Investigations on hormonal changes around parturition in the dog and the occurrence of pregnancy-specific non conjugated oestrogens

Summary

Concentrations of progesterone and estradiol-17ß were determined throughout pregnancy in 6 to 10 bitches (exp. 1); in experiment 2 peripartal changes of estradiol-17ß, estrone, progesterone, cortisol, prolactin and growth hormone were determined in 5 bitches; in experiment 3 total unconjugated oestrogens were determined by radioimmunoassay and radioreceptorassay in placenta1 tissue from 25, 53, 60 and 64 days pregnant bitches. No pregnancy specific increase of estradiol-17ß could be observed; estradiol-17ß levels decreased prior to parturition concomitant with the decrease of progesterone, suggesting a likewise luteal origin of estradiol- 17ß in the pregnant and non pregnant dog. Cortisol and growth hormone concentrations were elevated at the time of parturition, prolactin concentrations remained unchanged but were higher in pregnant than in non pregnant dogs. No hints in respect to a specific placental oestrogen production were obtained when examining placental tissue. The hypothesis is put forward that the high sensitivity of the haematopoietic System of the dog to oestrogens was an important factor in respect to evolution of endocrine control of pregnancy and parturition in this species which — in respect to placental oestrogen production — seems to be different from most other domestic animal species.

Key words

pregnancy - parturition - placenta - oestrogens - dog