alpha-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtle Trachemys scripta during anoxic submergence at 5 degrees C and 21 degrees C

摘要

Anoxic exposure in the anoxia-tolerant freshwater turtle is attended by substantial decreases in heart rate and blood flows, but systemic blood pressure (P-sys) only decreases marginally due to an increase in systemic peripheral resistance (R-sys). Here, we investigate the role of the alpha-adrenergic system in modulating R-sys during anoxia at 5degreesC and 21degreesC in the turtle Trachemys scripta, and also describe how anoxia affects relative systemic blood flow distribution (%Q(sys),) and absolute tissue blood flows. Turtles were instrumented with an arterial cannula for measurement of P-sys and ultrasonic flow probes on major systemic blood vessels for determination of systemic cardiac output (Q(sys)). alpha-Adrenergic tone was assessed from vascular injections of alpha-adrenergic agonists; and antagonists (phenylephrine and phentolamine, respectively) during normoxia and following either 6 h (21degreesC) or 12 days (5degreesC) of anoxic submergence. Coloured microspheres, injected through a left atrial cannula during normoxia and anoxia, as well as after a-adrenergic stimulation and blockade during anoxia at both temperatures, were used to determine relative and absolute tissue blood flows.