AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 5 1242-R1249, Copyright © 1990 by American Physiological Society
Role of catecholamines in regulating ovine median eminence blood flow
R. B. Page, M. Gropper, E. Woodard, J. Townsend, S. Davis and R. M. Bryan
Department of Surgery, Milton S. Hershey Medical Center of Pennsylvania State University, Hershey 17033.
Blood flow was measured in the ovine median eminence and neural lobe before
and after the intravenous infusion of dopamine (n = 7), the D1 agonist SKF
38393 (n = 4), the D2 agonist bromocriptine (n = 4), and the dopamine
antagonist haloperidol (n = 5). It was also measured before and after the
intracarotid infusion of dopamine into eight naive sheep and seven sheep
pretreated with phenoxybenzamine. Radiolabeled microspheres were used to
determine regional cerebral and regional neurohypophysial blood flows
(RNHBF) in these 35 adult female sheep anesthetized with pentobarbital
sodium. Samples for serum prolactin measurement by radioimmunoassay were
obtained before and after drug infusion. Intravenous dopamine infusion did
not change median eminence or neural lobe blood flow (RNHBF) but increased
renal and choroid plexus blood flow. Intravenous haloperidol caused a
significant fall in RNHBF and blood flow in choroid plexus, caudate
nucleus, and kidneys. Intracarotid dopamine infusion decreased RNHBF but
increased choroid plexus blood flow. RNHBF was significantly greater in the
seven sheep pretreated with phenoxybenzamine than in the eight naive sheep.
These findings do not support a role for dopamine in the regulation of
median eminence blood flow. The last observation does add support to the
hypothesis that norepinephrine or epinephrine interaction with
alpha-receptors plays a role in the control of ovine median eminence blood
flow and hence in the regulation of delivery of humoral messages from the
brain to the anterior pituitary gland.
