No acute effect of pimozide on the plasma GH levels in acromegaly

In 34 acromegalic patients either untreated or inadequately treated by surgery and/or radiotherapy the plasma GH levels and plasma Prl levels were determined during 8 h after the acute administration of the dopamine agonist bromocriptine and during 150 min after the administration of the dopamine antagonist pimozide. A 50% or more suppression of the basal GH levels was arbitrarily defined as a positive response. Seventeen patients displayed a positive response to bromocriptine, 17 patients displayed a negative response to bromocriptine. Plasma Prl levels were elevated in 6 of 17 bromocriptine responders and in 2 of 17 bromocriptine nonresponders. There was no difference in the plasma GH response to pimozide administration in the patients with a positive or a negative GH response to bromocriptine. With one exception there was in no patient a positive GH response to pimozide. In further experiments the plasma GH response to pimozide was measured during 11 h in 6 bromocriptine sensitive and 6 bromocriptine insensitive patients. Again no difference was found between bromocriptine responders and non-responders. There was also no difference in the Prl response to bromocriptine or pimozide between GH responders and GH non-responders. The Prl response to pimozide was blunted in comparison to a control group. The present study does not not lend support to the idea that there is a fundamental difference in the degree of hypothalamic dopaminergic control of GH or Prl secretion between bromocriptine sensitive and bromocriptine insensitive patients with acromegaly.