Assessment of Nutritional Status of Iodine Through Urinary Iodine Screening Among Local Children and Adolescents After the Fukushima Daiichi Nuclear Power Plant Accident

BACKGROUND

Iodine deficiency is an important modifier of the risk of thyroid cancer following irradiation. However, little information is available on the prevalence of iodine deficiency in Fukushima and its surroundings after the Fukushima Daiichi nuclear power plant accident that occurred in March 2011.

METHODS

In order to assess urinary iodine concentrations (UIC) and the prevalence of iodine deficiency and to elucidate any associations between demographic characteristics and UIC levels among children and adolescents aged ≤18 years at the time of the accident in Fukushima Prefecture and its surroundings, the data on voluntary UIC testing conducted by Hirata Central Hospital, Fukushima, were evaluated.

RESULTS

A total of 4410 children and adolescents with a median age of 10 years at examination underwent UIC testing between October 2012 and October 2015. Calculated for all the participants, the median UIC level was 204 μg/L (range 25-21,100 μg/L). There were 133 (3.0%), 732 (16.6%), and 1472 (33.4%) participants with UIC levels of <50, <100, or ≥300 μg/L, respectively. Based on the World Health Organization criteria for nutritional iodine status, no participants were severely iodine deficient (<20 μg/L), but 16.6% of the population were mildly (50-100 μg/L) or moderately (20-50 μg/L) iodine deficient. While no significant difference in UIC was noted between those who did and did not increase dietary iodine intake after the accident (p = 0.93), there were significant differences by year (p < 0.01), school level (p < 0.001), and residential area at the time of the accident (p < 0.001).

CONCLUSIONS

This study demonstrates that the children and adolescents examined had a sufficient amount of iodine during the period 1.5-4.5 years after the nuclear accident. In addition to the differences in the scale and the countermeasures undertaken between the Fukushima and Chernobyl accidents, differences in dietary iodine intake might have played an additional role in resulting in the reportedly different radiation doses to the thyroid between the two nuclear accidents.

The thyroid status of children and adolescents in Fukushima Prefecture examined during 20-30 months after the Fukushima nuclear power plant disaster: a cross-sectional, observational study

Background

A possible increase in thyroid cancer in the young represents the most critical health problem to be considered after the nuclear accident in Fukushima, Japan (March 2011), which is an important lesson from the Chernobyl disaster (April 1986). Although it was reported that childhood thyroid cancer had started to increase 3–5 yr after the Chernobyl accident, we speculate that the actual period of latency might have been shorter than reported, considering the delay in initiating thyroid surveillance in the then Soviet Union and also the lower quality of ultrasonographic testing in the 1980s. Our primary objectives in the present study were to identify any possible thyroid abnormality in young Fukushima citizens at a relatively early timepoint (20–30 months) after the accident, and also to strive to find a possible relationship among thyroid ultrasonographic findings, thyroid-relevant biochemical markers, and iodine-131 ground deposition in the locations of residence where they stayed during very early days after the accident.

Methods and Findings

This is a cross-sectional study. We targeted the Fukushima residents who were 18 yr old or younger (including fetuses) at the time of the accident. Our examinations comprised a questionnaire, thyroid ultrasonography, thyroid-related blood tests, and urinary iodine measurement. We analyzed a possible relationship among thyroid ultrasonographic findings (1,137 subjects), serum hormonal data (731 subjects), urinary iodine concentrations (770 subjects), and iodine-131 ground deposition (1,137 subjects). We did not find any significant relationship among these indicators, and no participant was diagnosed to contract thyroid cancer.

Conclusions

At the timepoint of 20–30 months after the accident, we did not confirm any discernible deleterious effects of the emitted radioactivity on the thyroid of young Fukushima residents. This is the first report in English detailing the thyroid status of young Fukushima residents after the nuclear disaster.

Limited internal radiation exposure associated with resettlements to a radiation-contaminated homeland after the Fukushima Daiichi nuclear disaster

Resettlement to their radiation-contaminated hometown could be an option for people displaced at the time of a nuclear disaster; however, little information is available on the safety implications of these resettlement programs. Kawauchi village, located 12-30 km southwest of the Fukushima Daiichi nuclear power plant, was one of the 11 municipalities where mandatory evacuation was ordered by the central government. This village was also the first municipality to organize the return of the villagers. To assess the validity of the Kawauchi villagers' resettlement program, the levels of internal Cesium (Cs) exposures were comparatively measured in returnees, commuters, and non-returnees among the Kawauchi villagers using a whole body counter. Of 149 individuals, 5 villagers had traceable levels of Cs exposure; the median detected level was 333 Bq/body (range, 309-1050 Bq/kg), and 5.3 Bq/kg (range, 5.1-18.2 Bq/kg). Median annual effective doses of villagers with traceable Cs were 1.1 x 10(-2) mSv/y (range, 1.0 x 10(-2)-4.1 x 10(-2) mSv/y). Although returnees had higher chances of consuming locally produced vegetables, Cochran-Mantel-Haenszel test showed that their level of internal radiation exposure was not significantly higher than that in the other 2 groups (p=0.643). The present findings in Kawauchi village imply that it is possible to maintain internal radiation exposure at very low levels even in a highly radiation-contaminated region at the time of a nuclear disaster. Moreover, the risks for internal radiation exposure could be limited with a strict food control intervention after resettlement to the radiation-contaminated village. It is crucial to establish an adequate number of radio-contaminated testing sites within the village, to provide immediate test result feedback to the villagers, and to provide education regarding the importance of re-testing in reducing the risk of high internal radiation exposure.

Leukemia inhibitory factor induces the chemomigration of immortalized gonadotropin-releasing hormone neurons through the independent activation of the Janus kinase/signal transducer and activator of transcription 3, mitogen-activated protein kinase/extracellularly regulated kinase 1/2, and phosphatidylinositol 3-kinase/Akt signaling pathways

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine of the IL-6 superfamily. LIF acts through a cell-surface receptor complex formed by two subunits, the specific LIF receptor beta (LIFRbeta) and the glycoprotein 130. Little is known about LIF involvement in modulating the neuroendocrine circuitry governing the reproductive function and, specifically, the development of GnRH-secreting neurons. In the present study, we evaluated the effect of LIF on the in vitro migration of GN11 cells, a model of immature and migratory GnRH neurons, and the signaling pathways involved in this process. GN11 cells expressed both LIFRbeta and glycoprotein 130 subunits. Exposure of GN11 cells to 100 ng/ml LIF resulted in activation of the Janus kinases (Jaks)/signal transducer and activator of transcription 3, MAPK/ERK1/2, and phosphatidylinositol 3-kinase/protein kinase B/Akt pathways. The selective inhibition of Jaks, MAPK kinase, and phosphatidylinositol 3-kinase indicated that these signaling pathways were activated independently by LIF and that Jak2 is not the main kinase involved in LIF signaling. Exposure of GN11 cells to LIF for 3 h induced a concentration-dependent chemotactic response, with a plateau at 100 ng/ml LIF. LIF was also found to induce chemokinesis of GN11 cells. Furthermore, LIF-promoted GN11 migration was the result of the partial and independent contribution of all the three signaling pathways activated by LIF. The present data, together with the observation that LIF and LIFRbeta are expressed prenatally in the mouse nasal compartment, would suggest that LIF might participate in the migration of GnRH neurons.

NMDA and group I metabotropic glutamate receptors activation modulates substance P release from the arcuate nucleus and median eminence

Glutamate participates in the regulation of secretion of several neuropeptides, including substance P (SP). Glutamate acts through ionotropic (iGluR) and metabotropic (mGluR) receptors. We have investigated whether glutamate receptor agonists and antagonists could affect SP release from the arcuate nucleus and the median eminence (ARC/ME). An increase in SP-like immunoreactivity (SP-LI) release from ARC/ME was induced by glutamate and N-methyl-D-aspartate (NMDA). This increase was prevented by D-(-)-2-amino-5-phosphono pentanoic acid (DAP5) (0.1mM), a specific NMDA antagonist and by (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) (0.1 mM), a selective antagonist of group I mGluR. The selective non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3(1H-4H)-dione (DNQX) (0.1mM) and (RS)-alpha-methyl-4-tetrazolylphenylglycine (MTPG) (0.1 mM), a group II and III mGluRs antagonist, did not affect the stimulatory effect of glutamate. A group I selective agonist, (S)-3,5-dihydroxyphenylglycine (DHPG) induced a significant increase in SP-LI release. Supporting the participation of nitric oxide (NO) in the effect of glutamate on SP-LI release, NAME (0.5 mM), a NO synthase inhibitor, reduced the glutamate-induced increase in SP-LI release from ARC/ME. Similarly, glutamate did not induce an increase in SP-LI release in the presence of meloxicam (0.1 mM) (a cyclooxygenase-2 (COX-2) specific inhibitor) indicating that prostaglandins production may also be involved in the glutamate effect. These data indicate that glutamate increases SP-LI release from the ARC/ME by acting through NMDA and group I mGluRs in the male rat. This stimulatory effect could be mediated by nitric oxide and prostaglandin production.

