Adrenal splanchnic innervation contributes to the diurnal rhythm of plasma corticosterone in rats by modulating adrenal sensitivity to ACTH

Activity of the hypothalamic-pituitary-adrenal axis is characterized by a diurnal rhythm with an AM nadir and PM peak. Splanchnic nerve transection disrupts the diurnal rhythm in plasma corticosterone; however, there is a controversy as to whether the nerve-mediated effect is 1) via inhibition in the AM vs. excitation in the PM, or 2) involves changes in adrenal sensitivity to ACTH. The present studies were designed to address these issues. Adult male rats were anesthetized and underwent bilateral transection of the thoracic splanchnic nerve or sham transection. One week after surgery, rats were killed in the AM or PM with collection of nonstress plasma for measurement of corticosterone and ACTH. Plasma corticosterone was increased in the PM relative to the AM; however, plasma corticosterone in the PM was attenuated by splanchnic nerve transection, without affecting plasma ACTH. This decrease in PM plasma corticosterone after nerve-transection was 1) associated with decreased adrenal responsivity to ACTH, 2) associated with decreased adrenal cAMP content, 3) prevented by adrenal demedullation, and 4) not affected by removal of adrenal capsaicin-sensitive afferent fibers. Repeated serial blood sampling from individual rats confirmed the excitatory effect of splanchnic innervation in the PM. These results support the hypothesis that the adrenal splanchnic innervation modulates the diurnal rhythm in plasma corticosterone by increasing adrenal responsivity to ACTH and augmenting steroidogenesis in the PM and suggest that alterations in adrenal corticosterone secretion obscured by pulsatile secretion are more clearly revealed with repeated serial blood sampling.     

Altered Entrainment to the Day/Night Cycle Attenuates the Daily Rise in Circulating Corticosterone in the Mouse

The suprachiasmatic nucleus (SCN) is a circadian oscillator entrained to the day/night cycle via input from the retina. Serotonin (5-HT) afferents to the SCN modulate retinal signals via activation of 5-HT_1B receptors, decreasing responsiveness to light. Consequently, 5-HT_1B receptor knockout (KO) mice entrain to the day/night cycle with delayed activity onsets. Since circulating corticosterone levels exhibit a robust daily rhythm peaking around activity onset, we asked whether delayed entrainment of activity onsets affects rhythmic corticosterone secretion. Wheel-running activity and plasma corticosterone were monitored in mice housed under several different lighting regimens. Both duration of the light∶dark cycle (T cycle) and the duration of light within that cycle was altered. 5-HT_1B KO mice that entrained to a 9.5L:13.5D (short day in a T = 23 h) cycle with activity onsets delayed more than 4 h after light offset exhibited a corticosterone rhythm in phase with activity rhythms but reduced 50% in amplitude compared to animals that initiated daily activity <4 h after light offset. Wild type mice in 8L:14D (short day in a T = 22 h) conditions with highly delayed activity onsets also exhibited a 50% reduction in peak plasma corticosterone levels. Exogenous adrenocorticotropin (ACTH) stimulation in animals exhibiting highly delayed entrainment suggested that the endogenous rhythm of adrenal responsiveness to ACTH remained aligned with SCN-driven behavioral activity. Circadian clock gene expression in the adrenal cortex of these same animals suggested that the adrenal circadian clock was also aligned with SCN-driven behavior. Under T cycles <24 h, altered circadian entrainment to short day (winter-like) conditions, manifest as long delays in activity onset after light offset, severely reduces the amplitude of the diurnal rhythm of plasma corticosterone. Such a pronounced reduction in the glucocorticoid rhythm may alter rhythmic gene expression in the central nervous system and in peripheral organs contributing to an array of potential pathophysiologies.     

