Lactation And Intra-Mammary Pressure In Rats Bearing Estrogen, Progesterone Or Norethindrone Mammary Implants - Effects Of Oxytocin

A study was made of the effect on lactation of progesterone, oestrogen or norehindrone implanted directly into the mammary gland of lactating rats compared to that in control animals. The results showed that progesterone did not disturb the milk yield of the mothers, growth of the pups or the action of oxytocin upon intra-mammary pressure. On the contrary, confirming earlier results, oestrogen showed a definitive deleterious effect upon lactation probably through an alteration of the milk ejection mechanism, since oestrogen reduced the mammary pressure effect of oxytocin. Norethindrone, a weak oestrogenic progestational compound, also showed an inhibitory action on lactation. These results support the hypothesis that oestrogen and progesterone have different direct actions upon the mammary function during lactation.