Franz Ellendorff

Endocrinology of parturition in the pig

Endocrine and physiological events that precede and accompany parturition in the sow occur in a sequential fashion starting with a slow increase in estrogens from about three weeks prior to parturition. The luteotrophic role of LH visible as a distinct LH-progesterone relation is present at three weeks prior to parturition but can no longer be seen at one to two days prior to expulsion. Progesterone has not completed its decline during expulsion. A rather sharp and transient increase in plasma relaxin is known at about one day prior to expulsion. Corticosteroids are elevated also during the last 24 hours before parturition with a peak during expulsion. Oxytocin levels remain at baseline levels till progesterone has reached values below 10 ng/ml when a two step sharp increase in plasma oxytocin can be observed; one step prior to expulsion and a second during expulsion. Concomitant to endocrine changes the uterine EMG displays characteristic patterns, but is insensitive to oxytocin four days prior to parturition.

The neurohypophysial hormones

Abstract Release of oxytocin and vasopressin during parturition in a number of domestic animals including the pig, sheep, goat and mare is discussed. The pattern is essentially similar in all species studied, oxytocin concentrations being low or undetectable in late pregnancy and increasing during labour until maximum concentrations are found with delivery of the fetus. Relatively little change in the circulating concentrations of vasopressin has been noted. Secretion of neurohypophysial hormones in the ovine and porcine fetus is also described, data from acute and chronically catheterised preparations being presented. While oxytocin release is unaffected by the stimuli employed, haemorrhage results in vasopressin release, the concentrations achieved being related to the pH of the blood. Hypoxia is confirmed as an effective stimulus of vasopressin release.

Prospects and problems of pregnancy and fertility diagnosis in the pig by aid of progesterone determination.

Plasma progesterone levels were measured in 536 sows of different breeds from 6 different farms to assess this test as a method of determining early pregnancy. It was found that progesterone curves of pregnant and nonpregnant animals began to diverge on Day 16 after mating; nonpregnant animals who turned out to have a prolonged cycle could be eliminated by testing on Days 17-24. From Day 17 on only 1 pregnant animal showed values lower than 9 ng progesterone/ml plasma while 86% of all nonpregnant animals had values below 5 ng. 3.6% of animals were incorrectly diagnosed on the basis of plasma progesterone .4% of pregnant animals considered nonpregnant and the rest nonpregnant animals diagnosed as pregnant mainly due to a delayed return of estrus. A 2nd study found that sows with values below 9 ng on Days 10-15 had a history of infertility. Very high progesterone levels (110-144 ng/ml far above those normally observed in pregnant animals) were not associated with any functional disturbances. The method shows promise as a means of fertility diagnosis and can also be used to detect animals with weak or no behavioral estrus.

In vitro characterization of secretion rates from silastic micropellets containing estradiol

For local, controlled steroid hormone administration into tissues, such as the brain, we have prepared cylindric micropellets of 1 mm in length and 1 mm diameter. The micropellets are a mixture of silicone glue (silastic) and 0.1%, 1.0%, or 10% estradiol (E2). To evaluate in vivo E2 secretion rates, micropellets were implanted into the brains of 40 rats for either 1, 4, 8, or 12 weeks. In vitro 24 h E2 secretion rates of these implants were compared-after removal from the rat brain-with 24 h secretion rates of micropellets that had been incubated for the same periods of time in vitro only. In vitro release of E2 decreased steadily but asymptotically from the first day of incubation to the 3rd or 4th week, when an apparent steady state is achieved. With any E2 concentration the coefficient of variation for 24 h release rates rarely exceeded 15% within a group. The release rates increased nonlinearly with the concentration of E2 in the pellet. Subsequent to in vivo implantation the in vitro secretion of E2 was slightly higher than the in vitro secretion of micropellets incubated for the same period of time in vitro. Thus (1) the secretion rate from a pellet can be predicted rather exactly by the mixing ratio of silastic and E2 and (2) the secretion rate from the micropellet in vitro and in vivo appears to be rather similar. It is concluded that the method described is very useful for short-term (days) or long-term (weeks, albeit not constant) local exposure of defined tissues to steroid hormones.