STUDIES ON THE PITUITARY.—III. THE VASOMOTOR ACTIVITY OF PITUITARY EXTRACTS THROUGHOUT THE VERTEBRATE SERIES

¹ The Department of Physiology, The University, Edinburgh

In this communication an attempt has been made to explore the possible existence of independent components of the vasomotor activity of pituitary extracts by studying their effects in terrestrial vertebrates other than mammals. A comparison of histamine and other reagents with that of commercial pituitary preparations and laboratory pituitary products free from the substances producing a depressor response in the mammal has been made in the bird (duck and fowl), reptile (tortoise), and amphibian (frog). Pituitary extracts do not produce perceptible effects on the blood-pressure of the reptile and amphibian, when administered in quantities which are of an order of magnitude to which physiological significance could be justifiably attached. Whereas adrenaline produces a rise in arterial blood-pressure in all four classes of airbreathing vertebrates, pituitary extracts which had no depressor action in the mammal consistently evoke depression in bird and reptile : and there seems to be a strong presumption in favour of the conclusion that the pronounced depressor action of small doses of pituitary extract on the avine circulation is not due to the substance or substances responsible for the lowering of blood-pressure in the mammal. It has been necessary to reinvestigate the depressor response in the mammal, and the results obtained demonstrate the part played by initial pressure in determining the character of the response to successive doses of pituitary extract and to histamine. Emphasis is laid on the misleading nature of comparisons indiscriminately based on testing with etherised and decerebrate animals in previous biochemical investigation into the nature of the pressor activity of pituitary extract.

The expenses of this research were defrayed in part by a grant from the Earl of Moray Fund.