The potential implication of neurokinin B in the modulation of prolactin secretion at the pituitary level in cyclic gilts.

Based on the previous studies, neurokinin B (NKB) participation in the modulation of prolactin secretion at the pituitary level can be assumed, but information concerning this topic is largely insufficient. Therefore, in the present study, we aimed: 1) to evaluate changes in the expression of NKB precursor (Tac3) and its receptor (Tacr3) genes as well as the content of NKB and TACR3 proteins in the porcine anterior pituitary throughout the estrous cycle (days 2 - 3, 9 - 10, 12 - 13, 15 - 16, 19 - 20); 2) to determine in vitro the influence of NKB on the expression of Prl, D2r and Trhr genes in the anterior pituitary cells (incubated for 4 h) as well as on prolactin secretion by these cells (incubated for 4 and 24 h) during chosen days of the estrous cycle (9 - 10, 15 - 16, 19 - 20). The experiments have shown alterations in the expression of Tacr3 mRNA and TACR3 protein content, but not in Tac3 mRNA and NKB protein. The treatment with NKB stimulated the expression of Prl (days 15 - 16), D2r (days 9 - 10) and Trhr (days 19 - 20) genes, but its potential to modulate prolactin secretion was observed only following 24-h incubation, specifically inhibition by NKB alone and stimulation by NKB with dopamine on days 19 - 10 of the cycle. These results indicate some implications of NKB in the modulation of prolactin secretion at the pituitary level in cyclic pigs, however further experiments are required to better clarify its role in this process.

The effect of selective agonists of opioid receptors on in vitro secretion of steroid hormones by porcine endometrium during the estrous cycle and early pregnancy.

Steroid hormones play an important role in the regulation of cyclic changes in the uterus and preparation of intrauterine environment for the egg fertilization, embryo implantation and maintenance of pregnancy. Their secretion by porcine uterus has been demonstrated. The present study aimed to establish the effect of opioid receptors (µ, δ and κ) activation by selective agonists (DAMGO, DPLPE and U 50.488, respectively) on in vitro secretion of steroid hormones (during 6-h and 24-h incubations) by the endometrial explants of gilts on days 2 - 3, 10 - 11, 12 - 3, 15 - 16, 18 - 20 of the estrous cycle and 10 - 11, 12 - 13, 15 - 16 of pregnancy. The agonists at certain of tested concentrations (10-9, 10-8 and 10-7 M) affected secretion of steroid hormones. Progesterone secretion was increased by µ-opioid receptor agonist on days 18 - 20 (6 h) and by δ-agonist on days 2 - 3 and 18 - 20 (24 h) of the cycle. During pregnancy (days 15 - 16), κ-agonist increased it (6 h), but µ-opioid agonist decreased (24 h). Androstenedione secretion was decreased during shorter incubation; by µ- and δ-receptor agonists on days 2 - 3, by all agonists on days 12 - 13, and by κ-receptor agonist on days 18 - 20 of the cycle. However, it was increased during longer incubation with agonists of κ- and µ-opioid receptors on days 10 - 11 and 18 - 20 of the cycle, respectively. Estradiol secretion was elevated by κ- and µ-agonists (6 h) on days 2 - 3 and 15 - 16 of the cycle, respectively, as well as following 24-h incubation with µ-agonist on days 15 - 16, and µ- and κ-agonists on days 18 - 20 of the cycle. During pregnancy, its secretion was increased (24 h) ondays 15 - 16 by µ- and κ-opioid agonists. Cortisol secretion did not significantly change (versus control) in response to applied treatments. These results indicate a potential involvement of EOPs in the modulation of endometrial steroidogenesis in the pig during the estrous cycle and pregnancy.