The reciprocal pattern of release observed in PRL and TSH following various types of administration of TRH

Abstract

Alterations of plasma TSH and PRL levels following various types of administration with TRH were studied in the luteal phase of women with normal menstrual cycles. The results were as follows: Plasma PRL response to a single i.v. injection of tRH with DHEA-S drop injection was not significantly different from that observed without it. The data suggest that DHEA-S does not affect the feedback mechanism in the short-term course of the experiment. Alterations in the plasma levels of PRL during intermittent as well as continuous infusion with TRH were quite different from those with TSH. Plasma TSH increased following the beginning of a continuous infusion with TRH and reached a peak at approximately 180 min, maintaining a plateau until the infusion was withheld. On the other hand, plasma PRL levels increased rapidly to reach peak levels in 30 min after the start of the infusion gradually following a decline in spite of continued TRH stimulation. Furthermore, a stepwise increase of TSH levels was observed following 4 intermittent injections of TRH; however, plasma PRL rapidly reached peak levels in 30 min following the 1st injection of TRH and a further 3 injections did not raise the levels of PRL. The results suggest that in humans, the synthesis and release of PRL occur independently in the pituitary.