Involvement of ovarian steroids and endogenous opioids in the fasting-induced suppression of pulsatile LH release in ovariectomized rats

1991 ◽  
Vol 129 (3) ◽  
pp. 321-328 ◽  
Author(s):  
F. R. A. Cagampang ◽  
K.-I. Maeda ◽  
H. Tsukamura ◽  
S. Ohkura ◽  
K. Ôta
Keyword(s):  
Body Weight ◽  
Opioid Peptides ◽  
Endogenous Opioids ◽  
Blood Sampling ◽  
Ovariectomized Rats ◽  
Opioid Antagonist ◽  
Blood Samples ◽  
Ovarian Steroids ◽  
Naloxone Hydrochloride ◽  
Lh Release

ABSTRACT The participation of the ovarian steroids and opioid peptides in the suppression of pulsatile LH release during acute fasting was examined in rats. Ovariectomized rats bearing silicone elastomer implants of oestradiol and/or progesterone were fasted for 48 h and subsequently blood samples were taken every 6 min for 3 h. Pulsatile LH release was suppressed after 48 h of fasting in the ovariectomized rats implanted with oestradiol but not in the oil-implanted controls. This suppression was enhanced after the administration of progesterone together with oestradiol. In a second experiment, ovariectomized rats bearing implants of oestradiol or oil were fasted for 48 h and injected s.c. (2·5 mg/kg body weight) with an opioid antagonist, naloxone hydrochloride, immediately before blood sampling. In the fasted oestradiol-treated ovariectomized rats, naloxone was able to prevent the suppression of pulsatile LH release. In the absence of oestradiol, however, naloxone was without effect on LH release in either the fasted or unfasted animals. These experiments indicate that the suppression of pulsatile LH release after 48 h of fasting is dependent upon oestradiol and that endogenous opioids are involved in the suppression. Journal of Endocrinology (1991) 129, 321–328

Effects of the opioid antagonist naloxone on release of luteinizing hormone in mares during the anovulatory season

1994 ◽  
Vol 142 (1) ◽  
pp. 139-144 ◽  
Author(s):  
C Aurich ◽  
S Schlote ◽  
H-O Hoppen ◽  
E Klug ◽  
H Hoppe ◽  
...  
Keyword(s):  
Luteinizing Hormone ◽  
Anterior Pituitary ◽  
Reproductive Activity ◽  
Endogenous Opioids ◽  
Opioid Antagonist ◽  
Lh Release ◽  
Lh Secretion ◽  
Opioid Systems ◽  
Follicular Activity

Abstract To investigate an involvement of endogenous opioids in the regulation of circannual changes in reproductive activity, effects of the opioid antagonist naloxone on the concentration of immunoreactive and bioactive luteinizing hormone (LH) in plasma were measured in mares during the anovulatory season. Naloxone (0·5 mg/kg i.v.) caused a significant increase (P<0·05) in immunoreactive as well as bioactive LH concentration in plasma. The amplitude of the increase in LH concentrations measured with an in vitro bioassay was more pronounced than the amplitude of the increase in LH secretion determined by radioimmunoassay. This indicates that although in seasonal anovulatory mares the bioactivity of LH in plasma is low, highly bioactive LH is present in the anterior pituitary and can be released by naloxone. The LH response to naloxone did not depend on the degree of ovarian follicular activity. It can be concluded that a tonic opioid inhibition of LH release is present in mares during at least part of the anovulatory season and that endogenous opioids seem to be involved in the regulation of seasonal reproductive activity in the horse. In contrast to the situation during the breeding season, the opioid systems regulating LH release are activated independently of luteal progesterone. Journal of Endocrinology (1994) 142, 139–144

Fasting impairs LH secretion in female rats by activating an inhibitory opioid pathway

1985 ◽  
Vol 105 (1) ◽  
pp. 91-97 ◽  
Author(s):  
R. G. Dyer ◽  
S. Mansfield ◽  
H. Corbet ◽  
A. D. P. Dean
Keyword(s):  
Sampling Period ◽  
Significant Rise ◽  
Female Rats ◽  
Opioid Antagonist ◽  
Endogenous Opioid ◽  
Opioid Mechanisms ◽  
Before And After ◽  
Naloxone Hydrochloride ◽  
Lh Release ◽  
Lh Secretion

