Effects of dexamethasone administration to diestrus cows on systemic progesterone,estrogen and uterine cyclooxygenase production

Parenteral administration of dexamethasone to diestrus cattle can extend the length of the natural estrous cycle. In mice, dexamethasone has been shown to inhibit production of the second isozyme of the cyclooxygenase (COX) enzyme (a rate limiting enzyme in prostaglandin formation). Therefore, the purpose of this study was to determine the effect of dexamethasone on estrous cycle length and COX-1 and -2 production by the uterine endometrium of cyclic cattle.Nine crossbred beef cows that exhibited two previous normal estrous cycles were randomly assigned to two treatments; a control group administered intramuscular injections of vehicle, and a dexamethasone group administered 8 mg of dexamethasone (Azium^®, Schering Corp., Kenilworth, NJ). Both groups received twice daily injections on day 13–22 of the treatment cycle. Uterine endometrial biopsies were collected on days 16, 19 and 22 of the treatment cycle. Blood samples were collected daily on day 13–22 of the treatment cycle for plasma progesterone and estradiol concentrations.The mean treatment cycle length was extended (P < 0.05) in the dexamethasone group (31 d) compared with the control group (24 d). However, no difference was noted in the time to progesterone decline between treatments. In contrast, estradiol levels were lower in the dexamethasone treated animals compared with the control group on day 19 to 22 of treatment. A western blot analysis revealed no COX-2 in the uterine samples of either treatment. The COX-1 isoform was found on all days examined, but no treatment effect was detected. These results suggest that dexamethasone extends the cycle length by inhibiting follicle growth, and that COX-2 may not be involved in prostaglandin formation by the uterus during luteolysis.     

Plasma and Urinary 11-Hydroxycorticosteroids in Differential Diagnosis of Cushing's Syndrome

Morning plasma 11-hydroxycorticoids, urinary 11-hydroxycorticoids, and urinary 17-oxogenic steroids were measured before and during a dexamethasone suppression test. This consisted in the administration by mouth of 2 mg of dexamethasone daily for 48 hours, followed by 8 mg daily for 48 hours. In addition midnight plasma 11-hydroxycorticoids were measured before the start of the test. The subjects investigated were 21 patients with Cushing''s syndrome, 27 obese female patients, 10 female patients with the Stein-Leventhal syndrome, and 8 female patients with idiopathic hirsutism.The results showed that the clearest distinction between the groups was made by measurement of the basal urinary 11-hydroxycorticoid excretion, where, in the group of patients with Cushing''s syndrome, all the levels were well above the upper limit of normal. In addition raised midnight plasma 11-hydroxycorticoid levels were of great diagnostic value. By using these results together with those of the dexamethasone suppression tests it was possible to make a firm preoperative diagnosis of pituitary-dependent Cushing''s syndrome in 90% of patients in this series.     

Estrous cycle characteristics and response to estrus synchronization in mammoth asses (Equus asinus americanus)

