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The coronary microcirculation: Locations of resistance and regulatory mechanisms
J Mol Cell Cardiol23
A-2-5
(Supplement
III) (1991)
GLUCOSE METABOLISM AND GLYCOGEN TURNOVER IN VASCULAR SMOOTH MUSCLE STUDIED BY 1%NMR Christopher D Hardin1 and Martin J KusbmerickiJ, Department of Radiology’ and Department of Physiology and
Biophysicss, University of Washington, Seattle,WA 98195 USA. Glucose utilization, including glycogen turnover, was studied in hog carotid artery segmentsby t3C-NMR. Lactate and glycogen were the major products of glucose utilization other than COZ. We examined the pattern of glycogen turnover in unmounted segmentsat 22cC superfused with a physiological saline solution (PSS). Glycogen contents of unmounted (control) segmentswere initially 3.5 p.mole/gm blot wt (+ 1.1 SD, n=16). Superfusion with glucose labelled at the 6 carbon (6-tsC-glucose) for 3 hours was followed by superfusion witb 1-lsC-glucose resulting in an accumulation of total glycogen to 9.2 ltmole/gm blot wt Q 2.0 SD, n=S). Carotids were then depleted of glycogen by equilibrating substrate-free PSSwith lOO%Nz. Glycogen levels decreasedover 3 hours to 2.3 pmol/gm blot wt (k 0.6 SD, n=lO). C-l glucosyl units of glycogen were utilized preferentially, indicating that the most recently synthesizedglucosyl units of glycogen were the first to be utilized. To determine whether the glycogen utilization was compartmentalired from glycolysis as proposed by Lynch and Paul (Science, u:1344-1346), we superfusedmounted segmentsat 37< with 2-X-glucose resulting in an accumulation of 2-tsC!-glucosyl units of glycogen. The increase in the glycogen peak was approximately linear for 8 hours. C-2 lactate was removed by superfusion with substrate-freePSS and tbe segmentscontracted with 50 mM KC1 in the presence of 1-1X:-glucose. Only lactate derived from the I-1X!-glucose was detected despite the progressive disappearanceof the C-2 labelled glycogen pool over 3 hours. This result indicates that the intermediates of glycolysis and glycogenolysis did not mix. However, when the segmentswere contracted in the presenceof 1-tsC-glucose and NaCN (to inhibit oxidative metabolism of glycogen), glycogen was depleted more rapidly and lactate was derived from both the labelled glycogen pool and the labelled glucose. Supportedby NlH: F32 AR08104 (CDH) and AR36281 (MJK).
RELATIONSHIP BETWEEN PROTEIN KINASE C (PKC) ACTIVATION, PHOSPHOINOSITIDE HYDROLYSIS AND CONTRACTION IN RAT AORTA Robert M Rapoport, Eulalia Bazan, Anita K Campbell. Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati and Veterans Affairs Medical Center, Cincinnati, OH 45267-0575 USA Although PKC has been proposed to serve a major role in the regulation of vascular smooth muscle contraction, relatively little information is available on the effects of agonists on PKC activation in intact vascular smooth muscle. The amounts of PKC activity in the cytosolic and particulate fractions of rat aorta increased and decreased, respectively, upon exposure to Ca2+-free solution. Prostaglandin F2a PMA, decreased cytosolic and increased particu(PGF2,), KCl, and the phorbol ester, late PKC activity, and the changes were associated with contraction. The ability to detect these changes depended upon Ca2+ removal following agonist exposure. PMA inhibited the norepinephrine (NE)-, and potentiated the PGF2,-, induced contraction in Ca2+-free solution, while contractions in normal solution remained unaltered. NE-elevated inositol phosphate levels were inhibited by PMA, but not by PGF2,, and were potentiated by staurosporine and PKC down-regulation. PGF2a-elevated inositol and PKC down-regulation. phosphate levels remained unaltered by PMA, staurosporine These results demonstrate that, depending upon the agonist and phase of contraction, PKC activation can potentiate or inhibit the agonist-induced contractile response.
