Effects of synthetic ovine corticotropin-releasing factor (CRF) on plasma ACTH and cortisol in 31 normal human males

Responses of plasma ACTH and cortisol to corticotropin-releasing factor (CRF) were evaluated in 31 normal human males. 1.0 micrograms/ks of sterilized synthetic ovine CRF was administered to the subjects, aged 19 to 53 yr and weighing 50 to 78 kg, at between 9:30 a.m. and 10:30 a.m. as an intravenous bolus injection after an overnight fast. Blood specimens were drawn before and 15, 30, 60, 90 and 120 min after injection for later determination of plasma ACTH and cortisol concentrations by radioimmunoassays. Plasma ACTH and cortisol levels for all subjects rose significantly (p less than 0.001) from the basal level (mean +/- SEM, 26.8 +/- 4.5 pg/ml and 12.6 +/- 0.9 micrograms/dl) to peak levels (58.4 +/- 5.5 pg/ml and 22.9 +/- 1.0 micrograms/dl) at 30 min and at 60 min, respectively. Although the plasma concentrations of ACTH and cortisol thereafter declined gradually, the levels at 120 min (43.4 +/- 5.2 pg/ml and 18.9 +/- 0.9 micrograms/ml, respectively) were still significantly higher than the basal levels (p less than 0.001). Significant inverse correlations were observed between the basal levels of each hormone and the ratio of the peak level to the basal level (p less than 0.01), and the increases in plasma ACTH and cortisol concentrations were either not significant or much smaller for the individuals in whom the basal levels were higher than 65 pg/ml and 17.0 micrograms/dl, respectively. No serious subjective symptom was observed during the experimental period in any of the subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of the pituitary-adrenal axis in chronically cannulated ovine fetuses

In the intact, unstressed ovine fetus, both plasma immunoreactive adrenocorticotrophin (ACTH) and blood cortisol concentrations increased after 121 days gestation. The mean ACTH and cortisol concentrations in intact fetuses of 90-121, 122-135 and 136-144 days gestation were for ACTH 20.4 +/- 3.9 (50) (mean +/- SEM, n), 30.2 +/- 5.6 (26) and 56.0 +/- 6.3 pg/ml (37) respectively, and for cortisol 0.07 +/- 0.01 (24), 0.17 +/- 0.03 (21) and 0.64 +/- 0.13 microgram/100 ml (15), respectively. After 121 days ACTH and cortisol concentrations were correlated positively. Cortisol infused into intact or adrenalectomized fetuses and corticosterone infused into adrenalectomized fetuses suppressed fetal plasma ACTH concentrations. In summary, ACTH and cortisol increase concomitantly after 122 days, so that it is highly probable that ACTH is the trophic stimulus for fetal adrenal maturation. The suppression of ACTH by cortisol and corticosterone suggests that these are the natural feedback regulators. It is proposed that while the mechanism for cortisol feedback may exist early in gestation, it is not until after 121 days that feedback control of ACTH becomes evident and physiologically important.     

Plasma cortisol and corticosterone concentrations in the golden hamster, (Mesocricetus auratus)

Because some recent studies of hamster adrenocortical function have depended on older studies that may have been inadequate or misinterpreted, the present study re-examined plasma corticosterone and cortisol concentrations in hamsters under several conditions to determine which plasma glucocorticoid predominated in this animal. Sensitive radioimmunoassays were used to measure separately the two glucocorticoids in the basal condition, after adrenocorticotropin (ACTH) treatment, after acute stress, and after chronic stress. In the basal condition, corticosterone concentrations were 3-4 times higher than those of cortisol. After stimulation, this difference disappeared, but rarely were any hamster's cortisol levels higher than their corticosterone levels. Both ACTH and acute stress elevated plasma corticosterone and cortisol concentrations, but only plasma cortisol concentrations were elevated following chronic stress. The dissociation between cortisol and corticosterone concentrations after chronic stress suggests that the two glucocorticoid hormones in the hamster may be regulated independently. The data also indicate that both corticosterone and cortisol should be measured when assessing adrenocortical function in the hamster.     

