AJP - Regulatory, Integrative and Comparative Physiology, Vol 259, Issue 3 405-R410, Copyright © 1990 by American Physiological Society
Central effects of substance P and somatostatin in conscious, streptozotocin-treated rats
K. C. Tomlinson, S. M. Gardiner and T. Bennett
Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham, United Kingdom.
Cardiovascular responses to intracerebroventricular (icv) injections of
substance P and somatostatin were measured in Long-Evans and Brattleboro
rats treated with streptozotocin (STZ) or saline. Substance P icv evoked
similar pressor responses and tachycardia in STZ-treated and saline-treated
Long-Evans rats, together with signs of behavioral activation (i.e.,
arousal). As a group, Brattleboro rats did not respond significantly to icv
substance P, although some individual rats showed clear cardiovascular and
behavioral responses. These findings may indicate a reduced sensitivity to
icv substance P in Brattleboro rats but show no differences attributable to
STZ treatment. Hence, diminished pressor responses to icv angiotensin II
(observed previously) may be specific to sympathoadrenal activation
associated with drinking. Somatostatin caused a pressor effect in
saline-treated, but not in STZ-treated, Long-Evans rats, which was probably
due to arginine vasopressin (AVP)-mediated mechanisms because it was not
present in either saline-treated or STZ-treated Brattleboro rats. Both
control and STZ-treated Long-Evans rats showed a bradycardic response to
somatostatin that was not seen in Brattleboro rats. These results indicate
that different AVP-mediated mechanisms might be responsible for the pressor
and bradycardic effects of icv somatostatin. It is possible that impairment
of central somatostatin-mediated AVP release contributes to the diminished
role of AVP in blood pressure recovery following ganglion blockade in
STZ-treated rats described previously.
