Circadian rhythms of urinary excretion: the relationship between the amount excreted and the circadian changes

Sleep-independent circadian rhythm of aldosterone secretion in healthy young adults

OBJECTIVE

A diurnal variation in urine output has been described in humans, whereby it is lowest at night. Fluid balance hormones such as vasopressin and aldosterone as well as urine output have a diurnal variation. Although the diurnal variation of vasopressin results in part from a circadian rhythm, the variation in aldosterone has until recently been reported to be due to the sleep/wake cycle. The present study used a specialized protocol to explore whether aldosterone has an underlying circadian rhythm.

METHODS

Ten healthy participants (average age 23.1) were enrolled in the 57.3-hour protocol that included an 8-hour baseline sleep episode, 40 hours in constant routine conditions (wakefulness, food and fluid intake, posture, and dim light), and a 9.3-hour recovery sleep. Blood samples for aldosterone were taken every 4 hours. Cosinor analysis was performed on the constant routine data to test the effect of the sleep/wake cycle on overall aldosterone secretion.

RESULTS

There was a significant circadian rhythm during the 40-hour constant routine, independent of sleep, with aldosterone higher at the end of the biological night and lower at the end of the biological day. When analyzing data from the entire 57.3-hour protocol and controlling for this circadian rhythm, aldosterone concentration was significantly higher during the recovery night following the 40-hour sleep deprivation compared to the night spent awake.

CONCLUSION

We found a significant endogenous circadian rhythm in the secretion of aldosterone, independent of sleep. In addition, as shown previously, there was a significant effect of the sleep/wake cycle on aldosterone secretion.

Estimated excretion and clearance of uric acid as optimal surrogate indices for daily urinary uric acid excretion

OBJECTIVES

Daily uric acid excretion (Eua) is an essential index for patients with gout/hyperuricaemia. We identified alternative indices most correlated with 24-hour uric acid clearance (Cua 24 h) and 24-hour Eua (Eua 24 h) using data from the reference interval of urinary clearance and excretion of urate study.

METHODS

The subjects were indoor workers aged 20-65 years who met the Clinical and Laboratory Standards Institute Guidelines C28-A3c. Alternative indices using spot urine were urine uric acid creatinine ratio, Cua-creatinine clearance ratio (Cua/Ccr), Eua-CCr ratio (Eua/Ccr), estimated Cua (eCua), and estimated Eua (eEua). eCua and eEua are the values obtained by multiplying Cua/Ccr and Eua/Ccr with the estimated glomerular filtration rate.

RESULTS

The final number of subjects analysed was 739. Among the indices using spot urine, eCua and eEua showed the highest correlation with Cua 24 h and Eua 24 h, respectively. Compared with Cua 60 min and Eua 60 min obtained from 60-min urine collection, eCua and eEua showed lower root means squared error, lower bias, and significantly higher accuracy of within 30% and within 15%.

CONCLUSIONS

The newly proposed eCua and eEua may be appropriate from a practical perspective.

Impact of sleep on chronobiology of micturition among healthy older adults

Nocturia (waking to void) is prevalent among older adults. Disruption of the well-described circadian rhythm in urine production with higher nighttime urine output is its most common cause. In young adults, their circadian rhythm is modulated by the 24-h secretory pattern of hormones that regulate salt and water excretion, including antidiuretic hormone (ADH), renin, angiotensin, aldosterone, and atrial natriuretic peptide (ANP). The pattern of hormone secretion is less clear in older adults. We investigated the effect of sleep on the 24-h secretion of these hormones in healthy older adults. Thirteen participants aged ≥65 yr old underwent two 24-h protocols at a clinical research center 6 wk apart. The first used a habitual wake-sleep protocol, and the second used a constant routine protocol that removed the influence of sleep, posture, and diet. To assess hormonal rhythms, plasma was collected at 8:00 am, 12:00 pm, 4:00 pm, and every 30 min from 7:00 pm to 7:00 am. A mixed-effects regression model was used to compare subject-specific and mean trajectories of hormone secretion under the two conditions. ADH, aldosterone, and ANP showed a diurnal rhythm that peaked during sleep in the wake-sleep protocol. These nighttime elevations were significantly attenuated within subjects during the constant routine. We conclude that sleep has a masking effect on circadian rhythm amplitude of ADH, aldosterone, and ANP: the amplitude of each is increased in the presence of sleep and reduced in the absence of sleep. Disrupted sleep could potentially alter nighttime urine output in healthy older adults via this mechanism.NEW & NOTEWORTHY Nocturia (waking to void) is the most common cause of sleep interruption among older adults, and increased nighttime urine production is its primary etiology. We showed that in healthy older adults sleep affects the 24-h secretory rhythm of hormones that regulate salt-water balance, which potentially alters nighttime urine output. Further studies are needed to elucidate the impact of chronic insomnia on the secretory rhythms of these hormones.

