T. Funabashi et al., LUTEINIZING-HORMONE-RELEASING HORMONE-RECEPTOR MESSENGER-RIBONUCLEIC-ACID EXPRESSION IN THE RAT PITUITARY DURING LACTATION AND THE ESTROUS-CYCLE, Journal of neuroendocrinology, 6(3), 1994, pp. 261-266
To study mechanisms underlying the modulation of luteinizing hormone-r
eleasing hormone receptor (LHRH-R) during lactation and the estrous cy
cle, we used a reverse transcriptase-polymerase chain reaction (RT-PCR
) procedure to generate a probe for rat LHRH-R messenger RNA (mRNA). U
sing primers based on the mouse sequence, we amplified an approximatel
y 300 bp fragment from rat pituitary complementary DNA. This PCR produ
ct was shown to be part of LHRH-R cDNA by direct sequencing and by com
paring to the rat LHRH-R cDNA reported recently. Then, this PCR fragme
nt was used as a probe for northern blotting analysis. The level of LH
RH-R mRNA in the pituitary was significantly decreased during lactatio
n, by approximately 80%, compared to that of ovariectomized and intact
(diestrous and metestrous cycling) rats while no statistical differen
ce in glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) mRNA level was
observed between groups. During the estrous cycle, the level of LHRH-R
mRNA in the pituitary was about two-fold higher on diestrous day 2 an
d the morning of proestrus than that on diestrous day 1 and quickly re
turned toward control level by noon of proestrus. In addition, we foun
d that GAPDH mRNA levels from a so-called housekeeping gene often thou
ght to be unchanged under different conditions, were significantly hig
her on proestrus while levels of 18S rRNA were not significantly chang
ed. The large decrease in LHRH-R mRNA during lactation could account f
or the changes in LHRH binding previously reported.