Remarkable blood catecholamine levels in forced dived ducks

Life under water: physiological adaptations to diving and living at sea

This review covers the field of diving physiology by following a chronological approach and focusing heavily on marine mammals. Because the study of modern diving physiology can be traced almost entirely to the work of Laurence Irving in the 1930s, this particular field of physiology is different than most in that it did not derive from multiple laboratories working at many locations or on different aspects of a similar problem. Because most of the physiology principles still used today were first formulated by Irving, it is important to the study of this field that the sequence of thought is examined as a progression of theory. The review covers the field in roughly decadal blocks and traces ideas as they were first suggested, tested, modified and in some cases, abandoned. Because diving physiology has also been extremely dependent on new technologies used in the development of diving recorders, a chronological approach fits well with advances in electronics and mechanical innovation. There are many species that dive underwater as part of their natural behavior, but it is mainly the marine mammals (seals, sea lions, and whales) that demonstrate both long duration and dives to great depth. There have been many studies on other diving species including birds, snakes, small aquatic mammals, and humans. This work examines these other diving species as appropriate and a listing of reviews and relevant literature on these groups is included at the end.

Noradrenergic modulation of avian kidney function

Norepinephrine (NE) infused at doses of 0.7, 2.2 and 6.7 micrograms/min/kg body weight into conscious, salt and water loaded ducks dose-dependently induced arterial hypertension, reflex bradycardia and diuresis/natriuresis at unchanged glomerular filtration and reduced renal blood flow. NE-induced changes in plasma concentrations of osmoregulatory hormones consisted of a slight increase for the antidiuretic hormone, no change for angiotensin II and a nearly 4-fold increase for atrial natriuretic factor. Sub-pressor doses of NE infused close to the origin of the renal arteries induced diuresis without a rise in urinary sodium concentration. The results suggest pressure diuresis in ducks as a response to hypertensive NE doses with a possible contribution of atrial natriuretic factor to natriuresis.

The evolution of asphyxial defense

From the time animals became dependent upon molecular oxygen as an integral part of their energy-producing processes, they have remained in the shadow of acute asphyxial threat--the blocking of respiratory exchange resulting in the intracellular triad of hypoxia, hypercapnia and acidosis. The most commonly occurring precipitant of acute asphyxia has always been the transfer between air and water environments. Over the last one hundred years studies on a wide range of living organisms, from single cells to complex multicellular organisms like mammals, have demonstrated the presence of well-defined metabolic and cardiovascular-respiratory mechanisms for protecting living things against acute asphyxia. Single-celled animals depend upon anaerobiosis and secondarily hypometabolism. In addition to these processes, animals with gills or lungs utilize "passive" protection such as increased oxygen storage and the "dynamic" cardiovascular adjustments of bradycardia and selective ischemia. These latter changes decrease overall oxygen consumption and hence utilize the oxygen stores in the most economical way to protect the cardiac and cerebral tissue, which are most sensitive to hypoxia and vital to continued survival of the organism. In this article an attempt is made to place these processes into an evolutionary context. As through a glass darkly we glimpse asphyxial defense running like a paleophysiological thread through hundreds of millions of years, being accentuated here and muted there, depending upon the particular needs of individual species.

The effect of anoxic submergence and recovery on circulating levels of catecholamines and corticosterone in the turtle, Chrysemys picta

The ability of some freshwater turtles to tolerate prolonged anoxia is well known. The role of hormones in the regulation of the metabolic adjustments that occur during anoxia, however, is unknown. This study examined the changes in plasma glucose, lactate, catecholamine, and corticosterone levels during submergence anoxia and recovery at 22 degrees C in the painted turtle, Chrysemys picta. Plasma catecholamine levels increased greatly during anoxia, while corticosterone levels decreased. During recovery from anoxia, plasma catecholamine levels fell rapidly while corticosterone levels increased 10-fold over controls. The results are consistent with a role for the catecholamines and corticosterone in the regulation of glucose metabolism in the turtle during anoxia and recovery, respectively. We hypothesize that the catecholamines function to stimulate hepatic glycogenolysis during anoxia and thereby increase plasma glucose levels. Corticosterone may function in the recovery from anoxia by enhancing the resynthesis of liver glycogen from lactate.

The effect of brain transection on the response to forced submergence in ducks

The effect of brain transection at two levels on cardiovascular responses to forced submergence has been investigated in ducks. Compared with intact ducks, neither decerebration nor brain stem transection at the rostral mesencephalic (RM) level had any effect on development of diving bradycardia, or heart rate at the end of two-min dives. Arterial blood pressure was maintained in brain transected ducks as well as in intact ducks. Furthermore, end-dive arterial blood gases and pH were also similar in intact and brain transected ducks confirming that the oxygen sparing cardiovascular adjustments, involving a massive increase in total peripheral resistance, were unimpaired by brain transection. In this respect, ducks with RM transections tolerated four-min dives. However, the increase in post-dive VE seen in intact and decerebrated ducks was prevented by RM transection. We conclude that control of the circulatory response to diving resides in the lower brainstem, is reflexogenic in nature, and does not depend on the cognitive perception of 'fearful' stimuli.