ABSTRACT Two experiments were undertaken to investigate the way that fasting impairs LH secretion and to assess whether endogenous opioid mechanisms might be responsible for the impairment. In the first experiment, pulsatile LH secretion was measured in a total of 51 chronically ovariectomized female rats. Initially 29 rats were subjected to food withdrawal for 24, 48, 72 or 120 h before the experiment. When compared with data collected from eight unfasted control rats, the 120-h fast was found to reduce significantly the mean peak and trough values of the LH pulses measured. However, in a subsequent study, the inhibition of pulsatile LH secretion by a 120-h fast was prevented in a group of eight rats given the opioid antagonist naloxone hydrochloride before the start of the blood-sampling period. Naloxone was without effect on pulsatile LH secretion in eight unfasted control rats. In the second experiment, plasma LH concentrations were measured before and after unilateral electrical stimulation of the ventral noradrenergic tract (VNAT) in ovariectomized female rats pretreated with oestradiol benzoate. In 17 rats VNAT stimulation caused a significant rise in plasma LH, but after a 72-h fast this rise was significantly less than in unfasted control rats. However, pretreatment of fasted rats with naloxone (n = 9) significantly enhanced the VNAT-stimulated release of LH to the control values. Naloxone did not potentiate VNAT-stimulated LH release in unfasted animals (n = 6) or LH release in control unstimulated rats (n = 12). The experiments indicate that both pulsatile LH secretion, and LH release caused by VNAT stimulation, are impaired by an acute fast. In both cases, the impairment is prevented by pretreatment with naloxone. Thus fasting probably activates an inhibitory opioid pathway within the brain to inhibit LH secretion. J. Endocr. (1985) 105, 91–97

Mapping episodic fluctuations in plasma LH in orchidectomized rats

1984 ◽  
Vol 247 (1) ◽  
pp. E130-E135 ◽  
Author(s):  
G. B. Ellis ◽  
C. Desjardins
Keyword(s):  
Simulated Data ◽  
Pulse Frequency ◽  
Sampling Interval ◽  
Blood Sampling ◽  
Male Rats ◽  
High Positive Correlation ◽  
Blood Samples ◽  
Sampling Intervals ◽  
Lh Release ◽  
Episodic Fluctuations

Reports of the frequency of pulsatile LH release in orchidectomized rats are surprisingly variable. Estimates of the period between LH pulses vary from 18.5 to 250 min in nine reports from six laboratories, published in 1981-1983. In these studies, blood samples were drawn at intervals ranging from 2.5 to 60 min. We examined the relationship between estimated LH pulse frequency and blood-sampling interval. Six castrated male rats were cannulated, and blood samples were drawn at 2.5-min intervals through 4 h. Plasma LH levels were determined by radioimmunoassay. Using the data obtained at 2.5-min intervals, we simulated blood-sampling intervals of 5, 7.5, 10, 12.5, and 15 min by sequentially deleting data points. The original and simulated data sets were analyzed by both the PULSAR and Cycle Detector computer programs. The results show that as the sampling interval increased from 2.5 to 15 min, the apparent period of pulsatile LH release rose steadily from about 20 min to about 100 min. We found a high, positive correlation between blood-sampling interval and the apparent period of LH pulses. Estimates of LH pulse frequency in castrated male rats vary directly with the frequency at which blood samples are taken. Sampling intervals greater than 5 min in orchidectomized rats yield an LH pulse period that is most likely exaggerated.

scholarly journals Reciprocal changes in leptin and NPY during nutritional acceleration of puberty in heifers

2014 ◽  
Vol 223 (3) ◽  
pp. 289-298 ◽  
Author(s):  
Rodolfo C Cardoso ◽  
Bruna R C Alves ◽  
Ligia D Prezotto ◽  
Jennifer F Thorson ◽  
Luis O Tedeschi ◽  
...  
Keyword(s):  
Cerebrospinal Fluid ◽  
Body Weight ◽  
Neuropeptide Y ◽  
Early Onset ◽  
Third Ventricle ◽  
High Gain ◽  
Blood Sampling ◽  
Juvenile Period ◽  
Lh Release ◽  
Juvenile Development

