Final answer:
Estrogen promotes osteoblastic activity and the production of bone matrix, key factors in bone density, making it the hormone likely responsible for the greatest improvement in vertebral bone density for the rats.
Step-by-step explanation:
The hormone that showed the greatest improvement in vertebral bone density for the rats is likely estrogen. Estrogen is known for promoting osteoblastic activity and the production of bone matrix, which are key factors in bone density. Additionally, estrogen is involved in several growth-related processes such as the adolescent growth spurt and conversion of the epiphyseal plate to the epiphyseal line, which signifies the end of longitudinal bone growth. In contrast, calcitonin has the specific role of inhibiting osteoclast activity, which prevents bone resorption and leads to the deposition of calcium in the bone. While this also contributes to bone density, estrogen's overall role in osteoblastic activity and bone matrix production makes it a strong candidate for improving bone density. Saline is merely a control solution and would not be expected to improve bone density. As for Follicle Stimulating Hormone (FSH), it does not have a direct role in the bone deposition process.