Circadian Rhythm Of Plasma Corticosterone Research Articles

Possible zeitgebers for external entrainment of the circadian rhythm of plasma corticosterone in blind infantile rats.

1. The phase angle of circadian rhythm of plasma corticosterone in individual blind pups was followed in order to find out an effective zeitgeber(s) during the post-natal development. 2. The retinal light pathway before the opening of eyes was not essential for the entrainment of pups' rhythm to the environmental light-dark (LD) cycle. 3. In blinded pups whose eyes were enucleated on the day of birth, no evidence was obtained for effective extra-retinal pathways for photic inputs. 4. Free-running circadian hormone rhythm of blind pups was not entrained by 'social contact' with other sighted pups in the same cage. 5. Even when the duration of nursing was varied from 2 to 4 weeks, the phase angle of pups' rhythm at the fourth week was not affected. 6. In mother-pups exchange experiments in which pups born from LD mother were reared by DL mother (LD-DL pups) and conversely, pups from DL original mother were reared by LD foster mother (DL-LD pups), about one half of the pups at the fourth post-natal week of both groups exhibited phase angles belonging to their original mothers and the other half showed phase angles of their foster mothers. 7. It is suggested that blind pups may retain the phase angle of circadian rhythm of the original mother and the overt hormone rhythm may be modifiable by the foster mother during the early phase of post-natal life.

Effects of maternal ethanol consumption in rats on basal and rhythmic pituitary - adrenal function in neonatal offspring

Neonatal corticoid treatment delays development of the circadian rhythm of plasma corticosterone in rats. We therefore sought to determine whether fetal or neonatal exposure to ethanol, a substance which activates the hypothalamo - pituitary - adrenal axis, produces similar effects. Subjects were the offspring of dams fed a 5.0% w/v ethanol-containing liquid diet or pair-fed an isocaloric control diet during gestation weeks two and three or during postnatal week one. At birth (day 1), the fetal ethanol-exposed pups had significantly higher brain and plasma corticosterone levels than the pair-fed or normal controls; brain and body weights were unaffected. By day 3, brain and plasma corticosterone titers in the fetal ethanol-exposed pups declined to the levels of the pair-fed and normal controls, although brain weights were significantly reduced. Significantly higher p.m. than a.m. levels of plasma corticosterone first occurred on day 18 both in the fetal ethanol-exposed pups and in the pair-fed and normal controls. Thus, despite its causing elevated corticosterone levels at birth, fetal exposure to ethanol did not affect the onset of the pituitary - adrenal circadian rhythm. On the other hand, exposure to ethanol during the first neonatal week delayed the onset of the pituitary - adrenal rhythm from day 18 to day 21. However, even greater delays occurred in the neonatal pair-fed controls, suggesting that the delays following neonatal exposure were due to nutritional deficits rather than to alcohol per se. The developmental and long-term influences of elevated corticoid levels at birth in fetal ethanol-exposed rats on other aspects of pituitary - adrenal function remain to be determined.

Circadian rhythm of plasma corticosterone in vagotomized rats.

In vagotomized rats, 2 weeks after surgery, the amplitude of the circadian rhythm of plasma corticosterone was extremely low, indicating that gastrointestinal activity may be in part involved in the hypothalamo-hypophyseal circadian rhythmicity.

Corticosterone Rhythmicity in the Rat: Interactive Effects of Dietary Restriction and Schedule of Feeding

Effects of changes in diet composition and schedule of restricted feeding on the circadian rhythm of plasma corticosterone in the adult rat were examined. Three restricted feeding schedules were used: diet presented 3 hours after lights-on, 1 hour before lights-off or continuously by automated feeder. Animals were paired to controls (consuming 24% protein diet ad libitum) and provided 80% of control food intake/g body weight/day. A fourth experimental group was offered 2.4% protein diet ad libitum. Plasma corticoids were measured every 4 hours from 0800 to 0400 hours. Corticoid levels 20 min after food presentation were also determined. Both control and protein-restricted animals displayed a typical circadian rhythm, with corticoids lowest at 0800 hours and a peak at 2000 hours. Animals fed at 0900 hours exhibited a 12-hour shift in peak corticoids, while the circadian rhythm was totally abolished in animals fed by automated feeder. Offering the restricted ration at 1700 hours, however, resulted in a diurnal rhythm similar to that of controls. While pre and post-feeding corticoids were similar in control and protein-restricted animals, a post-feeding suppression was found in all three food-restricted groups. Clearly, the relationship between feeding schedule and diurnal rhythm must not be ignored in nutritional paradigms.calorie restriction circadian rhythm corticosterone

Circadian periodicity of plasma corticosterone levels in rats subjected to hemorrhagic shock and surgical trauma.