B-2-1
THE CORONARY MICROCIRCULATION: LOCATIONS OF RESISTANCE AND REGULATORY MECHANISMS William M Chilian. Department of Medical Physiology, Texas A&M University, College Station, TX 77842 USA. Recenttechnological advancements have enabled direct measurementsof coronary microvascular pressures and diameters in the epicardial microcirculation of the beating heart, and in the subendocardial microcirculation of arrested hearts. From this information the distribution and control of coronary microvascular resistance can be directly ascertained. In the beating heart with vasomotor tone intact, approximately 20-25% of the pressure dissipation occurred proximal to small coronary arteries between 180 and 200 pm in diameter and pressures in arterfoles about 100 urn in diameterwere 40% lowerthan aortic pressure. In arrested heart preparations during maximal vasodilation, subendocardial arteriolar pressures were about 20% lower than those in Ihe subepicardtum. Also, the pressure drop across the subendocardial microcirculation was approximately 50% less than that in the subepicardium. To evaluate local regulation of arterial and artedolar resistances, reductions in coronary perfusion pressure were accomplished in situ to identify sites of coronary autoregulation. Reductions in coronary perfusion pressure from 100 to 80 mmHg caused predominately arterfolar vasodilation (vessels <100-l 50 urn in diameter), but a further reduction to 60 mmHg also produced ditation in small arteries (>150 pm in diameter), though less in magnitude than that of arterioles. In summary, the distributton of microvascular resistance across the coronary circulation suggests that small arteries constitute approximately 20-25% of coronary resistance, but arterioles cl00 urn in diameter are the primary site of coronary vascular resistance. Importantly, the distribution of resistance is non-uniform across the wall of the heart. Also, arterioles appear to be the primary site for autoregulatoryadjustments during reductions in perfusion pressure, but small arteries can be recruited to participate in this vasomotor adjustment. 5.12
A-2-5
(Supplement
III) (1991)
GLUCOSE METABOLISM AND GLYCOGEN TURNOVER IN VASCULAR SMOOTH MUSCLE STUDIED BY 1%NMR Christopher D Hardin1 and Martin J KusbmerickiJ, Department of Radiology’ and Department of Physiology and
Biophysicss, University of Washington, Seattle,WA 98195 USA. Glucose utilization, including glycogen turnover, was studied in hog carotid artery segmentsby t3C-NMR. Lactate and glycogen were the major products of glucose utilization other than COZ. We examined the pattern of glycogen turnover in unmounted segmentsat 22cC superfused with a physiological saline solution (PSS). Glycogen contents of unmounted (control) segmentswere initially 3.5 p.mole/gm blot wt (+ 1.1 SD, n=16). Superfusion with glucose labelled at the 6 carbon (6-tsC-glucose) for 3 hours was followed by superfusion witb 1-lsC-glucose resulting in an accumulation of total glycogen to 9.2 ltmole/gm blot wt Q 2.0 SD, n=S). Carotids were then depleted of glycogen by equilibrating substrate-free PSSwith lOO%Nz. Glycogen levels decreasedover 3 hours to 2.3 pmol/gm blot wt (k 0.6 SD, n=lO). C-l glucosyl units of glycogen were utilized preferentially, indicating that the most recently synthesizedglucosyl units of glycogen were the first to be utilized. To determine whether the glycogen utilization was compartmentalired from glycolysis as proposed by Lynch and Paul (Science, u:1344-1346), we superfusedmounted segmentsat 37< with 2-X-glucose resulting in an accumulation of 2-tsC!-glucosyl units of glycogen. The increase in the glycogen peak was approximately linear for 8 hours. C-2 lactate was removed by superfusion with substrate-freePSS and tbe segmentscontracted with 50 mM KC1 in the presence of 1-1X:-glucose. Only lactate derived from the I-1X!-glucose was detected despite the progressive disappearanceof the C-2 labelled glycogen pool over 3 hours. This result indicates that the intermediates of glycolysis and glycogenolysis did not mix. However, when the segmentswere contracted in the presenceof 1-tsC-glucose and NaCN (to inhibit oxidative metabolism of glycogen), glycogen was depleted more rapidly and lactate was derived from both the labelled glycogen pool and the labelled glucose. Supportedby NlH: F32 AR08104 (CDH) and AR36281 (MJK).
