W. Oelkers

Effects of estrogens and progestogens on the renin-aldosterone system and blood pressure.

Endogenous 17 beta-estradiol (E2) and low parenteral doses of exogenous E2 are vasodilators. High dose estrogens, especially ethinylestradiol (EE) and mestranol, stimulate the synthesis of hepatic proteins including coagulation factors, sex hormone binding globulin, and angiotensinogen (Aogen). In the steady state, high plasma levels of Aogen produce only a very small increase of angiotensin II (AII) and plasma renin activity, because AII inhibits the secretion of renin and lowers plasma renin concentration. However, the increase in AII is sufficient for a slight reduction in renal blood flow and a slight increase in exchangeable sodium and blood pressure; in susceptible women, blood pressure may rise considerably. Effects of estrogens on the brain may also be involved in blood pressure changes. Endogenous progesterone is a mineralocorticoid receptor antagonist. Endogenous or exogenous progesterone leads to sodium loss and a compensatory increase in renin secretion, plasma renin activity, AII, and plasma aldosterone, e.g. in the second half of the menstrual cycle. Synthetic progestogens are commonly devoid of the mineralocorticoid receptor antagonistic effect of progesterone, and some are weak estrogen receptor agonists. Combined use of EE and synthetic progestogens may therefore enhance estrogen effects on body sodium and blood pressure. A new progestogen (Drospirenone) with an antimineralocorticoid effect like that of progesterone is described that slightly lowers body weight and blood pressure in a contraceptive formulation together with EE. An almost ideal oral contraceptive would be progestogen like Drospirenone together with a low dose natural estrogen that does not stimulate Aogen synthesis. Since most oral formulations for postmenopausal estrogen replacement also stimulate hepatic protein synthesis (including Aogen) to some extent, the transdermal route of E2 application for contraceptive purposes should also be investigated, since it has reduced potential for undesirable side effects.

Drospirenone, a progestogen with antimineralocorticoid properties: a short review.

UNLABELLED Progesterone (P) has high affinity to the mineralocorticoid receptor (MCR), and it is an MCR antagonist. Almost all synthetic progestogens are devoid of this antimineralocorticoid (anti-MC) effect. They are unable to antagonize the salt retaining effect of estrogens. This could be one cause of weight gain and an increase in blood pressure with the use of combined oral contraceptives (OC) and, in some susceptible women, with postmenopausal estrogen/(progestogen) treatment. The purpose of this presentation is to review results of clinical studies with drospirenone (DRSP), a new progestogen developed by Schering A.G., with anti-MCR activity. DRSP is a derivative of 17-alpha-spirolactone. In rats, rabbits and in man, it is a PR-agonist and an MCR- and androgen-R antagonist with no effect on the glucocorticoid-R and the estrogen-R. In normally menstruating women, 2-3mg DRSP per day, taken from day 5 to 25 of the cycle, inhibit ovulation, lead to a mild natriuresis, and a slight compensatory activation of the renin-aldosterone system. Compared with an OC containing 30 microg ethinylestradiol (EE) and 150 microg levonorgestrel, a combination of 3mg DRSP with 30 microg EE given over 6 months led to a slight decrease in body weight and blood pressure. The reduction in mean body weight by a combination of DRSP with EE compared with a conventional OC could be confirmed in a study over 26 months in 900 young women. The OC containing DRSP has favorable effects in patients suffering from the premenstrual syndrome (PMS), and, partly due to the antiandrogenic effect of DRSP, in those with acne vulgaris. For postmenopausal women, a combination of DRSP with estradiol has been developed with the expectation that the slight blood pressure lowering and weight reducing effects will minimize cardiovascular morbidity in patients needing hormone treatment because of hot flushes and other climacteric symptoms. CONCLUSIONS DRSP, by its anti-MCR effect and its potential to slightly decrease body weight and blood pressure, shares many pharmacodynamic properties with progesterone, and it is a candidate for reducing cardiovascular morbidity in women using OCs or postmenopausal hormone treatment.

Endocrine activity of the "silent" adrenocortical adenoma is uncovered by response to corticotropin-releasing hormone.