Periodic maternal deprivation and lesion of anterodorsal thalami nuclei induce alteration on hypophyso adrenal system activity in adult rats

The hypothalamic-pituitary-adrenal (HPA) axis is normally regulated by extrahypothalamic limbic structures, among these, the anterodorsal thalami nuclei (ADTN), which exert an inhibitory influence on HPA, in basal and acute stress conditions in rats. In the present work we have investigated whether neonatal maternal deprivation (MD) produces long-term changes in the ADTN regulation of HPA activity. Maternal deprivation, in female rats, for 4.5 hs daily, during the first 3 weeks of life, produced at 3 months old, a significant decrease in plasma ACTH concentration (p<0.001) and an increase in plasma corticosterone (C) (p<0.001), compared to control non-deprived rats (NMD). Also MD showed higher plasma epinephrine (E) and norepinephrine (NE) levels than NMD rats. The increase of NE (66.6% p<0.001) was higher than that observed in E (19%). After 30 days of ADTN lesion, plasma ACTH values were higher than in sham lesioned rats, in both NMD and MD animals. ACTH response was greater in MD rats. Plasma C, in NMD, was higher, whereas in MD lesioned animals, it was significantly lower than in sham lesioned. In MD rats, lesion produced a significant increase in plasma E and NE (p<0.001), and again, NE increase was higher than E increase. The more accentuated increase of NE than E, suggests sympathetic nervous system hyperactivity. In summary, neonatal maternal deprivation induces long-term alterations on HPA axis sensitivity and medullo adrenal secretion; enhanced sympathetic nervous system activity and, therefore affected the ADTN inhibitory influence on ACTH and adrenal glands secretion.     

慢性应激抑郁状态对大鼠外周神经内分泌因子生物节律的影响

目的：探讨慢性不可预见性应激状态下大鼠外周神经内分泌因子昼夜节律的表达特点。方法：成年雄性SD大鼠60只,随机分为模型组和对照组（n=30）,采用束缚、摇晃、鼠笼倾斜、湿垫料、冷刺激、拥挤（整夜）、断食或断水、夹尾、昼/夜颠倒等慢性不可预知性温和刺激结合孤养方式,每天暴露于2种应激原中饲养21 d,建立抑郁症模型。测定应激前后大鼠糖水偏爱、旷场行为及高架十字迷宫行为学变化。连续24 h分6个时间点（ZT1、ZT5、ZT9、ZT13、ZT17、ZT21）处死动物取血,每个时间点处死5只大鼠。放免法测定6个时间点血清促肾上腺皮质激素（ACTH）含量,ELISA法测定6个相同时间点血浆皮质酮（CORT）、褪黑素（MT）、血管活性肠肽（VIP）含量,采用单一余弦法比较2组大鼠上述各指标的节律周期、振幅、峰值相位、中值的变化特点。结果：与对照组相比,模型大鼠体重增加值明显降低（P<0.01）,各项行为学评分均显著减少（P<0.01）。慢性应激至抑郁样行为充分表达后,血浆ACTH、CORT的相位完全相反,时相大幅度提前,含量波动幅度减小,昼夜分泌节律紊乱;MT的24 h分泌节律完全丧失且整体水平下降,表达量显著降低;VIP虽仍存在24 h节律,但振幅明显降低,峰相位也延迟6 h,且表达量显著提高。结论：慢性应激抑郁状态可导致大鼠外周神经内分泌激素的近日节律非同步于SCN,表现为昼夜节律性和激素分泌量的异常。     

Evaluation of the inhibitory effect of circulating corticosteroids on circadian stimulated and stress induced secretion of ACTH in rats

Male rats were bilaterally adrenalectomized in order to measure the extent of inhibition exerted by endogenous corticosteroids on both basal ACTH secretion along its circadian rhythm and ether-stress induced ACTH secretion. In intact controls, plasma ACTH levels at the circadian maximum exceeded by 4 times the circadian minimum, and ACTH response 15 min after ether-stress surpassed the circadian minimum by 20 times. In adrenalectomized rats, the daily minimum was 8 times that of the controls. Nevertheless the circadian maximum was 3 times above the rhythm's minimum, while the maximal stress response (15 min) surpassed the circadian minimum by 8 times. In adrenalectomized rats supplemented with a solid source of corticosterone inducing a stable plasma corticosterone level equivalent to the controls' circadian minimum (3 micrograms/100 ml), the ACTH rhythm still fluctuated twice as high as in intact controls. The tonic feed-back inhibition exerted by endogenous corticosteroids on ACTH secretion appeared thus significantly stronger than the GABAergic inhibition to the corticotropic system which was previously studied under similar standard conditions.     