Breeding records from a herd of mammoth asses (Equus asinus americanus) maintained on pasture in southeast Texas from 1990 to 1998 were reviewed. Jennies were pasture or hand mated, and estrus was either observed while the jennies were on pasture or when exposed to a jack after being penned. Eighty-one estrus periods and 43 diestrus intervals were recorded in 33 jennies over 4 seasons of the year (January-March, April-June, July-September, and October-December). Estrous cycle length and the duration of estrus were similar among seasons. Over all seasons, estrous cycle length was 23.3 +/- 2.6 d, duration of estrus was 5.9 +/- 2.1 d, and diestrus length was 17.4 +/- 2.6 d (mean +/- SD). During these same 9 yr, 58 injections of PGF2 alpha (5 mg, i.m.) were administered to 38 jennies without regard to stage of estrous cycle. Seventy-six percent (44/58) of the jennies showed signs of estrus after PGF2 alpha treatment, with an interval to estrus of 4.4 +/- 1.6 d and a duration of estrus of 5.6 +/- 1.7 d. Two estrus synchronization schemes were also assessed. Trial 1 was performed in October to November 1996, and Trial 2 was performed in February to March 1998. In Trial 1 (Group PE + PGF, n = 10), each jenny was injected intramuscularly once daily for 10 d with 150 mg progesterone and 10 mg estradiol-17 beta in sesame oil, and PGF2 alpha (10 mg) was injected intramuscularly on the last day of treatment. In Trial 2 (Group PGF-2X, n = 11), each jenny was injected intramuscularly twice, 16 d apart, with 10 mg PGF2 alpha. All Group PE + PGF jennies responded to treatment. One jenny in Group PGF-2X did not respond to either injection of PGF2 alpha, while 2 jennies responded to the first but not the second PGF2 alpha injection (8 of 11 jennies returned to estrus and ovulated after the second PGF2 alpha injection). Duration of estrus was 6.8 +/- 1.9 d for Group PE + PGF and 7.1 +/- 1.8 d for Group PGF-2X jennies. Interval to estrus and interval to ovulation following the last treatment were 9.0 +/- 0.9 d and 14.5 +/- 1.7 d, respectively, in Group PE + PGF jennies, and 4.5 +/- 0.9 d and 10.4 +/- 1.8 d, respectively, for Group PGF-2X jennies. In summary, estrous cycle characteristics of mammoth asses are similar to those reported for standard jennies, and estrus synchronization schemes used in horses are effective in mammoth asses.     

Effect of flushing of blastocysts on days 10-13 on the life-span of the corpora lutea in the pig

Blastocysts were flushed out of both uterine horns of gilts on Days 10, 11, 12 or 13. In mated non-pregnant gilts flushing had no effect on progesterone profile or cycle length (20.8 +/- 0.4 versus 20.6 +/- 0.6 days in the preflush cycle, N = 6, mean +/- s.e.m.). Flushing the blastocysts out of the uterine horns on Day 10 resulted in a cycle with a normal progesterone profile and a normal length (21.2 +/- 0.4 days, N = 5). Flushing on Days 11, 12 or 13 resulted in a normal cycle or in maintenance of the CL for 3-13 days as indicated by elevated progesterone concentrations and an increased interoestrous interval of, respectively, 22.0 +/- 1.2 versus 19.8 +/- 0.6 days (Day 11; N = 6), 24.8 +/- 1.4 versus 21.0 +/- 0.6 days (Day 12; N = 5; P less than 0.05) and 26.3 +/- 2.3 versus 20.5 +/- 0.4 days (Day 13; N = 6; P less than 0.05). There was a positive relationship between the change in interoestrous interval and the interval between the first observed standing oestrus and flushing of the blastocysts (rs = 0.350; n = 22; P less than 0.1). There was a large variation in the diameter of the blastocysts flushed on the same day. Only in those gilts in which the blastocysts were greater than or equal to 8 mm or filamentous were the CL maintained for 3 or more days. These results indicate that a first signal for maternal recognition of pregnancy is generated on Day 12 and that blastocysts greater than or equal to 8 mm are required for prolongation of CL function for 3 or more days. Since CL function is only extended for a maximum of 13 days (mean 7.4 +/- 1.0), a second signal seems necessary to maintain the CL for the whole period of pregnancy.     

Corticosteroid induction of Ig+Ia- B cells in vitro is mediated via interaction with the glucocorticoid cytoplasmic receptor

