The effect of transient dopamine antagonism on thyrotropin-releasing hormone-induced prolactin release in female rats during the estrous cycle

Life Sciences ◽  
1991 ◽  
Vol 48 (20) ◽  
pp. 1911-1918 ◽  
Author(s):  
D.J. Haisenleder ◽  
R.R. Gala ◽  
D.M. Lawson
Keyword(s):  
Estrous Cycle ◽  
Thyrotropin Releasing Hormone ◽  
Female Rats ◽  
Prolactin Release ◽  
Releasing Hormone

INFLUENCE OF PHOTOPERIOD ON THYROTROPIN RELEASING HORMONE-INDUCED PROLACTIN RELEASE IN EWES

1983 ◽  
Vol 63 (1) ◽  
pp. 67-73 ◽  
Author(s):  
B. E. HOWLAND ◽  
D. SONYA ◽  
L. M. SANFORD ◽  
W. M. PALMER
Keyword(s):  
Thyrotropin Releasing Hormone ◽  
Day Length ◽  
Constant Light ◽  
Serum Prolactin ◽  
Prolactin Release ◽  
Blood Samples ◽  
Releasing Hormone ◽  
Before And After ◽  
Release Curve ◽  
Short Days

The influence of photoperiod on serum prolactin levels and prolactin release induced by thyrotropin releasing hormone (TRH) was determined in ewes maintained under the following lighting regimes: Room 1, lighting mimicked natural changes in photoperiod; Room 2, annual photoperiod changes condensed into 6 mo with short days in June; Room 3, same as Room 2 except photoperiod changed abruptly from 16.5 to 8.0 h on 21 Mar. and back to 16.5 h on 21 June; Room 4, constant light. Weekly blood samples were obtained from February to August. Additionally, blood samples were collected before and after treatment with 10 μg TRH on 19 May, 13 June, 27 June and 19 July. Prolactin levels were elevated in ewes exposed to long days or constant light. The mean of all pre-TRH samples was significantly correlated with stress-induced elevations in prolactin (highest pre-TRH value) (r = 0.72) and area under the TRH-induced release curve (r = 0.56). The prolactin release in response to TRH was greatest in ewes exposed to long days or constant light. Abrupt increase of day length elevated pretreatment prolactin levels (P < 0.01) and increased area under the response curve (P < 0.05). Key words: Photoperiod, TRH, prolactin, ewes

Does Bromocriptine Block Thyrotropin-Releasing Hormone-Induced Prolactin Release during Pregnancy?*

1980 ◽  
Vol 50 (3) ◽  
pp. 600-602 ◽  
Author(s):  
OLAVI YLIKORKALA ◽  
SEPPO KIVINEN ◽  
LARS RÖNNBERG ◽  
LASSE VIINIKKA
Keyword(s):  
Thyrotropin Releasing Hormone ◽  
Prolactin Release ◽  
Releasing Hormone

Role of guanine nucleotide-binding proteins, Giα3 and Gsα, in dopamine and thyrotropin-releasing hormone signal transduction: evidence for competition and commonality

1996 ◽  
Vol 148 (3) ◽  
pp. 447-455 ◽  
Author(s):  
R D Kineman ◽  
T W Gettys ◽  
L S Frawley
Keyword(s):  
Signal Transduction ◽  
G Proteins ◽  
Cell Cultures ◽  
Intracellular Signaling ◽  
Receptor Activation ◽  
Pituitary Cell ◽  
Thyrotropin Releasing Hormone ◽  
Female Rats ◽  
Releasing Hormone

Abstract It is clear that dopamine (DA) at high concentrations (>100 nmol/l) inhibits the release of prolactin (PRL). Paradoxically, this monoamine at low concentrations (<10 nmol/l) has also been shown to augment PRL secretion. One possible explanation for these divergent effects is that DA binds receptors capable of interacting with multiple G protein subtypes that recruit opposing intracellular signaling pathways within lactotropes. To identify G proteins which couple DA receptor activation to PRL secretion, we have selectively immunoneutralized the activity of Giα3 and Gsα in primary cultures of rat pituitaries and subsequently tested the ability of these cultures to respond to high and low dose DA. Specifically, permeabilized pituitary cell cultures from random-cycling female rats were treated with control immunoglobulins (IgGs; 50 μg/ml) purified from preimmune serum (PII) or IgGs directed against the C-terminal portion of Giα3 or Gsα. After immunoneutralization of these G proteins, cells were challenged with 10 or 1000 nmol Da/l and the relative amount of PRL released was assessed by reverse hemolytic plaque assay. Results were expressed as % of basal values and compared. Under control conditions (PII), 1000 nmol DA/l inhibited (61·4 ±7·6% of basal values; mean ± s.e.m.) while 10 nmol DA/l augmented (120·0 ± 7·0%) PRL release in five separate experiments. Treatment of cells with anti-Giα3 attenuated the inhibitory effect of high dose DA (87·3 ± 14·5%). However, elimination of Giα3 activity did not significantly alter the PRL stimulatory effect of 10 nmol DA/l (121·0 ± 5·2%). Interestingly, immunoneutralization of Gsα resulted in a reciprocal shift in the activity of the lower dose of DA from stimulatory to inhibitory (69·7 ± 7·3%) while combined treatment of anti-Giα3 and anti-Gsα abrogated the responsiveness of pituitary cell cultures to either DA treatment (1000 nmol/l, 70·7 ± 12·5% and 10 nmol/l, 87·5 ± 21·4%). These data reveal that ligand-activated DA receptors can interact with both Giα3 and Gsα. Elimination of the stimulatory component (Gsα) favors the DA receptor activation of the inhibitory pathway (Giα3) suggesting a competition between negative and positive intracellular signaling mechanisms in normal lactotropes. In addition to DA treatment, we also challenged permeabilized pituitary cells with 100 nmol thyrotropin-releasing hormone (TRH)/1 as a positive control for secretory integrity. As anticipated, TRH stimulated PRL release to 188·0±31·0% of basal values under control conditions. Unexpectedly, immunoneutralization of Gsα completely blocked the ability of TRH to induce PRL release (101·8 ± 12·0% This neutralizing effect was specific to Gsα in that blockade of Giα3 activity had no significant effect on TRH-stimulated PRL release (166·2 ± 13·1%). These data are the first to support a direct role of Gsα in TRH signal transduction within PRL-secreting cells. Journal of Endocrinology (1996) 148, 447–455

