[Surgical treatment of primary liver cancer:a report of 10 966 cases]

Objective: To summarize the experience of surgical treatment of primary liver cancer. Methods: The clinical data of 10 966 surgically managed cases with primary liver cancer, from January 1986 to December 2019 at Hepatobiliary Center, the First Affiliated Hospital of Nanjing Medical University, were retrospectively analyzed. The life table method was used to calculate the survival rate and postoperative recurrence rate. Log-rank test was used to compare the survival process of different groups, and the Cox regression model was used for multivariate analysis. In addition, 2 884 cases of hepatocellular carcinoma(HCC) with more detailed follow-up data from 2009 to 2019 were selected for survival analysis. Among 2 549 patients treated with hepatectomy, there were 2 107 males and 442 females, with an age of (56.6±11.1) years (range: 20 to 86 years). Among 335 patients treated with liver transplantation, there were 292 males and 43 females, with an age of (51.0±9.7) years (range: 21 to 73 years). The outcomes of hepatectomy versus liver transplantation, anatomic versus non-anatomic hepatectomy were compared, respectively. Results: Of the 10 966 patients with primary liver cancer, 10 331 patients underwent hepatectomy and 635 patients underwent liver transplantation. Patients with liver resection were categorized into three groups: 1986－1995(712 cases), 1996－2008(3 988 cases), 2009‒2019(5 631 cases). The 5-year overall survival rate was 32.9% in the first group(1986－1995). The 5-year overall survival rate of resected primary liver cancer was 51.7% in the third group(2009-2019), among which the 5-year overal survival rates of hepatocellular carcinoma, intrahepatic cholangiocarcinoma and mixed liver cancer were 57.4%, 26.6% and 50.6%, respectively. Further analysis was performed on 2 549 HCC patients with primary hepatectomy. The 1-, 3-, 5-, and 10-year overall survival rates were 88.1%, 71.9%, 60.0%, and 41.0%, respectively, and the perioperative mortality rate was 1.0%. Two hundred and forty-seven HCC patients underwent primary liver transplantation, with 1-, 3-, 5-, and 10-year overall survival rates of 84.0%, 64.8%, 61.9%, and 57.6%, respectively. Eighty-eight HCC patients underwent salvage liver transplantation, with the 1-, 3-, 5-, and 10-year overall survival rates of 86.8%, 65.2%, 52.5%, and 52.5%, respectively. There was no significant difference in survival rates between the two groups with liver transplantation (P>0.05). Comparing the overall survival rates and recurrence rates of primary hepatectomy (2 549 cases) with primary liver transplantation (247 cases), the 1-, 3-, 5-, and 10-year overall survival rates in patients within Milan criteria treated with hepatectomy and transplantation were 96.3%, 87.1%, 76.9%, 54.7%, and 95.4%, 79.4%, 77.4%, 71.7%, respectively (P=0.754). The 1-, 3-, 5-year recurrence rates were 16.3%, 35.9%, 47.6% and 8.1%, 11.7%, 13.9%, respectively(P<0.01). The 1-, 3-, 5-, 10-year overall survival rates in patients with no large vessels invasion beyond the Milan criteria treated with liver resection and transplantation were 87.2%, 65.9%, 53.0%, 33.0% and 87.6%, 71.8%, 71.8%, 69.3%, respectively(P=0.003); the 1-, 3-, 5-year recurrence rate were 39.2%, 57.8%, 69.7% and 29.7%, 36.7%, 36.7%, respectively (P<0.01). The 1-, 3-, 5-, and 10-year overall survival rates in patients with large vessels invasion treated with liver resection and transplantation were 62.1%, 36.1%, 22.2%, 15.0% and 62.9%, 31.8%,19.9%, 0, respectively (P=0.387); the 1-, 3-, 5-year recurrence rates were 61.5%, 74.7%, 80.8% and 59.7%, 82.9%, 87.2%, respectively(P=0.909). Independent prognostic factors for both overall survival and recurrence-free survival rates of HCC patients treated with liver resection included gender, neoadjuvant therapy, symptoms, AST, intraoperative or postoperative blood transfusion, tumor number, tumor size, cirrhosis, macrovascular invasion, microvascular invasion, and pathological differentiation. Propensity score matching analysis of 443 pairs further showed that there was no significant difference in overall survival rate between anatomical liver resection and non-anatomical liver resection(P=0.895), but the recurrence rate of non-anatomical liver resection was higher than that of anatomical liver resection(P=0.035). Conclusions: In the past decade, the overall survival rate of HCC undergoing surgical treatment is significantly higher than before. For HCC patients with good liver function reservation, surgical resection can be performed first, and salvage liver transplantation can be performed after recurrence. The effect of salvage liver transplantation is comparable to that of primary liver transplantation. As for the choice of liver resection approaches, non-anatomical resection can reserve more liver tissue and can be selected as long as the negative margin is guaranteed.

[A clinicopathological classification analysis of ocular mass lesions in 7 910 cases]

Objective: To investigate the anatomical region, histopathological classification and histogensis distribution of ocular mass lesions in South China. Methods: Retrospective cases study. The clinical and pathological data of 7 910 samples with ocular (adnexal) tumors or proliferative lesions which were examined from January 2000 to May 2018 were retrospectively retrieved. The constituent ratios of ocular mass lesions in different anatomical regions and histogenesis have been analyzed. Results: There were 3 445 males and 4 465 females aged from 3 months to 106 years. Classification by anatomical region. Eyelid 4 976 cases (62.9%): benign-pigmented nevus (31.7%, 1 342/4 235), squamous cell papilloma (12.3%, 519/4 235), seborrheic keratosis (9.4%, 396/4 235); malignant-basal cell carcinoma (48.5%, 359/741), sebaceous gland carcinoma (34.4%, 255/741), squamous cell carcinoma (12.3%, 91/741). Ocular surface 1 449 cases (18.3%): benign-pigmented nevus (26.6%, 359/1 348), squamous cell papilloma (12.8%, 173/1 348); malignant-lymphoma (34.7%, 35/101), squamous cell carcinoma (30.7%, 31/101).Orbit 1 485 cases (18.8%): benign-hemangioma (28.5%, 332/1 167), lacrimal gland (duct) cyst(13.2%, 154/1 167); malignant-lymphoma (44.7%, 142/318), adenoid cystic carcinoma (10.1%, 32/318). Classification by histogenesis: epithelial 2 145 cases (27.1%), cutaneous appendages 378 cases (4.8%), cystoid 1 068 cases (13.5%), mesenchymal 748 cases (9.5%), lymph-hematopoietic 225 cases (2.8%), neurogenic 31 cases (0.4%), melanocytic 1 765 cases (22.3%), others 1 550 cases (19.6%). Conclusions: Over the past 18 years, the ocular tumors identified at the Second Affiliated Hospital, Zhejiang University School of Medicine most frequently occur in eyelid and originate from epithelium. The most common types are as followings. Benign lesions: pigmented nevus, squamous cell papilloma are the most common types for eyelid and ocular surface, whereas hemangioma, lacrimal gland (duct) cyst and epidermoid cyst are the most common types for orbit. Malignant cancers: basal cell carcinoma is the most prevalent disease in eyelid, whereas lymphoma occurs more frequently in ocular surface and orbit. (Chin J Ophthalmol, 2019, 55: 847-853).

[Association between miR-146a single nucleotide polymorphism and genetic susceptibility to hepatocellular carcinoma: a meta-analysis]

Objective: To investigate the association between miR-146a single nucleotide polymorphism and genetic susceptibility to hepatocellular carcinoma (HCC). Methods: PubMed, Web of Science, Cochrane Library, Wanfang Data, and Google Scholar were searched for case-control studies on the association between miR-146a single nucleotide polymorphism and genetic susceptibility to HCC published up to October, 2016 in Chinese or English. The Q-statistics test was used to evaluate the heterogeneity of these articles. Results: A total of 18 articles with 5 610 cases and 7 531 controls were included for the meta-analysis. There was no significant association between miR-146a single nucleotide polymorphism and genetic susceptibility to HCC. The odds ratio (OR), 95% confidence interval (95% CI), and P values for the five genetic models were as follows: the allele model C/G (OR = 0.99, 95% CI 0.88-1.06, P = 0.440); the heterozygous model CG/GG (OR = 0.99, 95% CI 0.90-1.10, P = 0.898); the homozygous model CC/GG (OR = 0.91, 95% CI 0.75-1.10, P = 0.314); the dominant model CC+CG/GG (OR = 0.97, 95% CI 0.79-1.19, P = 0.759); the recessive model CG+GG/CC (OR = 1.05, 95% CI 0.94-1.18, P = 0.405). A subgroup analysis of race, source of control population, and Hardy-Weinberg equilibrium were performed in these five genetic models, and miR-146a single nucleotide polymorphism increased the susceptibility to HCC only in the control population-based subgroups of the recessive model CG+GG/CC (OR = 1.20, 95% CI 1.02-1.40, P = 0.024). There was no association between miR-146a rs2910164 polymorphism and susceptibility to HCC in all the other subgroups. A stratified analysis of HBV infection revealed that miR-146a rs2910164 polymorphism increased the risk of HBV-positive HCC (OR = 1.26, 95% CI 1.10-1.49, P = 0.001). Conclusion: There is no significant association between miR-146a rs2910164 polymorphism and the risk of HCC, but miR-146a rs2910164 polymorphism may increase the risk of HBV-positive HCC.

