Structures of functional interest in the myocardium of lower vertebrates

Cardiac hypertrophy and structural and metabolic remodeling related to seasonal dormancy in the first annual cycle in tegu lizards

Morpho-functional adjustments in the heart of juvenile tegu lizards (Tupinambis merianae) were analyzed at distinct seasonal periods to investigate how the demands of growth and of energy saving are reconciled during the first annual cycle. The relative ventricular mass (Mv) was 31% and 69% larger in late autumn and winter dormancy, respectively, compared to early autumn. This effect did not persist during unfed arousal, suggesting that protein accumulates in the heart during hypometabolism and is degraded on arousal. Both the hypertrophy and the atrophy were disproportionate in the largest individuals. In contrast, Mv was smaller in lizards that were starved during spring activity compared to fed lizards, this effect being larger in smaller individuals. In late autumn and winter dormancy the spongy myocardium had 8% of the section area covered by lacunary spaces, which expanded after food intake during arousal and reached 29% in spring activity together with higher density of cardiomyocytes. Total and soluble proteins per mass unity were unchanged, and maximum activities of selected enzymes suggest sustained glycolytic and aerobic capacities during hypometabolism. Results indicate that important structural adjustments occur in the heart in anticipation of dormancy, and that the protein balance in the tissue is maintained at winter temperatures ~17°C.

Copper sulfate affects Nile tilapia (Oreochromis niloticus) cardiomyocytes structure and contractile function

Copper sulfate (CuSO(4))is an inorganic chemical product worldwide used as an algaecide and a fungicide in aquaculture and agriculture and being discharged into freshwater environments where it can affect the freshwater fauna, especially fishes. The impact of copper on fish cardiac function was analyzed in two groups of Nile tilapias, Oreochromis niloticus (control group and group exposed to 1 mg l(-1) of CuSO(4) for 96 h). Structural and ultra-structural changes were studied and related to perturbations of the inotropic and chronotropic responses of ventricle strips. Fish of Cu exposed group did not show significant alterations in the medium diameter and in the percentage of collagen in the cardiac myocytes when evaluated through the light microscope. However, the ultrastructural analysis revealed cellular swelling followed by mitochondrial swelling. The myofibrils did not show significant variations among groups. Force contraction was significantly decreased, and rates of time to tension increase (contraction) and decrease (relaxation) were significantly augmented after copper exposure. The results suggest that the copper sulfate impairs the oxidative mitochondrial function and consequently alters the cardiac performance of this species.

Physiological importance of the coronary arterial blood supply to the rattlesnake heart

The reptilian heart consists of a thick inner spongy myocardium that derives its oxygen and nutrient supply directly from the blood within the ventricular cavity, which is surrounded by a thin outer compact layer supplied by coronary arteries. The functional importance of these coronary arteries remains unknown. In the present study we investigate the effects of permanent coronary artery occlusion in the South American rattlesnake (Crotalus durissus) on the ability to maintain heart rate and blood pressure at rest and during short term activity. We used colored silicone rubber(Microfil) to identify the coronary artery distribution and interarterial anastomoses. The coronary circulation was occluded and the snakes were then kept for 4 days at 30°C. Microfil injections verified that virtually all coronary arteries had successfully been occluded, but also made visible an extensive coronary supply to the outer compact layer in untreated snakes. Electrocardiogram (ECG), blood pressure (Psys) and heart rate (fH) were measured at rest and during enforced activity at day 1 and 4. Four days after occlusion of the coronary circulation, the snakes could still maintain a Psys and fH of 5.2±0.2 kPa and 58.2±2.2 beats min–1, respectively, during activity and the ECG was not affected. This was not different from sham-operated snakes. Thus, while the outer compact layer of the rattlesnake heart clearly has an extensive coronary supply, rattlesnakes sustain a high blood pressure and heart rate during activity without coronary artery blood supply.

