Rat Auricles Research Articles

GENDER DIMORPHISM OF CHANGES IN THE SKIN MICROCIRCULATION OF RATS ON THE BACKGROUND OF ACUTE COLD TRAUMA

Gender factors play an important role in the prevention, preva- lence and specifics of the course of various pathological conditions, among which cold injury occupies an important place. The role of gender in its pathogenesis remains poorly understood. The aim. To assess sex-specific changes in the microcirculation of target organs exposed to extremely low temperatures during experimental acute cold trauma (ACT) in rats. Materials and methods. Experiments were performed on male and female sexually mature and castrated Wistar rats. Acute cold trauma (ACT) was modeled by keeping the animals at -180ºС for 2 hours. The microcirculation coefficients of the skin of the hind limbs, auricles, and tail of animals were determined using Biopas electrophysiological equipment (USA) non-invasively using a surface sensor. We compared the changes before and 30 minutes after the action of the cold factor. Statistical processing of the results was carried out using standard descriptive methods. The results. A 2-hour stay of animals under the influence of extremely low temperatures causes a significant drop in blood supply in animals of both sexes. The degree of changes has a clear sexual dimorphism with a predom- inance of pathological processes in male animals. In males, the coefficient of microcirculation of the lower limbs and auricles decreased by 72.2 and 55.3 %, and in the tail by 35.1 %, compared to this indicator before the effect of the cold factor (p < 0.05), on the other hand, in female rats changes in similar indicators were 66.5 and 44.3 % (lower limbs and auricles), and tail perfusion by 18.6 % (p < 0.05). ACT in castrated female rats caused more extensive hemoperfusion disorders compared to males: the microcirculation index of the tail, hind limbs, and auricle in male rats on the background of ACT decreased by 25.4, 66.4, and 40.7 %, respectively (p < 0.05), whereas in animals of the opposite sex – by 32.5, 78.8 and 47.4 %, respectively. Conclusion In sexually mature female rats without changes in hormonal status, a greater resistance to microcirculation disorders during experimental acute cold injury was found. The reason for these differences is the effect of sex hormones, since castration of males increases the resistance of the vascular system of animals to the action of a cold factor, while ovariectomy of females – on the contrary, increases the degree of microcirculatory lesions of the most vulnerable organs to the action of extremely low temperatures

Preliminary study on two analytical methods for evaluation of traditional Chinese medicine syndromes model in rats with blood stasis due to sleep deprivation

The comparison on evaluating blood stasis syndrome in sleep deprived rats was carried out by using R, G, B image analysis of Tongue and palm as well as auricle, palm surface laser Doppler flow perfusion. The experiment was performed by means of a small platform on the water environment for sleep deprivation. The rats were weekly weighed at fixed time, and their macroscopic signs were observed; and their tongue and palm images of the control and model group were respectively collected by the SLR camera at the 2nd, 4th and 6th week. Then the color saturation analysis was performed by means of proofreading with the standard colorimetric card. At the same time, the laser dopper flowmetry was used to analyze the perfusion of auricle and foot flow in rats. It turned out that there was no significant difference in the R,G,B value of the tongue and palm in rats between normal group and model group at the first stage(at the 2nd week), so were the perfusion of auricle and foot flow in rats. But at the second stage (at the 4th week), the R value of tongue in model group rats was obviously lower than that in normal group(P<0.01), and the other value (G,B) of tongue in module rats had a decease tendency, but there was no statistical significance. However, the perfusion of left and right auricle flow in model group rats were dramatically decreased as compared with the normal group(P<0.01); there was still no significant difference in the perfusion of the palm between two groups. It was found that R,G,B value in model group had a lower trend as compared with the control group of the tongue and palm images at the third stage (at the 6th week), but no statistically significant difference. The perfusion of left and right auricle flow in model group was constantly decreased as compared with the normal group(P<0.01).Right and left foot blood flow was lower than the normal group, but no statistically significant difference. We can safely conclude that the results of the R, G, B values of the tongue in rats could objectively reflect the characteristics of the rats with blood stasis syndrome, which were consistent with the diagnosis of clinical tongue image. As a method of microcirculation evaluation, the surface laser doppler perfusion of auricle can exhibit the characteristics of blood stasis in model rats, but also was more objective and reproducible. Therefore, the combination of R, G, B value of tongue as well as auricle laser doppler blood flow is more beneficial to the objective evaluation of index in the later study of traditional Chinese medicine blood stasis syndrome model.

