Dynamics of venous-arterial testosterone transfer in the pampiniform plexus of the rat.
The dynamics of venous-arterial testosterone transfer in the pampiniform plexus of the rat have been studied using [3-H] testosterone in controlled perfusion in the pampiniform plexus isolated from its testicle in vivo. The rate of transfer of testosterone increased in direct proportion to the testosterone concentration in spermatic vein blood over the range 0-100 ng/ml. When the venous-arterial concentration gradient was reversed by infusing [14-C] testosterone into the spermatic artery proximal to the pampiniform plexus, the label was transferred from the artery to the adjacent spermatic vein. Transfer of [3-H] methoxy-inulin infused concomitantly with the [14-C] testosterone was relatively insignificant in either direction. The testosterone transfer rate generally increased with increasing blood flow over the range 0.01-0.36 ml/min. However, transfer rate became less dependent on blood flow at the high end of the range. A comparison of transfer rates from whole blood and dextran (6% in saline) each containing 24-27 ng [1,2-3-H] testosterone/ml and flowing at 0.36 ml/min for one hour resulted in a maximum of 6.1% transfer from blood and 46% transfer from dextran. Transfer from blood reached plateau levels in less than 10 min, whereas transfers from dextran peaked between 30 and 40 min. At lower rates testosterone transfer from dextran reached equilibration levels, whereas transfer from blood rarely exceeded 5% of spermatic venous levels. We concluded that venous-arterial steroid transfer in the pampiniform plexus behaves like a passive countercurrent diffusion system that is concentration limited, depending principally on the concentration gradient of diffusible steroid between the closely juxtaposed spermatic vein and artery.
D000818:Animals; D001158:Arteries / Q000378:metabolism; D001692:Biological Transport; D001783:Blood Flow Velocity; D002250:Carbon Radioisotopes; D004058:Diffusion; D005263:Femoral Artery / Q000378:metabolism; D007444:Inulin / Q000031:analogs & derivatives / Q000097:blood; D008297:Male; D010477:Perfusion; D051381:Rats; D013085:Spermatic Cord / Q000098:blood supply; D013739:Testosterone / Q000097:blood*; D014316:Tritium; D014680:Veins / Q000378:metabolism
D002250:Carbon Radioisotopes; D014316:Tritium; D013739:Testosterone; D007444:Inulin