Although insulin-like growth factor I increases renal function, the renal haemodynamic abnormality underlying the glomerular hyperfiltration in acromegaly is unknown. In normal subjects, amino acids and low doses of dopamine increase the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), presumably by a predominant vasodilation of the afferent and efferent glomerular arterioles, respectively. We studied baseline GFR and ERPF (determined with 125I-iothalamate and 131I-hippuran, respectively), the renal stimulatory effects of amino acid and dopamine infusion, and albuminuria before and after 3 months octreotide treatment in seven acromegalic patients with metabolically active disease. Octreotide reduced growth hormone concentrations from 14.7 +/- 3.0 to 5.5 +/- 1.0 micrograms l-1 (mean +/- SEM, n = 7; P less than 0.001) and insulin-like growth factor I levels from 4.12 +/- 1.31 to 2.44 +/- 0.68 kU l-1 (P less than 0.02). Glucagon concentrations did not change. Baseline GFR and ERPF declined from 132 +/- 5 to 117 +/- 6 and from 547 +/- 32 to 478 +/- 31 ml min-1 1.73 m-2, respectively (P less than 0.05 for both). Initially the response to amino acids was impaired (increment in GFR: 4.8 +/- 6.0%, NS; ERPF: -1.5 +/- 6.8%, NS), whereas the response to dopamine was normal (GFR: 10.6 +/- 1.1%, P less than 0.05: ERPF: 33.2 +/- 3.1%, P less than 0.01). After octreotide, amino acid infusion increased GFR by 15.0 +/- 6.8% (P less than 0.02) and ERPF by 11.3 +/- 5.6% (P less than 0.02), while the dopamine response was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)