Central thyrotropin-releasing hormone increases hepatic cyclic AMP through vagal-cholinergic and prostaglandin-dependent pathways in rats

Central neuropeptides play roles in many physiologic regulations through the autonomic nervous system. We have demonstrated that central thyrotropin-releasing hormone (TRH), one of neuropeptides, induces a stimulation of hepatic proliferation through vagal-cholinergic pathways. Since cAMP is known to play an important role in the hepatic proliferation, effect of central TRH on hepatic cAMP was investigated. Rats were intracisternally injected with either a TRH analog, RX-77368 (1-100 ng), or saline. The liver was removed 2-72 h after the TRH analog and hepatic cAMP content was determined by radioimmunoassay. In some experiments, pretreatment with hepatic vagotomy, atropine methyl nitrate, or 6-hydroxydopamine (6-OHDA) was performed. Hepatic cAMP was dose-dependently increased by intracisternal TRH analog (5-100 ng) with a peak response occurring 12 h postinjection. The central TRH-induced increase in hepatic cAMP was abolished by vagotomy, atropine and indomethacin, but not by 6-OHDA. Intravenous injection of the TRH analog (10 ng) did not affect hepatic cAMP. These results demonstrate that TRH acts in the brain to increase hepatic cAMP through vagal-cholinergic and prostaglandin-dependent pathways, suggesting that central TRH modulates hepatic functions through cAMP-mediated signaling pathways.

Expression of functional ciliary neurotrophic factor receptors in immortalized gonadotrophin-releasing hormone-secreting neurones

Ciliary neurotrophic factor (CNTF), a cytokine of the interleukin-6 superfamily, is known to exert pleiotropic actions, including regulation of food intake and permissive effects on reproduction, by facilitating the release of gonadotrophin-releasing hormone (GnRH) and gonadotrophins. CNTF activates membrane receptors (CNTF-Rs) composed of one ligand-specific binding subunit, defined CNTFR alpha, and two signal transducing subunits, termed leukaemia inhibitory factor receptor (LIFR) and gp130. However, it is not clear whether the effects of CNTF on GnRH release result from either a direct or an indirect action on GnRH-secreting hypothalamic neurones, or from a combination of these events. The hypothesis of a direct effect of CNTF was thus tested using the GT1-7 GnRH-secreting cell line. CNTF-R expression and CNTF-induced modulation of the Janus kinase (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway and of GnRH release were evaluated. GT1-7 cells were found to express CNTFR alpha, LIFR and gp130 genes, as shown by reverse transcription-polymerase chain reaction analysis, and the corresponding proteins, analysed by immunofluorescence and western blot. CNTFR alpha, LIFR and gp130 immunoreactive bands had an approximate size of 50, 190 and 130 kDa, respectively. Treatment of GT1-7 cells with 10(-12) M CNTF for 15-60 min resulted in a marked and transient increase of STAT3 phosphorylation via activation of JAK2. A 30-min exposure of GT1-7 cells to different CNTF concentrations increased the accumulation of GnRH into the culture medium, with a maximal effect at 10(-11) M. In conclusion, the present results provide new information about the regulation of the reproductive axis by CNTF, and suggest that it might operate at the hypothalamic level by directly influencing the activity of GnRH-secreting neurones, in addition to the possible indirect effects via interneurones proposed by previous studies.

Effect of central corticotropin releasing factor on hepatic circulation in rats: the role of the CRF2 receptor in the brain

BACKGROUND

Corticotropin releasing factor (CRF) is distributed in the central nervous system and acts as a neurotransmitter to regulate gastric functions through vagal-muscarinic pathways. We have recently demonstrated that central CRF aggravates experimental acute liver injury in rats. In the present study, the central effect of CRF on hepatic circulation was investigated.

METHODS

Hepatic surface perfusion was determined by laser Doppler flowmetry in urethane anaesthetised rats. Portal pressure and portal blood flow was simultaneously monitored. CRF (0.1-4 nmol), urocortin II (a selective CRF2 receptor agonist 2.5-100 pmol), or saline vehicle was injected intracisternally, and changes in hepatic circulation were observed for 120 minutes. We examined the effects of various pretreatments with K41498, a selective CRF2 receptor antagonist, atropine, 6-hydroxydopamine, hepatic plexus denervation, or hepatic branch vagotomy, respectively.

RESULTS

Intracisternal injection of CRF (0.2-4 nmol) caused a dose dependent decrease in hepatic surface perfusion with a maximum response occurring 60 minutes post injection. Portal pressure was dose dependently elevated and portal blood flow was decreased by intracisternal CRF concurrently with the decrease in hepatic surface perfusion. These changes in hepatic circulation by intracisternal CRF were abolished by 6-hydroxydopamine and hepatic plexus denervation, but not by atropine or hepatic vagotomy. Urocortin II injected intracisternally decreased hepatic surface perfusion and elevated portal pressure at doses within the picomolar range. Intracisternal preadministration of K41498 inhibited the effect of central CRF on the hepatic circulation.

CONCLUSION

These data suggest that CRF acts in the brain to decrease hepatic surface perfusion and elevate portal pressure through central CRF(2) receptor and sympathetic-noradrenergic pathways.

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.

Evaluation of the role of melanocortin 3 and 4 receptors in leptin-stimulated and spontaneous growth hormone secretion in rats

It has been reported that the melanocortin 4-receptor (MC4-R) may act downstream of leptin to mediate its effects on food intake and several neuroendocrine functions (the reproductive system, the hypothalamo-pituitary-thyroid axis, and prolactin secretion). However, no previous study examined whether MC4-R mediates leptin stimulatory actions on growth hormone (GH) secretion, or whether MC4-R signaling is involved in spontaneous pulsatile GH release in fed rats. Therefore in this study we examined the involvement of both MC3-R and MC4-R (the predominant MC-R subtypes expressed in the brain) in these two aspects of GH secretion in freely-moving male rats. In both fed and 3-day fasted rats, plasma GH levels were determined every 15 min over 5 h after single intracerebroventricular injections of the following substances or vehicle. Fasting diminished and leptin (0.3 nmol) reinstated the GH pulse amplitude without affecting the pulse frequency. Neither HS014 (1.0 nmol, a selective MC4-R antagonist) nor agouti-related peptide (1.0 nmol, a non-selective MC3/4-R antagonist) was effective in altering leptin-stimulated or spontaneous GH secretion. In addition, neither melanotan-II (1.0 nmol, a non-selective MC3/4-R agonist) nor gamma(1)-melanocyte-stimulating hormone (10 nmol, a selective MC3-R agonist) affected significantly GH release in fasted rats. We have previously demonstrated that stimulation or blockade of MC4-R, achieved by the same drug dosage as in this study, significantly affect luteinizing hormone and prolactin secretion in rats. The present results thus suggest that neither MC4-R nor MC3-R is involved in leptin-stimulated or spontaneous GH secretion, or at least that the level of MC4-R involvement in GH secretion is much lower than that in luteinizing hormone and prolactin release regulation.