Contributions of polymorphisms in miR146a, miR196a, and miR499 to the development of hepatocellular carcinoma

Hepatocellular carcinoma is one of the most common malignant tumors worldwide; it is estimated that there were 782,000 new cases in 2012. MicroRNAs (miRNAs) play an important role in carcinogenesis by regulating oncogenes and tumor suppressors. We investigated the role of miR-146a, miR-196a2, and miR-499 polymorphisms in the risk of hepatocellular carcinoma in a Chinese population. Hepatocellular carcinoma patients (175) and healthy controls (302) were recruited between April 2013 and March 2015. Genotype analysis of miR-146a, miR-196a2, and miR-499 polymorphisms was carried out by polymerase chain reaction-restriction fragment length polymorphism. There was a significant difference between the genotype distribution of miR-196a2 in hepatocellular carcinoma patients and controls (X² = 17.23, P < 0.001). CG and GG miR-146a genotypes significantly elevated the risk of hepatocellular carcinoma compared with the CC genotype, with adjusted ORs (95%CI) of 3.05 (1.07-8.70) and 4.96 (1.64-14.97), respectively. In the recessive model, the CG + GG genotype had a 3.75-fold risk of hepatocellular carcinoma compared with the CC genotype, with an adjusted OR (95%CI) of 3.75 (1.39-10.11). However, no significant association was observed between miR-196a2 and miR-499 variants and risk of hepatocellular carcinoma in the co-dominant, dominant, and recessive models. The miR-146a polymorphism is a G to C substitution that causes a mismatch in the stem-loop of miRNA, which influences how the expression and transcriptional regulation of miRNA affects its target genes. Our study revealed that the GG and CG genotypes of miR-146a increased the risk of hepatocellular carcinoma in the Chinese population.

[Comparison between poly hydroxy acrylic acid and Van-clear replacing the traditional reagents to detect the cervical hTERC genes by adopting FISH technique]

OBJECTIVE

To observe the difference of the human telomeres RNA component (hTERC) genes' amplification in the cervical tissue by applying the environment-friendly fixative poly hydroxy acrylic acid and the transparent dewaxing solution Van-clear separately or jointly to replace the traditional fixative 4% (volume fraction) neutral buffered formalin and the conventional transparent dewaxing solution xylene in the use of fluorescence in situ hybridization (FISH) for detection.

METHODS

In the study, 255 cases of cervical tissue specimens submitted by the Department of Gynecology in Zhongshan Boai Hosipital were collected from Mar. 2013 to Apr. 2015. Four samples were taken from the same lesion site. All the cases were divided into 4 groups and named group A, B, C, and D. Group A used 4% neutral buffered formalin fixed and xylene dewaxing to make slices. Group B used poly hydroxy acrylic fixed and xylene dewaxing to make slices. Group C used 4% neutral buffered formalin fixed and Van-clear transparent to make slices. Group D used poly hydroxy acrylic fixed and Van-clear transparent dewaxing to make slices. The amplification of hTERC genes in the four groups of cervical specimens was also detected by FISH technique.

RESULTS

When the hTERC genes were detected by FISH method under the fluorescence microscope, it was obvious that the tissue profile and the background of group A, B, C and D were all clear. The probe was fixed in the accurate position so that the bright red or green fluorescence signals were easily found in these four groups. Compared with the positive rate of group A, there was no statistical significance in that of group B, C and D (P>0.05). At the same time, the coincidence rate of the FISH results was high, which showed that the new environment-friendly reagent had no significant difference in the detection of cervical hTERC genes by FISH technique.

CONCLUSION

It is possible for the environment-friendly reagent poly hydroxy acrylic acid and Van-clear to replace 4% neutral buffered formalin and xylene separately or jointly to detect the cervical hTERC genes by adopting FISH technique.

Vg1 orthology in the direct developing frog, Syrrhophus cystignathoides campi

Syrrhophus cystignathoides campi is a direct developing frog species that matures without passing through a larval (tadpole) stage. We have cloned and sequenced the Syrrhophus cDNA orthologous to the Xenopus Vg1 cDNA. The Syrrhophus Vg1 (sVg1) cDNA spans 1323 nucleotides and encodes a predicted protein of 345 amino acids which is 81% identical at its carboxyl terminal end to Xenopus Vg1. In addition, it contains seven conserved cysteine residues present in all Vg1 related proteins. Despite this high degree of similarity it is apparently missing a conserved N-linked glycosylation site and has an altered proteolytic processing sequence. Interestingly it is also missing a nine nucleotide sequence in its 3' UTR believed to be important for mRNA localization in Xenopus and Drosophila. These sequence variations could alter the functional expression and localization of the protein.

[On the difference of cardiovascular effects between caudal ventrolateral medulla pressor area (cVMP) and rostrolateral medulla pressor area (rVMP)]

In 56 urethane anesthetized Wistar rats, bilateral microinjection of glutamate (L-glu) was used to observe the difference of cardiovascular effects between caudal ventrolateral medulla pressor area (cVMP) and rostral ventrolateral medulla pressor area (rVMP). The results showed that the pressor effect of cVMP was weaker than that of rVMP and was not accampanied by responses in heart rate. In the latter case, an increase of heart rate was involved. The baroreflex was inhibited when rVMP was activated by L-glu but facilitated when cVMP was activated. The above results suggest that the pathway and functions of the cardiovascular effects of rVMP are different from those of cVMP.

[Endoscopic injection sclerotherapy for esophageal varices: studies on methodology and complication]

From November 1985 to February 1991, sixty patients were randomized to three groups of intravariceal sclerotherapy: (1) many punctures of low quantity sclerosant, (2) one puncture of large quantity sclerosant, and (3) one puncture of large quantity sclerosant with transendoscopic balloon. The early effects and complications were investigated. Varices eradication was reached 91.2% in group 1, significantly higher than group 2 (58.3%) (P < 0.05), similar to group 3(89.9%). However, balloon group (group 3) required shorter duration than group 1 (12.6 vs. 21.7 days) (P < 0.05). There were no significant differences in complications, but all 6 esophageal stenosis were in group 1, recurrent bleeding was 11.4% in group 1.35.7% in group 2 and 0 in group 3 during sclerotherapy sessions. Further more, we found though attempted to inject into variceal veins, accurate intravariceal injection reached only 46.8% in accordance with venographic findings. We conclude that sclerotherapy with transendoscopic balloon seems to be more simple, safer, and required short time to produce successful variceal sclerosis.

The thromboxane A2 mimetic U46619 worsens canine myocardial hypoperfusion during exercise in the presence of a coronary artery stenosis

OBJECTIVE

The aim was to test the hypothesis that thromboxane A2 can cause vasoconstriction of coronary resistance vessels during exercise in hypoperfused regions of myocardium distal to an arterial stenosis.

METHODS

Eight adult mongrel dogs were studied. Chronically instrumented animals with a left circumflex coronary artery Doppler flow meter, hydraulic occluder, and indwelling catheter underwent treadmill exercise at heart rates of 190-200 beats.min-1. Myocardial blood flow was measured with microspheres during unimpeded arterial inflow and in the presence of a coronary stenosis which decreased distal pressure to 42-45 mm Hg. Measurements were repeated during infusion of the thromboxane A2 analogue, U46619.

RESULTS

When the occluder was partially inflated to produce a stenosis, blood flow in the region perfused by the stenotic artery was 58 (SEM 6)% of flow in the normally perfused region (p less than 0.01). U46619 (0.01 microgram.kg-1.min-1) caused a further 21 (7)% decrease in blood flow in the region perfused by the stenotic artery (p less than 0.05). The vasoconstriction produced by U46619 was uniform across the left ventricular wall from epicardium to endocardium. U46619 did not significantly decrease myocardial blood flow in the absence of a coronary stenosis.

CONCLUSIONS

Even during hypoperfusion produced by a flow limiting arterial stenosis, the coronary resistance vessels remain responsive to the vasoconstrictor effect of thromboxane A2. Liberation of thromboxane A2 during platelet activation at the site of a proximal coronary stenosis may worsen myocardial hypoperfusion by causing vasoconstriction of the distal resistance vessels.

