Sc. Calaghan et E. White, Contribution of angiotensin II, endothelin 1 and the endothelium to the slow inotropic response to stretch in ferret papillary muscle, PFLUG ARCH, 441(4), 2001, pp. 514-520
We investigated the contribution of angiotensin II and endothelin to the sl
ow positive inotropic response observed following stretch of isolated ferre
t papillary muscle from 88% to 98% of the length at which maximum force is
generated. Angiotensin antagonists losartan and saralasin did not affect th
e magnitude of the slow response in ferret papillary muscle. The ETA-select
ive antagonist BQ123 slightly reduced the magnitude of the slow response (P
>0.05). In the presence of PD145065 (an ETA and ETB antagonist), the magnit
ude of the slow response was reduced significantly by 50%. Removal of the e
ndothelium with 1% Triton X-100 reversed the slow response to stretch. We c
onclude that, in the ferret, endothelin 1 acting through ETA and ETB recept
ors, contributes to the slow response although it is not the sole mediator.
Angiotensin II is not a prerequisite for the slow response to stretch. We
have shown for the first time that the endocardial endothelium plays a pivo
tal role in this phenomenon in cardiac papillary muscle.