peptide-phi and Hyperprolactinemia

We examined a possible GH-releasing activity of vasoactive intestinal peptide (VIP) and its homologous peptide, peptide histidine methionine (PHM), in 22 patients with hyperprolactinemia (HPRL) who comprised 19 cases of prolactinoma (PRLoma) and 3 cases of hypothalamic HPRL. Each patient underwent iv bolus injections of VIP (100 micrograms) and PHM (100 micrograms) on separate days, and plasma levels of GH and PRL were measured. The plasma GH response to VIP and PHM were considered positive (a paradoxical increase) when an increase over baseline of at least 50% occurred. In agreement with previous reports, the PRL-releasing activity of VIP and PHM in our patients with HPRL were subnormal. Thirteen (59%) patients showed a paradoxical rise in GH after VIP, and 4 (18%) patients did so after PHM. It is to be noted that all the 3 patients with hypothalamic HPRL responded to VIP with a significant rise in GH. 3 of the 4 PHM-responders were also responsive to VIP, which suggests that PHM may have activated VIP receptors in the pituitary of the PHM-responders as a partial agonist of the VIP receptor. The responders and nonresponders to VIP or PHM, respectively, had similar results with respect to the mean age, and the mean basal PRL and GH levels in the plasma. Since these paradoxical GH responses were observed in not only the patients with PRLoma but also those with hypothalamic HPRL, it may be that these anomalous GH responses in HPRL were due to the HPRL itself rather than due to the neoplastic lactotrophs.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adolescent; Adult; Female; Growth Hormone; Humans; Hyperprolactinemia; Hypothalamic Diseases; Male; Middle Aged; Peptide PHI; Pituitary Neoplasms; Prolactinoma; Sequence Homology, Amino Acid; Vasoactive Intestinal Peptide

In order to verify whether synthetic peptide histidine methionine (PHM-27) is able to induce serum prolactin (PRL) rise in normal subjects and to investigate its effect on PRL secretion in hyperprolactinemic conditions, PHM-27 (100 micrograms i.v. over 60 min at a rate of 3.3 micrograms/min) was given to 6 normal subjects and 11 hyperprolactinemic women, and serum PRL levels were measured before and at intervals up to 120 min after beginning the infusion. On a separate occasion, a saline infusion was administered to all these subjects as a control test. In normal subjects, PHM-27 caused PRL to increase from 7.8 +/- 1.4 micrograms/l (mean +/- SE) to 13 +/- 2.1 micrograms/l (p < 0.05), the peak occurring at 30 min, whereas it did not significantly modify serum PRL levels in 11 patients with prolactin-secreting adenomas. We also observed a significant difference of serum PRL pattern during PHM infusion when compared to saline in normal subjects. In contrast, in hyperprolactinemic states, PRL curves were similar in both tests. Continuous infusion of PHM-27 was very well tolerated and caused no important adverse events. These data suggest that PHM, like vasoactive intestinal peptide, can participate in the regulation of PRL release under physiological conditions and that the unsignificant PRL increase in PRL-secreting tumors may reflect abnormalities of the PRL secretion mechanism in these pathological states.

Topics: Adolescent; Adult; Female; Humans; Hyperprolactinemia; Peptide PHI; Pituitary Neoplasms; Prolactin; Prolactinoma