Effect of Total Alkali in Leonuri Herba on rat ear acne model of serum IL-6 level, Thymus and Spleen Tissue Morphology.

To investigate the effect of Total Alkali in Leonuri Herba (TALH) on rat ear acne model of serum IL-6 level, Thymus and Spleen Tissue Morphology. The rats were divided into the TALH group at high, medium and low doses (200 mg kg−1, 100 mg·kg−1, 50 mg·kg−1), the tanshinone group (360 mg·kg−1), model group and the blank group. All the rats were administrated once a day for 14 days. At the same time on the first day, the rats in the blank group were injected normal saline in the stomach and also had intradermal injection of sterile saline in the auricle. The rats in other groups (model group were lavaged with physiological saline) were injected intradermally auricle spare Staphylococcus epidermidis bacteria liquid. After the injection, the rat ear swelling rate was calculated for 5 consecutive days in terms of rat auricle thickness measurement. 1 h after the last administration, the eyeball blood was removed, centrifuged to separate serum, and measured to be at serum IL-6 level; The tissue sections of thymus and spleen were observed according to morphology criteria. Compared with the blank group, the level of IL-6 in serum of the rats in the model group was remarkably higher, and those in the thymus and spleen groups were remarkably lower, indicating the rat ear acne model is successful. Compared with the model group, the rats in the TALH group can remarkably make serum IL-6 level decrease, causing significant thymus cortical thickening and increased spleen sections, and remarkably increasing the lymphocytes of thymus and spleen. The effect of large dose in the TALH group is the best and increases with the increase of the dose and curative effect. The TALH treatment of acne may be related to the reduction of serum IL-6 levels and the resistance of the atrophy of the thymus and spleen on the rat ear acne model.

Morphological restructuring of myocardium during the early phase of experimental diabetes mellitus.

The purpose of this study was to determine the specific features of the morphological restructuring of the myocardium in the early stage of experimental diabetes mellitus (DM). Experimental type 1 DM rat model was developed by intraperitoneal injection of alloxan solution at a dose of 30 mg per 100 g body mass. After 1 month, 3 mL of blood was drawn by heart puncture and the plasma separated by centrifugation for biochemical analysis. Plasma glucose, insulin, and glycosylated haemoglobin in whole blood were determined. Light microscopy and morphometric studies were conducted of histological slices of the hearts of experimental animals. The investigation of heart morphology showed a statistically significant alteration in chamber wall thickness in the right auricle in rats with alloxan-induced DM. A change in cardiomyocyte diameter in myocardium slices was observed in all chambers of DM rats except for the left ventricle. Average cardiomyocyte diameter in rats with experimental DM increased by 26.6% and 15.5% in the right auricle and right ventricle, respectively, while average cardiomyocyte diameter in the left auricle decreased by 20.8%. Histological investigation of the heart following alloxan injection demonstrated, under the epicardium, distended vessels of the venous collecting microcirculatory system. Aggregation and agglutination of red blood cells and endothelial cell destruction were found in some vessels. In the early stage of DM development, structural alterations in the microcirculatory channels and myocardiocytes can be observed in the heart. These structural alterations were most evident in the right chambers of the heart.

Establishing a Composite Auricle Allotransplantation Model in Rats: Introduction to Transplantation of Facial Subunits

Allografts from cadaveric sources may be an alternative for replacing the missing auricle. In this report, the technical aspects of orthotopic composite auricle allotransplantation and an effective short-term immunosuppression protocol in a rat model are described. A total of seven transplantations were performed in the experimental group. The donors were Brown Norway (RT1(n)) rats and the recipients were Lewis (RT1(1)) rats. In the pilot study, 11 isotransplantations (Lewis to Lewis) were performed in either heterotopic (n = 4) or orthotopic (n = 7) locations to establish the surgical technique. Composite auricle allografts were harvested and transplanted based on the posterior facial vein, the external carotid artery, and the great auricular nerve. A plastic square mold sutured over the transplants was used to prevent mechanical trauma to the transplants. Cyclosporine A initiated as 16 mg/kg/day for 2 weeks and tapered to a dosage of 8 mg/kg/day for another 2 weeks was the only immunosuppression regimen. All allografts survived with perfect viability for the follow-up period of 30 days. There were no signs of rejection, infection, or graft-versus-host disease, although significant weight loss was observed resulting from the immunosuppressive treatment. However, signs of rejection started 4 to 6 days after cessation of the cyclosporine A treatment, including edema, localized epidermal desquamation, and erythema formation that eventually progressed to necrosis within 11 to 14 days. The histologic outcomes were well correlated with the macroscopic appearance. It is feasible to elevate and transplant the composite auricle in rats as a single neurosensorial facial subunit. A tapered dose of cyclosporine A from 16 mg/kg to 8 mg/kg allows maintaining allograft survival for 30 days across a strong major histocompatibility complex barrier. This model is reliable and reproducible and has the potential to be used for future immunologic studies to prevent or to induce transplantation tolerance.

