Pituitary Extract and the CO 2 Combining Power of the Blood Plasma

It has long been known that the injection of pituitary extract results in a marked rise in the level of the blood sugar. For this and other reasons the posterior lobe of the pituitary gland has been credited with some obscure rôle in carbohydrate metabolism. Such a physiological action on the part of extracts of the gland would appear to suggest a related action on the CO₂ combining power of the blood plasma and possibly on other properties and constituents of the blood. This problem is now under investigation in our laboratories.

Three typical experiments are given in the accompanying table. From Experiment No. 4, it will be seen that the intravenous injection of commercial pituitary extract is followed immediately by a marked fall in the CO₂ combining power of the blood plasma. In this experiment the extremely low level of 21.5 volumes per cent was reached in 10 minutes. Sixty minutes following the injection, the CO₂ combining power had risen to 40.9 volumes per cent. In view of the great rapidity of this fall it does not seem likely that ketogenesis is a factor.

The distribution of this acidosis-producing hormone between “Pitocin”∗ and “Vasopressin” has been determined. Reference to the table, Experiment 13, shows that the power to produce a fall in CO, combining power and a rise in the blood sugar is present in the preparation “Pitocin” which contains less than 1% of the normal pressor activity. This action, although similar, is not so marked as that possessed by ‘Vasopressin”, a preparation which is nearly free from oxytocic activity. The hormone in pituitary extracts which produces this acidosis and rise in blood sugar is, therefore, in all probability, chemically separate from both the pressor and oxytocic hormones.