Document Detail

Mechanisms of tyrosine hydroxylase regulation during pregnancy: evidence for protein dephosphorylation during the prolactin surges.
MedLine Citation:
PMID:  1682138     Owner:  NLM     Status:  MEDLINE    
This study examined tyrosine hydroxylase (TH) activity in the stalk-median eminence (SME) and TH messenger RNA (mRNA) signal levels in the arcuate nuclei of the hypothalamus during early, middle, and late pregnancy and related these to circulating levels of ovarian steroids. In addition, this study evaluated the intracellular mechanism(s) which contributes to the semicircadian rhythm in tuberoinfundibular dopaminergic neuronal activity during early pregnancy. The catalytic activity of TH in the SME was determined from the in vitro rate of 3,4,dihydroxyphenylalanine accumulation after inhibiting DOPA decarboxylase with brocresine. TH mRNA signal levels were evaluated by in situ hybridization. TH mRNA signal levels in the arcuate nuclei were 30% lower at 1000 h on day 20 of pregnancy as compared to days 7 and 11, whereas TH activity in the SME at 1000 h was not significantly different on days 7, 11, 16, and 20. Serum PRL levels were low (3-6 ng/ml) and unchanged at 1000 h on days 7, 11, 16, and 20. Circulating progesterone levels increased from 111 to 191 ng/ml on days 7 and 16, respectively, and then declined to 69 ng/ml by day 20. Serum estradiol levels increased from 38 to 106 pg/ml on day 7 and 16, respectively, and then remained elevated on day 20. Thus, the reduction in TH mRNA signal levels during late pregnancy is temporally related to the increased estradiol/progesterone ratio. Elevated serum PRL levels at 0330 h and 1800 h on day 7 were characteristic of the nocturnal and diurnal PRL surges of early pregnancy. Circulating PRL levels were low during the intersurge times (2330 and 1000 h) on day 7 and at all times examined on day 11. TH activity in the SME on day 7 was lower during the PRL surges as compared to the intersurge times, whereas TH activity on day 11 was similar at all times and comparable to the intersurge levels of early pregnancy. Okadaic acid, a protein phosphatase inhibitor, reversed the reduction in TH activity during the nocturnal and diurnal PRL surges, but did not significantly alter TH activity during the intersurge period on day 7. TH mRNA signal levels in the arcuate nuclei were similar throughout day 7. These data indicate that protein dephosphorylation, but not changes in the TH gene expression, may contribute to the semicircadian rhythm in TH activity during early pregnancy.
L A Arbogast; J L Voogt
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Endocrinology     Volume:  129     ISSN:  0013-7227     ISO Abbreviation:  Endocrinology     Publication Date:  1991 Nov 
Date Detail:
Created Date:  1991-12-02     Completed Date:  1991-12-02     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  0375040     Medline TA:  Endocrinology     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2575-82     Citation Subset:  AIM; IM    
Department of Physiology, University of Kansas Medical Center, Kansas City 66103.
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MeSH Terms
Arcuate Nucleus / metabolism
Hormones / blood
Median Eminence / metabolism
Phosphoprotein Phosphatases / antagonists & inhibitors
Pregnancy, Animal / metabolism*
Prolactin / metabolism*
RNA, Messenger / metabolism
Rats, Inbred Strains
Tyrosine 3-Monooxygenase / genetics,  metabolism*
Grant Support
Reg. No./Substance:
0/Hormones; 0/RNA, Messenger; 9002-62-4/Prolactin; EC 3-Monooxygenase; EC Phosphatases

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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