Inhibition of the ACTH adrenal response to stress by treatment with hydrocortisone, prednisolone and dexamethasone in the rat

16- and 4-week-old intact and adrenalectomized rats have been treated with different doses of the three glucocorticoids hydrocortisone, prednisolone and dexamethasone by gavage. The delayed feedback effect on plasma ACTH and corticosterone response to an ether stress have been assessed. Almost complete suppression of corticosterone response 20 min after an ether stress and an ACTH suppression to 20% of control values 5 min after an ether stress were observed with 25 micrograms of dexamethasone, 10 mg of prednisolone and 20 mg of hydrocortisone. Although the percent inhibition of corticosterone and ACTH response to stress was comparable, a striking dissociation of the ACTH and corticosterone release was observed in terms of absolute concentrations. A mean ACTH concentration of 462 ng/l after 25 micrograms of dexamethasone was measured together with a barely measurable corticosterone concentration of 3 micrograms%. Similarly, after 10 mg of prednisolone, the mean ACTH concentration was 404 ng/l, whilst the mean corticosterone concentration was 3 micrograms%. This dissociation demonstrates that the corticosterone concentration on its own does not necessarily reflect the ACTH release. At 4 weeks of age, the ACTH response to stress is more difficult to suppress than in adult animals. This is more obvious after adrenalectomy, where the excessive ACTH secretion was less inhibited by all glucocorticoids used. The time between the last steroid gavage and stress must be considered. In 4-week-old animals the ACTH response 16 h after 12.5 micrograms of dexamethasone was inhibited by 22%, whereas 4 h after the same dexamethasone dose the inhibition was 85%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of premature delivery in sheep following infusion of cortisol to the fetus. I. The effect of maternal administration of progestagens

Premature induction of delivery in fetuses infused with graded doses of cortisol was brought about in 123.5 +/- 7.7 h (mean +/- SEM, n = 6) after the start of cortisol infusion. This treatment caused a rise in fetal plasma cortisol similar to that observed at normal delivery. Maternal and fetal progesterone and 20 alpha-dihydroprogesterone concentrations decreased to basal levels during infusion of cortisol to the fetus. Induction of premature delivery was delayed or prevented by concomitant treatment of the ewe with progestagen. Maternal intramuscular injection of 100 mg progesterone, 2 times daily, prevented delivery in four of four ewes treated during the time that cortisol was infused into the fetus (11-13 days). Maternal plasma progesterone and 20 alpha-dihydroprogesterone concentrations were maintained during this period, but fetal plasma progesterone concentrations decreased to the same extent as in the fetuses infused with cortisol alone. A single intramuscular injection of 250 mg of medroxyprogesterone acetate to ewes on the day before commencement of infusion of cortisol to the fetus prevented delivery in four of six ewes during the time that cortisol was infused for 9, 13, 14, and 15 days, respectively. One ewe delivered a live lamb at 133.5 h and another at 147.7 h after the start of infusion of cortisol to the fetus. Maternal and fetal plasma cortisol, progesterone, and 20 alpha-dihydroprogesterone concentrations were similar to those observed during infusion of cortisol alone to the fetus. Although fetal cortisol concentrations rose in a similar fashion, and to a similar extent, in all three groups during infusion of cortisol to the fetus, fetal 11-desoxycortisol concentrations only rose above basal levels close to the time of delivery in cortisol-infused fetuses or, in the progestagen-treated groups, when the fetus showed signs of being stressed.     

Radioimmunoassay of 5-androstene-3 beta,17 beta-diol in plasma and in breast cyst fluid

