Possible mechanism for the antiarrhythmic effect of helium in anesthetized dogs.

Breathing a mixture of 75 percent helium and 25 percent oxygen instead of 75 percent nitrogen and 25 percent oxygen reduced the occurrence of dangerous cardiac arrhythmias after ligation of the circumflex coronary artery in open-chest dogs anesthetized with pentobarbital. In dogs not subjected to circumflex ligation, the sensitivity of blood pressure, heart rate, and extrasystoles to epinephrine injected intravenously was not altered by the substitution of helium for nitrogen; however, helium did reduce the baseline heart rate and the concentration of endogenous plasma catecholamines. The antiarrhythmic effect of helium may thus be mediated by changes in sympathetic activity.

Rabbit uterine oxytocin receptors and in vitro contractile response: abrupt changes at term and the role of eicosanoids.

We examined the relation between increased uterine oxytocin receptor concentration and increased in vivo sensitivity of the rabbit uterus to oxytocin at the end of gestation. We determined oxytocin receptor concentrations in myometrium and decidua on different days near term of gestation and postpartum. We also examined the in vitro contractile response to oxytocin on days 30 and 5 days postpartum, when the uterus is unresponsive in vivo, and on day 31 (term), when the uterus is exquisitely sensitive to this hormone in vivo. In addition, we tested the role of endogenous eicosanoids and decidual oxytocin receptors in the myometrial contractile response to oxytocin by examining the contractile response in the presence of the cyclooxygenase/lipoxygenase inhibitor sodium meclofenamate or in muscle strips from which the decidua had been removed by scraping. The concentration of specific binding sites for [3H]oxytocin in myometrial and also decidual membrane preparations was determined. We demonstrate that contractile sensitivity to oxytocin increases at least 4-fold between days 30 and 31 (term) of gestation, and this is accompanied by a nearly 10-fold increase in the concentration of oxytocin-binding sites in both decidua and myometrium. The lesser sensitivity to oxytocin on day 30 was, however, only apparent in the presence of meclofenamate, which suggests that endogenous eicosanoids contribute to the preterm response to oxytocin measured in vitro. The maximal response to oxytocin (integrated area) increased 2-fold between day 30 and term. Thus, an increase in both sensitivity and maximal response to oxytocin could be demonstrated at term in vitro. Five days after parturition, maximal response and uterine sensitivity measured in the presence of meclofenamate had returned to those of the preterm uterus, and the concentration of oxytocin-binding sites had declined. In contrast, sensitivity and maximal response to the cholinergic agonist carbamylcholine declined between day 30 and term. These results support a highly regulated physiological role for oxytocin in parturition which depends primarily on changes in receptor concentration.

Glucocorticoids increase pulmonary beta-adrenergic receptors in fetal rabbit.

beta-Adrenergic agonists stimulate surfactant release and decrease fluid in lung alveoli of fetuses. Both effects are most evident toward the end of gestation. We used [3H] dihydroalprenolol (DHA) to investigate the development of pulmonary beta-adrenergic receptors in rabbit fetuses and to study the effect of glucocorticoid treatment on the beta-receptor number. In the lung particulate preparation, DHA binding was rapid, reversible, stereoselective, and of high affinity. The order of potency for adrenergic agonists in competing for DHA binding was isoproterenol > epinephrine = norepinephrine, which is typical of interactions at a beta 1-adrenergic receptor. Using DHA, we demonstrated that the concentration of pulmonary beta-receptors increased significantly between 28 and 31 days of gestation; however, there was no change in the dissociation constant during gestation. After injecting betamethasone (0.17 mg/kg, 24 hours) into rabbits at 25 days of pregnancy, we found that the concentration of pulmonary beta-receptors increased from 44.2 +/- 6.6 fmol/mg protein in untreated fetuses to 77.9 +/- 5.6 fmol/mg protein in treated fetuses. However, this treatment did not affect the DHA binding sites in the fetal rabbit heart. Maternal treatment with the T3 analogue 3,5-dimethyl-3'-isopropyl-L-thyronine (0.5-1 mg/kg) at a dosage which increased both surfactant synthesis and release did not alter pulmonary receptor concentration. Our results indicate that the concentration of pulmonary beta-adrenergic receptors increases in the fetus at term and suggest that this increase is stimulated by endogenous glucocorticoid in fetal circulation.

Prostaglandins modulate hormonal effects on rabbit myometrial alpha 1-adrenergic responses.

