ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The relations between end-diastolic (D) and end-systolic (S) cavitary volumes (Vc), wall volumes (V10), and cavitary dimensions have been studied in the canine and human left ventricle. However, the models selected for left ventricular myocardium do not represent the real heart adequately for a fiber-by-fiber analysis of fiber orientation and sarcomere length during successive states of the ejection cycle. In this study, the endocardial and epicardial surfaces were postulated to be a nested set of truncated ellipsoidal shells of revolution where wall volumes were preserved fromDto S. Shell dimensions on the semiminor and semimajor axes,RandZ, respectively, were related toVcandVwby two representations: confocal and nonconfocal. If the focal lengthC= (Z2− R2)½andCis the same for each shell, then the shells are confocal, otherwise they are nonconfocal. From measuredVc,Vw, and epicardialZinD, shell dimensions were calculated for statesDand S, using both confocal and nonconfocal representations, and compared with the measured dimensions. When no empirical corrections were made, the calculated endocardialRin S underestimated the measuredRin S by 12%; moreover, the calculated epicardialRin S overestimated the measuredRin S by 4%. Endocardial and epicardial C measured 3.73 ± 0.33 (SE) cm and 3.79 ±0.34 cm, respectively, inDand 3.77±0.11 cm and 3.71 ±0.10 cm, respectively, in S.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The relations between end-diastolic (D) and end-systolic (S) fiber angles (α) and sarcomere lengths (s) have been previously studied at different sites in canine left ventricular myocardium. However, no postulates have been advanced for predicting a and s in successive states of the ejection cycle (Dor S) or at different sites in one state when the semimajor (Z) and semiminor (R) axes of the wall surfaces for successive states and the fiber orientations and sarcomere lengths at one site in one state are known. In this study, the myocardial fibers were regarded as the matrix of a myocardial continuum: they are prisoners of the heart wall and must comply with the movements of the wall. Using the same values as in the preceding article, the wall was treated as a nested set of truncated ellipsoidal shells of revolution with shell volumes preserved fromDto S. Both confocal and nonconfocal configurations were analyzed. In each shell, the fibers were assumed to follow a “helical” path with a constant advance in each turn about theZaxis (the simplest possible path). The results of this assumption were compatible with previously reported values of a and s measured at various sites in the left ventricular free wall in statesDandS. These results suggest a postulate for the heart wall: in the beating heart, each muscle fiber changes direction and length uniquely as the wall changes shape.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The way that contractility varies between beats—the force-frequency relationship—was determined for rabbit papillary muscles held at different lengths. When the maximum rate of rise of tension in a contraction, Fmax, was used as a measure of contractility, the way contractility changed between contractions was independent of length. That is, when the values of Fmaxobtained at one length were multiplied by an appropriate scaling factor, the force-frequency relationship determined at that length was indistinguishable from the force-frequency relationship determined at another length. If, however, the peak tension in a contraction was used as a measure of contractility, the Force-frequency relationship generally was not independent of muscle length. Therefore, it is proposed that the ratio of two values of Fmaxobtained by perturbing the rate of stimulation at any given length should be tried as a length independent index of the inotropic state of the muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Afferent receptor discharge originating in the atria was recorded from slips of the cervical vagus in the open-chest dog. The activity of two types of atrial receptor endings was identified. Type A receptors exhibited a discharge pattern that was synchronous with theawave of the atrial pressure pulse in the control recordings, and type B receptors discharged only during the v wave of the atrial pressure pulse in the control recordings. Atrial arrhythmias (flutter or fibrillation) were induced by mechanical stimulation of the area around the sinoatrial node. During atrial arrhythmias, there was a moderate rise in mean left atrial pressure (7.5 ± 0.7 cm H2O to 8.6 ± 0.6 cm H2O during arrhythmias in which type B receptors were studied, 6.1 ± 0.1 cm H2O to 7.8 ± 0.4 cm H2O during arrhythmias in which type A receptors were studied), a fall in aortic blood pressure, and a decrease in right atrial force. Atrial contractions were asynchronous and rapid. Type A atrial receptors showed a relatively greater increase in discharge (184.1%) during fibrillation than did type B atrial receptors (27.5%). These experiments demonstrated that both types of atrial receptors increased their discharge rate during atrial arrhythmias, indicating that they might be involved in a reflex diuresis which occurs during these arrhythmias in humans.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The reactivity of vascular smooth muscle in helical strips from femoral arteries of normotensive, spontaneously hypertensive, renal hypertensive, and deoxycorticosterone acetate— (DCA-) hypertensive rats was studied. Spontaneous rhythmic contractions occurred in 25 of the 30 strips from the three groups of hypertensive rats and in only 2 of the 10 strips from normotensive rats. Strips from renal and DCA hypertensive rats had lower thresholds to epinephrine and potassium chloride (KCl) than did strips from spontaneously hypertensive and normotensive rats. Lanthanum (2.5 mM) caused contraction of all 10 strips from spontaneously hypertensive rats but failed to cause contraction of any strip from the other three groups of rats. Strontium (5 mM) caused contraction in 8 of 10 strips from spontaneously hypertensive rats but caused contraction in only 7 of the 30 strips from the other three groups. The optimal calcium concentration for tension development in response to a KCl stimulus was approximately twice as high for strips from hypertensive rats as it was for strips from normotensive rats. Strips from DCA-hypertensive rats showed less tachyphylaxis to angiotensin II than did strips from the other three groups of rats. These results quantify our earlier observation that the reactivity of vascular smooth muscle from hypertensive rats is importantly different from that of normotensive rats. In addition, the study delineates individuality in vascular smooth muscle reactivity in different types of experimental hypertension. The results suggest that the cell membrane of the vascular smooth muscle in the hypertensive rat is more labile than that in the normal rat.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