Effect of serotonin and thromboxane A2 on blood flow through moderately well developed coronary collateral vessels

This study was performed to determine whether thromboxane A2 (as the analogue U46619) and serotonin can cause vasoconstriction of moderately well developed coronary collateral vessels. Studies were carried out in seven adult mongrel dogs 2 to 4 months after embolic occlusion of the left anterior descending coronary artery had been performed to stimulate collateral vessel growth. At the time of study this artery was cannulated to determine interarterial collateral flow from measurements of retrograde blood flow. Radioactive microspheres were administered during retrograde flow collection to determine continuing tissue flow for evaluation of microvascular collateral communications. Serotonin (50 micrograms/min) resulted in a 48 +/- 11% decrease in retrograde flow (p less than 0.01), with a 36 +/- 10% decrease in total collateral blood flow (p less than 0.02). Infusion of U46619 (0.01 microgram/kg per min) caused a 38 +/- 13% decrease in retrograde blood flow (p less than 0.01), with a 34 +/- 13% decrease in total collateral flow (p less than 0.05). Serotonin caused a significant increase in tissue flow to the subepicardium of the collateral-dependent region, whereas U46619 caused no change in tissue blood flow. These data demonstrate that both serotonin and thromboxane A2 can cause vasoconstriction of interarterial coronary collateral vessels. The findings suggest that platelet activation in coronary arteries from which collateral vessels originate has potential for causing collateral vasoconstriction, thereby compromising blood flow to the dependent myocardium.

Effect of alpha-adrenergic blockade with prazosin on large coronary diameter during exercise

BACKGROUND

Exercise-induced dilation of coronary resistance vessels is limited by alpha-adrenergic mechanisms. However, the effect of alpha-adrenergic mechanisms on large coronary arteries during exercise is not known.

METHODS AND RESULTS

In the present study, sonomicrometry was used to measure circumflex coronary arterial diameter during treadmill exercise before and after alpha 1-adrenergic blockade with prazosin in eight instrumented dogs. Before infusion of prazosin, exercise caused a fall in coronary vascular resistance (2.1 +/- 0.4 to 1.6 +/- 0.2 units, p less than 0.05) and dilation of the circumflex coronary artery (4.66 +/- 0.37 to 4.79 +/- 0.34 mm, p less than 0.05). Intracoronary infusion of prazosin during exercise caused a further decrease in coronary vascular resistance (1.6 +/- 0.2 to 1.4 +/- 0.2 units, p less than 0.05) and a further increase in circumflex coronary arterial diameter (4.79 +/- 0.34 to 4.83 +/- 0.34 mm, p less than 0.05). Intracoronary infusion of vehicle without prazosin during exercise did not cause a further decrease in coronary vascular resistance or increase in coronary diameter. Prazosin caused no significant increase in heart rate, aortic pressure, or coronary blood flow. Therefore, both small coronary resistance vessels and large epicardial coronary arteries dilated during exercise and dilated further after alpha-adrenergic blockade.

CONCLUSIONS

This finding indicates that alpha 1-adrenergic activity during exercise limits dilation of both large and small coronary arteries.

Coronary vasodilator reserve in ischemic myocardium of the exercising dog

BACKGROUND

Previous work has reported that coronary vasodilator reserve may persist in myocardium rendered ischemic by hypoperfusion. This study investigated the presence and extent of residual coronary vasomotor tone in myocardial regions made acutely ischemic by a flow-limiting coronary stenosis during exercise.

METHODS AND RESULTS

Studies were done in chronically instrumented dogs undergoing treadmill exercise in the presence of a coronary stenosis that decreased distal left circumflex coronary artery perfusion pressure to approximately 40 mm Hg. Measurements of myocardial blood flow were made with radioactive microspheres during exercise (6.5 km/hr, 6% grade) before and during intracoronary infusion of the potent coronary vasodilator adenosine (40 micrograms/kg/min). Distal coronary perfusion pressure was held equal before and during intracoronary adenosine infusion (43 +/- 5 versus 42 +/- 5 mm Hg) by adjusting the hydraulic coronary occluder. During exercise in the presence of a coronary stenosis, myocardial blood flow (milliliter per minute per gram) was significantly reduced in all layers of the ischemic posterior region compared with the nonischemic anterior region. During intracoronary adenosine infusion, with no change in coronary perfusion pressure, myocardial blood flow was significantly increased compared with preadenosine flows for both the subendocardial layer flow (1.03 +/- 0.74 versus 0.66 +/- 0.50; p less than 0.05) and mean transmural flow (1.54 +/- 0.59 versus 1.16 +/- 0.36; p less than 0.05). In the presence of a coronary stenosis, regional myocardial segment shortening in the ischemic region during exercise fell significantly to 49 +/- 8% of shortening in the absence of a coronary stenosis but improved modestly during adenosine infusion (65 +/- 7 versus 49 +/- 8%; p less than 0.05).

CONCLUSIONS

These results indicate that adenosine-responsive coronary vasodilator reserve persists during exercise-induced myocardial ischemia and suggest that residual microvascular vasoconstrictor tone may affect the extent of myocardial hypoperfusion occurring consequent to a flow-limiting coronary stenosis.

Vasoconstriction of canine coronary collateral vessels with vasopressin limits blood flow to collateral-dependent myocardium during exercise

This study was performed to test the hypothesis that active constriction of coronary collateral vessels can worsen hypoperfusion of collateral-dependent myocardium during exercise. Studies were performed in seven adult mongrel dogs in which intermittent followed by permanent occlusion of the left circumflex coronary artery produced an area of collateral-dependent myocardium without gross evidence of infarct. Myocardial blood flow was determined with microspheres while measurement of aortic and distal coronary pressures allowed calculation of collateral and small vessel resistance at rest and during treadmill exercise. The ability of collateral vessel constriction to limit blood flow was assessed by infusion of vasopressin during exercise. During control conditions, blood flow in the collateral zone underwent a subnormal increase during exercise in comparison with the normal zone (1.74 +/- 0.27 versus 2.50 +/- 0.40 ml/min/g, respectively, p less than 0.05). Infusion of vasopressin in a dose that caused no change in normal zone flow (0.01 microgram/kg/min i.v.) produced a 30 +/- 5% further decrease in flow to the collateral zone (p less than 0.01). This decrease in collateral zone flow resulted from a 48 +/- 14% increase in transcollateral resistance in response to vasopressin infusion (p less than 0.01), as well as a 40 +/- 9% increase in small vessel resistance in the collateral zone (p less than 0.01). These data demonstrate that active constriction of both collateral vessels and coronary resistance vessels can contribute to hypoperfusion of collateral-dependent myocardium during exercise.

Effect of alpha 1-adrenergic blockade on myocardial blood flow during exercise after myocardial infarction

The effect of alpha 1-adrenergic blockade with prazosin on myocardial blood flow at rest and during two levels of treadmill exercise was assessed in 16 chronically instrumented dogs 9-14 days after myocardial infarction had been produced by occlusion of the left circumflex coronary artery. During resting conditions prazosin did not alter mean myocardial blood flow or the subendocardial-to-subepicardial flow ratio in either normally perfused or collateral-dependent myocardium. However, during exercise at comparable external work loads and comparable rate-pressure products, prazosin significantly increased blood flow to normally perfused (27% increase at the second level of exercise, P less than 0.001) and collateral-dependent myocardium (35% increase at the second level of exercise, P less than 0.001) compared with control. In addition, prazosin caused a small but significant decrease in the subendocardial-to-subepicardial flow ratio in both normal (1.27 +/- 0.04 to 1.19 +/- 0.04; P less than 0.01) and collateral-dependent myocardium (0.57 +/- 0.11 to 0.52 +/- 0.11; P less than 0.01) compared with control, reflecting a disproportionally greater increase in subepicardial flow in response to alpha 1-adrenergic blockade. These data demonstrate that alpha 1-adrenergic vasoconstriction inhibits coronary vasodilation during exercise, even in areas of collateral-dependent myocardium relatively early after coronary artery occlusion.

Effects of amiodarone with and without polysorbate 80 on myocardial oxygen consumption and coronary blood flow during treadmill exercise in the dog

Since amiodarone has been reported to possess antianginal activity, this study examined the effects of amiodarone on coronary blood flow and myocardial oxygen consumption during exercise. Studies were performed in 14 chronically instrumented dogs trained to run on a motor-driven treadmill. Left circumflex coronary artery blood flow was measured with an electromagnetic flowmeter while aortic and coronary sinus catheters allowed measurement of myocardial oxygen extraction. During control conditions, graded exercise resulted in progressive increases in heart rate, aortic pressure, and coronary blood flow. Two preparations of amiodarone, 5 mg/kg, one dissolved in sterile water and the other in 10% polysorbate 80, were given intravenously to separate groups of dogs. Amiodarone in sterile water caused no hemodynamic changes at rest. However, the increase in heart rate during exercise was blunted after amiodarone, so that heart rate during the heaviest level of exercise was significantly less than during control exercise. Coronary blood flow and myocardial oxygen consumption were unchanged. Amiodarone with polysorbate 80 also blunted the increase in heart rate during exercise, but in addition caused a significant decrease in aortic pressure both at rest and during exercise. Myocardial oxygen consumption and coronary blood flow were significantly decreased after administration of amiodarone with polysorbate 80 at rest and during all exercise levels. Amiodarone with or without polysorbate 80 did not change myocardial oxygen extraction. These data demonstrate that amiodarone exerts a negative chronotropic effect during exercise. However, the decreased arterial pressure and myocardial oxygen consumption were not due to amiodarone, but was seen only with the combination of amiodarone dissolved in polysorbate 80.

