The renal portal circulation of the avian kidney contains a unique smooth muscle valve that can direct blood flow from the posterior extremities to the central circulation or through the kidney. The neural control of the valve and adjacent venous tissue from Rhode Island Red roosters was characterized by measuring the isometric force developed following transmural nerve stimulation (TNS). During TNS, the valve relaxed while the iliac vein contracted. In the valve, a poststimulus contraction followed the relaxation. Propranolol and guanethidine abolished the TNS-induced relaxation of the valve, leaving a contraction that was increased by physostigmine and partially blocked by atropine or prazosin. In contrast, the TNS-induced contraction of the vein was blocked by guanethidine or prazosin. Measurement of choline acetyltransferase activity and norepinephrine content confirms that the valve is densely innervated with both cholinergic and adrenergic nerves. Thus the vein shows a predominantly adrenergic contractile response typical of most vascular smooth muscle, but the valve demonstrates a dual control, i.e., adrenergic nerves producing relaxation and cholinergic nerves causing contraction. Knowledge of the nature of neuronal control of the valve should aid in the design of experiments to determine its functional role.
On the Fine Structure of the Proximal Segment in the Avian Kidney