Thyrotropin-releasing hormone in the dorsal vagal complex stimulates hepatic blood flow in rats

Central administration of thyrotropin-releasing hormone (TRH) enhances hepatic blood flow in animal models. TRH nerve fibers and receptors are localized in the dorsal vagal complex (DVC), and retrograde tracing techniques have shown that hepatic vagal nerves arise mainly from the left DVC. However, nothing is known about the central sites of action for TRH to elicit the stimulation of hepatic blood flow. The effect of microinjection of a TRH analogue into the DVC on hepatic blood flow was investigated in urethane-anesthetized rats. After measuring basal flow, a stable TRH analogue (RX-77368) was microinjected into the DVC and hepatic blood flow response was observed for 120 minutes by laser Doppler flowmetry. Either left or right cervical vagotomy or hepatic branch vagotomy was performed 2 hours before the peptide. Microinjection of RX-77368 (0.5-5 ng) into the left DVC dose-dependently increased hepatic blood flow. The stimulation of hepatic blood flow by RX-77368 microinjection into the left DVC was eliminated by left cervical and hepatic branch vagotomy but not by right cervical vagotomy. By contrast, microinjection of RX-77368 into the right DVC did not significantly alter hepatic blood flow. These results suggest that TRH acts in the left DVC to stimulate hepatic blood flow through the left cervical and hepatic vagus, indicating that neuropeptides may act in the specific brain nuclei to regulate hepatic function.

Hypothalamic interleukin-1 beta and tumor necrosis factor-alpha, but not interleukin-6, mediate the endotoxin-induced suppression of the reproductive axis in rats

It is well established that endotoxemia disrupts reproductive capability, and several proinflammatory cytokines, especially IL-1 beta, IL-6, and TNF-alpha in the brain, have been implicated in this endocrine aberration. However, no previous study has directly compared the effects of the three major proinflammatory cytokines (IL-1 beta, IL-6, and TNF-alpha) on the in vivo release of hypothalamic GnRH, a secretagogue of LH from the pituitary. Therefore, in this study, we addressed this issue with two complementary approaches involving push-pull perfusion in freely moving ovariectomized female rats. First, we examined the effects of systemic lipopolysaccharide (LPS) treatment on the release of plasma LH, and of GnRH, IL-1 beta, IL-6, and TNF-alpha in the hypothalamic medial preoptic area (MPOA), where the majority of GnRH neuronal perikarya are located. LPS inhibited the secretion of both LH and GnRH and concomitantly stimulated the release of all three cytokines. We next tested the effects of direct MPOA perfusion with the respective cytokines (at three different concentrations each) on the GnRH and LH secretion. IL-1 beta and TNF-alpha, at the concentrations that were observed in the MPOA after the LPS injection, were equipotent in inhibiting the GnRH-LH system, whereas IL-6 was ineffective (even at a supraphysiological concentration). These results strongly suggest that IL-1 beta and TNF-alpha may represent the major proinflammatory cytokines mediating the LPS-induced suppression of GnRH and LH release, whereas the role of IL-6 seems to be insignificant.

Involvement of calcitonin gene-related peptide and capsaicin-sensitive afferents in central thyrotropin-releasing hormone-induced hepatic cytoprotection

The involvement of capsaicin-sensitive afferent neurons and calcitonin gene-related peptide (CGRP) in central thyrotropin-releasing hormone (TRH)-induced hepatic cytoprotection was investigated in rats. Both systemic capsaicin pretreatment and intravenous administration of CGRP receptor antagonist, human CGRP-(8-37), completely abolished the protective effect of intracisternal TRH analog (RX-77368; p-Glu-His-(3,3'-dimethyl)-Pro-NH2, 5 ng) against carbon tetrachloride (CCl4)-induced acute liver injury, assessed by serum alanin aminotransferase levels and histological changes. These data demonstrate the involvement of capsaicin-sensitive afferent neurons and CGRP in central TRH-induced hepatic cytoprotection.

Adrenal glucocorticoids do not mediate impaired reproductive function induced by lipopolysaccharide in rats

It has been reported that the impaired reproductive function found in endotoxemia is mediated by proinflammatory cytokines, prostaglandins, and opioid peptides in the brain and that the synthesis of all these molecules is stimulated by endotoxins. The role of glucocorticoids in the endotoxin-induced hypogonadism may also be important, because endotoxins are potent stimulators of the hypothalamo-pituitary-adrenal axis, and glucocorticoids are inhibitory to the reproductive system. However, no previous study examined directly whether glucocorticoids contribute to the endotoxin-induced suppression of the reproductive competence until a very recent study performed in sheep. To examine directly such a role of glucocorticoids in rats, we compared the effects of lipopolysaccharide (LPS) on the pulsatile luteinizing hormone (LH) release between adrenal-intact orchidectomized rats and adrenalectomized plus orchidectomized rats. The latter group received a constant subcutaneous infusion of corticosterone to maintain physiological plasma levels of the steroid. An intravenous injection of LPS promptly decreased both amplitude and frequency of the LH pulses in the orchidectomized rats, and the LPS effects were very similar in the double endocrinectomy group which did not show an increased corticosterone release after LPS. These results strongly suggest that glucocorticoids do not have a significant role in mediating the LPS-induced acute suppression of pulsatile LH secretion in orchidectomized rats.

Functional role, structure, and evolution of the melanocortin-4 receptor

The melanocortin (MC)-4 receptor participates in regulating body weight homeostasis. We demonstrated early that acute blockage of the MC-4 receptor increases food intake and relieves anorexic conditions in rats. Our recent studies show that 4-week chronic blockage of the MC-4 receptor leads to robust increases in food intake and development of obesity, whereas stimulation of the receptor leads to anorexia. Interestingly, the food conversion ratio was clearly increased by MC-4 receptor blockage, whereas it was decreased in agonist-treated rats in a transient manner. Chronic infusion of an agonist caused a transient increase in oxygen consumption. Our studies also show that the MC-4 receptor plays a role in luteinizing hormone and prolactin surges in female rats. The MC-4 receptor has a role in mediating the effects of leptin on these surges. The phylogenetic relation of the MC-4 receptor to other GPCRs in the human genome was determined. The three-dimensional structure of the protein was studied by construction of a high-affinity zinc binding site between the helices, using two histidine residues facing each other. We also cloned the MC-4 receptor from evolutionary important species and showed by chromosomal mapping a conserved synteny between humans and zebrafish. The MC-4 receptor has been remarkably conserved in structure and pharmacology for more than 400 million years, implying that the receptor participated in vital physiological functions early in vertebrate evolution.

Pivotal roles of alpha-melanocyte-stimulating hormone and the melanocortin 4 receptor in leptin stimulation of prolactin secretion in rats

Leptin, the obese gene product, was reported to stimulate prolactin (PRL) secretion, but the neuroendocrine mechanism underlying this hormonal response is largely unknown. Thus, in this study we examined the involvement of several important PRL regulators in the leptin-induced PRL secretion in male rats. Compared with the values in normally fed rats, food deprivation for 3 days significantly decreased both PRL and leptin levels in the plasma. These changes were reverted to normal by a 3-day constant infusion of 75 microg/kg/day of leptin to the fasted rats, while 225 microg/kg/day of leptin further elevated both PRL and leptin levels. These four groups of animals were used for the following experiments. Results of dopamine and serotonin turnover studies in the brain and the pituitary indicated that neither of these biogenic amines plays a primary role in mediating leptin's effects on PRL. Repeated intracerebroventricular injections over 72 h of neutralizing antibodies against vasoactive intestinal peptide, PRL-releasing peptide, or beta-endorphin, did not significantly suppress the leptin actions. However, both the blockade of the melanocortin (MC) 4 receptor (R) and the immunoquenching of brain alpha-melanocyte-stimulating hormone (alpha-MSH) completely abolished the leptin-induced PRL release, and the stimulation of the MC4-R, but not the MC3-R, significantly elevated PRL levels in the fasted rats. These results suggest that alpha-MSH, a cleaved peptide from pro-opiomelanocortin of which synthesis is stimulated by leptin, may be the pivotal neuropeptide in the brain mediating the leptin's stimulatory influence on PRL secretion. It was also suggested that the MC4-R may be the primary subtype of the MC-Rs mediating this action of alpha-MSH.

