Yes a possible method of increasing oral availability might be through the inhibition of the CYP3A4 enzyme. Grapefruit is known to inhibit this enzyme. Note that all of the 17-alkylated anabolic steroids are virtually untouched by the CYP3A4 enzyme so grapefruit will have no effect on them. However absorption might be improved by grapefruit in unalkylated orals such as primobolan, testosterone undecanoate and many unalkylated prohormones such as Orastan.
Originally Posted by neverstop
There is a possibility that even a glass of grapefruit juice (GFJ) taken several hours before oral medication may enhance the bioavailability of many drugs, exaggerate the drug action, and increase the toxic effect by exaggerating the potency of the drug. This can be explained by inhibition of CYP3A4 in the small intestine by GFJ, thus suppressing drug metabolism. This interaction with GFJ is likely to occur mainly with those drugs that are metabolized by CYP3A4 and are associated with low bioavailability when given via an oral route. - INTERACTION BETWEEN GRAPEFRUIT JUICE AND DRUGS, Junichi AZUMA, Asian Med. J. 44(3): 136–141, 2001