Changes in cardiac performance during hypoxic exposure in the grass shrimp Palaemonetes pugio.

In hearts of higher invertebrates as well as vertebrates, the work performed by the ventricle is a function of both rate and contractility. Decapod crustaceans experience a hypoxia-induced bradycardia that is thought to result in an overall reduction in cardiac work; however, this hypothesis has not yet been tested and is the primary purpose of this study. In the grass shrimp Palaemonetes pugio, cardiac pressure and area data were obtained simultaneously, and in vivo, under normoxic (20.2 kPa O(2)) and hypoxic (6.8 or 2.2 kPa O(2)) conditions and integrated to generate pressure-area (P-A) loops. The area enclosed by the P-A loop provides a measure of stroke work and, when multiplied by the heart rate, provides an estimate of both cardiac work and myocardial O(2) consumption. Changes in intra-cardiac pressure (dp/dt) are correlated to the isovolemic contraction phase and provide an indication of stroke work. At both levels of hypoxic exposure, intra-cardiac pressure, dp/dt, stroke work and cardiac work fell significantly. The significant decrease in intra-cardiac pressure provides the primary mechanism for the decrease in stroke work, and, when coupled with the hypoxia-induced bradycardia, it contributes to an overall fall in cardiac work. Compared with normoxic P-A loops, hypoxic P-A loops (at both levels of hypoxia) become curvilinear, indicating a fall in peripheral resistance (which might account for the reduction in intra-cardiac pressure), which would reduce both stroke work and cardiac work and ultimately would serve to reduce myocardial O(2) consumption. This is the most direct evidence to date indicating that the hypoxia-induced bradycardia observed in many decapod crustaceans reduces cardiac work and is therefore energetically favorable during acute exposure to conditions of low oxygen.

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species.

Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

Cardiovascular system of the blue crab Callinectes sapidus.

The circulatory system of adult blue crabs, Callinectes sapidus, was mapped by either injecting barium sulfate into intact animals followed by radiography or by resin corrosion casts (Batsons Monomer). Seven arteries arise from the heart. The anterior aorta exits from the anterior dorsal surface of the heart and gives rise to the optic arteries; these arteries supply hemolymph to the supraesophageal ganglion and eyestalks. The paired anterolateral arteries also exit from the anterior dorsal surface of the heart and supply hemolymph to the gonads, hepatopancreas, stomach, antennal gland, mandibular muscles, and the hypodermis of the anterior cephalothorax. The paired hepatic arteries exit the heart anteriorly and ventrally and branch profusely within the hepatopancreas. A smaller side branch, the pyloric hepatic artery, supplies hemolymph to the pyloric stomach and midgut. The smallest artery, the posterior aorta, branches off the posterior ventral surface of the heart; it joins with the inferior abdominal artery in the region of the second abdominal segment and these arteries supply hemolymph to the hindgut and abdomen. The largest artery is the sternal artery, which exits from the ventral surface of the heart; the ventral thoracic artery branches off the sternal artery and supplies hemolymph to the chelae, the mouthparts, and to each pereiopod. The present study shows that the circulatory system is highly developed, with arteries dividing into smaller capillary-like vessels that ramify profusely within individual organs. The return vessels, the sinuses, are discrete channels rather than random open spaces, as previously described. The present study refines and advances descriptions of the circulatory system and is discussed in relation to recent work on hemolymph flow in crustaceans.

Changes in caridac output and hemolymph flow during hypoxic exposure in the gravid grass shrimp, Palaemonetes pugio.

The cardiovascular response of decapod crustaceans to hypoxic exposure is well documented; however, information is limited concerning the influence of reproductive state on cardiovascular demands during hypoxic exposure. Given the additional metabolic demand of reproduction, we investigated the cardiovascular adjustments employed by gravid grass shrimp Palaemonetes pugio to maintain oxygen delivery during hypoxic stress. Cardiac output values were elevated in gravid compared to nongravid grass shrimp. Gravid grass shrimp were exposed to hypoxia and the stroke volume, heart rate, cardiac output and hemolymph flow were determined using video-microscopy and dimensional analysis. Oxygen consumption rates were determined using respirometry. There where no changes in the cardiac output values of gravid females until reaching 6.8 kPa O2, with a significant redistribution of hemolymph flow at 13.7 kPa O2. Flow was significantly decreased to the anterior lateral arteries that supply the ovaries and hepatopancreas, the anterior aorta and the posterior aorta. The redistribution of hemolymph flow away from these vessels results in an enhanced hemolymph flow to the sternal artery that supplies the ventral segmental system, the gills, the buccal apparatus and the ventral nerve cord. The data suggest that during hypoxic stress, gravid females place a priority on survival.