Size homogeneity of plasma prolactin in the female rat following various natural, pharmacological and stressful stimuli

Gel filtration on Sephadex G-150 was performed on freshly drawn plasma from ovariectomized, estrogen-treated rats following 10 minutes of ether inhalation, intraperitoneal administration of TRH (1 μg/rat) or pimozide (500 μg/kg body weight) and at the peak of the estrogen-induced afternoon surge of prolactin (1700 h). Plasma from intact lactating rats 30 minutes after suckling was also subjected to gel filtration. For comparison, homogenates of fresh and frozen pituitaries from ovariectomized, estrogen-treated rats were chromatographed. Prolactin activity was determined by RIA in each fraction eluted between the void and total volumes of the column. Immunoreactive prolactin in plasma following all experimental procedures eluted as a single component with a K_av of approximately 0.6. Chromatography of the fresh pituitary homogenate showed prolactin immunoactivity at the void volume and at a K_av of 0.4 and 0.6. A homogenate of frozen pituitary contained a component with a K_av of 0.3 in addition to those seen in fresh pituitary. These studies demonstrate that although the rat pituitary contains multiple molecular forms of immuno-reactive prolactin, only one small component is found in plasma.