A simple and reliable radioimmunoassay for the determination of 5-androstene-3 beta, 17 beta-diol in peripheral plasma and in breast cyst fluid, after a chromatography on Celite microcolumn has been described and evaluated. The antiserum used was raised in rabbits injected with dehydroepiandrosterone-15 alpha-(O-carboxymethyl)-bovine serum albumin. In men below 40 years of age the levels ranged from 0.85 to 2.80 ng/ml (mean +/- SEM: 1.52 +/- 0.11; n = 24) and from 0.50 to 2.20 ng/ml (mean +/- SEM: 0.93 +/- 0.09; n = 20) in men aged between 41 and 62 years. The mean level was significantly different (P less than 0.001) between the 2 groups. A significant correlation (r = -0.56; P less than 0.01) was demonstrated between age and all male levels. In females the mean plasma level was in the follicular phase: 0.81 +/- 0.07 ng/ml (range: 0.40-1.50; n = 17; age: 19-41 years) and in the luteal phase: 0.83 +/- 0.05 ng/ml (range: 0.40-1.30; n = 29; age: 18-43 years). No cyclical change and no correlation with age could be evidenced. A significant difference (P less than 0.001) was shown between females and the young male group. In breast cyst fluid the levels ranged from 0.05 to 13.70 ng/ml (mean +/- SEM: 2.36 +/- 0.86; n = 20) whereas the sulfate concentrations ranged from 75 to 7500 ng/ml (mean +/- SEM: 1891 +/- 565; n = 15), thus demonstrating very wide inter-individual variations.     

Atrial natriuretic factor inhibits the CRH-stimulated secretion of ACTH and cortisol in man.

Corticotrophic secretion of ACTH is stimulated by corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and suppressed by glucocorticoids. In vitro and preclinical studies suggest that atrial natriuretic factor (ANF) may be a peptidergic inhibitor of pituitary-adrenocortical activity. The aim of this study was to elucidate a possible role of ANF as a modulator of ACTH release in humans. A bolus injection of 100 micrograms human CRH (hCRH) during a 30 min intravenous infusion of 5 micrograms/min human alpha atrial natriuretic factor (h alpha ANF) was administered at 19:00 to six healthy male volunteers. In comparison to saline, a blunted CRH-stimulated secretion of ACTH (mean maximum plasma level +/- SD 45 min after hCRH: saline 46.2 +/- 14.2 pg/ml, h alpha ANF 34.6 +/- 13.8 pg/ml, p-value = 0.007) and a delayed rise (10 min) in cortisol were detected. The maximum plasma cortisol levels remained nearly unchanged between saline and h alpha ANF administration (mean maximum plasma level +/- SD 60 min after hCRH: saline 182 +/- 26 ng/ml, h alpha ANF 166 +/- 54 ng/ml). No effects of h alpha ANF on basal cortisol levels were observed; in contrast, basal ACTH plasma levels were slightly reduced. Basal blood pressure and heart rate remained unaffected. In the control experiment, infusion of 3 IU AVP in the same experimental paradigm increased basal and stimulated ACTH and cortisol levels significantly in comparison to saline. These observations suggest that intravenously administered haANF inhibits the CRH-stimulated release of ACTH in man.     

Plasma somatostatin-like immunoreactivity responses to a mixed meal and the heterogeneity in healthy and non-insulin-dependent (NIDDM) diabetics

Peripheral plasma somatostatin-like immunoreactivity (SLI) was estimated in non-extracted plasma using a specific somatostatin-14 (SS-14) antiserum. The basal plasma SLI level in healthy subjects (n = 18) was 43 +/- 2.9 pg/ml (mean +/- SE) and rose significantly to 8.3 +/- 2.7, 7.3 +/- 1.1 and 5.8 +/- 2.1 pg/ml above the mean basal level 20, 30, and 40 min after a mixed meal, respectively (P less than 0.05). Basal plasma SLI levels in diet (n = 8), sulfonyl urea (n = 8), and insulin groups (n = 8) of non-insulin-dependent maturity onset diabetics (NIDDM) were 50 +/- 1.6, 59 +/- 4.5, and 74 +/- 5.8 pg/ml, respectively. The basal levels for patients with NIDDM were significantly higher than those for healthy subjects (P less than 0.05). No significant increases in plasma SLI were observed after a mixed meal in any group of NIDDM subjects. Elevated plasma SLI levels are considered to be closely related to the severity of the diabetes. The ratios of SS-14 and SS-28 to the total amount of basal plasma SLI were analyzed using high pressure liquid chromatography (HPLC). The ratio of SS-14 to the total SLI was 71-80% in healthy subjects. The ratio of SS-28 to the total SLI increased from 26-30% in the diet group to 50-55% in the group on insulin. These findings suggest a possible pathophysiological role for gastrointestinal somatostatin in NIDDM.     