RELATIONSHIP BETWEEN PROTEIN KINASE C (PKC) ACTIVATION, PHOSPHOINOSITIDE HYDROLYSIS AND CONTRACTION IN RAT AORTA Robert M Rapoport, Eulalia Bazan, Anita K Campbell. Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati and Veterans Affairs Medical Center, Cincinnati, OH 45267-0575 USA Although PKC has been proposed to serve a major role in the regulation of vascular smooth muscle contraction, relatively little information is available on the effects of agonists on PKC activation in intact vascular smooth muscle. The amounts of PKC activity in the cytosolic and particulate fractions of rat aorta increased and decreased, respectively, upon exposure to Ca2+-free solution. Prostaglandin F2a PMA, decreased cytosolic and increased particu(PGF2,), KCl, and the phorbol ester, late PKC activity, and the changes were associated with contraction. The ability to detect these changes depended upon Ca2+ removal following agonist exposure. PMA inhibited the norepinephrine (NE)-, and potentiated the PGF2,-, induced contraction in Ca2+-free solution, while contractions in normal solution remained unaltered. NE-elevated inositol phosphate levels were inhibited by PMA, but not by PGF2,, and were potentiated by staurosporine and PKC down-regulation. PGF2a-elevated inositol and PKC down-regulation. phosphate levels remained unaltered by PMA, staurosporine These results demonstrate that, depending upon the agonist and phase of contraction, PKC activation can potentiate or inhibit the agonist-induced contractile response.
B-2-1
THE CORONARY MICROCIRCULATION: LOCATIONS OF RESISTANCE AND REGULATORY MECHANISMS William M Chilian. Department of Medical Physiology, Texas A&M University, College Station, TX 77842 USA. Recenttechnological advancements have enabled direct measurementsof coronary microvascular pressures and diameters in the epicardial microcirculation of the beating heart, and in the subendocardial microcirculation of arrested hearts. From this information the distribution and control of coronary microvascular resistance can be directly ascertained. In the beating heart with vasomotor tone intact, approximately 20-25% of the pressure dissipation occurred proximal to small coronary arteries between 180 and 200 pm in diameter and pressures in arterfoles about 100 urn in diameterwere 40% lowerthan aortic pressure. In arrested heart preparations during maximal vasodilation, subendocardial arteriolar pressures were about 20% lower than those in Ihe subepicardtum. Also, the pressure drop across the subendocardial microcirculation was approximately 50% less than that in the subepicardium. To evaluate local regulation of arterial and artedolar resistances, reductions in coronary perfusion pressure were accomplished in situ to identify sites of coronary autoregulation. Reductions in coronary perfusion pressure from 100 to 80 mmHg caused predominately arterfolar vasodilation (vessels <100-l 50 urn in diameter), but a further reduction to 60 mmHg also produced ditation in small arteries (>150 pm in diameter), though less in magnitude than that of arterioles. In summary, the distributton of microvascular resistance across the coronary circulation suggests that small arteries constitute approximately 20-25% of coronary resistance, but arterioles cl00 urn in diameter are the primary site of coronary vascular resistance. Importantly, the distribution of resistance is non-uniform across the wall of the heart. Also, arterioles appear to be the primary site for autoregulatoryadjustments during reductions in perfusion pressure, but small arteries can be recruited to participate in this vasomotor adjustment. 5.12