Serum Concentrations of Progestins, Estrogens, Testosterone and Gonadotropins in Pseudopregnant Rats with Special Reference to the Effect of Prostaglandin F2α

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Abstract
Steroids and gonadotropins from the same blood samples throughout pseudopregnancy (PSP) in the rat were determined by radioimmunoassay. During the first 3 days of PSP, high levels of 20.alpha.-dihydroprogesterone (20.alpha.-DHP) were recorded and thereafter high concentrations of progesterone (.DELTA.4P) marked the luteal phase. Termination of PSP was characterized by high levels of 20.alpha.-DHP and low .DELTA.4P. The ratios between .DELTA.4P/20.alpha.-DHP rose from 0.2 on the first day of PSP to more than 1.5 between days 5-9 and declined thereafter. Estrogens maintained a basal level, but rose on day 3 of PSP. Testosterone (T) showed a slow, but steady rise during PSP and higher levels were recorded a day before the reappearance of proestrous smear. Both LH [lutropin] and SH [follitropin] were at basal levels except for significant rises towards the end of PSP. A s.c. implantation of a Silastic-PVP tube containing 600 .mu.g of PG2.alpha. resulted in a significant drop of .delta.4P and a rise of both 20.alpha.-DHP and T within 24-48 h and terminated PSP within 72 h of treatment.