Role of circadian rhythms and melatonin in bladder function in heath and diseases

The circadian system modulates all visceral organ physiological processes including urine storage and voiding. The "master clock" of the circadian system lies within suprachiasmatic nucleus of the hypothalamus while "peripheral clocks" are found in most peripheral tissue and organs, including the urinary bladder. Disruptions of circadian rhythms can cause organ malfunction and disorder or exacerbate pre-existing ones. It has been suggested that nocturia, which develops mostly in the elderly, could be a circadian-related disorder of the bladder. In the bladder, many types of gap junctions and ion channels in the detrusor, urothelium and sensory nerves are likely under strict local peripheral circadian control. The pineal hormone, melatonin, is a circadian rhythm synchroniser capable of controlling a variety of physiological processes in the body. Melatonin predominantly acts via the melatonin 1 and melatonin 2 G-protein coupled receptors expressed in the central nervous system, and many peripheral organs and tissues. Melatonin could be beneficial in the treatment of nocturia and other common bladder disorders. The ameliorating action of melatonin on bladder function is likely due to multiple mechanisms which include central effects on voiding and peripheral effects on the detrusor and bladder afferents. More studies are warranted to determine the precise mechanisms of circadian rhythm coordination of the bladder function and melatonin influences on the bladder in health and diseases.

Melatonin inhibits muscular-mucosal stretch-sensitive bladder afferents via the MT2 receptors

Melatonin is a circadian rhythm regulator capable of controlling a variety of physiological processes in the body. It predominantly acts via the melatonin 1 (MT1) and MT2 receptors expressed in the CNS neurons and peripheral organs and tissues. Melatonin can modulate urinary bladder function, however, to date it is not known if melatonin can regulate activity of sensory neurons innervating the bladder. Bladder afferents play an important role in urine storage and voiding. Therefore, this study aims to determine if melatonin can regulate mechanosensitivity of 2 major classes of sensory neurons in the guinea pig bladder: stretch-insensitive mucosal and low threshold stretch-sensitive muscular-mucosal afferents. The effects of melatonin on the mechanosensitivity of mucosal and muscular-mucosal afferents were measured ex vivo using single unit extracellular recording. Melatonin did not affect the responses of mucosal afferents to stroking of their receptive fields but did concentration-dependently, significantly inhibit 69% of muscular-mucosal afferents responses to stroking and bladder stretch. This inhibitory effect was not affected by the MT1 receptor antagonist, S26131 but was blocked by the selective MT2 receptor antagonists, K-185 and 4-P-PDOT. Forskolin significantly potentiated the responses of muscular-mucosal afferents to stroking and stretch, which were prevented by melatonin. These findings demonstrate a direct inhibitory effect of melatonin on the mechanosensitivity of low threshold stretch-sensitive muscular-mucosal bladder afferents acting via MT2 receptors, which is independent from its action on detrusor muscle. This may have important clinical implications for the treatment of many common bladder disorders including nocturia.