Manipulation of neonatal gonadal steroid milieu and leptin secretion in later life in male and female rats

The mechanism underlying the gender-based difference in circulating leptin levels (females>males) is still uncertain, because the difference persists even after adjustment for fat mass and sex steroid concentrations. In this study, we tested the possibility that the neonatal sex steroid milieu, which is critical for the sexual differentiation of the brain, may permanently affect leptin secretion in rats of both sexes. Male rats were neonatally castrated (NC), and females were neonatally androgenized (NA) by testosterone (T). Two subsets of the NC males were given T on postnatal day 1 or 29. Appropriate controls for all these groups were prepared. The animals were sacrificed on postnatal day 57, and at this age, the percent body fat was similar among all the male and female groups. NC males had a two-fold, significantly higher level of leptin than intact males. This hyperleptinemia induced by NC was prevented by T when it was given neonatally, but not on the day 29. By contrast, NA for females was without effect on leptin titers in later life. These results suggest that neonatal T in male rats may, at least in part, mediate the sex-related difference in leptin secretion that becomes apparent in later life. However, as intact females still had significantly higher leptin titers than NC males, it is very likely that additional factors may also be responsible for the sexually dimorphic leptin secretion in rats.

A mechanism underlying the sexually dimorphic ACTH response to lipopolysaccharide in rats: sex steroid modulation of cytokine binding sites in the hypothalamus

It is well established that the hypothalamic-pituitary-adrenal responses to immune stressors are sexually dimorphic in rodents (females > males), but the underlying mechanism is still unclear. To investigate the mechanism, in this study we examined whether the sex steroid environment affects the following variables in male and female rats: (1) plasma levels of ACTH, interleukin (IL)-1beta, IL-6 and tumour necrosis factor-alpha (TNF-alpha) after systemic lipopolysaccharide (LPS) administration; (2) static concentrations of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the mediobasal hypothalamus (MBH) and those of ACTH in the anterior pituitary (AP); and (3) the binding characteristics of IL-1beta, IL-6 and TNF-alpha in the MBH and AP. LPS-induced ACTH release was significantly higher in female than in male rats, and this sexual difference was abolished by performing gonadectomy in both sexes. Administration of physiological doses of testosterone and oestradiol to gonadectomized males and females, respectively, restored the altered ACTH responses to normal. Changes in the sex steroid milieu did not affect plasma cytokine responses to LPS, tissue contents of CRH, AVP and ACTH, or the IL-6 binding characteristics in the MBH and AP. However, the number of IL-1beta and TNF-alpha binding sites, but not their binding affinities, in the MBH showed significant changes according to altered sex hormone milieu, in the same direction as the LPS-induced ACTH response. These results suggest that the hypothalamic sensitivity to peripheral IL-1beta and TNF-alpha may be an important mechanism underlying the sexually dimorphic ACTH response to LPS in rats.

Lafutidine increases hepatic blood flow via potentiating the action of central thyrotropin-releasing hormone in rats

BACKGROUND

Lafutidine, (+/-)-2-(furfurylsulfinyl)-N-[4-[4-(piperidinomethyl)-2-pyridyl]oxy-(Z)-2 butenyl]acetamide, is a newly synthesized histamine H2 receptor antagonist and possesses a cytoprotective efficacy, which comprises mucin biosynthesis and stimulation of gastric blood flow mediated through capsaicin-sensitive sensory neurons and endogenous calcitonin gene-related peptide (CGRP). In the present study, an effect of lafutidine on hepatic blood flow was investigated in rats that received an intracisternal injection of a subthreshold dose of thyrotropin-releasing hormone (TRH) analog, RX 77368.

METHODS

Change in hepatic blood flow was determined by laser Doppler flowmetry. Male Wistar rats were anesthetized with urethane (1.5 g/kg, i.p.), and positioned on a stereotaxic apparatus. An abdominal incision was made, and a probe of laser Doppler flowmeter was placed on the surface of the liver. After a 60-min stabilization, basal hepatic blood flow was measured for 30 min, and lafutidine (0.5, 1, 3, 5 or 10 mg/kg) or vehicle was injected into the portal vein and a subthreshold dose (1.5 ng) of RX 77368 was injected intracisternally. Hepatic blood flow was monitored for 120 min postinjection. To investigate a role of capsaicin-sensitive sensory neurons and endogenous CGRP, systemic capsaicin treatment (125 mg/kg, s.c., 10-14 days before) and intravenous infusion of a CGRP receptor antagonist, human CGRP-(8-37) (15 micro g/kg as a bolus, followed by infusion at 3 micro g/kg/h) were performed, respectively.

RESULTS

Intracisternal injection of RX 77368 (1.5 ng) or intraportal lafutidine (10 mg/kg) by itself did not affect hepatic blood flow, but co-injection of intracisternal RX 77368 (1.5 ng) and intraportal lafutidine (5 mg/kg) increased it with peak response at 30 min postinjection. The effect of lafutidine on hepatic blood flow in rats given RX 77368 was dose-related over the range 1-5 mg/kg. By contrast, intracisternal injection of RX 77368 (1.5 ng) did not change hepatic blood flow in rats injected with another histamine H2 receptor antagonist, famotidine (5 mg/kg), intraportally. The stimulatory effect of co-injection of TRH analog and lafutidine was abolished by systemic capsaicin-treatment and CGRP antagonist.

CONCLUSION

These data suggest that lafutidine increases hepatic blood flow by sensitizing the liver to the action of central TRH via both capsaicin-sensitive sensory neurons and endogenous CGRP in urethane-anesthetized rats.

Central injection of astressin inhibits carbon tetrachloride-induced acute liver injury in rats

The effect of intracisternal astressin, a specific and potent corticotropin-releasing factor (CRF)(1) and CRF(2) receptor antagonist on carbon tetrachloride (CCl(4))-induced acute liver injury was investigated in rats. Intracisternal astressin inhibited the elevation of serum alanine aminotransferase level induced by CCl(4). Intracisternal astressin also reduced CCl(4)-induced liver histological changes. The protective effect of central astressin on CCl(4)-induced liver damage was abolished by sympathectomy but not by hepatic branch vagotomy. These findings demonstrate that astressin acts in the central nervous system to induce hepatic cytoprotection, possibly through the sympathetic pathways in rats. These results further establish a role of endogenous CRF in the brain in hepatic pathophysiological regulation.

Subtype selective binding properties of substituted linear melanocyte stimulating hormone analogues

The melanocortin receptors are peptide binding G-protein coupled receptors that play a role in important physiological functions such as energy balance, inflammatory processes and several aspects of reproduction. In this study, we synthesised 11 new linear MSH analogues and tested their binding to the human MC receptors (MC1, MC3, MC4 and MC5) expressed in COS cells. Our results show that introduction of Asp in position 4 similarly affects the binding to the MC1, MC4 and MC5 receptors, but drastically lowers the binding to the MC3 receptor. Arg(5) substitution shows relatively high affinity for the MC4 receptor, while the results also give further support for specific importance of His(6) for the MC1 receptor. Introduction of Asp in position 10, mimicking gamma-MSH, decreased the affinity for the MC3 receptor in similar manner as for the MC4 receptor, suggesting that there are important differences in the binding conformation of gamma-MSH and NPD-MSH. Our results provide further information about the ligand binding requirements for each of the MC receptor subtypes, and highlights differential influence of the core residues in the MSH peptides. The data set also provides useful information for further calculations and modeling of MC receptor binders.

Leptin directly acts within the hypothalamus to stimulate gonadotropin-releasing hormone secretion in vivo in rats

It is still not known whether leptin, an adipocyte-derived hormone, acts directly within the hypothalamus to stimulate the gonadotropin-releasing hormone (GnRH)-luteinizing hormone (LH) system. In order to address this question, the present study examined the effects of direct intrahypothalamic perfusions with leptin on the in vivo release of GnRH in ovarian steroid-primed ovariectomized rats utilizing the push-pull perfusion technique. Both alpha-melanocyte-stimulating hormone (alpha-MSH) and neuropeptide Y were also measured in the hypothalamic perfusates. In normally fed animals, the leptin infusion was without effect on the release of these three hypothalamic peptides and also without effect on plasma LH and prolactin (PRL), whether leptin was infused into the medial preoptic area (where the majority of GnRH neuronal cell bodies exist) or the median eminence-arcuate nucleus complex (where axon terminals of GnRH neurons are located). In contrast, in 3-day fasted rats leptin was effective in stimulating the secretion of GnRH, alpha-MSH, and LH, regardless of the site of perfusion. These three hormones were increased in a temporal order of alpha-MSH, GnRH and LH. Irrespective of the site of perfusion, leptin was without effect on the release of neuropeptide Y. Only when leptin was infused into the median eminence-arcuate nucleus complex was PRL secretion also stimulated, although its onset was 1 h behind that of LH. The leptin-induced elevations of GnRH, alpha-MSH, LH and PRL were all dose-dependently stimulated by subnormal (1.0 ng ml(-1)) and normal (3.0 ng ml(-1)) concentrations of leptin, but at higher concentrations (10 ng ml(-1)) it did not produce additional effects. Leptin infusion into the anterior hypothalamic area, a control site equidistant from both the medial preoptic area and the median eminence-arcuate nucleus complex, did not produce a significant change in any of the hormones in either the fed or fasted rats. These results demonstrate for the first time that leptin can act at both the cell bodies and axon terminals of GnRH neurons to stimulate the release of the neurohormone in vivo, and they also suggest that alpha-MSH may play a significant intermediary role in linking leptin and GnRH secretion.

