Seasonal Variation of Plasma Glucagon Concentrations in Men

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Abstract
In an attempt to understand a role of glucagon in seasonal acclimatization in men, measurements of plasma glucagon, blood free fatty acids (FFA), blood glucose, blood ketone body (.beta.-hydroxybutyrate) and hematocrit were made in 13 male and 8 female college staff members, aged 20-42, once a month for 1 yr. Blood samples were obtained at 1600 to 1700 h, between meals. Average monthly temperatures during the study were as follows; Jan. -7.8, Feb. -5.6, March -3.7, Apr. 4.6, May 11.4, June 18.3, July 23.9, Aug. 22.0, Sept. 14.7, Oct. 7.5, Nov. 1.4, Dec. -4.2 (.degree. C). Plasma glucagon, blood FFA and blood ketone body exhibited significant monthly variation in both sexes. Plasma glucagon and blood FFA level were significantly higher in winter (Dec., Jan., Feb.) than in summer (June, July, Aug.), whereas blood ketone body level was lower in winter than in summer. Plasma glucagon level was significantly lower in female than in male subjects. A significant positive correlation was observed between plasma glucagon and blood FFA levels throughout the year. Seasonal variations of blood glucose and hematocrit were not observed. Seasonal variation in glucagon secretion is apparently associated with seasonal changes in ambient temperatures as one of the strategies for climatic acclimatization through regulation of lipid metabolism.