Longitudinal changes in serum catecholamines, dopamine, serotonin, ACTH and cortisol in pregnant Spanish mares.

Systemic physiological changes required for placental and fetal development during pregnancy are associated with an activation of the sympathetic nervous system (SNS) and the hypothalamus-pituitary-adrenal axis (HPA) in women, but this fact has not been investigated in mares. Venous blood samples were taken monthly from 31 successful Spanish mares during the 11months of pregnancy. During the first 4months of pregnancy, adrenaline (AD), dopamine (DOPA) and ACTH increases, whereas 5-hydroxitryptamine (5-HT) decreased, and noradrenaline (NAD) and cortisol (CORT) did not change. Serum NAD increased at 8th month, 5-HT at 5th, 7th months, and DOPA increased progressively between the 5th and 8th months and CORT concentrations peak at 5th month. During the three last months of pregnancy, NAD, 5-TH and DOPA decreased, particularly at the 11th month. These results confirmed an activation of the SNS and the HPA axis in pregnant mares during successful pregnancies. The next step would be to elucidate whether these changes also appear in unsuccessful pregnancies.