Alterations in Prolactin Messenger Ribonucleic Acid Level During the Rat Estrous Cycle: Effect of Naloxone

흰쥐 성주기간동안 Prolactin mRNA의 변화:Naloxone

The present study exarnines the physiological alteradons in prolactin (PRL) messenger ribonucleic acid (mRNA) and serum PRL levels during the rat estrous cycle and the effed of naloxone, an endogenous oploid peptide receptor antagonist, on PRL gene expression during the rat estrous cycle. Adult female rats exhibiting at least two consecutive 4-day estrous cycles were used in this study. A single injection of naloxone (2mg/kg b.w.) or saline was given sc 30 mm prior to decapitation. Animals were sacrificed at 10:00 h of each stage of the estrous cycle, and at 2-h intervals from 10:00 h to 20:00 h during the proestrus. PRL mRNA and serum PRL levels were determined by a RNA-blot hybridization with the rat PRL cDNA probe and by a PRL radjoimmunoassay, respectively. PRL mRNA and serum PRL levels were not dramatically altered in the morning of each stage of diestrus I, II and proestrus, and naloxone failed to modify the two parameters. During estrus naloxone clearly suppressed serum PRL levels, but it was unable to modify PRL mRNA levels. A more detailed examination of the proestrus stage revealed that PRL mRNA and serum PRL levels were fluctuated as a function of time: PRL mRNA levels reached a maximum level at 12:00 h and gradually decreased until 18:00 h. PRL mRNA levels then rose at 20:00 h. No difference of PRL mRNA levels between the control and naloxone-treated groups was observed. Changes in serum PRL levek during proestrus were conversely related to changes in PRL mRNA: serum PRL levels were low from 10:00 h to 14:00 h, then increased and reached a maximum level at 16:00-18:00 h. Following then, serum PRL levels were decreased. Naloxone was effective in suppressing the charaderistic afternoon surge of PRL from 16:00 h to 20:00 h. These data clearly showed that alterations in PRL mRNA levels were conversely correlated with changes mn serum PRL levels on proestrus, indicating a differential regulation of PRL gene expression and secretion.

본 연구는 prolactin(PRL)유전자 발현, 분비의 생리적 변화와 성주기 특정 시기의 PRL mRNA수준 및 분비에 미치는 내인성 오피오이드의 영향을 조사하였다. 최소한 두번의 연속적인 성주기를 거친 성숙한 흰쥐에서 성주기의 각 시기(10:00시)에, proestrus시기에는 10:00-20:00 시동안에는 2시간 간격으로 도살하였고, naloxone (2mg/kg b.w.)은 도살 30분전에 피하주사 하였다. PRL mRNA의 수준의 흰쥐의 PRL cDNA를 probe로 하여 RNA-blot hybridization방법에 의해서, 혈중 PRL농도 변화는 방사면역측정법에 의해 측정하였다. 뇌하수체 PRL mRNA의 수준과 혈중 PRL수준은 diestrus I, II and proestrus그리고 estrus시기의 10:00시에는 급격한 변화를 보이이 않았다. 이때 naloxone처리는 영향을 미치지 못했다. proestrus시기를 세분화하여 조사한 결과 PRL mRNA의 수준은 정오에 최고 수준에 도달하였고, 오후 6:00까지 점차적으로 감소하였다. 그후 8:00시에 다시 증가하였다. estrus동안 naloxone은 혈중의 PRL수준을 명백히 억제하였으나 PRL mRNA수준에는 영향이 없었다. proestrus시기 동안 혈중 PRL변화와 뇌하수체 PRL mRNA변화는 서로 상이하게 조절되며,PRL mRNA수준이 흰쥐 성주기 동안 변화하고 있는 사실에서 PRL 유전자 발현이 생리적으로 조절되고 있음을 시사한다.