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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

The effects of salt-induced hypertension on ₁-adrenoreceptor expression and cardiovascular physiology in the rainbow trout (Oncorhynchus mykiss)

¹Department of Biology, University of Ottawa, Ottawa, Ontario, Canada; and ²Indiana University School of Medicine, South Bend, South Bend, Indiana

Submitted 17 April 2006 ; accepted in final form 1 June 2007

Experiments were conducted on rainbow trout to determine the impact of dietary salt on arterial blood pressure. After 4–6 wk, fish fed a salt-enriched diet exhibited a 37% elevation of dorsal aortic pressure (from 23.8 ± 1.2 to 32.6 ± 1.4 mmHg) and an 18% increase in ventral aortic pressure (from 33.0 ± 1.5 to 38.9 ± 1.3 mmHg). The hypertension presumably reflected the increase in cardiac output (from 31.0 ± 0.8 to 36.4 ± 2.2 ml·min^–1·kg^–1) because systemic and branchial resistances were statistically unaltered by salt feeding. The chronic hypertension was associated with a decrease in the pressor responses of the systemic vasculature to catecholamines and hypercapnia in the salt-fed fish. The reduction in -adrenergic responsiveness of the systemic vasculature is consistent with desensitization or loss of functional -adrenoceptors (-ARs). In support of this idea, the salt-fed fish exhibited significantly decreased levels of _1D-AR mRNA in the dorsal aorta and the afferent (ABA) and efferent branchial arteries (EBA). In contrast, however, the results obtained from norepinephrine dose-response curves for EBA and ABA vascular rings in vitro did not provide evidence for loss of function of branchial artery ₁-ARs in the salt-fed fish. Indeed, the EC₅₀ for the EBA norepinephrine dose-response curve was significantly reduced (from 3.75 x 10^–7 to 2.12 x 10^–7 M) in the salt-fed fish, indicating an increase in the binding affinity of the ₁-ARs.

norepinephrine; epinephrine; blood pressure; systemic resistance; salt feeding; hypercapnia; efferent branchial artery; afferent branchial artery

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