Impact of High Fat Style Diet and Ovarietomy: Baroreflex Regulation of Renal Sympathetic Nerve Activity (RSNA)

 

Obesity can lead to hypertension and increase in sympathetic nerve activity (SNA). SNA is one of the contributing factor to obesity induced hypertension. High fat diet-(Figure 1) induced visceral obesity, renal inflammation and injury that can lead to augmented renal sympathetic nerve activity (RSNA). Blunting of the arterial and cardiopulmonary baroreflexes because of inflammatory response seems to be the mechanism for the increase in RSNA.

 

We Investigated the impact of high fat style diet (HFSD) and loss of ovarian function on the low- and high-pressure baroreflex regulation of RSNA. We fed the ovary-intact and ovariectomised (OVX) Sprague Dawley rats for a period of 10 weeks. Mean blood pressure (MBP) as well as fasting blood glucose (FBG) were measured every 2 weeks. Similarly, 24h metabolic data collection that were also assessed for renal functional parameters every 2 weeks. Ovary-intact and OVX rats fed the ND or HFSD were anaesthetised for measurement of RSNA at the end of the study. Acute bilateral renal denervation (DNX) was executed, and baroreflex gain curves were constructed from the baroreflex changes in RSNA to vasopressor and vasodepressor drugs. This was done to measure the baroreflex regulation of RSNA by high-pressure baroceptors. Baroreflex regulation of RSNA by low-pressure baroreceptors was evaluated by acute saline volume expansion (VE) in which acute saline volume load was administered intravenously for period of 30 minutes. Qualitative and quantitative determination of noradrenaline content was performed in the kidney via immunohistochemistry and ELISA respectively.

Visceral adiposity was significantly greater in all HFSD rats compared to their ND counterparts. However, FBG and MBP increased in OVX-HFSD rats compared to HFSD rats. Renal dysfunction was detected in all HFSD rats compared to their corresponding control counterparts regardless of ovarian hormonal states. Baroreflex gain curve sensitivity (A2) of RSNA declined in both the HFSD and OVX-HFSD groups compared to their ND control groups but was normalised following DNX in the acute study. Volume expansion decreased RSNA in ND fed groups but did not alter RSNA in both HFSD and OVX-HFSD groups. This indicates that baroreflex regulation of RSNA by low-pressure baroreceptors in HFSD fed groups was impaired. Nevertheless, following DNX, HFSD and OVX-HFSD exhibited declined in RSNA. Increase in sympathetic output due to dysregulation of low- and high-pressure baroreflex control of RSNA and renal dysfunction in both HFSD fed groups was confirmed by measuring the renal noradrenaline content. It appears that renal noradrenaline content was similar in all HFSD-fed rats but was greatly decreased in the denervated groups. Similar HFSD-induced impairment of baroreflex control of RSNA occurred in both HFSD and OVX-HFSD rats although MBP was increased only in the ovarian hormones deprived-group suggesting that ovarian hormones could have modulatory role on other mechanisms that regulate BP in female obesity.

The take home message is that women should be careful with food they consume regardless of whether they are pre- or post-menopausal women since it is the main instigator for metabolic dysfunction.

 

Source

1)    Sucedaram, Y., Johns, E. J., Husain, R., Sattar, M. A., Abdulla, M., Khalilpourfarshbafi, M., & Abdullah, N. A. (2020). Comparison of high-fat style diet-induced dysregulation of baroreflex control of renal sympathetic nerve activity in intact and ovariectomized female rats: renal sympathetic nerve activity in high-fat style diet fed intact and ovariectomized female rats. Experimental Biology and Medicine, 245(9), 761-776.