Biosynthesis of gonadotrophins by rat pituitaries in vitro

A method has been developed for studying biosynthesis of FSH in the rat pituitary in vitro. Anterior pituitary glands were incubated with [3H]leucine; a specific and sensitive immunoprecipitation technique was used to isolate FSH from the pituitary homogenate. Total FSH content of the samples was measured by a double-antibody radioimmunoassay technique. Using this technique, a comparative study of LH and FSH synthesis in the same pituitary of adult male rats incubated for various intervals (0-5-6 h) was done. Increased incorporation of [3H]leucine into both LH and FSH with time was noted. The rate and amount of [3H]leucine incorporation into FSH was found to be higher than that into LH, indicating that either the rate of FSH synthesis is higher than that of LH or FSH has more leucine residues than LH. Greater susceptibility of LH to degradation by endogenous proteases during dialysis may also reflect less incorporation of [3H]leucine into LH. This method provides a reliable tool for evaluating FSH synthesis under various experimental conditions.