Methotrexate levels in the interstitial space and seminiferous tubule of rat testis
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Abstract:
The ability of methotrexate (MTX) to pass from the blood into the interstitial space and seminiferous tubule of the rat was investigated using testicular micropuncture. MTX was administered to anesthetized adult Wister rats via a femoral vein cannula. Constant plasma levels of MTX were achieved by giving a priming dose followed by a constant infusion of 1, 10, or 100 mg/kg/hr with 6 to 27 rats studied at each dose. Blood (via a jugular vein cannula), testicular interstitial fluid, and seminiferous tubule fluid (via direct micropuncture) were periodically sampled during the 4 hr of drug infusion. Under steady-state conditions, when compared to corresponding plasma values, MTX levels were 2- to 4-fold lower in the testicular interstitial fluid and 18- to 50-fold lower in the seminiferous tubule. These results indicate that, in the rat, a significant blood-testis barrier to MTX exists at the tubular but probably not at the capillary-interstitial level. If these results can be extrapolated to humans, they do not provide a pharmacological explantation for the frequent occurrence of leukemic relapse in the interstitium of the testes in boys with acute lymphocytic leukemia.
Insights
Methotrexate (MTX) has limited penetration into rat testicular fluids, with significantly lower levels in seminiferous tubules than plasma. This suggests a blood-testis barrier hinders MTX efficacy in testicular tissues.
Area of Science:
- Pharmacology
- Reproductive Biology
- Toxicology
Background:
- Methotrexate (MTX) is a chemotherapy agent used to treat various cancers.
- Understanding drug distribution within the testes is crucial for treating testicular cancers and managing drug toxicity.
Purpose of the Study:
- To investigate the ability of methotrexate (MTX) to cross the blood-testis barrier in rats.
- To quantify MTX concentrations in testicular interstitial fluid and seminiferous tubule fluid.
Main Methods:
- Adult Wistar rats were administered MTX intravenously.
- Steady-state plasma MTX levels were maintained via infusion.
- Testicular interstitial fluid and seminiferous tubule fluid were collected using micropuncture techniques.
- MTX concentrations in plasma, interstitial fluid, and tubule fluid were measured.
Main Results:
- MTX levels in testicular interstitial fluid were 2- to 4-fold lower than plasma levels.
- MTX levels in seminiferous tubule fluid were significantly lower, 18- to 50-fold less than plasma levels.
- A substantial barrier to MTX was observed at the tubular level, but not the capillary-interstitial level.
Conclusions:
- A significant blood-testis barrier exists in rats, primarily at the seminiferous tubule level.
- The limited penetration of MTX into testicular tubules may not explain leukemic relapses in the testicular interstitium in boys with acute lymphocytic leukemia.
- Further research is needed to understand MTX distribution in human testes.