Expression of candidate genes for residual feed intake in Angus cattle.

Residual feed intake (RFI) has been adopted in Australia for the purpose of genetic improvement in feed efficiency in beef cattle. RFI is the difference between the observed feed intake of an animal and the predicted feed intake based on its size and growth rate over a test period. Gene expression of eight candidate genes (AHSG, GHR, GSTM1, INHBA, PCDH19, S100A10, SERPINI2 and SOD3), previously identified as differentially expressed between divergent lines of high- and low-RFI animals, was measured in an unselected population of 60 steers from the Angus Society Elite Progeny Test Program using quantitative real-time PCR. Results showed that the levels of gene expression were significantly correlated with RFI. The genes explain around 33.2% of the phenotypic variance in RFI, and prediction equations using the expression data are reasonably accurate estimators of RFI. The association of these genes with economically important traits, such as other feed efficiency-related traits and fat, growth and carcass traits, was investigated as well. The expression of these candidate genes was significantly correlated with feed conversion ratio and daily feed intake, which are highly associated with RFI, suggesting a functional role for these genes in modulating feed utilisation. The expression of these genes did not show any association with average daily gain, eye muscle area and carcass composition.

Effects of increased pressure inside or outside ventricles on total and regional myocardial blood flow.

Increasing pressures to 30 mmHg in right (RV) and left (LV) ventricles and surrounding heart (SH) in isolated, arrested, maximally vasodilated, blood-perfused dog hearts shifted pressure-flow (PF) curves rightward and increased zero flow pressure (P(zf)) by an amount equal to the RV applied pressure, SH applied pressure, or two-thirds of the LV applied pressure. There were comparable increases in coronary venous pressures. Increasing LV or SH pressures decreased coronary blood flows, especially in the subendocardium. Decreases in driving pressure decreased flows in all layers, but even with driving pressure of 5 mmHg, a few subepicardial pieces had flow. We conclude with the following: 1) raising pressures inside or outside the heart shifts PF curves and raises P(zf) by increasing coronary venous pressure; 2) the effects are most prominent in the subendocardial muscle layer; and 3) as driving pressures are decreased, there is a range of P(zf) in the heart with the final P(zf) recorded due to the last little piece of muscle to be perfused.

Quantification of the extraction fraction for gadopentetate across breast cancer capillaries.

To quantify the extraction fraction, E, for gadopentetate across tumor capillaries, R3230 adenocarcinomas were implanted in the mammary fat pads of seven rats. The value of E was determined by using a two-compartment tissue model in which the endothelial transfer coefficient, K(PS) (ml x min(-1) x cc(-1) of tissue), was estimated from the model fitted to changes in R1 relaxation time (deltaR1; s(-1)) measured by dynamic three-dimensional spoiled gradient recalled magnetic resonance imaging after injection of 0.1 mmol x kg(-1) of gadopentetate dimeglumine. The plasma flow rate through the tumor capillaries, Fp, (ml x min(-1) x g(-1) of tissue), was independently measured with fluorescent microspheres. E could be calculated by the relationship, E = K(PS)/Fp. The mean E for gadopentetate in the R3230 tumor was 0.197 +/- 0.118 with a range of 0.123-0.454. The relatively small mean value of E for gadopentetate allows a fair approximation of the permeability surface area product by K(PS) in this R3230 tumor model.

Changes in contractility and afterload have only slight effects on subendocardial systolic flow impediment.

To test the hypothesis that contractility did not greatly influence systolic impediment to subendocardial flow we perfused the coronary artery at 70 mmHg and altered aortic pressure in 7 dogs and contractility in another 7. We measured myocardial systolic flow impediment (SFI) by comparing regional flows while beating and during asystole. Cardiac contraction impeded 29% of subendocardial asystolic flow, which was not affected by either intervention. In subepicardium, contraction increased flow by 25%, but dobutamine impeded systolic flow. Subepicardial SFI was only 16% of subendocardial SFI. Dobutamine slightly decreased estimated percent systolic myocardial blood flow (%SMBF) in subendocardium (+/- 12%) but decreased subepicardial %SMBF (45.5 to 17.4%). Phasic coronary flow pulsatility increased more with dobutamine than increased afterload, and pulsatility and SFI correlated only in subepicardium. Systolic-to-total coronary flow ratio and %SMBF did not correlate closely in subendocardium. SFI was most prominent in the subendocardium, whereas subepicardial SFI mainly determined epicardial coronary flow pulsatility. We conclude that the effects of contractility changes differ when evaluating regional SFI vs. phasic flow pulsatility.

