AUGMENTED SECRETION OF TSH IN RESPONSE TO TRH AFTER PRE-TREATMENT WITH DEXAMETHASONE FOR SIX DAYS IN RATS

Serum TSH and corticosterone concentrations were measured in rats given TRH or exposed to short-term cold, as well as in intact rats, after pre-treatment with dexamethasone for six days at two different dose levels (25 and 250 mug/100 g body weight). Both doses increased the secretion of TSH in response to TRH whereas cold-induced TSH secretion was not modified by pre-treatment with dexamethasone. In intact rats serum TSH levels did not differ significantly from controls. In all experiments the steroid blocked ACTH secretion. It was also found that administration of TRH produced a rise in serum corticosterone concentrations. Our results support the view that dexamethasone given for six days facilitates TRH stimulation of the pituitary whilst simultaneously inhibiting the secretion of TRH in response to cold.