Estrogen increases the alpha 1-adrenergic contractile sensitivity of the rabbit uterus. Since estrogen treatment increases prostaglandin (PG) production by the perfused rabbit uterus, and PGs contribute to the alpha 1-adrenergic contractile response, we postulated that estrogen's effects on PG production or response may play a role in the increased alpha 1-adrenergic sensitivity induced by estrogen. We studied the effects of the eicosanoid synthesis inhibitor meclofenamate (60 microM) on the response to epinephrine (10(-9)-10(-5) M) of uterine strips from ovariectomized, mature, and estrogen-treated rabbits in terms of both contractile response and PGE2 and PGF2 alpha production. We also measured the contractile response to PGE2 and PGF2 alpha (both 10(-10)-10(-5) M) and KCl (70 mM) of uterine strips from these groups. We found that in the ovariectomized rabbits, meclofenamate decreased PG production, but did not alter the alpha 1-adrenergic sensitivity. In the mature rabbit uterus, meclofenamate decreased both PGE2 and PGF2 alpha production and reduced the alpha 1-adrenergic sensitivity. In the estrogen-treated rabbit uterus, meclofenamate decreased PGF2 alpha, but not PGE2, production and did not alter the alpha 1-adrenergic sensitivity. Finally, meclofenamate reduced the contractile response to KCl in all three groups, and exposure to PGE2 increased the contractile response to KCl in both the mature and estrogen-treated rabbits. We conclude that PGs play a role in the increase in the alpha 1-adrenergic sensitivity of the uterus in mature rabbits, and that this may be the result of an estrogen-mediated alteration in the postreceptor effects of PGs.

Cyclic adenosine 3',5'-monophosphate increases beta-adrenergic receptor concentration in cultured human fetal lung explants and type II cells.

cAMP regulates the maturation of many biochemical processes that occur during normal lung development, including the changing levels of surfactant proteins and phospholipids. We examined the effect of cAMP on the beta-adrenergic receptor concentration in the developing human lung. Isobutylmethylxanthine, a cAMP phosphodiesterase inhibitor, increased both the tissue cAMP content and beta-adrenergic receptor concentration in treated explants above those in untreated explants. 8-Bromo-cAMP treatment also elevated the beta-adrenergic receptor concentration of lung explants compared to that in untreated controls. These data indicate the ability of elevated cAMP to increase the beta-adrenergic receptor concentration. Both lung cAMP and beta-adrenergic receptor concentrations increase spontaneously in culture. To test for a possible causal relationship, we cultured explants with protein kinase inhibitors. We found that H-8, a preferential inhibitor of the cAMP-dependent protein kinase [protein kinase-A (PKA)], but not H-7, which inhibits PKA and protein kinase-C with similar potency, blocked the spontaneous rise in beta-adrenergic receptor concentration in human fetal lung explants, indicating that PKA activity is required for this rise in beta-adrenergic receptor concentration. Type II cells isolated from cultured lung treated with H-8 had fewer beta-adrenergic receptors than cells isolated from untreated explants. These studies show that cAMP increases the beta-adrenergic receptor concentration in human fetal lung and specifically in type II cells through a PKA-dependent mechanism, consistent with a role for cAMP in beta-adrenergic receptor regulation during normal lung development.

Identification of beta-adrenergic binding sites in rabbit myometrium.

Rabbit uterine muscle may contract or relax with adrenergic stimulation depending on the hormonal milieu. This difference in contractile activity has been shown to be due to alteration of adrenergic response between alpha-adrenergic (contraction) and beta-adrenergic (relaxation). When rabbits are treated with estrogen followed by progesterone, norepinephrine produces myometrial relaxation. This effect is blocked by propranolol, indicating that it is mediated by beta receptor activation. A subcellular preparation of this myometrium has adenylate cyclase activity that can be stimulated by isoproterenol + guanyl-5'-yl-imidodi-phosphate (Gpp(NH)p). The radioligand [125I]iodohydroxybenzylpindolol binds to the same preparation. The binding is rapid, 80% maximal in 10 min, and readily reversible (t1/2 = 5 min). The binding is high affinity (Kd = 0.12 nM), low capacity (15 fmol/mg protein), and is to a single class of binding sites. Binding is competed for stereoselectively by beta adrenergic agonists and antagonists. The competition of beta adrenergic agonists for binding, isoproterenol = ritodrine greater than epinephrine greater than norepinephrine, is consistent with interactions at a beta2-adrenergic receptor.

Rabbit myometrial oxytocin and alpha 2-adrenergic receptors are increased by estrogen but are differentially regulated by progesterone.