[Characteristics of central acute resetting of high threshold baroreflex in rabbit's aortic nerves]

Experiments were performed on 37 urethane-anesthetized rabbits. The aortic nerves, carotid sinus nerves and vagus nerves were cut, MAP and renal sympathetic nerve activity (RSNA) were recorded. The conditional stimulation CSc (0.5 ms, 10 Hz, 4-6V, 5 min) was used to mimic the information of baroreflex non-medullated afferent fibers responding to acute increase of BP. Test stimulation TSa (0.02 ms, 0-80 Hz/30 s, 4-6V) and TSc (0.5 ms, 0-20 Hz/30s, 4-6V) was used to examine the responses of baroreflex A- and C-fibers. After CSc at 1 min the reflex MAP and RSNA of TSc was attenuated at 45.5% (P less than 0.01) and 10.6% (P less than 0.05), the MAP response of TSa was attenuated at 32.1% (P less than 0.05), but the RSNA response was not. From the further investigation it is concluded that the characteristics of central acute resetting are dependent on the components of baroreflex afferent fibers. The reflex responses are attenuated mainly by correspondent afferent components.

Adrenergic vasoconstriction limits coronary blood flow during exercise in hypertrophied left ventricle

This study was carried out to test the hypothesis that alpha-adrenergic vasoconstriction limits coronary blood flow (CBF) during exercise in the chronically pressure overloaded, hypertrophied left ventricle. Studies were performed in dogs in which left ventricular hypertrophy had been produced by banding the ascending aorta at 9 wk of age. Left circumflex coronary artery blood flow and myocardial O2 consumption (MVO2) were examined at rest and during treadmill exercise during control conditions, after selective alpha 1-adrenergic blockade with prazosin, and after nonselective alpha-adrenergic blockade with phentolamine. All studies were performed after beta-adrenergic blockade with propranolol. During control conditions CBF and MVO2 increased progressively during exercise, while coronary sinus O2 tension decreased. Neither prazosin nor phentolamine altered CBF at rest but, in comparison with control measurements, both agents significantly increased CBF during exercise and abolished the decrease in coronary sinus O2 tension that normally occurred during exercise. Both prazosin and phentolamine caused similar significant increases of MVO2 relative to the heart rate times systolic left ventricular pressure during exercise, indicating that the increased CBF produced by these agents enhanced MVO2. Similar findings after prazosin and phentolamine indicate that adrenergic restraint of CBF during exercise resulted principally from alpha 1-adrenergic vasoconstrictions with little additional contribution from postjunctional alpha 2-adrenergic mechanisms.

Effect of pinacidil on myocardial blood flow in the chronically pressure overloaded hypertrophied left ventricle

This study examined the effect of pinacidil on the transmural distribution of myocardial blood flow in the chronically pressure overloaded hypertrophied left ventricle. Studies were performed in six dogs in which banding of the ascending aorta had resulted in an 88% increase in left ventricular mass, as well as in six normal control animals. Two doses of pinacidil were administered to decrease mean arterial pressure by approximately 10 mm Hg (low dose) and 20 mm Hg (high dose). Animals with hypertrophy required significantly smaller drug doses to achieve the desired reductions in arterial pressure. During control conditions mean myocardial blood flow was significantly higher in animals with hypertrophy (1.90 +/- 0.21 ml/min/g) than in normal animals (1.12 +/- 0.08 ml/min/g; p less than 0.05). Subendocardial flow (endo) exceeded subepicardial flow (epi) in normal dogs during control conditions (endo/epi = 1.41 +/- 0.13), but not in animals with hypertrophy (endo/epi = 1.06 +/- 0.06; p less than 0.05). Pinacidil caused coronary vasodilation with similar relative increases in blood flow in both normal and hypertrophied hearts, so that after pinacidil, absolute blood flow rates remained higher than normal in animals with hypertrophy. Pinacidil caused a redistribution of blood flow away from the subendocardium in normal hearts (endo/epi = 0.90 +/- 0.11 during high-dose pinacidil) and in hearts with hypertrophy (endo/epi = 0.81 +/- 0.13 during high-dose pinacidil). The endo/epi ratios during high-dose pinacidil were not significantly different between the two groups. This study demonstrates that pinacidil is a potent coronary vasodilator in both normal and hypertrophied hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of coronary stenosis on myocardial blood flow during exercise in the chronically pressure-overloaded hypertrophied left ventricle

This study was performed to determine if a coronary artery stenosis would result in more-severe perfusion abnormalities in hypertrophied compared with normal canine hearts during exercise. Studies were performed in eight normal control dogs and in seven adult dogs in which a 67% increase in left ventricular mass wa produced by banding the ascending aorta at 9 weeks of age. Myocardial blood flow was measured by the microsphere method during treadmill exercise in the presence of a coronary artery stenosis that decreased distal coronary perfusion pressure to 55 or 42 mm Hg. At a coronary pressure of 55 mm Hg, mean myocardial blood flow was decreased by 23 +/- 5% in normal control dogs but was decreased by 53 +/- 10% in dogs with left ventricular hypertrophy (LVH) (p less than 0.05, comparing normal vs. LVH dogs). Similarly, at a coronary pressure of 42 mm Hg, mean blood flow was decreased by 53 +/- 6% below control in normal dogs but was decreased by 76 +/- 5% below control values in dogs with LVH (p less than 0.01, comparing normal vs. LVH dogs). In both groups of dogs, the stenosis caused a gradient of hypoperfusion, worsening from epicardium to endocardium. However, for each level of stenosis, subendocardial blood flow and the ratio of subendocardial to subepicardial blood flow was less in LVH than in normal canine hearts. These findings demonstrate that the presence of LVH secondary to long-term pressure overload is associated with an increased vulnerability to myocardial hypoperfusion during exercise in the presence of a coronary artery stenosis.

Myocardial oxygen consumption during exercise in the presence of left ventricular hypertrophy secondary to supravalvular aortic stenosis

The hypothesis that abnormally increased myocardial oxygen demands may contribute to increased vulnerability to ischemia during exercise in the chronically pressure-overloaded hypertrophied left ventricle was tested. Myocardial oxygen consumption was measured during a five stage graded treadmill exercise protocol in eight normal dogs and nine adult dogs in which a 90% increase in left ventricular mass was produced by banding the ascending aorta at 8 weeks of age. Heart rate increased progressively during exercise in both groups of dogs, but was significantly faster than normal in the group with aortic banding. Coronary blood flow increased progressively with exercise in both groups, but was significantly greater than normal in dogs with aortic banding during each exercise stage. Coronary sinus oxygen tension decreased significantly and similarly during exercise in normal and hypertrophied hearts. In dogs with hypertrophy, oxygen consumption per gram of myocardium averaged 52% greater than normal during exercise. This excess myocardial oxygen consumption in dogs with aortic banding resulted from an abnormally large increase in oxygen consumption per beat during exercise and from the faster heart rate in this group of dogs. Measurements of myocardial blood flow with microspheres demonstrated a lower subendocardial/subepicardial blood flow ratio in dogs with hypertrophy; this ratio decreased significantly during exercise in dogs with hypertrophy, but not in normal dogs. These data are consistent with the hypothesis that increased vulnerability to ischemia in the pressure-overloaded hypertrophied left ventricle is the result of both increased myocardial oxygen demands during exercise and abnormalities of myocardial perfusion.