Small GTP-binding protein, Rab6, is associated with secretory granules in atrial myocytes.

Rab proteins, a subfamily of small GTP-binding proteins, have been shown to play key roles in regulation of vesicular traffic in eukaryotic cells. In this study, we have intended to identify, the atrial granule-associated Rab proteins that seem to be required for formation or intracellular transport of the granules. Atrial granules contained at least four small GTP-binding proteins, and we have demonstrated by biochemical analysis that one of the small GTP-binding proteins associated with the atrial granules is a Rab6 protein (Rab6p). Rab6p was also detected in highly purified zymogen granules of pancreatic exocrine gland. Immunogold electron microscopy performed on ultrathin cryosections of rat auricle revealed that Rab6p was associated with the atrial granule membranes. Association of Rab6p with the atrial granule membranes was also confirmed by immunodiffusion electron microscopy in agarose-embedded atrial granules. These data indicate that Rab6p is associated with the atrial granules and that it might function in the intracellular traffic of the secretory granules in the atrial myocytes.

P-720 - Effect of Oren-gedoku-to on microvascular perfusion in the rat auricle measured using laser-Doppler flowmetry.

P-720 - Effect of Oren-gedoku-to on microvascular perfusion in the rat auricle measured using laser-Doppler flowmetry.

Effects of Water Deprivation and Morphine Administration on Atrial Natriuretic Peptide mRNA Levels in Rat Auricles

We investigated the influences of two potent stimuli, water deprivation (5 days) and morphine administration (100 mg/kg), on the level of atrial natriuretic peptide (ANP) mRNA in the rat auricles. The ANP mRNA level was measured by Northern blot hybridization analysis. The plasma concentration of ANP decreased in water deprived rats, and the ANP mRNA levels in both auricles of these rats were lower than those of the control, particularly in the left auricle. Thirty minutes after the injection of morphine, the plasma concentration of ANP markedly increased, while morphine increased the right auricular ANP mRNA level 4 hr after the administration. These data suggest that these stimuli can change ANP gene expression in the auricles and that the changes are induced differentially in both auricles.

The mechanism of positive inotropy induced by adenosine triphosphate in rat heart.

When applied extracellularly in the micromolar range, ATP and related compounds induced a positive inotropy in the rat papillary muscle. This was also true in the rat auricle after pertussis toxin treatment. Then, in both tissues, ATP further increased the contraction after a maximal beta-adrenergic stimulation. The increase in contractile force could be related to the increase in the calcium current. The L-type calcium current was measured by whole-cell patch-clamp recording in single cells isolated from the rat ventricle after the sodium and potassium currents were inhibited by tetrodotoxin and cesium, respectively. When added alone, 10 microM ATP increased the calcium current by 60%. Adenosine 5'-O-(3-thiotriphosphate) was also able to increase calcium current. Adenosine was much less effective, and GTP, UTP, CTP, and ITP were without effect. A similar increase in calcium current was observed when ATP was added in addition to a maximal stimulation by a beta-adrenergic agonist or after internal perfusion with cyclic AMP. However, this increase was preceded by a transient decrease whose origin could not be attributed to a P1-purinergic agonistic effect of ATP. The transient decrease was not elicited by adenosine or in a magnesium-free HEPES solution and was not suppressed after pertussis toxin treatment. This effect appeared related to the variations in the holding current also observed upon ATP application. Together with vasodilation, ATP and adenine compounds induced positive inotropy. The latter effect could be attributed in part to the increase in calcium current and was independent of cyclic AMP. Both effects are complementary with the beta-adrenergic stimulation and can help healthy cells to compensate the failing zone from which ATP could be released.

Cell-to-cell communication in the heart: structure-function correlations.