Feeding a high-concentrate diet to heifers during the juvenile period, resulting in increased body weight (BW) gain and adiposity, leads to early-onset puberty. In this study, we tested the hypothesis that the increase in GnRH/LH release during nutritional acceleration of puberty is accompanied by reciprocal changes in circulating leptin and central release of neuropeptide Y (NPY). The heifers were weaned at 3.5 months of age and fed to gain either 0.5 (Low-gain; LG) or 1.0 kg/day (High-gain; HG) for 30 weeks. A subgroup of heifers was fitted surgically with third ventricle guide cannulas and was subjected to intensive cerebrospinal fluid (CSF) and blood sampling at 8 and 9 months of age. Mean BW was greater in HG than in LG heifers at week 6 of the experiment and remained greater thereafter. Starting at 9 months of age, the percentage of pubertal HG heifers was greater than that of LG heifers, although a replicate effect was observed. During the 6-h period in which CSF and blood were collected simultaneously, all LH pulses coincided with or shortly followed a GnRH pulse. At 8 months of age, the frequency of LH pulses was greater in the HG than in the LG group. Beginning at 6 months of age, concentrations of leptin were greater in HG than in LG heifers. At 9 months of age, concentrations of NPY in the CSF were lesser in HG heifers. These observations indicate that increased BW gain during juvenile development accelerates puberty in heifers, coincident with reciprocal changes in circulating concentrations of leptin and hypothalamic NPY release.

Effect of opioid peptides on gonadotrophin secretion

1982 ◽  
Vol 99 (3) ◽  
pp. 321-325 ◽  
Author(s):  
M. Motta ◽  
L. Martini
Keyword(s):  
Opioid Peptides ◽  
Serum Levels ◽  
Ovariectomized Rats ◽  
Intraventricular Injection ◽  
Experimental Conditions ◽  
Serum Lh ◽  
Gonadotrophin Secretion ◽  
Intraventricular Injections ◽  
Lh Release

Abstract. The intraventricular injection of 25 μg of Methionine-Enkephalin (Met-Enk) induces a significant increase of serum LH levels in long-term ovariectomized rats 15, 30 and 60 min following administration. The synthetic Met-Enk agonistic analogue [D-Ala2]Methionine-Enkephalinamide ([D-Ala2]Met-Enk) also enhances significantly serum LH levels at 30 and 60 min; under the same experimental conditions neither Met-Enk nor [D-Ala2]Met-Enk modifies serum levels of FSH following intraventricular injections into ovariectomized animals. It is concluded that, under particular circumstances, opioid peptides of the Met-Enk family may stimulate LH release.

THE EFFECTS OF OVARIAN STEROIDS ON FOOD AND WATER INTAKE AND BODY WEIGHT IN THE FEMALE RAT

1973 ◽  
Vol 72 (3) ◽  
pp. 551-568 ◽  
Author(s):  
M. F. Tarttelin ◽  
R. A. Gorski
Keyword(s):  
Body Weight ◽  
Water Intake ◽  
Ovariectomized Rats ◽  
Daily Injection ◽  
Female Rat ◽  
Oestrogen Treatment ◽  
Ovarian Steroids ◽  
Food And Water Intake ◽  
Ovariectomized Animal

ABSTRACT The influence of ovarian steroids on food intake (FI), water intake (WI) and body weight (BWt) was measured under various conditions. Ovariectomy results in an increase in FI and BWt, which plateaued around one month after surgery. Daily injection of 1.5 μg oestradiol benzoate (OB) initiated at this time significantly reduced both FI and BWt. This effect of daily OB treatment on FI is only transitory since the FI returns to normal during OB treatment although the effect on BWt is maintained throughout and beyond OB treatment. Following ovariectomy, WI gradually falls, but is returned to normal by daily OB treatment. When oestrogen treatment is initiated at the time of ovariectomy, the increase in FI and BWt is prevented. In additional ovariectomized rats, 3 μg OB was injected every fifth day with either progesterone or oil administered on the intervening days. Although no influence of progesterone injection (either with OB or alone) was detected, the intermittent injection of OB induced cyclic suppression of FI, and the pattern of FI approached that of the intact cycling female. Adaptation to the intermittent injection of OB was not observed. Finally, OB treatment was found to decrease the increased FI seen during pseudopregnancy by a proportion similar to the effect of oestrogen in the long-term ovariectomized animal. These results suggest that oestrogen, but not progesterone, is the ovarian hormone active in the regulation of intake parameters and body weight in the female rat.

