Measurements of pituitary prolactin levels in breeding pigeons by crop sac radioreceptor assay

Abstract

A recently developed assay based on the ability of ovine prolactin to bind to pigeon crop sac receptors was used to measure changes in pituitary prolactin content and concentration in male and female pigeons during the reproductive cycle. Pituitaries were collected from six regularly breeding pairs of pigeons at each of four stages: active nest-building (2–3 days before egg-laying), egg-laying, midincubation, and Day 1 posthatching. In females, prolactin content and concentration declined progressively between nest-building and midincubation but rose to peak levels by Day 1 posthatching. Prolactin levels of males were generally lower than those of females, but the pattern of changes was similar for both sexes. Comparison of these results with the pattern of prolactin-dependent crop sac changes suggests that the decline in pituitary prolactin levels during early incubation reflects the release of the hormone into the circulation. A marked increase in prolactin content was observed in both sexes during the second half of the incubation period, which may function to insure that a sufficient amount of prolactin is available to stimulate the formation of crop “milk” for regurgitation to the newly hatched young.