Background and objective: To elucidate the effects of various degrees of hypotension induced by the calcitonin gene-related peptide (CGRP) on the splanchnic circulation, we investigated the renal and hepatic blood flow during hypotension induced by either the calcitonin gene-related peptide or sodium nitroprusside in the isofluraneanaesthetized dog.

Methods: Anaesthesia was maintained with 1.3% isoflurane in oxygen. After the baseline period, mean arterial pressure was reduced to 60 mmHg in the CGRP60 and nitroprusside groups, and to 50 mmHg in the CGRP50 group. The splanchnic organ blood flow was measured by hydrogen clearance.

Results: The cardiac index in the CGRP60 group increased (P < 0.01), but in the CGRP50 group it decreased (P < 0.01), and in the nitroprusside group it remained unchanged during hypotension. Mean pulmonary artery and pulmonary capillary wedge pressures in the CGRP60 group remained unchanged, but in the CGRP50 and nitroprusside groups they decreased (P < 0.01) during hypotension. Cardiac contractility in the CGRP60 group remained unchanged, whereas in the CGRP50 and nitroprusside groups it was reduced (P < 0.01) during hypotension. Renal blood flow in the CGRP60 group was relatively well maintained but in the CGRP50 and nitroprusside groups it was reduced (P < 0.01) throughout the observation. Hepatic blood flow in all three groups was reduced (P < 0.01) during hypotension. The reductions in hepatic blood flow between the Calcitonin gene-related peptide groups were associated with a dose-dependent decrease in mean arterial pressure.

Conclusions: The results suggest that calcitonin gene-related peptide acts as an arteriolar vasodilator at low doses but as a vasodilator of the arteriolar and venous systems at higher doses, and that profound hypotension induced by the calcitonin gene-related peptide may impair splanchnic circulation.