Circulating immunoreactive inhibin, gonadotropin, and prolactin levels during pregnancy, lactation, and postweaning estrous cycle in the rat

Serum inhibin levels were measured by heterologous RIA during pregnancy, lactation, and the post-weaning estrous cycle in the rat and correlated with changes in serum FSH and LH and prolactin. Blood was serially collected by cardiac puncture under light ether anesthesia from adult Sprague-Dawley rats on alternate days throughout the experimental period. For the first 8 days of pregnancy, immunoreactive inhibin levels remained high, then gradually decreased to reach a nadir at Day 16, and subsequently rose steeply until parturition. The pattern of serum immunoreactive inhibin levels during early pregnancy does not support a corpus luteum source and the dramatic rise from Day 16 to Day 22 correlates with the recommencement of follicular development in the ovary. Inhibin levels decreased rapidly on the day after birth and were suppressed until Day 8 of lactation, slowly increasing thereafter to reach a plateau from Day 14 until weaning (Day 22.5 of lactation). These changes in inhibin levels positively correlated with LH and FSH and negatively with prolactin, and are consistent with an ovarian source for inhibin associated with the recommencement of follicular development resulting from the diminution of the suckling stimulus. Immediately after weaning, serum immunoreactive inhibin levels showed a 4-day cyclic pattern corresponding to the estrous cycle identified by vaginal smear. Inhibin levels peaked on the day of proestrus, reached a nadir on the day of estrus, and rose slowly during metestrus and diestrus to a new peak at proestrus. Serum FSH levels showed an inverse correlation to inhibin levels consistent with a feedback relationship with inhibin.     

Changing characteristics of the milk-ejection reflex during pregnancy, lactation and after weaning in the rat

The pattern of reflex milk ejection during suckling was investigated in anaesthetized Wistar rats at various stages of pregnancy, lactation and after weaning. Milk-ejection responses were measured using intramammary pressure recordings, and the amount of oxytocin released was estimated from log dose-response lines compiled from the mammary responses to exogenous oxytocin. The number of rats showing intramammary pressure responses to oxytocin increased on Day 22 of pregnancy (the day of parturition) and decreased at 8 days after weaning. The dose-response lines from pregnant animals were shallow, but steepened and shifted to the left during lactation and after weaning. Reflex milk-ejection responses during suckling were detectable in primigravid animals, indicating that birth of the litter and previous suckling experience are unnecessary for the immediate functioning of the reflex. Reflex milk-ejection responses improved during early lactation (such that the frequency and the amount of oxytocin released at each response were maximal at Day 10 of lactation), and subsequently declined in late lactation. Although the frequency of responses in animals 2 and 4 days after weaning was similar to that in late lactating animals, the amount of oxytocin released at each response had risen again to mid-lactation values. In animals undergoing a second pregnancy and lactation the pattern of change in the milk-ejection responses was similar to that of primiparous animals.     

Puberty onset in the female offspring of rats submitted to protein or energy restricted diet during lactation

This study aims to determine the effects of maternal protein and energy malnutrition during lactation on the linear growth, body weight and onset of puberty of the female offspring. At parturition, dams were randomly assigned to the following groups: (C) control group, with free access to a standard laboratory diet containing 23% protein; (PR) protein-restricted group, with free access to an isoenergy and protein-restricted diet containing 8% protein; and (ER) energy-restricted group, receiving standard laboratory diet in restricted quantities. After weaning, the female pups had free access to standard laboratory diet. From day 30 onwards, the pups were inspected daily for vaginal opening. Cyclic stages of the ovaries were studied by daily vaginal smears after vaginal opening until day 40 when all animals were sacrificed with pentobarbital. From day 4 after birth until day 40, body weight and linear growth in the PR and ER rats were significantly lower than in controls (p < 0.001). In spite of the significant (p<0.05) delayed in the vaginal opening in PR and ER rats, the first estrous cycle occurred at the same time of vaginal opening in all groups. The PR and ER rats exhibited a lower uterine (PR = 42%, ER = 40%, p < 0.001) and ovarian (PR = 26%, ER=19%, p < 0.05) absolute weight and uterus relative weight (PR = 27%, ER = 22%, p < 0.05). Our data showed that maternal protein and energy malnutrition during lactation leads to growth retardation and delayed on the onset of puberty in female pups, with vaginal opening and estrous cycle occurring at the same time.     

