Abstract
Insulin-like growth f actor-I (IGF-I) affects growth and differentiation of connective tissues, and bone mineral density (BMD) in postmenopausal women. In the present study, the effects of estrogens and androgens on serum levels of IGF-I and IGF binding protein-3 (IGFBP-3) and BMD were studied in ovariectomized adult female guinea pigs. Twenty adult female guinea pigs (body weight, 650 to 700g) were divided into four groups : 15 guinea pigs were ovariectomized : 2 weeks later 5 recieved injections of estradiol (E2, 4 μ g / 100g weight) and 5 recieved injections of dihydrotestosterone (DHT, 40 μg/ 100g weight) once a week for 3 weeks. Five sham-operated animals were used as controls. Lumbar BMD (L1-L4) was measured with dual energy X-ray absorptiometry (DEXA, QDR-2000) 2 days after the last injection, after which animals were killed by decapitation. Blood was collected and centrifuged, and serum was kept frozen at -80°C until assayed. Serum levels of IGF-I and IGFBP-3 were measured with radio radioimmunoassay. No significant difference in body weight was observed between the groups. Ovariectomy resulted in a significant (p< 0.05) decrease in serum IGF-I levels and lumbar BMD. E2 administration could not restore serum levels of IGF-I and IGFBP-3, whereas DHT administration restored both levels to that in the controls. On the other hand, administration of E2 and DHT restored BMD in the ovariectomized animals to that in controls. Our results indicate the different effects of androgens and estrogens on BMD and serum IGF-I levels in adult female guinea pigs.
