Daily and Seasonal Rhythms of Melatonin, Cortisol, Leptin, Free Fatty Acids and Glycerol in Goats
Year: 2008
Type: dissertation
Abstract: This thesis examined the effect of daily and annual lighting conditions on the blood levels of the hormones melatonin, cortisol and leptin and the lipid metabolism of free fatty acids (FFAs) and glycerol in female goats. The blood levels of these substances were also measured in long-term total darkness (endogenous rhythm). The duration of melatonin secretion in goats closely follows the length of the dark phase of the day, except in winter, when the duration is significantly shorter. In total darkness, the goats display two types of endogenous melatonin patterns: a "winter pattern" in winter, early spring, early fall and late fall, and a "summer pattern" in late spring and summer. The results showed that in addition to the light-adjusted overt melatonin rhythm, the endogenous melatonin secretion can be modulated by circannual clock mechanisms and/or long-term photoperiodic history. Serum cortisol levels had no significant daily rhythm at any time of the year, nor are there any differences in the profiles between annual lighting conditions and total darkness. In winter the overall concentrations were higher than in any other season. The results suggest that any/the circadian variation of cortisol secretion is masked by external factors, probably by the feeding schedule, and that the seasonal variation in the overall cortisol levels is likely to be related to the changes in photoperiod. The lipid metabolism of goats seems to be regulated by light; no significant contribution of leptin levels could be shown. Concentrations of plasma FFAs and glycerol exhibit significant daily and seasonal variations. The photoperiod was found to trigger a nocturnal fall and morning rise of FFAs levels, while low levels of glycerol were associated with feeding. In total darkness, FFA and glycerol rhythms were unstable. The close relationships between the daily variations of melatonin and FFAs levels result from both variables being controlled by light-dependent mechanisms. The results do not rule out a possible effect of melatonin on the daily FFAs profiles, but they show that melatonin secretion alone could not completely explain the daily FFAs profiles.
Source: Työväentutkimus Vuosikirja
Author: Aino Alila‐Johansson
Language: English
Subfield: Endocrine and Autonomic Systems
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1145407213