The significance of urinary thyrotropin releasing hormone (TRH) excretion in man

These studies show that urinary TRH can be used as an index of endogenous TRH secretion and that men have higher TRH excretion than do women, possibly due either to the stimulating effects of testosterone or the inhibitory action of estrogens. The sex difference may be relevant to the observation that the pituitary of women is more sensitive to TRH stimulation. A clearcut conclusion about the effect of thyroid status on TRH excretion cannot be drawn. We are certain that TRH excretion is not inhibited by T3, thus suggesting that T3 does not exert a negative feedback effect on TRH secretion, supporting the concept of a positive feedback control. One cannot use this infomation to indiate hypothalamic function, however, because of the finding mentioned above, that both extrahypothalamic and hypothalamic brain are sources of urinary TRH.