Effect of repeated administration of prolactin releasing peptide on feeding behavior in rats

Prolactin releasing peptide (PrRP) has been reported to reduce food intake in rats. We tested the effect of i.c.v. administration of PrRP-31 on food intake in both food deprived and free-feeding rats. We did not find any effect of PrRP-31 on food intake after single injections of up to an 8-nmol dose, but observed a marked decrease in food intake and body weight in rats that received a repeated twice daily administration of 8 nmol of PrRP-31. This effect was associated with an adverse behavioral pattern, indicating that the repeated high doses of the peptide caused non-specific effects inducing anorexia. We also tested several other behavioral parameters like locomotion and exploratory time, grooming and resting time, using lower doses of PrRP that did not cause the adverse behavior. Moreover, we carried out locomotor and sensory motor activity tests at the doses that exerted the most pronounced effect on the food intake. None of these tests suggested any specific behavioral effect of PrRP. We conclude that the behavioral pattern induced by PrRP is likely to be different from those induced by many other neuropeptides affecting food intake in rats.

Pharmacological comparison of rat and human melanocortin 3 and 4 receptors in vitro

The melanocortin 3 and 4 receptors are G-protein-coupled receptors found in the hypothalamus with important role in regulation of the energy balance. In this study, we performed pharmacological comparison of the rat and human melancortin (MC) 3 and MC4 receptors. We transiently expressed the genes for these receptors individually in a mammalian cell line and determined the binding affinities to several MSH peptides. The results showed no major difference between the rat and human MC3 receptors while the rat MC4 receptor had higher affinity to several peptides compared with the human MC4 receptor. NDP-, alpha-, beta-, gamma-MSH, ACTH(1-24), HS014 and MTII had from 5- to 34-fold higher affinity for the rat MC4 receptor, while SHU9119, HS024 and HS028 had similar affinity for both the MC4 receptors. Pharmacological species difference have earlier been reported for the MC1 and MC5 receptors but this is the first report showing important differences between the rat and human MC4 receptors.

Food conversion is transiently affected during 4-week chronic administration of melanocortin agonist and antagonist in rats

The central melanocortin system is involved in the regulation of food intake and body weight. In this study, we investigated the effect of a 4-week intracerebroventricular infusion of the melanocortin receptor agonist MT-II and the selective melanocortin-4 receptor antagonist HS024 on food intake and body weight homeostasis. The MT-II-treated rats ate less and lost considerably more weight than the control rats during the first week of treatment. During the second and third week, they gained weight and, by the end of the treatment period, the weight gain was similar to that of the control rats. The HS024 treatment caused hyperphagia and development of obesity during the entire period. Extensive accumulations of fat and a sixfold increase in leptin levels were observed in the HS024-treated rats, as compared with controls, after the 4-week period. Food conversion ratio, defined as body weight increase relative to weight of ingested food, was clearly increased in the HS024-treated rats, while it was lowered in the MT-II-treated rats compared with controls. The effect on food conversion ratio was transient, being greatest for both experimental groups during the first week and it was then attenuated to reach the level of controls at the end of the study. The results suggest that long-term injection of exogenous melanocortin receptor active substances may have an important transient effect on food conversion.

Postnatal profile of plasma leptin concentrations in male and female rats: relation with the maturation of the pituitary-gonadal axis

Leptin, the ob gene product, has been implicated in the initiation of puberty in mice and humans. However, it is not yet clear whether leptin also plays a pivotal role in promoting sexual maturation in rats. Based on the assumption that circulating leptin levels would increase during the peripubertal period if this hormone triggers puberty, we examined the developmental profile of plasma leptin from neonatal (day 1) through adult (day 85) age in both male and female rats and simultaneously monitored several important indices of pituitary-gonadal function. A significant elevation of plasma leptin during the peripubertal period was not observed in either male or female rats. Although this finding may not support leptin as a humoral factor triggering puberty, we observed a rise in leptin in both sexes from the second postnatal week, which clearly preceded the first significant elevations of luteinizing hormone and gonadal steroids. Therefore, it is still possible that leptin may play a role in promoting sexual maturation in rats of both sexes already from an early postnatal period. It seems that the role for leptin in sexual development is permissive, but not decisive, in rats.

Melanocortins and reproduction

Obesity, anorexia and general body weight fluctuations cause a variety of effects on the reproductive system. Our understanding of the neuro-biological mechanisms of the connections between body weight and the reproductive axis is not especially developed despite a number of interesting physiological observations. Several reports suggest that leptin could play a key role in connecting energy balance and reproduction. The melanocortin system, involving melanocyte stimulating hormone, adrenocorticotrophic hormone, agouti related peptide and the central melanocortin 3 and 4 receptors, plays a major role in the hypothalamic regulation of energy balance. The melanocortins have also been suggested to participate in possible downstream events of the adipose cell derived hormone, leptin. Leptin has importance for several aspects of reproduction including regulation of luteinizing hormone and prolactin release. This review discusses the interplay of hypothalamic regulation of food intake and the hormones involved in the hypothalamic-pituitary-gonadal axis with special emphasis on putative roles of the melanocortin system.

Sexual dimorphism in the pituitary-adrenal response to tumor necrosis factor-alpha, but not to interleukin-6, in the rat

It is known that the pituitary-adrenal responses to lipopolysaccharide and interleukin (IL)-1 are sexually dimorphic in rodents, with females having an enhanced secretion of adrenocorticotropin (ACTH) and corticosterone. This study investigated whether the ACTH and corticosterone responses to tumor necrosis factor (TNF)-alpha and IL-6, two principal proinflammatory cytokines, are also modulated by the sex steroid milieu in the rat. Mature male and female rats received an intravenous administration of TNF-alpha(10 microg/kg) and IL-6 (10 microg/kg), and changes in plasma ACTH and corticosterone levels were determined over time. The effect of gonadectomy on the hormonal responses was also examined in both sexes. TNF-alpha induced significantly higher responses of ACTH and corticosterone in females than in males, and this sexual difference was abolished by gonadectomy in both sexes. By contrast, the hormonal responses to IL-6 were not significantly affected by either gender or gonadectomy. These results suggest a sex steroid-dependent modulation of the TNF-alpha-induced, but not the IL-6-induced, ACTH and corticosterone secretion in the rat. Further evidence for the sexually dimorphic neuroimmunoendocrine activity is reported herein.

Nitric oxide mediates leptin-induced preovulatory luteinizing hormone and prolactin surges in rats

The objective of this study was to investigate whether nitric oxide (NO) plays a significant role in mediating the facilitatory action of leptin on the reproductive system. The covariate of reproductive function we used for evaluation was preovulatory surges of luteinizing hormone (LH) and prolactin (PRL), which were simulated by priming ovariectomized rats with estradiol and progesterone. A systemic treatment of normally-fed rats with an NO synthase inhibitor (N(W)-nitro-L-arginine methyl ester) significantly decreased the magnitude of both LH and PRL surges. Three-day-fasted rats did not show a significant surge of either LH or PRL. An intracerebroventricular administration of leptin to fasted rats led to a significant recovery of these hormonal surges, but a simultaneous administration of both the NO synthase inhibitor and leptin significantly abrogated the effects of leptin. This is the first report to demonstrate a significant intermediary role of NO in leptin-induced preovulatory LH and PRL surges in rats.

