Mt. Dattani et al., AN INVESTIGATION INTO THE LABILITY OF THE BIOACTIVITY OF HUMAN GROWTH-HORMONE USING THE ESTA BIOASSAY, Hormone research, 46(2), 1996, pp. 64-73
We compared the bioactivity attributable to human growth hormone (hGH)
in serum samples, determined at the time of their collection, with th
at after storage for 2-18 months at -20 degrees C. The samples were ob
tained from volunteers and patients who underwent provocative tests of
hGH secretion, and the bioactivity was determined in the ESTA bioassa
y, which is based upon the use of Nb2 cells. We report that, in some s
ubjects, the bioactivity of samples collected at the response peaks de
teriorated on storage for as little as 2 months. The decrease in hGH b
ioactivity was systematic in that it consistently declined so as to ap
proach the values initially determined by an immunoassay (Hybritech IR
MA). This differential lability was a characteristic of the peak sampl
es, and was not observed for either samples collected before and after
the peaks of hGH secretion or for purified preparations of hGH which
were subjected to a range of freeze/thaw and storage regimens. We sugg
est that this unusual lability is indicative of transient shifts in th
e spectrum of the variants of hGH which are present in the circulation
following stimulation by provocative agents. This study emphasises th
e need to minimise the risk of introducing storage artefacts in invest
igations into the responses of hGH to provocation.