Radioimmunoassay of human plasma corticosterone: method, measurement of episodic secretion and adrenal suppression and stimulation

A radioimmunoassay for human plasma corticosterone has been developed. Antisera were obtained by immunizing rabbits with corticosterone-21-hemisuccinate-BSA. An antiserum titer of 1:4000 was used for standard curves ranging from 0–1000 pg. Interfering steroids were removed from plasma extracts by paper chromatography. Plasma blanks obtained from adrenalectomized or Addisonian patients ranged from 29 to 42 ng/dl. Recovery of radioactive corticosterone through the entire method was 67.6 ± 5.2%. The coefficient of variation within assays was 19% and between assays 13%. The average 8 a.m. value in males was 396 ± 228 ng/dl and in females it was 655 ± 271 ng/dl. Corticosterone was found to be secreted episodically, in parallel with cortisol. Secretion of this steroid was suppressed by dexamethasone and stimulated by ACTH infusion.     

Inhibition of cortisol production in isolated guinea-pig adrenal cells

Cortisol, added to 1 ml incubation medium containing 3-4 X 10(5) isolated guinea-pig adrenal cells, provoked a decrease in basal and ACTH (250 pg)-stimulated cortisol production, in correlation with the amounts used (50 ng-2,000 ng). A decrease in aldosterone production could be seen when cortisol concentrations reached or exceeded 1,000 ng/ml. There were no variations in either androgens (delta 4-androstenedione, dehydropiandrosterone) or 17-hydroxyprogesterone. Only 11-deoxycortisol was slightly increased. Using increasing concentrations of ACTH (50-250 pg), both in the absence and in the presence of 1,000 ng cortisol, it was noted that the inhibition induced by cortisol was of a competitive type and could be overcome by ACTH. This decrease in cortisol was concomitant with an increase in 11-deoxycortisol. Neither corticosterone nor dexamethasone reduced cortisol production. In addition, it was shown that the conversion of tritiated 11-deoxycortisol to radioactive cortisol increased significantly under the influence of 250 pg ACTH (mean relative variation of 21.7% +/- 7.7 (SEM), n = 6, P less than 0.05); but decreased significantly under the combined effect of 1,000 ng exogenous cortisol and the same dose of ACTH: (mean relative variation of 4.3% +/- 1 (SEM), n = 8, P less than 0.005). There is therefore reason to believe that the concentrations of cortisol at the adrenal level modulate the stimulation induced by ACTH and that this self-adjustment forms part of the control mechanisms involved in corticosteroidogenesis.     

Muscle glycogen utilization during shivering thermogenesis in humans

The purpose of the present study was to clarify the importance of skeletal muscle glycogen as a fuel for shivering thermogenesis in humans during cold-water immersion. Fourteen seminude subjects were immersed to the shoulders in 18 degrees C water for 90 min or until rectal temperature (Tre) decreased to 35.5 degrees C. Biopsies from the vastus lateralis muscle and venous blood samples were obtained before and immediately after the immersion. Metabolic rate increased during the immersion to 3.5 +/- 0.3 (SE) times resting values, whereas Tre decreased by 0.9 degrees C to approximately 35.8 degrees C at the end of the immersion. Intramuscular glycogen concentration in the vastus lateralis decreased from 410 +/- 15 to 332 +/- 18 mmol glucose/kg dry muscle, with each subject showing a decrease (P less than 0.001). Plasma volume decreased (P less than 0.001) markedly during the immersion (-24 +/- 1%). After correcting for this decrease, blood lactate and plasma glycerol levels increased by 60 (P less than 0.05) and 38% (P less than 0.01), respectively, whereas plasma glucose levels were reduced by 20% after the immersion (P less than 0.001). The mean expiratory exchange ratio showed a biphasic pattern, increasing initially during the first 30 min of the immersion from 0.80 +/- 0.06 to 0.85 +/- 0.05 (P less than 0.01) and decreasing thereafter toward basal values. The results demonstrate clearly that intramuscular glycogen reserves are used as a metabolic substrate to fuel intensive thermogenic shivering activity of human skeletal muscle.     

