Letrozole inhibits the osteogenesis of medullary bone in prelay pullets

This study was performed to investigate the effect of letrozole, an aromatase inhibitor, on osteogenesis of medullary bone in prelay pullets. Three hundred fifteen 95-d-old ISA prelay pullets were used. After 10 d of adaptation in the cages, 15 pullets were selected randomly to collect the serum and bone samples and the rest were randomly assigned to 2 groups with 3 replicates each. One group was control and the other was letrozole-treated, fed 0.5 mg of letrozole per prelay pullet per day for 18 d. The serum and bone samples from these birds were collected during the experiment. Estradiol and testosterone in serum were assayed using commercial RIA kits. The serum alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), Ca, and inorganic P were measured by an automatic biochemistry analyzer with commercial kits. The periosteum perimeter, endosteum perimeter, cortical bone index, cortical width, cortical bone area, and cortical area ratios of tibia were measured by transmitted scanner and a computer-assisted image analyzer. Our results showed that relative to the control-fed pullet, letrozole-fed pullets had reduced serum estrogen (57.5%), Ca (33.2%), ALP (33.6%), and TRAP (24.2%) and that values of serum estrogen, Ca, estrogen receptor expression, tibia radiographic density, serum ALP, and TRAP were all reduced (P < 0.05) and the serum P had a degressive trend in letrozole-treated groups. By contrast, the serum androgen and the tibia cortical bone index values were higher in the letrozole-treated group (P < 0.05). No differences were observed in the periosteum perimeter, endosteum perimeter, cortical width, and cortical area ratios of tibia between the 2 groups. The results showed that letrozole can inhibit the development of bone and medullary osteogenesis by inhibiting the synthesis of estrogen and its receptor in prelay pullets.