Opiate stimulation of prolactin secretion is reversed by ovarian hormone treatment

Meharvan Singh, William J. Millard, Meri P. Layden, Teresa M. Romano, James W. Simpkins

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Previous studies have indicated that during the estradiol-and progesterone (P4)-induccd surge in luteinizing hormone (LH), the effects of opiates on behavioral, autonomic and neuroendocrine functions are altered. In the present study, we further evaluated the apparent universality ofalterations in opiate-mediated function during the LH surge by investigating the effects of morphine sulfate (MS) on prolactin (PRL) secretion during both the estradiol benzoate (EB) and the EB + P4-indueed LH surges. All doses of MS tested (0.5, 2.0 and 5.0 mg/kg) resulted in significant increases in PRL secretion in n on estrogen-treated animals which did not show LH/PRLsurges. During the LH/PRL surge induced by EB/P4 treatment, MS caused no change in the PRL secretion, while in EB/oil treated animals, a paradoxical and dose-dependent decrease in PRL secretion was observed. The suppression of PRL was 52, 68 and 80% of baseline respectively for the 3 doses of MS. Evaluation of the time dependence of MS on PRL secretion showed that the paradoxical suppression in EB/oil-treated animals was seen only during the LH/PRL surge, occurring at 17.30 h (7.5 h post P4 injection), and not before (12.30 h) or after (23.00 h) the steroid-induced LH/PRL surge. Finally, we assessed the role of pituitary dopamine receptors on the phenomenon of MS-induced PRL suppression in EB/oil rats. Domperidone (1 mg/kg), a peripherally active D2 receptor antagonist, administered prior to the morphine challenge, attenuated the opiate-induced PRL suppression in EB/oil-treated animals suggesting that a dopaminergic mechanism is involved in this paradoxical response to morphine.

Original languageEnglish
Pages (from-to)195-203
Number of pages9
Issue number2
StatePublished - 1992


  • Dopamine anterior pituitary
  • Estrogen
  • Morphine opiate modulation
  • Ovarian steroids
  • Progesterone
  • Prolactin
  • Steroid-induced PRL surge


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