Photoperiodic modulation of the dopaminergic control of pulsatile LH secretion in sheep

1994 ◽  
Vol 143 (1) ◽  
pp. 25-32 ◽  
Author(s):  
D J Tortonese ◽  
G A Lincoln
Keyword(s):  
Dopaminergic System ◽  
Pulse Frequency ◽  
Inhibitory System ◽  
Pulsatile Gnrh ◽  
Photoperiodic Regulation ◽  
Series Of Experiments ◽  
Induced Changes ◽  
Lh Secretion ◽  
Short Days ◽  
Sustained Increase

Abstract This study was conducted to investigate whether the photoperiodic regulation of the seasonal changes in pulsatile LH secretion in the ram involves changes in the activity of inhibitory hypothalamic dopaminergic (DA) pathways. To test this hypothesis, a series of experiments was carried out in Soay rams in which the effects of a DA-D2 receptor antagonist (sulpiride) or a DA-D2 receptor agonist (bromocriptine) on the pulsatile secretion of LH were determined under both long and short days. In each experiment blood samples were collected every 10 min for 8 h starting at the time of vehicle, sulpiride or bromocriptine injections to assess concentrations of LH. Sulpiride (0·59 mg/kg, s.c.) administered to rams under long days induced an immediate and sustained increase in the secretion of LH that lasted for approximately 4 h (P<0·05; ANOVA); this LH response reflected both a rise in mean concentrations (0·247 ± 0·03 vs.0·452 ± 0·1 μg/1) and an increase in the frequency of LH pulses (0·5±0·5 vs. 2·33±0·42 pulses/8 h; P<0·01). In contrast, under short days sulpiride had no effect. Bromocriptine (0·06 mg/kg, s.c.) administered to rams under long days, when LH concentrations were low, was without effect, but when given to rams under short days significantly (P<0·05) suppressed mean LH concentrations (0·627 ±0·08 vs. 0·320 ± 0·02 μg/l) and LH pulse frequency (4·86 ±0·46 vs. 2·43 ±0·37 pulses/8 h). In an additional experiment, pimozide (total dose: 0·16 mg/kg, i.m.), a DA antagonist less specific for DA-D2 receptors than sulpiride, was ineffective in modifying LH secretion in sexually inactive rams exposed to long days. These results are consistent with the hypothesis that an inhibitory dopaminergic system is involved in the regulation of pulsatile LH secretion in the ram. The induced changes in LH pulse frequency under long days (increased by sulpiride) and under short days (decreased by bromocriptine) indicate that, under both photoperiods, DA acts within the hypothalamus, via a specific DA-D2 receptor, to influence pulsatile GnRH secretion. A photoperiodic-induced activation of this inhibitory system may therefore represent the mechanism whereby long days suppress LH secretion and lead to the sexually inactive state characteristic of the non-breeding season. Journal of Endocrinology (1994) 143, 25–32

Non-responsiveness of serum gonadotropins and testosterone to pulsatile GnRH in hemochromatosis suggesting a pituitary defect

1993 ◽  
Vol 128 (4) ◽  
pp. 351-354 ◽  
Author(s):  
Lise Duranteau ◽  
Philippe Chanson ◽  
Joelle Blumberg-Tick ◽  
Guy Thomas ◽  
Sylvie Brailly ◽  
...  
Keyword(s):  
Single Pulse ◽  
Serum Testosterone ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Gonadotropin Secretion ◽  
Pulsatile Gnrh ◽  
Serum Lh ◽  
Before And After ◽  
Gnrh Therapy ◽  
Lh Secretion

We investigated the potential pituitary origin of gonadal insufficiency in hemochromatosis. Gonadotropin secretion was studied in seven patients with hemochromatosis and hypogonadism, before and after chronic pulsatile GnRH therapy. Pulsatile LH secretion was studied before (sampling every 10 min for 6 h) and after 15-30 days of chronic pulsatile GnRH therapy (10-12 μg per pulse). Prior to GnRH therapy, all the patients had low serum testosterone, FSH and LH levels. LH secretion was non-pulsatile in four patients, while a single pulse was detected in the remaining three. Chronic pulsatile GnRH administration did not increase serum testosterone levels; similarly, serum LH levels remained low: neither pulse frequency nor pulse amplitude was modified. We conclude that hypogonadism in hemochromatosis is due to pituitary lesions.

