Final answer:
Calcitonin and estrogen are responsible for improving vertebral bone density in rats. Calcitonin stimulates the uptake of calcium by bones, while estrogen promotes osteoblastic activity and bone matrix production.
Step-by-step explanation:
The hormones responsible for improving vertebral bone density in the rats are calcitonin and estrogen. Calcitonin inhibits osteoclast activity and stimulates the uptake of calcium by bones, which leads to bone density improvement. Estrogen promotes osteoblastic activity and the production of bone matrix, which is also crucial for maintaining and improving bone density. Therefore, the correct answer is E) both calcitonin and estrogen.