Role of angiotensin II in altered baroreflex function of conscious rabbits during late pregnancy.
OBJECTIVE
Pregnancy alters baroreflex control of heart rate in conscious rabbits, but the mechanism for this action is unknown. This study tested the hypothesis that endogenous angiotensin II is the mediator.


METHODS
To test this hypothesis the baroreflex relationship between arterial pressure and heart rate in conscious rabbits was determined before and after administration of the angiotensin II AT1 receptor antagonist losartan (n = 7) before pregnancy and at the end of gestation.


RESULTS
Pregnancy decreased mean arterial pressure, increased heart rate, and modified the reflex by shifting the mean arterial pressure-heart rate relationship to a lower pressure level, by increasing minimum heart rate, and by decreasing baroreflex gain (P < .05). Before pregnancy, losartan decreased baroreflex gain but had no other effect on reflex function. In contrast, during late gestation losartan further decreased mean arterial pressure, further decreased reflex gain, decreased maximum heart rate, and shifted the curve to a lower mean arterial pressure level (P < .05).


CONCLUSIONS
These results suggest that in conscious rabbits during pregnancy endogenous angiotensin II contributes to hypotension-induced tachycardia but does not decrease reflex gain or elevate minimum heart rate.
Department of Physiology and Pharmacology, The Oregon Health Sciences University, Portland 97201-3098, USA.
V L
VL
Brooks
L S
LS
Welch
C M
CM
Kane
D000804:Angiotensin II / Q000502:physiology*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure; D005260:Female; D005328:Fetal Viability / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008098:Litter Size; D016015:Logistic Models; D019808:Losartan / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011817:Rabbits; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D057911:Angiotensin Receptor Antagonists; D000959:Antihypertensive Agents; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D009599:Nitroprusside; D010656:Phenylephrine; D019808:Losartan