Thyrotropin (TSH)-releasing hormone-stimulated TSH release and TSH concentration in the guinea pig pituitary, as determined by a heterologous radioimmunoassay

Endocrinology
W J DeVitoC H Emerson

Abstract

Little is known regarding how the guinea pig (GP) compares with the rat in terms of TSH economy. To develop a heterologous RIA for GP TSH, rabbits were injected with GP TSH. In one rabbit (anti-gpTSH-8), antibodies that bound 125I-labeled bovine (b) TSH and rat (r) TSH but not 125I-labeled bLH or rPRL were generated. The binding of anti-gpTSH-8 to [125I]bTSH was inhibited in a parallel manner by bTSH over a range of 0.047-5.42 ng, rTSH over a range of 0.24-25 ng, and dilutions of GP pituitary extracts. This system, with bTSH as the standard, was employed as the basis for a heterologous TSH RIA (GP TSH RIA). The cross-reactions of rTSH and bLH in the GP TSH RIA were 45% and 7%, respectively. Rat and bovine FSH, GH, and PRL had little or no cross-reaction. GP pituitaries were incubated in vitro and dosed with LHRH and TRH. The GP TSH RIA detected an 11-fold increase in TSH in the medium in response to TRH and no change in immunoreactivity in response to LHRH. In contrast, a RIA for bLH detected a 25-fold increase in LH in the medium in response to LHRH and no increase in response to TRH. The TSH content in GP pituitaries was significantly lower than that in the rat (GP, 16.8 +/- 1.6 ng/mg; rat, 80.3 +/- 6.2 ng/mg; P less than 0.0...Continue Reading

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