Piezo channels in the urinary system

The Piezo channel family, including Piezo1 and Piezo2, includes essential mechanosensitive transduction molecules in mammals. Functioning in the conversion of mechanical signals to biological signals to regulate a plethora of physiological processes, Piezo channels, which have a unique homotrimeric three-blade propeller-shaped structure, utilize a cap-motion and plug-and-latch mechanism to gate their ion-conducting pathways. Piezo channels have a wide range of biological roles in various human systems, both in vitro and in vivo. Currently, there is a lack of comprehensive understanding of their antagonists and agonists, and therefore further investigation is needed. Remarkably, increasingly compelling evidence demonstrates that Piezo channel function in the urinary system is important. This review article systematically summarizes the existing evidence of the importance of Piezo channels, including protein structure, mechanogating mechanisms, and pharmacological characteristics, with a particular focus on their physiological and pathophysiological roles in the urinary system. Collectively, this review aims to provide a direction for future clinical applications in urinary system diseases.

Diurnal rhythms of urine volume and electrolyte excretion in healthy young men under differing intensities of daytime light exposure

In humans, most renal functions, including urine volume and electrolyte excretions, have a circadian rhythm. Light is a strong circadian entrainment factor and daytime-light exposure is known to affect the circadian rhythm of rectal temperature (RT). The effects of daytime-light exposure on the diurnal rhythm of urinary excretion have yet to be clarified. The aim of this study was to clarify whether and how daytime exposure to bright-light affects urinary excretions. Twenty-one healthy men (21–27 years old) participated in a 4-day study involving daytime (08:00–18:00 h) exposure to two light conditions, Dim (< 50 lx) and Bright (~ 2500 lx), in a random order. During the experiment, RT was measured continuously. Urine samples were collected every 3 ~ 4 h. Compared to the Dim condition, under the Bright condition, the RT nadir time was 45 min earlier (p = 0.017) and sodium (Na), chloride (Cl), and uric acid (UA) excretion and urine volumes were greater (all p < 0.001), from 11:00 h to 13:00 h without a difference in total daily urine volume. The present results suggest that daytime bright light exposure can induce a phase shift advance in urine volume and urinary Na, Cl, and UA excretion rhythms.

Nondipping Blood Pressure: Predictive or Reactive Failure of Renal Sodium Handling?

Blood pressure follows a daily rhythm, dipping during nocturnal sleep in humans. Attenuation of this dip (nondipping) is associated with increased risk of cardiovascular disease. Renal control of sodium homeostasis is essential for long-term blood pressure control. Sodium reabsorption and excretion have rhythms that rely on predictive/circadian as well as reactive adaptations. We explore how these rhythms might contribute to blood pressure rhythm in health and disease.

Presence of multiple peripheral circadian oscillators in the tissues controlling voiding function in mice

Circadian clocks are the endogenous oscillators that harmonize a variety of physiological processes within the body. Although many urinary functions exhibit clear daily or circadian variation in diurnal humans and nocturnal rodents, the precise mechanisms of these variations are as yet unclear. In the present study, we demonstrate that Per2 promoter activity clearly oscillates in neonate and adult bladders cultured ex vivo from Per2::Luc knock-in mice. In subsequent experiments, we show that multiple local oscillators are operating in all the bladder tissues (detrusor, sphincter and urothelim) and the lumbar spinal cord (L4–5) but not in the pontine micturition center or the ventrolateral periaqueductal gray of the brain. Accordingly, the water intake and urine volume exhibited daily and circadian variations in young adult wild-type mice but not in Per1^−/−Per2^−/− mice, suggesting a functional clock-dependent nature of the micturition rhythm. Particularly in PDK mice, the water intake and urinary excretion displayed an arrhythmic pattern under constant darkness, and the amount of water consumed and excreted significantly increased compared with those of WT mice. These results suggest that local circadian clocks reside in three types of bladder tissue and the lumbar spinal cord and may have important roles in the circadian control of micturition function.

