Inhibitory influence of thyrotropin releasing hormone administration on growth hormone response to low doses of growth hormone-releasing hormone in normal man

Abstract

Literature data show that TRH may have either stimulatory or inhibitory actions on GH release according to pathophysiological conditions of the subject. In view of this dual effect of TRH, we studied the possible interaction of TRH and GRF on GH secretion. Six healthy male volunteers received iv in different occasions and in random order: 1) GRF 0.05 micrograms/Kg; 2) GRF 0.1 micrograms/Kg; 3) GRF 1 microgram/Kg; 4) GRF 0.05 micrograms/Kg + TRH 400 micrograms, simultaneously; 5) GRF 0.05 micrograms/Kg + TRH 20 micrograms, simultaneously; 6) GRF 1 microgram/Kg + TRH 400 micrograms, simultaneously, 7) the vehicle as control treatment. Blood samples were obtained at several time intervals and plasma GH, PRL and TSH were measured by RIA methods. Plasma GH significantly increased in all subjects after all the tested doses of GRF and after the combination of the highest and of the lowest doses of GRF + TRH (treatments 6 and 5). GH responses increased progressively with the dose of GRF administered, even if a clear dose-response relationship could not be demonstrated, owing to the considerable interindividual variability in the responsiveness. The administration of GRF 0.05 micrograms/Kg increased significantly plasma GH levels vs control treatment. The simultaneous administration of a low effective dose of GRF (0.05 micrograms/kg) plus a high dose of TRH (400 micrograms) was able to significantly inhibit the GH secretion elicited by GRF 0.05 micrograms/Kg alone. The other GRF + TRH combinations tested (treatments 5 and 6) did not modify the GH response to the same doses of GRF given alone. Plasma PRL and TSH did not change either after GRF at any dose or after the vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Ghrelin and Thyrotropin-releasing Hormone on Prolactin Secretion in Normal Women

“…This, however, was a weak action of TRH since this peptide was unable to counteract the potent stimulating eff ect of ghrelin. An inhibitory eff ect of TRH on GH secretion has been also shown in a previous study in male volunteers [33] . The reasons for these discrepancies are not known.…”

Effect of Enhancement of Cholinergic Tone on the Growth Hormone Response to Acute Hyperglycaemia or Thyrotropin‐Releasing Hormone in Dogs

“…One possible explanation for this discrepancy stems from the observation that, in humans, TRH failed to affect the GHRH-induced G H secretion when a maximal dose of GHRH was used, but inhibited it when the dose of GHRH was low (26). The fact that we used human instead of dog GHRH, and the GH-releasing effect of human GHRH in the dog was not so striking, might explain the discrepancy without ruling out species-related differences in the TRH-GHRH interaction.…”

Ο ρόλος της ghrelin στην έκκριση της προλακτίνης και των γοναδοτροφινών ορμονών σε γυναίκες

“…Η δράση όµως αυτή της ΤRH ήταν αρκετά ασθενής, αφού το πεπτίδιο αυτό δεν ήταν σε θέση να ανταγωνισθεί τη διεγερτική επίδραση της γκρελίνης, όταν οι δύο ουσίες χορηγήθηκαν ταυτόχρονα. Ανασταλτική δράση της ΤRH στην έκκριση της GH έχει βρεθεί και σε µία προηγούµενη µελέτη σε άνδρες εθελοντές (Zanoboni et al, 1988 Επίσης, όπως έχουν δείξει προηγούµενες µελέτες, η απάντηση της PRL στην TRH είναι παρόµοια σε διάφορες φάσεις του φυσιολογικού γεννητικού κύκλου σε γυναίκες (Sawin et al, 1978;Colon et al, 1988).…”