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DISAPPEARANCE AND UPTAKE OF [¹²⁵I]FSH IN THE RAT, RABBIT, EWE AND COW

Summary.: Follicle-stimulating hormone (NIH-FSH-S8) was labelled with ¹²⁵I to determine its disappearance rate after a single intravenous injection and to determine the level of circulating [¹²⁵I]FSH in the blood after a single intramuscular or subcutaneous injection in the rat, rabbit, ewe and cow. There was a difference in the disappearance and uptake rates among the four species, but the shape of the curve for rate of loss and uptake of labelled FSH was similar in all species. The disappearance of radioactivity occurred at two rates; the first from 1 to 8 min and the second from 16 to 96 min. The half-life, calculated from the total decay curve in each species was 94±21, 118±16, 334±41 and 301±23 min for the rats, rabbits, ewes and cows, respectively. Intramuscular injections resulted in an average of 56% higher [¹²⁵I]FSH blood levels than subcutaneous injections for all species.