scholarly journals Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

1999 ◽  
Vol 163 (2) ◽  
pp. 243-254 ◽  
Author(s):  
F Bertrand ◽  
J Thiery ◽  
S Picard ◽  
B Malpaux
Keyword(s):  
Median Eminence ◽  
Critical Role ◽  
Pulse Frequency ◽  
Prolactin Secretion ◽  
Dopaminergic Receptors ◽  
Long Day ◽  
Agonist And Antagonist ◽  
Lh Release ◽  
Lh Secretion ◽  
Short Days

In ewes, photoperiod modulates LH release and dopaminergic terminals in the median eminence (ME) have a critical role in the establishment of long-day inhibition of LH secretion. This study was undertaken to determine the type of dopaminergic receptors, D1-like or D2-like, that mediate the action of dopamine on LH secretion at the ME level in this situation. This was assessed, in ovariectomized and estradiol-treated ewes, with the use of reverse microdialysis in the ME in three experiments: first, when LH secretion was stimulated by short days, by determining the response to three doses (0.01, 0.1 or 1 mg/ml) of a D1-like (SKF38393) and a D2-like (quinpirole) agonist; secondly, during early long-day inhibition of LH secretion, by determining the ability of SKF38393 and quinpirole (1 mg/ml) to mimic the inhibitory effects of dopamine, after a blockade of its synthesis with alpha-methyl-para-tyrosine (alphaMPT; 2 mg/ml); and thirdly, during early long-day inhibition of LH secretion, by determining the response to three doses (0.009, 0.09 or 0.9 mg/ml) of a D1-like (SCH23390) and a D2-like (sulpiride) antagonist. In none of the conditions was effect of the D1-like analogs on LH secretion found, compared with the control treatments. In contrast, the D2-like analogs caused changes in LH secretion. First, with short days, quinpirole in the highest dose significantly reduced mean LH concentration (P<0.05) and LH pulse frequency (P<0.01). Secondly, with long days, addition of quinpirole to alphaMPT caused a significant decrease in LH secretion relative to alphaMPT alone (P<0.05). Thirdly, with long days, sulpiride at the highest dose significantly increased mean LH concentration (during the first 3 h of treatment, P<0.05) and LH pulse frequency (P<0.05). Prolactin secretion was also determined in these experiments, and D2-like agonist and antagonist caused an inhibition and a stimulation of prolactin secretion, respectively. These results demonstrate that, in the ME, inhibitory action of dopamine on LH secretion, critical for the initiation of long-day-induced inhibition, is mediated by D2-like, not D1-like, dopaminergic receptors.

scholarly journals A Reevaluation of the Question: Is the Pubertal Resurgence in Pulsatile GnRH Release in the Male Rhesus Monkey (Macaca mulatta) Associated With a Gonad-Independent Augmentation of GH Secretion?

Endocrinology ◽  
2015 ◽  
Vol 156 (10) ◽  
pp. 3717-3724
Author(s):  
M. Shahab ◽  
M. Vargas Trujillo ◽  
T. M. Plant
Keyword(s):  
Repeated Measures ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Detection Algorithm ◽  
Juvenile Male ◽  
Gh Secretion ◽  
Pulsatile Gnrh ◽  
Gnrh Release ◽  
Somatic Signal ◽  
Lh Secretion

