Uchenna C. Nwosu

Relaxation of isolated human myometrial muscle by β2 -adrenergic receptors but not β1 -adrenergic receptors

Abstract Objective: Human myometrium contains both β 1 -adrenergic and β 2 -adrenergic receptors. This study was designed to assess the importance of each β-adrenergic receptor subtype in relaxation of human myometrial muscle strips. Study Design: Radioligand binding studies were used to establish the presence of each β-adrenergic receptor subtype, whereas highly selective β 1 -antagonists and β 2 -antagonists were used to assess the contribution of β-adrenergic receptor subtypes to myometrial relaxation after exposure to (–)–isoproterenol. Results: Membranes prepared from myometrium contained 82% ± 4% β 2 -adrenergic receptors. After contraction produced by exposure to potassium chloride (35 mmol/L), isoproterenol produced relaxation with half maximal effect at 0.02 μmol/L and a maximal relaxation of 52% ± 3%. β 1 -Antagonist CGP-20712A had no significant effect, whereas β 2 -antagonist ICI-118551 produced a characteristic rightward shift of the isoproterenol concentration-relaxation relationship. Conclusions: Although both β 1 -adrenergic receptors and β 2 -adrenergic receptors are present in human myometrial tissue at term, relaxation by nonselective β-agonist isoproterenol is mediated exclusively by β 2 -adrenergic receptors. (Am J Obstet Gynecol 1998;179:895-8.)

Surge of fetal plasma triiodothyronine before birth in sheep

Plasma thyroid hormone and cortisol concentrations were measured from early third trimester to delivery in seven pregnant ewes and their fetuses. A surge in fetal plasma triiodothyronine was found during the six days prior to delivery, the mean values rising from less than 30 to 125 ng. per deciliter. During this period the fetal plasma cortisol also increased from less than 1 to 8.1 microgram per deciliter. During this period there was no significant change in fetal plasma thyroxine (T4) or reverse T3 concentrations and no change in maternal plasma concentrations of any of these hormones. The abrupt increase in fetal plasma T3 concentrations with no rise in plasma T4 suggests that there was an alteration in extrathyroidal conversion of T4 to T3 rather than an increase in thyroid secretion, since the latter would be expected to cause an increase in both plasma T4 and plasma T3. The changes in plasma T3 and cortisol concentrations in a fetus that died in utero eight to 10 days before term resembled those occurring prior to normal parturition.

Possible role of the fetal adrenal glands in the etiology of postmaturity

Plasma cortisol levels were studied in the cord blood and neonatal blood of the following vaginally delivered groups: (A) postmature; (B) postterm (but not postmature); and (C) term neonates. Significantly lower levels of 8 A.M. neonatal plama cortisol were found in postmature neonates when compared with term neonates (P LESS THAN 0.02) or merely postterm neonates (P LESS THAN 0.02). No difference was found in the cord blood cortisol levels in all three groups. Contrary to the traditional belief that postmaturity results from placental aging, our findings appear to indicate that postmaturity represents a specific fetal disorder. Fetal adrenal insufficiency may be a characteristic of this disorder. Prolonged pregnancy in these cases may be reflected inability of the affected fetus to initiate labor.

Possible adrenocortical insufficiency in postmature neonates

Total plasma cortisol in cord and neonatal blood was measured by a radioassay method in neonates resulting from (1) term vaginal delivery following uncomplicated labor (control group), (2) term vaginal delivery following fetal distress during labor, (3) postterm, postmature vaginal delivery following fetal distress during labor, and (4) postterm, postmature emergency cesarean section performed because of signs of severe fetal distress during labor. Comparison of the mean peripheral plasma cortisol values showed that whereas the mean level (plus or minus S.E.) of the distressed term neonates (22.2 plus or minus 5.3 mug per 100 ml.) use 180 per cent of that of the control group (12.3 plus or minus 1.1 mug per 100 ml.; P smaller than 0.01) the mean level for the vaginally delivered postmature group (7.5 plus or minus 1.8 mug per 100 ml.) was only 61 per cent of that of the control group (P smaller than 0.05). Furthermore, in the postmature group with sufficient intrapartum distress to warrant emergency cesarean section the mean level (4.6 plus or minus 1.5 mug per 100 ml.) was found to be only 37 per cent of that of the control group. No differences were observed among the cord plasma cortisol values. These results are strongly suggestive of a relative adrenocortical insufficiency in postmature neonates. Such insufficiency could result from a defect in any portion of the adrenal-pituitary-hypothalamic axis. Effort is under way to further define such a defect.

A New Look at the Etiology of Cervical Incompetence

Nwosu, C. U., Soffronoff, E. C. and Bolton, G. C. (Dept. of Obstetrics & Gynecology, Pennsylvania Hospital, University of Pennsylvania School of Medicine, Philadelphia, Pa.) A new look at the etiology of cervical incompetence, with review of seven‐year experience at Pennsylvania Hospital.

321 PRENATAL SURGE OF PLASMA T3 IN THE FETAL LAMB

Prenatal changes in iodothyronine levels with respect to parturition have not been clearly established. The present studies investigate the changes of fetal serum iodothyronine concentration preceeding labor. Seven fetal lambs 113-135 days gestation were chronically catheterized in-utero from early 3rd trimester to delivery. Daily plasma concentrations of Cortisol, T4, T3, and rT3 were measured. Simultaneous maternal blood samples were similarly analyzed. Mean fetal plasma T3 rose from a baseline of 30 ng/dl to 150 ng/dl one day prior to delivery with most of the increase occurring during the 4 days prior to labor. Fetal plasma Cortisol was found to increase in phase with T3. Mean Cortisol rose in the 4 days prior to labor from a baseline of 1 ng/dl to 8 ng/dl and sharply increased 1 day prior to delivery. Mean values for fetal plasma T4 and rT3 were 12 ng/dl and 450 ng/dl respectively, and although no significant changes occurred, a tendency to decrease was evident during the 10 days prior to delivery. Fetal and maternal hormone levels were independent at all times. Baseline maternal T3 and Cortisol were 2 times higher than fetal levels until the 4 days prior to delivery when fetal levels rose to 4 and 2 times the maternal levels respectively. Mean maternal T4 and rT3 levels remained ½ and ¼ of the mean fetal values. The abrupt increase in fetal T3 without a corresponding change in T4 suggests the basic alteration is in extrathyroidal T4 to T3 conversion,not in increased TSH secretion.

Impaction of term twins. A case report.

Twin entanglement during labor carri es a very high fetal mortality. Since recognition of this problem during the first stage of labor is notoriously difficult , th e following case is reported to illustrate the diagnostic clues and management. M. T ., a 24 year old black female primigrav ida, was registered at the prenatal clinic of the Pennsylvania Hospital on September 30, 1974. Except for moderate obesity (weight 252 lb )