DEVELOPMENT OF CARDIOVASCULAR RESPONSES IN THE KITTEN

¹ Sherrington School of Physiology, St. Thomas's Hospital Medical School, London, S.E.1
² Department of Medicine, St. Thomas's Hospital Medical School, London, S.E.1

In anæsthetized kittens the mean arterial pressure and the pulse pressure double during the first 6 weeks of life; the heart rates recorded were the same as in the adult cat and did not change during this period. The vasomotor sympathetic system was active within 4 days of birth: there was both tonic activity, as demonstrated by a rise in arterial pressure after carotid occlusion, and a rise in pressure during asphyxia; the carotid sinus-cardiac centre mechanism responded to a rise in arterial pressure at birth. All these responses increased with age but had not reached adult activity by the 6th week of life. The carotid sinus-cardiac centre mechanism did not respond to a fall in blood pressure until 4 weeks of age. The infant heart was apparently more sensitive to the direct action of acetylcholine and the peripheral blood vessels relatively less sensitive than in the adult.

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Acknowledgments from Dr. I. M. Young are due firstly, to the Leverhume Trust for the Fellowship, held jointly with Dr. J. D. Martin, enabling the purchase of the New Electronic Products' equipment; secondly, to the National Spastics Society for grants for the support of Miss Irene Leets who gave invaluable technical assistance.

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