Time course of the insensitivity of prolactin release to morphine administration in the lactating female rat.
The effect of morphine on circulating levels of prolactin and growth hormone (GH) in the lactating female model was determined at various time intervals following the termination of suckling. Morphine administration did not produce an increase in prolactin levels when dams remained suckling. Four days after suckling was terminated, 50% of the dams tested showed a morphine induced prolactin increase. The prolactin secretory response to morphine gradually returned in dams, so that after 8 days of non-suckling, all animals tested showed a morphine induced prolactin increase. Consistent with the lack of prolactin stimulation, the tuberoinfundibular dopaminergic (TIDA) neurons, were insensitive to the morphine induced inhibition of activity during lactation. In contrast, circulating levels of GH were increased in these dams following morphine administration. These results suggest that the lactating female rat is insensitive to the mu mediated stimulation of prolactin release while suckling. However, sensitivity begins to return following at least 4 days of non-suckling.
Callahan
P
P
Department of Biological Sciences, Rutgers University, Piscataway, New Jersey 08855.
Janik
J
J
Rabii
J
J
D000818:Animals; D004298:Dopamine / Q000378:metabolism; D005260:Female; D013006:Growth Hormone / Q000378:metabolism; D007774:Lactation / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008473:Median Eminence / Q000187:drug effects; D008954:Models, Biological; D009020:Morphine / Q000494:pharmacology*; D011247:Pregnancy; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D009020:Morphine; D011388:Prolactin; D013006:Growth Hormone; D004298:Dopamine