Prolactin Response to N3im-Methyl-Thyrotropin Releasing Hormone in Euthyroid Subjects

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Abstract
The N3im-methyl analogue of thyrotropin releasing hormone (methyl-TRH) wascompared with ordinary TRH as a prolactin (PRL) releaser in 32 euthyroid volunteers (20 male and 12 female, ages 17–66 years). The mean PRL response to 100 Mg of methyl-TRH was greater (P < 0.025) than the PRL response to 500/xg of TRH at 10 min and at all sampling times from 30 to 240 min after administration of the releasing factors. The mean peak PRL (at 10 min), maximum APRL, and integrated PRL response area were greater (P < 0.025) after administration of methyl-TRH than after TRH. The PRL response to methyl-TRH was greater (P < 0.005) for the 12 women than for the 20 men in this study. The mean baseline PRL was correlated with the peak PRL (r=0.74, P < 0.01) and the maximum ΔPRL(r=0.58, P < 0.01) after methyl-TRH. Following administration of methyl-TRH, the peak PRL was correlated with the peak TSH (r=0.43, P < 0.05), tlie maximum ΔPRL was correlated with the maximum ATSH (r=0.43,P < 0.05), and integrated PRL response area was correlated with the integrated TSH response area (r=0.44, P < 0.05). Similar correlations between PRL and TSH responses were seen after giving TRH. Age was inversely correlated with baseline PRL(r=−0.55, P < 0.01), with maximum APRL (r = −0.64, P < 0.01), and with the PRL response area (r=0.48, P < 0.01) afteradministration of methyl-TRH or TRH. Methyl-TRH did not significantly alter serum levels of growth hormone (16 subjects) and luteinizing hormone and follicle stimulating hormone (14 subjects). The results of this study indicate that methyl- TRH is a more potent prolactin releaser than TRH. Like TRH, methyl-TRH has specificity in its effects on the pituitary, releasing only TSH and PRL in normal man.