Increase In Maximal Response Research Articles

The effect of temperature changes on tachyphylaxis to angiotensin in vitro.

The effect of heat on the contractility and binding of 14C-angiotensin to guinea pig aortic strips was studied. It was found that heating strips to 47 °C for 20 min causes an increase in maximal response as well as a shift to the left of the dose–response curve for angiotensin while responses to noradrenaline (NA) remain unchanged. This procedure also increases the onset of tachyphylaxis to 10−5 M angiotensin. Heating (47 °C) for varying periods of time decreases the binding of 14C-angiotensin by about 60%. This effect does not seem to be related to the time of heating. It is postulated that this reduction in binding reflects denaturation of nonspecific binding sites on the cell membrane. Heating (47 °C, 20 min) enhanced the binding of 14C-angiotensin to aortic strips which had been rendered tachyphylactic to 10−5 M angiotensin. It is suggested that this is due to the induction of new binding sites.