Effects of inhibiting neutral endopeptidase and kininase II on coronary and systemic hemodynamics in rats.

To determine whether neutral endopeptidase (NEP) and kininase II (angiotensin-converting enzyme, ACE) influence coronary hemodynamics, we compared the effects of inhibiting NEP, ACE, or both before and after isoproterenol (50 mg/kg ip). We measured flow and resistance using radioactive microspheres in 90 anesthetized rats which received the NEP inhibitor phosphoramidon (2.5 mg/kg), the ACE inhibitor captopril (2.5 mg/kg), both combined, or vehicle alone. Before isoproterenol, inhibiting NEP, ACE, or both increased left ventricular blood flow by 48 +/- 10 (SE), 33 +/- 9, and 10 +/- 6%, respectively, and decreased left ventricular vascular resistance by 26 +/- 6, 31 +/- 10, and 10 +/- 6%, respectively. After isoproterenol, NEP inhibition augmented the decrease in left ventricular vascular resistance (25 +/- 6% decrease within 90 s of isoproterenol vs. 8 +/- 5% in controls). ACE inhibition did not augment the decrease in resistance but inhibiting both enzymes did so to a lesser extent than inhibiting NEP. These effects cannot be explained by vascular responses secondary to changes of myocardial oxygen consumption. We conclude that NEP and ACE are regulators of myocardial blood flow.

Fetal lamb pulmonary hypoplasia: pulmonary vascular and myocardial abnormalities.

Neonatal pulmonary hypoplasia resulting from a congenital diaphragmatic hernia (CDH) produces hemodynamic changes and morphologic abnormalities of the pulmonary vasculature. To characterize the myocardial and pulmonary vascular status of the fetus with pulmonary hypoplasia, we studied four chronically instrumented, near-term fetal lambs with pulmonary hypoplasia, induced by producing a diaphragmatic hernia. We found an elevation in the pulmonary arterial pressure (control, 43.8 +/- 5.9 mmHg; CDH, 58.8 +/- 9.1 mmHg; p < 0.05), an elevation in the systemic arterial pressure (control, 43.8 +/- 0.48 mmHg; CDH, 58.6 +/- 6.7 mmHg; p < 0.05), and an elevation in the pulmonary vascular resistance (control, 0.47 +/- 0.11; CDH, 3.87 +/- 1.9; p < 0.05). In addition, though the total pulmonary blood flow was reduced (control, 83.5 +/- 32.9 mL/min; CDH, 22.2 +/- 17.6 mL/min; p < 0.05), the blood flow reduction was proportional to the reduction in the lung mass (control, 79.8 +/- 28.1 [in flow per 100-g lung weight]; CDH, 85.4 +/- 71.7). The increase in the pulmonary vascular resistance in relation to the unit lung mass (control, 0.55 +/- 0.33; CDH, 0.99 +/- 0.5) was not as pronounced as its increase in relation to the total pulmonary blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cardiac contraction and cavity pressure on myocardial blood flow.

Regional impairment of cardiac contraction uncouples force generation from left ventricular pressure (LVP) and may alter the determinants of the phasic pattern and transmural distribution of coronary flow. In anesthetized, open-chest dogs with maximal coronary vasodilation, we studied the effects of abolishing local contraction and changing cavity pressure on phasic myocardial inflow and net transmural flow in a region of left ventricular free wall. With contraction present, the normalized amplitude of distal phasic coronary velocity (NAmp) was not significantly different at normal vs. low LVP (1.00 vs. 0.92 +/- 0.09, respectively, intracoronary lidocaine, however, NAmp varied with LVP (1.62 +/- 0.25 at normal LVP, 0.85 +/- 0.22 at low LVP, P < 0.0001). With contraction present, inner-to-outer flow ratio was not consistently different at normal vs. low LVP (0.47 +/- 0.15 vs. 0.64 +/- 0.28, respectively, P = NS) but was consistently higher at low than at normal LVP with contraction absent (1.01 +/- 0.30 vs. 1.84 +/- 0.38, respectively, P < 0.0001). During uniform global function, contraction is the main determinant of phasic amplitude and transmural distribution of myocardial flow. When regional contraction is abolished, allowing passive deformation of the wall during systole, LVP assumes a powerful role.