Effects of chronotherapy of benazepril on the diurnal profile of RAAS and clock genes in the kidney of 5/6 nephrectomy rats

This study investigated the effects of benazepril administered in the morning or evening on the diurnal variation of renin-angiotensin-aldosterone system (RAAS) and clock genes in the kidney. The male Wistar rat models of 5/6 subtotal nephrectomy (STNx) were established. Animals were randomly divided into 4 groups: sham STNx group (control), STNx group, morning benazepril group (MB) and evening benazepril group (EB). Benazepril was intragastrically administered at a dose of 10 mg/kg/day at 07:00 and 19:00 in the MB group and EB group respectively for 12 weeks. All the animals were synchronized to the light:dark cycle of 12:12 for 12 weeks. Systolic blood pressure (SBP), 24-h urinary protein excretion and renal function were measured at 11 weeks. Blood samples and kidneys were collected every 4 h throughout a day to detect the expression pattern of renin activity (RA), angiotensin II (AngII) and aldosterone (Ald) by radioimmunoassay (RIA) and the mRNA expression profile of clock genes (bmal1, dbp and per2) by real-time PCR at 12 weeks. Our results showed that no significant differences were noted in the SBP, 24-h urine protein excretion and renal function between the MB and EB groups. There were no significant differences in average Ald and RA content of a day between the MB group and EB group. The expression peak of bmal1 mRNA was phase-delayed by 4 to 8 h, and the diurnal variation of per2 and dbp mRNA diminished in the MB and EB groups compared with the control and STNx groups. It was concluded when the similar SBP reduction, RAAS inhibition and clock gene profile were achieved with optimal dose of benazepril, morning versus evening dosing of benazepril has the same renoprotection effects.

Peripheral circadian oscillators in mammals

Although circadian rhythms in mammalian physiology and behavior are dependent upon a biological clock in the suprachiasmatic nuclei (SCN) of the hypothalamus, the molecular mechanism of this clock is in fact cell autonomous and conserved in nearly all cells of the body. Thus, the SCN serves in part as a "master clock," synchronizing "slave" clocks in peripheral tissues, and in part directly orchestrates circadian physiology. In this chapter, we first consider the detailed mechanism of peripheral clocks as compared to clocks in the SCN and how mechanistic differences facilitate their functions. Next, we discuss the different mechanisms by which peripheral tissues can be entrained to the SCN and to the environment. Finally, we look directly at how peripheral oscillators control circadian physiology in cells and tissues.

Role of the renal circadian timing system in maintaining water and electrolytes homeostasis

Many basic physiological functions exhibit circadian rhythmicity. These functional rhythms are driven, in part, by the circadian clock, an ubiquitous molecular mechanism allowing cells and tissues to anticipate regular environmental events and to prepare for them. This mechanism has been shown to play a particularly important role in maintaining stability (homeostasis) of internal conditions. Because the homeostatic equilibrium is continuously challenged by environmental changes, the role of the circadian clock is thought to consist in the anticipative adjustment of homeostatic pathways in relation with the 24h environmental cycle. The kidney is the principal organ responsible for the regulation of the composition and volume of extracellular fluids (ECF). Several major parameters of kidney function, including renal plasma flow (RPF), glomerular filtration rate (GFR) and tubular reabsorption and secretion have been shown to exhibit strong circadian oscillations. Recent evidence suggest that the circadian clock can be involved in generation of these rhythms through external circadian time cues (e.g. humoral factors, activity and body temperature rhythms) or, trough the intrinsic renal circadian clock. Here, we discuss the role of renal circadian mechanisms in maintaining homeostasis of water and three major ions, namely, Na(+), K(+) and Cl(-).

Circadian rhythms in urinary functions: possible roles of circadian clocks?

Circadian clocks are the endogenous oscillators that harmonize a variety of physiological processes within the body. Although many urinary functions exhibit clear daily or circadian variation in diurnal humans and nocturnal rodents, the precise mechanisms of these variations are as yet unclear. In this review, we briefly introduce circadian clocks and their organization in mammals. We then summarize known daily or circadian variations in urinary function. Importantly, recent findings by others as well as results obtained by us suggest an active role of circadian clock genes in various urinary functions. Finally, we discuss possible research avenues for the circadian control of urinary function.

