Regulation of DNA synthesis in Leydig cells obtained from neonatal pig testes

Three distinct waves of Leydig cell development are found in the pig testes , which occur during fetal, perinatal, and prepubertal periods. Proliferati on of Leydig cells is primarily regulated by luteinizing hormone (LH); howe ver, effects of LH on proliferation of immature rat Leydig cells are mediat ed by specific growth factors and cytokines such as transforming growth fac tor-alpha (TGF alpha), insulin-like growth factor-1 (IGF-1), interleukin-1 beta (IL-1 beta), steroidogenesis-inducing protein (SIP), and TGF beta. The objective of the present study was to identify growth factors that could p ossibly be involved in the proliferation of Leydig cells in the neonatal pi g testis. Leydig cells were isolated from 3- to 5-d-old pig testes, culture d for 48 hr in serum-free media, washed, and treated with hCG and/or IGF-1, epidermal growth factor (EGF), IL-1 beta, SIP, and TGF beta for 18 hr. Tri tiated thymidine incorporation into DNA was assessed over a subsequent 4-hr period. Incorporation of [H-3]-thymidine was stimulated by hCG treatment w ith a 2.3-fold increase over control cultures. SIP also induced a significa nt increase (P < 0.0001) in the incorporation of [H-3]thymidine into Leydig cell DNA. Similarly, EGF and IGF-1 also increased DNA synthesis in neonata l porcine Leydig cells, whereas IL-1 beta had no effect. TGF beta had very little, if any, effect on DNA synthesis when added alone, but inhibited the stimulatory effects of other mitogens (SIP, hCG, EGF/TGF alpha, and IGF-1) . Our results indicate that these growth factors may play a role in the LH/ hCG-dependent proliferation of Leydig cells during the perinatal period of development. (C) 1999 Elsevier Science Inc. All rights reserved.