In vivo release of prolactin-releasing peptide in rat hypothalamus in association with luteinizing hormone and prolactin surges

Prolactin (PRL)-releasing peptide (PrRP) is a novel hypothalamic peptide reported to be a potent and specific stimulator of PRL secretion. This author recently reported that PrRP might play a significant role in mediating the steroid-induced PRL surge in the rat. In order to examine the secretory profile of PrRP in the rat hypothalamus before and during the luteinizing hormone (LH) and PRL surges, this study employed the push-pull perfusion technique and determined the in vivo release of PrRP and also of gonadotropin-releasing hormone (GnRH) in ovariectomized rats primed with estradiol and progesterone. In the medial preoptic area (MPOA) where the GnRH neuronal perikarya exist, GnRH release was increased prior to the initiation of the LH surge, and PrRP also started rising even earlier than GnRH. In the median eminence-arcuate nucleus complex (ME-ARC), where GnRH neuronal fibers terminate, GnRH secretion started increasing before the commencement of the LH surge, but the release of PrRP did not change significantly. These results suggest that PrRP may play a role in mediating the steroid-induced LH surge by activating GnRH neurons in the MPOA. A possible involvement of PrRP in the PRL surge was not suggested from the present data. The lack of a significant alteration in PrRP release in the ME-ARC may argue against a direct hypophysiotropic action of the peptide.

Effect of central urocortin on carbon tetrachloride-induced acute liver injury in rats

The effect of intracisternal injection of urocortin, an endogenous ligand for corticotropin-releasing factor (CRF) 2 receptor, on carbon tetrachloride (CCl4)-induced acute liver injury was investigated in rats. Intracisternal injection of urocortin dose-dependently enhanced elevation of serum alanine aminotransferase and aspartate aminotransferase levels induced by CCl4. Intracisternal urocortin also aggravated CCl4-induced histological changes of the liver. The aggravating effect of central urocortin on CCl4-induced acute liver injury was abolished by chemical sympathectomy, but not by vagotomy. These data demonstrate that urocortin acts in the brain to exacerbate acute liver injury through the sympathetic nervous system and suggest a possible involvement of the CRF2 receptor in the central CRF-induced exacerbation of acute liver injury in rats.

Ciliary neurotrophic factor, a gp130 cytokine, regulates preovulatory surges of luteinizing hormone and prolactin in the rat

Ciliary neurotropic factor (CNTF) is a neuroregulatory cytokine belonging to the interleukin-6 type cytokine superfamily. Although a few studies have reported a facilitatory action of CNTF on the reproductive axis in rodents, information along this line is still very limited. In this study, we examined a possible role of CNTF in the generation of ovarian steroid-induced luteinizing hormone (LH) and prolactin (PRL) surges in the rat, a crucial physiological event in mammalian reproduction. Experiments were performed on both normally-fed and 3-day-fasted rats, ovariectomized and primed with estradiol and progesterone. Blood was collected every 30 min between 11:00 and 18:00 h, to measure LH and PRL. Drugs were given intracerebroventricularly at 11:00 h. Compared to control serum, undiluted as well as threefold dilutions of anti-CNTF serum caused partial but significant suppression of LH surges. Both concentrations of the antibody also delayed the onset of PRL surge to a comparable degree. Fasted rats did not exhibit significant surges of the hormones, while 0.3 and 1.0 nmol, but not 0.1 nmol, recombinant human CNTF led to a dose-dependent recovery of both LH and PRL surges. These results demonstrate for the first time a significant role of CNTF in the generation of preovulatory LH and PRL surges in the rat. CNTF may thus be another humoral signal linking nutrition and reproductive function.

Central regulation of hepatic function by neuropeptides

In addition to classical neurotransmitters, such as acetylcholine and noradrenaline, neuropeptides have been recognized as new neurotransmitters and neuromodulators. Neuropeptides are widely distributed in the central nervous system as well as in peripheral nerves, and act as neurotransmitters to regulate various physiological functions. The digestive organs are no exception, and several neuropeptides in the central nervous system are shown to act in specific brain sites and control gastrointestinal functions, such as gastric acid secretion, and gastrointestinal motility, through the autonomic nervous system. Recently, a relationship between central neuropeptides and hepatic function through the autonomic nervous system has been revealed in animal models. Thyrotropin-releasing hormone acts in the medulla, in particular in the left dorsal vagal complex, to induce stimulation of hepatic blood flow and hepatic proliferation, and protect against experimental liver injury through vagal and cholinergic pathways. Corticotropin-releasing factor injected intracisternally elicits inhibition of the hepatic blood flow and exacerbates experimental liver injury through sympathetic and noradrenergic pathways. Neuropeptide Y acts in the left dorsal vagal complex, in particular in regard to the Y1 receptor subtype, to stimulate bile secretion. Other neuropeptides such as beta-endorphin and bombesin in the brain modulate hepatic proliferation and bile secretion. Through the use of neuropeptides, new knowledge of the central and peripheral mechanisms underlying brain regulation of hepatic function will be revealed. Further studies in regard to the physiological relevance of the central action of neuropeptides on specific brain sites should be performed to unravel the underlying pathways that mediate brain-liver interaction.

Marked uptake of technetium-99m pertechnetate by parathyroid adenoma

We herewith report an unusual case of primary hyperparathyroidism whose parathyroid adenoma strongly accumulated technetium (Tc)-99m pertechnetate. A 41-year-old woman was referred to our department under the tentative diagnosis of primary hyperparathyroidism. Scintigraphy by thallium-201 chloride showed homogeneous uptake in the whole thyroid, whereas Tc-99m image revealed a strong local accumulation in the middle portion of the right thyroidal lobe. Neck exploration revealed a 12x8x5 mm tumor in the posterolateral region of the right thyroidal lobe, the pathology of which was parathyroid adenoma. In addition, a small nodule (8 mm in diameter) with pathological findings revealing follicular adenoma of the thyroid, was found within the medial portion of the right thyroidal lobe. Both lesions were removed by surgery, and a postoperative Tc-99m scintigraphy no longer demonstrated a significant uptake in the right thyroidal lobe. Since the thyroid adenoma was too small to be detected by any scintigraphic study and located much closer to the median line than the site of the marked accumulation of Tc-99m pertechnetate, it was considered very likely that the parathyroid adenoma concentrated Tc-99m. Search of literature revealed that there have been only thirteen cases of parathyroid tumor reported to date which significantly accumulated Tc-99m pertechnetate. The present patient represents another rare case of parathyroid adenoma showing sueh an unusual scintigraphic image.

A significant participation of orexin-A, a potent orexigenic peptide, in the preovulatory luteinizing hormone and prolactin surges in the rat

Orexins are novel hypothalamic peptides which stimulate food intake. In view of the well-known tight connection between the nutritional state and the reproductive function, in this study we examined a possible role of orexin-A in the generation of ovarian steroid-induced luteinizing hormone (LH) and prolactin (PRL) surges in ovariectomized rats. Experiments were performed on both normally-fed and 3-day-fasted rats. Although fasting led to abolition of both LH and PRL surges, intracerebroventricular administration of orexin-A (0.3 and 3.0 nmol) resulted in a dose-dependent recovery of the hormonal surges. In addition, anti-orexin-A antisera given to normally-fed rats completely abrogated the surges of both hormones. These results demonstrate for the first time a significant participation of orexin-A in the preovulatory LH and PRL surges in the rat.

A significant participation of leukemia inhibitory factor in regulating the reproductive function in rats: a novel action of the pleiotropic cytokine

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine exhibiting diverse biological activities in various tissues and cell types. Accumulating evidence suggests a crucial role for LIF in regulating the hypothalamo-pituitary-adrenal axis, but information is limited regarding whether the cytokine also exerts a significant influence on other endocrine systems. In this study, we examined a possible involvement of LIF in the generation of ovarian steroid-induced luteinizing hormone (LH) and prolactin (PRL) surges in the rat. Experiments were performed on both normally fed and 3-day-fasted rats, which were ovariectomized and primed with estradiol and progesterone. From 11:00 to 18:00 h, blood was collected every 30 min to measure LH and PRL. All the following substances were given intracerebroventricularly at 11:00 h. Compared to control serum, undiluted and 5-times diluted preparations of anti-rat LIF serum caused a partial but significant suppression of LH surge to a similar extent. The two different concentrations of antibody also delayed the onset of PRL surge to a comparable degree. Fasted rats were devoid of significant surges of the hormones, while 1.0 and 3.0 nmol, but not 0.3 nmol, of recombinant murine LIF given to these animals led to a partial but significant recovery of both LH and PRL surges. This stimulatory potency of LIF on both hormones was already maximal at its 1.0-nmol dose. These results demonstrate for the first time a significant participation of LIF in the generation of LH and PRL surges in the rat. A novel action of the pleiotropic cytokine is reported herein.

