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

Robert K. Goldman, Afaf S. Azar, Julia M. Mulvaney, Carmen Hinojosa-Laborde, Joseph R. Haywood, Virginia Brooks

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Abstract

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.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume296
Issue number5
DOIs
StatePublished - May 2009

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Estrous Cycle
Baroreflex
Steroids
Arterial Pressure
Heart Rate
Diestrus
Proestrus
Estrus
Kidney
Gonadal Hormones
Luteal Phase
Gonadal Steroid Hormones
Ovariectomy

Keywords

  • Diurnal
  • Ovariectomy
  • Renal sympathetic nerve activity
  • Telemetry

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

Cite this

Baroreflex sensitivity varies during the rat estrous cycle : Role of gonadal steroids. / Goldman, Robert K.; Azar, Afaf S.; Mulvaney, Julia M.; Hinojosa-Laborde, Carmen; Haywood, Joseph R.; Brooks, Virginia.

In: American Journal of Physiology - Regulatory Integrative and Comparative Physiology, Vol. 296, No. 5, 05.2009.

Research output: Contribution to journalArticle

Goldman, Robert K. ; Azar, Afaf S. ; Mulvaney, Julia M. ; Hinojosa-Laborde, Carmen ; Haywood, Joseph R. ; Brooks, Virginia. / Baroreflex sensitivity varies during the rat estrous cycle : Role of gonadal steroids. In: American Journal of Physiology - Regulatory Integrative and Comparative Physiology. 2009 ; Vol. 296, No. 5.
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abstract = "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.",
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