Provocative stimulation of growth hormone: a monozygotic twin study discordant for spinal cord injury

A blunted growth hormone (GH) response to provocative testing and/or low levels of plasma insulin-like growth factor-I (IGF-I) have been reported in persons with spinal cord injury (SCI). A reduction in activity of the GH-IGF-I axis may have deleterious effects on body composition and function. Provocative testing for GH stimulation was performed to determine the response in monozygotic twins that were discordant for SCI.

GH stimulation testing was performed by the administration of intravenous arginine.

Nine SCI twins with paraplegia, a mean age of 39 +/- 9 years, and duration of injury of 14 +/- 9 years were studied. The twins with SCI had a significantly lower body mass index than non-SCI twins (22.5 +/- 4.0 vs 25.1 +/- 4.2 kg/m2; P < 0.05); percent fat mass was greater in the twins with SCI (30 +/- 11% vs 22 +/- 10%; P < 0.05). Baseline serum GH was correlated with percent fat only in the SCI twins. The response to GH provocative stimulation was less in the twins with SCI: peak GH response was 5.8 +/- 6.6 vs 13.0 +/- 7.3 ng/mL (P < 0.05), and sum GH response was 15.7 +/- 15.6 vs 30.2 +/- 17.3 ng/mL (P = 0.06). Although baseline serum GH was correlated with stimulated response in the SCI twins, this relationship was not found in the non-SCI twins. Adiposity was positively related to the provocative serum GH response in twins with SCI rather than negatively related, as noted in the non-SCI twins.

This study confirms and extends prior work that reported a reduction in stimulated GH release in persons with SCI, which was related to baseline values.