24-hour changes in ACTH, corticosterone, growth hormone, and leptin levels in young male rats subjected to calorie restriction

Calorie restriction of young male rats increases plasma prolactin, decreases luteinizing hormone (LH) and testosterone, and disrupts their 24 h secretory pattern. To study whether this could be the consequence of stress, we examined the 24 h variations of plasma adrenocorticotropic hormone (ACTH) corticosterone, growth hormone (GH), leptin, and adrenal corticosterone. Rats were submitted to a calorie restriction equivalent to a 66% of usual intake for 4 weeks, starting on day 35 of life. Controls were kept in individual cages and allowed to eat a normal calorie regimen. Significantly lower ACTH levels were detected in calorie-restricted rats. Plasma corticosterone levels during the light phase of the daily cycle were significantly higher in calorie-restricted rats. Time-of-day variation in plasma ACTH and corticosterone levels attained significance in calorie-restricted rats only, with a maximum toward the end of the resting phase. The daily pattern of adrenal gland corticosterone mirrored that of circulating corticosterone; however, calorie restriction reduced its levels. Plasma ACTH and corticosterone correlated significantly in controls only. Calorie restriction decreased plasma GH and leptin, and it distorted 24 h rhythmicity. In a second study, plasma ACTH and corticosterone levels were measured in group-caged rats, isolated control rats, and calorie-restricted rats during the light phase of the daily cycle. Plasma ACTH of calorie-restricted rats was lower, and plasma corticosterone was higher, compared with isolated or group-caged controls. The changes in the secretory pattern of hormones hereby reported may be part of the neuroendocrine and metabolic mechanisms evolved to maximize survival during periods of food shortage.     

Regulation of basal ACTH secretion by corticosterone is mediated by both type I (MR) and type II (GR) receptors in rat brain.

The mechanisms involved in the physiology of the secretion of ACTH are reviewed. The secretion is regulated by the biological consequences of the occupancy of high affinity mineralocorticoid (MR) and lower affinity glucocorticoid receptors (GR) for corticosterone at specific sites of the rat brain. The regulation by this mechanism of basal secretion during the circadian rhythm, the effect of adrenalectomy and of corticosterone replacement is discussed. Experiments with RU486, a specific glucocorticoid antagonist, suggest that occupancy of both MR and GR is required for normal control of ACTH at the time of peak activity. The occupancy of the GR for a few hours per day apparently suffices to maintain steady levels of the products of GR-responsive genes throughout the body.     

Attenuated corticosterone response to chronic ACTH stimulation in hepatic lipase-deficient mice: evidence for a role for hepatic lipase in adrenal physiology

Hepatic lipase (HL), a liver-expressed lipolytic enzyme, hydrolyzes triglycerides and phospholipids in lipoproteins and promotes cholesterol delivery through receptor-mediated whole particle and selective cholesterol uptake. HL activity also occurs in the adrenal glands, which utilize lipoprotein cholesterol to synthesize glucocorticoids in response to pituitary ACTH. It is likely that the role of adrenal HL is to facilitate delivery of exogenous cholesterol for glucocorticoid synthesis. On this basis, we hypothesized that HL deficiency would blunt the glucocorticoid response to ACTH. Furthermore, because exogenous cholesterol also is derived from the LDL receptor (LDLR) pathway, we hypothesized that LDLR deficiency would blunt the response to ACTH. To test these hypotheses, we compared the corticosterone response to eight daily ACTH injections in HL-deficient (hl-/-), LDLR-deficient (Ldlr-/-), and HL- and LDLR-doubly deficient (Ldlr-/- hl-/-) mice with that in wild-type (WT) mice. Plasma corticosterone levels were measured on days 2, 5, and 8. Differences in plasma corticosterone levels between genotypes were analyzed by Kruskal-Wallis one-way ANOVA on ranks and pairwise multiple comparisons by Dunn's test. Our results demonstrate a trend toward reductions in plasma corticosterone levels on day 2 and significant reductions on day 5 and day 8 in the knockout models. Thus, on day 5, plasma corticosterone levels were reduced by 57, 70, and 73% (all P < 0.05) and on day 8 by 76, 59, and 63% (all P < 0.05) in hl-/-, Ldlr-/-, and Ldlr-/- hl-/- mice, respectively. These results demonstrate that HL deficiency, like LDLR deficiency, blunts the adrenal response to chronic ACTH stimulation and suggest a novel role for HL in adrenal physiology.     

