Chronic Fetal Preparation Research Articles

Studies on the endocrinology of parturition: relative steroidogenesis in coexisting genetically dissimilar ovine fetuses, concomitant with the temporal patterns of maternal C18 and C19 steroids and prostaglandin F2 alpha release.

Ovine embryos collected from two breeds of ewes possessing different gestational periods [Finnish Landrace (Finn), 145.5 +/- 1.4 days; Rambouillet (Ra), 150.7 +/- 1.3 days] were transferred to common, randomly selected recipients. Fetal plasma samples were collected from mixed-breed (MB, one Finn and one Ra; n = 6) and single-breed (SB, single Finn, n = 3; single Ra, n = 3) chronic fetal preparations during the last trimester. In the MB pregnancy, the Ra sibling had temporal patterns of androstenedione similar to those observed in the Finn co-twin; however, these particular changes were greatly accelerated in comparison to the same day of gestation in SB Ra fetuses. Similarly, temporal patterns of change in unconjugated estrone, estrone sulfate, and 17 beta-estradiol were accelerated by as much as 4.6 to 5 days in Ra fetuses of MB pregnancies when compared to Ra fetuses in the SB pregnancies (P less than 0.001), with no difference noted between Ra and Finn co-twins. Maternal progesterone concentrations changed from 8 to 2 ng/ml, androstenedione from 200 to 400 pg/ml, estrone from 65 to 250 pg/ml, and 15-keto-13,14-dihydroprostaglandin F2 alpha from 200 pg/ml to 6000 pg/ml over the last 4 or 5 days of gestation. Chronic fetal manipulation accelerated parturition, with mean gestational lengths in MB, SB Finn, and SB Ra pregnancies being 141.5 +/- 0.7, 141.7 +/- 0.7, and 149.3 +/- 0.9 days, respectively. In this study fetal endocrine changes were largely controlled in the MB pregnancy by the fetal co-twin exhibiting a shorter gestational period.

A method for making chronic fetal preparation in the lamb: results of 4 year's experiences.

During the period between 1980 and 1983, a versatile experimental model for fetal physiology (chronic fetal preparation) was made using 26 pregnant Corriedale and Suffolk sheep. The sheep fetuses were removed from the uterus at the gestational ages of from 96 to 133 days. After performing cannulation of the carotid arteries, the jugular veins , and the trachea of the fetuses, applying tripolar cardioelectrodes, and attaching an occluder of the umbilical cord, the fetuses were returned to the uterus to complete the gestational period. The time left until the termination of the postoperative pregnancy and available for various intrauterine monitoring procedures varied from 3 to 800 hr. Eleven sheep (42.3%) continued their postoperative intrauterine term for 5 days or more. The continuation of the postoperative gestation for longer than 5 days indicated a return to the physiological state on the evidence of the measured PO2, PCO2 and pH values and rapid irregular breathing movements.

VASOPRESSIN RELEASE IN THE LAMB FETUS

Arginine vasopressin (AVP) release was studied in 16 chronic fetal preparations between 101 and 141 days gestation following the infusion of 5% NaCl. The mean baseline plasma AVP in fetuses from 101-120 (N=20) days was 1.90 ± 0.46 μU/ml with a plasma osmolality of 292.9 ± 1.75 mOsm/kg. In fetuses 121 days to 141 days gestation, the mean baseline plasma AVP (N=11) was significantly lower 0.77 ± 0.19 μU/ml (P=<0.05) whereas the plasma osmolality was similar to that in the younger fetuses (292.7 ± 1.9 mOsm/kg). The paired maternal baseline AVP concentrations at 101 and 120 days gestation were significantly lower (0.843 ± 0.17 μU/ml) than the mean fetal levels (1.59 ± 0.44 μU/ml) however fetal and maternal levels between 121-141 days were similar; 0.68 ± 0.27 μU/ml and 0.70 ± 0.22 μU/ml respectively. A linear regression of the logarithum of baseline plasma AVP and plasma osmolality in 30 fetuses showed a significant correlation (P=<0.001, r=0.62). Plasma AVP was elevated after 5% NaCl infusion in 16 of 19 experiments. Studies of the relationship between steady state plasma AVP and plasma osmolality in adult sheep show a slightly flatter slope (adult 0.0282, fetal 0.0395). This observation suggests that the fetal osmoreceptors are more responsive to changes in tonicity than the adult sheep. Furthermore, the response to 5% NaCl as measured by the difference in the log plasma AVP divided by the difference in plasma osmolality was greater in the fetus.

Diaphragmatic activity and lung liquid flow in the unanesthetized fetal sheep.

For some time it has been suggested that breathing movements are made "in utero" and recently measurements of tracheal pressure and lung liquid flow in chronic fetal preparations have led to the hypothesis that rapid changes in these parameters are the result of respiratory muscle activity. To test this hypothesis diaphragmatic electrical activity was measured in seven chronic unanesthetized fetal sheep preparations and correlated with lung liquid flow and tracheal pressure. Diaphragmatic activity led to a fall of tracheal pressure and movement of a small volume of lung liquid into the lung. After the activity ceased, tracheal pressure returned to normal and flow diminished to zero or was directed out of the lung. The breathing pattern was unassociated with the net movement of lung liquid out of the lung. A histogram of the interval between breaths revealed a changing pattern of activity throughout gestation. The pattern was significantly altered after premature delivery of one animal with a respiratory problem. These observations provide evidence that respiratory muscles are active "in utero" and that the pattern of activity changes throughout gestation.