Flow microfluorometry was used to examine the effect of dexamethasone on the expression of surface Ia (sIa) on resting and activated murine B cells. Although dexamethasone resulted in a 50% reduction in sIa expression 12 h after injection, it was significantly less suppressive when injected together with B cell activators. In vitro dexamethasone, but not other related steroid hormones, induced a population of cells that were sIg+sIa-. A 20% reduction in the expression of sIa was noted by 4 h of culture with 10 nM dexamethasone, but maximal inhibition of 70% was not reached until 12 h of culture, and this degree of suppression persisted as long as dexamethasone remained in culture. When the dexamethasone was washed out after 8 h of culture, the maximal reduction was still noted at 12 h, but by 24 h there was re-expression of sIa toward base line levels, indicating it did not induce irreversible lethal alterations in the B cell. The inhibition of sIa expression correlated with a specific reduction in the quantity of messenger RNA for sIa as measured by Northern blot analysis, indicating that this is mediated at least in part by suppression of the steady state levels of Ia mRNA. The corticosteroid receptor antagonist RU486 was able to reverse the suppressive effects of dexamethasone on sIa expression, thus demonstrating that its effect is mediated specifically by binding to its intracellular receptor. Furthermore, when protein synthesis was inhibited during the short period of time that cells were preincubated with dexamethasone, minimal suppression of Ia expression was noted, suggesting that the dexamethasone may be stimulating a protein that has suppressive effects on MHC class II expression. The suppressive effects of dexamethasone in vitro were substantially reduced when B cells were simultaneously activated by stimuli that increase the expression of sIa. These data indicate that the suppressive effects of corticosteroids on immune response Ag are corticosteroid specific; are greater in resting than in activated B cells; are induced via the classical steroid mechanism of action, which is receptor mediated; and may result from the induction of an inhibitory protein that suppresses Ia mRNA.     

The effects of zearalenone on reproduction in swine. I. The relationship between ingested zearalenone dose and anestrus in non-pregnant, sexually mature gilts

Ninety-nine sexually mature, non-pregnant gilts were checked for estrus daily with a mature boar and then allocated at estrus (D O) to receive 2 kg/d of a diet containing 0, 1, 5 or 10 ppm purified zearalenone between D 5 and 20 of the estrous cycle during two seasons of the year (winter and summer). None of the gilts exhibited any visual signs of "hyperestrogenism" and there was no effect of season on interestrous interval (P > 0.05). A significant effect of zearalenone dose on inter-estrous interval was detected (P < 0.001). Gilts receiving 0 or 1 ppm had similar inter-estrous intervals (21.0 +/- 0.3 and 21.5 +/- 0.8 d, respectively) whereas gilts receiving 5 and 10 ppm had extended cycles (29.2 +/- 2.9 and 32.7 +/- 3.3 d, respectively). Plasma progesterone concentrations at D 19 to 21 were higher in gilts with extended cycles (P < 0.001) and corpora lutea (CL) were present at laparotomy. Some 86% of these retained CL underwent spontaneous regression resulting in the onset of estrus within the next 30 d. Fecal zearalenone concentrations rose during ingestion of contaminated diets and declined to pretreatment values within 2 d (1 ppm) to 8 d (10 ppm) of the cessation of treatment. These data show that feeding zearalenone at concentrations of 5 to 10 ppm from D 5 to 20 of the estrous cycle causes luteal maintenance and extended inter-estrous intervals. Spontaneous regression of these CL usually occurs within 30 d after zearalenone is removed from the diet. Fecal zearalenone analysis does not appear to be an effective method for determining prior exposure to zearalenone when carried out more than a few days following the last ingestion of zearalenone.     

Overnight (1 mg) dexamethasone suppression testing reliably distinguishes non-cushingoid obesity from Cushing's syndrome.

To determine the sensitivity of the overnight 1-mg dexamethasone suppression test in diagnosing Cushing's syndrome, we evaluated the cortisol responses of 55 subjects (25 non-obese individuals with body mass index less than 25 kg/m2, 20 obese individuals with body mass index greater than 30 kg/m2, and 10 patients with surgically proven Cushing's syndrome) following ingestion of 1 mg dexamethasone at midnight. The basal 8 AM plasma cortisol levels among non-obese and obese individuals and patients with Cushing's syndrome were 310 +/- 85, 377 +/- 91, and 813 +/- 270 nmol/L, respectively. Following 1 mg of dexamethasone, Cushing's syndrome patients showed minimal suppression of cortisol to 609 +/- 180 nmol/L (P = 0.79). Non-obese and obese individuals suppressed to 18.7 +/- 6.0 nmol/L (P less than 0.001) and 22 +/- 7.1 nmol/L (P = 0.003), respectively. The results demonstrated similar cortisol responses to overnight dexamethasone suppression in obese and non-obese groups, and clearly distinguished these subjects from those with Cushing's syndrome. Obesity is not a confounding factor in the 1-mg dexamethasone suppression test.     

