The Quantitative Effect of Oxytocin (Pitocin) on Human Milk Yield NILES NEWTON Department of Psychiatry and Behavioral Sciences Northwestern University Medical School Chicago, Illinois 6061I
Using cows, Ely and Petersen demonstrated that the oxytocic factor was operative in the milk-ejection reflex (let-down reflex). Oxytocin (Pitocin) increased the availability of milk. The reflex was inhibited by disturbance and adrenaline.' Our experiments were designed to test some of these findings for their generalizability to humans,2 since the relation of oxytocin to milk ejection in humans had not been demonstrated at the time.* We used a posterior pituitary preparation containing 10 units of oxytocic substance per milliliter (Pitocin, Parke-Davis).
EXPERIMENT 1 The left breast of a breast-feeding woman at home was pumped for 10 minutes. Then 0.3 cc sterile saline (controls) or 0.3 cc Pitocin was injected intramuscularly. The first ten minutes yielded a mean of 10 cc of milk in both conditions. After injection of Pitocin, the next five minutes of pumping increased the milk yield to 24 cc. After saline injection milk yield decreased to 3 cc. Three experiments were done using Pitocin and three done using saline injection. The woman being tested was not informed of the nature of the solution. The amount of milk obtained before injection was very constant (11, 9, 9 cc pre-Pitocin and 8, 10, 11 cc pre-saline). The yield after Pitocin was eight times that of the saline control in the post-injection pumping (FIG. 1). The same electric breast pump, suction pressure, and times were used throughout the trials.
EXPERIMENT 2 A lactating woman nursed her infant for 10 minutes under three conditions, which were (1) no distraction, (2) distraction during nursing after saline injection, and (3) distraction during nursing after Pitocin injection. The no distraction and distraction plus Pitocin conditions produced yields that were similar. Both the mean amount of milk taken on the no disturbance days (163 cc) and on the disturbance days plus Pitocin (153 cc) were significantly higher than the mean amount of milk taken during the 481
ANNALS NEW YORK ACADEMY OF SCIENCES
482
injection
25
10
1occ
2
4
~
~
1occ
3cc 0
Before lniections 10 min. pumping
After Pitocin After saline injection injection 5 more min. pumping
FIGURE 1. Mean milk yield before and after Pitocin (oxytocin) and saline injection.
163
153
.05
< .05
No distraction No injection
Distraction with saline injection
Distraction with Pitocin (oxytocin) injection
FIGURE 2. Effect of disturbance on grams of milk obtained by infant.
disturbance plus saline (99 cc) (
Using cows, Ely and Petersen demonstrated that the oxytocic factor was operative in the milk-ejection reflex (let-down reflex). Oxytocin (Pitocin) increased the availability of milk. The reflex was inhibited by disturbance and adrenaline.' Our experiments were designed to test some of these findings for their generalizability to humans,2 since the relation of oxytocin to milk ejection in humans had not been demonstrated at the time.* We used a posterior pituitary preparation containing 10 units of oxytocic substance per milliliter (Pitocin, Parke-Davis).
EXPERIMENT 1 The left breast of a breast-feeding woman at home was pumped for 10 minutes. Then 0.3 cc sterile saline (controls) or 0.3 cc Pitocin was injected intramuscularly. The first ten minutes yielded a mean of 10 cc of milk in both conditions. After injection of Pitocin, the next five minutes of pumping increased the milk yield to 24 cc. After saline injection milk yield decreased to 3 cc. Three experiments were done using Pitocin and three done using saline injection. The woman being tested was not informed of the nature of the solution. The amount of milk obtained before injection was very constant (11, 9, 9 cc pre-Pitocin and 8, 10, 11 cc pre-saline). The yield after Pitocin was eight times that of the saline control in the post-injection pumping (FIG. 1). The same electric breast pump, suction pressure, and times were used throughout the trials.
EXPERIMENT 2 A lactating woman nursed her infant for 10 minutes under three conditions, which were (1) no distraction, (2) distraction during nursing after saline injection, and (3) distraction during nursing after Pitocin injection. The no distraction and distraction plus Pitocin conditions produced yields that were similar. Both the mean amount of milk taken on the no disturbance days (163 cc) and on the disturbance days plus Pitocin (153 cc) were significantly higher than the mean amount of milk taken during the 481
ANNALS NEW YORK ACADEMY OF SCIENCES
482
injection
25
10
1occ
2
4
~
~
1occ
3cc 0
Before lniections 10 min. pumping
After Pitocin After saline injection injection 5 more min. pumping
FIGURE 1. Mean milk yield before and after Pitocin (oxytocin) and saline injection.
163
153
.05
< .05
No distraction No injection
Distraction with saline injection
Distraction with Pitocin (oxytocin) injection
FIGURE 2. Effect of disturbance on grams of milk obtained by infant.
disturbance plus saline (99 cc) (
