STUDIES ON THE PITUITARY.—IV. QUANTITATIVE COMPARISON OF PRESSOR ACTIVITY

¹ The Physiology Department, Edinburgh University

1. A method of standardising pressor activity of pituitary extracts with an order of precision not significantly inferior to that obtained with the virgin uterus of the guinea-pig is described.

2. For quantitative or clinical purposes involving action on the circulatory system, pituitary extracts free of depressor substances can be prepared, as SCHAFER and VINCENT indicated, by alcoholic extraction.

3. For depressor-free extracts tolerance is a function of the dosage and time interval between successive injections.

4. With appropriate time intervals a remarkable constancy of response of the same character and order of magnitude as the initial rise in blood-pressure may be obtained with the spinal cat for periods up to twenty hours.

5. With submaximal doses the period of recovery for response of the same order as that obtained on initial injection is rather less than an hour.

6. Consistent discrimination tending to increase as the experiment proceeds may be obtained for ten or twelve hours between hourly doses differing by 10 per cent.

7. The curve obtained by plotting increase of pressure against dose shows the steepest gradient near a point corresponding to half the dose requisite to produce maximal response; and the best discrimination is obtained by working with a standard in the neighbourhood of this value.

8. It is therefore suggested that the match should be made against a standard for which a curve of reference is kept in use: the limit of accuracy can be defined in any instance by interpolating a known dilution between two injections of the standard.