Spectral Properties of Light Affect Plasma and Pituitary Gonadotropins in Male Rats

Abstract

In order to find out whether different light spectra have any role in regulating the gonadotropin levels in male rats, we compared the 24-hour patterns of plasma and pituitary gonadotropins in rats kept for 7 days in natural or in cool white artificial lighting (exp. I). The intensity and periodicity of the two lighting conditions were adjusted as similar as possible. Further, we measured plasma and pituitary gonadotropins in the middle of the light period and in the middle of the dark period in rats kept for 7 days under artificial lightings of three different spectra (exp. II). In both experiments, in all lighting conditions we found higher plasma levels of LH and FSH during the dark than the light period. The differences were statistically significant only when the illumination contained more long and/or short wavelengths than the usual cool white laboratory lighting. The pituitary contents of gonadotropins were not found to vary with the periodicity of lighting. In the 24-hour patterns the overall plasma levels were higher and the pituitary contents of gonadotropins lower in natural lighting than in cool white lighting. It was concluded that the spectral properties of light influence the secretion of gonadotropins in male rats, but the mechanism involved remains to be clarified.

Twenty-Four-Hour Patterns of Pineal Melatonin and Pituitary and Plasma Prolactin in Male Rats under ‘Natural’ and Artificial Lighting Conditions

“…A reason for the higheramplitude variation of melato nin in the natural lighting conditions may be the gradual changes of illuminance at dawn and dusk. The different pituitary and plasma prolactin patterns of the rats kept in the two lighting conditions might partly be explained by a stimulatory effect of melatonin on the production and secretion of prolactin, but other regulatory factors had to be involved, too.We have found earlier that in the male rats maintained in natural lighting conditions the plasma levels of gonado tropins were significantly higher at night than during the day, while in the rats under artificial lighting the day/night difference was smaller [23]. Although the biological meaning of such high-or low-amplitude daily variations is not clear, we found it interesting to measure whether other hormones would display similar 'strengthening of rhythms' in natural lighting.…”

“…The details of the experimental design have been published in connection with the results on the pituitary and plasma gonadotro pins which were measured from the same animals [23]. Only the most important facts are given here.…”

“…The periodicities of the lightings for the two experimen tal groups were adjusted equal, but there still remained sev eral differences between the lighting conditions: (1) the spectra of the daytime lightings were different -the colour temperature of natural sunlight >5,000 K [35], cool white artificial lighting 4,200 K; (2) in artificial lighting the daily illuminance was constant, but in natural lighting it varied from day to day and during the day [23]; (3) at night in natu ral lighting, but not in artificial lighting, there was a mea surable illuminance level (0.5-1 lx) produced by the street lamps outside the laboratory building, and (4) the natural illumination contained long twilight periods at dawn and dusk, while in artificial lighting there was an abrupt change from dark to light and vice versa.…”

Lighting Conditions Affect Testosterone Feedback Sensitivity in Castrated Rats

“…We used castrated rats to be able to quantify the testosterone dose. We also tested two different light spectra, because in our earlier experiments we found that light spectra has an impact on hormone secretion [ 13].…”

Effect of Neonatal Androgenization on the Testosterone Feedback Sensitivity in Adult Rats in Two Lighting Conditions

“…The Hormone Assays LH and FSH were measured by radioimmunoassay with re agents supplied by NIADDK (reference preparations: rLH-RP-2 and rFSH-RP-2) as described earlier [ 13]. The intra-assay variabili ty, calculated by the method of Abraham et al [14], was for LH 7-9% and for FSH 12-22%.…”