R. Patron-Lozano1, M. I. Rodriguez-Davalos1,2, A. Munoz-Abraham2, J. P. Geibel1,2 1Yale University School Of Medicine,Surgery,New Haven, CT, USA 2Yale University School Of Medicine,Transplantation/Surgery,New Haven, CT, USA
Introduction: The calcium sensing receptor (CaSR) has been identified and its functions described along the entire gastrointestinal tract. Recently, angiotensin receptors have been identified in the small bowel but their physiological function remains controversial. Since both systems are implicated in the regulation and modulation of transmembrane transport of fluids and electrolytes, and even inflammatory diseases, we chose to investigate if there was a connection between these two receptor classes.
Materials &
Methods: We used CaSR-/- and Gcmc2 double knockout mice and heterozygote (HET) mice for control. All mice were fasted for 18 hours to reduce intestinal residue; total body weight ranged between 23 and 50 grams. The mice were anesthetized with isoflurane and euthanized. We took 12cm of distal ileum and stripped it from its mesentery. The intestinal lumen was flushed with lactated ringer’s solution in order to remove any remaining intestinal contents. The intestinal loop was then attached to a custom perfusion chamber where it was filled with 2mL of angiotensin at a concentration of 1×10-11 M and weighed. This measurement was determined as weight at t0. The chamber was then filled with lactated ringer’s at 37C and connected to a roller pump which continuously exchanged the fluid and maintained a constant temperature. The experimental time period was 1 hour. The chamber was then emptied and weighed again; this measurement being t1.
Results: For the knockout mice we observed a significant increase in weight after the administration of angiotensin at 10-11 M concentration between t0 and t1. This difference was consistent in every experiment. The mean weight difference was 73mg or a 3.14% increment in graft weight. For the control HET samples, the weight diminished consistently at t1 96mg or 3.31% of the initial tissue weight.
Conclusion: After performing these experiments, we conclude that there is a functional relationship between angiotensin receptors and calcium sensing receptors in the small bowel of mice. By recording a difference in graft weight after the administration of angiotensin at a concentration of 10-11 M in CaSR -/-;Gcmc2-/- mice we observed that although the angiotensin receptors might be present and stimulated, the absence of CaSR prevents normal physiologic function. Furthermore, by conducting a control experiment with the HET mice, we demonstrated that functional calcium sensing receptors aid the normal physiology of fluid exchange in the small intestine in the presence of angiotensin. These findings can further help us comprehend the extent of the fluid and electrolyte regulators in the body thus providing novel targets for control of hypertension and other diseases.