Biphasic release of thyrotropin in response to thyrotropin-releasing hormone (TRH) from rat anterior pituitary cells in vitro: Possible dependence on protein synthesis

K. Shiota, K. Yoshida, T. Masaki, M. Kawase, R. Nakayama, K. Sudo

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Mechanisms related to the biphasic release of TSH were studied using primary cultured cells of the rat anterior pituitary gland on micro-carrier beads in a superfusion system. Release of TSH in response to continuous exposure to TRH exhibited a biphasic pattern; the first phase was characterized by a rapid, transient and high-rate release (phase I) and the second phase by a chronic and low-rate release (phase II). The shift of the release from phase I to phase II occurred with treatment with TRH at concentrations from submaximal to maximal. When the Ca2+ concentration in the medium was decreased, the phase I release was partially inhibited, while the phase II release was completely inhibited, suggesting a difference between the mechanisms in phase I and phase II release. The phase I release was not suppressed by cycloheximide. This protein synthesis-independent release of phase I seemed to be linked to the intracellular releasable pool of TSH. The phase II release was suppressed by the presence of a protein synthesis inhibitor. After the phase II release was suppressed by cycloheximide, the magnitude of phase I release in response to re-exposure to TRH markedly decreased. The decreased phase I release in response to TRH was observed with the cells which were previously stimulated by high K+ instead of TRH, suggesting that the decrease in the response of phase I reflects the depletion of a releasable pool of TSH rather than homologous desensitization of thyrotrophs with TRH. These results suggest that the phase I release of TSH depends on a portion of the previously prepared-releasable pool while phase II release depends on previously prepared plus newly prepared pools of TSH. Replenishment of the releasable TSH pool was considered to involve protein synthesis.

Original languageEnglish
Pages (from-to)165-175
Number of pages11
JournalEndocrinologia Japonica
Volume31
Issue number2
Publication statusPublished - 1984
Externally publishedYes

ASJC Scopus subject areas

  • Endocrinology

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