The communicating cell junctions that ensure the electrical and diffusional continuity of the intracellular space in the heart fibres can be switched from their normal conducting, or opened state, to an exceptional non-conducting, or closed state. This electrical uncoupling is observed after cell injury in the presence of Ca2+ ions in the extracellular fluid, after metabolic inhibition and in the presence of aliphatic alcohols (C6 to C9). The correlations between electrical uncoupling and gap junction morphology in the heart are briefly reviewed. A decrease of the distance between P-face particles and between the E-face pits has been found in all investigations, but the functional significance of this observation is not understood at present. A quantitatively very similar decrease of the average particle diameter (about -0.7 nm) has been measured in glutaraldehyde-fixed sheep Purkinje fibres and in unfixed, quickly frozen rat auricles that had been electrically uncoupled by three different procedures. About half of this decrease was reversible on short-term electrical recoupling (within 20 min). It is concluded that a measurable decrease of the connexon diameter correlates with electrical uncoupling.

Quantitative gap junction alterations in mammalian heart cells quickly frozen or chemically fixed after electrical uncoupling.

The gap junction morphology was quantified in freeze-fracture replicas prepared from rat auricles that had been either quickly frozen at 6 K or chemically fixed by glutaraldehyde, in a state of normal cell-to-cell conduction or in a state of electrical uncoupling. The general appearance of the gap junctions was similar after both preparative procedures. A quantitative analysis of three gap junctional dimensions provided the following measurements in the quickly frozen conducting auricles (mean +/- SD): P-face particles' diameter 8.27 +/- 0.74 nm (n = 5709), P-face particles' center-to-center distance 10.78 +/- 2.12 nm (n = 4800), and E-face pits' distance 9.99 +/- 2.19 nm (n = 1600). Corresponding values obtained from chemically fixed tissues were decreased by about 3% for the particle's diameter and about 5% for the particles' and pits' distances. Electrical uncoupling by the action of either 1 mM 2-4-dinitrophenol (DNP), or 3.5 mM n-Heptan-1-ol (heptanol), induced a decrease of the particle's diameter, which amounted to -0.69 +/- 0.01 nm (mean +/- SE) in the quickly frozen preparations and -0.71 +/- 0.01 nm in the chemically fixed ones. The particles' distance was decreased by -0.96 +/- 0.04 nm in the quickly frozen samples and by -0.90 +/- 0.03 nm in the chemically fixed ones and the E-face pits' distance was similarly reduced. All differences were statistically significant (P less than 0.001 for all dimensions). Electrical recoupling after the heptanol effect promoted a return of these gap junctional dimensions towards normal values, which was about 50% complete within 20 min. It is concluded that very similar morphological alterations of the gap junctional structure are induced in the mammalian heart by different treatments promoting electrical uncoupling and that these conformational changes appear independently of the preparative procedure. The suggestion that the observed decrease of the particles' diameter is genuinely related to the closing mechanism of the unit cell-to-cell channel set in their centers is thus confirmed.

Effect of the macrocyclic polyester 15-crown-5 on ionic permeability of excitable membranes

The macrocyclic polyether 15-crown-5 at a concentration of 5 . 10(-5)-10(-3) M reduced the frequency of the contractions of an isolated rat auricle, increasing the refractory period of the contractions. The polyether lowered the rate of activation of the slow input current of rat spinal ganglionic neurons and blocked the sodium channels of the electroexcitable membrane without disturbing the function of activation and inactivation mechanisms. The compound under study considerably delayed the onset of and decelerated reactivation of the sodium input current. These actions were calcium-dependent, becoming more demonstrable with reduction of Ca2+ concentration outside the cell. 15-Crown-5 interfered with the action of Ca2+ on the lipid bilayer membrane potential. It is assumed that all the effects described are determined by the formation of 15-crown-5-Ca2+ complexes, thereby leading to the impairment of the packing of the membrane lipoprotein matrix.

Acute toxicity of PR toxin, a mycotoxin from Penicillium roqueforti

The toxic effects of PR toxin were observed in mice, rats, anesthetized cats and isolated rat auricle preparations. In mice and rats the toxic effects included abdominal writhing, decrease of motor activity and respiratory rate, weakness of hindleg and ataxia. In mice, the i.p. ld 50 was 5.8 mg/kg. In mice, rats and cats PR toxin given i.p. caused ascites fluid and edema in the scrotum and lungs, and i.v. injection caused edema in the lungs, giving rise to a large volume of pleural and pericardial fluid. In rats, at the ld 50 dose level (11.6 mg/kg, i.p. and 8.2 mg/kg, i.v.), the water content in the lungs was increased, but in the skin it was decreased. Blood K +, hematocrit, red blood cell, white blood cell, hemoglobin, uric acid, cholesterol, blood urea nitrogen and alkaline phosphatase concentrations were all increased, while the total protein and albumin contents were decreased after i.p. injection of PR toxin. High content of protein was found in the pleural fluid and fluid due to ascites. In anesthetized cats the blood pressure and respiratory rate were progressively decreased and the heart rate was reflexly increased after i.p. injection. The i.v. injection produced a multiple response on the arterial blood pressure, but with a progressively decreasing heart rate. Arrhythmias were observed in the late shock stage in the case of i.p. or i.v. injection. In the isolated rat auricle preparations contractile force was more affected than heart rate. We conclude that PR toxin produced acute toxic effects in animals via an increase of capillary permeability and a direct damage to the lungs, heart, liver and kidneys.

