Production and secretion of an interleukin-1-like factor is stage-dependent and correlates with spermatogonial DNA synthesis in the rat seminiferous epithelium.

It has been shown previously that the intact adult rat testis produces large amounts of an interleukin-1 (IL-1)-like growth factor. The present study has investigated whether this testicular IL-1-like factor (tIL-1) is produced and secreted differentially by the fourteen stages of the seminiferous epithelial cycle in the rat testis. Seminiferous tubule segments representing defined stages were identified by transillumination-assisted microscopy and isolated by microdissection. Pooled segments were either homogenized and extracted with aqueous buffer or incubated for 24 h to produce conditioned media (CM). The recovered material was then analysed for IL-1 bioactivity in a sensitive murine thymocyte proliferation assay. When divided into four stage groups, extracts of stages II-VI, IX-XII and XIII-I showed equally high IL-1 activity whereas stage group VII-VIII showed much lower activity. More detailed analysis with 10 different stage groups showed that tIL-1 activity was undetectable in extracts of substages VIIab and VIIcd. The same pattern was seen when CM from cultured tubular segments were analysed. Labelling of seminiferous tubules with tritiated thymidine in vitro and analysis by autoradiography revealed that DNA-synthesizing spermatogonia were absent in substages VIIb and VIIc and sparse in substages VIIa and VIId. The results show that tIL-1 activity is produced in a stage-dependent manner and suggest that tIL-1 might be involved in the regulation of spermatogonial proliferation in vivo.