Corpuscles of Stannius and blood flow regulation in freshwater North American eels, Anguilla rostrata LeSueur.

Abstract

Cardiac output (CO), heart rate (HR), stroke volume (SV), dorsal aortic blood flow (DABF), dorsal aortic blood pressure (PDA) and plasma electrolytes were monitored in stanniectomized and sham-operated freshwater eels over a 3-week period; branchial shunting and systemic resistance (RSYS) were estimated. DABF was significantly reduced by 45% from 11.72 +/- 0.48 (control) to 6.55 +/- 0.41 (n = 6; day 21) ml.min-1.kg-1 within 3 weeks after the removal of the corpuscles of Stannius. This large reduction in blood flow was due to a 25% decrease in CO and a 100% increase in estimated branchial shunting which preceded the fall in CO. CO was decreased from 16.07 +/- 0.31 (control) to 11.91 +/- 1 (n = 6; day 21) ml.min-1.kg-1 through a reduction in SV; there was no significant change in HR. Estimated branchial shunting, a relative measure of branchial arterio-venous blood flow, corresponded to 2.53 +/- 0.18 ml.min-1.kg-1 (control; n = 12), which represents 16% of baseline CO. Ventral and dorsal aortic pulse flows also decreased following stanniectomy. The decrease in DABF occurred in conjunction with a reduction in PDA which was measured for 12 days in a separate group of eels. Baseline PDA (3.03 +/- 0.1 kPa) significantly decreased by 15% to 2.55 +/- 0.13 kPa 4 days after stanniectomy. However, this fall in PDA was transient and accompanied by an elevation in derived RSYS. These results support the hypothesis that the corpuscles of Stannius are closely linked to cardiovascular regulation in freshwater eels. Electrolyte changes (hypercalcemia, hypomagnesia, hyperkalemia and hyponatremia) were temporally coupled to the changes in blood flows. Impaired cardiovascular function and altered patterns of blood flow to osmoregulatory organs such as the gills, kidney and skin may have led to some or all of the electrolyte disturbances which followed stanniectomy.