Prolactin and growth hormone clearance in neonatal boars

The pharmacokinetics of prolactin (PRL) and growth hormone (GH) are not known in neonatal pigs. In this study, six boars, ages 13 and 26 d, were used to determine metabolic clearance rate (MCR), half-life (t1/2), and volume of distribution (Vd) of immunoreactive porcine PRL (ipPRL) and immunoreactive porcine GH (ipGH). Blood samples were collected through indwelling jugular catheters at 0, 1, 2.5, 5, 10, 15, 30, 45, and 60 min after a 20 ng/g of BW (per hormone) cocktail of porcine PRL and GH. Analysis of the ipPRL disappearance curves indicated an apparent MCR of 13.79 +/- 2.45 and 23.79 +/- 4.10 mL/min for boars at 13 and 26 d of age, respectively (P = .0008). The t1/2 of ipPRL did not differ between ages (P = .9201). The apparent MCR of ipGH at 13 and 26 d were 10.60 +/- 2.09 and 27.30 +/- 4.55 mL/min, respectively, and this difference was still evident after adjustment for BW (P = .0465). The ipGH t1/2 decreased with age (P = .0232), 21.32 +/- 2.55 vs 13.57 +/- 3.35 min for 13 and 26 d, respectively. The apparent distribution volume for ipPRL was higher than that for ipGH at both ages (P = .0021). Within each age, the apparent MCR of ipGH and ipPRL did not differ significantly. These data represent the first clearance measures reported for ipPRL and ipGH in neonatal pigs and indicate that under the conditions of this study the apparent MCR of ipPRL and ipGH are similar but change significantly during early development.