Life history characteristics of a lightly exploited stock of Squalus suckleyi

The purpose of this study was to examine the basic life history of a lightly exploited stock of Squalus suckleyi in the Gulf of Alaska to establish a baseline for future comparison and to provide critical information for stock assessments. Average total length (total length extended) of females (87·7 cm) was significantly larger (t-test, t = -12·57, d.f. = 1533, P < 0·01) than males (80·3 cm); size at 50% maturity (74·5 and 97·3 cm, males and females, respectively) and age at 50% maturity (21 and 36 years, respectively) were also significantly different between the sexes (i.e. bootstrapped 95% c.i. did not overlap). Total average fecundity was 8·5 pups per female, and individual fecundity was a linear function of either length or whole mass. The best estimate of instantaneous natural mortality was 0·097. The delayed age of maturity, low natural mortality and low rates of reproduction imply that only very low rates of fishing mortality are sustainable. Finally, this paper provides the first reported evidence that a small percentage of the adult females may undergo an extended resting period between pregnancies of ≥ 1 years.     

Selective effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and corticosteroid on in vitro lymphocyte maturation

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the corticosteroid dexamethasone have potent effects on lymphocyte function, although the effects of the former have not been well characterized. In the present studies murine B cell maturation was used as a model system to examine and compare the effects of TCDD and dexamethasone on cell function. Immunosuppression by TCDD and dexamethasone is mediated by binding to specific intracellular R referred to as the Ah and glucocorticoid R, respectively. Although both compounds were comparable in their ability to inhibit antibody responses to the T-independent antigen TNP-LPS, the events responsible for suppression were found to be distinct. Dexamethasone, although affecting multiple stages of B cell maturation, had its primary effect very early, manifested by inhibition of the phosphoinositide signal transduction pathway. This was evidenced by a decrease in accumulation of inositol phosphate and surface Ia antigen expression as well as an inability to enter the cell cycle after stimulation with anti-Ig. In contrast, neither early signaling events nor proliferation were affected in B cells treated with TCDD. However, TCDD inhibited Ig secretion after stimulation of B cells with T cell-replacing factor, suggesting that TCDD modulates the differentiation of B cells into plasma cells. These differential results were confirmed by monitoring the expression of surface antigens that occur on B cells, including Ia, 7D4, and PC.2, during this maturational process. Whereas dexamethasone inhibited the expression of surface antigens that occur early in maturation (Ia and 7D4), TCDD blocked only the expression of the plasma cell marker PC.2. Although TCDD altered later stages of the B cell cycle, the presence of TCDD was required at the time of initial activation to be effective, suggesting that TCDD may interfere with early cell programming.     

Non-invasive monitoring of male and female numbat (Myrmecobius fasciatus: Myrmecobiidae) reproductive activity

