A technique is described for perfusing the two legs of a frog simultaneously with different solutions containing the pituitary hormone and for determining the concentration of the hormone by comparison of the pigmentary reactions in the skin.
Control experiments show that differences in concentration of 30 per cent are practically always easily observed and that solutions of unknown strength can be determined with an average accuracy of about 15 per cent.
Three preparations of dry posterior lobe showing oxytocic activities of 100, 83, and 20, respectively have been examined, and the pigmentary effector activities determined as 100, 80, and 20, respectively.
The pigmentary effector activity deteriorates in solution at pH 4.5 to 2.5 both at room-temperature and at 0°C, while the oxytocic activity is retained. It is suggested that the different activities are due to separate atomic groups in the same hormone molecule.
The pituitary hormone is present in the circulating blood of the horse. The pigmentary effector activity of horse serum corresponds generally to about 100 x 10–6 international units per cubic centimeter. Direct comparisons show it to be about 50 per cent higher in the blood from the jugular vein than in the blood from the saphenous vein. A low concentration has been observed in the spinal fluid. The concentration in human blood is considerably lower than in the blood of the horse. It is suggested that the normal function of the pituitary hormone in circulation is to maintain capillary tonus.