The role of adrenoceptors in the hypertensive response to feeding
in the conscious calf.
Bowman, Emma C. J., G. P. Roderick, S. R. Bloom & A. V. Edwards.
Physiological Laboratory, University of Cambridge, Downing Street,
Cambridge CB2 3EG and Department of Medicine, Royal Postgraduate
Medical School, Hammersmith Hospital, Du Cane Road, London W12 9DS
United Kingdom
APStracts 3:0331R, 1996.
Ingestion of milk during suckling causes hypertension and tachycardia
in young, unweaned animals of many species, but these responses are
most pronounced in the calf. The present study was undertaken to
assess the extent to which this phenomenon depends upon activation of
adrenoceptors in these animals. Mean basal heart rate was 100+/-8
beats.min-1 and mean basal aortic blood pressure was 92+/-5 mm Hg.
The rise in heart rate during feeding was almost completely
suppressed after propranolol (2-4 mg.kg-1 i.v.) which also
significantly reduced the rise in blood pressure from 67+4 mm Hg to
44+3 mm Hg (P<0.005). Additional pretreatment with phentolamine
(1.0 mg.kg-1 and <0.1 mg.min-1.kg-1 i.v.) virtually eliminated
the rise in blood pressure during feeding which then rose by only 8+4
mm Hg (P<0.001). Section of both splanchnic nerves also
significantly reduced the rise in blood pressure during feeding,
especially after pretreatment with propranolol. Neither section of
the splanchnic nerves nor the administration of the blocking agents
significantly affected the rises in plasma insulin and pancreatic
polypeptide which occurred after feeding. There was no detectable
rise in plasma neuropeptide Y concentration in response to feeding.
The hypertensive response to direct electrical stimulation of the
peripheral end of a splanchnic nerve and to i.a. injections of
norepinephrine were completely abolished following combined
pretreatment with atropine, propranolol and phentolamine after the
ipsilateral adrenal vein had been tied off. It is concluded that the
cardiovascular changes which occur during feeding in these animals
are attributable very largely, if not entirely, to activation of
adrenoceptors.
Received 28 March 1996; accepted in final form 30 May 1996.
APS Manuscript Number R182-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996