Effect of chronic immunoneutralization of thyrotropin-releasing hormone on the hypothalamic-pituitary-thyroid axis, prolactin, and reproductive function in the ewe.

Abstract

The physiological role of TRH was studied by chronic neutralization of its action by actively immunizing six adult ewes against the synthetic TRH conjugated to BSA. The animals were followed for a period of 2 yr through the various reproductive states of estrous cyclicity, anestrus, pregnancy, and lactation and were subjected to tests known to stimulate PRL release. Changes in plasma concentrations of TSH, T4, T3, and PRL were compared with levels in six control ewes. All TRH-immunized ewes produced antibodies, which were maintained by booster immunizations throughout the study period. Effects on plasma contractions of immunoassayable TSH were slight and inconsistent, but there was a clear reduction in levels of T4 and T3 in the blood of the TRH-immunized ewes, although detectable amounts of the hormones were always present. The seasonal rises in PRL concentrations during the summer months and during pregnancy and lactation still occurred in the TRH-immunized ewes, although there was an indication that le...