Effect of pinacidil on myocardial blood flow in the presence of a coronary artery stenosis

This study examined the effect of pinacidil on transmural distribution of myocardial blood flow during normal conditions and in the presence of a coronary artery stenosis. Studies were performed in 11 awake dogs; blood flow was measured with radioactive microspheres. Two doses of pinacidil were administered to decrease mean arterial pressure (MAP) by approximately 10 mm Hg (low dose, 0.18 +/- 0.02 mg/kg) and 20 mm Hg (high dose, 0.32 +/- 0.03 mg/kg). Measurements were performed during unimpeded arterial inflow and with two levels of coronary stenosis that limited blood flow to approximately 60% above (moderate stenosis) and approximately 30% above basal flow (severe stenosis). With no stenosis, coronary flow increased 227 +/- 17% after low-dose and 321 +/- 31% after high-dose pinacidil (each p less than 0.01). During control conditions, subendocardial (endo) flow exceeded subepicardial (epi) flow (endo/epi ratio = 1.33). This ratio was not changed by low-dose pinacidil but decreased to 0.93 after high-dose pinacidil (p less than 0.05). During high-dose pinacidil, a coronary stenosis caused uniform reduction of blood flow across the left ventricular wall, with no further significant change in the ratio of endo/epi flow. With low-dose pinacidil, both moderate and severe degrees of stenosis caused redistribution of flow away from the subendocardium similar to that observed with high-dose pinacidil. Although a stenosis that limited the increase in mean coronary flow after pinacidil administration to 162% of the predrug control value had a 95% probability of not causing a decrease in absolute subendocardial flow, the data suggest that pinacidil could have potential for aggravating subendocardial ischemia in severe occlusive coronary artery disease.

Effect of atrial natriuretic peptide on coronary collateral blood flow

This study was carried out to examine the effects of atrial natriuretic peptide on coronary collateral blood flow. Studies were performed in nine adult mongrel dogs 3.4 months after embolic occlusion of the left anterior descending coronary artery had been performed to stimulate collateral vessel growth. At the time of study the anterior descending coronary artery was cannulated to allow estimation of interarterial collateral flow from measurements of retrograde blood flow. Injection of radioactive microspheres during retrograde flow collection allowed simultaneous determination of continuing tissue flow for evaluation of microvascular collateral communications. Atrial natriuretic peptide in doses of 20 and 200 micrograms administered into the left atrium resulted in 17 +/- 3.0% and 34 +/- 4.5% increases in retrograde flow, respectively (each p less than 0.01). Tissue flow in the collateral dependent myocardial region did not change in response to atrial natriuretic peptide. After the larger dose of atrial natriuretic peptide, the administration of nitroglycerin (10 micrograms/kg into the left atrium) caused no further increase of retrograde blood flow, and no further decrease of collateral vascular resistance. These data indicate that atrial natriuretic peptide causes vasodilation of moderately well-developed interarterial coronary collateral vessels.

The role of alpha 1- and alpha 2-adrenergic receptors in mediation of coronary vasoconstriction in hypoperfused ischemic myocardium during exercise

This study was carried out to test the hypothesis that adrenergic coronary vasoconstriction limits blood flow to hypoperfused regions of myocardium during exercise. The vasoconstrictor influence of alpha-adrenergic receptor subtypes was assessed by use of selective adrenergic blocking agents. Dogs chronically instrumented with a circumflex coronary artery hydraulic occluder and an intra-arterial catheter underwent treadmill exercise in the presence of a coronary stenosis that decreased distal perfusion pressure to 40 mm Hg. Myocardial blood flow was measured with radioactive microspheres (15 microns) before and during selective alpha 1- or alpha 2-adrenergic receptor blockade produced by intracoronary infusion of prazosin (1 microgram/kg/min x 10 min) or idazoxan (1 microgram/kg/min x 10 min), respectively. Coronary perfusion pressure was held equal before and during receptor blockade with the hydraulic occluder. Compared with control exercise, subendocardial blood flow increased during alpha 1-receptor blockade with prazosin from 0.60 +/- 0.14 to 1.12 +/- 0.17 ml/min/g (p less than 0.05), and mean transmural flow increased from 1.07 +/- 0.19 to 1.60 +/- 0.22 ml/min/g (p less than 0.05). In contrast, subendocardial and mean transmural blood flow were not different from control during selective alpha 2-adrenergic receptor blockade with idazoxan (0.48 +/- 0.10 vs. 0.67 +/- 0.14 ml/min/g, p = 0.33, and 0.82 +/- 0.15 vs. 1.02 +/- 0.20 ml/min/g, p = 0.45, respectively). These data indicate that even in the presence of a coronary stenosis that causes substantial myocardial underperfusion during exercise, residual coronary vasoconstrictor tone is present in ischemic myocardium, and this vasoconstriction is mediated predominantly by the alpha 1-adrenergic receptor.

Alpha-adrenergic effects of dopamine and dobutamine on the coronary circulation

After beta-adrenergic blockade, dopamine causes coronary vasoconstriction that is blocked by non-selective alpha-adrenergic antagonists. This study was carried out to determine the relative importance of alpha 1- and alpha 2-adrenoceptors in mediating coronary vasoconstriction in response to dopamine. Because dobutamine has been reported to cause alpha-adrenergic stimulation, the response to dobutamine was also examined. The circumflex coronary artery was cannulated and perfused at a constant blood flow rate in 14 dogs; coronary vasomotor responses were assessed from changes in perfusion pressure. Central effects were eliminated by vagotomy and stellate ganglionectomy; propranolol (1 mg/kg i.v.) was administered to block beta-adrenergic effects. The coronary responses to intracoronary bolus doses of dopamine and dobutamine were determined; the effects of selective alpha 1-blockade with prazosin (600 micrograms/kg i.v.) and selective alpha 2-blockade with idazoxan or rauwolscine (1-5 micrograms/kg per min intracoronary for 10 min) were examined. Dopamine produced dose-related coronary vasoconstriction; this response was not significantly altered by alpha 1-blockade with prazosin, but was abolished by the addition of alpha 2-adrenergic blockade with idazoxan or rauwolscine. Dobutamine did not produce coronary vasoconstriction at any dose tested. These data demonstrate that coronary vasoconstriction produced by dopamine is mediated through postjunctional alpha 2-adrenergic receptors.

Coronary flow during exercise after selective alpha 1- and alpha 2-adrenergic blockade

This study was carried out to determine the relative importance of alpha 1- and alpha 2-adrenergic vasoconstriction in opposing the increase in coronary blood flow, which occurs during exercise. The response of left circumflex coronary artery blood flow was examined during treadmill exercise in 16 chronically instrumented dogs during control conditions, after selective alpha 1-adrenergic blockade with intracoronary prazosin, and after alpha 2-blockade with intracoronary idazoxan. During control conditions, graded treadmill exercise resulted in progressive increases of coronary blood flow and decreases of coronary vascular resistance. Prazosin produced highly selective alpha 1-adrenergic blockade; coronary blood flow was significantly higher and coronary vascular resistance significantly lower during all but the heaviest exercise stage after prazosin. Idazoxan produced highly effective, but only moderately selective, alpha 2-adrenergic blockade. However, after idazoxan, coronary blood flow and coronary vascular resistance during exercise were not significantly different from control. Combined alpha 1- and alpha 2-adrenergic blockade was not more effective in increasing coronary blood flow during exercise than was alpha 1-adrenergic blockade alone. These data support a role for alpha 1-adrenergic coronary vasoconstriction in limiting the increase in coronary blood flow, which occurs during exercise, but do not support a role for alpha 2-mediated coronary vasoconstriction during exercise.

Vasomotor activity of moderately well-developed canine coronary collateral circulation

This study examined the ability of moderately well-developed coronary collateral vasculature to undergo vasoconstriction in response to alpha-adrenergic agonists, vasopressin and angiotensin, and vasodilation in response to nitroglycerin. Studies were performed in 20 dogs 4-16 wk after left anterior descending coronary artery occlusion had been produced by an Ameroid constrictor or hollow intravascular plug. Collateral flow was estimated from retrograde flow from the cannulated left anterior descending artery. Tissue flow was measured with microspheres. Agonists were introduced into the left main coronary artery to reach collaterals arising from the left circumflex and septal arteries. Vasopressin and angiotensin II decreased retrograde flow from 22.7 +/- 5.5 to 15.5 +/- 2.7 and from 19.2 +/- 2.8 to 14.3 +/- 1.9 ml/min, respectively (each P less than 0.05). Both agents also significantly decreased tissue flow to normally perfused and collateral dependent myocardium. Neither the selective alpha 1-adrenergic agonist phenylephrine nor the alpha 2-agonist B-HT 933 decreased retrograde flow. Nitroglycerin increased retrograde flow by 63 +/- 27% (P less than 0.01). Thus, although the moderately well-developed coronary collateral circulation is capable of vasoconstriction in response to vasopressin and angiotensin II, these data fail to support a role for alpha-adrenergic mechanisms in modulating collateral flow.

