'Bone-fide' link to low sperm count?

A bone cell hormone can regulate male fertility hormone testosterone, a study on mice has found. Male mice engineered to produce little osteocalcin, a hormone released by bone cells called osteoblasts, had smaller litters and testes than unmodified mice. US researcher Dr Gerard Karsenty and colleagues are investigating whether this hormone could treat men with infertility problems because many hormones have similar effects in mice and humans.

The researchers found male mouse testes cells grown in the presence of osteoblasts produced three times more testosterone than cells grown with fat or muscle cells. Osteocalcin was directly responsible for the increase in testosterone because growing testes cells in the presence of this hormone or injecting mice with it led to increased testosterone levels.

However, the scientists were surprised to discover osteoblasts grown alongside tissue from mice ovaries did not increase the levels of female fertility hormones oestrogen and progesterone. 'We were flabbergasted', Dr Karsenty from New York's Columbia University told New Scientist magazine. 'Don't ask me why it only affects males because I don't know'.

The study was published in Cell.