SummaryThe purpose of this study was to ascertain whether the pituitary-adrenal responses to human corticotropin-releasing hormone (hCRH) in “non-functioning” adrenocortical adenoma would uncover a functional activity in these adrenal nodules. Eleven patients with incidentally discovered “silent” adrenocortical adenoma and eleven controls were studied. The initial clinical and laboratory examination, including an overnight 1 mg dexamethasone suppression test, revealed no abnormalities in any of the subjects. IR-ACTH and serum steroids (F, S, P, 17OHP, 18OHB, and aldosterone) were normal in both controls and patients. After pulse IV injection of 100 νg hCRH, the cortisol response was significantly exaggerated (P=0.01). Stimulated plasma ACTH levels were, however, significantly lower in patients than in controls (P=0.01), indicating counter-feedback regulation of cortisol. The peak cortisol/peak ACTH ratio (Fmax/ACTHmax) in the patients was significantly elevated (26.8±4.37 nmol/ng vs. 14.6±2.16 nmol/ ng,P=0.02). Two further patients with incidentally discovered “pre-Cushings” adrenocortical adenoma displayed an even higher ratio (43.5 and 45.5 nmol/ng). In established Cushings syndrome due to an autonomous adrenocortical adenoma, suppression of ACTH and of the ACTH response to hCRH occurs with a very high basal cortisol/ basal ACTH ratio. Our findings suggest some functional activity even in clinically “silent” adrenocortical adenoma. Response to hCRH uncovers a continuous spectrum between adrenocortical adenoma, “pre-Cushings”, and Cushings syndrome.

Tubuloglomerular feedback in rat kidneys of different renin contents

SummaryVariations in flow rate through the loop of Henle in the range of 0–50 nl/min were induced using pressure controlled microperfusion. Simultaneously, with the aid of a second pressure-microperfusionsystem, the glomerular function of the same nephron was studied by continuous measurement of two parameters, early proximal flow rate (EPFR) and/or stop flow pressure (SFP). Elevation of loop perfusion above physiological values (40 nl/min) resulted in a drop of EPFR and SFP, whereas lowering perfusion rates had no effect. This feedback behaviour was studied in kidneys with different renin contents to test the role of the renin-angiotensin system in the mediation of the macula densa signal to the adjacent glomerular vessels. Renal renin content, measured after micropuncture experiments by incubation with substrate followed by radioimmunoassay of angiotensin I, was unaltered in control (Ia) and heminephrectomized rats (Ib), lowered in contralateral kidneys of 2 kidneys Goldblatt hypertensive rats (IIa), in DOCA- and salt-loaded rats (IIb), and in DOCA-, salt-loaded and heminephrectomized rats (IIc), and it was elevated in clipped kidneys of Goldblatt hypertension rats (IIIa). Micropuncture evaluation of the tubuloglomerular feedback behaviour in these experimental groups revealed the following results: 1. a feedback response under all conditions independent of the widely varying renin contents (1000-fold), 2. an asymmetrical behaviour of the feedback response in all kidneys as demonstrated by suppression of EPFR and SFP at elevated loop flow rates, but no change of these parameters when loop flow was interrupted, 3. compared to controls the decrease of each GFR parameter between 0 and 40 nl/min loop perfusion was lower in DOCA- and salt-loaded rats (IIb, IIc). Additional heminephrectomy (IIc) had no further influence on the reduced feedback response in DOCA- and salt-loaded rats, whereas this manoeuvre reduced the renal renin content drastically. A somewhat higher response than in controls was found in heminephrectomized rats (IIb) and in clipped kidneys of Goldblatt hypertensive rats (IIIa). These different magnitudes of feedback responses do not correlate with the renal renin content. It has been concluded, therefore, that renal renin activity is not the sole determinant of the effectiveness of the tubuloglomerular feedback response.

Effects of sodium salts on pressor reactivity in salt-sensitive men.

