Effect of naloxone on TRH-induced PRL and TSH response in normal man

The effect of naloxone on PRL and TSH response to TRH was studied in 8 normal men. PRL response to TRH was unaffected by the administration of naloxone. TSH response to TRH was significantly decreased by naloxone, considering the maximum absolute increment (p less than 0.01) and the areas under curves (p less than 0.05). In conclusion, the PRL response to TRH may be unaffected by endogenous opioids or naloxone and we were unable to reveal a possible opioid effect in our experimental conditions. TSH response to TRH seems to be affected by endogenous opioids, possibly due to an indirect or direct action on TRH and/or on the pituitary.