俺老家那地男孩子吵架说自己是人家的爹就算是站在至高点了，经常是两个小子争执谁是对方的爹。那句话充满着千年的哲理，说对方只不过是自己小腿里的东西，多年前还在那里“转筋”。等俺有了一定的科学知识认识到那是来源于哪里之后就苦思这句老话的道理，终于让俺等到了这一天。

Endocrine Regulation of Male Fertility by the Skeleton

Interactions between bone and the reproductive system have until now been thought to be limited to the regulation of bone remodeling by the gonads. We now show that, in males, bone acts as a regulator of fertility. Using coculture assays, we demonstrate that osteoblasts are able to induce testosterone production by the testes, though they fail to influence estrogen production by the ovaries. Analyses of cell-specific loss- and gain-of-function models reveal that the osteoblast-derived hormone osteocalcin performs this endocrine function. By binding to a G protein-coupled receptor expressed in the Leydig cells of the testes, osteocalcin regulates in a CREB-dependent manner the expression of enzymes that is required for testosterone synthesis, promoting germ cell survival. This study expands the physiological repertoire of osteocalcin and provides the first evidence that the skeleton is an endocrine regulator of reproduction.