The reproductive endocrinology of the highly endangered numbat (Myrmecobius fasciatus) is described for the first time. Patterns of faecal steroid secretion (progesterone [PM], oestradiol-17β [E2] and testosterone [TM] metabolites) were examined within a captive numbat population over 1 year and revealed a highly synchronized seasonal pattern of reproduction. TM secretion increased progressively from September to November, peaked in December and then decreased in February. All females displayed luteal phases (1-3), between late-November to late-March, in association with pregnant (Pr, n=4), non-productive mated oestrous cycles (NMEC, n=8) and non-mated oestrous cycles (NEC, n=6). The mean oestrous cycle length was 30.2±1.1d (n=11) and was comprised of a mean follicular (n=11) and luteal (n=18) phase length of 16.2±1.6d and 14.0±0.8d, respectively. No variation in mean luteal phase length or PM concentration according to cycle type (Pr, NMEC, NEC) or cycle number (1st, 2nd or 3rd cycle) was detected. Longitudinal profiling of PM secretion confirmed that the female numbat is seasonally polyoestrous and that the luteal phase occurs spontaneously. Changes in the secretion of E2 provided little instructive information on oestrous cycle activity. Mating success was 31%, with age and subject having no effect on mating success. Timing of introduction, of male to female, appeared to impact mating success, with paired animals introduced for a shorter time frame (≤14d) prior to the first observed mating successfully producing young. Collectively, results of the present study confirm that PM and TM can be reliably used to index numbat reproductive activity.     

Elevation of HeLa cell 3-hydroxy-3-methylglutaryl coenzyme a reductase activity by glucocorticoids: Possible relationship to the cell cycle

Elevation of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase, EC 1.1.1.34) activity by glucocorticoids was shown to be dependent on the concentration of hormone in the medium over a range of 5 × 10^?10 to 1 × 10^?8 M, although the presence of steroid in the assay at 10^?5 M elicited no increase in activity. There was a demonstrated time dependence for the addition of dexamethasone i.e., from zero to six hours after serum removal, addition of hormone resulted in the same peak activity; addition at 12 hours gave slight elevation but resulted in an extended maintenance of the peak level of activity; addition at 24 hours showed no effect. When cycloheximide was added at the above times, subsequent kinetics showed identical decay of the enzyme activities from control and treated cultures at 6 and 24 hours, but at 12 hours the activity from dexamethasone treated cells exhibited an extended lag before the onset of decay, which then proceeded at the same rate as the control. The continuous presence of the hormone was not necessary for the induction to continue and the addition of Actinomycin D to cultures incubated in the presence of hormone resulted in an immediate decay of catalytic activity without evidence of “superinduction”. The addition of progesterone at the same time as dexamethasone resulted in a concentration-dependent inhibition of the augmentation, suggesting the involvement of the glucocorticoid receptor in the aug-mentation, suggesting the involvement of the glucocorticoid receptor in the elevation of HMG-CoA reductase activity. Flow microfluorometric (FMF) analysis of hormone treated cells indicated a delayed entrance into the DNA synthesis (S) phase of the cell cycle. The temporal relationships between this cell cycle perturbation and HMG-CoA reductase elevation are discussed.     

Corpus luteum function in the ewe: Effect of PGF2α and prostaglandin synthetase inhibitors

A series of experiments were conducted to evaluate the effects of mode and frequency of administration and estrous cycle stage on the response of the cycling ewe to PGF_2α. The effects of dexamethasone, arachadonic acid and prostaglandin synthetase inhibitors on estrous cycle length and plasma progesterone levels were also determined.Intramuscular administration of 5 or 10 mg of PGF_2α, on days 8 and 9 after estrus (5 ewes/group), significantly (p<.01) shortened the mean length of the estrous cycle and the interval from the end of treatment to estrus. Mean plasma progesterone levels, 24 hours after initial injection, were significantly (p<.01) lowered. When administered on day 8 only, these doses were considerably less effective in shortening estrous cycle length or lowering plasma progesterone levels. Intravaginal administration of PGF_2α, by polyurethane tampon, was also largely ineffective.Treatment of ewes with 10 mg of PGF_2α i.m., on days 3 and 4 of the estrous cycle, resulted in a return to estrus in 2 days in 25% of the treated animals. Plasma progesterone levels of PGF_2α-treated ewes were significantly lower than controls on the second, third and fourth days after the start of dosing. It would appear that PGF_2α exerts a retarding effect on developing CL functionality.The prostaglandin synthetase inhibitors, aspirin, flufenamic acid and 1-p-chlorobenzylidene-2-methyl-5-methoxy-3-indenylacetic acid, were administered orally or parenterally for 16 days beginning on day 8 of the estrous cycle. These compounds failed to prolong estrous cycle length. Parenteral administration of dexamethasone did not result in PGF_2α release in the cycling ewe, at least not in quantities sufficient to induce luteolysis. The prostaglandin precursor, arachadonic acid, also was not luteolytic when given parenterally to cycling ewes.     

