Concentrations of hormones and metabolites in cerebrospinal fluid and plasma of dairy cows during the periparturient period.

During early lactation, high-yielding dairy cows often show insufficient feed intake (FI) and, as a consequence, they enter into a negative energy balance associated with an altered pattern of plasma metabolites and hormones. These act as short- and long-term hunger or satiety signals in the brain and play an important role in the control of FI. Metabolites and hormones also occur in cerebrospinal fluid (CSF), which surrounds the hypothalamus and brainstem, 2 major centers of FI regulation. The CSF hormone and metabolite concentrations are mainly under control of the blood-brain barrier. Consequently, CSF hormone and metabolite concentrations differ from those in blood. However, the contribution of putative orexigenic and anorexigenic CSF signals possibly leading to insufficient FI of high-yielding dairy cows during early lactation has not been studied so far. Therefore, the aim of this study was to elucidate associations existing between both plasma and CSF hormones and metabolites during the periparturient period. Ten multiparous German Holstein dairy cows were fed ad libitum and samples of CSF from the spinal cord and blood from the jugular vein were withdrawn before morning feeding on d -20, -10, +1, +10, +20, and +40 relative to calving. Feed intake started to decrease from d 5 before calving and increased thereafter. Glucose, β-hydroxybutyrate (BHBA), cholesterol, nonesterified fatty acids, urea (all enzymatic), lactate (colorimetric), amino acids (HPLC), osmolality (osmometer), ghrelin (RIA), leptin (ELISA), and resistin (Western immunoblot) were measured in both CSF and plasma, whereas free fatty acids (gas chromatography-mass spectrometry) and volatile fatty acids (gas chromatography-flame-ionization detector) were determined in plasma only. Whereas leptin concentrations decreased after calving in both plasma and CSF, ghrelin concentrations were not altered, and abundances of total resistin and its hexamers decreased only in plasma. Although plasma concentrations of cholesterol and nonesterified fatty acids changed during the periparturient period, their concentrations were not affected in CSF. In contrast, CSF Gln concentration tended to increase until calving, whereas CSF concentrations of BHBA, α-aminobutyric acid, Cit, Gly, Ile, Val, and Leu were increased in early lactation compared with the preparturient period. Because Gln is known to serve as neuronal substrate generating ATP, Gln is suggested to act as a central anorexigenic signal shortly before parturition. Moreover, due to their known anorexic effect, BHBA and Leu may potentially act as central signals and thereby suppress a sufficient increase in FI during early lactation.