Molecular clock is involved in predictive circadian adjustment of renal function

Renal excretion of water and major electrolytes exhibits a significant circadian rhythm. This functional periodicity is believed to result, at least in part, from circadian changes in secretion/reabsorption capacities of the distal nephron and collecting ducts. Here, we studied the molecular mechanisms underlying circadian rhythms in the distal nephron segments, i.e., distal convoluted tubule (DCT) and connecting tubule (CNT) and the cortical collecting duct (CCD). Temporal expression analysis performed on microdissected mouse DCT/CNT or CCD revealed a marked circadian rhythmicity in the expression of a large number of genes crucially involved in various homeostatic functions of the kidney. This analysis also revealed that both DCT/CNT and CCD possess an intrinsic circadian timing system characterized by robust oscillations in the expression of circadian core clock genes (clock, bma11, npas2, per, cry, nr1d1) and clock-controlled Par bZip transcriptional factors dbp, hlf, and tef. The clock knockout mice or mice devoid of dbp/hlf/tef (triple knockout) exhibit significant changes in renal expression of several key regulators of water or sodium balance (vasopressin V2 receptor, aquaporin-2, aquaporin-4, alphaENaC). Functionally, the loss of clock leads to a complex phenotype characterized by partial diabetes insipidus, dysregulation of sodium excretion rhythms, and a significant decrease in blood pressure. Collectively, this study uncovers a major role of molecular clock in renal function.

Variability of glomerular filtration rate estimation using single injection methods in Type 1 diabetic patients

AIM

Single-injection inulin clearance (SIIC) methods without urine collection have often been compared with classical constant-infusion inulin clearance methods. Therefore, we used repeated SIIC measurements to prove the hypothesis of a possible overestimation or variability of inulin clearance in Type 1 diabetic patients.

METHODS

Two SIIC periods, glomerular filtration rate 1 and 2 (GFR 1, GFR 2) were performed consecutively on the same day. In diabetic patients, GFR 3 was measured several days later at the same time of day as the GFR 1 had been done. The calculation used a two-compartment modelling system (TCM) which showed excellent agreement to ratio of dose over area under the curve (D/AUC) calculation.

RESULTS

Twelve normotensive Type 1 diabetic patients (mean and SD), age 39 (10.7) years, diabetes duration 20 (10.7) years, HbA1c 8.5% (0.82%), albuminuria 13.8 (15.7) mg/24 h and six controls, age 26 (2.6) years were examined. Healthy controls showed an excellent repeatability between GFR 1 111.8 (11.44) and GFR 2 110.8 (11.41) ml.min-1.1.73 m2-1. However, in diabetic patients there was a highly significant decrease between GFR 1 129.4 (11.86) and GFR 2 118.1 (13.05) ml.min-1.1.73 m2-1. GFR 1 with 129.4 (11.86) ml.min-1.1.73 m2-1 did not differ significantly from GFR 3 with 129.9 (12.40) ml.min-1.1.73 m2-1 in diabetic patients (P < 0.839).

CONCLUSIONS

In contrast to normal subjects, in Type 1 diabetic patients single-injection inulin clearance technique showed a clinically relevant decrease in GFR on two repeated measurements on the same day. Overestimation of GFR by the first inulin clearance may be caused by incomplete inulin distribution in the slow compartment. Diabet. Med. 18, 464-468 (2001)

Estimation of glomerular filtration rate by sinistrin clearance using various approaches

Two protocols for the determination of glomerular filtration rate (GFR) from sinistrin clearance are considered: a bolus injection and a bolus followed by infusion. On both occasions, serial blood and urine samplings are scheduled up to 6 h. Four calculation methods are compared for estimating GFR from the data obtained during each protocol: classical UV/P (ratio of urinary excretion rate over plasma concentration) after bolus or bolus plus infusion; 2-point (log-linear slope multiplied by apparent volume of distribution); D/AUC (ratio of dose over area under the curve) after bolus; and Rin/P (ratio of infusion rate over steady-state concentration) during infusion. Some refinements of the calculations are devised. Data are simulated by running a bicompartmental pharmacokinetic model with renal elimination, and contaminating the values with an array of random errors. The statistical performance of the respective calculation methods is assessed by graphical means. The UV/P method performs poorly during 2 hours following the bolus; on both bolus and infusion data, it suffers from imprecision on the urinary volume. The 2-point method is acceptable between 1 and 4 h after bolus; later, the estimates become much less precise. The D/AUC method appears highly reliable when integrating the concentrations up to 3 h after bolus; it requires extrapolation towards infinity. The Rin/P method is satisfactory if applied later than 3 to 4 h after the loading dose. The advantages and drawbacks of each methods must be evaluated in relation with the particular clinical setting in which GFR is to be estimated. D/AUC represents the most advisable approach for snapshot renal testing in subjects or patients without important renal impairment.

