Midpregnancy elevation of serum androstenedione levels in the C3H/HeN mouse: placental origin

The purpose of this study was to characterize the serum profile of androstenedione during pregnancy in the C3H/HeN mouse and to determine the site of its production. Serum androstenedione levels were characterized by a prominent midpregnancy elevation and were substantially higher than testosterone levels during pregnancy. The results of our studies support a placental site of production for androstenedione during midpregnancy: 1) uterine venous levels of androstenedione are higher than peripheral androstenedione levels at midpregnancy and during the second half of pregnancy, 2) developmental changes in the in vitro release of androstenedione by conceptuses coincide temporally with serum changes in androstenedione levels, 3) the day 10 placenta releases significantly more androstenedione in vitro than do other endocrine tissues from day 10 of pregnancy, and 4) serum androstenedione levels are maintained after bilateral ovariectomy on day 10 of pregnancy.

Effects of handling and ether anesthesia on serum prolactin levels in the golden hamster

The effects of handling and ether stress on serum prolactin (PRL) levels in gonadally active and gonadally regressed male golden hamsters and in females in different stages of the estrous cycle were examined. Males, regardless of reproductive state or photoperiod, showed no significant alterations in serum PRL levels following exposure to ether and cardiac puncture, in contrast to females, which showed a significant elevation in serum PRL following these two procedures. This increase was small and inconsistent in females etherized for 1 min, but it was very pronounced in females etherized for 6 min. In females there was also a slight but significant increase in PRL following transfer from the animal room to the laboratory. Thus, routine experimental manipulations, such as moving the animals to a laboratory and ether exposure, induce significant and variable elevations of serum prolactin in female hamsters.

Genetic and litter size effects on serum placental lactogen in the mouse

Placental lactogen (PL) and progesterone are important hormones of pregnancy in the mouse. The purpose of this study was to investigate the influence of genetic differences and litter size on serum PL levels in the mouse. Serum progesterone levels were also measured in some experiments. Two features of serum PL levels under genetic control were identified: 1) the gestational profile of serum PL and 2) absolute serum PL levels. Breeding combinations that resulted in profound effects on serum PL levels were without significant affect on serum progesterone levels. Serum concentrations of PL and progesterone were directly proportional to litter size. Conceptus number was found to significantly affect ovarian progesterone release. The presence of uterine tissue antagonized the luteotropic actions of the conceptus but did not affect serum PL levels.

Identification and partial characterization of a lactogen from the midpregnant mouse conceptus

Previously, we demonstrated that measurement of serum lactogenic hormones during pregnancy in the mouse by the rabbit mammary gland radioreceptor assay (RRA) and specific RIAs for mouse PRL (mPRL) and mouse placental lactogen (mPL) showed a large RRA to RIA activity ratio during midpregnancy. The purpose of this study was to begin to characterize this discrepancy in midpregnancy PRL-like activity. The elution profile of serum from midpregnant mice on Sephadex G-100 showed a characteristic peak in RRA activity (elution volume/void volume = 1.5), distinct from either mPRL or mPL (both approximately elution volume/void volume = 2.0). This PRL-like activity was not recognized by antisera to either mPRL or mPL. The source of the midpregnancy lactogen was localized to the conceptus. The hormone was found to have an apparent molecular weight of 50,000 (based on Sephadex G-100 chromatography) and an electrophoretic mobility similar to mPRL (Rf = 0.5-0.6) and to be lactogenic in the in vitro mouse mammary gland explant bioassay. We have demonstrated the existence of a midpregnancy lactogen that is different from mPL and mPRL and is of conceptus origin.

Development of a homologous radioimmunoassay for secreted hamster prolactin

A specific and sensitive homologous radioimmunoassay has been developed for secreted hamster prolactin. Hamster serum and pituitary extracts showed parallel dilution-response curves with hamster prolactin. The sensitivity of the assay ranged from 0.5 to 1.0 ng/ml, and the intra- and inter-assay coefficients of variation were 6 and 10%, respectively. Additionally we have demonstrated that the rat prolactin radioimmunoassay kit distributed by the National Institute of Arthritis, Metabolism, and Digestive Diseases is an inadequate method for the measurement of hamster prolactin.

