Opioid-dopaminergic interactions in primary empty sella

Previous studies have indicated different abnormalities of PRL secretion in patients with primary empty sella (PES). Since it is known that endogenous opiates and dopamine interact in modulating PRL secretion, we have studied the effect of an opiate receptor blockade (with Naloxone, NAL, 1.6 mg/h as a continuous infusion) on anterior pituitary hormones and on PRL responsiveness to metoclopramide (MCP), in 10 premenopausal normoprolactinemic patients with PES, studied in follicular phase, in order to investigate neurotransmitter abnormalities present in such a syndrome. NAL failed to significantly affect LH and FSH basal levels; on the contrary, slight but significant increases in PRL and GH secretion were observed. NAL partially blunted the PRL responsiveness to the dopaminergic blockade, which was very marked when tested after MCP alone. These data confirm that the modulation of anterior pituitary hormone secretion is different in PES patients, when compared with normal subjects. The infusion of NAL induced a "paradoxical" increase in hormones (PRL and GH) which are normally stimulated by endogenous opiates; but, on the other side, it blocked the marked PRL responsiveness to the dopaminergic blockade, which is characteristic of PES syndrome. This phenomenon seems to indicate that the relationships between dopaminergic and opiatergic neurons could be modified by the neuroanatomic alteration which is present in this complex syndrome.