AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 2 607-R614, Copyright © 1997 by American Physiological Society
Role of adrenoceptors in the hypertensive response to feeding in the conscious calf
E. C. Bowman, G. P. Roderick, S. R. Bloom and A. V. Edwards
Physiological Laboratory, University of Cambridge, United Kingdom.
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 on activation of adrenoceptors in
these animals. Mean basal heart rate was 100 +/- 8 beats/min and mean basal
aortic blood pressure was 92 +/- 5 mmHg. The rise in heart rate during
feeding was almost completely suppressed after propranolol (2-4 mg/kg iv),
which also significantly reduced the rise in blood pressure from 67 +/- 4
to 44 +/- 3 mmHg (P < 0.005). Additional pretreatment with phentolamine
(1.0 mg/kg and < or =0.1 mg x min(-1) x kg(-1) iv) virtually eliminated
the rise in blood pressure during feeding; it rose by only 8 +/- 4 mmHg (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 that 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
intra-arterial injections of norepinephrine were completely abolished after
combined pretreatment with atropine, propranolol, and phentolamine after
the ipsilateral adrenal vein had been tied off. It is concluded that the
cardiovascular changes that occur during feeding in these animals are
attributable very largely, if not entirely, to activation of adrenoceptors.
