Late pregnancy in conscious rats is associated with a 10 mmHg decrease in resting mean arterial pressure (P<0.01), increased heart rate, and enhanced baroreflex-mediated bradycardia.
Does pregnancy alter baroreflex control of heart rate and blood pressure responses to vasoactive drugs in conscious rats?
Late pregnancy in conscious rats is associated with decreased resting blood pressure, increased heart rate, diminished systemic pressor responses to alpha-adrenergic stimulation, and enhanced baroreflex-mediated bradycardia.
p-value: p=<0.01
The goal of the present study was to examine baroreflex control of heart rate during pregnancy in chronically instrumented unrestrained rats. The same rats (n = 6) were studied before conception, again on gestational days 5, 12, and 19, and last on postpartum day 6; thus each rat served as its own control. Time control experiments were also conducted in a separate group of virgin rats (n = 7). Resting mean arterial pressure decreased by 10 mmHg on gestational day 19 (P less than 0.01 vs. prepregnant), and heart rate significantly increased by approximately 10% relative to time control rats. Dose-response curves were constructed for methoxamine and sodium nitroprusside comparing the various dosages with systemic pressor and depressor responses, respectively. The dose-response relationship for methoxamine was shifted to the right in gravid rats of 19 gestational days (P less than 0.03 vs. prepregnant), indicating an attenuation of alpha-adrenergic receptor-mediated pressor responsiveness. In contrast, depressor responses to sodium nitroprusside were not significantly altered in pregnancy. Baroreflex-mediated bradycardia was unchanged until gestational day 19, when enhanced bradycardia responses to methoxamine were observed. Baroreflex-mediated tachycardic responses elicited by sodium nitroprusside were not affected at any stage of pregnancy. Baroreflex control of heart rate did not change significantly with either increases or decreases of blood pressure in time control experiments. We conclude that during late pregnancy in conscious rats 1) resting blood pressure decreases and heart rate increases, 2) systemic pressor responses to methoxamine are diminished, and 3) baroreflex-mediated bradycardia is enhanced.
Conrad et al. (Sun,) conducted a other in Pregnancy (n=13). Pregnancy vs. Prepregnant state and virgin time control rats was evaluated on Resting mean arterial pressure (p=<0.01). Late pregnancy in conscious rats is associated with a 10 mmHg decrease in resting mean arterial pressure (P<0.01), increased heart rate, and enhanced baroreflex-mediated bradycardia.