The physiological rhythms of subjects living on a day of abnormal length.

Abstract

4. On a 27 hr day two periods were less often present and a larger number of observed rhythms could be satisfactorily described by a single period, usually between 23 and 28 hr.5. In subjects spending a second week on a 21 hr day the circadian component was no less prominent than during the first week.6. When, after life on a 21 hr day, subjects were deprived of knowledge of time, there was evidence that the 21 hr component did not persist.7. The results are interpreted as evidence of the continuing existence of an influence with a period of around 24 hr, simultaneously with rhythmic influences resulting from the subjects' habits. On a 27 hr day there was sometimes evidence of entrainment, yielding an intermediate period.8. An attempt is made to compare the relative potency of the exogenous and of the persistent circadian influences on the several variables.

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

“…Thus it is generally accepted as having a high exogenous component (Lewis & Lobban, 1957;Mills et al 1977;Simpson et al 1970) and yet it is ranked very differently from calcium and urate (Table 3). A contributing factor might be that, under nychthemeral conditions, increases in 24 h mean excretion will result from increased diurnal uptake and, because the renal response to water intake is so rapid, this will result in an increased diurnal output.…”

“…Thus, whether the changes after non-24 h days (Mills, Minors & Waterhouse, 1977;Simpson, Lobban & Halberg, 1970), time-zone shifts (Aschoff, Hoffmann, Pohl & Wever, 1975;Elliott et al 1972) or shift work (Chaumont, Laporte, Nicolai & Reinberg, 1979;Vieux, Ghata, Laporte, Migraine, Nicolai & Reinberg, 1979) are considered, some constituents (for example, flow, calcium and urate) have large, others (potassium) small, and others (sodium, chloride) moderate exogenous components. For these reasons, the constant routine experiments were performed in which exogenous rhythmicity was minimized.…”

Does ‘anchor sleep’ entrain circadian rhythms? Evidence from constant routine studies.

“…Earlier work established that adjustment of the endogenous component to imposed time-zone shifts (Mills et al 1978b) or non-24-h days (Simpson et al 1970;Mills et al 1977) could be misinterpreted if measured under nychthemeral conditions. (Indeed the process of 'entrainment by partition' (Aschoff, 1978) seems far more common if measured under conditions that minimize exogenous influences.)…”

“…Indeed the variables have been grouped for the purposes of analyses with urinary water, phosphate, calcium and urate excretion in one group, urinary sodium and chloride in another and urinary potassium and deep-body temperature in a third. These subdivisions were based upon previous experiments (Simpson et al 1970;Mills et -al. 1977; Minors & Waterhouse, 1982) which indicated that the first group was affected mainly by exogenous influences, the last by endogenous factors and that sodium and chloride were intermediate in these respects.…”

“…This is clearly seen when human subjects live on non-24-h 'days' (Simpson, Lobban & Halberg, 1970;Mills, Minors & Waterhouse, 1977). Under these conditions, variables manifest two components to their rhythms: an exogenous component with a period equal to that of the artificial day and one which is endogenous and has a free-running period in excess of 24 h. In the isolation unit experiments (Mills et al 1977) urinary flow, urate, calcium and phosphate excretory rhythms showed marked exogenous components, deep-body temperature and urinary potassium excretory rhythms showed a marked endogenous component and urinary sodium and chloride ANCHOR SLEEP AND CIRCADIAN RHYTHMS excretory rhythms were intermediate. An implication of this is that 4-h anchor sleeps will be more likely to produce stability by masking in the cases of urinary flow, urate, etc., than temperature and urinary potassium rhythms.…”