M olecular and Cellular Endocrinology, 31 (1984) 159-168 Elsevier Scientific Publishers Ireland. Ltd. 159 MCE 01194 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Intratesticular secretion of a factor(s) with major stimulatory effects on Leydig cell testosterone secretion in vitro Richard M. Sharpe and Irene Cooper MRC Reproductive Biology Unit, Centre for Reproductive Biology, 37 Chalmers Street, Edinburgh EH3 9E W, Scotland (U.K.) (Received 23 February 1984; accepted 21 May 1984) Keywords: Leydig cell; testicular interstitial fluid; testosterone secretion; Sertoli cell; intratesticular regulatory factors. zyxwvutsrqponmlkjih Summary As intratesticular communication between the Sertoli and Leydig cells must take place via testicular interstitial fluid (IF), we have tested whether this fluid contains a factor(s) which has effect on testosterone secretion by Percoll-purified Leydig cells in vitro. Addition of increasing concentrations of charcoal-stripped IF to Leydig cells caused dose-dependent stimulation of basal testosterone secretion and greatly enhanced the response to a maximally stimulating dose of hCG. These effects were first evident after 2 h of incubation and were progressive up to 24 h. Charcoal-stripped serum from the same donor animals also had some stimulatory effect on basal and, occasionally, on hCG-stimulated testosterone secretion, but the magnitude and pattern of this effect and its limited dose-dependence were very different from the effects seen with IF. The effects of IF and serum were not altered by the addition of an antiserum to LH. It is therefore concluded that testicular IF contains a factor(s), not derived from serum, which can alter Leydig cell testosterone responsiveness. This factor(s) was heat-sensitive with a MW of > 10000 daltons. IF from the abdominal testes of adult rats which had been made unilaterally cryptorchid contained much higher levels of the stimulatory factor(s) compared to the contralateral scrotal testes, and this is of interest because of the well-documented alteration in Sertoli-Leydig cell interaction that occurs in this situation. These results provide the first direct evidence that one or more factors capable of altering testosterone secretion are produced within the testis of the normal adult rat, and raises the possibility that this factor(s) may be involved in the local regulation of the intratesticular testosterone levels. There is growing evidence that local factors play an important role in the day-to-day regula- tion of testicular function (for review see Sharpe, 1983) and there are compelling reasons for believ- ing that communication between the Sertoli and Leydig cells comprises an important aspect of this paracrine control (Sharpe, 1983, 1984). Although many factors, mostly small peptides, have been identified as possible locally acting agents in the testis (Sharpe, 1984), there is as yet relatively little direct evidence to implicate these compounds in the physiological interaction of the Sertoli and Leydig cells. Any such communication has to take place via the interstitial fluid (IF) which permeates the interstitial spaces of the testis and which sep- arates the seminiferous tubules from the Leydig cells (Fawcett et al., 1973; Clark, 1976). As IF can be collected with relative ease from the rat testis (Sharpe, 1981; Sharpe and Cooper, 1983), we have investigated whether such fluid contains a factor 0303-7207/84/$03.00 Q 1984 Elsevier Scientific Publishers Ireland, Ltd.