Ontogenetic diurnal variation of adrenal responsiveness to ACTH and stress in rats

We performed studies in 8-, 16-, 24-, 30 and 35-day-old Wistar rats at 8.00 h (AM) and 20.00 h (PM) to investigate the relationship between the diurnal variations of basal plasma corticosterone (compound B, CB) and its responses to ACTH and ether stress during the postnatal period. Basal plasma CB levels increased at PM from 8 to 35 days of age and an AM-PM difference was observed at 16 days. Although an AM-PM difference in CB responsiveness to ACTH was detected only at 24 and 35 days, ACTH induced an increasingly higher CB response at PM than at AM from 8 to 35 days. A stress-induced CB response was observed starting at 8 days of age and presented an age-dependent increase; however, no AM-PM difference was observed at any age. The stress-induced CB levels were higher than ACTH-induced CB values at all ages tested except at PM in 8-day old rats. These data demonstrate that the basal CB levels and adrenal sensitivity to ACTH rise during the evening as a function of neonatal development.     

Effect of cortisone on the developmental pattern of the neutral and the acid β-galactosidases of the small intestine of the rat

1. The developmental pattern and effect of cortisone on acid beta-galactosidase and neutral beta-galactosidase were studied in postnatal rats by a recently proposed method for their independent determination. 2. After birth the acid beta-galactosidase activity increases in the ileum, whereas it decreases slightly in the jejunum. On day 16 after birth the activity in the ileum decreases and in 20-day-old rats activity in both parts of the intestine decreases to adult values. In suckling animals the activity in the ileum exceeds the jejunal activity severalfold and in adult animals the activity in the jejunum is slightly higher than that in the ileum. 3. Neutral beta-galactosidase activity is high after birth and decreases in both jejunum and ileum after day 20 after birth. In 12-20-day-old rats activity in both parts is essentially the same, but in adult animals jejunal activity exceeds ileal activity four-to five-fold. 4. Cortisone (0.5, 2.0 or 5.0mg/100g body wt. daily for 4 days) does not influence the activity of either enzyme in 60-day-old rats. Acid beta-galactosidase activity is decreased after cortisone treatment in 8-, 12-, 16-and 18-day-old rats, with sensitivity to cortisone increasing with the approach of weaning. No effect of cortisone on acid beta-galactosidase is seen in 8-day-old rats. Neutral beta-galactosidase activity is increased in the ileum of 8-, 12-, 16- and 18-day old rats, but only in the jejunum of 8-and 12-day-old rats.     

The effect of ambient temperature on body temperature and on ultrasonic behaviour in litters of albino laboratory mice deprived of their mothers

Litters of mouse pups of various ages when deprived of their mother and kept for one hour at ambient temperatures of 3°C, 12°C and 22°C lose heat less rapidly than pups isolated individually at similar temperatures. The litters are able to maintain constant body temperatures of 35–37°C by day 8 at 22°C, by day 19 at 12°C and by day 21 at 3°C. Very little ultrasound is detected from litters of any age up to 21 days at 22°C while at 12°C ultrasound is mainly detected from pups of 4 and 6 days; very few calls are produced by older pups at this temperature. Considerably more calls are emitted at 3°C than at either of the two higher temperatures. At 3°C the total number of calls emitted during the hour-long exposure period varied markedly with age. There were two peaks of calling, one on day 6 and the other on day 16. The temporal pattern of calling throughout the hour-long exposure period at 3°C was similar in pups of 4 and 6 days and in pups of 8, 10, 12, 14 and 16 days, but differed between these two groups. In the younger group of pups the rate of calling rose to a peak and then decreased to zero as the pups became comatose; in the older pups the rate of calling was low initially then either rose throughout the rest of the hour or rose to a high level that was maintained. It is suggested that the various patterns of ultrasonic calling can be associated with the physiological development of mouse litters.     

Effects of synchronization and frequency in insemination on fertility.