Sinistrin clearance for determination of glomerular filtration rate: a reappraisal of various approaches using a new analytical method

Several approaches are available to estimate the glomerular filtration rate (GFR) from the sinistrin clearance. To compare such approaches, GFR was estimated in six healthy volunteers, both after a bolus injection and a bolus dose followed by a 6-hour infusion. A recently developed high-performance liquid chromatography method was used for the determination of sinistrin levels, enabling precise measurements in plasma and urine samples with high sensitivity. Blood and urine were sampled up to 6 hours. Four calculation methods for estimating GFR were applied: 1) classical ratio of urinary excretion rate over plasma concentration (UV/P); 2) two-point (log-linear regression slope times monocompartmental volume of distribution) after bolus; 3) ratio of dose over area under the curve (D/AUC) after bolus; and 4) ratio of infusion rate over steady-state concentration during infusion (Rinf/P). The results obtained by fitting a pharmacokinetic model to all the plasma and urine data served as the standard against which the performance of the respective calculation methods were examined. The UV/P method performed poorly on bolus data, mainly by underestimating GFR at late times; on both bolus and infusion data, it suffered from important imprecisions on the urinary volume. The two-point method appeared applicable only between 2 and 4 hours after the bolus dose. The D/AUC method with extrapolation to infinity was highly reliable when integrating the concentrations up to 3 hours or more after the bolus dose. The Rinf/P method was satisfactory if applied later than 2 to 3 hours after the loading dose. The advantages and drawbacks of each method have to be evaluated in relation to the particular clinical setting in which GFR is to be estimated.

Endogenous variations and sodium intake-dependent components of diurnal sodium excretion patterns in dogs

1. Automated, sequential, 20 min urine collections were made to provide a record of diurnal variations of urinary sodium excretion (UNaV) in seven dogs, in which the same daily intake of sodium, potassium and water was administered, at first orally (between 08.30 and 08.50 h) on day 1 and then by i.v. infusion at a constant rate on days 2 and 3. This basic protocol was employed for two different levels of sodium intake: normal (NSI; 2.5 mmol (kg body wt)-1 (24 h)-1) and high (HSI; 14.5 mmol (kg body wt)-1 (24 h)-1). 2. The aims were: firstly, to establish the diurnal pattern of UNaV under these circumstances; secondly, to find out whether the quantity of sodium administered influences this diurnal pattern; and thirdly, to distinguish endogenous fluctuations from intake-dependent components in the UNaV excretion patterns. 3. On day 1 (oral intake) all dogs exhibited a similar excretion pattern, which peaked between 13.00 and 15.00 h on both diets and then diminished again over the remainder of the 24 h period. 4. On days 2 and 3 (infusion) UNaV fluctuated within a considerable range. 5. On HSI, the maximal UNaV rates on day 1 were about double those observed on infusion days. On HSI, UNaV during infusion days seems to consist of a constant basal component of about 5-6 mumol (kg body wt)-1 min-1 upon which a fluctuating component is superimposed. The basal component may be a reactive homeostatic response to the high sodium intake, whereas the superimposed fluctuating component may reflect endogenous variations.(ABSTRACT TRUNCATED AT 250 WORDS)

Masking in humans: the problem and some attempts to solve it

Different types of masking are discussed together with an account of the masking effect that the sleep-wake cycle exerts upon the circadian rhythms of body temperature and urinary excretion. The relative importance to masking of the several components of differences between sleeping and wakefulness are then assessed. Means to deal with the problem of masking fall into two major categories. These attempt to minimise masking effects by protocols such as constant routines or control days, and mathematical models which separate results obtained in the presence of masking influences into endogenous and exogenous components. (The problem of the extent to which masking influences can render the endogenous component of a rhythm an impure reflection of the internal oscillator is considered also.) These different techniques are compared with respect to their usefulness and assumptions. Finally, a brief speculation is given of the usefulness of masking.