A somatic signal has been posited to trigger the pubertal resurgence in pulsatile GnRH secretion that initiates puberty in highly evolved primates. That GH might provide such a signal emerged in 2000 as a result of a study reporting that circulating nocturnal GH concentrations in castrated juvenile male monkeys increased in a 3-week period immediately preceding the pubertal resurgence of LH secretion. The present study was conducted to reexamine this intriguing relationship, again in an agonadal model. Four castrated juvenile male monkeys were implanted with indwelling jugular catheters, housed in remote sampling cages, and subjected to 24 hours of sequential blood sampling (every 30 min) every 2 weeks from 19.5 to 22 months of age. Twenty-four-hour profiles of circulating GH concentrations were analyzed using the pulse detection algorithm, PULSAR, and developmental changes in pulsatile GH release with respect to the initiation of the pubertal rise of LH secretion (week 0; observed between 22.5 and 32 mo of age) were examined for significance by a repeated-measures ANOVA. Changes in the parameters of pulsatile GH secretion, including mean 24-hour GH concentration and GH pulse frequency and pulse amplitude for 3 (n = 4) and 6 (n = 3) months before week 0 were unremarkable and nonsignificant. These findings fail to confirm those of the earlier study and lead us to conclude that the timing of the pubertal resurgence of GnRH release in the male monkey is not dictated by GH. Reasons for the discrepancy between the two studies are unclear.

scholarly journals Influence of steroids and GnRH on biosynthesis and secretion of secretogranin II and chromogranin A in relation to LH release in LbetaT2 gonadotroph cells

2002 ◽  
Vol 174 (3) ◽  
pp. 473-483 ◽  
Author(s):  
L Nicol ◽  
M Stridsberg ◽  
JL Crawford ◽  
AS McNeilly ◽  
Keyword(s):  
Chromogranin A ◽  
Secretory Granules ◽  
Close Correlation ◽  
Pulse Frequency ◽  
Mrna Levels ◽  
Secretogranin Ii ◽  
Mouse Pituitary ◽  
Induced Changes ◽  
Lh Secretion ◽  
Dose Dependent

The granin proteins secretogranin II (SgII) and chromogranin A (CgA) are commonly found associated with LH and/or FSH within specialised secretory granules in gonadotroph cells, and it is possible that they play an important role in the differential secretion of the gonadotrophins. In this study we have examined the regulation of the biosynthesis and secretion of SgII and CgA, in relation to LH secretion, in the LbetaT2 mouse pituitary gonadotroph cell line. Three experiments were carried out to investigate the effects of oestradiol (E2) and dexamethasone (Dex) in the presence and absence of GnRH (experiment 1), differing GnRH concentrations (experiment 2) and alterations in GnRH pulse frequency (experiment 3). In experiment 1, exposure to E2, Dex or E2+Dex, either with or without GnRH treatment, resulted in increased LH secretion. Steroids alone had no effect on LHbeta mRNA levels, but in the presence of GnRH LHbeta mRNA levels were increased in Dex- and E2+Dex-treated cells. GnRH receptor (GnRH-R) mRNA levels were up-regulated by Dex and E2+Dex, but were unaffected by GnRH. There were no steroid-induced changes in SgII or CgA mRNA, but increased levels of CgA mRNA were observed after GnRH treatment in cells cultured in the presence of Dex. In experiment 2, increasing concentrations of GnRH resulted in increases in LH secretion that were inversely dose-dependent. No changes in LHbeta, GnRH-R or SgII mRNA levels were observed, but there were dose-dependent increases in CgA mRNA levels. In experiment 3, GnRH was given as either 1 pulse/day or 4 pulses/day for 3 days. Both pulse regimes resulted in increased LH, SgII and CgA secretion compared with controls during the first 15 min pulse on day 3. Exposure to GnRH at 4 pulses/day increased LH and SgII secretion compared with controls during all 4 pulses, but secretion of both proteins was reduced during pulses 2-4 compared with pulse 1. CgA secretion also increased due to GnRH in pulse 1, but was decreased by GnRH treatment during pulse 2, and unchanged by GnRH during pulses 3 and 4. Total daily secretion of LH and SgII from cells given 1 pulse/day of GnRH increased compared with controls on all three treatment days, while total CgA secretion increased in response to GnRH on days 2 and 3 only. Intracellular levels of SgII, but not LH, decreased after GnRH treatment. In contrast, intracellular CgA was increased, but only after 4 pulses/day of GnRH. Levels of LHbeta, but not SgII, mRNA were increased by both pulse regimes, while CgA mRNA levels increased after 1 pulse/day of GnRH. These results indicate that there is a close correlation between the GnRH-stimulated release of LH and SgII from LbetaT2 cells, suggesting that SgII may have an influential role in the regulated secretion of LH, possibly by inducing LH aggregation to facilitate trafficking into secretory granules. CgA secretion does not appear to be closely associated with that of LH, but CgA expression does appear to be regulated by GnRH, which may indicate involvement in the control of LH secretion, possibly by influencing the proportion of LH in the different types of secretory granules.

