A convenient method for obtaining bovine arterial blood

Abstract

The value, both academic and practical, of accurate knowledge regarding the mechanism of mammary secretion requires no emphasis. Our relative ignorance of what is actually going on in the mammary gland during its activity has been justly lamented from time to time by several writers. Attempts have recently been made to remedy this lack of knowledge, particularly in regard to the nature of the precursors, in the blood as it reaches the gland, of the characteristic milk constituents. It is with a major point in the technique of conducting experiments on bovine blood constituents that this paper is mainly concerned. An apparently direct method of obtaining information on the question of milk precursors is to make an accurate comparison between the composition of blood entering and that of blood leaving the udder of an actively lactating animal, the samples being taken approximately simultaneously. With due care, it is now possible to obtain useful information by this method. It does not, however, necessarily follow that a change in the amount of any given organic constituent of the blood during its passage through the mammary gland is due to such a substance being withdrawn to form a milk constituent. Part at least may be used up—in fact, some organic material borne by the blood must be used up—to provide the energy required for maintenance and secretory activity. The metabolic activity of the gland is evidenced by the marked change in the colour of the blood of the mammary vein as compared with the arterial blood, despite the speed ( see following paper) with which blood flows through the gland.

The Uptake of Plasma Lipid and Some Non-Lipid Constituents by the Mammary Gland of the Cow

“…The results indicate that the arteriovenous difference for glucose can account for most if not all that observed for total reducing substances by other workers (Graham et al 1936;Shaw 1943). In the goat, much of the glucose taken up by the mammary gland is utilized for the production of lactose and glycerol as has been demonstrated in isolated perfused goat udders (Hardwick, Lin~ell, and Mepham 1963).…”

“…Although it islmown that large amounts of plasma triglycerides are taken up and incorporated into milk fat by the mammary gland of the lactating· goat (Barry et al 1963;Lascelles et al 1964) the situation is not as clear for the cow. Arteriovenous studies have demonstrated an uptake of plasma neutral lipids (glycerides and possibly cholesterol esters) by the mammary gland of the cow (Lintzell 1934;Graham, Kay, and McIntosh 1936;Voris, Ellis, and Maynard 1940;McClymont and Vallance 1962) but have not shown any uptake of phospholipids. However, recent experiments with a lactating cow, which was given 14 0_ and 32P-Iabelled piasma lipids intravenously, have suggested that triglycerides, cholesterol esters, and phospholipids were involved in the transport of fatty acids to the )llammary gland.…”

Mammary‐gland blood flow and oxygen, glucose and volatile fatty acid uptake in the conscious goat

“…The presence of a stranger in addition to the experimenter did not appear to upset them. These precautions were taken because it has been shown in the cow that the disturbance of obtaining arteriovenous samples without local anaesthesia may seriously alter the blood composition, chiefly in respect of haemoglobin and fat (Graham, Kay & McIntosh, 1936;Shaw & Petersen, 1939). The maximum arteriovenous difference for haemoglobin or haematocrit was 3 00 and on average was less than 0-5 % in these experiments.…”