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

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, approximately 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.

SUBMITTER: Goldman RK

PROVIDER: S-EPMC2689823 | biostudies-other | 2009 May

REPOSITORIES: biostudies-other

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

Goldman Robert K RK Azar Afaf S AS Mulvaney Julia M JM Hinojosa-Laborde Carmen C Haywood Joseph R JR Brooks Virginia L VL

American journal of physiology. Regulatory, integrative and comparative physiology 20090304 5

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) c ...[more]

PMID: 19261912

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Project description:Recent studies in rabbits suggest that insulin resistance and reduced brain insulin contribute to impaired baroreflex control of heart rate (HR) during pregnancy; however, the mechanisms are unknown. The rat model is ideal to investigate these mechanisms because much is known about rat brain baroreflex neurocircuitry and insulin receptor locations. However, it is unclear in rats whether pregnancy impairs the HR baroreflex or whether insulin resistance is involved. Therefore, this study tested the hypothesis that in rats pregnancy decreases HR baroreflex sensitivity (BRS) and that this decrease is related to concurrent decreases in insulin sensitivity (IS). BRS was quantified before, during, and after pregnancy using complementary methods: 1) spontaneous BRS (sBRS) derived from sequence method analysis of telemetric, continuous arterial pressure recordings; and 2) maximal BRS of complete sigmoidal baroreflex relationships. IS was measured (hyperinsulinemic euglycemic clamp) to determine whether BRS and IS change in parallel. sBRS was reduced at midgestation [pregnancy day 10 (P10)], returned to nonpregnant (NP) levels on P18, and fell again at late gestation (P20) (sBRS in ms/mmHg: NP, 1.66 + or - 0.04; P10, 1.17 + or - 0.11; P18, 1.55 + or - 0.12; P20, 1.31 + or - 0.05; n = 5; P < 0.05). Similar triphasic patterns were observed for both maximal BRS [in beats x min(-1) x mmHg(-1): NP, 4.45 + or - 0.52 (n = 10); P11-12, 2.76 + or - 0.11 (n = 7); P17-18, 3.79 + or - 0.14 (n = 5); P19-20, 2.32 + or - 0.40 (n = 8); P < 0.0001] and previous and current measurements of IS (in mg glucose x kg(-1) x min(-1): NP, 32 + or - 2; P19-20, 15 + or - 1; P < 0.0005). Furthermore, during pregnancy, the standard deviation (SD) of MAP increased, and the SD of HR decreased, indirectly suggesting baroreflex impairment. sBRS increased transiently during parturition, and sBRS, maximal BRS, and IS normalized 3-4 days postpartum. In conclusion, pregnancy decreases HR BRS in rats. The parallel temporal changes in BRS and IS suggest a mechanistic link.

Dataset Information

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

Publications

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

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