title: Modification of aortic contractility in the cardiomyopathic hamster.
abstract: 1. The functional arterial response in the cardiomyopathic hamster compared with inbred control, was investigated in thoracic aortae. For this purpose, vessels were cut into 6-mm rings and mounted in 20-ml organ baths. 2. In a first experimental series, the function of the endothelium was evaluated. Dose-response curves to acetylcholine (0.1 nM-10 microM) on phenylephrine (0.3 microM)-preconstricted rings of cardiomyopathic hamsters and inbred age-matched controls were comparable (log[EC50] of -7.08 +/- 0.12 and -7.18 +/- 0.12, respectively; n = 4). 3. Changes in contractility of cardiomyopathic hamster endothelium-denuded aortae were investigated. Dose-response curves to phenylephrine (1 nM-0.1 mM), angiotensin II (10 pM-0.3 microM), 5-hydroxytryptamine (5-HT) (1 nM-0.1 mM) and KCl (1 mM-0.1 M) were performed. Increased sensitivity in cardiomyopathic hamster aortae, compared to controls, was observed with phenylephrine (log[EC50] of -7.25 +/- 0.05 and -6.83 +/- 0.05, respectively, n = 6, P < 0.001) and angiotensin II (log[EC50] of -8.67 +/- 0.07 and -8.26 +/- 0.06, respectively, n = 6, P = 0.001) but not with 5-HT or KCl. A decreased maximum response in cardiomyopathic, compared to control, was observed with 5-HT (1.28 +/- 0.06 g vs 1.56 +/- 0.07 g, respectively, n = 6, P = 0.03). Comparable results were found in aortae with an intact endothelium. 4. No difference in the maximum contractile response to the G-protein activator, NaF (3, 10 and 30 mM) was observed in either group of animals. 5. Phorbol 12-myristate 13-acetate (PMA, 1-10 microM) was used to assess changes in the activity of protein kinase C (PKC). Contractility to PMA was increased in cardiomyopathic hamster aortae compared to controls (0.22 +/- 0.02 g vs 0.07 +/- 0.03 g at 3 microM, respectively, n = 6, P = 0.003). 6. Finally, cardiomyopathic hamsters aortae were found to be less sensitive when exposed to increasing concentrations of Ca2+ (10 microM-1 mM) in KCl-depolarized rings (0.58 +/- 0.04 g in cardiomyopathic vs 0.79 +/- 0.06 g in control aortae at 0.3 mM, n = 8, P = 0.03). 7. In conclusion, aortae from cardiomyopathic hamsters are more sensitive to phenylephrine and angiotensin II, but not to 5-HT, than those of controls. The increase in sensitivity does not implicate Ca2+ channels or Ca2+ itself since cardiomyopathic hamsters aortae are not more sensitive to KCl- and Ca(2+)-induced contraction. The greater effect of PMA on cardiomyopathic hamster aortae suggests that the increase in sensitivity to phenylephrine and angiotensin II involves an enhanced activity of PKC.
authors.affiliation: Faculté de pharmacie, Université de Montréal, Québec, Canada.
authors.forename: E C
authors.initials: EC
authors.lastname: Dumont
authors.forename: C
authors.initials: C
authors.lastname: Lambert
authors.forename: D
authors.initials: D
authors.lastname: Lamontagne
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D006224:Cricetinae; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology*; D005260:Female; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000503:physiopathology*; D009200:Myocardial Contraction / Q000187:drug effects*; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000494:pharmacology; D015398:Signal Transduction; D012969:Sodium Fluoride / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D011189:Potassium Chloride; D012969:Sodium Fluoride; D011493:Protein Kinase C; D000109:Acetylcholine