NK1 receptors mediate neurogenic inflammatory increase in blood flow in rat airways.

We studied the effect of neurogenic inflammation on airway blood flow in anesthetized F-344 rats. Three successive determinations of blood flow were made by injecting radionuclide-labeled microspheres suspended in 70% dextrose into the left ventricle. A selective agonist of the tachykinin receptor neurokinin 1 (NK1) increased airway blood flow, but NK2- and NK3-selective agonists were without effect. The natural agonist of NK1 receptors, substance P (1 micrograms/kg), increased airway blood flow, an effect that was abolished by the selective NK1 receptor antagonist CP-99,994 [(+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine] but not by the (2R,3R)-enantiomer CP-100,263. Capsaicin (25 micrograms/kg), a drug that releases tachykinins and calcitonin gene-related peptide from sensory nerves, increased airway blood flow, and again this effect was abolished by CP-99,994. We also studied the effect of a selective inhibitor (captopril, 2.5 mg/kg) of the tachykinin-degrading enzyme kininase II [or angiotensin-converting enzyme (ACE)] on substance P-induced airway vasodilation. Captopril potentiated and prolonged the vasodilator effect of substance P. We conclude that neurogenic vasodilation in rat airways is due to the release of substance P, acts via NK1 receptors, and may be modulated by ACE.

Neurogenic vasodilation in the rat nasal mucosa involves neurokinin1 tachykinin receptors.

We studied the role of different tachykinin receptors in mediating neurogenic vasodilation in the nasal mucosa of anesthetized pathogen-free rats. Three successive determinations of blood flow were made by injecting radionuclide-labeled microspheres suspended in 70% dextrose into the left ventricle. A selective agonist of the tachykinin NK1 receptor increased nasal blood flow, but neurokinin NK2- and NK3-selective agonists were without effect. The natural agonist of NK1 receptors, substance P (1 microgram/kg), increased nasal blood flow, an effect that was abolished by the selective NK1 receptor antagonist (+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine (CP-99,994). Capsaicin (25 micrograms/kg), a drug that releases tachykinins from sensory nerves, increased nasal blood flow, and this effect was significantly reduced by CP-99,994. We conclude that a significant component of neurogenic vasodilation in rat nasal mucosa is due to the stimulation of NK1 tachykinin receptors.

New nonradioactive microspheres and more sensitive X-ray fluorescence to measure regional blood flow.

We developed new nonradioactive microspheres and used more sensitive X-ray fluorescence spectrometers than used previously to measure regional blood flow in the heart and other organs. We demonstrated the chemical stability of eight kinds of heavy element-loaded microspheres and validated their use for regional blood flow measurement by comparing duplicate flows measured with radioactive and/or nonradioactive microspheres in both acute and chronic dog experiments. The wavelength-dispersive spectrometer (Philips PW 1480) has a higher sensitivity than the previously described X-ray fluorescent system and reduced the number of microspheres required for accurate measurement. The fine energy resolution of this system makes it possible to increase the numbers of different kinds of microspheres to be quantitated, but at present only eight kinds are available. We also used a synchrotron radiation-excited energy dispersive spectrometer. The monochromatic synchrotron radiation allowed us to obtain much higher signal-to-background ratios of X-ray fluorescence spectra than with the wavelength-dispersive system (50 dB more for Zr-loaded microspheres) and will enable analysis of fluorescent activity in smaller regions (< 20 mg) than the radioactive method does.

Does systolic subepicardial perfusion come from retrograde subendocardial flow?