Fifty-four normally cycling, non-lactating mares were given 2 injections (i.m.) of PGF-2 alpha (10 mg) 14 days apart without regard to stage of the oestrous cycle. At 19 days after the first PGF-2 alpha treatment, a single i.m. injection of either hCG (3300 i.u.) or a GnRH-analogue (500 micrograms) was administered. Each mare was inseminated with 100 X 10(6) motile spermatozoa at one of the following frequencies: once only on Day 20; every other day during oestrus or at least on Days 19 and 21; or daily during oestrus or at least on Days 19, 20, 21 and 22. Eighteen control mares received saline injections on Days 0 and 14, and were inseminated either on the 4th day of oestrus or every other day or daily beginning on the 2nd day of oestrus. More (P greater than 0.05) PGF-2 alpha treated mares displayed their 1st day of oestrus on Days 14 to 20 than control mares (80.6 versus 27.8%). During cycle 1, fewer (P greater than 0.05) treated mares became pregnant compared to controls; 38.9, 25.0 and 66.7% for PGF-2 alpha + hCG, PGF-2 alpha + GnRH-A and control mares, respectively. After three cycles, the pregnancy rates for mares inseminated every other day or daily were higher (P less than 0.05) than mares inseminated only once during oestrus (88.9 and 88.2 versus 64.7%).     

Absence of direct effects of prostaglandins on rabbit blastocysts in vitro

A total of 27 monkeys (M. Fascicularis) whose control cycle lengths ranged from 28 to 32 days were used in this study. All the treatments described below started either on day 17 or 18 of the cycle. Six monkeys received daily injections of 20 μg estradiol-17β (E₂) for 5 consecutive days. Although a drop in blood progesterone (P) did occur due to this treatment, no shortening of the luteal phase of the cycle was recorded. Seven monkeys received daily injections of 15 mg PGF_2α (prostaglandin-F_2α) for 4 or 5 days. These monkeys also showed a drop in blood P levels; moreover 5 of these monkeys had vaginal bleeding for 2–3 days starting either on day 19 or 20 of the cycle. This bleeding did not appear to be a normal physiological menstrual flow, since all of the monkeys commenced menstrual flow at the expected time. Four monkeys received daily injections of 10 mg P for 3 days. These monkeys also had normal cycle lengths in spite of the treatment. Finally 9 monkeys received daily injections of 20 μg E₂ for 3 days, and starting on the third day of E₂ treatment these monkeys also received injections of 15 mg PGF_2α for 4 or 5 days. Shortened cycle lengths were recorded in 8/9 monkeys in this group. Six monkeys had 22-day cycles, 2 monkeys had 24-day cycles and the remaining monkey had a cycle length of 26 days. Thus 8/9 monkeys had shortened luteal phases due to sequential treatment of E₂ and PGF_2α. The cycle lengths in all the treatment groups were normal subsequent to treatments. These results provide potentially useful information for further studies in the human as a method of contraception.     

Thyroxine-induced changes in the glycosylation pattern and in brain and serum levels of rat alpha-fetoprotein

We have studied the effect of thyroid disfunction during the postnatal period, on the serum and brain levels of rat alpha-fetoprotein (AFP) and albumin. Hypothyroidism was induced by treatment of pregnant rats and their newborn pups with 2-mercapto-1-methylimidazole(methimazole). Hyperthyroidism was provoked in newborns by daily injections of thyroxine (0.25 micrograms/g body wt) from the 3rd postnatal day weaning. Impaired growth, lower brain size, altered behaviour and morphological features observed were according to an altered thyroid status. Hypothyroid rats showed a significantly reduction in serum AFP concentration (78% of control values at 8 days of age) and a slight increase in that of albumin. level could be appreciated. Thyroxine supplementation (0.2 micrograms/rat/day) corrected most of these alterations. Hyperthyroidism induced a drastic fall in both serum and brain AFP levels (about 48% of the corresponding control values). Albumin concentration in serum was augmented significantly from the 12th postnatal day, but its brain levels did not change significantly. In hyperthyroid rats, a significant reduction (37% relative to controls) in the concanavalin A-non reactive microform of AFP, was observed. This alteration of the glycosylation pattern of AFP could be due to the inhibition by thyroxine of the activity of the hepatic enzyme GlcNAc-transferase III.     

