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Oestrogen and weight loss decrease isoproterenol-induced Fos immunoreactivity and angiotensin type 1 mRNA in the
Eric G Krause1, Kathleen S Curtis, Todd L Stincic
1Department of Psychology, Program in Neuroscience, Florida State University, Tallahassee, FL 32303-1270, USA.
Abstract:
Studies from our laboratory and others show that oestrogen reduces angiotensin II (Ang II)-induced water intake by ovariectomized rats. Elimination of endogenous oestrogen by ovariectomy causes weight gain that can be reversed or prevented by oestrogen replacement. Changes in body weight modify cardiovascular responses to Ang II but whether such changes have similar effects on central and behavioural responses to Ang II is unknown. The goal of this study was to evaluate the contributions of oestrogen and weight loss to isoproterenol (isoprenaline; Iso)-induced Fos immunoreactivity (IR) and to angiotensin type 1 (AT1) receptor mRNA in forebrain regions implicated in the control of fluid balance. Isoproterenol significantly increased Fos IR in the hypothalamic paraventricular and supraoptic nuclei, the subfornical organ (SFO), and the organum vasculosum of the lamina terminalis, but had no effect on AT1 mRNA expression. However, both Iso-induced Fos IR and the AT1 mRNA were attenuated in the SFO of the oestrogen and weight loss groups compared with that of the control group. Consequently, we examined the effect of weight loss on Iso-induced water intake and plasma renin activity (PRA) and found that weight loss decreased water intake after Iso, but had no effect on PRA. Thus, we propose that weight loss decreases Ang II-elicited water intake in the female rat by down-regulating the expression of the AT1 receptor.
Insights
Weight loss, not estrogen, reduces isoproterenol-induced water intake in female rats by decreasing angiotensin II type 1 receptor expression in the brain.
Area of Science:
- Neuroendocrinology
- Behavioral Neuroscience
- Cardiovascular Physiology
Background:
- Estrogen influences angiotensin II (Ang II) effects on water intake and body weight.
- Ovariectomy-induced weight gain can alter cardiovascular responses to Ang II.
- The impact of weight changes on central Ang II responses is not well understood.
Purpose of the Study:
- To investigate the roles of estrogen and weight loss in isoproterenol (Iso)-induced Fos immunoreactivity (IR) and angiotensin type 1 (AT1) receptor mRNA.
- To examine the effects of weight loss on Iso-induced water intake and plasma renin activity (PRA).
Main Methods:
- Rats were ovariectomized and treated with or without estrogen, or subjected to weight loss.
- Fos IR and AT1 mRNA expression were measured in brain regions controlling fluid balance.
- Water intake and PRA were assessed after Iso administration.
Main Results:
- Isoproterenol increased Fos IR in key hypothalamic and forebrain nuclei.
- Both estrogen and weight loss attenuated Iso-induced Fos IR and AT1 mRNA in the subfornical organ (SFO).
- Weight loss, but not estrogen, reduced Iso-induced water intake without affecting PRA.
Conclusions:
- Weight loss, independent of estrogen, decreases Ang II-elicited water intake.
- This effect is likely mediated by reduced AT1 receptor expression in the SFO.
- Findings highlight the role of weight changes in modulating central Ang II signaling.
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