Old, new and the newest concepts of inhibition of luteolysis during early pregnancy in pig

• Published in: Domestic animal endocrinology 2002-07, Vol.23 (1), p.265-275
• Main Author: Ziecik, A.J.
• Format: Article
• Language: English
• Subjects: Animals; Corpus Luteum - physiology; Cytokines - physiology; Dinoprost - secretion; Dinoprostone - physiology; Female; Growth Substances - physiology; Interferons - physiology; Oxytocin - physiology; Pregnancy; Swine - physiology; Uterus - secretion
• ISSN: 0739-7240; 1879-0054
• DOI: 10.1016/S0739-7240(02)00162-5

In 1977 Bazer and Thatcher proposed that maternal recognition of pregnancy in the pig involves the secretion of PGF 2α towards the uterine lumen (exocrine) rather than towards the uterine venous drainage (endocrine) as occurs in the non-pregnant pig during the mid to late stages of the estrous cycle. The retrograde transfer of PGF 2α from the venous blood and uterine lymph into the uterus and the ability of the uterine vein and artery wall to accumulate PGF 2α could constitute a part of putative mechanism of corpus luteum protection during early pregnancy. A luteotropic/anti-luteolytic effect of PGE 2 in the pig also has been frequently demonstrated and it seems that the most effective agent in changing PGE 2:PGF 2α secretion is estradiol. The role for oxytocin during luteolysis and early pregnancy is controversial. It appears, however, that the main function of this hormone is autocrine and/or paracrine stimulation of PGF 2α secretion. Pig trophoblastic interferons, unlike those of ruminants, do not themselves exert an anti-luteolytic effect in pigs. It is likely, that cytokines and angiogenic growth factors are involved in the initiation of luteolysis and/or maintenance of corpora lutea (CL). A discovery of functional LH receptors in porcine endometrium opened a new possibility for this hormone in luteolysis and perhaps in recognition of pregnancy in pigs. The endogenous LH pulses can provoke prostaglandin secretion from endometrium in pigs. On the other hand prolongation of up-regulation of LH receptors in endometrium of early pregnant gilts can additionally increase angiogenic factor production before the process of implantation is completed. Finally new integrated concepts of luteolysis and inhibition of luteolysis in pigs based on selectively reviewed information are presented.