Effect of active and passive immunization with TRH on plasma TSH response to propylthiouracil. 
The role of thyrotropin-releasing hormone (TRH) in the secretion of TSH from the anterior pituitary was investigated in rats by active and passive immunization with TRH.  The plasma TSH response to propylthiouracil (PTU) in TRH-bovine serum albumin (BSA)-immunized rats was significantly lower than that of BSA-immunized or non-immunized rats.  Similarly, the increased plasma TSH level following PTU treatment was significantly suppressed after iv injection of antiserum to TRH.  However, the decline in plasma TSH levels was not complete.  The results of the present study indicate, at least in part, the physiological significance of endogenous TRH in the regulation of pituitary TSH secretion.