Increased systemic vascular resistance in Atlantic salmon, Salmo salar L., affected with amoebic gill disease

Previous investigations into the pathophysiology of amoebic gill disease (AGD) have suggested that there are probable cardiovascular effects associated with this disease. In the present study Atlantic salmon, Salmo salar L., were experimentally infected by cohabitation with diseased individuals. Two commonly used vasodilators, sodium nitroprusside (SNP) and captopril, the angiotensin-converting enzyme (ACE) inhibitor, were used as tools to investigate possible vasoconstriction and/or renin–angiotensin system (RAS) dysfunction in AGD-affected animals. Within the SNP trial, results showed that AGD-affected fish exhibited lowered cardiac output (Q), lowered cardiac stroke volume (V_S) and a significantly elevated systemic vascular resistance (R_S) compared with non-affected naïve counterparts. These effects were totally abolished following SNP administration (40 μg kg⁻¹), however significant cardiovascular effects associated with SNP were not observed. Within the captopril trial, where AGD-affected fish were more diseased compared with the SNP trial, a significant hypertension was observed in AGD-affected fish. Captopril administration (10⁻⁴ mol L⁻¹ at 1 mL kg⁻¹) resulted in a significant drop in dorsal aortic pressure (P_DA) for both AGD-affected and naïve control fish. In terms of peak individual responses, captopril administration effectively lowered P_DA in both AGD-affected and naïve control groups equally. The drop in P_DA following SNP administration however was significantly greater in AGD-affected fish potentially suggesting disease-related vasoconstriction. The lack of significant cardiovascular effects directly associated with both SNP and captopril administrations possibly relate to the 6 h recovery period following surgical procedures. However, while variable, these results do suggest that there are significant cardiovascular effects including vasoconstriction and hypertension associated with AGD.     

卡托普利对腹水综合征肉鸡右心功能的影响

150只15日龄AA肉鸡随机分为常温组、低温组和卡托普利组,探讨卡托普利对腹水综合征肉鸡右心功能的影响。结果:卡托普利降低低温诱发肉鸡腹水的发生率;卡托普利降低低温诱发肉鸡肺动脉高压;卡托普利与低温组比降低肉鸡腹水心脏指数;28、36日龄和44日龄,卡托普利组右心室收缩压低于低温组(P0.05);28、36日龄和44日龄,卡托普利组右心室舒张压分别极低于低温组((P0.01)。本试验证明卡托普利可以降低腹水发生率和右心肥大,有效维护右心功能。     

Antidiuretic action of vasoactive endothelins in the in situ perfused rainbow trout kidney

The present studies examined, for the first time, the renal actions of endothelin-1 (ET-1) and Sarafotoxin S6b (SRTX-6b) (an endothelin-like peptide from snake venom) at 10^-11 M and 10^-9 M, using the in situ perfused kidney of the rainbow trout, Oncorhynchus mykiss. In further studies ET-1 (10^-9 M) was accompanied by Captopril (5 × 10^-4 M) to inhibit angiotensin II formation and determine whether the newly-identified intrarenal renin-angiotensin system (RAS) in the trout kidney was involved in ET-1's actions. These studies demonstrated that ET-1 and SRTX-S6b constrict the trout trunk vasculature, increasing vascular resistance and decreasing perfusate flow rates. Captopril did not affect this response and therefore angiotensin II is not implicated in the vascular responses. Direct action of endothelins on vascular receptors is indicated which, in vivo, is likely to be involved in regulation of renal vascular tone. Both ET-1 and SRTX-6b induced immediate decreases in glomerular filtration rates (GFR) reaching 30% and 34% decrease with 10^-11 M ET-1 and SRTX-6b respectively and 50% and 57% decrease with 10^-9 M ET-1 and SRTX-6b respectively. Urine flow rates decreased to a slightly lesser extent because of decreased tubular reabsorption of water; relative free water clearances increased from approximately 17% to 21% while urine/plasma inulin concentration ratios decreased slightly. This significant depressed urine osmolarity. Captopril completely blocked the effects of endothelins on tubular water reabsorption suggesting intrarenal RAS involvement in this action, although a kinin-mediated effect cannot, at this stage, be excluded. The glomerular antidiuretic action of ET-1 and SRTX-6b partially reflected a decreased population of filtering nephrons (41% filtering in control kidneys, 32–36% filtering in the presence of 10^-11 M M ET-1/SRTX-6b, 31–32% filtering in the presence of 10^-9 M ET-1/SRTX-6b). In addition, 25–40% reductions of single nephron filtration rates were estimated. Glomerular actions of endothelins were partially inhibited by Captopril, suggesting either that renal endothelins have both direct renal actions and secondary effects through activation of the renal RAS, or that kinins can modulate the renal actions of endothelins.     

Characterization of angiotensin-converting enzyme in the gills of rainbow trout,Salmo gairdneri (Richardson)

Several physical and chemical parameters of angiotensin-converting enzyme (ACE) were determined using a spectrophotometric assay of gill tissue homogenates from rainbow trout. This assay is based on the evolution of free hippuric acid via enzymatic cleavage of histidyl-leucine from the synthetic substrate hippuryl-l-histidyl-l-leucine (HHL). Piscine ACE exhibited enzymatic and kinetic properties similar to those reported for the partially purified mammalian enzyme. Proteolytic activity was both temperature and pH dependent and demonstrated hyperbolic kinetics with an apparent Km of 2.5 mM. Hydrolysis of HHL was activated by Cl^– at concentrations between 20 mM and 100 mM. Captopril (1 × 10^–6 M) and MK-422 (1 × 10^–6 M) blocked trout gill ACE activity, however, EDTA was inhibitory only at high concentrations (1 × 10^–3 M). These results demonstrate that trout ACE is functionally similar to mammalian ACE and that the spectro-photometric assay for ACE developed by Cushman and Cheung can be applied to analysis of converting enzyme activity in fish tissue homogenates.