Plasma Luteinizing Hormone and Progesterone in the Adult Female Pig During the Oestrous Cycle, Late Pregnancy and Lactation, and After Ovariectomy and Pentobarbitone Treatment

Abstract

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.

Relationship between peri-oestrus progesterone levels and time of ovulation by echography in pigs and influence of the interval between ovulation and artificial insemination (AI) on litter size

“…The pattern of LH was similar to that previously observed around the time of ovulation [4,18,19,21]. The timing of LH surge relative to the onset of oestrus and ovulation was the same as that obtained by others [6,15,27].…”

Endocrinology of parturition in the pig

“…The hypophyseal luteotrophic factor had been suggested long ago to be LH (Brinkley et al, 1964;Anderson et al, 1967;Cook et al, 1967). It was not until recently that our group (Parvizi et al, 1976) found a very peculiar relationship between prepartal circulating LH and progesterone levels (Fig. 1).…”

“…41 to 17 hrs before parturition, however, progesterone values fluctuated erratically on a lower level and were independent of the still present LH episodes. This effect is likely to start earlier than 48 hrs prior to parturition, since there is general agreement, that progesterone has commenced its decline by then (Killian et al, 1973;Molokwu and Wagner, 1973;Robertson and King, 1974;Baldwin and Stabenfeldt, 1975;Parvizi et al, 1976).…”

“…The pig differs from other species in several aspects: it is intolerant to ovariectomy right to the very end of pregnancy which implies that extraovarian progesterone is not sufficient to maintain pregnancy (Kimura and Cornwell, 1938;Short, 1956;Rombauts et al, 1965;Parvizi et al, 1976). Only excessively high levels of exogenous corticosteroids will induce parturition (First and Staigmiller, 1972;BOSC, 1974), and the pig is polytoccous.…”

Endocrine bases of lactational anoestrus in the sow

“…The levels of LH in early and mid-pregnancy are similar to those observed in the mid-luteal phase of the oestrous cycle (Ziecik et al, 1982(Ziecik et al, /1983 (Parvizi etal, 1976;Kraeling etal, 1992). In miniature pigs, ovariectomy during the follicular phase, and ovariectomy on day 100 of pregnancy followed by abortion, result in a similar increase in LH secretion (Parvizi et al, 1976). Taken together, these results strongly suggest that high concentrations of progesterone inhibit LH pulsatility throughout pregnancy and that high concentrations of oestrogens amplify this inhibition during the last month of pregnancy.…”