Prolactin and thyrotropin responses to nursing during the early puerperium.

: This study investigated the possible role of thyrotropin-releasing hormone (TRH) as a physiologic prolactin-releasing factor by measuring prolactin (PRL) and thyrotropin (TSH) responses to nursing. Eight women had serum samples drawn at 15-minute intervals for 1 hour while nursing during three separate periods in the hour while nursing during three separate periods in the first month postpartum. The samples were frozen and assayed in a single batch for PRL and TSH. Mean PRL levels during suckling increased greater than 50% over baseline values in all three sampling sessions. In contrast, suckling had no effect on circulating TSH. Our data fail to support the previously reported observation of a release of TSH in response to nursing and provide further indirect evidence that TRH is not responsible for the brisk release of PRL with suckling.