The relationships between human pineal function and thermoregulation at rest and during exercise

• Main Author: Marrin, Kelly
• Published: Liverpool John Moores University 2012
• Subjects: 612.492
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570700

The pineal gland and its secretory product, melatonin, have a fundamental role in the control of human circadian rhythms. Most studies have investigated circadian variation in Pineal function at rest, and an inverse relationship between melatonin and core temperature rhythms has been reported. Nevertheless, there is a lack of research on these relationships during exercise. Such research is important for ascertaining how much exercise 'masks' endogenous secretion of melatonin as well as for explaining how exercise itself influences the circadian system in humans. The studies in this thesis are designed to help fill this dearth of knowledge in exploring relationships between circadian variation in melatonin 'and core body temperature at- rest and during exercise Because most past studies have involved small sample sizes, meta-analytical methods were employed in study 1 to determine the precise effects of exogenous melatonin on core body temperature and explore the impact of various moderating variables on this temperature change. Following an extensive literature search, 33 studies involving a total of 193 participants and 429 separate melatonin ingestions were meta-analysed. The weighted mean (95% CI) reduction in body temperature was found to be 0.21 (0.18-0.24) DC. Gender and time of day of melatonin ingestion had negligible effects on this reduction (P>0.05). A linear, but shallow, dose- response relationship between melatonin and temperature reduction of 0.013 QC.mg-l within the dose range of 0.03 to 10 mg (P<O.OOOl) was found. The mean hypothermic effect was 0.13 (0.05-0.20) DC for oral temperature compared with 0.26 (0.20-0.32) DC for tympanic and 0.22 (0.19-0.25) DC for rectal temperature. These data indicate that the hypothermic effect of melatonin is clinically significant and robust across genders and time of day. The meta-regression revealed a linear dose- response relationship that was, nevertheless, quite shallow in practical terms, thus suggesting that low-dose melatonin-containing foods may mediate hypothermic effects. The hypothermic effect was lowest for oral temperature, probably because this site is more prone to the masking influences of the environment.