Effects of growth hormone replacement therapy on levels of cortisol and cortisol-binding globulin in hypopituitary adults.
OBJECTIVE
To determine if human growth hormone (hGH) replacement therapy alters pharmacokinetics of hydrocortisone (CS) substitution in hypopituitary adults.


METHODS
To this aim, we analysed serum and salivary CS profiles 270 min after oral CS administration at baseline and 6 and 12 months after initiation of hGH replacement therapy.


METHODS
Serum IGF-I, cortisol-binding globulin (CBG), thyroxine-binding globulin (TBG) and sex hormone-binding hormone (SHBG) were measured using commercially available radioimmunoassays. In-house immunofluorometric assays were employed for measurements of CS and hGH.


RESULTS
hGH replacement did not change total serum CS bioavailability (area under the serum cortisol profile curve). Interference of orally administered CS with salivary measurement of free CS (fCS) caused significant bias. Therefore, fCS levels were calculated from their total CS and cortisol-binding globulin (CBG) levels. CBG decreased by approximately 30% after both 6 and 12 months of hGH replacement therapy (n=20, P<0.01). A significant negative correlation between deltaCBG (CBG6months-CBGbaseline) and deltaIGF-I (IGF-I6months-IGF-Ibaseline) was observed (P=0.04). The calculated values of free CS tended to increase with physiological hGH replacement, but this effect was marginal and did not reach statistical significance. In contrast to the CBG concentrations, plasma levels of sex hormone-binding globulin and thyroxine-binding globulin were essentially stable.


CONCLUSIONS
Given that no clinically relevant alterations in pharmacokinetics of CS were evoked by initiation of hGH replacement in hypopituitary adults, we conclude that CS substitution does not require dose adjustment after initiation of hGH replacement.
Tschöp
M
M
Innenstadt University Hospital, Munich, Germany.
Lahner
H
H
Feldmeier
H
H
Grasberger
H
H
Morrison
K M
KM
Janssen
O E
OE
Attanasio
A F
AF
Strasburger
C J
CJ
D000328:Adult; D015415:Biomarkers / Q000097:blood; D002352:Carrier Proteins / Q000097:blood*; D005260:Female; D020249:Hormone Replacement Therapy; D019382:Human Growth Hormone / Q000627:therapeutic use*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007018:Hypopituitarism / Q000097:blood* / Q000188:drug therapy* / Q000209:etiology; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010911:Pituitary Neoplasms / Q000150:complications; D012738:Sex Hormone-Binding Globulin / Q000032:analysis / Q000378:metabolism; D013975:Thyroxine-Binding Proteins / Q000032:analysis / Q000378:metabolism
D015415:Biomarkers; D002352:Carrier Proteins; D012738:Sex Hormone-Binding Globulin; D013975:Thyroxine-Binding Proteins; C027091:cortisol binding globulin; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D006854:Hydrocortisone