Regulation of LH secretion during seasonal anestrus by dopaminergic pathways in Rasa Aragonesa ewes treated or not with melatonin

2003 ◽  
Vol 83 (2) ◽  
pp. 311-313 ◽  
Author(s):  
F. Forcada ◽  
J. A. Abecia ◽  
O. Zúñiga
Keyword(s):  
Luteinizing Hormone ◽  
Key Words ◽  
Dopaminergic System ◽  
Pulse Frequency ◽  
Steroid Dependent ◽  
Dependent Inhibition ◽  
And Control ◽  
Lh Secretion ◽  
Dopaminergic Pathways

The involvement of the dopaminergic system in the steroid-dependent inhibition of luteinizing hormone (LH) secretion during anestrus in ovariectomized, estradiol-implanted adult Rasa Aragonesa ewes was investigated in both ewes treated with melatonin on 8 March (n = 10) and in control (n = 8) ewes. Melatonin implants did not significantly increase LH secretion. However, treatment with pimozide induced a significant increase (P < 0.05) in LH pulse frequency in both groups during early anestrus. We conclude that, in the absence of males, the dopaminergic system is clearly involved in the inhibition of LH secretion during anestrus in both melatonin-treated and control ewes. Key words: Sheep, melatonin, pimozide

scholarly journals Progesterone Positive Feedback on Pulsatile LH Secretion and FSH Release May Be Blunted in Estradiol-Pretreated Women With PCOS

2021 ◽  
Vol 5 (Supplement_1) ◽  
pp. A744-A744
Author(s):  
Christopher Rolland McCartney ◽  
Su Hee Kim ◽  
Jessica A Lundgren ◽  
Christine Michele Burt Solorzano ◽  
James T Patrie
Keyword(s):  
Positive Feedback ◽  
A Priori ◽  
Pulse Frequency ◽  
Research Unit ◽  
Analysis Of Covariance ◽  
Clinical Research Unit ◽  
Exogenous Progesterone ◽  
Secondary Hypothesis ◽  
Induced Changes ◽  
Lh Secretion