Responses of plasma adrenocorticotropin and cortisol to intravenous injection of synthetic ovine corticotropin releasing factor in the morning and early evening in normal human subjects

This study was designed to compare the responsiveness of adrenocorticotropin (ACTH) and cortisol secretion to corticotropin-releasing factor (CRF) in the morning and early evening in normal human subjects. Synthetic ovine CRF (1.0 micrograms/kg) or normal saline, was administered as an i.v. bolus injection to six normal males at 900 h and 1700 h. Blood samples were obtained before and 15, 30, 60, 90 and 120 min after CRF or saline injection. Significant increases in plasma ACTH and cortisol levels were observed in all subjects at the both time of testing after CRF injection. The net increments in the areas under the concentration curve (areas in the CRF experiment minus those in the saline control experiment) were not statistically different for both ACTH (mean +/- SEM: 41.0 +/- 10.6 pg/ml h in the morning: 51.1 +/- 8.9 pg/ml h in the evening) and cortisol (mean +/- SEM: 28.5 +/- 5.0 micrograms/dl h in the morning; 36.2 +/- 4.0 micrograms/dl h in the evening). Also no significant difference was observed in net increment, peak level and the ratio of peak level to the basal level of ACTH and cortisol after CRF injection. There were no appreciable changes in plasma concentrations of growth hormone, thyroid-stimulating hormone or prolactin, although slight but statistically significant rises in plasma levels of luteinizing hormone and follicle-stimulating hormone were observed. These results suggest that there is no significant difference in responsiveness of the pituitary-adrenal axis to CRF in the morning (900 h) and early evening (1700 h), and thus the time of day will not necessarily have to be considered when CRF is used between these times in a clinical test to evaluate pituitary ACTH reserve.     

A specific, non-chromatographic radioimmunoassay for human plasma cortisol.

A radioimmunoassay technique has been developed for the measurement of cortisol in a single methylene chloride extract of human plasma without chromatography. The antiserum, obtained by immunizing rabbits with cortisol-3-carboxymethyl-oxime conjugated to bovine serum albumin, had a high affinity (KA = 1.8 X 10(9) 1/mole) and capacity (2.3 X 10(-6) moles/L undiluted serum) for cortisol. The minimum detectable amount determined at the lower 95% confidence limit of the buffer control tubes was 8.3 +/- 4.7 pg/tube and a log dose - logit response standard curve was linear between 20 pg and 20 ng/tube. The antiserum was highly specific for cortisol with only corticosterone, cortisone, 11-deoxycortisol and 21-deoxycortisol showing significant cross-reaction (12.4, 6.6, 3.8 and 3.7%, respectively). The cross-reaction for the other tested naturally occurring and synthetic steroids did not exceed 1%. Regression analysis of cortisol concentration estimates obtained on 20 samples before and after Sephadex LH-20 column chromatography gave a coefficient of correlation (r) of 0.995 and a regression coefficient (b) of 1.04. Recovery of cortisol added to plasma samples was quantitative. The intra-assay error was 8.5% and the inter-assay error averaged 5.7%. The method is simple requiring a single solvent extraction of plasma, therefore permitting large numbers of samples to be handled efficiently by a single technician.     

Evidence for direct inhibitory effects of dopamine on zona glomerulosa secretion of 18-hydroxycorticosterone in rhesus monkeys

