Is alanine the active component in anterior pituitary extracts proposed to contain a thymotropic factor?

Abstract

SAXENA AND TALWAR have reported the occurrence of a factor in extracts of the anterior pituitary which stimulates thymidine incorporation into thymocytes in vitro¹. The possible existence of a previously unknown thymotropic pituitary factor was discussed. The test system used by Saxena and Talwar consisted of isolated rat thymocytes cultured in a defined glucose salt medium without serum or other additives. Anterior pituitary extract (APE) was added and the uptake of ³H-thymidine into acid-insoluble material during short-term incubation was greatly stimulated. It was briefly mentioned that stimulation was also obtained when thymocytes were cultured in RPMI or Parker 199 medium. No effect was observed on tissue slices from liver, heart, kidney and diaphragm. The factor was said to have a molecular weight of 500 and an isoelectric point of 7.9, but the methods of determining these properties were not described. We report here on the isolation of an active component in the APE and its identification as the amino acid alanine. APE was tested for the ability to stimulate thymidine incorporation and mitotic activity in guinea pig thymocytes in our in vitro systems (test systems are described in the legends to Table 1 and Fig. 1). The incorporation of thymidine and the mitotic activity were both stimulated in our experiments (Fig. 1a). The stimulatory effect on thymidine incorporation was dose dependent and varied between 129 and 156% in different experiments.