THE PENETRATION OF IODINE-LABELLED FOLLICLE-STIMULATING HORMONE AND ALBUMIN INTO THE SEMINIFEROUS TUBULES OF SHEEP AND RATS

SUMMARY The entry of 125I-labelled ovine follicle-stimulating hormone (FSH) and human serum albumin into the seminiferous tubules of rams has been studied by measuring radioactivity in blood plasma and rete testis fluid after an intravenous injection of the labelled protein. After the injection of FSH, radioactivity/mg total protein in rete testis fluid exceeded that in blood plasma from the first day onwards, but after the injection of human serum albumin, radioactivity/mg total protein in rete testis fluid only reached that in plasma after 4–5 days and never exceeded it. Protein-bound radioactivity disappeared from the blood more quickly after an injection of FSH than after an injection of albumin. The volume of distribution for ovine FSH in the testes of rats was greater than that for human serum albumin. The volume of distribution for FSH was greater, in absolute terms, in the testes with the efferent ducts ligated 24 h previously than in the contralateral control testes when the FSH was injected at the time of efferent duct ligation. The volume of distribution for albumin was slightly less in the ligated testes than in the control testes. This suggests that FSH but not albumin had penetrated into the fluid trapped inside the testis. The liver and kidney had much higher concentrations of protein-bound radioactivity per unit weight than did the testis after the injection of FSH, so it does not seem that FSH is selectively taken up by the testis.