This study was designed to more selectively investigate the dopaminergic regulation of 18-hydroxycorticosterone (18-OHB) and aldosterone production by the adrenal zona glomerulosa. Mature rhesus monkeys received either an infusion of dopamine (2 micrograms/kg/min) or 5% dextrose (0.2 ml/min) over a 60 min period (N=6). Dopamine had no effect on plasma levels of renin activity, cortisol, corticosterone, aldosterone or blood pressure. However, dopamine suppressed (p less than 0.05) plasma 18-OHB levels from a baseline of 31.6 +/- 3.5 ng/dl to 23.6 +/- 2.1 ng/dl at 60 min after onset of infusion. This observation is in agreement with some studies in humans but differs from others in which no depression in 18-OHB was observed following dopamine infusion. Dopamine infusion markedly (p less than 0.001) suppressed plasma PRL levels by 30 min after onset of infusion. Corticosteroid responses to metoclopramide (200 micrograms/kg) after dexamethasone 1 mg im every 6 h X 5 days or placebo treatment (vehicle im every 6 h X 5 days) was then evaluated. Dexamethasone significantly suppressed basal cortisol, corticosterone, 18-OHB and aldosterone. Although dexamethasone blunted the prolactin response, it did not inhibit the aldosterone response to metoclopramide. The 18-OHB response to metoclopramide was increased (p less than 0.01) following dexamethasone treatment. Following dexamethasone suppression, 18-OHB levels were still lowered (p less than 0.05) by dopamine infusion. These results suggest that dopamine selectively inhibits zona glomerulosa production of 18-OHB and aldosterone in rhesus monkeys.     

Plasma cortisol in cattle: Circadian rhythm and exposure to a simulated high altitude of 5,000 m

After a 2 week control period at 400 m, cattle were exposed to 5,000 m simulated altitude for 2 weeks, which was followed by a 2-week post-altitude control period. Plasma cortisol values from blood samples taken every 30 min for a total of 24 h indicated that cortisol was secreted episodically and that a circadian rhythm existed. When cortisol values were grouped into 4, 6-h periods, plasma cortisol was most abundant from 06:00 to 12:00 h with an average of 0.96µ g/100 ml and least abundant from 00:30 to 06:00 h with an average of 0.55µ g/100 ml. Plasma cortisol increased from 0.42 to 3.08µ g/100 ml during the 4 h ascent to 5,000 m and decreased to near normal levels the following day. A rhythmic plasma cortisol pattern was maintained after one day at simulated high altitude.     

Determination of corticosterone and 17-hydroxycorticosterone in plasma and urine samples by sweeping techniques using micellar electrokinetic chromatography

The analysis of corticosterone in mouse blood serum (metabolic-stress experiment) and 17-hydroxycorticosterone in human urine (exercise-stress experiment) samples by means of capillary electrophoresis/UV absorbance in conjunction with online sample concentration techniques is described. The use of normal MEKC had an analyte detection limit of 7 microg/ml (S/N=3); whereas when online sample concentration methods, including sweeping-micellar electrokinetic chromatography (Sweeping-MEKC) and cation-selective exhaustive injection-sweep-micellar electrokinetic chromatography (CSEI-sweep-MEKC) were used, the detection limits could be improved to 3 and 5 ng/ml, respectively. In the analysis of actual samples from animal metabolic-stress experiments (39 mouse), chronically stressed animals showed a higher level (552+/-152 ng/ml) and acute stressed animals showed an intermediate level (375+/-105 ng/ml). In comparison, normal animals show a lower concentration level of corticosterone (153+/-109 ng/ml). In addition, based on a human exercise-stress experiment (seven volunteers), the acute stressed humans (after exercise, 800 m of running) show a higher concentration of 17-hydroxycorticosterone (113+/-55 ng/ml for males; 128+/-25 for females) and the non-stressed humans (before exercise) show a lower concentration (63+/-37 ng/ml for male; 60+/-20 for female), respectively.     

Sex differences in reserve capacity of the pituitary-adrenal system in rats

Female rats exposed to complex emotional stress for 1 hour (restriction in the penal, vibration, loud dissonance music, interrupt light) simultaneously showed more considerable increases in plasma and adrenal corticosterone values than did male animals. Female rat corticosterone levels returned to basal values within 20-120 minutes of stressor-off. As for males the processes of restoration were delayed and accompanied by a 6-fold decrease in the plasma corticosterone levels compared with basal values. The response to additional acute stress (immobilization for 10 minutes) in various times after termination of complex emotional stress (0, 40, 120, 180, 240 minutes) was facilitated in females and remained unchanged in males. Plasma corticosterone levels under stressful conditions were 2-4-fold higher in females than in males. It is concluded that reserve capacity of adaptation system is significantly higher in female rats than in male ones.     

