Serum prolactin levels in lactating rats after suckling or exposure to ether

Prolactin was measured by radioimmunoassay (RIA) in blood samples withdrawn through chronic intracardiac cannulas from undisturbed lactating mother rats after isolation from their pups for 6.5–12hr. Each mother was then caged with 6 of her pups for suckling or placed in an ether jar for 6 min. Additional blood samples for RIA were withdrawn at various times during and after suckling or treatment with ether. Plasma prolactin levels remained very low in mothers caring for their pups unless suckling occurred. With the onset of suckling, the plasma prolactin levels rose rapidly after a latency of 4 min to values elevated 14–fold within IS min. On the other hand, ether “stress” caused a 2–fold increase beginning 1–2 min after exposure and reaching its maximum by 4 min. The results suggest that suckling and ether “stress” trigger the release of prolactin by different mechanisms.