| 1 | Suckling causes the release of oxytocin and prolactin in the mother. | |
| 2 | Beral thinks a more interesting candidate for study is prolactin. | |
| 3 | In tests, animals injected with prolactin became drowsy immediately. | |
| 4 | Hormone levels. Hormone imbalances, such as testosterone deficiency or too much of the hormone prolactin, can cause erectile dysfunction. | |
| 5 | Hormone imbalances, such as testosterone deficiency or too much of the hormone prolactin, can cause erectile dysfunction. |