Discordant changes in pituitary concentrations of LH and TSH subunits following hormonal manipulation

We have recently shown that mouse pituitary concentrations of free TSH-beta and alpha-subunits respond divergently to thyroid hormone manipulations in vivo. This study contrasts the changes in free LH-beta and alpha-subunits after castration and polyestradiol phosphate (E2) administration with those in free TSH-beta and alpha-subunits after thyroidectomy and thyroxine (T4) administration. Target hormone depletion (castration or thyroidectomy) resulted in an increase in plasma concentrations of the respective tropic hormones and their subunits; target hormone administration (E2 or T4) resulted in a decrease in plasma concentrations. In contrast, pituitary subunit concentrations of LH and TSH responded discordantly to target hormone depletion or administration, and the nature of the discordance for alpha-subunit and LH-beta was opposite to that for alpha-subunit and TSH-beta. Hypogonadism caused a decrease in pituitary LH and LH-beta concentrations to 65% (P less than 0.01) and 48% (P less than 0.001) of values in control (eugonadal) mice, respectively, while alpha-subunit was unchanged. Hypothyroidism caused a two-fold (P less than 0.001) and 20-fold (P less than 0.001) increase in pituitary TSH and TSH-beta concentrations, respectively, while alpha-subunit fell to 68% (P less than 0.01) of values in control (euthyroid) mice. Administration of E2 to hypogonadal mice resulted in a two-fold increase in pituitary LH and LH-beta after 11 days, while alpha-subunit fell to 55% (P less than 0.01) of values in control (untreated hypogonadal) mice.(ABSTRACT TRUNCATED AT 250 WORDS)