Effect of environmental lighting on sexual behavior and testosterone levels of female rats

Lack of evidence for meteorological effects on infradian dynamics of testosterone

Climatic factors are known to influence the endocrine system. Previous studies have shown that circannual seasonal variations of testosterone might be partly explained by changes in air temperature. Whether infradian variations are affected by meteorological factors is unknown. To analyze possible effects of meteorological parameters on infradian variations of salivary testosterone levels in both sexes, daily salivary testosterone levels were measured during 1 month in 14 men and 17 women. A correlation analysis between hormonal levels and selected meteorological parameters was performed. The results indicate that high testosterone levels are loosely associated with cold, sunny and dry weather in both sexes. However, only the correlations between testosterone and air temperature (men) and actual cloudiness (women) were statistically significant (p < 0,05). Although some correlations reached the level of statistical significance, the effects of selected meteorological parameters on salivary testosterone levels remain unclear. Further longer-term studies concentrating on air temperature, cloudiness and average relative humidity in relation to the sex hormone axis are needed.

Effects of constant bright illumination on reproductive processes in the female rat

Physiological and behavioral reproductive changes in the female rat which occur under constant bright illumination (LL) are examined. The development of LL-induced persistent estrus (PE) is discussed first in relation to other conditions in which PE is displayed. Next, mechanisms are reviewed which may account for the LL-induced changes. These include: (1) role of the retina, the retinohypothalamic tract and the suprachiasmatic nucleus; (2) influence of adrenal, pineal and Harderian glands; and (3) disruptions in either the 4-day endocrine rhythms or circadian neural component of the estrous cycle. Additional topics which are examined include the ontogeny of age-induced PE and the effects of LL on hormone receptor binding, puberty, sexual receptivity and mating.

Similarities in the regulatory patterns of pregnant and cycling rats

The patterns of food intake, water intake and body weight of the female rat during the estrous cycle and pregnancy were determined. During the 4-day estrous cycle, intake and body weight were reduced on the day of ovulation. In contrast, animals with 5-day estrous cycles reduced intake and body weight for 2 days, the day prior to ovulation as well as on the day of ovulation. Intake of pregnant rats around the time of birth was compared to that of cycling females and similarities were observed. The peripartum pattern of food intake was systematically related to the length of the gestation period. Rats that littered 22 days after mating showed depressed food intake only on the day of birth. Those with 23-day gestation periods decreased food intake both on the day of birth and on the following day. The similarities in the intake patterns during 4- and 5-day estrous cycle to that of the peripartum segment of 22- and 23-day pregnancies suggest that there may be common neuroendocrine factors controlling these behaviors during the two reproductive periods.