Blood pressure in patients with essential hypertension is raised by sodium chloride but not by nonchloride sodium salts. Although a high sodium chloride diet is known to augment the pressor response to norepinephrine and angiotensin II, the effect of nonchloride sodium salts on pressor responsiveness has not been studied so far. To examine whether sodium chloride and nonchloride sodium salts evoke different pressor responses to these agonists, we performed graded norepinephrine and angiotensin II infusions in salt-sensitive (n = 7) and salt-resistant (n = 8) normotensive subjects. The subjects were given a low salt diet (20 mmol/day) for 3 weeks, to which a supplement of 200 mmol sodium per day, provided as either sodium chloride or sodium citrate, or a placebo was added for 1 week each. We found that, although sodium chloride raised mean arterial blood pressure in the salt-sensitive subjects (p less than 0.005), sodium citrate did not. However, under both sodium salts pressor response to norepinephrine and angiotensin II was significantly greater than under placebo (p less than 0.02). Furthermore, with both sodium salts, pressor response in the salt-sensitive subjects was greater than in the salt-resistant subjects (p less than 0.01). This study thus demonstrates that, although blood pressure in salt-sensitive individuals is raised by sodium chloride only, both sodium chloride and sodium citrate evoke similar increases in pressor response to norepinephrine and angiotensin II. Since pressor response increased with both sodium salts but resting blood pressure increased only with sodium chloride, enhanced pressor responsiveness alone cannot account for the sodium chloride-induced rise in resting blood pressure.

Metabolism of Synthetic Corticosteroids by 11β-hydroxysteroid-Dehydrogenases in Man

The presence of an 11 beta-hydroxyl group is essential for the anti-inflammatory and immunosuppressive effects of glucocorticoids. Interconversion of the 11 beta-hydroxyl into the corresponding 11 beta-keto group and vice versa by 11 beta-hydroxysteroid-dehydrogenase (11 beta-HSD) may thus play a pivotal role in the efficacy of these steroids. Therefore, we have compared the metabolism of the endogenous glucocorticoid cortisol (F) with that of synthetic 9 alpha-fluorinated steroids by 11 beta-HSDs in humans in vivo and in vitro. Whereas 30% of the free steroids in urine after oral administration of 5 mg of F is F itself and 70% the inactive keto-product cortisone (E), the urinary excretion of an identical dose of oral 9 alpha-fluorocortisol (9 alpha FF) is 90% 9 alpha FF and 10% inactive 9 alpha-fluorocortisone (9 alpha FE). Kidney slices similarly convert F much faster to E than 9 alpha FF to 9 alpha FE; conversely, renal 11 beta-reduction of 9 alpha FE to 9 alpha FF is much more effective than that of E to F. Kinetic analyses in human kidney cortex microsomes prove that the preference of fluorinated steroids for reduction in human kidney slices is catalyzed by 11 beta-HSD type II: the NADH-dependent conversion of 11-dehydro-dexamethasone (DH-D), another fluorinated steroid, to dexamethasone (D) is very effective (high affinity, high Vmax), whereas reduction of E to F is very slow. In human liver microsomes (11 beta-HSD type I), nonfluorinated (E) and fluorinated 11-dehydrosteroids (DH-D) are both reduced to their corresponding active 11-hydroxyderivatives but with a Michaelis-Menten constant about 20-fold higher than for kidney microsomes (11 beta-HSD-II). Our results suggest that the decreased renal 11 beta-oxidation of 9 alpha-fluorinated steroids may offer pharmacokinetic advantages for renal immunosuppression. Furthermore, administration of fluorinated 11-dehydrosteroids is a new and exciting idea in glucocorticoid therapy in that small amounts of oral DH-D may pass the liver largely unmetabolized (11 beta-HSD-I has low affinity for such steroids) and may then be activated to D by high-affinity 11 beta-HSD-II, thus allowing selective immunosuppression in organs expressing 11 beta-HSD-II (kidney and colon).

Torsemide inhibits aldosterone secretion in vitro

Torsemide inhibited aldosterone secretion by adrenal cells from rats, cows, and guinea pigs stimulated in vitro by potassium, angiotensin, dibutyryl cyclic AMP, ACTH, or corticosterone. Inhibitory concentrations for adrenal cells (micromolar) were comparable with those reported to inhibit ion transport in isolated renal tubules. Inhibition of aldosterone secretion could reduce kaliuresis, and that may explain why torsemide causes less kaliuresis than other diuretics.

Time course of aldosterone and corticosterone plasma levels in rats during general anaesthesia and abdominal surgery.