The influence of testosterone in the brain of the male rat on levels of serotonin (5-HT) and hydroxyindole-acetic acid (5-HIAA)

There were two groups of rats: one was injected with testosterone propionate (10 mg/kg) every 7 days starting from weaning (23 days old); the other group had gonadectomy on the same day. The levels of 5-HT and 5-HIAA were measured by spectrofluorometry. The concentrations of 5-HT in the diencephalon of the testosterone propionate injected rats decreased significantly at 45 days, tending to become reestablished at 60 days; the rest of the brain followed the same pattern, but was less pronounced. The concentrations of 5-HIAA in the diencephalon and the rest of the brain decrease throughout postnatal development, although the differences are not significant. The castrated rats showed a marked increase at 45 days and later decreased at 60 days without recovering their initial values, in both brain areas. 5-HIAA concentrations were similar to those found in the injected animals. These facts can have various interpretations: early modifications in the brain, feed-back regulation mechanisms at the level of the hypothalamus, decrease in the release of the amine or reduction of its catabolism.     

Age-associated changes and sex differences in urinary 6-sulphatoxymelatonin circadian rhythm in the rat.

The circadian rhythm of 6-sulphatoxymelatonin (aMT6s) excretion has been determined in male and female rats at 3 weeks and at 2, 8, 14 and 20 months of age. All animals have a pronounced circadian pattern of aMT6s excretion under a 12 hour dark: 12 hour light cycle. A significant increase in aMT6s excretion is observed from 3 weeks to 14 months followed by a decrease at 20 months. There is a highly significant correlation between aMT6s excretion and body weight (r = 0.73 for female rats and r = 0.74 for male rats; p values are all less than 0.001). Thus, a decrease in aMT6s excretion associated with increasing age occurs when body weight is taken into consideration. aMT6s excretion is higher in males at 3 weeks and at 2 and 8 months of ages. Urinary testosterone in male rats and estradiol in female rats increase from 3 weeks to 8 months and decrease at older ages. These data suggest that increase of body weight from 3 weeks to 14 months is an important factor responsible for the age-related alteration. The sex differences in aMT6s excretion in younger rats may be associated with their sex hormonal milieu.     

Neonatal exposure to propylthiouracil induces a shift in lymphoid cell sub-populations in the developing postnatal male rat spleen and thymus

Evidence of the connections between the immune system and the thyroid axis is increasingly strong; however, much of the data are focused on immune effects of altered thyroid status in adults or rodents with congenital defects of the pituitary/thyroid axis. The object of the present study was to determine the effects of PTU-induced hypothyroidism on the developing immune system of the rat by focussing on both the spleen and thymus gland. Male Sprague-Dawley rat pups were exposed to PTU through maternal milk by giving the mothers 0.02% PTU in their drinking water starting on the pups' day of birth until day 24 (d24), shortly before weaning on d28. Animals were sampled on days 14, 22, 30, and 91. The mean body weight was decreased in the PTU-treated animals on days 14, 22, and 30. The mean spleen and thymic weights and cellularity were all decreased in the PTU-treated animals on d22 and d30. PTU exposure increased the proportion of NK cells in the spleen on days 14, 22, and 30. The proportion of T-cells was increased on days 22 and 30 with a particular increase in the CD4+ T-cells, resulting in an increase in the ratio of helper T-cells to suppressor/cytotoxic T-cells at d22. PTU also decreased the proportion of splenic B-cells at days 14, 22, and 30 which could explain the increased proportion of both NK and T-cells during these sampling periods. PTU treatment decreased the lytic ability of NK cells at d22, but no functional differences were observed at days 14, 30, 91, despite the increased proportion of NK cells in PTU-exposed animals at days 14, 22, and 30. PTU exposure also increased the proportion of CD4+CD8- cells in the thymus on d22 and caused an increase in both the CD4+CD8- and CD4-CD8+ populations on d30. These data suggest that the effects of temporary, PTU-induced hypothyroidism on the cell populations in the spleen partially result from transient changes in thymic T-cell development, including a shift towards increased CD4+CD8- cells. The data also suggest that temporary hypothyroidism early in development decreases B-cell development in a transient fashion. Temporary hypothyroidism induced from birth to the latter stages of the weaning period induced transitory effects on the spleen, thymus, and immune cell sub-populations--all of which recovered to normal values when the animals matured.     

