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Chronobiological Studies of Plasma Prolactin in Women in Kyushu, Japan, and Minnesota, USA^*

Department of Pathology, St. Paul-Ramsey Medical Center St. Paul,Minnesota 55101
the Chronobiology Laboratories, Department of Laboratory Medicine and Pathology, University of Minnesota Minneapolis, Minnesota 5545
the Second Department of Internal Medicine, Kyushu University Fukuoka, Japan

Address requests for reprints to: Dr. Erhard Haus, Department of pathology, St. Paul-Ramsey Medical Center, 640 Jackson Street, St. Paul, Minnesota 55101.

Rhythm characteristics in the about-daily (circadian), about-monthly (circatrigintan), and about-yearly (circannual) frequency ranges were assessed for plasma PRL, which is possibly involved in the development of human breast cancer. Clinically healthy subjects in Minnesota, USA, and Kyushu, Japan, were sampled around the clock once in each season. Possible differences that could reflect the large difference in breast cancer incidence in these two geographic locations wereinvestigated. If sampling techniques as extensive and systematic as those used in this study are employed, Japanese women have a slightly higher plasma PRL concentration than women in Minnesota, but these differences depend largely on nightly values during the winter. A prominent circadian rhythm characterizes plasma PRL in most subjects investigated. In winter and spring, Japanese women have a much larger circadian amplitude than Minnesotan women, mostly as a result of markedly highe concentrations during nightly rest and/or sleep. The larger circadian amplitude in winter and spring of the Kyushuans is the result of a circannual cycle, which, with the sampling schedule used, is not detected in Minnesotans. Rhythm parameters also differed as a function of age.

Certain rhythm characteristics correlated with breast cancer risk. This result should be checked on much broader populations. The task is facilitated by sampling requirements based costeffectively on fewer yetpertinent sampling times, selected on the basis of the time-specified tolerance intervals here documented.

^* This work was supported by the National Cancer Institute (CP- 55702 and CA-14445); the General Clinical Research Centers Program, Division of Research Resources, NIH (RR-400); the USPHS (GM- 13981); the St. Paul-Ramsey Medical Education and Research Foundation; the National Institute of Aging (AG-00158), and the National Institute of Occupational Safety and Health (OH-00631).

Received December 6, 1979.

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