Reproduction in Domestic Animals

Regulation of Luteal Function 61bovine CL. These data suggest that NO produced bytwo NOS isoforms is involved in structural and functionalchanges that occur in the bovine CL through thewhole oestrous cycle. Luteolytic or luteotropic actionsof NO on the bovine CL is strictly dependent on thestage of CL, and cell interactions (cell-to-cell contact)and composition (Jaroszewski et al. 2003a; Klipperet al. 2004; Weems et al. 2004; Rosiansky-Sultan et al.2006). Nitric oxide donor (S-NAP) stimulated PGE 2secretion by steroidogenic CL cells in the early and midlutealphases (Skarzynski et al. 2000). During developmentand maintenance of the CL, PGE 2, which is bothluteotropic and antiluteolytic, stimulated NO production(Boiti et al. 2000). Nitric oxide donors and ET-1increased PGE 2 secretion by bovine CL slices in vitro ondays 13–14 of the cycle without any effect on P4secretion (Weems et al. 2004). Therefore, increased NOproduction during early stages of the cycle and pregnancyis likely to play a role in CL development andangiogenesis (Skarzynski et al. 2000; Weems et al. 2004;Vonnahme et al. 2005; Rosiansky-Sultan et al. 2006).In the late luteal phase PGF 2a might simulate a shearstress-like reaction of endothelial CL cells resulting incompensative NO release during the first steps ofluteolysis – up to 2–4 h after PGF 2a treatment (Li et al.2002; Skarzynski et al. 2003b; Acosta et al. 2007). Intralutealadministration of a NOS inhibitor (L-NAME)during the late luteal phase increased P4 secretion andprolonged the functional lifespan of bovine CL (Jaroszewskiand Hansel 2000; Sasahara et al. 2007). Whenan analogue of PGF 2a (aPGF 2a , cloprostenol) wasinjected on day 15 of the cycle in combination withL-NAME, the luteolytic effect of aPGF 2a was counteractedby the NOS inhibitor (Fig. 4; Jaroszewski et al.2003b; Skarzynski et al. 2003b). Nitric oxide has beenfound as the most potent inhibitor of P4 secretionin vitro (Skarzynski et al. 2003b; Korzekwa et al. 2004,2006) and in vivo (Sasahara et al. 2007). Moreover, aNO donor (Spermine NONOate) strongly stimulatedproduction of PGF 2a and LTC 4 by bovine CL bothin vitro and in vivo, showing that NO is involved in theprocess of luteal regression by bovine CL (Fig. 3;Progesterone (ng/ml)129630L-NAME/aPGF (n = 5)Saline/aPGF(n = 6)L-NAME/Saline (n = 4)Saline/saline (n = 4)aPGF0 3 6 9 12 15 18 0 4Day of the estrous cycle– EstrusEstrusFig. 4. The effect of 2 h infusion of saline or nitric oxide synthaseinhibitor-L-NAME (400 mg ⁄ h) and injection of saline or PGF 2aanalogue, cloprostenol (aPGF; 100 lg; Bioestrophan, Biowet, GorzowWielkopolski, Poland) at 30 min of infusion on progesterone concentrationsin peripheral blood plasma of heifers on day 15 of the oestrouscycle. Different subscript letters indicate significant differences(p