The vasoconstrictor response of uterine and mesenteric resistance arteries is differentially altered in the course of pregnancy.

OBJECTIVES: The purpose of the present study was to test the hypothesis that pregnancy is associated with an attenuation of the vasoconstrictor response not only in the uterine, but also in the systemic circulation. Decreased vascular reactivity should be characterized by an early onset to account for the rapid fall in peripheral resistance which was observed during the first third of gestation. STUDY DESIGN: Dose-response curves for phenylephrine hydrochloride (PE), angiotensin II (ANG II), and endothelin 1 (ET 1) were recorded from isolated pressurized uterine and mesenteric arterioles. Vessels were obtained from virgin, early (day 7-9) pregnant (EP) and late (day 19-21) pregnant (LP) rats. RESULTS: (1) In uterine resistance arteries, the response to PE and ANG II decreased early, but for ANG II the reduction did not persist. ET 1 sensitivity was unchanged in early, and diminished in late gestation; (2) in mesenteric vessels, sensitivity to ET 1 was enhanced in early pregnancy and did not differ from the non-pregnant level in late gestation. Sensitivity to PE and ANG II was unchanged in early, and reduced in late pregnancy. CONCLUSIONS: The vasoconstrictor response is not uniformly blunted during pregnancy. Changes in vascular reactivity are differentially regulated with respect to the agonist, to their time course, and. to the origin of the vessel. The relative increase of vasoconstrictor sensitivity in the splanchnic circulation during early pregnancy may prevent hypotensive dysregulation, while concentrations of endogenous vasodilators rise and the vascular filling state normalizes only gradually.

[Neonatal ascites: meconium ileus with perforation in mucoviscidosis]. / Neonataler Aszites: Mekoniumileus mit Perforation bei Mukoviszidose.

Many conditions are known associated with neonatal ascites such as cardiac and vascular malformations, as well as malformations of the brain, kidney, lung and bone, chromosomal abnormalities, infections, fetal anemias, tumors, metabolic and maternal conditions. In 30% no reason can be found. Meconium ileus is a causal gastrointestinal abnormality. We report about a preterm infant 35 weeks of gestation with complicated meconium ileus because of mucoviscidosis.

Human chorionic gonadotropin dilates uterine and mesenteric resistance arteries in pregnant and nonpregnant rats.

Membrane receptors for human chorionic gonadotropin (hCG) are expressed in a variety of steroidogenic cells, and also in extragonadal tissues such as vessels of the female genital tract. We examined the possible contribution of hCG to the endocrine control of prearteriolar mesenteric and uterine vessels before and during pregnancy. Lumen diameters of isolated pressurized resistance arteries from Sprague-Dawley rats were measured using a video-electronic system. hCG produced marked and dose-dependent vasodilation. Uterine radial arteries were found to be highly sensitive to hCG (EC50 approximately =60 mU/ml) before and throughout gestation. Second-order mesenteric arteries from nonpregnant animals were even more sensitive (EC50=38 mU/ml), but, in these vessels, responsiveness to hCG was significantly attenuated by the pregnant state. Mechanical removal of the vascular endothelium did not reduce the degree of vasodilation mediated by hCG. The expression of hCG receptor mRNA in intact vessels could be demonstrated using reverse transcriptase polymerase chain reaction (RT-PCR). hCG appears to be an important embryonic signal, which could trigger adaptive cardiovascular changes in early pregnancy, simultaneously preserving a sufficient utero-placental perfusion during the entire gestation period by an endothelium-independent mechanism.

ATP-sensitive and Ca-activated K channels in vertebrate axons: novel links between metabolism and excitability.

Two types of metabolically regulated K channels have been identified for the first time in enzymatically demyelinated fibres of amphibian sciatic nerve using the patch-clamp technique. A maxi K channel with a single-channel conductance of 132 pS (105 mM K on both sides of the membrane, 15 degrees C) is activated both by micromolar concentrations of internal Ca and by depolarization. A second type of K channel with a conductance of 44 pS is inhibited by intracellular adenosine 5'-triphosphate (ATP) with a half-maximal inhibitory concentration (IC50) of 35 microM. It is blocked by submicromolar concentrations of external glibenclamide. Both channels are sensitive to external tetraethylammonium chloride (IC50 = 0.2 mM for the maxi K channel and 4.2 mM for the ATP-sensitive channel). They may be part of a complex feedback system regulating axonal excitability under various metabolic conditions.

Single-channel recording in myelinated nerve fibers reveals one type of Na channel but different K channels.

Amphibian myelinated nerve fibers were treated with collagenase and protease. Axons with retraction of the myelin sheath were patch-clamped in the nodal and paranodal region. One type of Na channel was found. It has a single-channel conductance of 11 pS (15 degrees C) and is blocked by tetrodotoxin. Averaged events show the typical activation and inactivation kinetics of macroscopic Na current. Three potential-dependent K channels were identified (I, F, and S channel). The I channel, being the most frequent type, has a single-channel conductance of 23 pS (inward current, 105 mM K on both sides of the membrane), activates between -60 and -30 mV, deactivates with intermediate kinetics, and is sensitive to dendrotoxin. The F channel has a conductance of 30 pS, activates between -40 and 60 mV, and deactivates with fast kinetics. The former inactivates within tens of seconds; the latter inactivates within seconds. The third type, the S channel, has a conductance of 7 pS and deactivates slowly. All three channels can be blocked by external tetraethylammonium chloride. We suggest that these distinct K channel types form the basis for the different components of macroscopic K current described previously.