Abstract
Insulin-like growth f actor-I (IGF-I) plays an important role in the regulation of growth during puberty. Although IGF-I levels are known to be related to sex steroids, sex difference related to the effect of sex steroids on IGF-I is still unknown. To investigate the effect of sex steroids on IGF-I production in both sexes of immature rats, the following study was undertaken. Immature female rats (Wistar) were ovariectomized (OVX, n= 20) and male rats were orchitectomized (ORX, n=20) 14 days after birth. Estradiol (E2, 0.01 nmol/body, n=5), testosterone (T, 1 nmol/body, n=5) and dihydrotestosterone (DHT, 0.1 nmol/body, n=5) were administered daily for 4 weeks. A sham operation (n=5) was also performed as the control. On day 48, rats were sacrificed and blood samples and liver tissues were obtained. Serum IGF-I concentrations were measured by the RIA method. Northern blot analysis was used to study the IGF-I mRNA expression in the liver. Body weights were increased by OVX, while no change by ORX was observed when compared with the sham group. Estrogen administration to OVX/ORX decreased body weight. Administration of androgen increased the weight in both sexes. Serum IGF-I levels and IGF-I mRNA expression in the liver were increased by OVX, but there were no changes by ORX. Serum IGF-I levels and IGF-I mRNA expression in livers were decreased in OVX rats but were increased in ORX rats by estrogen administration. On the other hand, administration of androgen to OVX/ORX rats increased serum IGF-I levels and IGF-I mRNA expression in livers. From the results obtained above, it was demonstrated for the first time that estrogen has different effects on IGF-I production between male and female immature rats although androgen stimulates IGF-I production in both sexes.
