Thyroid Hormones (T4, T3, and rT3) in Serum of Rats Injected with Relaxin, Progesterone And/ Or Estradiol Benzoate

Abstract

An experiment was undertaken to investigate the effect of relaxin, progesterone and/or estradiol benzoate and their combinations on circulating thyroid hormones in ovariectomized rats. Blood samples were obtained after 20 days of daily subcutaneous injection. Serum samples were analyzed by radioimmunoassay for thyroxine (T4), 3,5, 3’-triiodothyronine (T3) and 3, 3’, 5'-triiodothyronine (rT3). Analysis of variance showed a significant decrease (P < .01) in body weight in response to estradiol benzoate (EB), progesterone (P), the combination of two hormones and all three hormones (p < .01), but there was no difference with relaxin. Serum T4 was significantly decreased (P < .01) from control in response to estradiol benzoate, relaxin and the combination. but there was no significant difference with progesterone (p > .05). Serum T3 was significantly increased (p < .01) with estradiol benzoate, progesterone, and the combination, but there was no significant change due to relaxin. Reverse T3 increased with progesterone (p < .05) and decreased with relaxin (p < .05), but did not change with estradiol benzoate and progesterone or the combination of all three hormones. Changes in serum rT3 were thought to reflect peripheral conversion at the target cell level from T4. Progesterone appeared to increase the conversion rate while relaxin decreased it.