Large amounts of proopiomelanocortin (POMC) peptides may be secreted in response to exercise training programs and various physical and psychological stressors. These peptides are also frequently released from hyperplastic pituitary tissues, pituitary adenomas and as part of the endogenous response to various infectious diseases. Work largely performed in other species indicates that the POMC peptides may have dramatic effects on immunological function and related resistance to disease. The present study tested the effects of selected POMC peptide fragments on equine immune cells in order to gain a better understanding of related neuroimmunological interactions in the equine species. Peripheral blood mononuclear cells (PBMCs) and peripheral Tcells were collected from mature Thoroughbreds (n=6). Unconditioned animals were stalled and samples collected between 7 and 9 AM. 5 Quadruplicate wells of 2 X 10 cells were cultured with suboptimal phytohemagglutinin (PHA) in the presence or absence of 10-5, 10-7, 10-9 and 10-11 M hormone concentrations. Hormone treatments included synthetic adrenocorticotropic hormone (ACTHI.39; A39/ ACTH), camel-β-endorphin (β-E), α-melanocyte-stimulating hormone (αMSH), ACTH1-24 (A1), ACTH4.10 (A4) and ACTHl18-39(A18). Hormone or vehicle and mitogen were added at the beginning of culture and the proliferative response was measured on day 3. Results were analyzed by ANOVA and means compared with LSD analysis. The proliferative response of PBMCs from geldings was reduced (P<.05) by 10-5 A39/ACTH and A18 treatments. The 10.9 M A39/ACTH treatment stimulated (P<.01) proliferation of gelding PBMCs whereas proliferation was not altered by A4 or A1 fragments. The proliferative response of mare PBMCs was reduced (P<.01) by 10-5 to 10.9 M dosages of all truncated ACTH fragments and the 10-5 M A39/ACTH treatment. T cell proliferation was stimulated (P<.05) by all doses of ctMSH and A4 as well as the 10-7 M to 10-9 M A1 and the 10-5 M β-E treatment. T cell proliferation was inhibited by (PP<.05) by 10-5 and there was no effect of the remaining treatments. Results from this experiment indicate that POMC peptides and various ACTH fragments may function to regulate proliferation of equine immune cells. The response of PBMCs may be mediated by distinct receptors since A18 extends outside of the core tetradecapeptide sequence normal- ly associated with ACTH effects. Further, the response of equine immune cells to truncated ACTH fragments suggests that peptides released in response to infection may act to coordinate the immunological response. Further work is needed to characterize the physiological significance of these effects.
|Number of pages||6|
|Journal||Journal of Equine Veterinary Science|
|State||Published - 1993|
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