HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Muir, L. A. Articles by Wien, S. Search for Related Content PubMed PubMed Citation Articles by Muir, L. A. Articles by Wien, S.

Effects of Thyrotropin-Releasing Hormone and a Thyrotropin Releasing Hormone Analog on Growth and Selected Plasma Hormones in Lambs

Merck Institute for Therapeutic Research^1,2,, Rahway, NJ 07065

Abstract

An 8-wk growth trial was conducted to assess the effects of continuous infusion of thyrotropin-releasing hormone (TRH) and an active TRH analog <Aad-His-Pro-NH₂ (the <Aad is L-pyro--aminoadipic acid) on growth trial performance, carcass composition and hormone profiles of growing lambs. Both drugs were infused at 600 βg*lamb^–1 *d^–1 with 16 lambs/treatment. Both TRH and <Aad-His-Pro-NH₂ decreased average daily gain (ADG; P<.Q1) and increased feed conversion (FC; P<.01) compared with saline infused controls. Average daily feed intake was not altered. Carcasses of lambs given TRH or <Aad-His-Pro-NH₂ contained fewer kilograms of moisture (P<.05) and appeared to contain fewer kilograms of protein. Thyrotropin-releasing hormone and <Aad-His-Pro-NH₂ increased thyroid gland weights (P<.05), but pituitary gland weights were not different. Plasma thyrotropin (TSH) concentrations were increased by both drugs compared with control lambs, peaking at 4 to 7 d after initiating infusion. However, by 14 d, TSH concentrations returned to control levels. Triiodothyronine (T₃) and thyroxine (T₄) were elevated by both drugs over the entire 8-wk trial, with peak levels reached at 10 d and maintained for the duration of the study. Both TRH and <Aad-His-Pro-NH₂ increased prolactin over the entire period. Growth hormone levels were not altered by either drug. The effects of <Aad-His-Pro-NH₂ infusion on growth trial performance, carcass composition and hormone profiles of growing lambs were very similar to TRH. The negative effects of TRH and <Aad-His-Pro-NH₂ infusion on ADG, FC and carcass protein appear to be the result of elevated T₃ and T₄ levels.

¹ Dept. of Anim. Nutr. and Physiol.

² The authors express their appreciation to Paul Duquette and Eric Rickes for their technical assistance and to Dr. Martin Hichens for preparing ¹²⁵I-labeled hormones.