Paired recordings from supraoptic and paraventricular oxytocin cells in suckled rats: recruitment and synchronization

Oxytocin cells in the paraventricular (p.v.) and contralateral supraoptic (s.o.) nuclei were pair-recorded (with two micro-electrodes) in suckled rats after being anaesthetized with urethane (1.2 g/kg), to study the synchronization of their neurosecretory bursts, the importance of cell recruitment and their firing characteristics. The synchronization of paired bursts was determined by measuring the onset time-lag (time in milliseconds between the onset of two corresponding bursts) and the maximum firing time-lag (time in milliseconds between the two shortest interspike intervals for the corresponding bursts). For each cell, the characteristics studied were: the background activity and the frequency and amplitude (total number of spikes) of the neurosecretory bursts. All paired p.v.-s.o. cells recorded were activated simultaneously 12-18 s before each milk ejection. The onset of a burst could vary either way, up to 680 ms, in relation to the other (mean onset time-lag was 206 +/- 18 ms; n = 85) but the maximum activation periods fitted more closely, the mean maximum firing time-lag being 122 +/- 14 ms (n = 64). Both parameters varied randomly, in duration and order from one pair of cells to another, from one pair of bursts to another for successive bursts of a given pair of cells and independently, whether the cells were in the p.v. or the s.o. nucleus. However, in most cases, the neurosecretory burst with the highest amplitude began and reached its peak firing rate before the corresponding burst from the other cell. Cell recruitment was observed when the milk ejection reflex began, for both the p.v. and the s.o. cells. The bursts of the non-responsive cells developed progressively with the reflex, but, as soon as a cell was recruited, all its successive bursts were simultaneous with those of the first-recruited oxytocin cells. During a regular pattern of milk ejections, the mean background activity of sixty p.v. cells (3.1 +/- 0.2 spikes/s) was significantly higher than that of their s.o. counterparts (1.9 +/- 0.2 spikes/s). Nevertheless, the mean amplitude of the neurosecretory bursts of the sixty p.v. cells (49 +/- 3 spikes) did not differ significantly from that of their s.o. counterparts (55 +/- 4 spikes).(ABSTRACT TRUNCATED AT 400 WORDS)

Electrophysiological evidence for facilitatory control of oxytocin neurones by oxytocin during suckling in the rat

Antidromically identified paraventricular neurones were recorded simultaneously with intramammary pressure in urethane (1.2 g/kg) anaesthetized rats during suckling. The correlation of the firing pattern of these neurones with milk ejection enabled distinction between oxytocin and vasopressin neurones. Oxytocin neurones displayed a short (2-6 s) characteristic high-frequency burst of spikes. This activation probably occurred simultaneously in all oxytocin neurones 12-18 s before milk ejection and was regular in both frequency and amplitude (total number of spikes). The role of neurohypophysial peptides and analogues in the control of these characteristics was studied. Injecting 10 pg, 100 pg and 1 ng of oxytocin into the 3rd ventricle increased background activity of slow-firing oxytocin neurones (less than 3 spikes/s) and had a strong dose-dependent facilitatory effect on the milk ejection reflex, increasing both the amplitude and frequency of neurosecretory bursts. No effect was observed on non-neurosecretory neurones. Such injection also triggered the milk ejection reflex when it had not appeared an hour after suckling began. Oxytocin did not itself induce neurosecretory activation, which only appeared if the young rats were sucking. Injecting oxytocin into the lateral ventricle was less effective than into the 3rd ventricle. No effect was observed after injection into the venous blood or into the 4th ventricle, which suggested that oxytocin acts in the hypothalamus. Injecting mesotocin or isotocin into the 3rd ventricle had a facilitatory effect similar to that of oxytocin but vasopressin, vasotocin, MIF I (pro-leu-gly-NH2, terminal triplet oxytocin) or bovine neurophysins I and II did not modify neurosecretory activation or the milk ejection pattern. Injecting an oxytocin antagonist, ([1(beta-mercapto-beta, beta cyclopentamethylene propionic acid), 8-ornithine] vasotocin, d(CH2)5OVT) into the 3rd ventricle decreased milk ejection frequency and considerably delayed the reappearance of the first milk ejection. This resulted from a decrease in both frequency and amplitude of neurosecretory bursts, which were too small to induce detectable oxytocin release. Moreover, d(CH2)5OVT suppressed the facilitatory effect of exogenous oxytocin. Under normal conditions, endogenous oxytocin seemed to be involved in the control of neurosecretory activation. Injecting 1 ng oxytocin or 1 or 10 ng vasopressin into the 3rd ventricle did not modify the firing pattern of vasopressin neurones whether activated by hyperosmotic stimulation (1 ml NaCl, 9% solution (w/v) I.P.) or not.(ABSTRACT TRUNCATED AT 400 WORDS)

