Changes of serum and pituitary TSH, LH and FSH concentrations following the slow infusion of TRH and LRH.

Wistar-Imamichi male rats were slowly infused with synthetic TRH (T), LRH(L) and T +L in combination for of 1, 3, 24, 48 and 72hr. Doses of the releasing hormones were 1ƒÊg/hr. For each duration of infusioi,pituitary and serum TSH, LH and FSH concentrations were radioimmunoassayed. , When T is infused, the pituitary TSH concentration increases at 72hr. When L is infused, it increases at 48hr but decreases at 72hr. When T and L are combindedly infused, it decreases at 24hr, but increases at 72hr. The serum TSH concentration increases at all the durations of T infusion, but is not changed after the L infusion. The T +L infusion results in a rise of the serum TSH concentration at 1, 24 and 72hr. The pituitary LH concentration increases at 48 and 72hr of the T infusion, but decreases for the whole duration of the L infusion. The T-FL infusion increases the pituitary LH concentration at 24 and 48hr. The serum LH concentration does not tend to rise after the T infusion, but increases at 24, 48hr after the L infusion. The T+L infusion increases less progressively the serum LH concentration at 24, 48 and 72hr than the L infusion at the corresponding hours. The pituitary FSH concentration decreases after the 3-hr T infusion and after the 24and 72-hr L infusions. The T+L infusion does not change the pituitary FSH concentration. The serum FSH concentration declines with the prolongation of T infusion, and a tendency of slight decreaseis observed after the L and Tr-FL infusions. It is postulated from these results that T may be either an inhibitor to the FSH-release or a stimulator to the pituitary LH-synthesis. It is also speculated that T may act antagonistically upon the releasing effect of L, and that L may suppress the FSH-release.