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Clin Endocrinol (Oxf). 1996 Sep;45(3):333-9.

Bioavailability and bioactivity of intravenous vs subcutaneous infusion of growth hormone in GH-deficient patients.

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Medical Department M (Diabetes and Endocrinology), Aarhus University Hospital, Denmark.



The bioavailability of GH immunoreactive serum concentrations is reduced following subcutaneous (s.c.) as compared with intravenous (i.v.) administration. Whether this difference also translates into a different biological activity remains to be investigated. The aim of the present study was to evaluate the short-term metabolic effects of GH following i.v. and s.c. delivery.


In a cross-over design 10 GH-deficient patients were randomized to receive GH (0.03 microgram (0.1 mU/kg/min) as a continuous i.v. or s.c. infusion for 39 hours on two different occasions. Preceding each study GH therapy was discontinued for 5 days. Serum profiles of GH, IGF-I, IGF-II, IGF binding protein 3 (IGFBP-3), insulin, glucose and non-esterified fatty acids (NEFA) were recorded during the studies. Serum GH was measured by a polyclonal radio-immunoassay (RIA) and by a double monoclonal immunofluorimetric assay (DELFIA).


Higher mean integrated values (AUC) of serum GH (mU/l) were obtained with i.v. GH delivery [47.4 +/- 5.1 (i.v.), 33.3 +/- 3.0 (s.c.), P < 0.05]. The two GH assays showed qualitatively similar results, but higher mean GH concentrations were measured by RIA following both s.c. (P < 0.001) and i.v. infusion (P < 0.001). Serum IGF-I levels displayed different patterns following i.v. and s.c. GH infusion (P < 0.05 by ANOVA) and mean IGF-I levels (micrograms/l) were lower following s.c. GH infusion [159.5 +/- 21.8 (s.c.), 185.2 +/- 27.7 (i.v.), P = 0.002]. Serum IGF-II levels were unaffected by short-term GH treatment and by the route of GH administration. Serum IGFBP-3 levels increased in response to GH administration (P < 0.001), irrespective of route (P = 0.76). The IGF-I/IGFBP-3 molar ratio increased significantly following GH administration (P < 0.001), and a higher ratio was obtained following i.v. infusion (P < 0.005). Subcutaneous GH infusion resulted in significantly lower mean levels of serum NEFA (P < 0.02), whereas similar mean levels of serum insulin (P = 0.54), blood glucose (P = 0.24), energy expenditure (P = 0.13), and respiratory exchange ratio (P = 0.09) were observed on the two occasions.


A reduced bioavailability of s.c. as compared with i.v. administered GH has been recorded with two independent GH assays, and this was also accompanied by a significant, albeit modest, reduction in biological activity.

[Indexed for MEDLINE]

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