[Morphological characteristics of the thyroid glands of Macaca rhesus monkeys normally and in different types of hypokinesia]. / Morfologicheskie osobennosti shchitovidnykh zhelez obez'ian makaka reuz v norme i pri razlichnykh vidakh gipokinezii.

Thyroid glands and C-cells of Macaca rhesus were examined histologically, electron microscopically and morphometrically. The examinations were performed on 6 intact and 7 hypokinetic rhesus monkeys which were kept in a suspension device for 2 months, small cages for 2 months or in a head-down position (7 days in a horizontal position and then 11 days in a head-down position at -6 degrees). The experiment with a diminished motor activity and a normal support function of the lower limbs (maintenance in small cages), in spite of its long duration, produced no structural changes in the parenchyma or C-cells. The 18-day bed rest test was followed by a hypofunction of the thyroid gland, inhibition of hormonal synthesis and secretion without distinct changes in C-cells. Unlike previous experiments, the suspension study led to hyperplasia and hypertrophy of C-cells and increase of their nuclear volume. Activation of C-cells can be regarded as an adaptive reaction aimed at stabilizing bone calcium.

[Diurnal and seasonal variations in the plasma levels of cortisol and its precursors in Macaca mulatta]. / Sutochnye i sezonnye kolebaniia urovnei kortizola i ego predshestvennikov v plazme krovi obez'ian makak rezusov.

The presence of circadian and seasonal rhythms of cortisol, 11-desoxycortisol, 17 alpha-hydroxyprogesterone and 17 alpha-hydroxypregnenolone in the blood plasma of rhesus monkeys was found by the radioimmunological technique. The circadian rhythm was characterized by the highest content of all the steroids early in the morning followed by its decrease to the minimum in the late evening. The time-course of the precursor content was in good agreement with the hormonal level throughout 24 hours. The circadian rhythm pattern did not depend on the season, though the average diurnal concentrations varied considerably, being the highest in spring. Possible mechanisms of circadian and seasonal rhythms of the adrenal gland activity are discussed.

[Diurnal and seasonal rhythms of androgen content of the plasma in Macaca mulatta]. / Tsirkadnye i sezonnye ritmy soderzhaniia androgenov v plazma krovi obez'ian makak rezusov.

Circadian and seasonal rhythms of testosterone-, 5 alpha-dihydrotestosterone and androstendione content were studied in the blood plasma of adult male macaca rhesus by radioimmunoassay. The circadian changes in androgen concentration depended on the seasonal and experimental conditions. Circadian variations of androgen concentration had a definite, significant character in the animals, which were previously adapted to experimental conditions. Minimum testosterone and 5 alpha-dihydrotestosterone content was noted at 18 o'clock and maximum at 21 to 24 o'clock. Circadian rhythm of androstendione content was characterized by a decrease in the evening, by a rise within the night and by the maximum value at 6 to 9 o'clock. Significant seasonal changes were observed in mean daily testosterone- and 5 alpha-dihydrotestosterone-, but hot in androstendione content. High levels of both steroids were recorded in autumn and winter, being lower in spring and the lowest in summer.

[Circadian rhythm of hormonal activity of Macaca mulatta adrenal glands in hypokinesia]. / Tsirkadnye ritmy gormonal'noi aktivnosti nadpochechnikov makak rezusov pri gipokinezii.

The influence of the limited motion activity on circadian rhythm of cortisol. 11-desoxycortisol, 17-hydroxyprogesterone, 17-hydroxypregnenolone and aldosterone content in the blood plasma was studied in experiments on male Macaca rhesus monkeys. Under conditions of free behavior, the maximum steroid content in the blood plasma was seen early in the morning and minimum in the evening hours. The muscle activity restriction did not change the character of circadian variations but corticosteroid peak levels were markedly decreased after 7 days of hypokinesia in comparison with the control period. On the experiment prolongation the steroid content decreased throughout the whole day. The mean circadian cortisol, 11-desoxycortisol and aldosterone concentrations were significantly reduced following 2 weeks of hypokinesia. Potential mechanism of alterations mentioned and their relationships with circadian rhythms of other physiological systems under conditions of the restricted motion activity are discussed.

[Dynamics of the concentration of aldosterone, cortisol, and its precursors in the plasma of M. rhesus during long-term restriction of motor activity]. / Dinamika soderzhaniia al'dosterona, kortizola i ego predshestvennikov v plazme krovi M. rhesus pri dlitel'nom ogranichenii dvigatel'noi aktivnosti.

A significant increase in the content of cortisol and its precursors was detected in blood plasma from rhesus monkeys during the first six hours of the motor activity restriction. In the three days following, the peak concentrations of cortisol were accompanied by a fall of 17-hydroxylated precursors to the basal and lower levels. The content of cortisol attained the basal level by the end of the first week of fixation. The levels of cortisol, 11-deoxycortisol, 17-hydroxyprogesterone and 17-hydroxypregnenolone on the 17th day of hypokinesia were 77, 62, 39 and 15%, respectively, as compared with the pre-experimental period. The maximum rise of the aldosterone level in monkey plasma was seen on the 2--3d day followed by a gradual decrease in its concentrations over the entire experimental period. It is suggested that the reduced blood content of steroids during the restriction of motor activity is related to the adaptation of pituitary-adrenal system function to the decreased environmental requirements.