Oxygen consumption and coronary reactivity in postischemic myocardium

Coronary vascular responses in regions of reversible postischemic myocardial contractile dysfunction (stunned myocardium) were examined in chronically instrumented, awake dogs. Left anterior descending coronary artery blood flow and oxygen extraction, aortic and left ventricular pressures, and regional myocardial segment shortening were determined. Regional myocardial blood flow was measured with microspheres. Coronary reactive hyperemia and vasodilator reserve, and regional myocardial oxygen consumption were determined. Three sequential 10-minute left anterior descending coronary artery occlusions separated by 30-minute reperfusion periods resulted in progressive postischemic dysfunction so that 1 hour after the final coronary artery occlusion, myocardial segment shortening was reduced to 37% of baseline. Despite this decrease in contractile function, left anterior descending artery flow (19.6 +/- 2.6 vs. 18.4 +/- 3.0 ml/min), myocardial blood flow and the transmural distribution of flow measured with microspheres, and regional myocardial oxygen consumption were unchanged. Although the coronary vasodilator reserve in response to adenosine was unaltered (63 +/- 9 vs. 70 +/- 15 ml/min), the reactive hyperemia response to a 10-second coronary occlusion was decreased in intensity (debt repayment ratio = 474 +/- 78% vs. 322 +/- 74%; p less than 0.05) and duration (57 +/- 9.1 vs. 35 +/- 4.5 seconds; p less than 0.05), while the peak flow response was unchanged (57 +/- 6.8 vs. 60 +/- 7.1 ml/min). Thus, in the intact awake animal postischemic myocardial contractile dysfunction was not associated with decreased myocardial oxygen consumption and did not impair the normal relation between coronary blood flow and myocardial oxygen utilization. Although coronary vessels showed a normal ability to vasodilate in response to adenosine, coronary reactive hyperemia was reduced.

Postsynaptic adrenoceptor-mediated vasoconstriction in coronary and femoral vascular beds

This study examined the response to intra-arterial norepinephrine and sympathetic nerve stimulation on perfusion pressure of cannulated dog femoral and left circumflex coronary arteries perfused at constant flow rates. Sympathetic nerve stimulation was delivered through the decentralized inferior cardiac nerve and the lumbar sympathetic chain; beta-adrenergic blockade was maintained with propranolol. In the coronary artery, the vasoconstrictor response to norepinephrine was blunted by alpha 1-adrenergic blockade with prazosin but was abolished by alpha 2-adrenergic blockade with rauwolscine, indicating postsynaptic alpha 2-adrenoceptor-mediated vasoconstriction. In the femoral artery, prazosin decreased norepinephrine-induced vasoconstriction by 20-40%; the subsequent addition of rauwolscine completely abolished vasoconstriction, indicating that both alpha 1- and alpha 2-adrenoceptors contributed to vasoconstriction. Sympathetic nerve stimulation produced frequency-dependent increases of perfusion pressure in both coronary and femoral vascular beds. Prazosin caused approximately 50% reduction in the vasoconstrictor response of the coronary vascular bed and approximately 30% reduction in the femoral bed. The addition of rauwolscine completely blocked the response to sympathetic nerve stimulation in coronary and femoral vascular beds. These studies demonstrate that postsynaptic alpha 2-adrenoceptor-mediated mechanisms participate in vasoconstriction in response to both exogenous norepinephrine and sympathetic nerve stimulation in the canine coronary and femoral vascular beds.

Differences in the effects of alpha-1 adrenergic blockade with prazosin and indoramin on coronary blood flow during exercise

This study compared the effects of two selective alpha-1 adrenergic blockers, prazosin and indoramin, on the response of coronary blood flow and myocardial oxygen consumption during treadmill exercise in chronically instrumented dogs. Left circumflex coronary artery blood flow was measured with an electromagnetic flowmeter, whereas myocardial arteriovenous oxygen difference was determined with indwelling aortic and coronary sinus catheters. During control conditions, coronary blood flow, arteriovenous oxygen extraction and myocardial oxygen consumption increased regularly with exercise. Both prazosin and indoramin decreased arterial pressure at rest and during exercise, but during heavier levels of exercise blood pressure was lower and heart rates were higher after prazosin. Prazosin did not alter myocardial oxygen consumption, whereas indoramin tended to decrease oxygen consumption; myocardial oxygen consumption was significantly less after indoramin than after prazosin during the heaviest levels of exercise. Prazosin, but not indoramin, significantly decreased coronary vascular resistance both at rest and during exercise, and blunted the decrease in coronary sinus oxygen tension which occurred during exercise. In comparison with prazosin, during heavy exercise coronary blood flow was significantly decreased, myocardial oxygen extraction significantly increased and myocardial oxygen consumption significantly decreased after indoramin.

Role of adenosine in coronary vasodilation during exercise

This study examined the hypothesis that increases in myocardial blood flow during exercise are mediated by adenosine-induced coronary vasodilation. Active hyperemia associated with graded treadmill exercise and coronary reactive hyperemia were examined in chronically instrumented awake dogs during control conditions, after intracoronary infusion of adenosine deaminase (5 units/kg/min for 10 minutes), and after adenosine receptor blockade with 8-phenyltheophylline. Both adenosine deaminase and 8-phenyltheophylline caused a rightward shift of the dose-response curve to intracoronary adenosine; 8-phenyltheophylline was significantly more potent than adenosine deaminase. Adenosine deaminase caused a 33 +/- 7 to 39 +/- 3% decrease in reactive hyperemia blood flow following coronary occlusions of 5-20 seconds duration, respectively, while 8-phenyltheophylline produced a 40 +/- 6 to 62 +/- 8% decrease in reactive hyperemia. Increasing myocardial oxygen consumption during treadmill exercise was associated with progressive increase of coronary blood flow. Neither adenosine deaminase nor 8-phenyltheophylline attenuated the increase in coronary blood flow or the decrease of coronary vascular resistance during exercise. Neither agent altered the relation between myocardial oxygen consumption and coronary blood flow. Thus, although both adenosine deaminase and 8-phenyltheophylline antagonized coronary vasodilation in response to exogenous adenosine and blunted coronary reactive hyperemia, neither agent impaired coronary vasodilation associated with increased myocardial oxygen requirements produced by exercise. These findings fail to support a substantial role for adenosine in mediating coronary vasodilation during exercise.

Effects of atrial natriuretic peptide on coronary vascular resistance in the intact awake dog

Atrial natriuretic peptide has been reported to cause vasoconstriction, vasodilation or no change of coronary vascular resistance in isolated perfused hearts or in open chest animal models. Because general anesthesia and acute surgical trauma may perturb baseline coronary hemodynamics and alter responses to experimental interventions, this study examined the effects of human atrial natriuretic peptide (arginine-102-tyrosine-126) and rat atriopeptin II (serine-103-arginine-125) on the coronary circulation of unsedated, awake dogs. Studies were performed in 12 chronically instrumented animals in which a surgically implanted electromagnetic flow probe and intracoronary catheter allowed measurement of left circumflex coronary blood flow during intraarterial administration of the atrial natriuretic peptides. Bolus doses of both human atrial natriuretic peptide and rat atriopeptin II produced dose-dependent coronary vasodilation; the threshold for coronary vasodilation was 0.2 micrograms/kg body weight for both agents. Coronary vasodilation produced by human atrial natriuretic peptide was not antagonized by adenosine receptor blockade or by cyclooxygenase inhibition with indomethacin. Thus, atrial natriuretic peptides produced dose-dependent coronary vasodilation in intact awake dogs that was not dependent on adenosine-mediated or prostaglandin-mediated mechanisms.

Effects of atrial natriuretic peptide in the canine coronary circulation

Atriopeptin II has been reported to cause profound coronary vasoconstriction in the isolated perfused guinea pig heart and in the blood perfused canine heart. Consequently, this study was carried out to examine possible mechanisms by which vasomotor effects of human atrial natriuretic peptide (ANP) occur in the canine coronary circulation. Bolus dosages of ANP were administered into the left circumflex coronary artery of in situ dog hearts perfused at constant flow rate. ANP produced dose-related coronary vasodilation with a threshold dosage of 2 ng/kg; a dosage of 2 micrograms/kg caused a 27 +/- 4% decrease in coronary vascular resistance. Coronary vasodilation produced by ANP was not altered by beta-adrenergic blockade with propranolol (1 mg/kg i.v.). In addition, neither adenosine receptor blockade with 8-phenyltheophylline (5 mg/kg i.v.) nor cyclooxygenase inhibition with indomethacin (5 mg/kg i.v.) significantly altered the response to intra-arterial ANP. These data demonstrate that in the in vitro blood perfused canine heart, ANP administered intra-arterially results in coronary vasodilation that does not utilize adenosine-dependent or prostaglandin-dependent mechanisms.

