Brain mood hormone linked to milk production

Milk production in mammalian breast tissue is regulated by serotonin - the same hormone that acts in the brain to control a person’s mood, according to researchers at the University of Cincinnati, US.

A study by Nelson Horseman’s team in the department of molecular and cellular physiology shows that blocking serotonin production in the mammary gland increases the amount of milk produced - suggesting that treating dairy cattle with a drug that inhibits the hormone could help to satisfy the growing demand for dairy products.

Lactation in mammals is stimulated by the action of a number of hormones including prolactin and oxytocin. But there must be some method of switching the process off to prevent damage to breast tissue during periods between nursing or artificial milking, and earlier research suggested a chemical signal.

In studies on mouse and human mammary cells, Horseman shows that blocking the receptor to serotonin (5-hydroxytryptamine) causes an increase in the expression of milk protein genes and an accumulation of the lipids found in milk. He has now begun studies in cattle, supported by the US Department of Agriculture, to assess whether serotonin blocking treatment can increase milk production on commercial dairy units. Growing demand for milk is pushing up milk prices worldwide and the US is exporting increasing amounts to satisfy the thirst of Asian consumers.

Horseman told Chemistry World that the university has taken out a patent on a new use for carbidopa, an established drug which inhibits the final stage of serotonin synthesis. The drug has not yet been tested in cattle but he predicts that treatment may increase milk production by about 10-12 per cent. 

That is roughly the same increase in cows treated with bovine somatotrophin, a compound banned from commercial use in Europe, mainly because it increases the incidence of mastitis. But Horseman does not expect the new treatment to cause the same problems. ’From what we know of the biology, I would predict that it is likely to reduce mastitis symptoms,’ he said.

Low levels of the same hormone in the brain are linked to depression in humans and treated with serotonin reuptake inhibitors (SRIs). Will treatment with serotonin blockers create productive but not very contented cows? Horseman thinks it is unlikely that the drugs chosen will affect levels in the brain because they only act peripherally and cannot cross the blood brain barrier into the central nervous system. Similarly, there is no evidence that milk production is affected in women receiving SRIs for their depression.  

However, Ian Givens, director of the animal science research group at Reading University School of Agriculture is sceptical about the practical applications of these studies. ’It is an interesting finding but certainly within the EU the use of drugs of some sort to reduce serotonin synthesis in the mammary gland would be a non-starter,’ he told Chemistry World.

Givens points out that extrapolating from cell culture and laboratory animal findings to large dairy cows is a ’big step to take’. He says any further studies in cattle would need to rule out the risk of side effects. Dairy cattle are already producing milk in volumes that mean they have to break down stored body tissue to balance the energy lost at milking. Pushing them any harder risks causing damage to their general health, he warned.

John Bonner