TY - JOUR
T1 - Mechanisms for attenuated pressor responses to α-agonists in ovine pregnancy
AU - Magness, Ronald R.
AU - Rosenfeld, Charles R.
N1 - Funding Information:
From the Departments of Pediatrics and Obstetrics and Gynecology, The University of Texas Southwestern Medical Center at Dallas. Supported by National Institutes of Health Grant Nos. HD08783 and HL34150. Received for publication August 31, 1987, revised January 8, 1988; accepted February 29, 1988. Reprint requests: Charles R. Rosenfeld, MD, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75235. *Postdoctoral fellow in reproductive biology, September 1982 through August 1984.
PY - 1988/7
Y1 - 1988/7
N2 - Attenuated pressor responses to angiotensin II and α-agonists normally occur during ovine pregnancy; however, for α-agonists it is not known to what extent this reflects alterations in cardiac output. We therefore compared peripheral and cardiac responses to α-agonists in pregnant (n = 6) and nonpregnant (n = 6) sheep, measuring mean arterial pressure, heart rate, and cardiac output before and during steady-state dose responses to norepinephrine (0.458 to 45.84 μg/min) and phenylephrine (1.29 to 129 μg/min). Both α-agonists caused dose-dependent increases in mean arterial pressure and systemic vascular resistance, more so in nonpregnant than pregnant sheep (p < 0.01), and decreases in cardiac output and heart rate (p < 0.01). In both nonpregnant and pregnant sheep the percent change in systemic vascular resistance generally exceeded the percent change in mean arterial pressure, reflecting decreases in cardiac output; however, at equivalent increases in percent change in mean arterial pressure and percent change in systemic vascular resistance, the fall in the percent change in cardiac output was greatest in pregnant sheep (p < 0.05). Also, at similar increases in mean arterial pressure the percent change in heart rate was greatest in pregnant sheep (p < 0.01). In contrast to angiotensin II, the attenuated pressor responses to α-agonists observed during ovine pregnancy are partly a result of reflex decreases in cardiac output mediated mainly through falls in heart rate.
AB - Attenuated pressor responses to angiotensin II and α-agonists normally occur during ovine pregnancy; however, for α-agonists it is not known to what extent this reflects alterations in cardiac output. We therefore compared peripheral and cardiac responses to α-agonists in pregnant (n = 6) and nonpregnant (n = 6) sheep, measuring mean arterial pressure, heart rate, and cardiac output before and during steady-state dose responses to norepinephrine (0.458 to 45.84 μg/min) and phenylephrine (1.29 to 129 μg/min). Both α-agonists caused dose-dependent increases in mean arterial pressure and systemic vascular resistance, more so in nonpregnant than pregnant sheep (p < 0.01), and decreases in cardiac output and heart rate (p < 0.01). In both nonpregnant and pregnant sheep the percent change in systemic vascular resistance generally exceeded the percent change in mean arterial pressure, reflecting decreases in cardiac output; however, at equivalent increases in percent change in mean arterial pressure and percent change in systemic vascular resistance, the fall in the percent change in cardiac output was greatest in pregnant sheep (p < 0.05). Also, at similar increases in mean arterial pressure the percent change in heart rate was greatest in pregnant sheep (p < 0.01). In contrast to angiotensin II, the attenuated pressor responses to α-agonists observed during ovine pregnancy are partly a result of reflex decreases in cardiac output mediated mainly through falls in heart rate.
KW - Cardiac output
KW - baroreflex
KW - heart rate
KW - pregnancy
KW - sheep
KW - systemic vascular resistance
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U2 - 10.1016/0002-9378(88)90531-5
DO - 10.1016/0002-9378(88)90531-5
M3 - Article
C2 - 3394743
AN - SCOPUS:0023808860
SN - 0002-9378
VL - 159
SP - 252
EP - 261
JO - American journal of obstetrics and gynecology
JF - American journal of obstetrics and gynecology
IS - 1
ER -