Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/1997
Publication Date: N/A
Interpretive Summary: Neonatal pigs do not have a completely competent immune system until 5 wk of age. Therefore during early neonatal life, they are more susceptible to diseases. The pituitary-derived hormone prolactin (PRL) is known to affect immune system function in rodents and, in particular, restores depressed immune function in aging rodents. Hence, studies were conducted to determine if PRL would stimulate immune system development in young pigs. The results of our studies indicate, however, that in young pigs PRL-- directly or indirectly--is inhibitory to specific aspects of immune system function. Such information indicates, therefore, that administration of PRL to young pigs could be detrimental to their health.
Technical Abstract: Prolactin (PRL) has been shown to play an immunomodulatory role in adult animals. Little information is available concerning PRL's effects on immune function during the neonatal period. Therefore, 2 experiments were designed to evaluate the effects of hyper- and hypoprolactinemia and age on immunity in neonatal pigs. In Exp 1, 4-d-old neonatal pigs were treated with bromocriptine, an inhibitor of PRL release (3 mg/d, sustained release pellet) or vehicle (placebo pellet) for 1, 2 or 3 wk. Mitogen-induced lymphocyte proliferation was evaluated in splenic lymphocytes at 11, 18 and 25 d of age. In Exp 2, porcine PRL (1.5 mg/ d) or vehicle were administered to 6-d-old neonatal pigs for 2 wk, and lymphocyte proliferation, in vitro interleukin 2 (IL2), and plaque forming cell (PFC) assays were performed. Bromocriptine administration suppressed (P=.0001) plasma PRL concentrations to .35 +/- .04 ng/ml from 1.17 +/- .07 ng/ml in controls. For Exp 1, lymphocyte proliferation was expressed on a body weight basis to reduce response variation by adjusting pigs at a common age to a common stage of development. Following stimulation with concanavalin A (ConA) and pokeweed mitogen (PWM), proliferation of peripheral lymphocytes was enhanced (P=.09) in bromocriptine-treated pigs. In contrast, prolactin administration increased circulating plasma PRL concentrations (7.60 +/- 2.46 ng/ml) compared to controls (1.49 +/- .18 ng/ml) and decreased peripheral lymphocyte proliferation (P=.08) and suppressed the numbers of PFC/ug DNA (3.5 +/- 1.6) vs control pigs (8.7 +/- 3.3). Both in vitro IL2 production and proliferation in response to PWM were decreased (P=.0004 and P=.002, respectively) in older vs younger pigs. Results suggest PRL is able to limit specific aspects of immune system function in neonatal pigs.