Hydrogenated soybean oil (HSO) as a vehicle for the chronic and controlled administration of testosterone in the orchidectomized rat.
The use of a novel vehicle, hydrogenated soybean oil (HSO) for the chronic and controlled release of testosterone (T) in the orchidectomized rat is described. At 60 degrees C, HSO is a liquid in which T is readily soluble. When cooled at approximately 43 degrees C, HSO can be injected into experimental animals without the need of special equipment. At body temperature, the oil forms a solid depot from which T is released over prolonged periods of time. Our studies indicate that a single injection of 5 mg T in HSO in the orchidectomized rat, maintains sex accessory gland weights (AGW) above castrate levels, decreases serum concentrations of LH and maintains serum concentrations of T within the intact range for 10 days after injection. In contrast, these parameters of functional androgenicity are maintained for only three days when T is administered at the same dosage in a conventional oil vehicle. A dose of 15 mg T in HSO maintained serum T concentrations and AGW within intact range for 55 days after injection, but was unable to maintain LH suppression in these castrated animals beyond 14 days after injection.