Action of thyrotropin-releasing hormone on mammotrophs and thyrotrophs

1981 ◽  
Vol 241 (4) ◽  
pp. E298-E304
Author(s):  
G. Snyder ◽  
Z. Naor ◽  
C. P. Fawcett ◽  
S. M. McCann
Keyword(s):  
Anterior Pituitary ◽  
Thyrotropin Releasing Hormone ◽  
Female Rats ◽  
Pituitary Cells ◽  
Cell Distribution ◽  
Camp Content ◽  
Releasing Hormone ◽  
Gravity Sedimentation ◽  
Unit Gravity Sedimentation ◽  
Region Ii

Anterior pituitary cells from 15-day female rats were separated by unit gravity sedimentation into four populations (designated regions I-IV) based on the profile of cell distribution and the resulting content of radioimmunoassayable (RIA) hormones. The cells in regions II and IV released thyrotropin (TSH) in response to thyrotropin-releasing hormone (TRH, 5 ng/ml); however, those in region IV released only approximately 5% of their RIA content, whereas those in region II released approximately 26% in response to the same stimulus. Concomitant elevation of cAMP and of cGMP occurred in region II cells but only cGMP was elevated in region IV cells. Mammotrophs were localized in region III. They responded to TRH by releasing prolactin (PRL) and exhibiting increased cAMP content. These data provide support for the existence of two functionally distinct populations of thyrotrophs in 15-day-old female rats. The data also imply that cAMP is involved in TRH induced PRL release, whereas cGMP is involved in TRH-induced TSH release.

Pups removal enhances thyrotropin-releasing hormone mRNA in the hypothalamic paraventricular nucleus

1995 ◽  
Vol 133 (3) ◽  
pp. 354-360 ◽  
Author(s):  
Rosa Maria Uribe ◽  
Patricia Joseph-Bravo ◽  
Jean-Louis Charli
Keyword(s):  
Estrous Cycle ◽  
Paraventricular Nucleus ◽  
Northern Blot Analysis ◽  
Preoptic Area ◽  
Thyrotropin Releasing Hormone ◽  
Hypothalamic Paraventricular Nucleus ◽  
Negative Regulator ◽  
Neuron Activity ◽  
Mrna Levels ◽  
Releasing Hormone

Uribe RM, Joseph-Bravo P, Charli J-L. Pups removal enhances thyrotropin-releasing hormone mRNA in the hypothalamic paraventricular nucleus. Eur J Endocrinol 1–60. ISSN 0804–4643 Previous studies have shown that lactation and suckling alter thyrotropin-releasing hormone (TRH) biosynthesis in hypothalamic paraventricular neurons. The amounts of paraventricular TRH mRNA and mediobasal hypothalamus (MBH) TRH were determined following removal of the pups to examine whether paraventricular TRH neuron activity is altered during the transition from lactation to estrous cycle. Paraventricular TRH mRNA and MBH TRH levels were determined by Northern blot analysis and radioimmunoassay, respectively. We had shown previously that after an 8-h withdrawal of the pups at mid-lactation the MBH TRH and paraventricular TRH mRNA levels are not modified. This condition was compared to one where pups were removed for 56 h, finding a significant decrease (46%, p < 0.005) of MBH TRH and a significant increase (156%, p < 0.02) of paraventricular TRH mRNA. The effect observed in the paraventricular TRH mRNA was correlated negatively with the serum corticosterone levels, a potential negative regulator of paraventricular TRH mRNA. The results were similar if a 1-h suckling period was introduced 8 h after withdrawal of the pups to induce a transient increase of corticosterone levels. The pattern of TRH mRNA was specific to the paraventricular nucleus because there was no enhancement in the preoptic area-anterior hypothalamus. In summary, our data suggest that TRH biosynthesis in paraventricular neurons is slowly adjusted after withdrawal of the pups, possibly to prepare TRH neurons to the new secretory demands of the estrous cycle. JL Charli, Instituto de Biotecnologia, UNAM, AP 510-3, Cuernavaca, Mor. 62271, México

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