Formation of the early canine CL and the role of prostaglandin E2 (PGE2) in regulation of its function: An invivo approach

The mechanisms governing corpus luteum (CL) function in domestic dogs remain not fully elucidated. The upregulated expression of cyclooxygenase 2 and prostaglandin (PG) E2 synthase (PGES) at the beginning of the canine luteal phase indicated their luteotrophic roles, and the steroidogenic activity of PGE2 in the early canine CL has been confirmed in vitro. Recently, by applying a cyclooxygenase 2 (COX2)-specific inhibitor (firocoxib [Previcox]; Merial) from the day of ovulation until the midluteal phase, the luteotrophic effects of PGs have been shown in vivo. This is a follow-up study investigating the underlying endocrine mechanisms associated with the firocoxib-mediated effects on the canine CL. Experimental groups were formed with ovariohysterectomies performed on Days 5, 10, 20, or 30 of firocoxib treatments (10 mg/kg bw/24h; TGs = treated groups). Untreated dogs served as controls. A decrease of steroidogenic acute regulatory (STAR) protein expression was observed in TGs. The expression of PGE2 synthase was significantly suppressed in TGs 5 and 10, and both PGE2 and PGF2α levels were decreased in luteal homogenates, particularly from CL in TG 5. Similarly, expression of the prolactin receptor (PRLR) was diminished in TGs 5 and 20. The expression of PGE2 receptors PTGER2 (EP2) and PTGER4 (EP4), the PG- transporter (PGT) , and 15-hydroxy PG dehydrogenase (HPGD) was not affected in TGs. Our results substantiate a direct luteotrophic role of PGs in the early canine CL, i.e., by upregulating the steroidogenic machinery. Additionally, the possibility of an indirect effect on PRL function arises from the increased prolactin receptor expression in response to PGE2 treatment in canine lutein cells observed in vitro

The effect of particle size and volume fraction on the aging behavior of a liquid-phase sintered SiC/aluminum composite

The aging response of a SiC particulate reinforced powder metallurgy aluminum composite was examined as a function of particle size and volume fraction. The addition of SiC particles ranging in size from 24 to 142 μm at 9 vol pct had no effect on the aging kinetics of the composites. Acceleration of the aging behavior or inhibition of the initial stage of the age-hardening process was observed at 18 and 27 vol pct. The accelerated aging kinetics were consistent with smaller particles creating larger thermal misfit dislocation densities. In addition, it was shown that different combinations of ceramic particle size and volume fraction lead to similar effects on the aging behavior. Loss of the initial hardening response was attributed to the suppression of Guinier-Preston (GP) zone formation due to the annihilation of excess vacancies at the thermal misfit dislocations. © 1995 The Minerals, Metals & Material Society