PubMed · 7087620
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1982-02-17. [Sleep research].. https://pubmed.ncbi.nlm.nih.gov/7087620/
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Cortisol has a pivotal role in physical and mental health, but relatively few studies have paid attention to individual differences in cortisol levels and the etiology of these differences, in particular their possible genetic basis. In this article we review the existing literature on the heritability of cortisol levels. Most of the studies, which have been carried out in genetically informative samples, lack methodological consistency with regard to frequency and timing of sample collection. The circadian rhythm in cortisol levels was often not taken into account. A power analysis shows that none of these studies used adequate sample sizes to distinguish genetic from shared environmental influences as a cause for familial aggregation. Results of a simultaneous analysis of 5 comparable twin studies suggest a heritability of 62%. Hence, we conclude that, to understand the contribution of genetic and (shared) environmental influences to variation in basal cortisol levels, future studies should be designed more rigorously with strict collection and sampling protocols, sufficient sample size and repeated measures across multiple days.
Compensation by dark-period uptake of NH(4)(+) and NO(3)(-) in the grasses Phleum pratense L. and Festuca pratensis Huds. following N deprivation during the preceding light period was investigated in flowing solution culture under an artificial 10/14 h light/dark cycle. N was supplied as either NO(3)(-), NH(4)(+) or NH(4)NO(3) at 20+/-5 mmol m(-3), available continuously or only during the dark period, for 5-10 d. Intermittent N supply did not affect total daily N uptake, growth rate or net partitioning of dry matter. Net uptake and influx of NO(3)(-) varied similarly throughout the diurnal cycle when NO(3)(-) was supplied continuously, with a marginal contribution by NO(3)(-) efflux. Influx was significantly higher and efflux slightly higher following interruption of NO(3)(-) supply during the light period. Nitrate accounted for 80% of N in xylem exudate except between hours 6-9 of the light period when the amino acid concentration increased 3-fold, primarily as glutamine. Diurnal variation in relative NO(3)(-) uptake exhibited five phases of constant acceleration/deceleration, described reasonably well assuming NO(3)(-) influx was subject to metabolic co-regulation by NO(3)(-) and amino acid levels in the cytoplasmic compartment of the roots. Accordingly, influx is determined by variation in root NO(3)(-) levels throughout the dark period and the first half of the light period, but is down-regulated by increased amino acid levels during the second half of the light period. The sharp light/dark transitions affect transpiration rate and hence xylem N flux which, in turn, affect NO(3)(-) levels in the cytoplasmic compartment of the roots and the rate of NO(3)(-) assimilation in the shoot.
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