The effects of surgical trauma and hemorrhagic shock on the circadian rhythmicity of corticosteroid secretion in the rat were investigated. The estimations were performed at 4-hour intervals for a 24-hour period. Control animals exhibited a characteristic circadian rhythm of plasma corticosterone with peak concentrations occurring at 8 p.m. followed by a gradual fall during the night, reaching a minimum at 8 a.m. Severe stress induced by hemorrhagic shock or surgical trauma caused a dramatic alteration in corticosterone rhythms which persisted up to 72 h following surgery or hemorrhage. It is apparent that the physiological mechanisms which regulate adrenal rhythmicity are disrupted for a prolonged period following major stress or trauma.

Effect of lesions of the locus coeruleus complex on the circadian rhythm of plasma corticosterone in the mouse

An apparently transient elevation of basal morning (08.00 h) plasma corticosterone levels in male mice was found 48 h after bilateral electrolytic lesions of the brainstem locus coeruleus complex but was not observed 6 weeks after lesioning.

Participation of brain catecholaminergic neurons in a self-sustained circadian oscillation of plasma corticosterone in the rat

Circadian rhythms of locomotor activity and plasma corticosterone were determined simultaneously in individual rats which were injected intraventricularly with 6-hydroxydopamine (6-OHDA), a specific depletor of catecholamines. In light-dark cycles (LD), 6-OHDA-treated rats showed essentially normal circadian rhythms of both functions. In 200 lux continuous light (LL) the locomotor activity in the drug-treated rats ran freely with a period slightly longer than 24 h: free-running parameters (mesor, amplitude and period) of the locomotor activity were the same as those of control rats. The circadian rhythm of plasma corticosterone in control rats also ran freely in LL, resulting in a reversal of their phase after 12 days exposure to LL. However, the rhythm disappeared in 6-OHDA-treated rats under LL: instead in these rats 3–4 episodes of secretion were observed over a 24 h period. These results suggest a difference in the biochemical background between the regulatory mechanism of circadian rhythm of locomotor activity and that of plasma corticosterone. It is also apparent that brain catecholaminergic components are indispensible for the circadian rhythm of plasma corticosterone to freerun normally in LL, but are dispensible in LD. A plausible model consisting of two oscillators is proposed to explain these findings.

Effects of parachlorophenylalanine and 5, 6-dihydroxytryptamine on the free-running rhythms of locomotor activity and plasma corticosterone in the rat exposed to continuous light

Parachlorophenylalanine (PCPA) and 5,6-dihydroxytryptamine (5,6-DHT), depletors of brain serotonin, were administered to the rat and circadian rhythms of locomotor activity and plasma corticosterone were determined simultaneously in individual rats in light-dark cycles (LD) and in 200 lux continuous light (LL). Free-running periods and acrophases on the 12th day in LL (LL12) were calculated by a least squares spectrum method. In PCPA-treated rats which showed 70% depletion of brain serotonin, circadian rhythns of locomotor activity in LL and of plasma corticosterone and ACTH in LD disappeared for several days after the drug injection. Circadian rhythms of locomotor activity reappeared after the LL7 day and free-ran with a phase shift. Free-running periods of these rats did not differ significantly from that of control rats. However, the acrophase of PCPA-treated group on the LL11 day was 5 h advanced as compared to that of control. Circadian rhythm of plasma corticosterone in the PCPA-treated rats was detected on the LL12 day but their peak times were distributed around 24:00 h instead of 08:00 h observed in control rats. The 5,6-DHT-treated rats which showed only 40% depletion of brain serotonin exhibited normal free-running rhythms in both locomotor activity and plasma corticosterone in LL and no difference in the acrophases of these functions on the LL12 day as compared to controls. These results suggest that PCPA affects the circadian clock (or clocks) itself in such a way that it blocks the clock to free-run or at least it effectively shortens the free-running periods of locomotor activity and plasma corticosterone in the rat.

Effect of midbrain raphe nuclei lesions on the circadian rhythm of plasma corticosterone in the rat

Effect of midbrain raphe nuclei lesions on the circadian rhythm of plasma corticosterone in the rat

Sex difference in ontogenesis of circadian adrenocortical rhythm in cortisone-primed rats.

