Growth hormone synthesis by individual rat anterior hemipituitaries in vitro was studied by determining the incorporation of 3H-leucine. A specific and sensitive immunoprecipitation technique was used for the isolation of growth hormone from pituitary extracts and from media. Growth hormone content of the samples was determined by radioimmunoassay, permitting the calculation of growth hormone specific activity. Tritiated growth hormone was first detected at 30 min in pituitary tissue and synthesis was found to be linear over a 6-hr period. No labeled growth hormone appeared in the media until after 3 hr. By 6 hr less than 5% of the newly synthesized growth hormone was secreted into the media. The rate of growth hormone synthesis by adult male pituitaries was 2-3 times greater than that of adult female pituitaries despite equal growth hormone content or concentration. Male and female weanling pituitaries demonstrated little difference in growth hormone synthesis rates. Progressive increases in growth hormone synthesis were seen with advancing age in pituitaries of male rats. Only slight increases were noted between weanling and adult female rats. This method provides a reliable evaluation of growth hormone synthesis in vitro using small amounts of tissue and permitting handling of large numbers of samples.
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