TY - JOUR T1 - A COMPARISON OF THE OFFICIAL AND THE CHICKEN METHODS FOR THE OXYTOCIC BIOASSAY OF POSTERIOR PITUITARY PREPARATIONS JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 342 LP - 349 VL - 75 IS - 3 AU - R. BLACKWELL SMITH, JR. Y1 - 1942/07/01 UR - http://jpet.aspetjournals.org/content/75/3/342.abstract N2 - 1. The finding of Coon that the chicken method yields higher oxytocic values than the official method for preparations which have high pressor-oxytocic ratios is confirmed. 2. This discrepancy is explained by the difference between the low magnesium concentration of the official Locke-Ringer solution and the higher magnesium concentration of chicken blood serum. When the magnesium titer of the Locke-Ringer solution used in the official uterine method is raised to 2.5 mgm.%, the approximate serum magnesium level of the chicken, the discrepancy disappears. 3. The conclusion of Fraser that "the degree of oxytocic activity observed in an assay depends on the magnesium concentration of the uterine bath, when the ratio between the oxytocic and pressor activities of the standard preparation is different from that of the unknown preparation" is confirmed and extended. 4. Raising the serum magnesium level of the chicken by the intravenous injection of magnesium chloride increases the sensitivity of the depressor response to preparations having high pressor-oxytocic ratios but not to preparations having a ratio of one or less. The effect wears off rapidly, disappearing entirely at approximately the same time that the serum magnesium level returns to normal. 5. The oxytocic activity which a preparation with a high pressor-oxytocic ratio will exert when used in man is probably indicated more accurately by the chicken method and the uterine method, using a Locke-Ringer solution with a magnesium concentration of 2.5 mgm. %, than by the official uterine method. 6. Neither the progressive decrease in sensitivity of the avian depressor response, which accompanies the injection of a series of small doses of posterior pituitary preparations, nor the abolition of the response after a massive dose of pitocin is due to a fall in the blood serum magnesium level. 7. The claims of Coon as to the many practical advantages of the chicken method are confirmed. The technique should receive consideration for recognition as an official method of assay. ER -