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Objectives: Ghrelin, an endogenous growth hormone secretagogue, is a known accelerator of feeding behavior and suppresses pulsatile secretion of luteinizing hormone (LH) in ovariectomized rats. However, the mechanisms underlying this action remain unclear. We examined the effects of naloxone (NAL), a specific opioid antagonist, on the suppression of pulsatile LH secretion by ghrelin to determine whether β-endorphin (β-END) is involved in this suppressive effect. Methods: Ghrelin was administered intracerebroventricularly, and NAL was injected intravenously in ovariectomized rats; then, serum LH concentrations were measured by radioimmunoassay in blood samples drawn every 6 min for 2 h to analyze pulsatile secretion. Results: Administration of ghrelin significantly reduced mean LH concentration and pulse frequency. Coadministration of NAL with ghrelin significantly restored mean LH concentration and pulse frequency. Conclusion: Suppressive effect of intracerebroventricular injection of ghrelin on pulsatile LH secretion was mediated by β-END, suggesting that hypothalamic ghrelin suppressed pulsatile gonadotropin-releasing hormone secretion via β-END in female rats.

Pregnancy and lactation induce dynamic changes in maternal bone and calcium metabolism. A novel cytokine termed osteoprotegerin (OPG)/osteoclastogenesisinhibitory factor (OCIF) was recently isolated; this cytokine inhibits osteoclast maturation. To define the effects of pregnancy and lactation on circulating OPG/OCIF in mothers, we studied the changes in the levels of OPG/ OCIF as well as those of calcium-regulating hormones and biochemical markers of bone turnover in the maternal circulation during pregnancy (at 8-11 weeks, at 22-30 weeks, at 35-36 weeks and immediately before delivery) and lactation (at 4 days and at 1 month postpartum).Serum intact parathyroid hormone levels did not change and were almost within the normal range in this period. In contrast, serum 1,25-dihydroxyvitamin D levels increased with gestational age and were above the normal range during pregnancy. After delivery, they fell rapidly and significantly (P<0·01) to the normal range. The levels of serum bone-specific alkaline phosphatase, one of the markers of bone formation, increased with gestational age.After delivery, these levels were further increased at 1 month postpartum. The levels at 1 month postpartum were significantly higher than those at 8-11 and 22-30 weeks of pregnancy (P<0·01 and P<0·05 respectively). The levels of serum C-terminal telopeptides of type I collagen, one of the markers of bone resorption, did not change during pregnancy. After delivery, they rapidly and significantly (P<0·01) rose at 4 days postpartum, and had then fallen by 1 month postpartum. Circulating OPG/ OCIF levels gradually increased with gestational age and significantly (P<0·01) increased immediately before delivery to 1·40 0·53 ng/ml (means S.D.) compared with those in the non-pregnant, non-lactating controls (0·58 0·11 ng/ml). After delivery, they fell rapidly to 0·87 0·27 ng/ml at 4 days postpartum and had fallen further by 1 month postpartum.These results suggest that the fall in OPG/OCIF levels may be partially connected with the marked acceleration of bone resorption after delivery.

Background: Leptin, which is the product of the obese gene, is believed to play important roles in pubertal development and reproductive function in females. In a study using adult male rats, it was found that leptin stimulated secretion of gonadotropin from the pituitary in a dose-related manner. However, there has been no such study in female rats. Objective: To investigate the effects of leptin on the production of LH and FSH from the pituitary in female rats, using primary cultured pituitary cells. Methods: In this study, we determined body weight, serum leptin concentration and serum estradiol (E 2 ) concentration in female Wistar rats at 3, 5, 6, 7, 9 and 11 weeks of age, and cultured pituitary cells from 6-week-old female Wistar rats with leptin (0±10 27 mol/l) and GnRH (0 or 10 28 mol/l). Then basal and GnRH-stimulated extra-and intracellular LH and FSH were assayed by RIA. Results: Serum leptin concentration increased with increases in body weight and E 2 concentration. The pubertal serum leptin concentration was about 10 210 mol/l. At a lower or moderate concentration, leptin produced dose-related increases in both basal and GnRH-stimulated extraand intracellular LH and FSH in pituitary cells. At a concentration of 10 210 mol/l, leptin significantly P , 0X05 stimulated both basal and GnRH-stimulated extra-and intracellular LH and FSH. However, at greater concentrations, these effects diminished. Conclusions: These results indicated that leptin induced pituitary cells to produce and secrete both LH and FSH, with or without GnRH. The concentration of leptin that induced the greatest production of gonadotropins by pituitary cells was 10 210 mol/l, which was the same as the physiological pubertal concentration. Leptin may be involved in the onset of puberty. It is also conceivable that leptin may be a cause of ovulatory failure, not only in weight loss but also in weight gain.