The changes in plasma cortisol and urinary free cortisol by an overnight dexamethasone suppression test in patients with Cushing's disease

We studied the suppressibility of cortisol secretion in 15 patients with Cushing's disease by measuring morning plasma cortisol level as well as the 24-hour urinary free corisol (UFC) excretion following single doses of increasing amounts of dexamethasone (ranging from 0.5 to 32 mg) given at 11 p.m. The mean plasma cortisol level in patients with Cushing's disease was twice as high as in normal subjects, whereas the mean UFC in these patients was 6 times as high. Plasma cortisol in seven patients were suppressed by less than 4 mg of dexamethasone (in 2 cases, less than 0.5 mg; in 3 cases, less than 2 mg; and in 2 cases less than 4 mg). In these cases, basal plasma cortisol and UFC were less than 25 micrograms/dl and 350 micrograms/day, respectively. Among the other eight patients, plasma cortisol was partially suppressed in 5 cases and not suppressed in 3 cases by high doses of dexamethasone (16-32 mg). In these cases the basal plasma cortisol and UFC were more than 25 micrograms/dl and 350 micrograms/day, respectively. There was a significant correlation between the basal plasma cortisol and UFC (r = 0.687, p less than 0.01). These data suggest that the suppression by increasing amounts of dexamethasone in most cases with Cushing's disease was related to the severity of hypercortisolism.     

Single-dose four hour dexamethasone suppression test in normal men and its application for the diagnosis of cushing's syndrome

As a four hour morning test, plasma cortisol levels were radioimmunoassayed before and at two and four hours after dexamethasone (0, 0.5 mg, 1.0 mg or 2.0 mg) was administered at 8–9 a.m. in 20 normal subjects. The 1.0 mg four hour test was most effective in suppression of cortisol and it showed the same suppressibility as the widely used single-dose overnight test. With the 1.0 mg four hour test, 2 patients with Cushing's syndrome due to adrenal hyperplasia could be differentiated from normal and obese subjects.The four hour morning test would be more useful than the widely used overnight test from the reasons; i) it shows the same suppressibility as the overnight test, ii) it obviates the need for bothersome midnight administration of dexamethasone, iii) because it takes only one morning to perform, it can save a day, iv) and it might be applicable for the differential diagnosis of Cushing's syndrome because 4.0 mg morning test resulted in complete suppression of plasma cortisol in a tested Cushing's syndrome, whereas with even 8.0 mg, plasma cortisol was not suppressed in the overnight test in 2 such patients examined.     

Seasonal variations of plasma prolactin and LH concentrations in the female blue fox (Alopex lagopus)

A heterologous radioimmunoassay system developed for the rabbit and suitable for a wide range of mammalian species has been shown to measure prolactin in the plasma of the blue fox. Evaluation of prolactin levels throughout the year showed the concentrations displayed a circannual rhythm with the highest values occurring in May and June. Prolactin concentrations remained low (approximately 2.5 ng/ml plasma) from July until April with no consistent changes found around oestrus (March-April). In 8 pregnant females, the prolactin increase in late April and May coincided with the last part of gestation and lactation: concentrations (mean +/- s.e.m.) increased to 6.3 +/- 0.6 ng/ml at mid-gestation, 9.7 +/- 2.1 ng/ml at the end of gestation and 26.7 +/- 5.0 ng/ml during lactation. In 10 non-pregnant animals, the mean +/- s.e.m. values were 7.2 +/- 1.2 ng/ml in April, 8.8 +/- 2.2 ng/ml in May and 9.8 +/- 1.3 ng/ml in June. The prolactin profile in 4 ovariectomized females was similar to that observed in non-pregnant animals, but the plasma values tended to be lower during the reproductive season (April-June). In intact females, the only large LH peak (average 28 ng/ml) was observed around oestrus. During pro-oestrus, baseline LH levels were interrupted by elevations of 3.1-10.4 ng/ml. During the rest of the year, basal levels were less than 3 ng/ml. In ovariectomized females, LH concentrations increased within 2 days of ovariectomy and remained high (35-55 ng/ml) at all times of year.