The Uptake of Human Luteinizing Hormone (hLH) by Slices of Luteinized Rat Ovaries

Rats were made pseudopregnant with PMS and HCG. Slices of heavily luteinized ovaries were made and incubated with 5 ng/ml of 125I-hLH in a Krebs-Ringer bicarbonate buffer, containing glucose, at 37 C under an atmosphere of 95% O2-5% Co2. Uptake was expressed as a T/M ratio (cpm/gm tissue/cpm/ml medium). In a 2-hour incubation, the T/M ratio for 125I-hLH was 6.6 while the ratios for 125I, 125I-hFSH and 125I-hTSH were all less than 1.0. No 125I-hLH was concentrated by slices of rat muscle, renal cortex, liver or spleen. The 125I-hLH taken up by the ovarian slices was precipitable with either phosphotungstic acid or antibody to hLH. After induction of pseudopregnancy, a sharp increase of the uptake occurred at 2 days, reached a plateau at 5 days and remained there until at least day 10. The kinetic studies revealed that the uptake is a temperature-sensitive, reversible and saturable process, and that the uptake follows Michaelis-Menten type kinetics. The Vmax of the uptake is 6 × lO-14 moles/mg tissue and th...