Postsynaptic alpha 1- and alpha 2-adrenergic mechanisms in coronary vasoconstriction

This study examined the relative importance of postsynaptic alpha 1- and alpha 2-adrenoceptors in mediating coronary vasoconstriction in open chest dogs in which the left circumflex coronary artery was cannulated and perfused at a constant rate. The cervical vagus nerves and central connections of the stellate ganglia were transected, and beta-adrenergic blockade was produced with propranolol. Coronary vasoconstriction occurred in response to intraarterial administration of both the alpha 1-agonist phenylephrine and the alpha 2-agonist BHT 933. The response to phenylephrine was partially blocked with prazosin and nearly completely eliminated by yohimbine. The response to BHT 933 was resistant to prazosin, but almost completely blocked by yohimbine. Coronary vasoconstriction produced by norepinephrine was resistant to prazosin, but was blunted by alpha 2-adrenergic blockade with yohimbine or idazoxan. Prazosin produced some blunting of coronary vasoconstriction in response to small doses of epinephrine, while yohimbine markedly attenuated epinephrine-induced vasoconstriction at all doses used. Measurements of regional myocardial blood flow with radioactive microspheres demonstrated no transmural redistribution of perfusion during vasoconstriction produced by either alpha 1- or alpha 2 stimulation. Thus, although stimulation of both alpha 1- and alpha 2-adrenoceptors is capable of causing coronary vasoconstriction, vasoconstriction in response to norepinephrine and epinephrine is mediated principally by postsynaptic alpha 2-adrenoceptors.

Effects of nonselective and selective alpha 1-adrenergic blockade on coronary blood flow during exercise

This study was made to evaluate the relative importance of alpha 1- and alpha 2-adrenergic vasoconstrictor influences in opposing the increase in coronary blood flow that occurs during exercise. The effects of selective alpha 1-adrenergic blockade with prazosin were compared with nonselective alpha-adrenergic blockade with phentolamine on coronary hemodynamics during exercise in chronically instrumented dogs. During control conditions, graded treadmill exercise resulted in progressive increases of myocardial oxygen consumption; this was associated with increased coronary blood flow as well as with increased myocardial oxygen extraction. Although prazosin and phentolamine caused similar reductions of arterial pressure, phentolamine increased heart rate, myocardial oxygen consumption, and coronary blood flow at equivalent exercise levels, and prazosin did not significantly alter these variables. These effects of phentolamine appeared to result from blockade of presynaptic alpha 2-adrenergic receptors, which normally modulate norepinephrine release, that resulted in increased sympathetic effects on the heart. However, at comparable levels of myocardial oxygen consumption, prazosin and phentolamine resulted in similar significant increases of coronary venous PO2 and decreases of coronary vascular resistance. These data support a modest role for alpha 1-adrenergic coronary vasoconstriction during exercise but fail to document an additional role for postsynaptic alpha 2-adrenergic coronary vasoconstriction during exercise.

Myocardial blood flow during exercise in dogs with left ventricular hypertrophy produced by aortic banding and perinephritic hypertension

This study tested the hypothesis that for similar degrees of left ventricular hypertrophy, subendocardial blood flow would be facilitated by the increased diastolic coronary perfusion pressure associated with arterial hypertension, as compared with hypertrophy produced by banding the ascending aorta. Left ventricular hypertrophy was produced with perinephritic hypertension in seven adult dogs and by banding the ascending aorta in nine adult dogs. Left ventricular/body weight ratios were 6.15 +/- 0.59 g/kg in the hypertensive animals and 6.87 +/- 0.47 g/kg in dogs with aortic banding, as compared with 4.23 +/- 0.23 g/kg in seven normal dogs (p less than .01). Studies were performed at rest and during two stages of treadmill exercise to achieve heart rates of 195 and 260 beats/min. Diastolic aortic pressure was increased in animals with hypertension but not in dogs with aortic banding. Systolic ejection period was prolonged in dogs with aortic banding but not in hypertensive dogs. Mean blood flow per gram of myocardium measured with microspheres was similar at rest and during light exercise in all three groups of animals, whereas during heavy exercise blood flow was significantly greater than normal in both groups with hypertrophy. In normal dogs subendocardial/subepicardial (endo/epi) flow ratios did not change significantly during exercise. In both groups with hypertrophy, endo/epi ratios were normal at rest but decreased significantly during exercise. During heavy exercise the endo/epi ratio decreased to 0.73 +/- 0.08 in dogs with aortic banding as compared with 1.07 +/- 0.12 in hypertensive dogs (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nifedipine on coronary reactive and exercise induced hyperaemia

The effects of nifedipine on coronary vasodilation were studied during reactive hyperaemia after a transient coronary occlusion and during active hyperaemia associated with graded treadmill exercise. Studies were performed in 10 chronically instrumented dogs in which left circumflex coronary artery flow was measured with an electromagnetic flowmeter and myocardial oxygen extraction was determined from indwelling aortic and coronary sinus catheters. Thirty minutes after administration of nifedipine (10 micrograms.kg-1 iv), when coronary blood flow, arterial pressure, and heart rate had returned to control values, the vasodilatation following a 10 s coronary occlusion was significantly blunted, so that reactive hyperaemia blood flow debt repayment (mean(SEM)) was reduced from 387(39)% during control conditions to 270(33)% after nifedipine (p less than 0.05). In contrast, nifedipine did not alter the coronary vasodilatation that occurred in response to graded treadmill exercise so that the increase in coronary blood flow during exercise was not different from the control response. Thus, although nifedipine blunted ischaemic coronary vasodilatation during reactive hyperaemia, it did not alter coronary vasodilatation during active hyperaemia resulting from physiological increases of myocardial oxygen consumption.

Vasomotor properties of immature canine coronary collateral circulation

This study examined the ability of the immature coronary collateral circulation to undergo vasodilation in response to nitroglycerin and vasoconstriction in response to alpha-adrenoceptor stimulation. Studies were performed in 12 anesthetized dogs. Collateral flow was estimated from measurements of retrograde flow from the acutely ligated and cannulated anterior descending branch of the left coronary artery. Antegrade flow into the collateral-dependent myocardium was minimized by embolizing the anterior descending artery with 25-microns microspheres. Drugs to be tested were introduced into the left main coronary artery to reach collateral vessels arising from the left circumflex and septal arteries. Intracoronary administration of nitroglycerin (6 micrograms X kg-1 X min-1) resulted in a 33 +/- 7.7% increase in retrograde blood flow (P less than 0.01) and a 23 +/- 3.8% decrease in calculated collateral resistance (P less than 0.01). No significant change occurred in retrograde blood flow or calculated collateral resistance during cardiac sympathetic nerve stimulation after beta-adrenergic blockade with propranolol, selective alpha-adrenergic stimulation with phenylephrine (1 microgram X kg-1 X min-1), or selective alpha 2-stimulation with BHT 933 (2 micrograms X kg-1 X min-1). Thus, the immature coronary collateral circulation was capable of active vasomotion, as demonstrated by vasodilation in response to nitroglycerin, but did not undergo vasoconstriction in response to alpha-adrenoceptor stimulation.

Myocardial blood flow in left ventricular hypertrophy developing in young and adult dogs

This study was performed to test the hypothesis that growth of coronary vasculature would be facilitated if myocardial hypertrophy occurred during the period of normal body growth rather than in mature adult animals. Left ventricular hypertrophy was produced by banding the ascending aorta in eight young dogs 7 wk of age and in nine adult dogs. Adult dogs were studied 2 mo after aortic banding, whereas young dogs were allowed to grow to adulthood before study. Left ventricular weight-to-body weight ratios were increased to 6.88 +/- 0.36 g/kg in the young dogs and 6.64 +/- 0.47 in adult dogs; both were significantly greater than seven normal control animals (4.32 +/- 0.05; each P less than 0.01). Myocardial blood flow per gram measured with microspheres during quiet resting conditions was significantly higher in young dogs with left ventricular hypertrophy than in normal dogs. Myocardial blood flow rates during maximum coronary vasodilation with adenosine (4 mumol X kg-1 X min-1 iv) were similar in all three groups. However, since mean coronary perfusion pressure was higher in the dogs with aortic banding, minimum coronary vascular resistance per gram of myocardium was significantly higher in both young (21.1 +/- 3.1 mmHg X ml-1 X min X g) and adult dogs with left ventricular hypertrophy (21.8 +/- 2.2) than in the normal dogs (16.8 +/- 3.1; each P less than 0.01). Mean coronary vascular resistance for the total left ventricle was similar in all three groups of animals, suggesting that growth of coronary vasculature did not occur as the myocardium underwent hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nifedipine on the myocardial and vascular response to myocardial ischemia

Nifedipine reduces reactive hyperemia following brief coronary artery occlusions. To determine whether this is related to improvement in collateral blood flow to ischemic myocardium or alterations in myocardial oxygen consumption, ten chloralose anesthetized dogs were instrumented with coronary sinus catheters, circumflex artery flowmeters, and ultrasonic microcrystals for measurement of myocardial segment shortening. Myocardial oxygen consumption and circumflex coronary artery flow were determined at rest and during incremental infusions of isoproterenol. Myocardial blood flow measured with microspheres and segmental function were assessed during and following 30- and 60-second coronary artery occlusions. Thirty minutes after the intravenous administration of nifedipine, 10 micrograms/kg iv, all measurements were repeated. Nifedipine did not alter myocardial oxygen consumption or the relationship between oxygen consumption and circumflex coronary artery flow either at rest or during isoproterenol infusion. Following 60-second coronary occlusions, nifedipine reduced peak circumflex coronary artery flow (176 +/- 99 vs. 128 +/- 68 cc/min) and reactive hyperemia debt repayment (221 +/- 84 vs. 158 +/- 66%; p less than 0.01). Nifedipine did not alter flow to ischemic segments during coronary artery occlusions (0.16 +/- 0.10 vs. 0.19 +/- 0.13 ml/min/g mean transmural flow). Furthermore, nifedipine did not affect the severity of ischemic segment dysfunction, nor the rate of recovery of ischemic segment function following release of coronary artery occlusion. We conclude that the reduction in reactive hyperemia induced by nifedipine was not related to alterations in the severity of hypoperfusion in ischemic areas, or alterations in myocardial oxygen consumption. Reductions in reactive hyperemia produced by nifedipine did not impair recovery of mechanical function in postischemic myocardium.

