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Preliminary investigations on the action of pepsin on human pituitary growth hormone.

A slight modification of the original procedure for the isolation of human pituitary growth hormone has been described. The purity of the preparation was further examined by chromatography on carboxymethylcellulose, zone electrophoresis on starch, and electrodialysis. The hormone was found to be stable in a pH 7.0 solution at 100 degrees C and in 10 M urea at 25 degrees C. Digestion with pepsin to an extent of 40 per cent did not diminish the biological activities of the hormone. Bioassays of an active core derived from such digests exhibited essentially the same specific growth-stimulating activity in the hypophysectomized rat and crop sac stimulation in the pigeon. It was concluded that the integrity of the protein is not required for the activity of human growth hormone.

Animals↗

Pharmacological actions of pepsitensin.

In confirmation of the results of Croxatto and his co-workers, plasma proteins incubated with pepsin yielded a substance (pepsitensin) with pressor activity. Euglobulin gave a much higher yield than the other plasma protein fractions. Incubation for 4 hr at pH 4 gave high yields of pressor activity (pepsitensin) but no antidiuretic activity; incubation of euglobulin for 4 hr at pH 2.5 yielded extracts with antidiuretic as well as pressor activity. Incubation for 8 to 11 hr at pH 2.5 produced the highest yield of both activities. Further incubation, at the same pH, up to 20 hr caused a rapid decline in the pressor activity of the extracts, but the antidiuretic activity was much more resistant to destruction by pepsin. Pepsitensin was found to be very soluble in water and poorly soluble in organic solvents. It is not inactivated by thioglycollate. In blood pressure assays some animals did not respond to pepsitensin, and nephrectomized (17 to 24 hr) rats were found to be more suitable preparations. Pepsitensin was shown to exert pressor effect by direct action on the blood vessels. Its pressor action could be differentiated from that of tyramine, dimethylphenylpiperazine, nicotine, noradrenaline and Pitressin but not from that of angiotensin. The isolated guinea-pig ileum and the rat uterus were equally sensitive to angiotensin and pepsitensin. In paper chromatograms, in the solvent system butanol-acetic acid-water, the R(F) of pepsitensin was very similar to that of angiotensin.

Angiotensin Amide↗