Changes of enzyme activity in the rat liver at different age in circadian cycle

Most of the biological processes in the living organisms of both animals and man are known to be of rhythmical nature. Variability of enzymatic activity in circadian cycle depends on many factors among other on age, sexual maturity, diet as well as medication. The results obtained in our studies indicate, that the activity changes of acid phosphatase and ATP-ase Mg++ dependent in the liver of all the examined age groups were of 24 hour circadian rythm. As to the acid phosphatase activity the results of this experiments showed that in circadian cycle in all examined age groups there is only one peak of elevated activity. ATP-ase Mg++ dependent showed two activity peaks appearing at the same hour both in 30 and 60 days old animals. It should be noticed that the activities of ATP-ase Mg++ dependent in 100 day old animals were two times higher than in 30 and 60 days old rats.     

Effect of aging on 24-hour pattern of stress hormones and leptin in rats

This work analyzes the 24-hour changes of hypothalamic-pituitary-adrenal (HPA) axis activity and leptin release in aged rats. Three- and 22-month-old male Wistar rats were killed at 6 time intervals during a 24-hour cycle (n=8-10 rats/group). Aging augmented plasma ACTH while it decreased plasma and adrenal gland corticosterone levels. Plasma and adrenal corticosterone levels attained high levels during all the scotophase, concomitantly with the maxima in ACTH levels, whereas in aged rats only a brief plasma corticosterone peak at the early scotophase and no time of day variations of adrenal corticosterone were observed. Aging augmented circulating leptin, with a significant interaction "agextime" in the factorial ANOVA, i.e. only in young rats time of day changes were significant, with the lowest values of leptin at the middle of the light period and higher values at night. When plasma leptin was expressed on body weight basis, the age-related differences became not significant but the daily pattern of plasma leptin found in young rats persisted. Plasma and adrenal corticosterone levels correlated significantly with plasma ACTH only in young rats. Likewise, plasma leptin correlated with plasma corticosterone only in young rats. These changes can be attributed to a disrupting effect of aging on the homeostatic mechanisms modulating HPA activity and leptin release.     

Adenylate cyclase activity in rat submandibular gland during postnatal development

Adenylate cyclase activity was measured in homogenates of submandibular glands of 1 to 42 day old rats. During this period of time the gland reached its final stage of differentiation. Adenylate cyclase activity was higher in the glands of one day old rats than in those of 7 and 14 day old animals. Between 14 and 28 days of age the enzyme activity more than doubled and approached the level that characterized the glands of adult animals. Fluoride (10mM) stimulated the enzyme activity in all age groups but the stimulation was less in the case of one day old rats as compared to older animals. Isoproterenol (10^?4 M) stimulated adenylate cyclase by 50–60% in the gland of adult rats but had no effect on the enzyme activity in 7 to 28 day old animals. Administration of isoproterenol for 5 days to 9 day old rats increased the weight of the submandibular gland by 70 per cent. Total adenylate cyclase activity increased parallel with the weight of the gland but the specific activity of the enzyme remained unchanged. It is concluded that during the postnatal development of the submandibular gland the rapid increase in adenylate cyclase activity occurs after weaning and it coincides with an accelerated rate of functional differentiation of the acinar cells.     

EGFR is involved in control of gastric cell proliferation through activation of MAPK and Src signalling pathways in early-weaned rats

Objectives: Early weaning (EW) increases proliferation of the gastric epithelium in parallel with higher expression of transforming growth factor alpha and its receptor epidermal growth factor receptor (EGFR). The primary objective of the present study was to examine involvement of EGFR signalling in regulating mucosal cell proliferation during the early weaning period. Materials and methods: Fifteen‐day‐old rats were split into two groups: suckling (control) and EW, in which pups were separated from the dam. Animals were killed daily until the 18th day, 3 days after onset of treatment. To investigate the role of EGFR in proliferation control, EW pups were injected with AG1478, an EGFR inhibitor; signalling molecules, proliferative indices and cell cycle‐related proteins were evaluated. Results: EW increased ERK1/2 and Src phosphorylation at 17 days, but p‐Akt levels were unchanged. Moreover, at 17 days, AG1478 administration impaired ERK phosphorylation, whereas p‐Src and p‐Akt were not altered. AG1478 treatment reduced mitotic and DNA synthesis indices, which were determined on HE‐stained and BrdU‐labelled sections. Finally, AG1478 injection decreased p21 levels in the gastric mucosa at 17 days, while no changes were detected in p27, cyclin E, CDK2, cyclin D1 and CDK4 concentrations. Conclusions: EGFR is part of the mechanism that regulates cell proliferation in rat gastric mucosa during early weaning. We suggest that such responses might depend on activation of MAPK and/or Src signalling pathways and regulation of p21 levels.     

