Prolactin release in cattle

Several 'physiological fluctuations ' of the prolactin level in peripheral blood have dubious functional implications. Hence some of these may be explained symptomatically rather than functionally. Concerning the basal prolactin level, the correlation with seasonal variations is dominant but circadian rhythmicity also has to be taken into account. With regard to exteroceptive stimuli, stressful situations are likely to include prolactin release in the complex of reactions. In the physiological sense the increase of prolactin secretion after stimulation of the teats is probably the most specific. There is a reciprocal dose/response relationship between ovarian oestrogens and progesterone administered and the immediate prolactin release. A most efficient procedure for demonstrating a positive influence on prolactin secretion is treatment with the synthetic tripeptide, TRH. A specific inhibitor of prolactin release is 2 Br α ergocryptine methanesulfonate. Experiments using these compounds were helpful in elucidating the physiological participation of prolactin in mammogenesis and lactogenesis in which it appears to be essential, in galactopoiesis in which it appears to play a minor role and as a luteotrophin, which seems to be of no importance in the bovine species. The use of these compounds for manipulation of the onset of lactation and milk yield should be considered to be of practical interest.