Changes in the metabolic clearance rate and plasma production rate of testosterone in the pregnant guinea-pig.

The metabolic clearance rate of testosterone (MCRT) in the pregnant and non-pregnant guinea-pig was established by a constant infusion method to steady state levels of 3H testosterone (T). Simultaneously, the concentration of endogenous T was determined by radioimmunoassay and the production rate of T (PRT) was calculated from the product of MCRT and endogenous T concentration. Results indicate important alterations in the three parameters between non-pregnant (MCRT = 64.0 +/- 2.6 1/24 hr; T concentration = 51 +/- 8 pg/ml; PRT = 3.24 +/- 0.13 micrograms/24 h) and the pregnant guinea-pig. In these animals mean values from day 43 were about 33 1/24 h for MCRT, 378 pg/ml for T concentrations and 12.5 micrograms/24 h for PRT. The significance of these results is discussed in relation to the specific binding of testosterone with the progesterone binding globulin during pregnancy in this species.