Investigating local regulation of the testes of ruminants.

In addition to endocrine regulation by the gonadotrophic hormones, the functions of the testes are regulated locally by paracrine and autocrine factors. Some attempts have been made to isolate cells from the testes of immature bulls and rams for investigation of cell function in vitro. However, most studies have used in vitro cultures of cells isolated from the testes of rats and a large variety of factors have been identified as potential local regulators. This review examines the importance of Sertoli cell-germ cell interactions, Leydig cells and steroidogenesis, blood flow and vascular permeability, and cytokines and immune cells as local regulators of the testes. The small amount of work undertaken on the testes of ruminants is reviewed together with approaches such as the transilluminated dissection of staged seminiferous tubules and in vivo cell depletion models used with rats. The suitability and limitation of these approaches for ruminants are considered, and immunological and molecular probes are raised as options for future investigations of the local regulation of the testes of ruminants.