Abstract
Paired TRH (thyrotropin releasing hormone) and CPZ (chlorpromazine) stimulation tests
were performed on 3 and 5 normal male volunteers respectively. During one of the paired
tests, Intralipid plus heparin was administered i.v. for 3 hours to assess the effect
of FFA and TG elevations on prolactin (PRL) secretion. At the end of the first hour
of Intralipid plus heparin (or saline for control stimulations), either CPZ (25 mg
i.m.) or TRH (250 units i.v.) was given. In the Intralipid experiments, plasma TG
and FFA values more than doubled. The PRL responses to CPZ and TRH were not significantly
affected by the lipid infusion. In addition, intravenous lipid did not suppress the
elevated prolactin levels observed in drug induced chronic hyperprolactinemia.
Since earlier investigations using "metabolic" stimuli (insulin, arginine) have shown
inhibition of GH response by lipids, and since the stimuli used for the above experiments
were "nonmetabolic", it was proposed that the response of GH and PRL to different
types of stimuli might be controlled by different mechanisms, the "metabolic" mechanism
being affected by FFA. To investigate this possibility, a non-metabolic stimulus for
GH (L-dopa) and a metabolic stimulus for PRL (insulin) were employed using the above
experimental design. The GH response to L-dopa was significantly inhibited by the
lipid infusion. However, the PRL response to insulin was not suppressed by the lipid
infusion. These data show that FFA and TG have no inhibitory effect on the response
of prolactin to metabolic as well as non-metabolic stimuli, whereas the GH response
to both types of stimuli is inhibited by lipids.
Key words
Lipids - Prolactin - Growth Hormone