Photoperiod regulates corticosterone rhythms by altered adrenal sensitivity via melatonin-independent mechanisms in Fischer 344 rats and C57BL/6J mice

Most species living in temperate zones adapt their physiology and behavior to seasonal changes in the environment by using the photoperiod as a primary cue. The mechanisms underlying photoperiodic regulation of stress-related functions are not well understood. In this study, we analyzed the effects of photoperiod on the hypothalamic-pituitary-adrenal axis in photoperiod-sensitive Fischer 344 rats. We first examined how photoperiod affects diurnal variations in plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone. ACTH levels did not exhibit diurnal variations under long- and short-day conditions. On the other hand, corticosterone levels exhibited a clear rhythm under short-day condition with a peak during dark phase. This peak was not observed under long-day condition in which a significant rhythm was not detected. To analyze the mechanisms responsible for the photoperiodic regulation of corticosterone rhythms, ACTH was intraperitoneally injected at the onset of the light or dark phase in dexamethasone-treated rats maintained under long- and short-day conditions. ACTH induced higher corticosterone levels in rats examined at dark onset under short-day condition than those maintained under long-day condition. Next, we asked whether melatonin signals are involved in photoperiodic regulation of corticosterone rhythms, and rats were intraperitoneally injected with melatonin at late afternoon under long-day condition for 3 weeks. However, melatonin injections did not affect the corticosterone rhythms. In addition, photoperiodic changes in the amplitude of corticosterone rhythms were also observed in melatonin-deficient C57BL/6J mice, in which expression profiles of several clock genes and steroidgenesis genes in adrenal gland were modified by the photoperiod. Our data suggest that photoperiod regulates corticosterone rhythms by altered adrenal sensitivity through melatonin-independent mechanisms that may involve the adrenal clock.     

Facilitation of Feedback Inhibition Through Blockade of Glucocorticoid Receptors in the Hippocampus

In the present study the effects of intracerebroventricular (icv) and intrahippocampal administration of corticosteroid antagonists on basal hypothalamic-pituitary-adrenal (HPA) activity around the diurnal peak were compared in male Wistar rats. In two separate experiments the glucocorticoid receptor (GR) antagonist RU 38486 and the mineralocorticoid receptor (MR) antagonist RU 28318 were tested. One hour after GR antagonist injection, significant increases in plasma ACTH and corticosterone levels were observed in the icv treated rats, when compared to vehicle. In contrast, a significant decrease in ACTH levels, and a slight, but non-significant decrease in corticosterone concentrations were attained one hour after intrahippocampal injection of the GR antagonist. Injection of the MR antagonist, on the other hand, resulted in enhanced ACTH and corticosterone levels irrespective of the site of injection. These findings suggest that negative feedback inhibition at the circadian peak involves hippocampal MRs and extrahippocampal (hypothalamic) GRs. The latter feedback inhibition overrides a positive feedback influence exerted by endogenous corticosteroids through hippocampal GRs.     

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.     

Circadian rhythm of serotonin binding in rat brain--II. Influence of sleep deprivation and imipramine

Sleep deprivation (SD) modified the circadian rhythm of specific high affinity serotonin (5-HT) binding to rat brain membranes. In control rats a 24-hr rhythm was evident with a trough at 1000-1200 and a nadir at 0000. During the last 26 hr of a 49 hr SD period, trough and peak values were delayed by 4-6 hr. The 24-hr mean binding was significantly (P less than 0.001) different from that of controls. If sleep deprivation was followed by recovery sleep (RS), the normal rhythm of 5-HT binding was obtained already within 1 hr after SD. The effects of SD and RS were ascertained by plasma ACTH and corticosterone assay. No significant change in the hormone rhythms were observed through the mean plasma level of ACTH and corticosterone were enhanced to about 180 and 150%, respectively. Chronic treatment with the antidepressant imipramine resulted in a decrease of the 24-hr mean 5-HT binding by about 50% and a 2-hr delay of peak and trough values. Imipramine treatment decreased the peak value of 5-HT concentration at 1000 to about 65% and appears to abolish the rhythm of 5-HT concentration.     

