CARDIOVASCULAR RESPONSES IN RABBITS OF DIFFERENT AGES TO HYPERTENSIN AND ADRENALINE

¹ Nuffield Institute for Medical Research, University of Oxford

In intact rabbits from birth to maturity, the rise of arterial pressure on intravenous injection of hypertensin, adrenaline and vasopressin (doses calculated per kg body weight) was used as an index of cardiovascular sensitivity. On this basis, sensitivity to hypertensin fluctuated with age but was similar at birth and in adults; in contrast, sensitivity to adrenaline and vasopressin decreased progressively with age.

The ganglion and adrenal medullary blocking agent presidal caused a progressively greater increase in sensitivity to injected hypertensin in older than in younger rabbits. Baroreceptor nerve section caused proportionately similar increases in sensitivity at all ages.

Acute nephrectomy caused a fall of 54 per cent in resting arterial blood pressure in newborn rabbits, but only 16 per cent in adults; this contrasted with falls of 1 per cent and 10 per cent respectively in dummy operations.

These observations are consistent with the view that the autonomic nervous system is not fully developed in the newborn rabbit. At this age the renin-angiotensin system appears to be of relatively greater importance than in the adult.

Note:

This work was supported by MRC grant G.969/29/B. Dr A. F. Green kindly supplied presidal. I should like to thank Dr G. S. Dawes for constructive criticism and Dr J. C. Mott for much helpful advice and discussion.