Agouti-related peptide prevents steroid-induced luteinizing hormone and prolactin surges in female rats

We studied the effect of Agrp (agouti-related peptide) on LH (luteinizing hormone) and PRL (prolactin) surges in ovariectomized rats primed with estradiol and progesterone. The rats displayed characteristic LH and PRL surges that were completely abolished by starving. Injection of either 1 nmol or 3 nmol Agrp (83-132), a potent antagonist of the orexigenic MC3 and MC4 receptors, completely prevented both the LH and PRL surges. We also investigated the effects of either a single or double injection of anti-Agrp serum to fasted animals, which were without LH and PRL surges. A single injection of the antiserum was without effect, but the rats that received double injection of anti-Agrp serum partially reinstated both the LH and PRL surges. Although the onset of LH and PRL surges was significantly delayed in the double treated group, the highest levels of the surges for both hormones were statistically indistinguishable compared with the control group. These data give a clear indication that endogenous Agrp may be involved in LH and PRL surges during starvation, providing further evidence that the melanocortin system is important for these hormonal surges in female rats.

Further evidence for a significant participation of the melanocortin 4 receptor in the preovulatory prolactin surge in the rat

We previously reported that the melanocortin 4 receptor may play a significant role in mediating the preovulatory surges of luteinizing hormone and prolactin in the rat. In order to confirm this previous finding, in the present study we examined and compared the effects of intracerebroventricular administrations of 1.0 nmol of MT II (a non-selective melanocortin 3 and 4 receptor agonist) and 10 nmol of gamma(1)-melanocyte-stimulating hormone (a selective melanocortin 3 receptor agonist) on luteinizing hormone and prolactin surges in starved, gonadal steroid-primed ovariectomized female rats, which is a model deprived of inherent surges of the two hormones. MT II significantly recovered the surge of prolactin, but not of luteinizing hormone (although a tendency to increase was seen), and gamma(1)-melanocyte-stimulating hormone was without effect on both hormones. This study corroborated our previous report through a different and direct approach that the melanocortin 4 receptor, but not the melanocortin 3 receptor, plays a significant role in mediating the preovulatory prolactin surge in the rat.

Normalization of circulating leptin levels by fasting improves the reproductive function in obese OLETF female rats

In order to examine a possible detrimental effect of hyperleptinemia on the reproductive system, we examined whether a decrease in circulating leptin levels by fasting affects the estradiol/progesterone-induced luteinizing hormone (LH) and prolactin (PRL) surges in genetically obese OLETF (Otsuka-Long-Evans-Tokushima-Fatty) rats. Experiments were performed on both normally fed and 3-day starved groups from ovariectomized OLETF rats and their controls LETO (Long-Evans-Tokushima-Otsuka). Starved LETO rats, whose leptin levels were less than 0.5 ng/ml, did not show a significant surge of either LH or PRL. Normally fed OLETF rats, whose leptin levels were 9.7 +/- 1.8 ng/ml, showed a significant but small surge for both LH and PRL. Interestingly, starved OLETF rats, whose leptin levels (4.1 +/- 0.7 ng/ml) were similar to those in normally fed LETO rats (3.3 +/- 0.4 ng/ml), had significantly greater surges of both hormones than normally fed OLETF group. This study demonstrates for the first time that the normalization of circulating leptin levels in female OLETF rats augments the steroid-induced LH and PRL surges, and also suggests a deleterious effect of hyperleptinemia on the reproductive axis.

Stimulation of prolactin secretion by chronic, but not acute, administration of leptin in the rat

Leptin, the product of obese (ob) gene, has been reported to affect the secretion of all six anterior pituitary hormones, but data are especially scarce regarding the interplay between leptin and prolactin (PRL). Thus, in this study we examined and compared in vivo the effects of acute and chronic administrations of recombinant mouse leptin on PRL secretion in male rats. Normally-fed and 3-day-fasted rats received an intraperitoneal bolus injection of leptin [1.0 mg/kg body weight (BW)] or vehicle only. The leptin treatment was without effect on plasma PRL levels up to 5 h postadministration. Food deprivation for 3 days significantly decreased both PRL and leptin levels. This decrease in plasma PRL was prevented by a 3-day constant infusion of 75 microg/kg BW/day of leptin, which maintained plasma leptin levels similar to those of normally-fed rats. The administration of three times the higher dose of leptin (225 microg/kg BW/day) to fasted rats led to further increases in both PRL and leptin in the plasma. Thus, a dose-dependent stimulatory effect of chronic leptin treatment on PRL secretion was indicated. This study demonstrates that chronic, but not acute, administration of leptin stimulates PRL secretion in the rat.

Involvement of prolactin-releasing peptide in the preovulatory luteinizing hormone and prolactin surges in the rat

Prolactin (PRL)-releasing peptide (PrRP) is a novel hypothalamic peptide reported as a potent and specific stimulator of PRL secretion. In this study, we examined a possible role of PrRP in the ovarian steroid-induced PRL surge in the rat, simultaneously observing the change in luteinizing hormone (LH) surge. Experiments were performed on both normally-fed and three-day-fasted rats, which were ovariectomized and primed with estradiol and progesterone. From 11:00 to 18:00 h, blood was collected every 30 min to measure LH and PRL. All the following substances were given intracerebroventricularly at 11:00 h. Compared to control serum, anti-rat PrRP31 serum caused a significant reduction of the LH and PRL surges. The antiserum also delayed the onset of PRL surge. Fasted rats were devoid of significant surges of the hormones, while 3.0, but not 0.5 nmol of rat PrRP31 given to these animals produced a significant recovery of PRL surge. Although LH surge was not reinstated, basal LH secretion was transiently stimulated by 3.0 nmol of PrRP31. These results demonstrate for the first time a significant participation of PrRP in the preovulatory LH and PRL surges in the rat. Possible indirect pathways mediating this effect of PrRP were discussed, in view of the unique anatomical distribution of PrRP in the hypothalamus.

A significant role of leukemia inhibitory factor in the brain and periphery in endotoxin stimulation of adrenocorticotropin secretion in the rat

Leukemia inhibitory factor (LIF) is considered as another important cytokine regulating the activity of the hypothalamo-pituitary-adrenal axis. In this study, we examined the effects of intravenous (iv) and intracerebroventricular (icv) administrations of anti-LIF antibody on plasma adrenocorticotropin (ACTH) responses induced by intraperitoneal administration of lipopolysaccharide (LPS, 250 microg/kg) in male rats. Fifteen minutes before the LPS injection, anti-rat LIF antibody or control serum was given iv or icv. The antibody was administered at two different concentrations, i.e. undiluted and five-times diluted. Irrespective of the route of administration, the anti-LIF antibody partially but significantly suppressed ACTH responses to LPS, and its suppressive effect was similar between its two different concentrations. These results indicate that the anti-LIF antibody already exerted its maximal effects at its diluted preparation, and hence that the role of LIF in LPS-stimulated ACTH secretion is essentially partial. This is the first study to demonstrate in vivo that LIF in both the brain and general circulation plays a significant role in mediating endotoxin-stimulated ACTH secretion in the rat.

Evaluation of the role for prolactin-releasing peptide in prolactin secretion induced by ether stress and suckling in the rat: comparison with vasoactive intestinal peptide

Prolactin (PRL)-releasing peptide (PrRP) is a recently discovered hypothalamic peptide possessing a specific stimulatory action on PRL secretion. In this study, we examined whether PrRP plays a role in mediating ether stress- and suckling-induced PRL secretion in rats through administering anti-PrRP antisera intracerebroventricularly. For comparison, we also tested the effect of anti-vasoactive intestinal peptide (VIP) antisera on the hormonal responses, since VIP is another candidate for a physiological PRL-releasing factor. The immunoneutralization of VIP, but not of PrRP, led to a significant suppression of PRL responses to both ether and suckling. These results suggest that PrRP may not play a significant role, or at least play a much weaker role than VIP, in mediating PRL release induced by ether stress and suckling in the rat.