Circadian control of the daily plasma glucose rhythm: an interplay of GABA and glutamate

The mammalian biological clock, located in the hypothalamic suprachiasmatic nuclei (SCN), imposes its temporal structure on the organism via neural and endocrine outputs. To further investigate SCN control of the autonomic nervous system we focused in the present study on the daily rhythm in plasma glucose concentrations. The hypothalamic paraventricular nucleus (PVN) is an important target area of biological clock output and harbors the pre-autonomic neurons that control peripheral sympathetic and parasympathetic activity. Using local administration of GABA and glutamate receptor (ant)agonists in the PVN at different times of the light/dark-cycle we investigated whether daily changes in the activity of autonomic nervous system contribute to the control of plasma glucose and plasma insulin concentrations. Activation of neuronal activity in the PVN of non-feeding animals, either by administering a glutamatergic agonist or a GABAergic antagonist, induced hyperglycemia. The effect of the GABA-antagonist was time dependent, causing increased plasma glucose concentrations only when administered during the light period. The absence of a hyperglycemic effect of the GABA-antagonist in SCN-ablated animals provided further evidence for a daily change in GABAergic input from the SCN to the PVN. On the other hand, feeding-induced plasma glucose and insulin responses were suppressed by inhibition of PVN neuronal activity only during the dark period. These results indicate that the pre-autonomic neurons in the PVN are controlled by an interplay of inhibitory and excitatory inputs. Liver-dedicated sympathetic pre-autonomic neurons (responsible for hepatic glucose production) and pancreas-dedicated pre-autonomic parasympathetic neurons (responsible for insulin release) are controlled by inhibitory GABAergic contacts that are mainly active during the light period. Both sympathetic and parasympathetic pre-autonomic PVN neurons also receive excitatory inputs, either from the biological clock (sympathetic pre-autonomic neurons) or from non-clock areas (para-sympathetic pre-autonomic neurons), but the timing information is mainly provided by the GABAergic outputs of the biological clock.     

Passive immunization with an anti-oCRF41 immune serum inhibits the circadian increase of plasma ACTH in rats

For 24 hrs. after i.v. injection of 1 ml of an undiluted immune serum raised against oCRF41, the diurnal surge of plasma ACTH dropped to a short-lived limited rise above baseline level. On the second day after injection, the ACTH level in treated rats rose to a subnormal level, although both plasma dilution of the immune serum and its binding capacity in the plasma remained unchanged throughout the experiment. Plasma corticosterone, on the contrary, displayed a normal circadian rhythm during the entire experiment. However, in animals given a second injection of 0.5 ml oCRF41 immune serum 32 hrs. after the first, both ACTH and corticosterone titers fell rapidly below their circadian minimal levels in controls. Concomitantly, the concentration of immune serum in the peripheral plasma, and its capacity to bind to oCRF, rose by 50%. The major role of CRF41 as a diurnal trigger of the circadian rhythm of ACTH is discussed, as well as the limits of passive immunization.     

Effects of ACTH on the ligand-binding properties of the glucocorticoid receptor exerted not only via elevated levels of corticosteroids

Treatment of mice with ACTH not only increased plasma corticosterone levels, but also reduced the ligand-binding capacity of the glucocorticoid receptor in skeletal muscle cytosol. Non-linear Scatchard plots were obtained for the glucocorticoid receptor following ACTH treatment. This upward concave curvilinearity could not be reproduced by simply adding to the cytosol an amount of corticosterone corresponding to the increase, even though this treatment resulted in reduced binding capacity. The addition of corticosterone resulted in a slower formation of ligand-receptor complexes (lower association rate constant), which offered a partial explanation for the low binding. In addition, ACTH treatment was also found to reduce the binding capacity in adrenalectomized mice that did not respond with corticosterone elevation. However, in this case Scatchard plots were linear.     

