2011 年 73 巻 1 号 p. 77-82
To define the source of circulating inhibin in female Asian elephants, the immunolocalizations of the inhibin α, βA and βB subunits, 3β-hydroxysteroid dehydrogenase (3β-HSD), aromatase cytochrome P450 (P450arom) and cytochrome 17α-hydroxylase P450 (P450 c17) were investigated. Concentrations of immunoreactive (ir-) inhibin, progesterone and follicle-stimulating hormone (FSH) during the estrous cycle were measured by radioimmunoassay. Inhibin immunoreactivity in follicular fluid and homogenate of corpora lutea was also measured. Immunolocalizations of inhibin subunits, 3β-HSD, P450arom and P450c17 were detected in the granulosa cells of antral follicles and luteal cells. The follicular fluid contained high levels of ir-inhibin and bioactive inhibin. The homogenate of corpora lutea also contained ir-inhibin. Serum ir-inhibin remained at low levels during the early non-luteal phase, began to increase from the late non-luteal phase and continued to increase during the early luteal phase. Serum ir-inhibin showed maximal levels in the middle of the luteal phase and gradually decreased to baseline three weeks prior to progesterone decline. The serum ir-inhibin levels were positively correlated with progesterone throughout the estrous cycle. On the other hand, ir-inhibin was negatively correlated with FSH during the late non-luteal and early luteal phases. These findings strongly suggest that the corpus luteum is one of the sources of inhibin as well as granulosa cells in the Asian elephant.