Downregulation of melanocortin receptors in brain areas involved in food intake and reward mechanisms in obese (OLETF) rats

The melanocortin (MC)4 receptor is important for food intake and weight homeostasis as it mediates the orexigenic and anorexigenic effects of the MCs. OLETF (Otsuka-Long-Evans-Tokushima-Fatty) rats are a selective inbred strain of polygenic variant rats which overeat and develop obesity with elevated leptin levels. We investigated by autoradiography if the expression of MC receptors were altered in ovariectomized estradiol-replaced female OLETF rats compared to their controls (Long-Evans-Tokushima-Otsuka (LETO) rats). We found that OLETF rats show a reduction in total [125I]NDP-MSH MC receptor binding in the ventromedial hypothalamic nucleus, perhaps reflecting an increased release of MC peptides in this region. The levels of MC receptors in the arcuate nucleus and the paraventricular hypothalamic nucleus were not changed. Interestingly, the OLETF rats also showed reduced MC-receptor binding in areas such as the nucleus accumbens shell, and the ventral tegmental area, both of which are believed to be involved in reward systems. Similarities in the changes of MC receptor expression in obese animals and in animals treated with opiates may suggest a neurobiological link between food intake mediated through the MC receptors and reward.

Evidence that physiological levels of circulating leptin exert a stimulatory effect on luteinizing hormone and prolactin surges in rats

Increasing evidence suggests that leptin, an adipocyte-derived hormone, may positively regulate the reproductive axis, and serve as a critical metabolic signal linking nutrition and the reproductive function. However, along this line there remains an as-of-yet unresolved important issue whether physiological levels of circulating leptin exert a stimulatory effect on the reproductive axis. It is also unknown whether hyperleptinemia affects the reproductive function. In this study, we attempted to examine these unexplored issues, employing as an indicator the estradiol/progesterone-induced luteinizing hormone (LH) and prolactin (PRL) surges in ovariectomized female rats. Experiments were performed on normally fed, 3-day starved, 3-day starved + murine leptin (100 microg/kg/day), and normally fed + murine leptin (300 microg/kg/day) groups. Leptin was administered utilizing osmotic minipumps during 3 days immediately before experimentation. From 11:00 to 18:00 h, blood was collected every 30 min to measure LH and PRL. The 3-day starvation completely abolished both LH and PRL surges, but 3-day starved + leptin (100 microg/kg/day) group, whose plasma leptin levels (3.7 +/- 0.4 ng/ml) were similar to those in normally fed group (3.4 +/- 0.5 ng/ml), showed a significant recovery of the hormonal surges. On the other hand, the magnitudes of LH and PRL surges in normally fed + leptin (300 microg/kg/day) group, whose leptin levels were 10.8 +/- 1.5 ng/ml, were statistically the same as those in normally fed group. These results indicate for the first time that physiological concentrations of circulating leptin exert a stimulatory effect on the steroid-induced LH and PRL surges in the rat. It was also suggested that mild hyperleptinemia of 3 days' duration may not significantly affect the hormonal surges.

Temporal profiles of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the plasma and hypothalamic paraventricular nucleus after intravenous or intraperitoneal administration of lipopolysaccharide in the rat: estimation by push-pull perfusion

Lipopolysaccharide (LPS) is known to stimulate the synthesis and secretion of various proinflammatory cytokines in both the peripheral immune cells and the brain. Yet, the relative contribution of peripheral and central cytokines to the LPS-induced activation of the hypothalamo-pituitary-adrenal axis is still poorly understood. In this study, utilizing the push-pull perfusion technique of the rat brain, we attempted to characterize in detail the temporal profiles of interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha after intravenous (i.v.) or intraperitoneal (i.p.) administration of LPS in both the general circulation and the hypothalamic paraventricular nucleus (PVN), which is the primary source of corticotropin releasing hormone (CRH). Temporal changes in plasma adrenocorticotropic hormone (ACTH) and CRH levels in the PVN were also monitored. We collected blood and perfusates every 30 min from 11:00 to 17:00 h. At 12:00 h, 1.0 or 2.5 mg/kg body weight of LPS was given via an i.v. or i.p. route, respectively. Peak ACTH response occurred 30 min after i.v. LPS and 1.5 h after ip LPS. Of the three cytokines measured in the plasma, TNF-alpha showed the fastest rise in synchrony with peak ACTH secretion after both i.v. and i.p. LPS. Although plasma IL-6 also showed a robust rise, its peak level occurred later than the ACTH peak. Elevation of plasma IL-1beta was the smallest among the three cytokines. CRH levels in the PVN reached their peaks 1 and 2.5 h after the ACTH peak following i.p. and i.v. LPS, respectively. Irrespective of the route of LPS administration, IL-6 and TNF-alpha levels in the PVN showed significant rises 1-2 h after the ACTH peak, but IL-1beta in the PVN did not significantly change during the entire period of observation. The results of the present study suggest that circulating TNF-alpha may play the most important role in triggering the early, peak phase of ACTH secretion after both i.v. and i.p. LPS. Although it is possible that brain TNF-alpha, IL-6, and circulating IL-6, may be involved in the later, protracted phase of ACTH secretion induced by LPS, IL-1beta in both the brain and peripheral circulation seems to play the smallest role in ACTH secretion. This is the first study to characterize the LPS-induced temporal changes in IL-1beta, IL-6, and TNF-alpha in both plasma and PVN simultaneously in conscious, freely moving rats.

A detailed study on the role of sex steroid milieu in determining plasma leptin concentrations in adult male and female rats

We examined the effects of sex steroid milieu on plasma leptin levels in adult male and female rats. Since the body weight is known to influence leptin concentrations, the hormone was measured in rats with a very similar body weight (about 250 g) throughout this study. Plasma leptin levels were significantly higher in female than in male rats. Orchidectomy (ODX) caused a significant rise in leptin, and replacement of a physiological dose of testosterone (T) completely abolished the effect of ODX. Since the effect of tamoxifen (estrogen antagonist) coadministered with T on leptin levels in ODX rats was the same as that of T alone, it was suggested that the suppressive effect of T on leptin may be mediated by the androgenic potency of T, but not by its aromatized product, estradiol. In female rats, plasma leptin concentrations did not change significantly during the estrous cycle. Furthermore, leptin levels were not affected either by ovariectomy alone or by the administration after ovariectomy of physiological doses of estradiol, progesterone, or both. This is the first study to demonstrate in rats with a very similar body weight the existence of a clear sexual difference in plasma leptin levels, and also a suppressive action of T on the adipocyte hormone concentrations.

The melanocortin 4 receptor mediates leptin stimulation of luteinizing hormone and prolactin surges in steroid-primed ovariectomized rats

We have previously reported that leptin, the product of the obese (ob) gene, may play a physiologically relevant role in the generation of estradiol/progesterone-induced luteinizing hormone (LH) and prolactin (PRL) surges in female rats. In the present study, we examined whether the stimulatory effect of leptin on the hormonal surges is mediated through the melanocortin (MC) 4 receptor in the brain, as is leptin's effect on feeding behavior. We also explored whether the MC4 receptor participates in tonic stimulation of steroid-induced LH and PRL surges. Experiments were performed on both normally fed and 3-day starved rats, which were ovariectomized and primed with estradiol and progesterone. At 11:00 h on the day of the experiments, the normally fed rats received an intracerebroventricular administration of artificial cerebrospinal fluid (vehicle), SHU 9119 (a nonselective MC3/MC4 receptor antagonist, 1.0 nmol), or HS014 (a selective MC4 receptor antagonist, 1.0 nmol). The 3-day starved rats were given vehicle, recombinant mouse leptin (0.3 nmol), leptin (0.3 nmol) + SHU9119 (1.0 nmol), or leptin (0.3 nmol) + HS014 (1.0 nmol). From 11:00 to 18:00 h, blood was collected every 30 min to measure LH and PRL. The 3-day starvation completely abolished both LH and PRL surges, but leptin significantly reinstated these hormonal surges. Both SHU9119 and HS014 significantly decreased the magnitude of LH and PRL surges in normally fed rats and also significantly blocked the leptin stimulation of the hormonal surges in starved rats. These results suggest that the MC4 receptor may be the pivotal subtype of MC receptors mediating the leptin stimulation of LH and PRL surges. The data also suggest that endogenous MC(s) may tonically stimulate the hormonal surges in normally fed rats via the MC4 receptor. This is the first report describing a physiological role of a specific MC receptor in regulating the reproductive axis.