High levels of which hormone would be least likely to promote bone formation?

The hormone that would be least likely to promote bone formation is parathyroid hormone. This hormone primarily regulates calcium levels in the blood, and when its levels are high, it actually promotes the resorption of bone, leading to an increase in calcium release into the bloodstream. Parathyroid hormone acts on bone cells called osteoclasts, which break down bone tissue, thereby releasing calcium and phosphate into the circulation. This process contrasts with the actions of other hormones listed.

Calcitonin, on the other hand, works to lower blood calcium levels by inhibiting osteoclast activity and promoting bone formation. Growth hormone plays a significant role in promoting the growth and development of bone by stimulating the activity of osteoblasts, cells responsible for bone formation. Androgens also have an anabolic effect on bone, leading to increased bone density and growth.

Therefore, while parathyroid hormone has important regulatory functions, its role in promoting bone resorption makes it the least likely hormone to support bone formation compared to the others listed.