Preliminary study of ovariectomy and chronic losartan-induced alterations in brain AT1 receptors.

Women who undergo oophorectomy prior to the age of natural menopause have a higher risk of neurological and psychological impairment. Treatment with the angiotensin receptor blocker (ARB) losartan for 10 weeks following ovariectomy of Long-Evans rats at 3 months of age reduced the ovariectomy-induced cognitive decrements. Following completion of the behavioral experiments, (Campos et al., 2019), the brains were harvested for preliminary receptor autoradiographic studies of AT1 receptor (AT1R) binding in selected brain regions using quantitative densitometric analysis of autoradiograms of 125I-sarcosine1, isoleucine8 angiotensin II binding. Four of the brain regions (amygdala, ventral subiculum, piriform cortex, and cingulate cortex) are associated with cognitive and emotional behavior while one (lateral hypothalamus) is associated with homeostasis. The density of AT1R varied by region: ventral subiculum > amygdala and cingulate cortex, and piriform cortex > cingulate cortex. Losartan treatment decreased AT1R binding in the ventral subiculum of sham and ovariectomized rats by 41.6%, and 46% in the piriform cortex of the sham rats, but tended to increase AT1R binding in the piriform cortex and cingulate cortex 77% and 107%, respectively, in the ovariectomized rats. AT1R binding did not differ significantly between intact male and sham-vehicle female rats among surveyed brain regions. These results suggest that losartan-induced changes in brain AT1R expression may contribute to the reduced anxiety-like behavior and memory impairments seen in ovariectomized rats, but replication of these observations will be needed to determine the extent to which brain AT1R changes mediate the adverse behavioral effects of ovariectomy.

Chronic administration of pharmacological doses of angiotensin 1-7 and iodoangiotensin 1-7 has minimal effects on blood pressure, heart rate, and cognitive function of spontaneously hypertensive rats.

Cardiovascular diseases are the principal cause of death worldwide, with hypertension being the most common cardiovascular disease risk factor. High blood pressure (BP) is also associated with an increased risk of poor cognitive performance and dementia including Alzheimer's disease. Angiotensin 1-7 (Ang 1-7), a product of the renin-angiotensin system (RAS), exhibits central and peripheral actions to reduce BP. Recent data from our lab reveals that the addition of a non-radioactive iodine molecule to the tyrosine in position 4 of Ang 1-7 (iodoAng 1-7) makes it ~1000-fold more potent than Ang 1-7 in competing for the 125 I-Ang 1-7 binding site (Stoyell-Conti et al., 2020). Moreover, the addition of the non-radioactive iodine molecule increases (~4-fold) iodoAng 1-7's ability to bind to the AT1 receptor (AT1R), the primary receptor for Ang II. Preliminary data indicates that iodoAng 1-7 can also compete for the 125 I-Ang IV binding site with a low micromolar IC50. Thus, our aims were to compare the effects of chronic treatment of the Spontaneously Hypertensive Rat (SHR) with iodoAng 1-7 (non-radioactive iodine isotope) and Ang 1-7 on arterial pressure, heart rate, and cognitive function. For this study, male SHRs were divided into three groups and treated with Saline, Ang 1-7, or iodoAng 1-7 administrated subcutaneously using a 28-day osmotic mini pump. Systolic BP was measured non-invasively by the tail-cuff technique. Cognitive function was assessed by Y-Maze test and novel object recognition (NOR) test. We have demonstrated in SHRs that subcutaneous administration of high doses of iodoAng 1-7 prevented the increase in heart rate with age, while Ang 1-7 showed a trend toward preventing the increase in heart rate, possibly by improving baroreflex control of the heart. Conversely, neither Ang 1-7 nor iodoAng 1-7 administered subcutaneously affected BP nor cognitive function.