Parallel assessment of male reproductive function in workers and wild rats exposed to pesticides in banana plantations in Guadeloupe

BACKGROUND

There is increasing evidence that reproductive abnormalities are increasing in frequency in both human population and among wild fauna. This increase is probably related to exposure to toxic contaminants in the environment. The use of sentinel species to raise alarms relating to human reproductive health has been strongly recommended. However, no simultaneous studies at the same site have been carried out in recent decades to evaluate the utility of wild animals for monitoring human reproductive disorders. We carried out a joint study in Guadeloupe assessing the reproductive function of workers exposed to pesticides in banana plantations and of male wild rats living in these plantations.

METHODS

A cross-sectional study was performed to assess semen quality and reproductive hormones in banana workers and in men working in non-agricultural sectors. These reproductive parameters were also assessed in wild rats captured in the plantations and were compared with those in rats from areas not directly polluted by humans.

RESULTS

No significant difference in sperm characteristics and/or hormones was found between workers exposed and not exposed to pesticide. By contrast, rats captured in the banana plantations had lower testosterone levels and gonadosomatic indices than control rats.

CONCLUSION

Wild rats seem to be more sensitive than humans to the effects of pesticide exposure on reproductive health. We conclude that the concept of sentinel species must be carefully validated as the actual nature of exposure may varies between human and wild species as well as the vulnerable time period of exposure and various ecological factors.

Effects of temperature and adrenaline on the atrial myocardium of the cultured Atlantic salmon (Salmo salar)

The effects of acute temperature changes (2-17°C) on myocardial contractility with or without adrenergic activation were studied in the isolated spontaneously beating atrium of the Atlantic salmon (Salmo salar) reared at 8°C.The atrial frequency was markedly elevated (from 7 to 46 beats/min) by the rise in temperature from 2-17°C. Both the time to peak tension and to relaxation time were shortened. In contrast, the temperature effect on the maximal tension was modest.Exposure to exogenous adrenaline (1.1 nM-11 μM) resulted in a substantial enhancement of the maximal tension, notably at 2°C, while potentiation of the frequency at 2, 8 and 14°C, was less pronounced. The apparent affinity (pD2) for adrenaline on the chronotropy was higher at 8 and 14°C than at 2°C. For the inotropic responses pD2 was highest at the acclimation temperature (8°C).By comparison with data for the rainbow trout (Oncorhynchus mykiss) obtained by the same experimental design (Ask et al. 1981), species differences were apparent both in temperature dependence of contractile parameters and in their adrenergic activation. The Q10 for the frequency in absence of adrenaline was higher in the salmon than in the trout for the temperature interval 2-17°C. The apparent affinities for adrenaline for the frequency at 8°C and 14°C and for the maximal tension responses at 2°C and 8°C were also highest for the salmon atrium.

Isolation and characterization of single myocardial cells from the quail, Coturnix coturnix japonica

1. The enzymatic cell isolation technique was applied to the bird heart resulting in myocytes of which 10-50% maintained their spindle-shaped morphology, excluded the vital dye, Evans blue and tolerated physiological concentration of Ca2+ ions. 2. The length of spindle-shaped myocytes was on average 289 +/- 7 microns, and the maximum width was 10.2 +/- 0.3 microns. The mean length of the sarcomeres was 2.18 +/- 0.03 microns. 3. In electron micrographs the fine structure of the spindle-shaped myocytes looked normal--regular sarcomeric organization with clear A and I bands, mitochondria with tightly located cristae and well-developed sarcoplasmic reticulum (SR). 4. Most (80%) of the spindle-shaped myocytes were quiescent in physiological calcium concentration and practically all of them could be induced to twitch by electric field stimulation. Some beat spontaneously showing mostly slowly-propagating (135 +/- 6 microns/sec at 20 degrees C) contraction waves, so-called phasic contractions. Sometimes spontaneous twitch-type contractions could also be seen.