Coronary blood flow during exercise following nonselective and selective alpha 1-adrenergic blockade with indoramin

Studies were performed to compare the effects of alpha 1-adrenergic blockade with indoramin and nonselective alpha-adrenergic blockade with phentolamine on coronary blood flow and myocardial oxygen consumption during exercise. Nine dogs trained to run on a motor-driven treadmill were instrumented with electromagnetic flowmeter probes on the left circumflex coronary artery, and aortic and coronary sinus catheters for determination of myocardial arteriovenous oxygen difference. During control conditions, myocardial oxygen consumption and coronary blood flow increased as a direct function of heart rate during exercise. Phentolamine caused a significant decrease in blood pressure, while heart rate, coronary blood flow, and myocardial oxygen consumption were significantly increased at rest and during all exercise stages. Although alpha 1-adrenergic blockade with indoramin caused a similar reduction of arterial pressure, heart rate was unaltered both at rest and during exercise. Coronary blood flow and myocardial oxygen consumption were unchanged by alpha 1-adrenergic blockade at rest and during light exercise: however, during the heaviest exercise stages alpha 1-blockade caused a significant decrease in myocardial oxygen consumption. These findings are in agreement with the concept that phentolamine, by blocking presynaptic alpha 2-adrenoceptors which normally modulate norepinephrine release, increases sympathetic activity during exercise while indoramin, by acting as a selective alpha 1-adrenergic blocker, does not produce this effect.

Persistence of regional left ventricular dysfunction after exercise-induced myocardial ischemia

To determine whether regional myocardial dysfunction occurring after exercise-induced ischemic might be caused by continued abnormalities of myocardial blood flow in the post-exercise period, nine dogs were instrumented with ultrasonic microcrystals for determination of circumferential segment shortening, circumflex artery electromagnetic flow probes, and hydraulic coronary artery occluders. Dogs performed treadmill exercise during partial inflation of the coronary artery occluder. When the stenosis was maintained after exercise (persistent stenosis), subendocardial flow = 0.79 +/- 0.42 ml/min per g vs. 1.39 +/- 0.43 ml/min per g control), and this was associated with continued dysfunction in the ischemic zone (segment shortening 45.4 +/- 36.9% of resting control). When the stenosis was released immediately after exercise (temporary stenosis), however, flow was markedly increased 1 min post-exercise (mean transmural flow 4.24 +/- 1.22 ml/min per g; subendocardial flow 4.18 +/- 1.52 ml/min per g), and this was associated with a transient increase in segment shortening to 104.5 +/- 9.3% of resting control. 5 min after exercise, however, moderate reductions in ischemic segment shortening were noted after both temporary stenosis and persistent stenosis runs, and these persisted for 30 min post-exercise. It is concluded that regional left ventricular dysfunction may persist for a significant period of time after exercise-induced ischemia. Furthermore, early after exercise, dysfunction is related to persistent abnormalities of myocardial blood flow, whereas late after exercise it is independent of primary reductions in myocardial blood flow.

Alterations of myocardial blood flow associated with experimental canine left ventricular hypertrophy secondary to valvular aortic stenosis

Experimental renovascular hypertension or supravalvular aortic constriction results in left ventricular hypertrophy and impaired minimum coronary vascular resistance. However, these experimental models expose the coronary arteries to increased intra-arterial pressure, so that hypertensive vascular changes might be responsible for the impaired minimum coronary resistance. This study was performed to test the hypothesis that left ventricular hypertrophy in the absence of increased coronary pressure results in abnormalities of myocardial perfusion. Aortic valve stenosis was produced by plication of the noncoronary aortic cusp of 11 dogs at 6-8 weeks of age. Studies were carried out when the animals reached adulthood; mean left ventricular:body weight ratio was 7.1 +/- 0.4 as compared to 4.4 +/- 0.3 g/kg in 11 normal dogs (P less than 0.01). Under quiet resting conditions, myocardial blood flow measured with microspheres was significantly greater than normal in dogs with aortic stenosis. However, during maximum coronary vasodilation with adenosine, mean left ventricular blood flow in dogs with hypertrophy (3.29 +/- 0.39) was substantially less than in normal dogs (6.19 +/- 0.54 ml/min per g; P less than 0.01), whereas minimum coronary resistance was increased from 14.1 +/- 1.7 in normal dogs to 23.7 +/- 5.4 mmHg. min X g/ml (P less than 0.01). To examine the response of myocardial perfusion to cardiac stress, blood flow was measured during pacing at 200 and 250 beats/min. Compared with normal dogs, animals with hypertrophy had a subnormal increase in myocardial blood flow during tachycardia; this perfusion deficit was most marked in the subendocardium. These data demonstrate that left ventricular hypertrophy alone, without increased coronary artery pressure, is associated with impaired minimum coronary vascular resistance and with abnormalities of myocardial blood flow during pacing stress.

Effect of indomethacin on coronary blood flow during graded treadmill exercise in the dog

This study tested the hypothesis that metabolites of arachidonic acid may contribute to the coronary vascular response to physiological increases of myocardial O2 consumption that occur during exercise. Studies were performed in eight chronically instrumented dogs with electromagnetic flowmeter probes on the left circumflex coronary artery and aortic and coronary sinus catheters. Data were obtained at rest and during graded treadmill exercise during control conditions and after administration of the cyclooxygenase inhibitor indomethacin. During control conditions heart rate, aortic pressure, and coronary blood flow increased progressively during exercise; this was accompanied by a significant increase in myocardial O2 extraction, as evidenced by a decrease in coronary venous O2 tension (Po2) particularly during the first stage of exercise. Indomethacin (5 mg/kg iv) resulted in marked blunting of the coronary vasodilator response to intracoronary arachidonic acid in anesthetized open-chest dogs. After administration of indomethacin to awake dogs, resting heart rate, aortic pressure, and coronary venous Po2 were unaltered, and the response of these variables to exercise was not changed. The increase in coronary blood flow during exercise was also unchanged after indomethacin, so that the relationship between myocardial O2 consumption and coronary blood flow was unaltered by cyclooxygenase inhibition. Thus we were unable to demonstrate a significant effect of the prostaglandin system in mediating the coronary vascular response to exercise.

Effect of nifedipine on myocardial blood flow during exercise in dogs with chronic coronary artery occlusion

The effect of nifedipine, 0.010 mg/kg intravenously, on myocardial blood flow was studied in 15 dogs 4 weeks after placement of an Ameroid constrictor on either the left circumflex or left anterior descending coronary artery to produce total coronary occlusion. Myocardial blood flow was measured with radionuclide-labeled microspheres at rest and during two levels of treadmill exercise to achieve a heart rate of 190 (light exercise) and 230 (heavy exercise) beats/min. During control conditions, increasing exercise resulted in a progressive increase in myocardial blood flow in normally perfused areas, but was associated with worsening subendocardial hypoperfusion in collateral-dependent areas. Nifedipine administration resulted in a transient reduction of arterial pressure and an increase in heart rate. To determine whether nifedipine exerted significant persistent effects on the coronary collateral circulation, measurements of myocardial blood flow were repeated beginning 30 minutes after nifedipine administration, at a time when heart rate and arterial pressure had returned to control levels. In normally perfused areas, nifedipine did not significantly alter myocardial blood flow at rest, but increased mean myocardial blood flow from 2.06 +/- 0.15 to 2.40 +/- 0.20 ml/min per g during light exercise (p less than 0.01), while blood flow during heavy exercise was not significantly altered. In collateral-dependent myocardial areas, the volume and transmural distribution of myocardial blood flow were not significantly altered after nifedipine administration either at rest or during exercise. These results fail to demonstrate persistent vasodilation of the coronary collateral vessels after the systemic hemodynamic effects of nifedipine have subsided.