The effect of somatostatin on the release of thyrotropin and its subunits from bovine anterior pituitary cells in vitro.

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 X 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 less than 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.