Neuroendocrine evaluation of CCK-peptides on dopaminergic function in man.

CCK-33 (225 Ivy Dog Units iv) antagonized the growth hormone response to the dopamine receptor agonist, apomorphine HCl (0.5 mg sc), and increased basal prolactin secretion in normal male volunteers. A stress mediated prolactin effect could not be excluded. CCK-8 (5 ug iv) antagonized the growth hormone response to apomorphine but had no effect on basal prolactin or plasma homovanillic acid. Ceruletide (0.3 ug/kg im) had no effect on basal prolactin or apomorphine-induced growth hormone secretion. CCK-33, CCK-8 and ceruletide had no effect on basal growth hormone secretion which suggests that they do not inhibit the release of growth hormone. These findings are compatible with an inhibitory effect of CCK-33 and CCK-8 (or fragments) on dopaminergic function in man, at least in the hypothalamic-pituitary axis and point to a simple way to study the effect of peptides on dopaminergic function in man including those which may not cross the blood brain barrier.