Plasma prolactin in goats measured by radioimmunoassay: the effects of teat stimulation, mating behavior, stress, fasting and of oxytocin, insulin and glucose injections.

Results are reported of measuring prolactin in goatplasma by a radioimmunoassay.Changes in concentration in plasma prolactin over time scales from minutes to hours were noted in animals not subject to experimental stimuli. It is presumed that these changes reflect the rapid removal of prolactin from plasma (t ½ 19 min) and the secretion of prolactin in response to unknown internal stimuli. Stimuli are reported which cause rises in plasma concentration suggestive of bursts of secretion from the pituitary. Copulation, in both males and females, sexual excitement in males and milking caused the largest increases in plasma concentration. Oxytocin injections and mild stress caused significant but smaller increases in plasma prolactin sometimes seen as a rise in jugular vein concentrations only. Plasma prolactin fell on fasting and after insulin and it rose on refeeding, but there was not a direct correlation with changes in blood glucose concentration.