Continuous subcutaneous octreotide infusion markedly suppresses IGF-I levels whilst only partially suppressing GH secretion in diabetics with retinopathy.

The response to GH releasing hormone (GHRH 1-29) and 24-h serum GH and IGF-I levels were measured in 9 insulin-dependent diabetics with retinopathy and 6 normal volunteers before and after different treatment regimens with octreotide, a long-acting somatostatin analogue. Octreotide, 50 micrograms by sc injection, completely suppressed GHRH-stimulated GH release in both groups. Thrice daily sc injections for up to 20 weeks were associated with variable plasma octreotide levels and failed completely to suppress GH secretion in either the patients or the normal controls. Three days of continuous sc pump infusion (500 micrograms/24-h) resulted in consistently high plasma octreotide levels and completely suppressed 24-h GH in 4 normal subjects, whilst treatment for up to 16 weeks only partially suppressed GH levels in 6 patients (AUC mU.l-1.h-1; 209 +/- 81 vs 121 +/- 82; P = 0.01). Mean +/- SD IGF-I levels (micrograms/l) in the patients (but not controls) were suppressed into the hypopituitary range by median 6 weeks (range 2-16) pump administration (203 +/- 62 vs 60 +/- 25; P = 0.02). Pump treatment achieved total GH suppression in normal subjects; diabetics with retinopathy seem more resistant to the GH suppressing effects of the drug. However, the reduction of serum IGF-I with prolonged treatment may be of clinical value in arresting the progress of diabetic retinopathy.