Differential regulation of the nocturnal and diurnal prolactin surges in pregnant rats revealed by dopamine receptor antagonism.
We have explored temporal changes in the magnitude of dopamine (DA) interaction (DA tone) at the anterior pituitary lactotrophs related to both the nocturnal and diurnal prolactin (PRL) surges on day 8 of pregnancy, by utilizing a competitive DA D2 antagonist, domperidone (DOM). After withdrawal of blood from pregnant rats on day 7 in order to demonstrate the presence of a PRL surge, experimental rats received DOM (100 micrograms/kg i.v. or i.a.) at various times on day 8. Blood samples were taken immediately before and following injection of DOM at 5, 15, 30 and 60 min. The peak PRL response to DOM occurred 15 min after injection. Comparisons were made between circulating PRL levels immediately prior to and at several times following DOM administration for the various times of the day, and represented as incremental increases in PRL following DOM. During times on day 8 when PRL levels were normally low (24:00, 06:00, 12:00 and 16:00 h), pregnant rats exhibited a substantial PRL response to DOM. However, during the nocturnal PRL surge (02:00, 04:00 h) the peak PRL response to DOM was significantly lower. In sharp contrast, the PRL response to DOM administered during the diurnal PRL surge (18:00 h) was significantly higher than all other times of the day tested. In a dose-response study in which 10, 100 and 1,000 micrograms/kg DOM was administered at the two critical times when the response to DOM differed greatly, 02:00 and 18:00 h, there was a significantly reduced PRL response to DOM at 02:00 h compared to 18:00 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Mathiasen
J R
JR
Department of Physiology, Kansas University Medical Center, Kansas City 66103.
Voogt
J L
JL
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D004294:Domperidone / Q000008:administration & dosage / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D005260:Female; D007700:Kinetics; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D065127:Dopamine D2 Receptor Antagonists; D004294:Domperidone; D011388:Prolactin