Stanniectomy attenuates the renin–angiotensin response to hypovolemic hypotension in freshwater eels (<Emphasis Type="Italic">Anguilla rostrata</Emphasis>) but not blood pressure recovery

Plasma Angiotensin II (ANG II) concentrations were measured in SHM (sham-operated 2 weeks) and CSX (corpuscles of Stannius removed 2 weeks) eels before and after the induction of hypovolemic hypotension (HH) by the rapid withdrawal of 8 ml kg bw⁻¹ of caudal venous blood. Baseline (before exsanguination) plasma ANG II concentrations were similar in SHM and CSX eels (81.3 ± 18.8 fmol ml⁻¹ cf. 106 ± 31.6 fmol ml⁻¹, respectively) but the elevation in plasma ANG II following HH (1,732 ± 82 fmol ml⁻¹) was attenuated by CSX (368 ± 127 fmol ml⁻¹) showing that the CS are linked to plasma ANG II concentrations. Plasma ANG II in both groups returned to baseline levels within 48 h. Dorsal aortic blood pressures (DABP) were measured in both experimental groups before, and during the 60 min after, blood withdrawal. A 44% decrease in mean DABP was observed in both SHM and CSX eels within 2 min and followed by similar rapid patterns of recovery of systolic, diastolic, and pulse pressures in both groups during the next 60 min showing that short-term recovery of DABP is not CS-dependent. Stanniectomy increased plasma Ca and K⁺ and decreased plasma Mg, Na⁺, Cl⁻ and osmolality which confirms some earlier observations in eels and other freshwater teleosts.     

Osmoregulation in North American eels (Anguilla rostrata LeSueur) on land and in freshwater: effects of the corpuscles of Stannius

Hypercalcemia, hypomagnesia and hypophosphatemia were observed in freshwater (FW) eels (Anguilla rostrata LeSueur) after removal of the corpuscles of Stannius. These changes did not occur if Stanniectomized (CSX) eels were removed from FW and placed on land for 12 days but did occur after the eels were returned to FW. Therefore, changes in plasma electrolyte concentrations after CSX depended upon the branchial and/or integumental influx of ions. Plasma Na⁺, Cl⁻ and osmolal concentrations decreased gradually in both sham-operated (SHM) and CSX eels on land (12 days) and in FW (12 days). Plasma K⁺almost doubled in both SHM and CSX eels after 4 days on land, remained elevated, and fell abruptly to normal within a day after the eels were returned in FW. After 2 days on land, urine flow rates in SHM and CSX eels had decreased by approximately 85%, osmolar clearance by 50% and positive free-water clearance by more than 90%. Body weights did not decrease when eels were on land so it was concluded that the reduced but continuous renal loss of water was counterbalanced by the integumental uptake of condensed water. Accepted: 21 October 1998     

Fractional reabsorption of calcium,magnesium and phosphate in the kidneys of freshwater North American eels (Anguilla rostrata LeSueur) following removal of the corpuscles of Stannius

Renal function was observed in freshwater North American eels (Anguilla rostrata LeSueur) 2 weeks after the removal of the corpuscles of Stannius. There was a positive linear correlation between glomerular filtration rates and urine flow rates in both sham-operated and stanniectomized eels but there was no difference in slope or elevation between the two groups nor did urine flow rates ever exceed glomerular filtration rates. Osmolar clearance and free-water clearance were unchanged following stanniectomy. Plasma Ca²⁺ and K⁺ concentrations increased and plasma Mg²⁺, phosphate, Na⁺ and Cl^- concentrations decreased following stanniectomy. Plasma ultrafilterable Ca increased and ultrafilterable Mg decreased after stanniectomy but neither changed relative to its total plasma concentration. Stanniectomy was followed by a decreased renal tubular reabsorption of Mg²⁺ relative to the amount filtered (C _Mg/C _In); the same applies to C _Na/C _In. Even though the filtered load of Ca increased in conjuction with the predictable hypercalcemia, there was no change in the fraction of filtered Ca reabsorbed. Net tubular secretion of phosphate was observed in both sham-operated and stanniectomized cels together with a slight increase in C _phos/C _In following stanniectomy. Some or all of these changes in plasma electrolytes and/or the modified renal transport of Na⁺, Mg²⁺ and possibly phosphate may be caused by the changes in cardiovascular function that were recently shown to follow stanniectomy.Abbreviations CSX Stanniectomized/stanniectomy - ER endoplasmatic reticulum - FW fresh water - GFR glomerular filtration rate - Pi inorganic phosphate - RAS renin-angiotensin system - SHM sham-operated - SW sea water - UFR urine flow rate - U/P ratio urine/plasma ratio