The Effect of Somatostatin on the Release of Thyrotropin and Its Subunits from Bovine Anterior Pituitary Cells in Vitro*

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Abstract
The effects of somatostatin (SRIF) on the production and release of TSH and its subunits have been investigated in bovine anterior pituitary monolayer cultures. SRIF caused a dose-dependent inhibition of TSH and subunit release by TRH, with a half-maximal effective dose of 3 × 10-8 M. This effect was time dependent and was greater for TSH than for its subunits. However, the basal release and total production of TSH and its subunits over a 24-h period were not affected by SRIF. The effect of SRIF was additive to that of thyroid hormones in suppressing the release of TSH and its subunits by TRH. A combination of SRIF and thyroid hormone completely suppressed the release of TSH and its subunits by TRH. In contrast, thyroid hormones caused a dose-dependent inhibition of the total production, as well as the release, of TSH and its subunits induced by TRH. Furthermore, thyroid hormones produced a dose-dependent increase (r = 0.81; P < 0.001) in the effectiveness of a single dose of SRIF in suppressing TSH release by TRH. Analysis, of these data revealed that thyroid hormones interacted synergistically with the SRIF effect to suppress TRH-mediated TSH and subunit release.

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