Morphine-like peptides: their regulation in the neuroendocrine system and the effect of guanyl nucleotides and divalent ions on opiate receptor binding.

Glucocorticoids such as dexamethasone and prednisolone at physiological concentrations inhibit the synthesis, and hence the release, of endorphins by AtT/20 pituitary cells. Several other steroids, including progesterone, estradiol benzoate and testosterone, have no such effect and do not compete with dexamethasone. Incorporation of 3H-dexamethasone into nuclei of AtT/20 cells was inhibited by a much lower concentration of dexamethasone or prednisolone than that of several other steroids studied. This study indicates for the first time that glucocorticoids directly inhibit synthesis of endorphins by pituitary cells. The effect of GTP and GMP-PNP on the binding of 3H-D-ala-methionine enkephalin to rat brain opiate receptors was studied. Different brain regions showed different sensitivity to GMP-PNP. Manganese, calcium and magnesium selectively inhibited the effect of GMP-PNP but barium and strontium had no effect. The possibility that divalent cations alter the coupling of opiate receptors to internal components is suggested.