Abstract In women pretreated with estradiol (E2), exogenous progesterone (P4) acutely augments LH and FSH release (P4 positive feedback). Women with PCOS exhibit impaired P4 negative feedback on LH pulse frequency, but it remains unclear whether such women exhibit impaired P4 positive feedback on LH/FSH release. We sought to explore the latter notion as an a priori secondary hypothesis in a study primarily designed to assess whether P4 acutely suppresses LH pulse frequency. We studied 12 women with PCOS and 12 normally-cycling, non-hyperandrogenic controls. After 3 days of transdermal E2 pretreatment (0.2 mg/day), subjects were admitted to the Clinical Research Unit (CRU) for a 24-hour frequent blood sampling protocol starting at 2000 h. (CRU admissions occurred no earlier than cycle day 7 in PCOS and between days 7 and 11 inclusive in controls.) At 0600 h, subjects received either 100 mg oral micronized P4 or placebo (PBO). In a subsequent menstrual cycle, subjects underwent an identical CRU protocol except that P4 was exchanged for PBO or vice versa. LH secretion was analyzed using Autodecon, a deconvolution program that provides estimates of LH pulse frequency, pulsatile LH secretion (amount of LH secreted as pulses), and basal (non-pulsatile) LH secretion. Results were analyzed using 2-period crossover design analysis of covariance. In both groups, neither LH pulse frequency nor basal LH secretion changed significantly with P4 (compared to changes with PBO). Mean LH increased with P4 in both groups—3.1-fold (95% CI, 2.4–4.0) in controls and 2.7-fold (95% CI, 2.1–3.5) in PCOS; in both groups, P4-related changes were significantly greater than PBO-related changes (Bonferroni-corrected p=0.012 and 0.010, respectively). In controls, pulsatile LH secretion increased 3.5-fold (95% CI, 2.3–5.2) with P4—significantly more than with PBO (p=0.029); while in PCOS, a 2.6-fold (95% CI, 1.8–3.9) increase with P4 was not significantly different from changes with PBO (p=0.911). In controls, mean FSH increased 2.0-fold (95% CI, 1.7–2.3) with P4—significantly more than with PBO (p=0.004); but in PCOS, a 1.5-fold (95% CI, 1.3–1.8) increase was not significantly different from changes with PBO (p=0.072). Despite the above, between-group (PCOS vs. controls) differences in P4-induced changes in pulsatile LH secretion and mean FSH were not formally (statistically) demonstrable. Between-group differences representing potential confounders included age (median 25.5 vs. 19.0 y; p=0.029), body mass index (29.9 vs. 21.8 kg/m2; p=0.006), and cycle day of CRU admissions (day 45.0 vs. 10.4 for P4 admissions; 30.0 vs. 10.0 for PBO admissions). In summary, these data suggest that P4-induced increases in pulsatile LH secretion and mean FSH may be blunted in PCOS compared to controls, which could contribute to ovulatory dysfunction in PCOS. However, our results do not confirm this possibility, and further study is needed.

Control of luteinizing hormone secretion in ewes by endogenous opioids and the dopaminergic system during short seasonal anoestrus: rôle of plane of nutrition

1997 ◽  
Vol 65 (2) ◽  
pp. 217-224 ◽  
Author(s):  
F. Forcada ◽  
J. M. Lozano ◽  
J. A. Abecia ◽  
L. Zarazaga
Keyword(s):  
Luteinizing Hormone ◽  
Receptor Antagonist ◽  
Dopaminergic System ◽  
Hormone Secretion ◽  
Pulse Frequency ◽  
Endogenous Opioids ◽  
Endogenous Opioid ◽  
Luteinizing Hormone Secretion ◽  
Lh Secretion

AbstractThe role of endogenous opioids and the dopaminergic system on the inhibition of luteinizing hormone (LH) secretion during early and late anoestrus, together with its modulation by the plane of nutrition were investigated in ewes with a short anoestrous season. In early anoestrus (22 March; day 0), two groups of ovariectomized, oestradiol-treated adult Rasa Aragonesa ewes, maintained under natural photoperiod at 41°N, were given enough food to provide 1·4 × (high; H; no. = 6) or 0·5 × (low; L; no. = 6) energy requirements for maintenance. The effects of administration of the opiate receptor antagonist naloxone (1 mg/kg at four 1-h intervals) (day 15) and of the dopaminergic2 receptor antagonist pimozide (0·08 mg/kg) (day 21) on LH secretion were assessed. A second experiment was carried out in late anoestrus (21 June) using the same protocol. A significant increase in LH pulse frequency after naloxone treatment for both H and L groups was detected in late anoestrus. Number ofLH pulses after naloxone injections in early anoestrus also increased in H (P < 0·05) and L ewes (P = 0·08). The effect of pimozide injection on mean LH pulse frequency was greater in early than in late anoestrus, especially in ewes receiving a high plane of nutrition (P < 0·05 and P = 0·07 for H and L ewes, respectively in April and P = 0·07 for H ewes in July). A significant increase of LH pulse amplitude was also detected in early anoestrus in H ewes (P < 0·01). These results provide evidence that endogenous opioid mechanisms are involved in the inhibition ofLH pulsatile release both in early and late anoestrus in ewes with a short seasonal anoestrus. The ability of pimozide to increase LH pulse frequency in early anoestrus could be enhanced by a high plane of nutrition in the breed studied.