Cytofluorometric study of small highly fluorescent cells in rat auricles after a single injection of guanethidine

Small highly fluorescent cells (SHF cells) in the tissue of the mammalian auricles have been found close to vessels and nerves in zones of distribution of autonomic intramural ganglia [7]. Two types of SHF cells are distinguished: type I) single cells with wellmarked outgrowths; type II) round cells, grouped in clusters. According to Bjorklund et al. [3], SHF cells in rat auricles contain dopamine. Type I SHF cells have been classed by some workers as interneurons, whereas type II cells are generally regarded as performing an endocrine function. Activity of type I cells may evidently be regulated by the parasympathetic innervation, for cholinergic synapses have been found on some of them [6]. Type II cells may probably be under the influence of the sympathetic nervous system. Investigations by Jacobowitz [4] have demonstrated changes in fluorescence of auricular SHF cells by Falck's method after injection of reserpine. It is interesting to study how parameters characterizing catecholamine metabolism in SHF cells depend on the sympathetic mediator level in the heart. The absence of any marked effect of the cytotoxic action of guanethidine on SHF cells and the sharp fall in the noradrenalin (NA) level in the heart after a single injection of guanethidine indicate that this is a suitable model for use when assessing how SHF cell function depends on the sympathetic innervation.

In vivo and in vitro studies on the mechanism of cardiovascular effects of Wu-Chu-Yu (Evodiae fructus).

The effects of the Chinese herb Wu-Chu-Yu (Evodiae fructus) on the cardiovascular function were assessed in anesthetized cats, conscious rats, and isolated preparations of rat aortic strip and auricle. In anesthetized cats, intravenous administration of alcohol-water crude extracts of Wu-Chu-Yu (0.03-0.24 g/kg) produced a dose-dependent hypertension and an increased contractile force of nictitating membrane which lasted for more than 5 min in higher doses. Phentolamine, but not tetraethylammonium antagonized hypertension and the increased contractile force of nictitating membrane induced by Wu-Chu-Yu. In conscious rats, hypertension was also observed by intraperitoneal administration of Wu-Chu-Yu (6 g/kg). Bilateral nephrectomy, administration of phentolamine or propranolol, all significantly decreased the hypertensive effect of Wu-Chu-Yu. Pretreatment with reserpine 24 hours in advance did not change the pressor effect of the crude extract. In aortic strip preparations, Wu-Chu-Yu caused the increase of contractile force, and the dose-response curve was parallel shift to the right in the presence of phentolamine. In auricle preparations, Wu-Chu-Yu produced positive inotropic and positive chronotropic effects, and the presence of propranolol changed the slope of Wu-Chu-Yu's dose-inotropic effect curve and reversed the chronotropic effect from positive to negative. Both in vivo and in vitro results suggested that alpha and beta adrenoceptors were directly involved in the cardiovascular effects of Wu-Chu-Yu.

Papaverine enhances the negative inotropic effect of acetylcholine in rat auricles

The negative inotropic effect of acetylcholine in rat left auricles is enhanced in the presence of the phosphodiesterase inhibitor papaverine. This result favours the idea of a cyclic GMP-mediated action of acetylcholine in the heart.

Activation of DNA synthesis in cells of the atrium and auricle in rats with infarction of the left ventricle

From the first to the 15th day of experimental infarction of the left ventricle the number of DNA-synthesizing nuclei of connective-tissue cells was increased in the auricle and atrium of the rat heart. The number of labeled myocyte nuclei reached a maximum on the 5th day of the experiment and the number of mitoses in the muscle cells of the auricle on the 7th day. In the muscle cells of the atrium very few nuclei with incorporation of [3H]thymidine and only solitary pathological mitoses were observed. After healing of the infarct an increased number of polyploid nuclei was observed in the cardiomyocytes of the auricle and atrium.