Δ1-11-oxa-11-deoxycortisol: A new antiglucocorticoid with activity in vivo

A new steroid-like compound, Δ¹-11-oxa-11-deoxycortisol, was tested in a one-week growth suppression, thymus suppression and adrenal weight suppression bioassay for possible glucocorticoid antagonist activity in $\text{vivo}$. We hypothesized that this compound would have antiglucocorticoid activity based on previous studies of 11-deoxycortisol and Δ^1,9(11)-11-deoxycortisol, which were optimal glucocorticoid antagonists $\text{in vivo}$ in adrenalectomized rats, but which lost antiglucocorticoid activity in intact animals, apparently due to adrenal 11β-hydroxylation. Thus, Δ¹-11-oxa-11-deoxycortisol, a compound which cannot undergo llβ-hydroxylation, was synthesized and tested as an antiglucocorticoid. This analog had an affinity for the rat thymus glucocorticoid receptor similar to that of its parent compounds (Ki 0.9-3.1×10^?7M). A dose of 1 $\text{mg}\text{rat}$ antagonized the effect of 15μg of dexamethasone in the growth suppression assay (p<0.05) and in the thymus suppression assay (p<0.06), but did not antagonize dexamethasone-induced adrenal weight suppression. Δ¹-11-oxa-11-deoxycortisol did not exhibit glucocorticoid activity in any of the three assays. These data suggest that Δ¹-11-oxa-11-deoxycortisol may be a pure competitive antagonist of dexamethasone.     

Serum concentrations of deoxycorticosterone in women during the luteal phase of the ovarian cycle are not suppressed by dexamethasone treatment

We determined the serum levels of deoxycorticosterone (DOC) in plasma of six healthy, apparently ovulatory women during the mid-follicular and mid-luteal phases of their ovarian cycles; and we evaluated the effect of dexamethasone (1 mg by mouth) on the concentrations of DOC and cortisol in serum at times when plasma progesterone levels were high or low. The serum levels of DOC, unlike those of cortisol, did not vary significantly in single blood samples obtained in the morning (8-10 a.m.) and afternoon (3-5 p.m.); and serum DOC levels in women were significantly higher (P less than 0.05) during the mid-luteal phase than during the mid-follicular phase of the cycle. There were unmistakable diurnal variations in serum levels of cortisol, and cortisol concentrations were reduced to less than 20% of pretreatment levels after the ingestion of 1 mg dexamethasone during the mid-follicular or mid-luteal phase. The serum concentrations of DOC were reduced only to approx 70% of pretreatment levels after dexamethasone ingestion during the follicular phase. The serum levels of DOC did not decline significantly after administration of dexamethasone during the mid-luteal phase, when progesterone levels in serum are high (14-16 ng/ml). Blood samples also were obtained at hourly intervals during the 24 h before and after dexamethasone administration in one woman during the follicular phase and in another woman the during the early luteal phase (progesterone levels = 1-3 ng/ml) of the ovarian cycle. DOC levels (pre-dexamethasone) fluctuated in synchrony with those of cortisol in the woman studied during the follicular phase but not in the woman studied during the early luteal phase of the cycle. In the post-dexamethasone period, plasma cortisol levels were suppressed for at least 24 h in both women whereas DOC levels were decreased only partially. We conclude that plasma DOC is derived from both adrenal secretion and from extraadrenal 21-hydroxylation of progesterone--the latter source of DOC is not affected by dexamethasone suppression of ACTH secretion.     

Dexamethasone suppressibility of plasma pregnenolone or dehydroepiandrosterone in gonadectomized patients.

