Some effects of adrenaline, noradrenaline and acetylcholine on the foetal circulation in the lamb

Abstract

In the mature foetal lamb most of the blood which reaches the coronary arteries comes from the inferior vena cava through the foramen ovale. A substance injected into a femoral vein will be carried up into the inferior vena cava, and be diluted with a large quantity of blood returning from the placenta; about two-thirds will pass to the left atrium, and one-third to the right atrium (Dawes, Mott & Widdicombe, 1954). The two-thirds which passes into the left atrium will be still further diluted with blood returning from the lungs, and will then be ejected from the left ventricle into the aorta, whence a small fraction may reach the coronary vessels. But a substance injected into a jugular vein will not reach the coronary arteries until it has passed through the lungs, the placenta or the lower part of the foetus.These considerations led to the hypothesis that substances such as adrenaline and acetylcholine, which are readily destroyed in animal tissues, should have a different effect upon the foetal heart rate and blood pressure according to the route of injection. This paper describes observations which were made to test this hypothesis in lambs of different gestational ages, and also describes some effects of sympathetic amines upon umbilical blood flow. METHODSFifteen mature foetal lambs ( >132 days gestation) and ten immature foetal lambs (67-1 10 days gestation) were used. Pregnant ewes, mainly of a Clun-Hampshire cross-breed, but including a few Kerry Hill, were anaesthetized with sodium pentobarbitone. The initial intravenous injection was supplemented by an intravenous infusion of about 10-20 mg/kg/hr, sufficient to keep both ewe and lamb lightly anaesthetized. The lamb was delivered by Caesarean section and laid on a small warm table so arranged that the umbilical cord was not under tension.The blood pressure of the ewe was recorded by a mercury manometer from a carotid artery. The blood pressure of the foetus was recorded by a condenser manometer from a femoral artery. In the

Development of Baroreflex Activity in Unanesthetized Fetal and Neonatal Lambs

“…Barcroft and Barron (1) detected acute bradycardia in response to injection of epinephrine or norepinephrine and found that it was abolished by vagal section. This was confirmed by Dawes et al (2) in fetuses as young as 90 days. In animals near term, acute carotid occlusion causes a rise of arterial pressure, and impulses with the same periodicity as the heart rate can be detected in the afferent nerve from the carotid sinus (4, 11).…”

“…Although other workers have shown that baroreflex responses could be elicited in fetal (1)(2)(3)(4) and newborn (1) animals, all previous studies have been conducted in anesthetized animals with the fetus exteriorized. Since it is now well known that cardiovascular function in the fetus may be altered by anesthesia or exterioration (5), we studied fetal lambs in utero while the unsedated ewe stood quietly.…”

Relationship of arterial pressure and heart rate in fetal, new‐born and adult sheep.

“…It is well established in the fetal lamb that the heart slows when the arterial pressure is raised (Barcroft & Barron, 1945;Dawes, Mott & Rennick, 1956;Biscoe, Purves & Sampson, 1969;Brinkman, Ladner, WVeston & Assali, 1969). This has been confirmed in recent studies with unanaesthetized fetal lambs in utero, and the fall of heart rate has been attributed to baroreflex mechanisms (Shinebourne, Vapaavouri, Williams, Heymann & Rudolph, 1972;Maloney, Cannata, Dowling, Else & Ritchie, 1977;Ismay, Lumbers & Stevens, 1979).…”

Vasomotor responses in the hind limbs of foetal and new‐born lambs to asphyxia and aortic chemoreceptor stimulation

“…Injection of the same doses of cyanide into a jugular vein, the right ventricle, pulmonary or common carotid arteries of foetal lambs caused INTRODUCTION It was concluded from previous observations that the foetal circulation might well be under effective reflex control by systemic arterial chemoreceptors (Campbell, Dawes, Fishman & Hyman, 1967 a). Since cervical vagotomy caused a fall in arterial pressure near term (Reynolds, 1954;Dawes, Mott & Rennick, 1956;Born, Dawes & Mott, 1956), and the observations of Snyder & Rosenfeld (1937), Barcroft & Karvonen (1948) and Purves & Biscoe (1966) suggested that the carotid chemoreceptors were relatively inactive, it seemed possible that the aortic chemoreceptors might be involved.…”