Role of daylength in the regulation of reproductive function in the male mongoose, Herpestes auropunctatus

The male mongoose, Herpestes auropunctatus, displays a distinct seasonal reproductive rhythm in environments which show minimal changes in daylength. This investigation was designed to evaluate whether the reproductive system of the male mongoose was responsive to photoperiodic manipulations. Four experiments were conducted; two during the breeding season, one during the inactive season, and one during the recrudescence phase. Serum androgen levels and reproductive organ weights were similar in males exposed to either short (6L:18D) or control photoperiods (14L:10D) when the photoperiodic adjustment was initiated in April; however, serum androgen levels were significantly depressed after 60 days exposure to short photoperiods as were weights of prostate glands when the photoperiodic manipulation was initiated in May. An increase in the number of hours of light per day during the inactive season did not affect serum androgen levels or reproductive organ weights. Exposure to a very short photoperiod (2L:22D) during the recrudescence phase delayed, but did not prevent, the increase in serum androgen levels. Although the reproductive system of the male mongoose is responsive to daylength adjustments, the response is less pronounced when compared to the effects of photoperiod in other seasonal breeders.

Placental and serum hormone changes during the second half of pregnancy in the hamster

The concentrations of androgen, estrogen, progesterone, and prolactin-like hormones in serum, placentae, and media from placental incubations during the second half of pregnancy in the hamster were determined. Concentrations of prolactin-like activity in serum, placentae, and media from placental incubations increased from Day 8 to Day 14 of gestation. On Day 16 of pregnancy the content and in vitro release of placental prolactin-like activity declined; however, serum prolactin-like activity increased. The in vitro release of 3H-protein by hamster placentae showed gestational changes resembling the pattern of in vitro placental lactogen release. Serum and placental content of progesterone increased from Day 8 to Day 14 of gestation and declined from Day 14 to Day 16. In vitro placental progesterone release increased from Day 8 to Day 12 and declined from Day 12 to Day 16. Serum estrogen levels were elevated during the second half of pregnancy, whereas serum androgen levels were minimal. Neither estrogen nor androgen production by hamster placentae could be detected.

Gestational effects on placental and serum androgen, progesterone and prolactin-like activity in the mouse

The concentrations of androgen, progesterone and prolactin-like activity in serum, placentae and media from placental incubations during the second half of pregnancy in the C3H mouse were evaluated. Serum concentrations, placental content and in-vitro placental release of androgen were raised on day 10 of pregnancy. Serum progesterone levels showed minor fluctuations during the second half of gestation, whereas placenta content and in-vitro release of progesterone were increased on day 10 of gestation. The serum profile of prolactin-like activity showed a significant mid-pregnancy increase on day 10 which did not correlate with placental content or in-vitro placental release of prolactin-like activity. The placental content and in-vitro release of prolactin-like activity were low during mid-pregnancy and increased during the latter days of gestation when serum prolactin-like activity was reduced.

The development and characterization of a homologous radioimmunoassay for mouse placental lactogen

A highly specific and sensitive homologous radioimmunoassay (RIA) has been developed for mouse placental lactogen(mPL). Mouse pregnancy serum and placental extracts showed parallel dilution-response curves, and no significant cross-reaction was seen with either mouse growth hormone or mouse prolactin. The sensitivity of the assay ranged from 0.5 to 1.0 ng/ml, and the intra- and inter-assay coefficients of variation were 5 and 11%, respectively. By RIA, mPL levels were detectable on day 9 of pregnancy (1 ng/ml) and increased until day 14 (100-150 ng/ml) in both C3H and BALB/c strains. On days 14-18 of pregnancy, mPL levels were maintained (95-125 ng/ml) in C3H mice, while they continued to increase (greater than 250 ng/ml) in BALB/c mice. In both strains, a midpregnancy peak in prolactin-like activity was detected by a radioreceptor assay but not by the mPL RIA.

Critical time period for the vagino-cervical stimulus to induce pseudopregnancy in the dioestrous rat

Groups of rats experienced mechanical stimulation of the vagino-cervical region in induce pseudopregnancy at various intervals from 0900 h on dioestrus -- 1 (D -- 1) to 1800 h on D -- 2. Twenty-four of 26 rats which were stimulated on D -- 1 experienced immediate pseudopregnancy whereas when the stimulus was given on D -- 2, 39 of 45 rats continued to cycle and the latest time when such mechanical stimulation would reliably induce immediate pseudopregnancy was 2400 h on D -- 1. Abolition of the dark phase between 1800 h D -- 1 and 0600 h D -- 2 did no alter this critical time period (2400 h on D -- 1). Stimulation as late as 1200 h on D -- 2 caused alterations in the normal pattern of 4-day cyclicity in 8 of 11 rats.

Progestagen effects on elicitation of aggressive behaviour in male mice

Effects of progesterone on production of androgen-dependent aggression-eliciting pheromones were investigated. Two groups of anosmic (non-fighting) castrated mice treated with testosterone or with testosterone and progesterone, respectively, were attacked to the same degree by intact, isolated (fighting) mice while control mice (castrated only) were attacked less. The findings support the ideas that progesterone may inhibit androgen-induced aggression via a neural and not via a somatic mechanism.