Contractile reserve but not tension is reduced in monocrotaline-induced right
ventricular hypertrophy.
Versluis, J. Pieter, Johannes W. Heslinga, Pieter Sipkema, and Nico Westerhof.
Laboratory for Physiology, Institute for Cardiovascular Research, Vrije University
Medical Center, 1081 BT Amsterdam, The Netherlands
APStracts 10:0398H, 2003.
The objective of this study was to evaluate the role of right ventricular hypertrophy on
developed tension and contractile reserve of rat papillary muscle using a model of
Monocrotaline-induced pulmonary hypertension. Calcium handling and influence of
«hco3» were also addressed by using two different buffers (Bicarbonate and HEPES).
Wistar rats were injected with either MCT (40 mg/kg sc) or vehicle (CON). Isometrically
contracting right ventricular papillary muscles were studied at 80% of Lmax. Contractile
reserve (1 «minus» Fdev/Fmax) was calculated from developed tension (Fdev) and
maximal tension (Fmax). Calcium recirculation was determined with postextrasystolic
potentiation. Both groups of muscles were superfused with either bicarbonate (CON-B
and MCT-B, both n = 6) or HEPES (CON-H and MCT-H, both n = 6) buffer. With
hypertrophy, contractions were slower but developed tension was not changed. However,
maximal tension was decreased (P < 0.05). With bicarbonate, maximal tension
decreased from 23.8 ± 6.5 mN•mm«minus»2 in CON-B, to 13.7 ± 3.3 mN•mm«minus»2
in MCT-B. With HEPES it decreased from 16.3 ± 3.5 mN•mm«minus»2 (n = 6, CON-H)
to 8.3 ± 1.6 mN•mm«minus»2 (MCT-H). Contractile reserve during hypertrophy was
therefore also decreased (P < 0.05). With Bicarbonate it decreased from 0.73 ± 0.03
(CON-B) to 0.55 ± 0.04 (MCT-B). With HEPES it decreased (P < 0.001) from 0.64 ±
0.07 (CON-H) to 0.19 ± 0.06 (MCT-H). The recirculation fraction decreased (P < 0.05)
from 0.59 ± 0.04 in CON-B to 0.44 ± 0.04 in MCT-B. We conclude that contractile
reserve and recirculation fraction are impaired during hypertrophy, with a stronger effect
under HEPES than bicarbonate superfusion.
Received 27 June 2002; accepted in final form 16 September 2003
APS Manuscript Number H536-2.
Article publication pending Am J Physiol Heart Circ Physiol
ISSN 1080-4757 Copyright 2003 The American Physiological Society.
Published in APStracts on 21 November 2003