The source of circulating catecholamines in forced dived ducks

Plasma catecholamines have been measured in chronically adrenalectomized (ADX) ducks, in chronically adrenal-denervated ducks (DNX), and in their respective shamoperated controls (SH-adx, SH-dnx) after 3 min forced submergence. The results showed that 100% of the plasma epinephrine (EP) and 70 to 80% of plasma norepinephrine (NE) released during the dive came from the adrenal glands. Only 20 to 30% of plasma NE came from the endings of the autonomic vascular sympathetic nerves which are strongly stimulated during diving. Adrenal catecholamines were released by nerve activation only; nonneural mechanisms did not play any role in their release. The action of adrenal catecholamines on the cardiovascular system during dives was investigated by measuring heart rate and arterial blood pressure in operated and sham-operated ducks. Cardiovascular adjustments, associated with 3 min of forced diving, were not affected by any differences in the levels of plasma catecholamines.

Effects of treadmill exercise on the distribution of blood flow between the hindlimb muscles and abdominal viscera of the laying fowl

1. Blood flow distribution between the abdominal viscera and the leg muscles of regularly-laying Rhode Island Red hens was measured at rest and immediately following treadmill exercise, using the radioactive microsphere technique. 2. Exercise brought about a 150% increase in metabolic rate and this was maintained continuously for 90 min. 3. Although there was a small shift in blood flow distribution towards the hindlimb muscles at the expense of the kidneys and reproductive organs, this was not statistically significant. 4. There was a significant reduction in blood flow to the preovulatory follicles of the ovary during exercise, relative to the rest of the abdominal viscera. 5. It is concluded that exercise of this intensity is insufficient to bring about gross changes in blood flow distribution between the abdominal viscera and the hindlimb muscles. The implications of this finding are discussed in relation to the nutrient and blood flow requirements of the reproductive organs.

Effects of activity, hemorrhage, and dehydration on plasma catecholamine levels in the marine toad (Bufo marinus)

Resting plasma epinephrine and norepinephrine levels were 13.1 and 2.1 nmol liter-1 for the marine toad (Bufo marinus). Plasma catecholamine levels increased during enforced activity by five- to sixfold. Marine toads are remarkably tolerant of graded hemorrhagic loss of blood (over 10% mass loss). Plasma catecholamine levels did not increase at moderate blood loss, but increased substantially when cardiovascular variables (blood pressure, blood flow) were compromised and peripheral resistance was increased. Plasma catecholamine levels did not increase with dehydrational mass loss until a 15-20% loss of mass. The increase in plasma catecholamine concentration was correlated with an increase in vivo vascular resistance. Vascular resistance measured in vitro was unaltered at physiological catecholamine concentrations, although systemic resistance increased at pharmacological concentrations. The lack of effects of adrenalectomy on plasma catecholamine levels suggests that nerve terminal release, rather than adrenal secretion, may be the primary source of circulating catecholamines. We therefore suggest that circulating catecholamine levels are not an important endocrinological mechanism for defense of activity blood pressure, at least until it is compromised to the resting value.

The density of beta-adrenoreceptors in cardiac muscle membranes of muskrats and guinea pigs

1. Cardiac membranes were prepared and then incubated with a range of concentrations of the beta-adrenergic ligand, dihydroalprenolol. Specific binding to the receptor was measured and receptor density and binding affinities were determined. 2. The receptor density was about 40% greater in the guinea pig heart than in the muskrat heart. The reduced beta-receptor density in the muskrat heart helps explain the previous findings of a lesser pumping ability and decreased responsiveness to isoproterenol in the muskrat compared with guinea pig hearts. 3. The decreased beta-receptor density may aid the muskrat in diving by reducing the oxygen consumption of the heart and thus prolonging diving time.

Circulation during hypoxia in birds

The effects of hypoxia on the avian cardiovascular system are reviewed. The avian cardiovascular system seems well adapted to deal with the stress of hypoxia. In general, birds are remarkably tolerant of hypoxia, with some species being capable of performing vigorous exercise at extreme altitude. During hypoxia at rest, the circulation maintains arterial pressure, increases cardiac output, and redistributes blood flow so oxygen delivery to the heart and brain is maintained. During exercise, further adjustments are required, since exercising muscle has large oxygen requirements. The mechanisms responsible for producing these circulatory changes are largely unknown. The transport steps that limit O2 delivery during hypoxia are also poorly understood.

Blood flow distribution during hypocapnic hypoxia in Pekin ducks and bar-headed geese

The purpose of this study was to determine the effects of hypocapnic hypoxia on regional blood flow in birds. Regional blood flow was measured using the radioactive microsphere method in unanesthetized Pekin ducks (Anas platyrhynchos) and bar-headed geese (Anser indicus) breathing 21, 10 and 5% O2. In both birds, arterial PO2 was reduced from about 96 Torr during normoxia to about 28 Torr during severe hypoxia. Severe hypocapnic hypoxia produced a change in the pattern of blood flow in ducks; blood flow to some organs increased (brain, adrenal glands, heart, and eyes) while flow to other organs decreased (liver, spleen, small intestine, shell gland). Compared with ducks, bar-headed geese were able to provide higher levels of O2 delivery to their tissues since blood flow to a variety of organs and skeletal muscles was either unchanged or increased during severe hypoxia. The redistribution of blood flow in Pekin ducks during severe hypocapnic hypoxia may help to support large increases in cerebral and coronary blood flow but may also contribute to the development of a metabolic acidosis.