Both myometrial oxytocin and alpha 2-adrenergic receptors are induced by estrogen. To compare the regulation of these two receptor populations by progesterone, we measured myometrial receptor concentration in ovariectomized steroid-treated and in pregnant rabbits. To control for the effects of estrogen withdrawal, we used concomitant rather than sequential presentation of estrogen and progesterone in ovariectomized rabbits. Estradiol increased both myometrial oxytocin and alpha 2-adrenergic receptor concentrations in ovariectomized rabbits after 8 days of treatment. Simultaneous progesterone administration during the last 4 days of estradiol treatment reversed the induction of oxytocin, but not alpha 2-adrenergic, receptors. Similarly, administration of the antiprogestin RU 38486 to pregnant rabbits on day 27 of gestation resulted in premature delivery and evoked an increase in myometrial oxytocin receptor concentration mimicking that observed at term (day 31). However, RU 38486 did not significantly affect alpha 2-adrenergic receptor concentration. Our data provide further support for involvement of oxytocin receptors in parturition, but do not indicate a comparable function for myometrial alpha 2-adrenergic receptors.

Exposure of human amnion to amniotic fluid obtained before labor causes a decrease in chorion/decidual prostaglandin release.

Prostaglandin (PG) production by fetal membranes has been implicated in the initiation of human parturition, but its regulation is not well understood. We used an in vitro system to study paracrine control of term, fetal membrane PG production. Using a modified Ussing chamber, full thickness fetal membranes with attached decidua were sealed into a chamber so that each hemichamber was a compartment for either the fetal (amnion) or maternal (chorion/decidua) side. Released PGs from maternal and fetal sides were then measured after exposure of the amnion to either buffer or amniotic fluid. We found that basal release of PGs from both the fetal and maternal sides was 2- to 3-fold higher in membranes obtained after labor compared to those obtained before labor. When amnion obtained after labor was exposed to amniotic fluid, we found a 3- to 5-fold increase in the net release of PGE2 from the amnion; however, the maternal side showed an unexpected relative decrease in PGE2 and PGF2 alpha release. This was a paracrine effect, since direct exposure of chorion/decidua to amniotic fluid caused increased release of the PG precursor, arachidonic acid. Direct transfer of radiolabeled PG from fetal to maternal side was minimal.

Decreased concentration of myocardial alpha-adrenoceptors with increasing age in foetal lambs.

Using [3H]-dihydroergocryptine, we identified myocardial alpha-adrenoceptor binding sites in foetal lambs and demonstrated that the concentration of receptors decreased with increasing foetal age. The presence of the receptor in the foetus correlated with the presence of myocardial alpha-adrenergic responsiveness. However, we found neither the alpha-receptor binding site nor responsiveness to alpha-adrenoceptor stimulation in the myocardium of adult sheep.

The epidemiology of premenstrual symptoms in a population-based sample of 2650 urban women: attributable risk and risk factors.

This epidemiologic survey achieved a reliable measure of the prevalence of premenstrual symptoms by avoiding the biases of small or selected samples, anamnestic error, and subjective expectation. From 6232 women (a 78.8% response), aged 20-49 years, identified through a random sample of urban households, the 24-hour prevalence of symptoms was obtained using the Moos' Menstrual Distress Questionnaire, administered without reference to the menstrual cycle. For 71% of the naturally cycling women, current cycle phase was determined by follow-up (n = 2650); but a higher prevalence of severe or moderately severe affective symptoms in the premenstrual compared to the mid-cycle phase was not found. However, observed risk factor interactions led to the conclusion that premenstrual distress is a discrete mood disorder, affecting women aged 25-35 years, with probable ovulatory cycles, and vulnerable to stress; and that the risk of affective symptoms attributable to the premenstrual state was one percent.

Clinical and biochemical evidence of endothelial cell dysfunction in the pregnancy syndrome preeclampsia.

The pregnancy disorder preeclampsia continues as a major cause of maternal and infant mortality and morbidity. Despite intensive research since its recognition 100 years ago, our lack of understanding is evidenced by therapy which remains empiric, early delivery. Part of our failure to more completely understand the syndrome is due to excessive attention to the blood pressure elevation which accompanies the disorder, to the exclusion of a panoply of other physiologic aberrations. Although hypertension, if markedly elevated, can lead to maternal morbidity, it is not usually an important contributor to the pathophysiology of preeclampsia. It is primarily important as a marker for vasoconstriction, which in association with activation of coagulation reduces perfusion to many organs, including the fetal-placental unit. The earliest and likely most important pathophysiologic change is reduced placental perfusion secondary to abnormal implantation and/or a relative increase in placental mass. We propose that reduced placental perfusion results in the production of agent(s) by this organ, which injures or activates endothelial cells. The resulting endothelial cell dysfunction increases sensitivity to normal endogenous pressors, activates the coagulation cascade, and increases vascular permeability. These changes produce the characteristic pathophysiologic changes of the disorder. Evidence supporting this hypothesis includes abnormal endothelial morphology long recognized in glomerular capillaries, increased circulating fibronectin, and increased plasma mitogenic activity that long antedates the clinical disorder. In addition, an agent(s) is present in the blood of these women which activates endothelial cells in vitro as evidenced by increased release of [51Cr] chromium and increased production of PDGF. Preeclampsia is clearly more than "pregnancy induced hypertension."

