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This Article Full Text Full Text (PDF) Supplemental Figures All Versions of this Article: 296/5/R1419    most recent 91030.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Goldman, R. K. Articles by Brooks, V. L. Search for Related Content PubMed PubMed Citation Articles by Goldman, R. K. Articles by Brooks, V. L.

NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Baroreflex sensitivity varies during the rat estrous cycle: role of gonadal steroids

¹Portland Veteran Affairs Medical Center, Department of Surgery, Portland, Oregon; ²Oregon Health & Science University, Department of Physiology and Pharmacology, Portland, Oregon; ³University of Texas Health Science Center at San Antonio, Department of Anesthesiology, San Antonio, Texas; and ⁴Michigan State University, Department of Pharmacology and Toxicology, East Lansing, Michigan

Submitted 18 December 2008 ; accepted in final form 25 February 2009

Baroreflex sensitivity (BRS) increases in women during the luteal phase of the menstrual cycle, when gonadal hormones are elevated, but whether a similar cycle-dependent variation in BRS occurs in rats is unknown. In addition, whether cyclic BRS changes depend on gonadal steroids has not been previously investigated. To test these hypotheses, BRS was determined in cycling female rats using two approaches: 1) baroreflex control of renal sympathetic nerve activity (RSNA) in anesthetized rats; 2) cardiovagal spontaneous BRS (sBRS) in conscious rats instrumented for continuous telemetric measurements of mean arterial pressure (MAP) and heart rate (HR). MAP, HR, and sBRS were also measured in rats 2–3 and 5–6 wk following ovariectomy (OVX), to eliminate gonadal steroids. In anesthetized rats, RSNA BRS gain was increased (P < 0.01) during proestrus (–4.8±0.5% control/mmHg) compared with diestrus/estrus (–2.8 ± 0.3% control/mmHg). Similarly, a proestrous peak in sBRS was observed in conscious rats (1.66 ± 0.07 ms/mmHg, proestrus; 1.48 ± 0.06 ms/mmHg, diestrus/estrus; P < 0.001). OVX eliminated estrous cycle-induced variation in sBRS. In addition, OVX reduced (P < 0.05) diurnal variations in MAP (5.9 ± 0.3 vs. 3.9 ± 0.5 mmHg) and HR [54 ± 4 vs. 39 ± 3 beats per minute (bpm)], and abolished diurnal variations in sBRS. Finally, while MAP, HR, and sBRS were decreased 2–3 wk following OVX, 3 wk later, MAP and sBRS increased, and HR decreased further. No changes in MAP, HR, or sBRS were seen with time in sham OVX controls. In summary, RSNA and cardiovagal sBRS vary during the rat estrous cycle, and this variation is abolished by OVX. We conclude that sex steroid hormones are required for both cyclic and diurnal changes in BRS in rats.

renal sympathetic nerve activity; ovariectomy; diurnal; telemetry