Changes in vascular and extravascular volumes of eel muscle in response to catecholamines: the function of the caudal lymphatic heart

1. Vascular volume changes in an isolated saline-perfused eel tail preparation in response to catecholamines were small (less than 2%) and are explicable in terms of changes in volume of pre-capillary resistance vessels. 2. Extravascular-extracellular (interstitial) volume increased less than 3% during infusion of adrenaline (AD) at concentrations of 1 × 10(−6) to 1 × 10(−3) M. Injection of doses of AD and noradrenaline (NA) between 1 nmol and 100 nmol caused maximum interstitial volume changes of less than 11%. 3. Isoprenaline caused only very small changes in vascular and interstitial volume. 4. Caudal lymph heart frequency increases when high concentrations (greater than 1 × 10(−6) M) and doses (greater than 1 nmol) of AD and NA were administered. 5. Caudal lymph heart frequency increases were significantly correlated with changes in outflow after vascular volume adjustments. One function of the caudal lymph heart is to return interstitial fluid to the vascular system.

Neuroanatomy and control of the caudal lymphatic heart of the short-finned eel (Anguilla australis schmidtii)

The caudal lymphatic heart of the short-finned eel is found in the most posterior segment of the tail. This organ pumps lymph from lateral, caudal, and caudal fin lymphatic vessels into the caudal vein. The anatomy of the heart was studied using light and electron microscopic techniques. Lymph heart muscle is typical of vertebrate fast-acting skeletal muscle. The muscles on each side are innervated by a spinal nerve from the penultimate vertebra. Neuromuscular junctions are of the "en plaque" type and contain spherical vesicles about 60 nm in diameter. Ablation experiments show that the lymph heart beat is neurogenic. It is suggested that action potentials from the penultimate segment of the spinal cord, which are transmitted to the lymph heart by spinal motor axons, initiate lymph heart contractions.

The caudal heart of the eel a lymphatic heart.—Effect of the force with which the lymph- stream is propelled therefrom on the flow of blood in the vein into which the heart opens. — Explanation of the appearance of blood propelled in successive drops, as if from the heart, along the caudal vein.— Influence which the force of the lymph-stream from the heart exerts in accelerating and promoting the flow of blood in the caudal vein

To explain the true nature of the phenomenon of drops of blood propelled in rapid succession, as if from the caudal heart, along the caudal vein,—to prove thereby that the caudal heart belongs, not to the blood-vascular system, but to the lymphatic system,—and to inquire into the influence which the force of the lymph-stream from the caudal heart exerts in accelerating and promoting the flow of blood in the caudal vein, constitute the object of this paper. The great caudal vein of the eel is formed by the junction of two trunks, a larger and a smaller. It is into the smaller trunk, near its junction with the larger, that the caudal heart opens. At the opening, there is a valve which prevents regurgitation of the lymph back from the vein into the heart.

On the phenomena observed to attend the propulsion of lymph from one of the lymphatic hearts into a vein in the frog

An anæmic frog, killed, as regards sensation and voluntary motion, without stoppage of the circulation, by plunging into water at 110 or 120° Fahr., was laid open, and the posterior part of the anterior lymphatic heart of one side, in the niche behind and below the extremity of the large transverse process of the third vertebra, brought into view. By the removal of the skin of the back from over the scapular region, the part of the heart mentioned admitted of examination by transmitted light under a simple microscope—the lens 1/2-inch focus. It was seen that when the lymphatic heart contracted, a stream of lymph was propelled from it into a vein at its posterior border, and swept before it the blood in that vessel, whilst the flow from behind was arrested. As soon, however, as diastole of the lymphatic heart supervened, the flow of blood from behind became reestablished, and drove the lymph onward in its turn. Systole of the heart now again ensuing, the lymph-stream propelled into the vein swept forward the blood in that vessel as before, whilst the flow of blood from behind was arrested; and so the same series of phenomena was repeated. It was thus seen that the phenomena attending the propulsion of lymph from the anterior lymphatic hearts of the frog into the veins at their posterior border, with which they communicate by a valvular opening, are essentially similar to those attending the propulsion of the lymph from the caudal heart of the eel into the caudal vein.

XXVIII. The caudal heart of the eel a lymphatic heart.—Effect of the force with which the lymph-stream is propelled therefrom on the flow of the blood in the vein into which the heart opens.— Explanation of the appearance of blood propelled in successive drops, as if from the heart, along the caudal vein.—Influence which the force of the lymph-stream from the heart exerts in accelerating and promoting the flow of blood in the caudal vein

The remarkable pulsating organ in the tail of the eel, which forms the subject of this paper, was discovered by the late Dr. Marshall Hall. He viewed it as belonging to the blood-vascular system, and named it the “Caudal Heart." His description of it was founded on observations made on small eels under the micro­scope. In large eels the heart may, as he also pointed out, be seen with the naked eye by spreading the tail on a plate of glass and viewing it against the light. Not only, however, are the pulsations of the organ itself thus visible, but also the very peculiar appearance of successive drops of blood propelled, as if from the heart, with great velo­city along the caudal vein, which was observed by Dr. Marshall Hall in his microsco­pical examinations, though incorrectly interpreted by him: To explain the true nature of the phenomenon here referred to,—to prove thereby that the caudal heart belongs, not to the blood-vascular system, but to the lymphatic system, and to inquire into the influence which the force of the lymph-stream from the heart exerts in accelerating and promoting the flow of blood in the caudal vein, constitute the object of the communication here presented to the Royal Society.