Effect of a long-acting somatostatin analogue (octreotide) on circulating tachykinins and the pentagastrin-induced carcinoid flush.

Cutaneous flushing was provoked in seven patients with metastatic carcinoid tumours and the carcinoid syndrome by an intravenous injection of pentagastrin (0.6 micrograms.kg-1 body weight). The patients were studied before and 1 h after a subcutaneous injection of the long-acting somatostatin analogue octreotide 50 micrograms (Sandostatin). The severity of the carcinoid flush in all the patients was reduced by administration of the analogue. The rise in facial temperature was 1.3 (0.3) degree C before and 0.8 (0.2) degree C after octreotide. Six patients responded to pentagastrin with a rise in the circulating neurokinin A-like immunoreactivity (NKA-LI) and five patients with a rise in circulating substance P-like immunoreactivity (SP-LI). No cutaneous flushing or rise in tachykinin concentration was observed in healthy subjects (n = 6) after injection of pentagastrin. The rise in NKA-LI in the patients was decreased by 61 (14)% and the rise in SP-LI by 54 (13)% after octreotide. Although flushing still occurred, the tachykinin response in two patients was completely abolished. The data demonstrate that the release of tachykinins from carcinoid tumours during pentagastrin-induced flushing is subject to partial inhibition by octreotide. However, the occurrence of a flush in some patients in the absence of a detectable rise in circulating tachykinins indicates that the latter peptides cannot be the sole causative agent of the carcinoid flush.