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The mechanism that links the production of a daylight recognising hormone and reproductive hormones in ewes has been discovered by scientists at the University of Bristol and University of Nottingham.
The seasonal breeding cycle in sheep is caused by ewes coming on heat as daylight time reduces each year due to the hormone melatonin being produced in the pineal gland located in the brain.
“It has not been known how melatonin, which is produced at night, signals to the area of the pituitary gland (located in the base of the brain) that controls sex hormones,” Professor David Bates from the University of Nottingham said.
However, the study published in Proceedings of the National Academy of Sciences has found that melatonin controls production of two different types of a protein called vascular endothelial growth factor (VEGF).
These proteins are produced in a separate area of the pituitary gland from where the sex hormones are produced.
Mechanism
The study found that in winter increased production of melatonin due to reduced daylight leads to a form of VEGF being produced which stops blood vessels growing in the pituitary gland and begins the reproductive cycle.
In summer, lower melatonin production due to increased daylight means sheep make a different VEGF that allows vessels to grow between the two areas of the pituitary which inhibits production of sex hormones.
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