Influence of photoperiod on the time of parturition in the rat. I. — Effect of the length of daily illumination on normal or adrenalectomized animals

Abstract

Summary. Four groups of normal rats have been studied to elucidate the effect on the time of birth of four different light regimes applied throughout pregnancy (day 1 : beginning of pregnancy). The results showed that the time of parturition (onset of expulsion) depended on the light treatment : the longer the duration of the daily illumination, the longer pregnancy lasted. With a 14 hrs light regime, the births occurred during two main periods : 50 p. 100 before 8 p.m. on (Signoret, 1969) rats (Naaktgeboren and Slijper, 1970) and humans (Kaiser and Halberg,1962). In the rat, a specific effect of light on the time of parturition has been suggested in experiments involving shifts of the light/dark cycle (Lincoln and Porter, 1976) or different lengths of daily illumination (Plaut et al., 1970 ;Mitchell and Yochim, 1970 (Boer et al., 1975 ;Cohen, 1976).Attempts to establish if the pineal gland was involved in this effect of light in the rat have been unsuccessful Lincoln and Doyle, 1978) (Krieger, 1974 ;Ixart et al.,1977). Parturition was found to occur invariably during the period when the corticosterone levels were minimal for two different photoperiodic treatments (Lincoln and Porter, 1979). Some studies have also suggested that these adrenal secretions play a role in the initiation of parturition (Yoshinaga, 1978), even if there are controversial interpretations as to the action of the fetal hypophyseal-adrenal axis on the duration of pregnancy in this species (Swaab et al., 1977). Metopirone which inhibits 11! and 18 steroid hydroxylase activity, passes through the placenta (Dupouy, 1972) and leads to a prolongation of gestation (Parvez et al., 1972 (Fuchs, 1969) since the duration of expulsion varies and seems independent of the day of parturition (Boer et al.,1975 figure 3. Under the control light regime (14L-10D) parturition occurred earlier in the adrenalectomized rats (group CA-) than in the corresponding rats (group C ; P < 0.05). Thus, 17.4 (Plaut et ai., 1970 ;Boer et al., 1975 ;Cohen, 1976 ;Lincoln and Porter, 1976)

Influence of photoperiod on the time of birth in the rat. IV. Effects of an imposed feeding rhythm

“…&horbar; We used rats originating from strain 03 of our colony. Their management has been described previously (Bosc and Nicolle, 1980a Observations. &horbar; Observations were made as previously described (Bosc and Nicolle, 1980a (Siegel, 1956).…”

“…Their management has been described previously (Bosc and Nicolle, 1980a Observations. &horbar; Observations were made as previously described (Bosc and Nicolle, 1980a (Siegel, 1956). Litter size and stillbirth rates were also analysed by the appropriate parametric tests (Vessereau, 1960 (Lincoln and Porter, 1976 ;Bosc, 1981).…”

Time of birth and daily activity mediated by feeding rhythms in the pregnant rat

“…Two definite periods of birth are often observed, depending on the photoperiod (Bosc, 1981) or the feeding regime (Bosc and Nicolle, 1985) (Reynolds, 1965 ;Bosc and Nicolle, 1980). In this experiment, the total activity time decreased as gestation progressed.…”

“…Observations were done as previously described (Bosc and Nicolle, 1980). The rats were checked every two hours on days 22 and 23 of gestation, and their births were therefore plotted at two-hour intervals, the onset of expulsion being the time of delivery.…”

Influence of photoperiod on the time of parturition in the rat. II. Demonstration of a photoinducible phase and determination of some of its characteristics

“…The time of birth in the rat depends on the photoperiod (Plaut et al, 1970 ;Mitchell and Yochim, 1970 ;Bosc and Nicolle, 1980). However, it is not known how the daily illumination influences the physiological process leading to parturition.…”