Opiates and their antagonists modulate luteinizing hormone acting outside the blood brain barrier

The effects of morphine methyl-iodide and naloxone methyl-bromide, two quaternary derivatives of morphine and naloxone, were evaluated on the modulation of luteinizing hormone secretion in intact and gonadectomized rats. Quaternary compounds are effective in modulating LH release, indicating a site outside the blood brain barrier for their action. More precisely, the median eminence and not the pituitary seems to be the site of action of opiates in modulating LH secretion, since the effect of the quaternary derivatives is abolished by surgical ablation of the median eminence.