The 9 AM dexamethasone suppression test was carried out in gonadectomized patients, and plasma pregnenolone or dehydroepiandrosterone (DHA) was radioimmunoassayed following various amounts of dexamethasone administration. Pregnenolone, as well as the plasma ACTH level, was completely suppressed with 1 mg dexamethasone, whereas 4 mg or 8 mg of dexamethasone was needed to induce a complete DHA suppression. These findings suggest that the gonads alone contribute to the poor dexamethasone suppressibility of pregnenolone in normal subjects, and that adrenal DHA secretion might be also regulated by an unidentified factor other than ACTH, which would be suppressed with large doses of dexamethasone.     

Inhibiting cortisol response accelerates recovery from a photic phase shift

Jetlag results when a temporary loss of circadian entrainment alters phase relationships among internal rhythms and between an organism and the outside world. After a large shift in the light-dark (LD) cycle, rapid recovery of entrainment minimizes the negative effects of internal circadian disorganization. There is evidence in the existing literature for an activation of the hypothalamic-pituitary-adrenal (HPA) axis after a photic phase shift, and it is possible that the degree of HPA-axis response is a determining factor of reentrainment time. This study utilized a diurnal rodent, Octodon degus, to test the prediction that the alteration of cortisol levels would affect the reentrainment rate of circadian locomotor rhythms. In experiment 1, we examined the effects of decreased cortisol (using metyrapone, an 11beta-hydroxylase inhibitor) on the rate of running-wheel rhythm recovery after a 6-h photic phase advance. Metyrapone treatment significantly shortened the length of time it took animals to entrain to the new LD cycle (11.5% acceleration). In experiment 2, we examined the effects of increased cortisol on the rate of reentrainment after a 6-h photic phase advance. Increasing plasma cortisol levels increased the number of days (8%) animals took to reentrain running-wheel activity rhythms, but this effect did not reach significance. A third experiment replicated the results of experiment 1 and also demonstrated that suppression of HPA activity via dexamethasone injection is capable of accelerating reentrainment rates by approximately 33%. These studies provide support for an interaction between the stress axis and circadian rhythms in determining the rate of recovery from a phase shift of the LD cycle.     

A longitudinal study of estrous cyclicity in aging C57BL/6J mice: I. Cycle frequency, length and vaginal cytology

Cycle frequency, length, and vaginal cytology were measured longitudinally in three cohorts of singly housed virgin mice staggered across a 3-year interval. The age profiles of these parameters were qualitatively similar, but quantitatively different, among cohorts. Cycle frequency was initially low (Phase I), due to prolonged cycles and late-starting cycles, and did not peak (Phase II) until mice were 3-5 months old. Phase II lasted for 7-10 months, depending on the cohort. Thereafter cycle frequency declined steadily (Phase III). The average age of cessation of cyclicity varied among cohorts, occurring between 13 and 16 months of age. Age changes in cycle length paralleled those of cycle frequency. During Phase II, median cycle length was less than 5 days and variance was lowest. During Phases I and III, variance was about twofold greater and median cycle length was greater than 5 days. Although median cycle length remained stable for several months during Phase II, the peak period of 4-day cycles was much shorter. In all cohorts, 4-day cycles did not peak until 7-8 months of age and began to decline by 9 months. The decrease in 4-day cycles was associated with a progressive lengthening of cycles-first from 4 to 5 days, then to longer cycles. The fraction of cycles with extended cornification (greater than 2 days) increased with advancing age from less than 0.35 during the initial period of cycle lengthening to a maximum of 0.60. The observation that the initial phase o cycle prolongation was not usually associated with extended cornification is consistent with earlier evidence that this period is characterized by a delayed, rather than prolonged, preovulatory rise of estradiol. However, the increased fraction of prolonged cycles with extended cornification at later ages suggests that the preovulatory elevation of estradiol may ultimately be prolonged.     