Evidence for reorganization of the neuroendocrine centres regulating pulsatile LH secretion in rats receiving neonatal monosodium-l-glutamate treatment

1987 ◽  
Vol 113 (2) ◽  
pp. 261-269 ◽  
Author(s):  
P. A. Rose ◽  
R. F. Weick
Keyword(s):  
Anterior Part ◽  
Ovariectomized Rats ◽  
Brain Surgery ◽  
Blood Samples ◽  
Neonatal Treatment ◽  
Pulsatile Secretion ◽  
Electrolytic Lesions ◽  
Lh Release ◽  
Arcuate Nuclei ◽  
Lh Secretion

ABSTRACT Previous research has shown that the combination of anterior hypothalamic deafferentation (AHD) and electrolytic lesions of the anterior part of the arcuate nuclei blocks pulsatile LH secretion in ovariectomized rats, but that neither lesion alone was effective. Furthermore, the combination of AHD with arcuate lesions produced by neonatal treatment with monosodium-l-glutamate (MSG) does not block pulsatile LH release. To distinguish between the various possible reasons for this result, AHD and electrolytic lesions of the arcuate nuclei were combined in rats which had been treated neonatally with MSG or saline of equal osmolarity. One week after brain surgery, venous catheters were installed and blood samples taken at 5-min intervals for up to 3 h for assay of plasma LH. Rats treated with MSG and bearing AHD and electrolytic lesions of the arcuate nuclei continued to show pulsatile secretion of LH. Where the electrolytic lesions were posterior and dorsal to the anterior arcuate nuclei, however, LH release was blocked whether AHD was performed or not, but only in rats treated with MSG. None of the lesion combinations blocked pulsatile LH secretion in rats treated with saline. These results suggest that neonatal MSG treatment leads to a reorganization of the hypothalamus such that the role normally played by the arcuate nuclei in the regulation of pulsatile LH secretion is taken over by other hypothalamic structures. J. Endocr. (1987) 113, 261–269

Endogenous opioids modulate fetal rabbit lung maturation

1987 ◽  
Vol 62 (6) ◽  
pp. 2141-2146 ◽  
Author(s):  
C. R. Comer ◽  
J. S. Grunstein ◽  
R. J. Mason ◽  
S. C. Johnston ◽  
M. M. Grunstein
Keyword(s):  
Body Weight ◽  
Fetal Lung ◽  
Dry Weight ◽  
Endogenous Opioids ◽  
Opioid Antagonist ◽  
Saline Control ◽  
Lung Maturation ◽  
Rabbit Lung ◽  
Lung Weight ◽  
Air Space

To test the hypothesis that endogenous opioids modulate fetal lung development, separate groups of pregnant rabbits received daily injections of saline, morphine (1 mg/kg body wt), or the opioid antagonist naloxone (0.4 and 5.0 mg) for 10 days during their last trimester of pregnancy. The corresponding groups of fetuses were then delivered prematurely on day 28 of gestation (term approximately 31 days) and evaluated with respect to differences in body weight, lung weight, and the ratios of wet to dry lung weight and lung dry weight to body weight, the static inflation and deflation air and saline pressure-volume (P-V) characteristics of the lungs, and lung morphology. Mean values for body weight, lung weight, and the ratios of lung wet to dry weight and lung dry weight to body weight were not significantly different among the saline control (C), morphine (M)-, and naloxone (NLX)-treated fetuses. On the other hand, the fetal air P-V curves varied significantly (P less than 0.001), wherein the M-treated group depicted increased lung distensibility and alveolar stability on lung deflation, whereas the opposite was obtained in the NLX-treated fetuses. Moreover, morphometric analyses demonstrated that the mean alveolar air space-to-tissue ratio in lungs from M-treated fetuses were significantly greater than that observed either in C or in NLX-treated fetuses (P less than 0.05); however, the air space-to-tissue ratio did not significantly vary between the C and NLX-treated animals. These observations provide new evidence that endogenous opioids enhance fetal lung maturation.

Effect of acute immunoneutralization of endogenous leptin on prolactin and LH secretion during the afternoon of pro-oestrus or in steroid-treated ovariectomized female rats

Reproduction ◽  
2000 ◽  
pp. 39-45 ◽  
Author(s):  
LC Gonzalez ◽  
L Pinilla ◽  
M Tena-Sempere ◽  
C Dieguez ◽  
FF Casanueva ◽  
...  
Keyword(s):  
Prolactin Secretion ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Rabbit Serum ◽  
Normal Rabbit Serum ◽  
Blood Samples ◽  
Lh Release ◽  
Lh Secretion

