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The aim of the study was to determine an in vitro effect of specific agonists of opioid receptors on basal prolactin secretion and in the presence of dopamine or thyreoliberin (TRH) by porcine anterior pituitary cells. The cells were isolated from anterior pituitaries of gilts on days 8–10, 15–17 and 19–21 of the oestrous cycle and submitted to in vitro culture with mu-, delta- and kappaopioid receptor agonists – FK 33-824, DPLPE and U 50,488, respectively. Differentiated effects of the opioid agonists on prolactin secretion by isolated pituitary cells of gilts in chosen days of the oestrous cycle were shown. In the midluteal phase (days 8–10), a reduced prolactin secretion was demonstrated after activation of mu-, delta- and kappa-opioid receptors under all tested conditions. In the early follicular phase (days 15–17), the activation of mu-, delta- and kappa-opioid receptors increased prolactin secretion under basal conditions, as well as mu- and delta-opioid receptors – in the presence of TRH, but the stimulation of mu- and kappa-opioid receptors reduced the hormone secretion in the presence of dopamine. In the late follicular phase (days 19–21), kappa-opioid receptor agonist stimulated prolactin secretion under all tested conditions. The activation of mu- and delta-opioid receptors increased prolactin secretion under basal conditions and in the presence of dopamine, but decreased – in the presence of TRH. The results suggest a possibility of diverse participation of endogenous opioids, depending on stage of the oestrous cycle, in the modulation of prolactin secretion at the pituitary level in gilts during the oestrous cycle.
This study was designed to check whether intravaginal application of estradiol and progesterone on chosen days of early pregnancy affects the development and survival of porcine embryos. Crossbred gilts were assigned to control (C-land C-2) or experimental (T-l and T-2) groups. Systemic blood samples were collected in groups C-l and T-l on days 3-18 of pregnancy. Gilts of control groups were supplied on days 2-6 and 12-17 of pregnancy with intravaginal cocoa butter suppositories. Gilts of experimental groups were intravaginally supplied on days 2-6 of pregnancy with estradiol (0.2 mg) to improve uterine blood supply and on days 12-17 of pregnancy gilts were supplied with progesterone (0.25 mg) to stimulate the secretory function of the endometrium during the periimplantation period. Systemic concentration of progesterone was elevated on days 3-6 and of estradiol on days 4, 5 and 10 of pregnancy in the experimental groups in comparison with the control gilts. The weight of the ovary and number of corpora lutea were similar in the control and experimental groups, but the number of follicles over 3 mm in diameter was higher in the experimental groups than in control (P < 0.01) on day 30 of pregnancy. The mean ovulation rate, total number of embryos and rate of embryo survival on day 30 of pregnancy were similar in the control and experimental groups. However, the weight, crown-rump length and width of embryos were greater in the experimental groups than in control (P < 0.001). The results demonstrated that the intravaginal application of estradiol and progesterone on precisely chosen days of early pregnancy stimulated embryo development. This study demonstrated that the timing of hormone administration must comply with the physiological effect of estradiol and progesterone on uterine blood supply to ensure embryo development and survival.
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