TRH (10 and 1000μg/kg body weight (BW)) was injected ip into pregnant rats daily from day 0 to 20 of pregnancy, and the pituitary-thyroid axis of their pups (Mat-TRH rats) was examined on days 0, 4, 10, 21 and 90 after birth. The pituitary TSH content of male Mat-TRH rats was significantly lower on day 4, and higher on day 10 than that of control rats. The serum TSH was significantly higher on day 10 (except female 10μg/kg group).
An exaggerated TSH response to exogenous TRH (10μg/kg BW; ip) was observed on day 10 (males, 1000μg/kg group). The serum T⁴ level of female Mat-TRH rats was low on day 4 (1000μg/kg group), and higher on day 10. On days 21 and 90, the levels of pituitary TSH, serum TSH and T₄ in Mat-TRH rats were similar to those in controls, but the TSH response to TRH was still exaggerated (1000μg/kg group).
No significant difference between control and TRH-treated mothers was seen on days 10 and 90 postpartum except for a decreased pituitary TSH content on day 10 in the 1000μg/kg group. It is concluded that repeated administration of TRH to pregnant rats shows an effect on the pituitary-thyroid axis function of their progeny in later life.