This study was aimed at elucidating the possible effects of a large annual variation in photoperiodicity on the secretory activities of the pineal gland, pituitary and testes. Serum daytime melatonin, FSH, LH, prolactin (Prl), testosterone and oestradiol concentrations were determined monthly over a year in 24 healthy young adult men (except for melatonin which was analysed only in 11 subjects) in northern Finland, where the day length is 22 h in mid-summer and 3.5 h in mid-winter. Serum daytime melatonin levels showed two annual peak values, in December and May, and a nadir was observed in August. The absolute values of the other hormones measured did not show significant month to month variation over the observation period. When hormone levels were calculated as percentages of the individual annual means, several significant differences were found between monthly levels. The melatonin peak in May (133 +/- 20%, SE, of the annual mean) was associated with significant increases in LH (110 +/- 4%) and FSH (107 +/- 3%). Prl levels (115 +/- 9%) reached a maximum in January. The nadirs of melatonin and the pituitary hormones measured were seen in August. Oestradiol showed the highest values in April-June, but no significant variation was found in serum testosterone levels. Positive correlations were observed between FSH and LH (r = 0.41, P less than 0.01), and Prl and LH (r = 0.26, P less than 0.01), whereas Prl and testosterone (r = -0.17, P less than 0.01) were inversely correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

Circannual concentrations of melatonin, gonadotrophins, prolactin and gonadal steroids in males in a geographical area with a large annual variation in daylight.

Low ambient temperature during winter seasons is typical for all circumpolar areas. This sets definite demands for every day life and work. Naked, man is quite helpless in polar winter, but he has been able to inhabit all corners of the ear th using technical developments in clothing and housing. Yet there are situations, especially in circumpolar areas, when bodily exposure to cold environment cannot be avoided. Homeothermic animals protect themselves from the cold by increasing heat production and decreasing heat losses. For practical reasons man has very few means of reducing heat loss by natural ways. Heat is produced by muscular work and by chemical reactions. Oxidative phosphorylation of dietary fuels such as carbohydrates and fats brings forward energy-rich phosphate compounds, at the same time liberating heat for bodily uses. Thyroid and adrenal hormones and the sympathetic nerve system maintain and regulate the oxidative phosphorylation that occurs mainly in the mitochondria of brown and white fat and skeletal muscle tissues. It is notewor thy that animals from which thyroid or adrenal glands are removed do not tolerate cold. (Int J Circumpolar Health 2002; 61(3):265-276)

Cold exposure and hormonal secretion: A review

A group of fourteen men (73 +/- 5 yr of age), and eighteen women (77 +/- 7 yr of age) institutionalized at the Berceni Clinical Hospital, Bucharest, Romania, were studied over a 24-hr span once during each season (winter, spring, summer and fall). All subjects followed a diurnal activity pattern with rest at night and ate three meals per day with breakfast at about 0830, lunch at about 1300 and dinner at about 1830. The meals were similar, although not identical for all subjects during all seasons. On each day of sampling blood was collected at 4-hr intervals over a 24-hr span. Seventeen hormonal variables were determined by radioimmunoassay. Statistically significant circadian rhythms were detected and quantitated by population mean cosinor analysis in pooled data from all four seasons in both sexes for ACTH, aldosterone, cortisol, C-peptide, dehydroepiandrosterone-sulfate (DHEA-S), immunoreactive insulin, prolactin, 17-OH progesterone, testosterone, total T4 and TSH. In women, estradiol and progesterone also were determined and showed a circadian rhythm during all seasons. Total T3 and FSH showed circadian rhythm detection by cosinor analysis in the men only; LH showed no consistent circadian rhythm as group phenomenon in men or women. A circannual rhythm was detected using the circadian means of each subject at each season as input for the population mean cosinor in the women for ACTH, C-peptide, DHEA-S, FSH, LH, progesterone, 17-OH progesterone and TSH. In the men, a circannual rhythm was detected for ACTH, FSH, insulin, LH, testosterone and T3. There were phase differences between men and women in ACTH, FSH and LH. In those functions in which both the circadian and circannual rhythms were statistically significant, a comparison of the amplitudes showed in the women a higher circannual rather than circadian amplitude for DHEA-S. In 17-OH progesterone, TSH and C-peptide, the circadian amplitude in women was larger. In men, the circannual amplitude of T3 was larger than the circadian amplitude and in insulin the circadian amplitude was larger than the circannual amplitude. There was no statistically significant difference between the circadian and circannual amplitudes in the women in ACTH and progesterone and in the men in ACTH and testosterone.

Circadian and Circannual Rhythms of Hormonal Variables in Elderly Men and Women

Eighteen 24-h profiles of plasma prolactin (PRL) were obtained at 15- or 30-min intervals in 10 healthy male volunteers, investigated in summer, autumn, and winter. The sleep-associated elevation of PRL concentration was observed in all profiles. Sixteen of 18 profiles were bimodal with a daytime, as well as a nighttime, elevation of plasma PRL. On the average, the magnitude of the daytime acrophase corresponded to about 50% of the magnitude of the nocturnal acrophase. The absolute increment of PRL from morning nadir to nocturnal acrophase appeared to be independent of the basal PRL level. Approximately 40% of the variability of plasma PRL values corresponded to episodic fluctuations. A total of 210 PRL spikes were found in the 15 24-h profiles obtained at 15-min intervals. Each PRL spike was evaluated in terms of its significance, of the duration of its ascending and declining portions, of its magnitude defined as the relative elevation over the preceding trough, and of the apparent half-life. Sixty-five percent of the spikes lasted less than 75 min. The apparent half-lives were longer (median, 42 min) than other estimations of the half-life of PRL (around 20 min) and were positively correlated with the level before spiking, suggesting that PRL is secreted in pulses of variable amounts superimposed to a continuous basal secretion. The magnitude of the spikes corresponded to an average relative increment of 116%. No seasonal modulation could be demonstrated. The 24h pattern of PRL secretion, although occurring around basal levels varying considerably from one individual to another, was otherwise very reproducible. The 24-h mean plasma PRL level and the number of secretory spikes appeared to be characteristic of a given individual.

Quantitative analysis of spontaneous variations of plasma prolactin in normal man.

BACKGROUND: The role of prolactin in the regulation of ovarian folliculogenesis and corpus luteal function and in particular its relationship to atresia in these structures is as yet unclear. We established a model of apoptosis in which to examine the actions of prolactin. METHOD: Granulosa cells collected from IVF-flush were cultured at 0.1‐0.3310 6 cells/well in growth media for 48 h, placed into serum-free media for 24 h prior to dosing for 24 h. Dose responses to C2-ceramide and prolactin were performed. Cells were then treated with an apoptotic dose of C2-ceramide alone, prolactin (100 ng/ml) alone or a combination of the two. Cell death was assessed by Trypan Blue cell counting and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; Thiazolyl Blue] assay and apoptosis confirmed by morphological assessment and flow cytometry. RESULTS: C2-ceramide (0‐40 mmol/l) induced a dose-dependent increase in cell death (63.8% increase at 40 mmol/l) and, morphologically, cells exhibited classical features of apoptosis. Prolactin alone had no effect on metabolic activity or total cell number. On coincubation, prolactin alone had no effect on cell death, whereas C2-ceramide induced an ~62.6% increase in apoptosis, which was inhibited in the presence of prolactin. CONCLUSIONS: Prolactin may contribute significantly to early corpus luteum formation and survival by acting as a potent antiapoptotic factor for human granulosa cells.

Prolactin acts as a potent survival factor against C2‐ceramide‐induced apoptosis in human granulosa cells

Serum samples were obtained from 7 subjects (6 men and 1 woman) in the morning (09.00 h) and in the afternoon (15.00 h) of each week for a period of 13 months and assayed for prolactin by RIA. In addition, 4 female monkeys were sampled once weekly in the afternoon for approximately two years. The data were analyzed for cyclicity by power spectrum analysis. In both species a serum prolactin circannual cycle was not obvious. In most subjects statistically significant (P less than 0.05) cycles were observed; however, there was considerable variability among individuals in the duration of the cycle, which ranged between 4 and 50 weeks. A similar result was also observed for the monkey data; here the cycles ranged between 7 and 51 weeks. The physiologic significance of these cycles is unknown at present. It is suggested that although there appears to be no diurnal serum prolactin circannual cycle, this does not rule out the possibility that there may be a nocturnal circannual cycle.

Lack of a circannual cycle of daytime serum prolactin in man and monkey.

Follicular fluid from mature preovulatory follicles was examined for the presence of prolactin (PRL) heterogeneity. Two pools of follicular fluid aspirates were used: one from follicles in which the ova were successfully fertilized in vitro and the other from follicles in which the ova were not successfully fertilized. Follicular fluid aspirates were concentrated by ultrafiltration and subjected to Sephadex G-100 gel chromatography. Fractions were assayed for immunoactive PRL by radioimmunoassay (RIA-PRL) and for bioactive PRL by the Nb2 lymphoma cell bioassay (BA-PRL). The major portion of RIA-PRL activity appeared as a low-molecular-weight component and accounted for 88% of the total PRL activity in the fertilized group and 87% in the unfertilized group. A high-molecular-weight component was also evident (12% and 13% for the two groups, respectively). The high-molecular-weight component in both groups was not active as PRL in the bioassay. These results demonstrate that while two immunoactive, heterogeneous forms of PRL exist in human follicular fluid when measured by RIA, it is only the low-molecular-weight form of PRL that is biologically active as established by Nb2 lymphoma cell bioassay.

Prolactin size heterogeneity in human follicular fluid: a preliminary study.

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Lack of a circannual cycle of daytime serum prolactin in man and monkey.

Prolactin size heterogeneity in human follicular fluid: a preliminary study.