Peripheral blood and ovarian levels of sex steroids in the cyclic hamster

Abstract

Changes in progesterone (P), testosterone (T), estrone (E₁) and estradiol-17β (E₂) in peripheral blood, ovary, corpora lutea (CL) and in the nonluteal portion of the ovary (NLO) were studied in the cyclic hamster by RIA. In addition, androstenedione (A) was measured, but only in serum. Serum P levels were the same on Days 1 (day of ovulation) and 2 at 0900 h (5 ng/ml), but declined markedly on Day 3 and on the morning of Day 4 (proestrus). After the LH surge on the afternoon of Day 4, serum and ovarian levels of P increased abruptly until 1900 h to 11-18 ng/ml and declined slowly thereafter. Peak T levels in both serum (209 pg/ml) and the ovary occurred between 1400-1500 h of Day 4, paralleling the rising P levels. However, T levels declined rapidly after 1600 h to undetectable levels by 1900 h, but there was a second peak of T by 2300 h in serum which was matched by the ovary. Serum levels of E₁ and E₂ began to rise on Day 2, reaching peak values by Day 4 between 1200 and 1400 h (41 pg/ml and 152 pg/ml, respectively). Peak ovarian concentrations of E₁ and E₂ were reached on Day 4 at 0900 h. These high levels were maintained up to 1600 h of Day 4 and declined rapidly thereafter. The serum levels of E₁ were about one-third as high as E₂ and were not as drastically affected on the evening of Day 4. Serum androstenedione ranged from 1-2 ng/ml, but changes throughout the cycle were not as striking as for the other steroids. However, increased levels of A were associated with decreased levels of estrogens and vice-versa. Therefore, the circulating levels of A probably reflect altered secretion rates of other steroids. Administration of 5 μ g LH on the evening of Day 4 (when all steroid levels are declining) caused significant increases in P and T but not E₂. Hence, the refractory period of estrogen synthesis on the evening of Day 4 cannot be attributed to insufficient levels of LH during the preovulatory period.