Journal of investigative medicine : the official publication of the American Federation for Clinical Research
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Comparative Study
Relationship of endogenous circadian melatonin and temperature rhythms to self-reported preference for morning or evening activity in young and older people.
Morningness-eveningness refers to interindividual differences in preferred timing of behavior (i.e., bed and wake times). Older people have earlier wake times and rate themselves as more morning-like than young adults. It has been reported that the phase of circadian rhythms is earlier in morning-types than in evening types, and that older people have earlier phases than young adults. These changes in phase have been considered to be the chronobiological basis of differences in preferred bed and wake times and age-related changes therein. Whether such differences in phase are associated with changes in the phase relationship between endogenous circadian rhythms and the sleep-wake cycle has not been investigated previously. ⋯ These findings demonstrate an association between circadian phase, the relationship between the sleep-wake cycle and circadian phase, and morningness-eveningness in young adults. Furthermore, they demonstrate that age-related changes in phase angle cannot be attributed fully to an age-related shift toward morningness. These findings have important implications for understanding individual preferences in sleep-wake timing and age-related changes in the timing of sleep.
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The pituitary thyroid axis is frequently effected in human depression possibly due to alteration in hypothalamic thyrotropin releasing hormone (TRH) secretion. Since clinical recovery is associated with normalization of thyroid function, the direct effect of antidepressants on TRH expression in a well established fetal rat hypothalamic neuronal culture system was investigated. ⋯ This raises the possibility that the enhanced thyroid function in depression, which we postulate, may result in part from glucocorticoid stimulation of TRH gene expression, can be reversed by antidepressants through a direct effect on the TRH neuron. However, other mechanisms may need to be invoked in addition since basal TRH content was also reduced.
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Comparative Study
Hemodynamic response to vasopressin in dehydrated human subjects.
Despite the known potent vasoconstrictor effects of vasopressin, the role of this hormone in the maintenance of blood pressure is incompletely understood. In studies performed in animals with increased plasma vasopressin concentrations, several complex cardiovascular effects have been noted, including decreases in heart rate and cardiac output, which may account for a lack of effect on arterial pressure despite the vasopressin-induced increase in total peripheral resistance. Only a few studies have been done to assess the cardiovascular effects of vasopressin in human subjects, and most of these have been limited to measurement of heart rate and arterial pressure only. The present study was designed to identify more fully the cardiovascular effects of vasopressin when plasma vasopressin concentrations are increased by osmotic stimulation without the superimposition of major nonosmotic stimuli associated with severe volume depletion. ⋯ It is concluded from these studies that small increases in Pavp associated with moderate dehydration do not play a role in the maintenance of arterial pressure in normal human subjects in either supine or erect posture.