Enhanced plasma GH responses to simultaneous administration of TRH and GHRH in patients with primary hypothyroidism.

Abstract

The mechanism of aberrant GH responses to TRH was indirectly evaluated in 7 patients with primary hypothyroidism. All patients showed GH response to TRH. When TRH was administered together with GHRH, the plasma GH response was much greater than after a single administration of TRH or GHRH (TRH+GHRH vs. TRH or GHRH: max. delta GH, 16.4 +/- 3.2 vs. 5.4 +/- 1.3 or 6.0 +/- 0.8 microgram/L; AUC, 1282.7 +/- 234.7 vs. 384.0 +/- 95.0 or 441.8 +/- 66.2, both P < 0.01). The combined administration of TRH and GHRH caused an additive, but not a synergistic, GH response. In contrast, 8 normal subjects showed neither any plasma GH response to TRH nor enhancement by TRH of GHRH-induced GH response following combined administration. It is concluded that the sites of action of TRH seemed to be different from GHRH in patients with primary hypothyroidism.