The effects of the systemic administration of N-methylmorphine chloride, a quaternary analogue of morphine that does not cross the blood-brain barrier, on the release of anterior pituitary hormones in the rat.

The acute administration of morphine elicits changes in the release of anterior pituitary hormones. The locus of this action is thought to be in the central nervous system, specifically the hypothalamus. There are some data suggesting that systemically administered opiates and opioid peptides can act outside of the blood-brain barrier to influence anterior pituitary hormone release. To test this hypothesis we examined the effects of the systemic administration of N-methylmorphine chloride, a quaternary analogue of morphine that does not cross the blood-brain barrier, on the release of corticosterone, growth hormone, prolactin, luteinizing hormone, and thyroid stimulating hormone in the rat. N-methylmorphine caused increases in the release of growth hormone and prolactin, but serum levels of corticosterone, luteinizing hormone and thyroid stimulating hormone were unaffected. These results indicate that the opiate-induced release of growth hormone and prolactin may be mediated in part by sites outside of the blood-brain barrier.