Ether releases large amounts of prolactin from rat pituitaries previously "depleted" by short term suckling

The effect of ether inhalation upon plasma PRL levels was assessed in lactating rats whose pituitary stores of the hormone first had been depleted by a short term (10-min) period of suckling in comparison with those whose PRL stores had not been depleted by prior suckling. Ether, unlike suckling or handling-decapitation stress, did not deplete pituitary PRL and caused only a small increase (36 to 52 ng/ml) in the plasma concentration of the hormone. However, when ether was given 10, 60, or 120 min after the plasma concentration had subsided from a prior 10-min period of suckling, the plasma concentration of PRL in each instance rose within 5--10 min to 200--250 ng/ml and was sustained at that level for the remainder of the 30-min exposure period. The amplitude and profile of the plasma PRL concentration after ether inhalation were similar to those obtained when a second suckling, rather than ether, was administered after the short term suckling. These data support the hypothesis that releasable PRL derives from depleted PRL and also indicate that, once it is formed, releasable PRL remains available for discharge into the circulation for a relatively long period of time.