Adrenocorticotropin and corticosterone levels in pre-weanling spontaneously hypertensive rats

Circulating plasma ACTH and corticosterone levels were measured in spontaneously hypertensive rats (SHR) and the corresponding, normotensive Wistar-Kyoto (WKY) strain at 10 and 20 days of age. In addition, stored levels of ACTH were measured in the pituitary glands of these animals. Circulating corticosterone levels were significantly lower, in both strains, at 10 days than at 20 days. Although the glucocorticoid was undetectable in WKY animals at 10 days, significant levels were observed in age-matched SHR. No difference in corticosterone concentrations was observed between the two strains at 20 days. Circulating ACTH levels did not reflect the values for circulating glucocorticoids. There were no significant differences in the levels of ACTH between strains or between age groups. Moreover, pituitary stores of ACTH between animals of different strains and ages were not found to be significantly different among any of the groups tested. These results demonstrate that there is a difference in circulating corticosterone levels between spontaneously hypertensive and Wistar-Kyoto rats at 10 days postnatally which is not evident just prior to weaning (20 days). This difference is not due to variations in stored or circulating ACTH. Indeed, ACTH levels are high at a time (10 days) when corticosterone is low - thus suggesting that the difference may reside within the responsiveness of the adrenal cortex.     

Distribution and daily fluctuation of the available glucocorticoid binding sites in different areas of the quail brain

The distribution and daily fluctuation of available glucocorticoid binding sites was studied in the brain of the quail Coturnix coturnix japonica, under physiological circumstances. A high level of triamcinolone acetonide binding was observed in some limbic structures (hippocampus and archistriatum), in the nucleus medialis and lateralis posterioris hypothalami and in the cerebellar cortex. The daily fluctuation of the available glucocorticoid binding sites in the preoptic area, hippocampus, archistriatum and cerebellar cortex can be described with a curve antiphased to the daily rhythm of plasma corticosterone concentration and seems to be synchronized by the plasma corticosterone level.     

Bombesin-induced HPA and sympathetic activation requires CRH receptors

Central administration of bombesin (BN) (into the ventricular system) increased circulating levels of ACTH, corticosterone, epinephrine, norepinephrine and glucose, indicating that this peptide activates the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system. We then assessed the potential contribution of corticotropin-releasing hormone (CRH) system, in the mediation of these BN effects. Blockade of CRH receptors with alphah-CRF (10 microg) attenuated or blocked the BN-induced rise in plasma ACTH, epinephrine, norepinephrine, glucose and corticosterone levels. These findings support the notion that BN-induced HPA axis and sympathetic activation are mediated, at least in part, via activation of CRH neurons.     

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.     

Effects of (D-ala2, met5)-enkephalinamide and naloxone on ACTH and corticosterone secretion

An intravenous administration of (D-ala2, met5)-enkephalinamide (DALA) caused a significant elevation of plasma ACTH and corticosterone at 10 to 20 min after injection in unanesthetized freely moving rats. An intraperitoneal administration of cyproheptadine tended to reduce plasma ACTH and corticosterone levels at 60 min after injection, but it did not attenuate the DALA-induced ACTH and corticosterone elevation. A large dose of naloxone (1-10 mg/kg body weight) caused a significant elevation in plasma corticosterone, but naloxone at 10 mg/kg body weight reduced the basal ACTH level and DALA-induced ACTH elevation. When both DALA and naloxone were injected, the steroidogenic effect was attenuated. Neither DALA nor naloxone affected the basal ACTH release and CRF-induced ACTH stimulation in rat anterior pituitary cell cultures. These results suggest that DALA acts at the extra-hypophyseal level to stimulate ACTH and corticosterone and that the naloxone stimulatory effect on steroidogenesis acts on the adrenal gland or is mediated by stimulating corticosterone stimulating factors other than ACTH.