Objective: Leptin is an adipocyte-derived hormone, which is the product of the obese gene and it is thought to play important roles in pubertal development and maintenance of reproductive function in the female. In a study using adult male or female rats, it was found that leptin stimulated the secretion of gonadotropin directly from the pituitary in a dose-related manner. However, there is no study in juvenile female rats before puberty. Methods: In this study, we cultured pituitary cells from 4-, 6-and 8-week-old female Wistar rats with leptin (0 -10 27 mol/l) and gonadotropin-releasing hormone (GnRH) (0 or 10 28 mol/l). Basal or GnRH-stimulated secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and their synthesis within cells were determined by radioimmunoassay (RIA). Results: Leptin induced bell-shaped dose -response curves of basal LH and FSH secretion from cultured cells of every age-group of rats studied. The most effective concentration of leptin on the basal secretion of LH and FSH from 6-and 8-week-old cultured pituitary cells was 10 210 mol/l. This leptin concentration was consistent with circulating physiological serum leptin levels at each age. As for juvenile 4-week-old pituitary cells, the most effective concentration was 10 211 mol/l which was lower than that of 6-and 8-week-old rats. It was consistent with the circulating serum leptin levels of 4-week-old rats. Also, the synthesis and the GnRH-stimulated secretion of LH and FSH were effectively controlled by leptin at concentrations similar to the serum leptin levels of given ages. Conclusions: Leptin induced pituitary cells to synthesize and secrete both LH and FSH regardless of the presence or absence of GnRH. The concentration of leptin that induced the greatest synthesis and secretion of gonadotropins from pituitary cells changed around the pubertal period. The most effective leptin concentrations in each experiment were similar to the physiological serum leptin level at each animal age. These results indicate that leptin stimulates gonadotrophs not only in the pubertal and the mature period but also in the juvenile period before puberty. It is also conceivable that leptin may modulate the sensitivity of gonadotrophs until the appearance of GnRH stimulation, and may be the factor that brings about puberty onset.

Orexins are thought to be regulatory factors of the arousal and sleep patterns. They also affect immune, feeding, autonomic and neuroendocrine systems. We have previously shown that intracerebroventricular (i.c.v.) injection of orexin decreases pulsatile luteinising hormone (LH) secretion in ovariectomised (OVX) rats. However, the details of this mechanism have not been fully examined. Intracerebroventricular injection of orexin A also stimulates corticotrophin-releasing hormone (CRH) systems, which have been implicated in the stress-induced suppression of reproductive function. In the present study, we investigated the role of CRH systems in orexin-induced LH suppression. OVX rats were implanted with i.c.v. and intravenous (i.v.) cannulae. After i.c.v. injection of orexin and/or CRH receptor antagonists, blood samples were collected through the i.v. cannula at 6-min intervals for 120 min for LH measurement. Intracerebroventricular injection of orexin A or B (3 nmol/2.5 microl) suppressed pulsatile LH secretion. Coadministration of orexin A and alpha-helical corticotrophic-releasing factor (CRF), a nonselective CRH receptor antagonist (13 nmol/2.5 microl), or astressin(2)B, a selective type2 (CRH-R2) CRH receptor antagonist (28 nmol/2.5 microl), partly restored pulsatile LH secretion. Orexin B-induced LH suppression was not restored by alpha-helical CRF. In addition, i.c.v. injection of orexin A increased CRH and urocortin II (UcnII), but not Ucn mRNA levels, in the hypothalamus. These findings suggest that CRH-R2 mediates orexin A-induced LH suppression and it is possible that CRH and UcnII in the hypothalamus are involved in this pathway.

It has been reported that prenatal immune stress induced by lipopolysaccharides or cytokines increases food intake and leads to obesity and other features of metabolic syndrome in adulthood. Using Sprague-Dawley rats, we evaluated whether neonatal LPS injection altered their body weight regulation systems under non-stress and immune stress conditions. On Day 10 after birth, all pups were injected with LPS (100 microg/kg, i.p.) (PND(10)LPS) or saline (PND(10)Saline). After weaning, body weight was significantly elevated in PND(10)LPS compared with PND(10)Saline. Thereafter, the rats were injected with LPS (100 microg/kg, i.p.) or saline (used as a basal condition) from 7 to 8 weeks of age. Under basal conditions, cumulative food intake were significantly higher, serum leptin concentration was significantly increased, and hypothalamic NPY mRNA expression was significantly decreased in PND(10)LPS compared with PND(10)Saline. Under adult LPS injected conditions, body weight gain and cumulative food intake were suppressed in both the PND(10)LPS and PND(10)Saline groups compared with those observed under basal adult saline-injected conditions. The suppressive effects induced by adult LPS injection were less evident in the PND(10)LPS group than in the PND(10)Saline group. Adult LPS injection increased the serum leptin concentration in the PND(10)Saline rats, but not in the PND(10)LPS rats. In addition, adult LPS injection increased the mRNA expression of anorexinergic factors (IL-1beta, and TNF-alpha), and decreased that of the orexinergic factor NPY in both groups. However, the influence of adult LPS injection upon these factors was less evident in the PND(10)LPS group than in the PND(10)Saline group. These results suggest that neonatal LPS injection alters body weight regulation under both non-stress and immune stress conditions in male rats. Changes in the endocrine, neuropeptide, and cytokine regulation systems might be involved in these alterations.