Estrogen fails to reduce tuberoinfundibular dopaminergic neuronal activity and to cause a prolactin surge in lactating, ovariectomized rats.
The activity of tuberoinfundibular dopaminergic (TIDA) neurons was estimated by measuring the concentrations of dihydroxyphenylacetic acid (DOPAC) in the median eminence of ovariectomized lactating rats, ovariectomized non-lactating female rats and castrated male rats in correlation with the estrogen-induced prolactin (PRL) surge. PRL surge with a peak at 17.00 h was observed in ovariectomized non-lactating rats but not in the other groups. DOPAC levels were significantly lower at 17.00 h than at 11.00 h in non-lactating female rats, but there was no change of DOPAC levels in lactating rats and male rats. These results indicate that TIDA neuronal activity is inhibited at the time of estrogen-induced PRL surge and that the TIDA neurons may alter their function to result in refractoriness of PRL response to estrogen in the lactating rat.
Higuchi
T
T
Department of Physiology, Fukui Medical School, Japan.
Honda
K
K
Takano
S
S
Negoro
H
H
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D004298:Dopamine / Q000502:physiology*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007774:Lactation / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008473:Median Eminence / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009919:Orchiectomy; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D015102:3,4-Dihydroxyphenylacetic Acid; D004958:Estradiol; D011388:Prolactin; D004298:Dopamine