Calcium paradox from cyclostome to man: a comparative study

In seven poikilotherm species, i.e. cyclostome, Myxine glutinosa; teleosts, Gadus morrhua; Platichtys flesus; amphibia, R. pipiens; R. temporaria; Xenopus laevis; reptiles, Vipera berus. Ca paradox could not be obtained in ventricular strips at 8-12 degrees C. In similar preparations from human atria at 30 degrees C and 37 degrees, Ca paradox was obtained similarly as in other homoiotherms. In homoiotherms, lowered temperature (below 30 degrees C) has a protective effect. Viper myocardium did not display Ca paradox at 12, 22 or 32 degrees C, whereas human myocardium displayed Ca paradox even at 30 C. It is postulated that the absence of Ca paradox in poikilotherms is not due to the low temperature. In hagfish (Myxine glutinosa) the absence of Ca paradox seems to be due to the specific conditions concerning Ca exchange in the myocardial cell (large glycocalyx).

Aging changes in the heart of a poeciliid fish, the guppy Poecilia reticulatus

Histological surveys of the hearts of guppies Poecilia reticulatus throughout their lifespan showed no aging changes until the fish were three years old. In younger fishes the hearts were healthy, even in three individuals with "wasting" disease, where there was considerable loss of muscle throughout the body. There was a loss of muscle fibers in the ventricle in old fish, and deposition of collagen in the bulbus arteriosus. Guppies of three years and older also had a marked accumulation of melanomacrophages in the atrium. It seems unlikely that degeneration of the heart is involved in mortality of guppies in the wild.

Absence of calcium paradox in the cardiac ventricle of the Atlantic hagfish (Myxine glutinosa)

Spontaneously beating strips of the cardiac ventricle of the cyclostome Myxine glutinosa were characterized with respect to dependence on extracellular calcium for the cardiac contractility at 8 degrees C. The force developing (Tmax) was reduced by 20-50% when exposed to calcium-free medium (+/- 10(-3)M EDTA) for 15-60 min. Return to normal Myxine Ringer (4.5 mM Ca2+) resulted in 120-130% recovery to Tmax without change in resting tension. These experiments show that the heart of this primitive vertebrate, analogous to that of other poikilotherms, does not display the "Ca-paradox" phenomenon. Being relatively insensitive to changes in extracellular Ca2+ the Myxine myocardium differs from that in most poikilotherms in other respects, e.g. in the mechanisms regulating beat to beat changes in intracellular Ca2+.

Comparative aspects of adrenergic receptors in the hearts of lower vertebrates

The cardiac adrenoceptors of lower vertebrates were characterized in atrial preparations. Adrenaline (A) potentiated the force and frequency of contraction in the spontaneously beating atria of the frog, trout and flounder and in electrically paced atrial strips from the shark. The inotropic responses of A were most pronounced at the lower temperatures for the frog and trout, while A enhanced frequency to a greater extent at higher temperatures in the frog atria. Atrial alpha-receptors activated by A at 8 degrees C could not be detected in any of the species under study. The apparent affinities for the inotropic and chronotropic responses of agonist in the frog (15 degrees C) and trout (8 degrees C) atria were: Iso greater than Sal greater than or equal to A greater than NA. A cocaine-sensitive uptake for A and NA was apparent in these atria, consistent with sympathetic innervation. The affinities for the catecholamines in the flounder and shark atria were not increased by cocaine, in accordance with absence of sympathetic innervation of the atria in these species. These atria were also insensitive to corticosterone. The affinities for A and NA were on the other hand higher in the sympathetically non-innervated atria of the flounder than in the innervated atria of the frog and trout. The apparent orders of relative affinities for agonists were Iso greater than A = NA greater than Sal for the flounder, and of the relative potencies Iso = A greater than NA greater than Sal for the shark atrium. The results are consistent with the hypothesis that catecholamines enhance cardiac performance in lower vertebrates chiefly via "adrenaline" receptors which resemble the beta 2-type of mammalian adrenoceptors in many respects. Unlike that in mammals, cardiac adrenaline receptors in the frog and trout are activated by the sympathetic neurotransmitter ("innervated" receptors). On the other hand, the adrenaline receptors of the flounder and shark are responding to the circulating catecholamines ("humoral" receptors). However, the flounder atrium, with equal affinities for A and NA, appears as an exception to the rule by having a mixed population of humoral beta 1- and beta 2-adrenoceptors, indicating a role for circulating NA in cardiac regulation in this species.