To examine the influence of cardiac contraction on systolic coronary flow and transmural blood flow distribution, we measured phasic blood flow velocity in distal extramural coronary arteries by Doppler velocimeter and regional myocardial blood flow by radiolabeled microspheres while the heart was beating and during prolonged diastoles in 12 dogs. A servo-controlled coronary perfusion circuit allowed mean coronary pressure to be selected and maintained during beating and diastolic conditions. In epicardial arteries just proximal to their entrance into the myocardium, blood flow was either negligible or reverse in direction during systole. When the heart was beating, subepicardial blood flow was 24.2 +/- 12.3% higher than during asystole (5.05 +/- 0.91 and 4.11 +/- 0.79 ml.min-1.g-1 for beating and prolonged diastoles, respectively; P less than 0.01). In the subendocardium, flow was 49.8 +/- 14.7% lower in the beating condition than during prolonged diastoles (4.23 +/- 1.46 and 8.26 +/- 1.71 ml.min-1.g-1 for beating and asystole, respectively; P less than 0.01). When heart rate was increased stepwise from 60 to 150 beats/min, subendocardial flow fell approximately linearly; flow to the superficial layer was relatively unaffected. In beating hearts, lowering mean left main coronary artery (LMCA) pressure from 80 to 50 mmHg resulted in more systolic reverse flow and a fall in inner-to-outer flow ratio from 0.82 +/- 0.18 to 0.66 +/- 0.34 (P less than 0.05). Because mean LMCA pressure was held constant when the heart was stopped, differences in regional blood flow between beating and diastolic conditions were primarily due to cardiac contraction. Because little or no blood entered the myocardium from the extramural arteries during systole, we conclude that the decrease in subendocardial flow and the increase in subepicardial flow were caused by retrograde pumping of blood from the deep layer to the superficial layer of the left ventricle. Systolic retrograde flow to the subepicardium may help explain this layer's relative protection from ischemia.

Effect of neuropeptides released from sensory nerves on blood flow in the rat airway microcirculation.

Stimulation of sensory nerves in the airway mucosa causes local release of the neuropeptides substance P and calcitonin gene-related peptide (CGRP). In this study we used a modification of the reference-sample microsphere technique to measure changes in regional blood flow and cardiac output distribution produced in the rat by substance P, CGRP, and capsaicin (a drug that releases endogenous neuropeptides from sensory nerves). Three sets of microspheres labeled with different radionuclides were injected into the left ventricle of anesthetized F344 rats before, immediately after, and 5 min after left ventricular injections of capsaicin, substance P, or CGRP. The reference blood sample was withdrawn from the abdominal aorta and was simultaneously replaced with 0.9% NaCl at 37 degrees C. We found that stimulation of sensory nerves with a low dose of capsaicin causes a large and selective increase in microvascular blood flow in the extrapulmonary airways. The effect of capsaicin is mimicked by systemic injection of substance P but not by CGRP, suggesting that substance P is the main agent of neurogenic vasodilation in rat airways.

Cardiac contraction affects deep myocardial vessels predominantly.

To evaluate the roles of intramyocardial forces and systolic ventricular pressure in myocardial flow in the different layers separately, we measured myocardial flow in rabbit hearts during stable systolic contracture with left ventricular pressures of 60 (n = 5) and 0 mmHg (n = 5) and during stable diastolic arrest (n = 5). We also measured the number and size of the intramyocardial vessels after perfusion fixation (systolic arrest, n = 5; diastolic arrest, n = 5). In 25 rabbits, hearts were excised and perfused from the aortic root. Systolic arrest was achieved by perfusion of a low-Ca2+ Tyrode solution containing 2.0 mM Ba2+. Diastolic arrest was achieved by intraventricular injection of 700-1,000 mg pentobarbital sodium and was maintained by perfusion with St. Thomas cardioplegic solution. At perfusion pressure of 100 mmHg, subendocardial flow was lower than subepicardial flow during systolic arrest regardless of left ventricular pressure, whereas during diastolic arrest, subendocardial flow was higher than subepicardial flow. Subendocardial-to-subepicardial flow ratios for a physiological range of perfusion pressures were lower during systolic arrest with low rather than with high left ventricular pressure. Small arteriolar and capillary densities showed no difference between subendocardium and subepicardium. During systolic arrest, diameters of subendocardial terminal arterioles (4.6 +/- 1.3 microns) and capillaries (4.0 +/- 1.3 microns) were smaller than those in the subepicardium (8.8 +/- 1.7 and 7.1 +/- 1.6 microns, respectively; P less than 0.0001), whereas during diastolic arrest, diameters of subendocardial terminal arterioles (10.1 +/- 2.0 microns) and capillaries (7.6 +/- 1.8 microns) were slightly larger than those in the subepicardium (9.5 +/- 1.5 and 6.7 +/- 1.0 microns, respectively; P less than 0.01). We conclude that cardiac contraction predominantly affects subendocardial vessels and impedes subendocardial flow more than subepicardial flow regardless of left ventricular pressure.

