Role of calcium/calmodulin-dependent protein kinase II in gonadotrophin-induced ovulation in in vitro perfused rabbit ovaries

The objectives of these experiments were to determine (i) the role of calcium/calmodulin-dependent protein kinase II-mediated signal transduction in hCG-induced ovulation and (ii) whether there is an association between arachidonic acid metabolites, nitric oxide and calcium/calmodulin-dependent protein kinase II in the overall scheme of ovulation induction. Ovarian arteries were cannulated in situ, and the ovaries were excised and perfused in vitro. Ovulatory efficiency ([number of ovulated follicles/number of mature follicles > 1.5 mm] x 100) was calculated for each experiment. Calcium/calmodulin-dependent protein kinase II substrate induced ovulation in the absence of gonadotrophin (calcium/calmodulin-dependent protein kinase II substrate: 66.3%; control: 0%). In the next experiment, perfusion medium of the experimental ovary was supplemented with KN 62, a potent inhibitor of calcium/calmodulin-dependent protein kinase II, while the contralateral ovary served as control. Ovulations were induced in both ovaries with hCG (50 iu (150 ml)^-1) and perfusion was continued for 8 h. In the third experiment, ovaries were perfused with prostaglandin F(2a) (PGF(2a)) with and without KN 62, while the contralateral ovary was perfused with medium alone. KN 62 reduced the ovulatory efficiency of hCG-treated ovaries in vitro during perfusion (hCG ± 10^-7 mol KN 62 l^-1: 32.9%; hCG: 80.9%). Furthermore, it significantly reduced the ovulatory efficiency of PGF(2a)-treated ovaries (PGF(2a) + KN 62 = 21.5%; PGF(2a) = 59.9%). In the final experiment, N-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, reduced ovulation calcium/calmodulin-dependent protein kinase II substrate, indicating an interaction between ovarian nitric oxide synthesis and calcium/calmodulin-dependent protein kinase II. These findings suggest that the calcium/calmodulin-dependent protein kinase II signal transduction system plays a significant role in hCG-induced ovulation. Furthermore, the data demonstrate an interaction between the arachidonic acid metabolites, nitric oxide and calcium/calmodulin-dependent protein kinase II pathway.