14C-Labeled adenosine, inosine, hypoxanthine, and adenine were extracted by the isolated rat heart in amounts proportional to their concentration in the perfusion medium between 0.05 and 5 μM. With each of the precursor materials, nearly all of the radioactivity retained by the heart was identified as acid-soluble nucleotide. Nucleotide formation from the four isotopic precursors occurred at similar rates when the concentration of the precursors was below 1 μM. Above this concentration, the heart appeared to utilize adenosine for nucleotide synthesis at rates three to five times those for the other purines. Several experimental approaches were employed to determine the predominant enzymatic routes in the rat heart for the conversion of the nucleosides adenosine and inosine to nucleotides. The results indicated that adenosine was directly phosphorylated to 5'-adenosine monophosphate by a nucleoside kinase. Inosine appeared to proceed to the nucleotide, at least partially, through an initial conversion to hypoxanthine.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

A highly specific, sensitive (25 pg) radioimmunoassay for prostaglandin A is described; the assay is characterized by high reproducibility (coefficient of variation 1–2%) and low cross-reactivity with respect to PGE1and PGE2(10%), PGB2(15%), and PGF2α(0.01%). High specificity for PGA was obtained by chromatographic separation of the prostaglandins. Since it has been suggested that PGA is a natriuretic “hormone,” the concentration of PGA in the renal cortex, outer medulla, and papilla was determined in rabbits on low-sodium and high-sodium diets in the presence and the absence of the prostaglandin synthetase inhibitor indomethacin. In rabbits on the low-sodium diet (12 mEq/24 hours). PGA2 was 15 ± 4 pg/mg in the cortex, 502 ± 67 pg/mg in the outer medulla, and 3740 ± 640 pg/mg in the papilla. In rabbits on saline loading (56 mEq/24 hours), cortical and outer medullary PGA2 rose to 32 ± 6 pg/mg and 1275 ± 290 pg/mg, respectively, but papillary PGA decreased to 1842 ± 480 pg/mg. PGA concentration in the outer medulla and papilla was markedly inhibited by indomethacin (50 mg/day), and this inhibition was associated with sodium retention. The results indicated that sodium induced papillary synthesis of PGA and intrarenal circulation of the prostaglandin to the outer medulla and the cortex possibly via the long veins of the outer medulla occurred. The results are compatible with PGA2involvement in salineinduced natriuresis.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The combined effects of low-frequency stimulation of the renal sympathetic nerves and reductions in renal arterial blood pressure on various hemodynamic parameters of the in situ kidney and on renal venous renin levels were determined in 17 dogs. Autoregulation of flow (measured using noncannulating electromagnetic probes) and glomerular filtration (measured using continuous extraction of131I-iothalamate) was followed before, during, and after nerve stimulation. Stimulation of isolated renal nerves (0.5 msec, 10–15 v, 0.1–3.0/sec) produced distinct changes in the release of renin with only minimal changes in the autoregulatory curves for glomerular filtration rate and renal plasma flow. Reducing arterial blood pressure from 150 to 50 mm Hg caused an increase in the release of renin from 4 to 35 ng/ml hour−1. Stimulation of the renal nerves increased renin production at both pressures (from 4 to 10 ng/ml hour−1at 150 mm Hg and from 35 to 50 ng/ml hour−1at 50 mm Hg). In fact, renal nerve stimulation elicited increases in renin release at all pressures examined. In contrast, sodium excretion following nerve stimulation was depressed at comparable sodium loads in spite of minimal changes in renal hemodynamics. It appears that the effect of the renal sympathetic nerves on renin release is evident at all pressures; however, the sympathetic nerves are proportionately more important at pressures above 100 mm Hg and the renal artery pressure plays a greater role at pressures below 115–100 mm Hg.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

In closed-chest atropinized dogs anesthetized with chloralose and ventilated artificially, the aortic nerves were cut beneath the nodose ganglion, and the carotid sinuses were either denervated or vascularly isolated and maintained at a pressure of 40 mm Hg. Denervation was established by the failure of the pressoreceptor systems to respond to mechanical stimulation. Cold block or section of the cervical vagi resulted in statistically significant increases in arterial blood pressure (18%), heart rate (3%), central venous pressure (13%), hind-limb perfusion pressure (12%), pressure within the occluded spleen (18%), and efferent renal sympathetic nerve activity (28%). There was no change in saphenous vein perfusion pressure. The vascular responses were abolished by a-receptor blockade and were not affected by section of the vagi at the diaphragm. When the pressure in the vascularly isolated innervated carotid sinuses was varied from 40 to 220 mm Hg, the vascular responses to vagal block decreased steeply between 100 and 160 mm Hg and were absent at 200 mm Hg. Thus, receptors in the cardiopulmonary region with afferent vagal fibers exert a continuous restraint on the sympathetic adrenergic outflow to resistance and capacitance vessels, especially when the input from the carotid baroreceptors is decreased.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID