Pineal Arginine Vasotocin Activity Increases 200‐Fold During August in Adult Rats and Hamsters

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Abstract
In a previous study, measurements of arginine vasotocin-immunoactivity (iAVT) in immature rats over a period of 14 mo., led to the discovery of a significant yearly variation, with peak levels of iAVT in Aug. In the present study, iAVT was measured in pineals obtained from mature male and female rats and hamsters once or twice weekly from July until early Sept. 1982. For all groups, mean pineal AVT-immunoactivity was < 7 pg/gland in early July, but then increased significantly by Aug. 11-13. For hamsters, maximum values of 1272 .+-. 49 (mean .+-. SE: n = 3) and 1065 .+-. 62 pg/gland were recorded for males and females, respectively. For rats, peak values measured were 940 .+-. 12 pg/gland for males and 1040 .+-. 34 for females. The AVT-activity levels then decreased to less than 100 pg/gland by early Sept. Thus, a dramatic Aug. elevation of pineal iAVT is characteristic of hamsters as well as rats, and of mature as well as immature animals.