Evaluation of cholesteryl ester transfer in the seminiferous tubule cells of immature rats in vivo and in vitro

Sertoli cells and germ cells are separated from the interstitial blood capi llaries by an extracellular matrix and the peritubular cells, which constit ute a barrier to the movement of plasma lipoproteins. The present study was undertaken to evaluate in vivo and in vitro the high density lipoprotein ( HDL) cholesteryl ester transfer from plasma to seminiferous tubule cells in the testis of 30-day-old rats. Firstly, the transfer of HDL cholesteryl ol eate from plasma to testicular compartments was evaluated and, secondly, th e role of apolipoproteins A-I and E in the uptake of cholesteryl ester by S ertoli cells was investigated. At 2 h after the administration of HDL recon stituted with [H-3]cholesteryl ester, dimyristoyl phosphatidylcholine and a polipoproteins, the tissue space in the interstitial cells (740 +/- 60 mu l g(-1) cell protein) was fourfold higher than that in the seminiferous tubu le cells (170 +/- 10 mu l g(-1)). Sertoli cells were isolated and incubated with [H-3]cholesteryl ester HDL reconstituted with apolipoprotein A-I or E to evaluate the mechanisms of cholesteryl ester influx. At the same apolip oprotein concentration (50 mu g apolipoprotein ml(-1) medium), the uptake o f [H-3]cholesteryl oleate from phospholipid-apolipoprotein E vesicles was t wo fold higher than that with phospholipid-apolipoprotein A-I vesicles. The presence of heparin reduced the uptake of cholesteryl ester from apolipopr otein E vesicles but not with apolipoprotein A-I vesicles, indicating that uptake of apolipoprotein A-I vesicles via a secretion of apolipoprotein E b y the cells themselves was not involved. These results demonstrate that pla sma lipoprotein cholesterol is able to cross the testis lamina propria and that Sertoli cells take up cholesteryl ester for seminiferous tubule cell m etabolism mainly via an apolipoprotein E pathway.