Recent data indicate that leptin is involved in the control of reproductive function. Experiments were carried out to analyse the role of endogenous leptin in the regulation of LH and prolactin secretion during the afternoon of pro-oestrus and that induced by ovarian steroids in ovariectomized rats. In the first experiment, cyclic female rats were implanted with intra-auricular and intracerebroventricular (i.c.v.) cannulae and, at pro-oestrus, were injected (i.c.v.) with 10 microliters normal rabbit serum or leptin antiserum (at 13:00 and 14:00 h). Blood samples were obtained at 10:00 h and at intervals of 1 h between 13:00 and 20:00 h. In the second experiment, female rats in pro-oestrus were injected with normal rabbit serum or leptin antiserum at 16:00 and 18:00 h and blood samples were taken every 10 min between 18:00 and 20:00 h. In the third experiment, adult female rats that had been ovariectomized 2 weeks before were implanted with intra-auricular and i.c.v. cannulae and treated with oestradiol benzoate (30 micrograms s.c.) at 10:00 h and progesterone (2 mg s.c.) 48 h later. Normal rabbit serum (10 microliters) or leptin antiserum (10 microliters) were injected (i.c.v.) at 13:00 and 14:00 h, and blood samples were obtained at 10:00 h and at intervals of 1 h between 13:00 and 20:00 h. In the fourth experiment, hemipituitaries from ovariectomized steroid-treated female rats were incubated in the presence of leptin116-130 (an active fragment of the native molecule), GnRH or leptin + GnRH. Prolactin and LH secretion during the afternoon of pro-oestrus in females treated with leptin antiserum was similar to that observed in animals injected with normal rabbit serum. In ovariectomized female rats, the steroid-induced LH surge increased slightly after administration of leptin antiserum, whereas the prolactin surge remained unchanged. In vitro, leptin116-130 (10(-5) to 10(-8) mol l-1) inhibited LH secretion and modulated the effect of GnRH on LH release, depending on the concentration of GnRH: leptin116-130 (10(-6) mol l-1) reduced the effectiveness of 10(-7) mol GnRH l-1 and increased that of 10(-9) mol GnRH l-1. In conclusion, these experiments indicate that acute immunoneutralization of endogenous leptin does not interfere with spontaneous or steroid-induced LH and prolactin surges. In addition, the finding that leptin116-130 inhibited LH release and modulated the effectiveness of GnRH in vitro provides evidence of the direct modulatory role of leptin on LH secretion acting at the pituitary.

INFLUENCE OF AGE, WEIGHT AND GROWTH RATE ON BASAL LH, GROWTH HORMONE AND CORTISOL, AND ESTROGEN-INDUCED LH RELEASE IN PREPUBERTAL GILTS

1987 ◽  
Vol 67 (4) ◽  
pp. 1001-1010 ◽  
Author(s):  
R. N. KIRKWOOD ◽  
F. D. EVANS ◽  
F. X. AHERNE
Keyword(s):  
Growth Hormone ◽  
Body Weight ◽  
Treatment Effects ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Estradiol Benzoate ◽  
Early Morning ◽  
Blood Samples ◽  
Lh Release

Thirty-six Yorkshire × Landrace gilts were selected at 74 d of age and 32 kg body weight and assigned equally to one of six treatments. The first three treatments involved feeding gilts to achieve weights of 90 kg at 175 d, 90 kg at 195 d, or 70 kg at 175 d (treatments 1, 2 and 3, respectively). A further three groups of gilts were fed to achieve the same weights (90, 90 or 70 kg) 20 d younger than those above. Upon the achievement of their final weight the latter three groups of gilts were subjected to a feed restriction in order to achieve a zero net weight for 20 d until they achieved the required age (treatments 4, 5 and 6). At the achievement of the specified age-weight end point blood samples were taken from all gilts at 2-h intervals for 24 h (2400–2200 h) for the determination of plasma concentrations of luteinizing hormone (LH), growth hormone (GH) and Cortisol. Additionally, during a 4-h period on the same day (0800–1200 h) all gilts were sampled at 15-min intervals for determination of pulsatile LH secretion. Following the initial 24-h sampling, all gilts received an intramuscular injection of estradiol benzoate (EB; 15 μg kg−1 body weight) and blood samples were collected at 6-h intervals for 72 h for determination of plasma LH. No treatment effects were noted on the mean daily plasma levels of cortisol, LH or GH. Plasma concentrations of cortisol tended to decrease with increasing age or weight, but these differences were not significant. Significant elevations of plasma GH occurred in the early morning and evening, but rarely between 0400 and 1600 h. A similar nycterohemeral rhythm was noted for plasma LH levels. There were no treatment effects on LH pulse frequency but LH pulse amplitude was greater at a given age (P < 0.07), in the heavier gilts (treatments 1 and 4 vs. 3 and 6). There was no effect of treatment on the LH response to EB injection, although two patterns of LH release were observed, involving either a single or a double peak of LH. Key words: Gilts, age, weight, puberty

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