Effect of hindlimb unloading on interlimb coordination during treadmill locomotion in the rat

Effects of hindlimb unloading on interlimb coordination were examined in adult rats walking on a treadmill at moderate speed. In the first group of animals, the electromyographic activity (EMG) of soleus muscle of both hindlimbs was recorded after 7 and 14 days of unloading. In the second group, the EMG was recorded daily until the 14th day of unloading. The general organization of locomotion was preserved in the two groups whatever the duration of the unloading. The step cycles of the two hindlimbs were always strictly alternating. However, the locomotor pattern was very irregular. A lateral instability was observed. It was accompanied by an abduction of the hindlimbs, and frequent hyperextensions of the ankle when walking. The EMG analysis showed an increase in step cycle duration and in coactivation duration of the soleus muscles (i.e. in the double stance duration). In the rats recorded daily, mean EMG was dramatically reduced the 1st day of unloading, suggesting a decrease in the neural drive. Taken together, these data indicate that 14 days of hindlimb unloading can alter the neuromuscular pattern during locomotion. It is proposed that these changes are related to changes in the peripheral sensory information. Accepted: 29 June 1998     

Characterization of the oestrous cycle and mating season of squirrel monkeys from copulatory behaviour.

Observations of the behaviour of squirrel monkeys, including 8 opposite-sex pairs during daily 30-min social encounters and 2 mixed-sex permanent groups during daily 30-min observation sessions, over a 14-month period were used to determine the periodicity of the oestrous cycle and annual mating season. The median and modal length of the oestrous cycle was 8 days, within which copulations were limited to a 1--2 day period. In a cyclic female, plasma progesterone levels over a 24-day period dropped from 85--151 ng/ml to 25 ng/ml 2 days before oestrus. In non-cyclic females plasma progesterone values were less than 15-4 ng/ml. Males exhibited a 6-8--19-7 week 'season' of copulation and ejaculation. The onset of this 'mating season' in August coincided with the annual peak in male body weight (the 'fatted male' phenomenon).     

Luteinizing hormone,total estrogens and progesterone secretion during lactation and after weaning in sows

Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low (< 1 ng/ml) during lactation and averaged 1.9 ± .3, .6 ± .3 and 1.2 ± .3 on days 1, 3 and 5 after weaning. Estrogens were variable during lactation, averaged 121 ± 36 pg/ml on day 1 after weaning and decreased thereafter. Estrus began on day 3 after weaning in 1 sow and on day 5 in the remaining 10 sows.In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low (< 1 ng/ml) until after ovulation when progesterone increased. Estrus began on day 4 after weaning in all seven sows.Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.     

Effects of prior androgen exposure upon adrenal function in maturing rats

Gonadectomy in the newborn produced an elevated or “female” pattern of serum corticosterone levels when basal levels of corticosterone (B) were measured at the trough and peak of the daily rhythm and when the response to a 2 minute ether stress was recorded after weaning age. Administration of 1.25 mg testosterone propionate (TP) at two days of age did not significantly alter corticosterone patterns in intact males but did prevent the rise in serum B noted in gonadectomized (Gondx) males. In contrast with oil-injected females, females androgenized with 1.25 mg TP showed precocious vaginal opening,persistent estrous and a failure of serum B to become elevated at noon on the day of vaginal opening. Gonadectomy at weaning age had no effect on basal levels of B but there was a more rapid elevation of B after ether stress in Gondx males. By 30 minutes post-stress, the levels of B were the same in both groups. Gonadectomy at 60 days of age had no effect on B levels except for a transient decrease in B at 8 p.m. one week after surgery. The stress response was also normal in castrated males. It can be concluded that early androgen exposures does alter the functional properties of the adrenal but that continued secretion of androgen is not necessary to maintain adrenal function at a “male” level in adults.