The transepithelial voltage (Ψms) of rat rectum in vivo increases for several hours in experiments under general anaesthesia. So far this was attributed by indirect evidence to increasing aldosterone plasma levels during the course of the experiment.We performed direct measurements of aldosterone and corticosterone plasma concentrations during intestinal perfusion experiments on barbiturate anaesthetized rats. Experiments were terminated for blood sampling at 10, 75, 300, 400, 800, or 1,800 min, respectively.(i) After 75 min of anaesthesia, surgical preparation was finished and plasma levels of aldosterone and of corticosterone were found increased by the factors 5 and 3, respectively, as compared to conscious controls. (ii) During the following 12 h, aldosterone further increased to levels 10 times as high as those of controls. In contrast, during the same period corticosterone slowly decreased but still remained elevated as compared to controls. (iii) The increase of both hormones was attenuated when abdominal surgery was omitted. (iv) The use of pentobarbital (Nembutal) instead of thiobarbital (Inactin) did not influence the adrenal response. (v) In adrenalectomized rats a continous substitution with 65 ng·h−1·kg−1 BWT aldosterone resulted in plasma levels as high as in conscious intact animals. (vi) RectalΨms started to move to higher lumen-negative values with a time delay of 1–1 1/2 h as compared with the increase of hormone levels.Ψms then stayed elevated until to the end of the experiments.We conclude that in vivo experiments of several hours duration in thio- or pentobarbital anaesthetized rats take place under conditions of aldosterone and corticosterone plasma levels which are high as compared to those of conscious unstressed animals. The different time course of aldosterone and corticosterone plasma levels after the end of surgery would be in accord with a stimulatory effect of anaesthesia on both renin and ACTH, plus an additional stimulatory effect of abdominal surgery on ACTH alone.

Dose–response relationship between plasma ACTH and serum cortisol in the insulin–hypoglycaemia test in 25 healthy subjects and 109 patients with pituitary disease

OBJECTIVE The insulin hypoglycaemia test (IHT) is believed to be the most reliable test for evaluating the entire hypothalamo-pituitary-adrenal (HPA) axis. The lower limit for the normal peak serum cortisol response has been reported to be between 500 and 580 nmol/l. Reference levels for a normal plasma ACTH response have not been reported recently. DESIGN AND PATIENTS We performed the IHT in 25 healthy subjects and in 109 patients with proven or suspected pituitary disorders with serial measurements of serum or plasma cortisol and of plasma ACTH, in order to establish reference levels and to study the dose-response relationship between ACTH and cortisol in this test. In most patients, other pituitary hormonal axes were evaluated in addition. RESULTS With the cortisol kit from Diagnostic Products Corporation (DPC), serum cortisol was about 13% lower than plasma (EDTA) levels with an excellent correlation between serum and plasma (r = 0.976; P<0.001). In the normals, the lower limit of the cortisol response (mean cortisol peak level minus 2 SD.) was 570 nmol/l for plasma and 500 nmol/l (calculated) for serum, while the lower limit of the ACTH response was 17.6 pmol/l (80 ng/l). In normals, the cortisol response was independent of the magnitude of the ACTH response. Seventeen out of 30 patients with ACTH responses to levels < 8.8 pmol/l (< 40 ng/l) had subnormal cortisol responses. However, 38 of the patients with pituitary disease had normal cortisol responses in spite of subnormal ACTH responses (group 2), while 47 patients had completely normal IHT results (group 1). Patients in group 2 had more often additional pituitary hormone deficiencies than those of group 1. The dose-response relationship between ACTH and cortisol in the patients resembled a dose-response curve that had been set up previously in normal subjects who received incremental doses of subcutaneous human ACTH (1-39). CONCLUSIONS The normal increment of plasma ACTH in the IHT is greater than necessary for stimulating serum cortisol to levels > 500 nmol/l. Patients with a subnormal ACTH but normal cortisol response in the IHT have a decreased ACTH secretory reserve. It is unlikely that they are at increased risk of developing an adrenal crisis perioperatively or in other stressful situations unless pituitary function deteriorates. The ACTH-cortisol relationship in the IHT performed in patients with pituitary disease shows no sharp dividing line between normality and disease, and whether a patient needs permanent glucocorticoid substitution is a discretionary decision.

Differential diagnosis of polyuric/polydipsic syndromes with the aid of urinary vasopressin measurement in adults

OBJECTIVE A water deprivation test or a hypertonic saline infusion test with the measurement of plasma osmolality and plasma vasopressin are the gold standard tests in the differential diagnosis of polyuric syndromes. Because commercially available vasopressin kits are too insensitive for this approach, and the concentration of vasopressin in urine is much higher than in plasma, urinary vasopressin measurements may be an alternative to the more difficult plasma vasopressin measurement.