Alpha adrenergic stimulation reduces cyclic adenosine 3',5'-monophosphate generation in rabbit myometrium by two mechanisms.

Rabbit myometrium contains postsynaptic alpha-1, alpha-2, and beta-2 adrenoreceptors. The response to endogenous catecholamines depends on the summation of interactions at these receptors and is influenced by the hormonal environment. Estrogen treatment of ovariectomized rabbits increases the alpha adrenergic contractile response whereas progesterone treatment of estrogen primed animals results in a predominance of the beta adrenergic response, which is inhibition of contractions. Of the receptor subtypes, only the alpha-2 receptor concentration is increased at physiological estrogen concentrations. However, alpha-2 receptors have not been shown to be directly involved in myometrial contraction, which appears to be mediated solely by alpha-1 adrenergic interactions. To test whether alpha-2 receptors might indirectly affect contraction by opposing interactions at the beta receptor, we examined the ability of alpha adrenergic stimulation to reduce myometrial cyclic adenosine 3',5'-monophosphate (cAMP) generation. We find that alpha-2 receptors inhibit myometrial ade adenylate cyclase through the guanine nucleotide regulatory protein, Gi. In addition, we find that activation of alpha-1 receptors also reduces cAMP generation. This interaction, which can be demonstrated in the absence but not the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, does not appear to be mediated through Gi. These findings illustrate the complexity of adrenergic interactions in tissues containing several adrenergic subtypes.

Rabbit myometrial adrenergic sensitivity is increased by estrogen but is independent of changes in alpha adrenoceptor concentration.

The ability of estrogen to increase the alpha-1 adrenergic sensitivity of rabbit uterine smooth muscle was compared with its effects on the concentration of alpha adrenoceptor subtypes in myometrium. Compared to ovariectomized controls, estrogen treatment was found to increase the adrenergic contractile sensitivity of rabbit uterus determined in vitro. Estrogen treatment increased uterine alpha-2 adrenoceptor concentration nearly 5-fold. Mature rabbits (endogenous estrogen) had the same uterine sensitivity and alpha-2 adrenoceptor concentration as estrogen-treated rabbits. Alpha-1 receptor concentration was increased only in the estrogen-treated group, and was accompanied by increased maximal contractile response. Thus, the increase in adrenergic sensitivity after estrogen was correlated closely with an increased concentration of alpha-2 adrenoceptors. However, enhanced adrenergic sensitivity persisted after alpha-1 and alpha-2 receptor concentration returned to pre-estrogen levels in rabbits pretreated with estrogen before ovariectomy. Studies utilizing subtype-selective competitive antagonists verified that contractile response is mediated primarily by alpha-1 adrenoceptors, with no apparent influence of alpha-2 adrenoceptors. Finally, we found that adrenergic sensitivity is altered by temperature and divalent cation concentration, but these effects do not prevent the expression of the regulatory action of estradiol. We conclude that estrogen increases the alpha-1 adrenergic sensitivity of rabbit uterus without changes in alpha-1 receptors, and thus may act on postreceptor response events.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen increases adrenergic- but not cholinergic-mediated production of inositol phosphates in rabbit uterus.

alpha 1-Adrenergic and muscarinic cholinergic stimuli activate uterine contraction. Estrogen increases adrenergic but not cholinergic sensitivity of rabbit myometrium independent of its effects on adrenoceptor concentration. Since both alpha 1-adrenergic and muscarinic receptors are coupled to phosphatidylinositol hydrolysis, we tested the hypothesis that estrogen increases adrenergic- but not cholinergic-mediated inositol triphosphate production. We found that maximal production of inositol phosphates stimulated by norepinephrine was increased approximately 3-fold following estrogen treatment. Cholinergic-stimulated production was not increased by estrogen treatment. These results demonstrate that the effect of estrogen to enhance uterine adrenergic sensitivity is associated with an increased post-receptor response. The nature of the selectivity of estrogen for adrenergic versus cholinergic response remains obscure, but the results suggest the presence of parallel pathways for receptor activation of a common post-receptor response.