Enterohepatic circulation of oestriol: a study of the effects of ampicillin on plasma oestriol levels

Enterohepatic circulation: physiological, pharmacokinetic and clinical implications

Enterohepatic recycling occurs by biliary excretion and intestinal reabsorption of a solute, sometimes with hepatic conjugation and intestinal deconjugation. Cycling is often associated with multiple peaks and a longer apparent half-life in a plasma concentration-time profile. Factors affecting biliary excretion include drug characteristics (chemical structure, polarity and molecular size), transport across sinusoidal plasma membrane and canniculae membranes, biotransformation and possible reabsorption from intrahepatic bile ductules. Intestinal reabsorption to complete the enterohepatic cycle may depend on hydrolysis of a drug conjugate by gut bacteria. Bioavailability is also affected by the extent of intestinal absorption, gut-wall P-glycoprotein efflux and gut-wall metabolism. Recently, there has been a considerable increase in our understanding of the role of transporters, of gene expression of intestinal and hepatic enzymes, and of hepatic zonation. Drugs, disease and genetics may result in induced or inhibited activity of transporters and metabolising enzymes. Reduced expression of one transporter, for example hepatic canalicular multidrug resistance-associated protein (MRP) 2, is often associated with enhanced expression of others, for example the usually quiescent basolateral efflux MRP3, to limit hepatic toxicity. In addition, physiologically relevant pharmacokinetic models, which describe enterohepatic recirculation in terms of its determinants (such as sporadic gall bladder emptying), have been developed. In general, enterohepatic recirculation may prolong the pharmacological effect of certain drugs and drug metabolites. Of particular importance is the potential amplifying effect of enterohepatic variability in defining differences in the bioavailability, apparent volume of distribution and clearance of a given compound. Genetic abnormalities, disease states, orally administered adsorbents and certain coadministered drugs all affect enterohepatic recycling.

Aldosterone 21-sulphate in man

Using a rigorous extraction procedure and radioimmunoassay we have established that aldosterone 21-sulphate concentrations in adrenal vein specimens are higher than peripheral concentrations. Incubations of homogenates of adrenal glands and adenomata in vitro also produced aldosterone 21-sulphate. Peripheral plasma concentrations in normal and hypertensive subjects are about one-tenth those of aldosterone. Mineralocorticoid activity, as assessed in adrenalectomized rats, is less than 1% of that of aldosterone. [3H]-Aldosterone 21-sulphate administered to normal and hypertensive subjects is excreted in an irregular manner, and in four out of six subjects the major metabolite was an unidentified less polar compound. We have characterized this compound chromatographically and discussed the mechanism which may be involved in its production.

Late third trimester unconjugated serum oestriol levels in normal and hypertensive pregnancy: relation to birth weight

In 100 normal singleton pregnancies and in 44 patients with pregnancy hypertension (pre-eclampsia) linear regression analyses demonstrated highly significant positive correlations between birth weights and late third trimester maternal serum unconjugated oestriol (O3) levels. Correlation coefficients increased, though not significantly, after standardising birth weights according to maternal size, parity and sex of infant. Pregnancy hypertension was classified according to the duration of clinical signs. In 23 patients with short duration pregnancy hypertension (onset 14 days or less before delivery) neither maternal age nor birth weight differed from normal controls. Mid-pregnancy weights were greater and unconjugated O3 levels lower and only one infant was growth retarded. Twenty one patients with long duration pregnancy hypertension (onset more than 14 days before delivery) were found on average to be heavier at mid-pregnancy and older than those in whom the condition was short-lived. Unconjugated O3 levels in patients with long duration hypertension were significantly below those in the short duration group. One third of infants born following long duration hypertension were growth retarded.

Effect of ampicillin or amoxycillin administration on plasma and urinary estrogen levels during normal pregnancy

Urinary estrogen excretion and plasma levels of conjugated and unconjugated 17 beta-estradiol and estriol were measured in 10 healthy, pregnant women before, during and after a 5-day course of orally administered ampicillin (2 g/day) or the same dose of amoxycillin. On the second and third day of ampicillin treatment the plasma level of conjugated estriol and the urinary estrogen level were lower than pretreatment values, but then returned to basal values despite continuing treatment. Plasma concentrations of conjugated and unconjugated 17 beta-estradiol and of unconjugated estriol did not show any significant change during treatment. Hormone changes in women on amoxycillin were qualitatively similar to but smaller and less consistent than those induced by ampicillin. The results indicate (1) that the use of amoxycillin instead of ampicillin in pregnancies that require estrogen monitoring of feto-placental function, has little clinical advantage, and (2) that the adverse effect of therapeutic doses of ampicillin (and amoxycillin) on estrogen levels during pregnancy may be less important than is commonly assumed.

Oxytocinase versus estriol for the assessment of fetal well-being

In a group of 26 primiparae, 48 hours after cesarean section, we have examined the urinary estriol (E3) and serum cystine aminopeptidase (CAP). 13 patients received ampicillin treatment, and 13 patients did not. In the group of patients without antibiotic treatment the urinary estriol after 48 h reached an average value of 5.55 mg/24 h. in the group of treated patients the drastic decrease of E3 reached a mean value of 1.62 mg/24 h. This fact may be explained by the arrest of the feto-placental inflow after delivery, and the blocking effect of the antibiotic on the enterohepatic circulation, compartment which afford for 50% of the maternal circulating estrogen. From the present work it results that the determination of the serum CAP activity, which is not affected by antibiotic treatment, is an appropriate test for the assessment of the fetoplacental unit activity. It must be mentioned that all the biochemical tests complete one another and may have a decisive role in taking immediate obstetrical decisions, together with the additional fetal heart rate monitoring and oxytocin challenge test.