Effect of stress on the course of labor and parturition time in normal or adrenalectomized rats

Abstract

Summary. We report two experiments studying the effect of stress on the course of labor and on the time of parturition in the parturient rat. In the first experiment, different stresses were applied after expulsion of the first fetus. A simple manipulation of the female or a change of territory did not modify the whole expulsion phase but increased variability in the birth of the second fetus. By comparison, a strong stress lengthened the duration of expulsion and influenced the time intervals between the first births. A comparison of these results with those obtained after adrenalectomy indicated that the inhibitory effect of a strong stress was probably due to maternal adrenal epinephrin secretion. In the second experiment, a stress was applied before labor in normal rats submitted to two light regimes. In these conditions, the treatment essentially stimulated the last parturitions, which occurred earlier than in control animals.The course of labor and the time of fetal expulsion are known to be influenced by an environmental change or by any event felt as stress. The bitch, for example, often has a labor affected by a disturbance of its usual life conditions (Bleicher, 1962 ;Freak, 1962). In domestic animals such as the pig (Signoret, 1969) Figure 4, which includes the 5 groups of normal rats, shows that this perinatal mortality is related to duration of the labor expulsion phase.After adrenalectomy, with or without a stress after expulsion of the first fetus (lots A-and A-+ S), the total lenght of the expulsion phase did not differ from that of the normal rats (lot N) (P > 0.05). But figure 5 shows that the mean increase of expulsion time at each additional birth was slightly higher in the adrenalectomized rats than in the normal ones. This was partially due to the greater variability of the first two intervals between the first three births ( fig. 5) in lots A-and A-+ S. As the number of animals was too small in these lots, interval distributions have not been compared to the control. On the other hand, figure 5 shows the close evolution of the mean increase of expulsion time at each additional birth in normal rats submitted to a strong stress (lot 5) fig. 3).These results demonstrate that a stress at this stage of pregnancy has not only an inhibitory effect on the course of labor, as has often been emphasized (Newton et al., 1968 ; Naaktgeboren and Bontekoe, 1976), they also show this effect can be attributed to epinephrin secretion since 5 !.g of this catecholamine produced the strong stress response of normal rats in adrenalectomized ones (fig. 5). These data agree with observations obtained on the uterine activity of parturient rabbit or sheep (Naaktgeboren and Bontekoe, 1976). But epinephrin causes three types of response in the myometrium and it has been stated that they depend on the hormonal status of the animal. Abe (1970) gives evidence that the rat uterus has both alpha and beta receptors and that their number in that organ may be steroid-dependent (Williams and Lefkowitz, 1977 ;Roberts et...

Influence of photoperiod on the time of parturition in the rat. III. Comparison of different daily light lengths with changes in light timing or light pulse given during darkness

“…Mated animals were isolated on the day of mating (day 1 of pregnancy ; spermatozoa in the vaginal smear) in individual boxes and assigned to an experimental group. Two or three sessions per group were needed, and the females were allowed two or three pregnancies (Bosc and Nicolle, 1980 (Bosc and Nicolle, 1979). This study, showing that the time of birth in rat is influenced by photoperiodic timing, supports the view that in this species there exists a phase which may be stimulated by light.…”

Effect of photoperiod, injection of pentobarbitone sodium or lesion of the suprachiasmatic nucleus on pre-partum decrease of blood progesterone concentrations or time of birth in the rat

“…Although the reason for failure of birth by lesion of the SCN is not clear, large lesions of the hypothalamus may be the cause (Honma et ai, 1984). Parturition in the rat is brought about by intricate mechanisms (Fuchs, 1973;Thorburn & Challis, 1979) involving adrenal function (Bosc & Nicolle, 1979, 1980, pituitary hormones (Fuchs et ai, 1974;Gordon & Sherwood, 1985), relaxin , prostaglandins (Dukes et ai, 1974;Labhsetwar & Watson, 1974;Strauss et ai, 1975;Buckle & Nathanielsz, 1975), ovarian steroids (Cátala & Deis, 1973;Thorburn & Challis, 1979), or relation¬ ship between fetus and mother (Sherwood et ai, 1985). The mechanism affected by lesion of the SCN is uncertain.…”

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

“…The still-birth rate, which increases with the duration of expulsion (Bosc and Nicolle, 1979), was low in all groups (table 2) and thus provides an indirect argument for this statement. In contrast, it is known in this species that the interval (about 25 h) between the necessary decline in blood progesterone concentration and the onset of birth remains constant under photoperiodic conditions which have been studied (Bartholomeusz et al, 1976 ;Nicholas and Hartmann, 1981 ;Puri and Garfield, 1982 ;Sherwood et a/., 1983).…”