Evaluation of the effects induced by four opiate drugs, with different affinities to opioid receptor subtypes, on anterior pituitary LH, TSH, PRL and GH secretion and on cortisol secretion in normal men.

In order to ascertain the subtype(s) of opioid receptors involved in the control of pituitary function the effects of four different opiate drugs (morphine, pentazocine, nalorphine and buprenorphine) were studied in four groups of six normal male volunteers. Each of the drugs tested induced, with varying degrees, both a significant increase in PRL and a significant decrease in LH and cortisol. On the contrary TSH secretion was stimulated by buprenorphine and morphine only and GH by nalorphine only. FSH did not change significantly after administration of any drug. Taking into account the different affinities of the drugs used by us for the different opioid receptors, our data do not allow to demonstrate a well-defined correlation between subtypes of opioid receptors and the control of pituitary hormone secretion. The possible explanations of this fact are discussed.