Acute Blockade of α-1-Adrenoreceptors has Similar Effects in Pregnant and Nonpregnant Rats

Abstract

Objective: To determine whether the level of activity of the sympathetic nervous system (SNS) is altered during pregnancy, specifically whether blood pressure (BP) control and control of renal hemodynamics are under greater tonic SNS control in pregnancy, indicative of an “underfilled” state.

Methods: Studies were conducted on 6 nonpregnant and 14 pregnant female rats and 9 males, measuring BP, renal hemodynamics, and electrolyte excretion in the conscious, unstressed state. Rats were studied in an initial baseline state and then following acute blockade of the α-1-adrenoceptor with prazosin.

Main Outcome Measures: Preplanned measurements were of systemic blood pressure and renal function in virgin rats and in mid- and late pregnancy. In view of the unexpected observations that α-1-adrenoceptor blockade caused renal vasoconstriction in conscious females, additional experiments were conducted on male rats.

Results: The usual midgestational rises in GFR and renal plasma flow were seen and BP fell in late pregnancy despite substantial plasma volume expansion, indicated by falls in hematocrit. In response to acute prazosin, similar falls occurred in BP in mid- and late pregnancy and in virgin females and males. In all groups, prazosin caused increased renal vascular resistance (RVR) and falls in GFR, RPF, and sodium excretion.

Conclusion: The activity of the SNS in control of BP and renal function is not altered during pregnancy in the rat. These studies suggest that the SNS senses the plasma volume as normal during pregnancy.

Key Words:

• Blood pressure
• Prazosin
• Renal vascular resistance
• Sodium excretion