Gluconeogenesis in rat liver parenchymal cells in primary culture: Permissive effect of the glucocorticoids on glucagon stimulation of gluconeogenesis

Primary cultures of parenchymal cells isolated from adult rat liver by a collagenase perfusion procedure and maintained as a monolayer in a serum-free culture medium were used to study glucoeogenesis and the role that the glucocorticoids play in the control of this pathway. These cells carried out gluconeogenesis from three-carbon precursors (alanine and lactate) in response to glucagon and dexamethasone added alone or in combination. Maximum glucose production was observed with cells pretreated for several hours with dexamethasone and glucagon prior to addition of substrate and glucagon (8- to 12-fold increase over basal glucose production). Half-maximum stimulation of gluconeogenesis was seen with 3.6 × 10^?10 M glucagon and 3.6 × 10^?8 M dexamethasone. Maximum stimulation was oberved with 10^?7 M glucagon and 10^?6 M dexamethasone. The length of time of dexamethasone pretreatment was found to be important in demonstrating the effect of glucocorticoids on glucagon-stimulated gluconeogenesis. Treeatment of cells with dexamethasone for 2 hours did not result in an increase in glucose production over identical experimental conditions in the absence of dexamethasone, wherease pretreatment for 5 hours (1.2-fold increase) or 15 hours (1.7-fold increase) did result in an increase in glucose production. The results establish that the adult rat liver parenchymal cells in primary culture are a valid model system to study hepatic gluconeogenesis. In addition, we have established directly that the glucocorticoids amplify the glucagon stimulation of gluconeogenesis.     

Effect of vasopressin and naloxone alone and in combination on cortisol secretion after dexamethasone pretreatment

In order to further examine the possible role of endogenous opioid peptides and vasopressin in the phenomenon of dexamethasone nonsuppression, we studied the effect of naloxone, vasopressin, and vasopressin-naloxone combination on cortisol secretion following dexamethasone pretreatment. Nine healthy males were given 1 mg dexamethasone at 23.00 h. The following day starting at 12.30 h and at 90-min intervals they received intravenously naloxone (0.2 mg/kg), arginine vasopressin 3 units, or the two drugs combined. The order of drug administration was counterbalanced using a Latin square design. Blood samples were drawn at 15-min intervals, and plasma aliquots were assayed for cortisol and dexamethasone. Naloxone failed to induce an escape from dexamethasone suppression. Four of the 9 subjects responded with an escape from dexamethasone suppression in response to vasopressin alone. The observed variability in response to vasopressin was unrelated to dexamethasone plasma levels but was associated with a decrease in systolic blood pressure. Peak cortisol levels were lowest in response to naloxone and highest in response to vasopressin. There was no evidence of an increased cortisol response to the coadministration of naloxone with vasopressin compared to vasopressin alone. These results fail to implicate an opioidergic mechanism in the pathophysiology of dexamethasone nonsuppression.     

Corticosteroid-induced suppression of murine B cell immune response antigens

The quantitative variation in expression of B cell surface immune response-associated antigens (sIa) that is induced by in vivo i.v. administration of dexamethasone was studied by flow microfluorometry. Injection of 40 micrograms of dexamethasone resulted in a 35 to 40% reduction in the expression of sIa within 3 hr, reached its maximum effect within 6 hr, which on average resulted in 75% suppression of control values of sIa, and by 12 hr after injection began returning towards baseline levels. The suppressive effect of dexamethasone on B cell sIa was dose dependent with respect to the length of time required to reach maximal suppression, as well as with respect to the duration of suppression that was attained. When injections of dexamethasone were repeated on consecutive days, no additional increase in the level of sIa suppression achieved was observed. B cell sIa was also diminished after injection of dexamethasone into athymic nude mice, which suggests that the suppressive effect of dexamethasone on B cell expression of sIa is not a T cell-dependent phenomenon. Taken together, these data suggest that the suppression of B cell sIa by corticosteroids may be a means whereby endogenous or exogenous corticosteroids are able to influence the normal as well as abnormal immunologic state.