Estrogen attenuates the cardiovascular and ventilatory responses to central command in cats

Abstract

. Estrogen attenuates the cardiovascular and ventilatory responses to central command in cats. J Appl Physiol 92: 1635-1641, 2002; 10.1152/japplphysiol.00981. 2001.-Static exercise is well known to increase heart rate, arterial blood pressure, and ventilation. These increases appear to be less in women than in men, a difference that has been attributed to an effect of estrogen on neuronal function. In decerebrate male cats, we examined the effect of estrogen (17␤-estradiol; 0.001, 0.01, 0.1, and 1.0 g/kg iv) on the cardiovascular and ventilatory responses to central command and the exercise pressor reflex, the two neural mechanisms responsible for evoking the autonomic and ventilatory responses to exercise. We found that 17␤-estradiol, in each of the three doses tested, attenuated the pressor, cardioaccelerator, and phrenic nerve responses to electrical stimulation of the mesencephalic locomotor region (i.e., central command). In contrast, none of the doses of 17␤-estradiol had any effect on the pressor, cardioaccelerator, and ventilatory responses to static contraction or stretch of the triceps surae muscles. We conclude that, in decerebrate male cats, estrogen injected intravenously attenuates cardiovascular and ventilatory responses to central command but has no effect on responses to the exercise pressor reflex. exercise pressor reflex; heart rate; arterial blood pressure; tendon stretch; muscle afferents TWO NEURAL MECHANISMS, namely, central command and the exercise pressor reflex, are widely believed to evoke the cardiovascular and ventilatory responses to exercise (17, 36). Central command is defined as the parallel activation of neural circuits in the brain stem and spinal cord that control motor, ventilatory, and cardiovascular function. Central command does not require feedback from the periphery (10). The exercise pressor reflex arises from the stimulation of group III and IV muscle afferents. This reflex is believed to be evoked by mechanical and metabolic factors in muscles while they are contracting (4,18,24).The cardiovascular responses to exercise have been reported to be less in premenopausal women than in postmenopausal women or men (11,12). The difference has been attributed to estrogen, a hormone that is well known to decrease vascular resistance (28). In addition, estrogen administration to postmenopausal women with mild hypertension has been reported to attenuate the pressor response to exercise (27). These studies, however, provided no direct evidence that estrogen exerted its effect on central command or the exercise pressor reflex. Consequently, we were prompted to investigate this issue in decerebrate cats. Using this preparation, we were able to examine the effect of estrogen on the cardiovascular and ventilatory responses to central command and to the exercise pressor reflex, each of which was evoked separately. METHODSGeneral. Adult male cats were anesthetized with a mixture of 5% halothane and oxygen. Catheters were placed in the right jugular vein and common carotid artery for de...

Effect of menstrual cycle and gender on ventilatory and heart rate responses at the onset of exercise

“…3). One possible reason for the discrepancy between the Hayes et al (2002) study and the present study is related to the differences in experimental design. Their experiment dramatically increased the concentration of estrogen over a short of time by giving it to the male cats as a bolus.…”

“…It is considered that brief voluntary exercise mobilizes not only peripheral reflex but also central command and that brief passive movement is a form of movement in which peripheral reflex functions almost exclusively (Miyamura et al 1992;Ishida et al 2000). Recently, Hayes et al (2002) administered estrogen (17b-estradiol) to decerebrate male cats and examined the cardiovascular and ventilatory responses while stimulating parts related to central command and peripheral reflex for 60 s every 15 min. They reported that estrogen attenuated these responses to central command but not to peripheral reflex.…”

“…It has been shown in experiments with cats that progesterone exerts a respiratory effect on the hypothalamus (Bayliss et al 1990) and that estrogen (17b-estradiol) attenuates the cardiovascular and ventilatory responses not to peripheral reflex but to central command (Hayes et al 2002).…”

New insights into the effects of age and sex on arterial baroreflex function at rest and during dynamic exercise in humans

“…Recent evidence suggests that estrogen can attenuate both central command and the exercise pressor reflex (Ebert et al, 1992; Ettinger et al, 1998; Hayes et al, 2002; Schmitt et al, 2003), which as indicated above, are key contributors to ABR resetting during exercise. Given these findings, we investigated whether sex and/or physiological fluctuations in ovarian hormone concentration could modulate ABR resetting and function during dynamic exercise (Kim et al, 2012).…”

Effect of sex and ovarian hormones on carotid baroreflex resetting and function during dynamic exercise in humans

“…Women had a mean menstrual cycle length of 29 Ϯ 2 days, which was identified prior to studies. For experimental protocol 2 (Menstrual cycle and CBR resetting and function during exercise), 10 of the women who participated in protocol 1 were also studied during two additional phases of their menstrual cycle, late follicular (LF, days 10 -12) and midluteal (ML, days [22][23][24][25][26]. These participants were asked to use a ClearblueR Easy ovulation self test kit between days 9 and 15 of the menstrual cycle to detect the surge of luteinizing hormone in urine and more accurately identify the LF phase.…”