THE hormonal milieu in the neonatal period has profound influences on the morphological, biochemical and functional development of the brain1,2. Krieger reported that the administration of corticosteroid (dexamethasone or hydrocortisone) to 2–4-d-old rats suppressed the circadian rhythm of plasma corticosterone at 30 d of age3, whereas treatment at 12–14 d of age did not affect the rhythmicity. We have investigated whether the suppression of corticosterone rhythm results in its permanent derangement throughout adult life or merely indicates its delayed appearance. After this paper was submitted, Krieger published the results of a similar study4.

Effect of meal feeding on daily rhythms of plasma corticosterone and growth hormone in the rat.

After rats had adapted to regular meal feeding in the morning they demonstrated an altered circadian rhythm of plasma corticosterone (B) even under the normal light-dark cycle. The altered daily rhythm of plasma B consisted of two peaks, with one peak at 08.00 h in anticipation of meal feeding and a second peak corresponding to the normal peak of plasma B prior to lights-off seen in ad libitum-fed animals. Neither peak of plasma B in the meal-fed animals achieved the magnitude of the single peak observed in control animals. In spite of some quantitative differences during certain periods of the day, after the animals had adapted to meal feeding there was no difference in the basic profile of the daily rhythm of plasma immunoactive growth hormone (GH).

The relation of hepatic in vitro inactivation of corticosteroids to the circadian rhythm of plasma corticosterone.

Plasma corticosterone levels and the in vitro capacity of the liver to reduce the delta(4)3-ketone group of corticosterone were ascertained at 4 hr intervals in male rats maintained on a normal lighting schedule (12L:12D). The rates of delta(4)3-ketone reduction, as well as wet liver weight, were highest during the early portion (08.00 hr) of the light period when liver protein and plasma corticosterone concentrations were low. Shortly (2000 hr) after the beginning of the dark period plasma corticosterone reached peak levels, while hepatic inactivation of corticosterone was markedly depressed. This inverse relationship suggests that the rhythmicity in the capacity of the liver to inactivate corticosterone may contribute to the circadian periodicity of plasma corticosterone.

Disturbances of the hypothalamo-hypophysial-adrenocortical system in the alloxan diabetic rat.

In insulin-treated alloxan diabetic rats some parameters of the hypothalamo-hypophysial-adrenocortical (HHA) system are normal: half-life and circadian rhythm of plasma corticosterone, maximal and submaxirnal stimulation of the adrenal cortex by exogenous and endogenous ACTH, dex-amethasone suppression of stress stimuli of different strengths. If insulin treatment is withheld, 40 hr after the last insulin injection morning levels of plasma corticosterone are elevated, adrenocortical response to exogenous ACTH is increased, the onset of dexamethasone inhibition of weak stress signals is delayed, different stress stimuli overcome the dexamethasone blockade. These disturbances of the regulation of the HHA-system could be interpreted as counter regulation in insulin-deficient alloxan diabetic rats. (Endocrinology 95: 760, 1974)

Effects of methamphetamine on daily rhythms of hypothalamic norepinephrine, serotonin and plasma corticosterone levels in the rat

The relationship between daily rhythms of hypothalamic norepinephrine (NE) and serotonin (5HT) contents and the circadian rhythm of plasma corticosterone (Comp. B) levels was studied in the rat. It was found that levels of hypothalamic NE, 5HT and plasma Comp. B exhibited distinct daily flucturations in the control condition. In animals treated with methamphetamine, the daily rhythms of hypothalamic 5HT contents and plasma Comp. B levels remained unchanged, whereas the daily rhythm of hypothalamic NE contents was completely abolished. As a result, it was suggested that the daily rhythm of hypothalamic NE is not functionally related to the circadian change of pituitary-adrenocortical activity.

Maturation of the circadian rhythm of plasma corticosterone in the rat.

The maturation of certain features of the hypothalamic-pituitary adrenocortical system was studied in rats from birth to the 40th postnatal day. Increases in plasma corticosterone concentration were observed following exposure to ether and after exogenous ACTH in animals 2 weeks before diurnal variation in plasma corticosterone appeared. A definite, though slight, plasma B response to exogenous ACTH was present even at birth but did not begin to approach adult responsiveness until after the 15th day. The plasma B response to ether began on day 15. The afternoon plasma B was higher by the 25th day than on any previous afternoon of the study, but a definite circadian variation was not present until day 30–32. These data suggest that maturation of the central nervous system’s ability to regulate rhythmic ACTH secretion is delayed well beyond the time when the pituitary is capable of secreting ACTH and the adrenal cortex is capable of secreting corticosterone. (Endocrinology80: 926, 1967)