGs in the adrenal. When ETOH was administered together with RRS, a decrease in iNOS and PGE release was noted consequent to a reduction in iNOS. Thus, ETOH probably reduced RRS-induced adrenocorticotropic hormone release. Adrenals were incubated in vitro to further evaluate the role of NO in these processes. Results indicated that NO released by sodium nitroprusside increased corticosterone release presumably by activating guanylyl cyclase with production of cyclic guanosine monophosphate (cGMP), because although NO also increased PGE release, PGE(2) (10(-5)-10(-9) M) decreased corticosterone release, an effect that was highly significant at a concentration of 10(-7) M PGE(2). ETOH (100 mM) had no effect on corticosterone release and did not block the increase in corticosterone caused by NO; however, ETOH reduced PGE release into the medium and blocked PGE(2) release induced by NO. Consequently, NO activated corticosterone release not by PGs, but by activation of guanylyl cyclase and release of cGMP. PGs have a negative feedback to suppress corticosterone release.

Interaction among beta-endorphin, nitric oxide and prostaglandins during ovulation in rats

The aim of this study was to investigate the relationship between beta-endorphin and nitric oxide (NO) during the ovulatory process in rats. Immature rats were treated with equine chorionic gonadotrophin-hCG to induce ovulation. An intrabursal injection of beta-endorphin stimulated nitric oxide synthase (NOS) activity. This effect was completely reversed when naltrexone was co-injected with beta-endorphin. The stimulatory action of beta-endorphin on NOS activity was studied to determine whether it was exerted via prostaglandins. Treatment with prostaglandin E(2) (PGE(2)) completely reversed the beta-endorphin-induced stimulation of NOS activity. Moreover, intrabursal injection of meloxicam, an inhibitor of cyclooxygenase 2, increased NOS activity, but this effect was not altered by co-injection with beta-endorphin. The presence of both endothelial NOS (eNOS) and inducible NOS (iNOS) in the ovary at 10 h after hCG treatment was studied by western blot analysis. Local administration of beta-endorphin inhibited the expression of eNOS protein, whereas expression of iNOS protein was not detectable. Ovarian beta-endorphin content was diminished at 10 h after hCG injection. Treatment with prostaglandin synthesis inhibitors in vivo augmented the ovarian beta-endorphin content. In conclusion, these results indicate that beta-endorphin stimulates the activity of ovarian NOS indirectly by inhibiting prostaglandin production.

The effect of anandamide on prolactin secretion is modulated by estrogen

Recent research has revealed that endogenous cannabinoid receptors (CB1 and CB2) react with the active ingredient of marijuana, Delta(9)-tetrahydrocannabinol. Two endogenous ligands activate these receptors. The principal one, anandamide (AEA), activates CB1. AEA and CB1 are localized to various neurons within the brain. Because Delta(9)-tetrahydrocannabinol inhibited prolactin (Prl) secretion following its intraventricular injection into male rats, we hypothesized that AEA would have a similar effect. Estrogen modifies many hormonal responses and is known to increase Prl secretion. Therefore, we hypothesized that responses to intraventricular AEA would change depending on the gonadal steroid environment. Consequently, we evaluated the effects of lateral cerebral ventricular microinjection of AEA (20 ng) into male, ovariectomized (OVX), and estrogen-primed (OVX-E) rats. AEA decreased plasma Prl in male rats, had little effect in OVX females, and increased Prl in OVX-E rats. The results were at least partially mediated by changes in dopaminergic turnover, altering the inhibitory dopaminergic control of Prl release by the anterior pituitary gland. Thus, dopamine turnover was increased in the male rats and decreased significantly in OVX and in OVX-E rats. The changes in Prl may be caused not only by altered dopamine input to the anterior pituitary gland but also by effects of AEA on other transmitters known to alter Prl release. Importantly, in OVX-E rats, the elevated Prl release and the response to AEA were blocked by the AEA antagonist, indicating that AEA is a synaptic transmitter released from neurons that decrease inhibitory control of Prl release.

Steroid hormones augment nitric oxide synthase activity and expression in rat uterus

Nitric oxide (NO) is synthesized in a variety of tissues, including rat uterus, from L-arginine by NO synthase (NOS), of which there are three isoforms, namely neuronal, endothelial and inducible NOS (nNOS, eNOS and iNOS, respectively). Nitric oxide is an important regulator of the biology and physiology of the organs of the reproductive system, including the uterus. Some studies have shown increased variation in NO production and NOS expression during the oestrous cycle. However, the factors that regulate NO production in the uterus remain unclear. Therefore, in the present study, we investigated the effect of sex steroids on NOS expression and activity in the ovariectomized rat uterus. Ovariectomized rats received progesterone (4 mg per rat) or 17β-oestradiol (1 μg per rat). All rats were killed 18 h after treatment. Both progesterone and oestradiol were able to augment NOS activity. The effect of oestradiol was abolished by pre-incubation with 500 μM aminoguanidine, an iNOS inhibitor, or by coadministration of oestradiol with 3 mg kg−1 dexamethasone, but the effect of progesterone was not affected by these treatments. Uterine nNOS, eNOS and iNOS protein levels were assessed using Western blots. Ovariectomized rat uteri expressed iNOS and eNOS. Progesterone increased the expression of eNOS and iNOS, whereas oestradiol increased iNOS expression only. These results suggest that oestradiol and progesterone are involved in the regulation of NOS expression and activity during pregnancy and implantation in the rat.

The effect of D-aspartate on luteinizing hormone-releasing hormone, alpha-melanocyte-stimulating hormone, GABA and dopamine release

Since D-aspartate stimulates prolactin and LH release, our objective was to determine whether D-aspartate modifies the release of hypothalamic and posterior pituitary factors involved in the control of their secretion and whether its effects on these tissues are exerted through NMDA receptors and mediated by nitric oxide. In the hypothalamus, D-aspartate stimulated luteinizing hormone-releasing hormone (LHRH), alpha-melanocyte-stimulating hormone (alpha-MSH) and GABA release and inhibited dopamine release through interaction with NMDA receptors. It increased nitric oxide synthase (NOS) activity, and its effects on LHRH and hypothalamic GABA release were blunted when NOS was inhibited. In the posterior pituitary gland, D-aspartate inhibited GABA release but had no effect on dopamine or alpha-MSH release. We report that D-aspartate differentially affects the release of hypothalamic and posterior pituitary factors involved in the regulation of pituitary hormone secretion.