Effect of ergocristine on prolactin secretion in the male rat with pituitaries grafted beneath the kidney capsule

Male rats in which three pituitaries were grafted beneath the kidney capsule showed approximately a fourfold increase in circulating plasma prolactin concentration. The elevated plasma prolactin concentration did not remain at a constant level but fluctuated with time. The elevated prolactin concentration declined immediately after a single bolus injection of ergocristine (30 μg/kg). The slope of the prolactin decay curve, determined by sequential blood sampling, was parallel to a theoretical slope having a 7-min half-life. This result indicates that ergocristine blocked prolactin secretion immediately and completely as the decay curve (T 1/2 = 6.5 min, confidence interval 4.5–11.3) resulting from the administration of ergocristine is the same as the endogenous prolactin decay curve (T 1/2 = 7 min).