Circadian variation in human stature

The aim of this study was to monitor the creep in stature due to compression and its recovery over 24 hr in eight adult males. Measurements of stature were made at nine times during the 24-hr cycle using a purpose built metal frame tilted 5 degrees to the vertical. Accessories for standardization of posture and prevention of unwanted muscular tension included a series of microswitches on the frame, cross-beams for controlling spinal curvatures, slit spectacles used in conjunction with a mirror for proper head alignment. A dead load BAYE micrometer recorded stature to 0.01 mm. A significant circadian rhythm was established, the trough to peak variation being 19.3 mm or 1.1% of overall stature. Peak stature was measured at 0730 on awakening and the trough occurred at midnight before assuming a recumbent posture for sleep. Altogether 71% of the height gained during the night was achieved in the first half of the night's sleep. Over 50% of the height loss in a day was lost within the first hour of rising, 80% being lost within 3 hr of arising: the rate of creep decelerated throughout the remainder of the waking day. It is concluded that the rate of change in creep throughout the day varies, being greatest in the morning whilst distension is most pronounced in the early hours of sleep.

The use of constant routines in unmasking the endogenous component of human circadian rhythms

A major problem in the study of the internal clock(s) that drives human circadian rhythms is that due to the effect produced by rhythmicity of habits and external influences ('masking'). A particularly potent factor in this respect is the sleep-wake cycle. It is anomalous that, even though this masking influence is widely accepted, most studies of circadian rhythmicity have been performed in the presence of such interferences. A protocol is described, the constant routine, by which these exogenous influences can be minimized, thereby enabling a closer scrutiny of the internal clock(s) to be made. An account is given of the different circumstances in which the constant routines have been used together with the results derived from such studies. Briefly, they indicate that nychthemeral studies can give misleading information about the rate of adjustment of the internal clock to various manipulations, e.g. time-zone transition, shift work. In addition, future studies making use of constant routines are described, in particular those which might enable the presence of more than one internal clock to be established.

Does 'anchor sleep' entrain circadian rhythms? Evidence from constant routine studies

Experiments have been performed in an isolation unit to investigate the effects of abnormal sleep-waking schedules upon circadian rhythms of renal excretion and deep-body temperature. In confirmation of previous work, nychthemeral rhythms appeared to be 'anchored' to a 24 h period if 4 h sleep was taken regularly each day, even though another 4 h was taken irregularly. The endogenous components were investigated by assessing circadian rhythmicity under constant routine conditions, that is, when rhythmic influences in the environment and sleep-waking pattern had been minimized. Analysis of the constant routine data indicated the presence of a rhythmic component which had been stabilized to a period of 24 h by the 'anchor sleep'. In addition, a delayed component was also present. The starting time of the constant routines produced a direct effect upon the rhythms, which was presumed to result from removing the 'masking' effect that sleep normally exerts upon rhythms. There was some evidence that the relative importance of the masking effect and the delayed component depended upon the variable under consideration. The implications of these findings, in terms of the effects of anchor sleep, the presence of more than one internal clock and the usefulness of constant routines, are discussed.