PLASMA LEVELS OF LUTEINIZING HORMONE IN GONADECTOMIZED JAPANESE QUAIL EXPOSED TO SHORT OR TO LONG DAYLENGTHS

1975 ◽  
Vol 64 (1) ◽  
pp. 87-101 ◽  
Author(s):  
W. R. GIBSON ◽  
B. K. FOLLETT ◽  
BARBARA GLEDHILL
Keyword(s):  
Luteinizing Hormone ◽  
Japanese Quail ◽  
Plasma Levels ◽  
Photoperiodic Regulation ◽  
Male Plumage ◽  
Low Levels ◽  
Lh Secretion ◽  
Very High ◽  
Cloacal Gland ◽  
Short Days

SUMMARY Plasma levels of luteinizing hormone (LH) were measured by radioimmunoassay in gonadectomized male and female Japanese quail, exposed either to 8 h light: 16 h darkness per day (8L:16D; short days) or to 20L:4D (long days). In both sexes, exposure to long days increased LH levels and in the gonadectomized quail LH continued to rise over several weeks. Eventually the castrated quail had levels about five times higher than the control birds and the ovariectomized quail had levels about 14 times higher than their controls. Quail kept on short days had low LH levels while birds kept on long days and returned to short days resumed low levels after a delay of some days. Since very high levels of LH occurred in gonadectomized quail only when they were on long days, we conclude that the photoperiodic regulation of LH secretion does not operate solely by adjusting sensitivity to gonadal feedback, but works in a more direct manner. Ovariectomized females whether on long days (high LH) or short days (low LH) grew masculine plumage and castrated males retained male plumage. This confirms that the ovary is responsible for sexual dimorphism of plumage and shows that the action of the ovary is not mediated by LH (through feedback). The remaining rudimentary (right) gonad in ovariectomized females did not undergo visible hypertrophy and did not secrete enough hormone to stimulate the cloacal gland or oviduct.

Effects of enclomiphene on estradiol-induced changes in LH secretion in ewes.

1990 ◽  
Vol 68 (10) ◽  
pp. 3293
Author(s):  
D W Gregg ◽  
T M Nett
Keyword(s):  
Induced Changes ◽  
Lh Secretion

Nitric oxide decreases lung liquid production via guanosine 3′,5′-cyclic monophosphate

2001 ◽  
Vol 280 (5) ◽  
pp. L923-L929 ◽  
Author(s):  
James J. Cummings ◽  
Huamei Wang
Keyword(s):  
Nitric Oxide ◽  
Pulmonary Epithelium ◽  
Fetal Sheep ◽  
Cgmp Analog ◽  
Pulmonary Arterial ◽  
Series Of Experiments ◽  
Lung Liquid ◽  
Tracer Dilution ◽  
Induced Changes

We studied the role of cGMP in nitric oxide (NO)-induced changes in lung liquid production ( J v ) in chronically instrumented fetal sheep. Forty-five studies were done in which J v was measured by a tracer dilution technique. Left pulmonary arterial flow (Qlpa) was measured by a Doppler flow probe. There were two series of experiments. In the first, we gave 8-bromo-cGMP, a cGMP analog, by either the pulmonary vascular or intraluminal route; in the second, we used agents to inhibit or enhance endogenous cGMP activity. When infused directly into the pulmonary circulation, 8-bromo-cGMP significantly increased Qlpa but had no effect on J v. Conversely, when instilled into the lung liquid, 8-bromo-cGMP had no effect on Qlpa but significantly reduced J v. Inhibition of guanylate cyclase activity with methylene blue totally blocked, whereas phosphodiesterase inhibition with Zaprinast significantly enhanced, the effect of instilled NO on J v. Thus the reduction in lung liquid caused by NO appears to be mediated by cGMP, perhaps through a direct effect on the pulmonary epithelium.

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