Diurnal rhythms in neurohypophysial function

Abstract

The neurohypophysial hormones oxytocin and vasopressin show daily rhythms of secretion with elevated hormone release during the hours of sleep. This pattern can be modulated by ovarian steroids and alters with age. The pattern appears to he due in part to the nocturnal increase in melatonin secretion, which stimulates hormone release in man, while being inhibitory in the rat. Pinealectomy alters both the 24 h pattern of neurohypophysial hormone release in the rat and the firing rate of magnocellular supraoptic nucleus neurones. There is also a reduced hormone release in response to hypovolaemia and raised plasma sodium concentration compared to sham operated animals, with a smaller increase in neuronal activity, as determined by immediate-early gene expression. The normal responses can be restored by nocturnal administration of melatonin. Melatonin also influences the neurohypophysial hormone response in the human to known stimuli of release, such as raised plasma osmolality, exercise and insulin-induced hypoglycaemia. Recent studies have revealed that not only does the release of vasopressin and oxytocin vary over each 24 h, but the respective renal and pregnant uterine responses also show diurnal variations. Experimental Physiology (2000) 85S, 17YS--186s.

Mood and Oxytocin Blood Levels in Physically Active Women with and without Oral Contraceptive Use in Relation to Seasonal Daylight Variation

“…Because significant circadian and seasonal periodicity in various endocrine functions can occur [15,19,20] we found it crucial to determine if that was applicable to Oxytocin levels and to investigate if seasonal variability in daylight hours interacts with Oxytocin, POMS, and their relationship. Measuring seasonal variation in hormonal systems is important for providing a general background and to provide basic data for research in this field.…”

“…Oxytocin can be modulated by ovarian steroids [20] hence to elucidate basic hormonal data in women, the use of OC has to be considered. Our findings indicated seasonal differences in Oxytocin, which showed a different pattern in women using OC compared to those not using OC (Figure 1).…”

“…Studies have shown that secretion of Oxytocin increased during sleep in humans [15,20] although Nathorst Boos, et al [14] found minimal diurnal variation of Oxytocin but substantial differences in basic levels between individuals. No studies have so far been performed concerning seasonal periodicity of Oxytocin.…”

Oxytocin and Epstein‐Barr virus: Stress biomarkers in the postpartum period among first‐time mothers from São Paulo, Brazil

“…The reliability and physiological relevance of salivary OT remains in question (Horvat-Gordon et al, 2005), while drawing and storing whole blood in this field setting was impracticable. Participants expressed and collected a milk sample between 8am and 6pm on the day of each interview; samples were collected between 9 these hours to avoid registering the nocturnal circadian increase of OT (Forsling, 2000). In most cases participants expressed the sample during the interview.…”

Melatonin: pregnancy and labor

“…Мелатонин как регулятор суточных и годовых циклов физи-ологических функций организма и, в частности, репродуктив-ной системы животных и человека в последние годы все боль-ше привлекает внимание исследователей [19,34,87,88,105]. Однако не только изменения продукции мелатонина в зави-симости от продолжительности светового и темного времени суток, определяющие сезонные и суточные ритмы перестрой-ки системы репродукции, но его уникальные антиоксидант-ные, иммуномодулирующие свойства так же, как и участие в метаболических процессах на клеточном и тканевом уров-нях обеспечивают репродуктивное здоровье человека [22,39,61,91,102].…”