Route of Administration as a Factor Influencing the Biological Activity of Certain Androgens and Their Corresponding 3-Cyclopentyl Enol Ethers

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Abstract
The biological activity of testosterone (TE), methyltestosterone (MT), their corresponding 3-cyclopentyl enol ethers (TECPE, MTCPE) and testosterone propionate (TP) following subcutaneous, intraperitoneal or oral administration has been studied in castrated male rats. The greater activity of TE, TP and MT following subcutaneous as compared with intraperitoneal or oral administration is attributed to a slower release from the site of injection and direct absorption into the general circulation, thus avoiding liver inactivation. When given by single subcutaneous injection at relatively high dose, steroid enol ethers display a more prolonged and intense activity than the parent ketones. The relative lack of activity of MTCPE and TECPE when given in small doses, either by daily or single subcutaneous injections, as compared with the intraperitoneal or oral routes is attributed to their insufficient release from the subcutaneous site of injection rather than to the failure of their transformation to a biologically active form. The greater effectiveness exhibited by TP and TECPE following intraperitoneal as compared with oral administration is attributed to metabolic transformations these compounds undergo in the gut rather than to a direct local activity on the target organs.