In a series of experiments on female miniature pigs, the pattern of plasma LH and progesterone levels during the oestrous cycle, late pregnancy and lactation and after ovariectomy were characterized, and the effect of pentobarbitone treatment was tested. The preovulatory surge of LH occurred in seven out of eight animals between 00.00 and 12.0 h on day 0 of the oestrous cycle (day 1 of standing heat). Plasma progesterone strated to decline 8 days before oestrus and reached its lowest value 5 days before the preovulatory LH peak. Increases in progesteron concentration were already noticeable 48 h after the LH surge. During late pregnancy, parturition and lactation, plasma LH was low and showed only minor fluctuations, while plasma progesterone declined 4 to 5 days before parturition. Both hormones remained at low levels throughout lactation. Three weeks before parturition increases in LH were always followed by an increase in progesterone. This dependency was greatly diminished immediately before delivery. Four to 12 days after weaning the animals came into oestrus which was followed by an increase in LH and later an increase in progesterone concentrations. Ovariectomy during dioestrus resulted in a steady increase in plasma LH levels of 35-39 days. Ovariectomy caused abortion if performed on day 100 of pregnancy. It was followed by a rapid increase of plasma LH concentration. Normal parturition (around day 115) and lactation took place when animals were spayed on day 112 of pregnancy. In this case, plasma LH levels remained even lower than before ovariectomy as long as lactation was maintained. Immediately after weaning a rapid increase in the normal postovariectomy pattern of LH secretion was observed. Pentobarbitone anaesthesia (30-35 mg/kg body wt, initial dose), during pro-oestrusoestrus, for less than 5 h had no effect on the preovulatory LH increase. However, pentobarbitone anaesthesia for more than 6 h inhibitied the LH peak and ovulation if the animal was under deep anaesthesia before 24.00 h on the day before oestrus. Pentobarbitone treatment of ovariectomized pigs resulted in a clear decrease in LH levels 40 min after a single i.v. dose.
PIP: Plasma luteinizing hormone (LH) and progesterone in the adult female pig during the estrous cycle, late pregnancy and lactation and after ovariectomy and pentobarbitone treatment was investigated. The preovulatory LH surge occurred in 7 of 8 animals between 0000 and 1200 hours on Day 0 of the estrous cycle (Day 1 of standing heat). Progesterone fell 8 days before estrus and reached its lowest value 5 days prior to the preovulatory LH peak. LH was low and showed only minor fluctuations during late pregnancy, parturition and lactation, while progesterone declined 4-5 days before parturition. Both were low during lactation. 3 weeks prior to parturition, LH increases were followed by progesterone increases. 4-12 days after weaning the animals came into estrus followed by a LH increase and later a progesterone increase. Ovariectomy during diestrus resulted in an increase (p less than .001) in LH for 35-39 days. Ovariectomy caused abortion when performed on Day 100 of pregnancy, followed by a rapid increase in LH. Around Day 115 normal parturition and lactation took place when animals were spayed on Day 112 of pregnancy. As long as lactation was maintained LH levels remained lower than before ovariectomy (p less than .01). After weaning a rapid increase in the normal postovariectomy LH pattern was seen. Less than 5 hours of 30-35 mg pentobarbitone anaesthesia/kg body weight during proestrus has no effect on the preovulatory LH increase. However, more than 6 hours inhibited the LH peak and ovulation when the animal was under deep anaesthesia before 2400 hours on the day before estrus. A clear decrease in LH 40 minutes after a single intravenous dose of pentobarbitone was seen in ovariectomized pigs.