The action of a toxin from the sea anemone Anemonia sulcata upon Mammalian heart muscles.

The cardiac activity of toxin II, a basic polypeptide (m.w.: 4770) from the sea anemone Anemonia sulcata, was investigated in isolated electrically driven guinea-pig and rat auricles, Langendorff heart preparations of guinea-pigs and cat heart-lung preparations. Low concentrations of toxin II (2-100 nM) evoked a dose-dependent positive inotropic effect in the three different heart muscle preparations investigated. Higher concentrations of toxin II produced toxic symptoms like contracture and arrhythmia in auricles and atria (about 25 nM). In isolated cat hearts high toxin II concentrations (about 160 nM) caused unusual toxic symptoms such as long periods of ventricular fibrillation alternating with periods of normal cardiac activity. In rat and guinea-pig auricles as well as in Langendorff hearts of guinea-pigs the extent and rate of the positive inotropic effect induced by toxin II depended on the extracellular calcium concentration (0.45 to 2.7 mM). Toxin II did not alter the heart rate in spontaneously beating isolated cat hearts. In electrically driven guinea-pig auricles, the rate of the inotropic effect induced by toxin II was accelerated by increasing stimulation frequencies. Toxin II did not change the coronary flow in Langendorff heart preparations of guinea-pigs.

Cyclic AMP and cyclic GMP may play opposing roles in influencing force of contraction in mammalian myocardium

CYCLIC AMP and cyclic GMP have been suggested to play opposing regulatory roles in several biological systems1. Supporting evidence for the yin yang hypothesis of opposing biological regulation has been obtained in sympathetic ganglia2,3 and pyramidal neurones in the rat cerebral cortex4. In the mammalian heart, the role of cyclic AMP in mediating the positive inotropic response to catecholamines was advanced by the observation that the inotropic effect was preceded by an increase in cyclic AMP levels5. On the other hand, the levels of cyclic GMP were found to be increased after cholinergic stimulation6. In frog, oscillations of cyclic AMP7 and cyclic changes in the levels of cyclic AMP and cyclic GMP8 during the cardiac cycle have been reported. The importance of cyclic AMP for the inotropic effects of catecholamines was confirmed by the observation that the dibutyryl derivative of cyclic AMP exerted a positive inotropic effect in cat papillary muscles9 and in the isolated perfused hearts from rabbits, rats and guinea pigs10. I now report a direct negative inotropic effect of 8-Br-cyclic GMP on force of contraction (Fc) in rat auricles and papillary muscles from cats.

Adrenaline, DB-c-AMP and myocardial 45Ca exchange. Comparative studies in rat and guinea-pig auricles.

The positive inotropic effect of adrenaline has been assumed to result from an increase in the intracellular level of c-AMP which, in turn, might enhance the permeability of the cardiac cell membrane to Ca2+. In order to further test this hypothesis, the effects of cyclic N6-2′-O-dibutyryl-adenosine-3′,5′-monophosphate (DB-c-AMP; 10−3 M) on mechanical performance, 45Ca uptake and total tissue calcium concentration were investigated in electrically stimulated (120 beats/min) left auricles isolated from female rats weighing 180–220 g. The experiments were performed in Tyrode solution containing 0.9 mM CaCl2; the duration of 45Ca exposure was 3–60 min. In this study, DB-c-AMP markedly enhanced contractile force but the drug failed to detectably increase 45Ca exchange (Figs. 1 and 2). This finding seemed to indicate that the effects of DB-c-AMP on myocardial 45Ca exchange were completely different from those of adrenaline which previously (and in this study; Fig. 4) has been shown to accelerate 45Ca exchange in auricles obtained from guinea-pigs of “normal” size. However, under the conditions used, adrenaline (2.2–5.5×10−6 M) also failed to significantly enhance 45Ca exchange not only in rat auricles (Fig. 3) but also in small auricles isolated from very light guinea-pigs (body-weight 75–150 g; Fig. 4). From these findings it is concluded that druginduced changes in membrane calcium fluxes, which possibly occur, only might have escaped detection under the present experimental conditions. The “pool saturation phenomenon” previously described by Grossman and Furchgott (1964b; 1964c) is discussed to be the underlying mechanism. Thus, substantial conclusions on the effects of DB-c-AMP on myocardial Ca fluxes can as yet not be drawn. They must await experiments in which an adrenaline induced increase in cardiac 45Ca exchange becomes detectable.