Porcine growth hormone and prolactin secretion: the first month of postnatal life.

Plasma concentrations of growth hormone (GH) and prolactin (PRL) in male pigs during the first 28 days after birth were quantitated. Growth hormone declined precipitously during the first 3 days and thereafter fluctuated about a mean of approximately 7 ng/ml. Prolactin declined from over 5 to 3-4 ng/ml during the first week. A significant increase in plasma concentrations of GH was observed in nonsuckled pigs during the 12 h after birth. This increase did not occur in pigs allowed to nurse. Blood samples were collected via jugular cannulae at 5-20 min intervals for 4-5 h at 3, 9 and 18 days of age. Overall mean concentration of GH significantly declined with age. Overall and baseline mean concentrations of prolactin also significantly declined with age. These data indicate that significant changes occur in the secretion of GH and PRL in pigs during the first month of postnatal life.