Angiotensin II increases intracellular calcium concentration in pig endometrial stromal cells through type 1 angiotensin receptors, but does not stimulate phospholipase C activity or prostaglandin F2α secretion

Abstract

Although the presence of endometrial receptors for angiotensin (Ang) II has been demonstrated, a specific function for AngII in the uterus has not been identified. Cytosolic free Ca²⁺ concentration [Ca²⁺]_i, phospholipase C (PLC) activity and prostaglandin (PG) F_2α secretion in response to AngII and oxytocin (OT) were measured in pig endometrial stromal cells collected 16 days after oestrus. Treatment with 100 nm OT or AngII increased (P<0.001) [Ca²⁺]_i in stromal cells similarly (720 v. 690 m, respectively). Subsequent administration of OT or AngII to the same cells induced smaller [Ca²⁺]_i increases (25% or 35% of the initial responses, respectively) that occurred only if the second exposure to the same agent took place at least 5 min after the first. When administered sequentially, OT and AngII each induced a full response within 1 min of the previous treatment, regardless of which peptide was applied first. Whereas OT increased PLC activity and PGF_2α secretion in stromal cells (P<0.01), AngII did not increase either PLC activity or PGF_2α secretion. Type 1 AngII (AT₁) receptors were present on stromal cells, whereas AT₂ receptors were absent. Therefore, the effect of AngII in stromal cells was mediated via AT₁ receptors. That AngII increased [Ca²⁺]_i in stromal cells, but did not increase PLC or PGF_2α secretion, indicates that either AngII releases a pool of Ca²⁺ through a mechanism that is not mediated by PLC and is not involved in PGF_2α secretion or that a mechanism for PGF_2α production other than one involving Ca²⁺ may exist.