Effect of SP on pLH Secretion by Porcine Pituitary Fragments in Superfusion A superfusion system was employed to analyze the dynamics of the response of porcine gonadotrophs to SP and/or GnRH treatment. After 8-10 h of superfusion, stable baseline levels of pLH secretion were observed, with mean values for control chambers of 128.7 ± 10.7 ng LH/ml per 105 cells. Figure 5 depicts representative pLH secretory profiles from porcine pituitary fragments in response to pulsatile infusions (for 20 min every 2 h) of 100 nM GnRH, 1 |л,М SP, or a combination of both peptides. In all treatments, a maximum LH peak amplitude was reached 20 min after application of the secretagogue; then LH release declined progressively toward basal levels over the next 60 inin.
Three successive stimulations with 100 nM GnRH caused a rapid rise of pLH secretion from pituitary fragments, yet peak amplitudes decreased progressively from 161.7 ± 24% to 99.5 ± 21.8% and 60 ± 8.1%. SP treatment induced a similar profile of response. However, the relative rise above basal levels was lower than that evoked by GnRH alone. Peak amplitude after the first pulse reached 111.5 ± 18.3% and, as in the GnRH-treated group, decreased in subsequent SP pulses (58.25 ± 11.5% and 32.5 ± 10.1%, after second and third pulse, respectively). Combined treatment with GnRH and SP also stimulated pLH secretion, but, contrary to that observed in static cultures, the amplitude of the increase was not statistically different from that observed for the GnRH-treated group. Analysis of total pLH secreted by calculating the area under the 60-min response curve (AUC) after pulses confirmed these observations (Table 1). buy prednisone
Thus, AUCs were also greater for the GnRH-treated group than for the SP-treated group, although differences were significant only after the first pulse, and combined administration of both peptides did not result in values of pLH secretion different from those evoked by GnRH alone (Table 1). FIG. 5. Response of porcine pituitary fragments in a dynamic culture system to treatment with SP and/or GnRH. Representative profiles of LH release from 4 superfusion chambers containing anterior pituitary fragments in response to either DMEM alone (control) or three pulses of 20 min (solid bars) of DMEM plus 100 nM GnRH, 1 (jlM SP, or 100 nM GnRH + 1 (xM SP. Samples were collected at 10-min intervals. Each treatment was repeated in 3 additional chambers obtained from two independent experiments, and similar results were observed. Table 1. Cumulative LH release (AUC) from superfused pituitary fragments in response to GnRH and/or SP treatment.3
|Pulse||100 nM GnRH||1 (iM SP||100 nM GnRH + 1 |xM SP|
|1||719.8 ± 47.6||508.9 ±||59.3C||826.6 ± 20.4|
|2||454.0 ± 70.8b||260.1 ±||65.9b||503.7 ± 95.5b|
|3||546.5 ± 46.4b||418.8 ±||54.4||430.7 ± 95.9b|
* Data represent the mean AUC ± SEM in ng LH calculated from 4 superfusion chambers obtained from 2 independent experiments; in each experiment, AUC was calculated by summing up the net values of pLH secretion, after subtracting the corresponding basal values. b p < 0.05 vs. the corresponding AUC after the first pulse. c p < 0.05 vs. AUC after the first pulse with GnRH or GnRH + SP.