THE RATE OF DISAPPEARANCE OF EXOGENOUS PROGESTERONE FROM THE BLOOD*†

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Abstract
The intramuscular injection of 40 mg. of progesterone produced a maximum concentration in the blood of the rabbit in 1-2 hours with a complete disappearance from the blood by 12 hours. Following the intravenous injection of progesterone in a propylene glycol-albumen vehicle, 90% of the hormone was lost from the blood of a normal rabbit in 10 minutes. Seventy per cent of the hormone disappeare from the blood of a nephrectomized rabbit, 70% from the blood of a traumatized animal and 60% from the blood of a hepatectom-ized animal over a similar period of time, i.e., 10 minutes. Data were presented to show that neither plasma protein binding nor inactivation by enzymes in the blood could account for the extreme ly rapid loss. Since the hormone was found to appear in fat and to lesser extent in the muscle within 15 minutes, it was concluded that the initial and rapid loss of progesterone is due to a diffusion from the blood into the tissues.