Local blood flow measured by fluorescence excitation of nonradioactive microspheres.

An X-ray fluorescence system with low Compton background and high counting efficiency was developed to measure regional blood flow with nonradioactive microspheres. The performance of the system was tested in vitro by counting mixed aqueous solutions of either Mo, Ag, and I; Nb, Ag, and Ba; or Zr, Mo, Rh, Ag, Sn, I, and Ba, as well as a mixture of Ag and Ba nonradioactive microspheres. Mixtures containing 2-20 ppm of each element were counted for 10 min by the fluorescence system, and the individual elements in mixtures of three to seven nonradioactive elements were measured with high accuracy. The best counting statistics were obtained for Ag. For 10-min counts, the system measures as few as 120 Ag microspheres with 30% standard deviation but measures 800 Ag microspheres per sample with 3.6% standard deviation. We compared regional myocardial blood flows determined simultaneously by fluorescence and radioactive microsphere methods; the latter samples were counted by a 3-in. NaI (Tl) well detector and pulse-height analyzer. The radioactive and nonradioactive measurements showed good correlations.

Heterogeneous delivery of cardioplegic solution in the absence of coronary artery disease.

The prevention of intraoperative myocardial damage with cardioplegic solution depends in large measure on the completeness of its delivery. We created a model to study the regional flow distribution of cardioplegic solutions in nondiseased, diastolically arrested, maximally vasodilated canine hearts. Global and regional myocardial flows were measured at different perfusion pressures in hearts perfused either with blood cardioplegic solution (n = 8) or oxygenated crystalloid cardioplegic solution (n = 2). As coronary perfusion decreased, flow in all layers fell significantly (p less than 0.001). This fall was most dramatic in the subendocardium (p less than 0.05). With both types of cardioplegic solutions, the relationship between pressure and flow was nonlinear: At low coronary perfusion pressures, a given change in pressure resulted in a smaller change in flow than at higher perfusion pressures. In addition, we found that in all dogs and at all pressures there was profound variability in the delivery of cardioplegic solution to different small regions of the left ventricular free wall. At a perfusion pressure of 40 mm Hg, the extremes of regional flow differed on average by 203%. This heterogeneity increased significantly with decreasing perfusion pressures. At the lowest perfusion pressure measured (20 mm Hg), the extremes of regional flow differed on average by 365%. These findings emphasize the importance of coronary pressure on the delivery of cardioplegic solution. At low perfusion pressures, not only is mean flow reduced, but a greater number of regions receive limited amounts of cardioplegic solution. These observations may explain the patchy nature of subendocardial damage seen with inadequate myocardial protection.

Usefulness and limitations of regional cardiac sympathectomy by phenol.

We evaluated the completeness and extent of regional sympathetic denervation of the left ventricle after epicardial painting with phenol in anesthetized dogs. In a region encircled by phenol, the effect of electrical stimulation of efferent sympathetic fibers on myocardial contractility and coronary vascular resistance was completely abolished within 30 min. Denervation extended to untreated regions innervated by sympathetic fibers crossing the phenol line. For at least 4 h after phenol application, intravenous infusion of isoproterenol or coronary arterial infusion of tyramine increased myocardial contractility in the denervated region; norepinephrine content and neurotransmitter uptake were normal, indicating that nerve terminals, postjunctional receptors, and myocardium remained functional. However, after 3-14 days, tissue catecholamine content and transmitter uptake in the encircled area were markedly reduced. The results suggest that careful evaluation is necessary in selecting a fully innervated control region in studies employing regional sympathetic denervation with phenol.