Physiological Significance of Angiotensin AT1A Receptors in Vasopressin‐Producing Cells
Authors: Linggonegoro Danny W , Sandgren Jeremy A , Claflin Kristin E , Perschbacher Katherine J , Ni Jonathan , Pearson Nicole A , Pierce Gary L , Santillan Mark K , Grobe Justin L 
Published: November 2023

Low‐renin and salt‐sensitive forms of hypertension are characterized by elevated activity of the brain renin‐angiotensin system and secretion of arginine vasopressin (AVP). While angiotensin in the brain is a known stimulant of AVP secretion through its AT1 receptor, the localization of relevant AT1 receptors remains unclear. We tested whether AT1A receptors localized to AVP‐producing cells are important for AVP secretion. To examine AVP and AT1A co‐localization, mice expressing Cre‐recombinase via the AVP gene (AVP‐Cre) were bred with mice expressing a conditional red fluorescent ROSA‐stopflox‐tdTomato construct and GFP via an AT1A BAC transgene. Dual‐fluorescent cells were detected in supraoptic nuclei (SON) but not paraventricular nuclei. Mice lacking AT1A specifically in AVP‐producing cells (AT1AAVP‐KO) were then generated by breeding AVP‐Cre mice with mice harboring a conditional endogenous AT1A gene. AT1AAVP‐KOmice exhibited normal serum (littermate n=18, 302±35 vs AT1AAVP‐KOn=8, 308±42 pg/mL, p=NS) and urine (n=26, 145±33 vs n=11, 170±54 pg/mL, p=NS) copeptin (the stable C‐terminal fragment of AVP) as well as hematocrit (n=14, 46.3±0.7 vs n=7, 47.5±1.3 %, p=NS), despite a physiologically and statistically significant increase in serum osmolality (n=33, 324±1.3 vs n=19, 330±1.6 mOsm/kg, p<0.01), supporting a role for AT1A in AVP‐producing cells in modulating the osmotic control of AVP release. Systolic blood pressure (SBP) (n=18, 109±1.3 vs n=5, 107±1.2 mmHg), urine volume (n=27, 1.1±0.1 vs n=12, 0.9±0.2 mL/d), and fluid intake (n=27, 4.0±0.2 vs n=12, 3.9±0.2 mL/d) were all normal (p=NS) in AT1AAVP‐KO mice. Two‐bottle choice between water and escalating concentrations of NaCl uncovered minor alterations in sodium intake behavior. Serum osmolality (n=22, 336±2 vs n=9, 333±3 mOsm/kg), SBP (n=23, +10.4±2.1 vs n=8, +12.9±2.0 mmHg), urine output (n=23, +12.7±0.8 vs n=9, +12.7±1.5 g/day), and fluid intake (n=23, +16.2±1.3 vs n=9, +14.8±2.5 mL/day) all increased normally (p=NS) in response to deoxycorticosterone acetate (DOCA)‐salt treatment. Unexpectedly, AT1AAVP‐KO mice (n=12) exhibited decreased body mass compared to littermate controls (n=24) regardless of sex between 5–18 weeks of age (3‐way ANOVA; genotype p<0.05), yet no major differences in body composition were observed. Between 12–15 weeks of age, there were no differences in calories ingested (n=27, 14.4±0.3 vs n=12, 14.6±0.5 kcal/day) or digestive efficiency (79.3±0.7 vs 77.9±1.1 % ingested), indirectly implicating AVP in the control of energy expenditure. To examine a role for AVP in energy expenditure, resting metabolic rate (RMR) was assessed by respirometry in a cohort of female C57BL/6J mice chronically infused with AVP (24 ng/hr, sc). Preliminary results indicate a possible 20% reduction in RMR with 3 week AVP infusion (n=4, 0.171±0.003 vs n=5, 0.136±0.014 kcal/hr, p=0.06). Collectively these data support a role for AT1A receptors, localized to AVP‐expressing cells, in osmotic control of AVP secretion as well as energy homeostasis through the modulation of energy expenditure.