Plasma Progesterone Levels during Pregnancy in the Little Brown Bat Myotis Lucifugus (Vespertilionidae)1

Abstract

Plasma progesterone was measured by radioimmunoassay in individual female Myotis lucifugus throughout pregnancy and lactation. Progesterone levels, which averaged 6.7 +/- 0.7 ng/ml in late hibernation, rose to a mean of 18.9 +/- 6.7 ng/ml in unimplanted bats collected in the first two weeks after arrival at a maternity roost. Analysis of progesterone levels in bats in which the developmental stage of the embryo was known revealed two sharp, transient increases in plasma progesterone during the preimplantation period. The first, with values of 30-45 ng/ml, occurred at ovulation. The second, with values of 20-30 ng/ml, coincided with blastocyst formation. Progesterone levels increased exponentially from a mean of 7.4 +/- 1.0 ng/ml during early implantation to peak values of 100-200 ng/ml (means = 136.2 +/- 15.6) in the last two weeks of pregnancy, and showed no evidence of either a midpregnancy or prepartum decline. Despite involution of the corpus luteum at the end of pregnancy, progesterone levels averaged 9.0 +/- 1.0 ng/ml during lactation and did not decline until the end of lactation. In bats undergoing abortion, mean levels of plasma progesterone were already less than 6 ng/ml, equivalent to levels in nonbreeding females. The results indicate that the progesterone profile of pregnant M. lucifugus, though generally resembling those of other bats, exhibits several distinctive features. The sharp rise in plasma progesterone coinciding with blastocyst formation has not been reported in other mammals and suggests a possible role of progesterone in the cavitation process. In addition, peak values of plasma progesterone in late pregnancy were conspicuously higher than levels reported in other verpertilionid bats. The levels did not appear to fall before parturition, although such falls have been reported in other bats.

Plasma progesterone concentrations in the female Natal clinging bat (Miniopterus schreibersii natalensis)

“…Values recorded during delayed implantation, however, were higher than baseline values recorded in this subspecies. This is in agreement with observations on a variety of mammals experiencing delayed implantation (see Kimura et al, 1987, for references) but at variance with the transient peaks in plasma progesterone found in the little brown bat, Myotis lucifugus, at ovulation and blastocyst formation (Buchanan & YoungLai, 1986). Since our data for the early stages of pregnancy were grouped by date of collection and since collections were made at 5-6-week intervals transient changes in progesterone concentrations may have gone undetected.…”

Sperm fertility and skewed paternity during sperm competition in the Australian long‐eared bat Nyctophilus geoffroyi (Chiroptera: Vespertilionidae)

“…Burns & Easley, 1977;Oxberry, 1979;Buchanan & YoungLai, 1986), but are similar to those reported for Pipistrellus pipistrellus (Racey & Swift, 1981) and C. gouldii (Hosken, O'Shea et al, 1996) which also experience low plasma progesterone concentrations during winter and peak values of about 10±14 ng ml 71 .…”

Fetal development, and placental and maternal plasma concentrations of progesterone in the little brown bat (Myotis lucifugus)

“…At the very early stages when uterine length was < 1-5 mm, there was a distinct possibility that the animals included non-pregnant or at least pre¬ implantation specimens (see Buchanan & YoungLai, 1986, for a detailed analysis of the early developmental stages). These smallest uteri were not opened to verify the presence of a conceptus so all animals with uteri of length < 1-5 mm were adjudged to be non-pregnant and the data were excluded from analysis.…”

“…However, the pregnant status of these animals was not established so this study does not consider the very earliest stages of the initiation of pregnancy. The reader is referred to Buchanan & YoungLai (1986) for a compre¬ hensive description of changes in progesterone concentrations related to the stage of development of the conceptus of little brown bats. They aroused torpid bats from a hibernaculum to synchronize ovulation and determined the stage of development through early embryogenesis along with measurement of plasma progesterone.…”

“…During initial review of this manuscript, a directly complementary study of plasma progester¬ one concentrations in little brown bats (M. lucifugus) was published by Buchanan & YoungLai (1986). These authors provide detailed information especially for the earliest stages of pregnancy.…”