Thyrotrophin-releasing hormone receptor 1 and prothyrotrophin-releasing hormone mRNA expression in the central nervous system are regulated by suckling in lactating rats.
BACKGROUND
The accepted function of the hypothalamic peptide, thyrotrophin-releasing hormone (TRH), is to initiate release of thyrotrophin (TSH) from the pituitary. A physiological role for TRH in lactating rats has not yet been established.


METHODS
Tissues were prepared from random-cycling and lactating rats and analysed using Northern blot, real time RT-PCR and quantitative in situ hybridisation.


RESULTS
This study demonstrates that TRH receptor 1 (TRHR1) mRNA expression is up-regulated in the pituitary and in discrete nuclei of the hypothalamus in lactating rats, while proTRH mRNA expression levels are increased only in the hypothalamus. The results were corroborated by quantitative in situ analysis of proTRH and TRHR1. Bromocriptine, which reduced prolactin (PRL) concentrations in plasma of lactating and nursing rats, also counteracted the suckling-induced increase in TRHR1 mRNA expression in the hypothalamus, but had an opposite effect in the pituitary. These changes were confined to the hypothalamus and the amygdala in the brain.


CONCLUSIONS
The present study shows that the mechanisms of suckling-induced lactation involve region-specific regulation of TRHR1 and proTRH mRNAs in the central nervous system notably at the hypothalamic level. The results demonstrate that continued suckling is critical to maintain plasma prolactin (PRL) levels as well as proTRH and TRHR1 mRNA expression in the hypothalamus. Increased plasma PRL levels may have a positive modulatory role on the proTRH/TRHR1 system during suckling.
Fjeldheim
Ase-Karine
AK
Institute of Basic Medical Science, Department of Biochemistry, University of Oslo, PO Box 1112 Blindern, N-0317 Oslo, Norway.
Høvring
Per Ivar
PI
Løseth
Ole-Petter
OP
Johansen
Per Wiik
PW
Glover
Joel C
JC
Matre
Vilborg
V
Olstad
Ole Kristoffer
OK
Reppe
Sjur
S
Gordeladze
Jan O
JO
Walaas
S Ivar
SI
Gautvik
Kaare M
KM
D000818:Animals; D000833:Animals, Suckling; D001971:Bromocriptine / Q000494:pharmacology; D018491:Dopamine Agonists / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000502:physiology; D007031:Hypothalamus / Q000502:physiology*; D007774:Lactation / Q000502:physiology*; D010902:Pituitary Gland / Q000502:physiology; D011388:Prolactin / Q000097:blood / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D018025:Receptors, Thyrotropin-Releasing Hormone / Q000235:genetics*
D018491:Dopamine Agonists; D011498:Protein Precursors; D012333:RNA, Messenger; D018025:Receptors, Thyrotropin-Releasing Hormone; D001971:Bromocriptine; D011388:Prolactin