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Angiotensin-converting enzyme (ACE) has 2 different active sites: a C-site (in the carboxy terminal region) and an N-site (in the amino terminal part). Some ACE inhibitors have a relatively greater affinity for the C-sites, whereas others bind to the 2 sites with equal affinity. The different ontogenesis of lung and heart endothelial cells can be related to binding differences to the C- and N-sites. We labeled Ro31 – 8472, a cilazapril derivative, which has the same affinity for the 2 ACE sites. Binding of 125 I-Ro31-8472 to human left ventricle and lung plasma membranes was saturable, inhibited by ethylene diaminetetraacetic acid and displayed affinities of 360 ± 41 p M in heart and 320 ± 51 p M in lung. For captopril the Hill slope was 0.57 ± 0.03 for heart and 0.48 ± 0.05 for lung; for delaprilat, a nonsulfhydryl analogue of captopril, the slope was 0.43 ± 0.05 for heart and 0.55 ± 0.05 for lung. These drugs were characterized by biphasic competition isotherms. The Hill slope of enalaprilat was 1.01 ± 0.06 for heart and 0.93 ± 0.06 for lung, and Ro31-8472 had a slope of 0.97 ± 0.04 for heart and 0.93 ± 0.03 for lung. The affinity of ACE inhibitors with Hill slope different from unity varied according to the source of ACE; in fact, delaprilat had greater affinity for the high-affinity sites of heart than lung (pK i , 9.89 and 9.47, respectively), whereas captopril had greater affinity for the high-affinity sites of lung than heart (9.40 and 8.85, respectively). The pK i of these drugs for the second site was 7.18–7.90 for each drug in each tissue. The affinity of Ro31-8472 was similar for heart and lung, but enalaprilat had greater affinity for lung ACE (pK i = 9.21) than heart ACE (pK i = 8.76). In conclusion, different ACE inhibitors can interact with the ACE binding sites exhibiting a selectivity that varies depending on the source of the enzyme. Some drugs are site- and tissue-selective (delaprilat is C-site and heart-selective; captopril is C-site and lung-selective); other inhibitors are site- and tissue-nonselective (Ro31-8472) or site nonselective but tissue-selective (enalaprilat).

A certain number of HIV-infected patients (about 17% in our series) manifest symptoms of cortisol resistance--weakness, weight loss, hypertension, chronic fatigue and intense mucocutaneous melanosis--symptoms which are also typical of Addison's disease. The diagnosis of cortisol resistance is determined through the increased plasma and urinary cortisol values and limited increases in ACTH values. Compared with patients with primary glucocorticoid resistance, AIDS patients have no symptoms of mineral-corticoid or androgen excess, only of glucocorticoid deficiency at target tissues. Mononuclear leukocytes from these patients show receptor changes which consist of an increased receptor number and decreased receptor affinity for glucocorticoids. They also show defective glucocorticoid-induced inhibition of [3H]thymidine incorporation. Glucocorticoid-resistant AIDS patients have a characteristic persistent increase in interferon-alpha production. The inverse correlation between plasma values of interferon-alpha and the receptor affinity for glucocorticoids clearly suggests that interferon production is regulated by the glucocorticoid receptor: the smaller the glucocorticoid effect on lymphocyte cells is, the greater interferon production is. Owing to the antiviral effect of interferon-alpha, it is possible that glucocorticoid-resistant AIDS patients have greater defences against viral infection than other AIDS patients. As interferon-alpha is melanogenetic, its increased production may also explain the intense skin pigmentation found in patients with the glucocorticoid-resistance syndrome.

Data reported in the literature show in the majority of cases an increased basal cortisol level in HIV-positive patients compared with controls, although the plasma concentration of cortisol in HIV-positive patients is generally within the physiological range. It is well known that pharmacological doses of glucocorticoids are immunosuppressive, but little is known about the effects of physiological concentrations of cortisol on the immune system. If a dialogue really exists between the HPA axis and the immune system, immune responses should be modulated by physiological concentrations of cortisol, as well as pathological levels of cortisol (high as in Cushing's syndrome or low as in Addison's disease), which are known to be associated with impaired immune system responses. We suggest that in HIV-positive patients, a chronic increase in the basal endogenous cortisol levels may provoke an imbalance in cytokine production, with a decrease in the production of type 1 and an increase in that of type 2. The type 1 to type 2 shift might be synergic with the increased cortisol levels in enhancing viral replication and apoptotic phenomena, and finally in causing the progression of HIV infection.

Nimesulide, the prototype of a new class of anti-inflammatory drugs, dose-dependently decreases the production of the superoxide anion (O 2 ⨪ ) in N -formyl-methionyl-leucyl-phenylalanine (fMLP)-and in phorbol myristate acetate (PMA)-stimulated polymorphonuclear leukocytes. The inhibition of O 2 ⨪ ) is possibly related to its inhibitory effect on polymorphonuclear leukocyte cytosolic phosphodiesterase type IV (IC 50 = 39 ± 2 μ M), to the related increase in cAMP ( P μ M) and the subsequent increase in protein kinase A activity. In fact H-89, a specific protein kinase A inhibitor, counteracts the inhibitory effect of nimesulide on O 2 ⨪ production by fMLP and PMA. The activation of protein kinase A may prompt the phosphorylation of a number of substrates, thus inhibiting the assembly of NADPH-oxidase in the plasma membrane. Accordingly, nimesulide decreases PMA-induced assembly of NADPH-oxidase in polymorphonuclear leukocytes plasma membranes by about 35%. Protein kinase A activation may also interfere with chemotaxis. Nimesulide inhibits stimulated chemotaxis and the effect is decreased by H-89. Inhibition of phosphodiesterase type IV may explain many of nimesulide's effects.

Beta adrenergic receptors were identified in rat myocardial left ventricle and human papillary muscle by using the antagonist radioligand 3H-dihydroalprenolol. The number (37.3 and 44.5 fmol/mg of protein, respectively in rat and man), and the KD (1.6 and 2.8 nM, respectively in rat and man) of beta receptors were not significantly fifferent. Adrenergic receptors of both beta 1 and beta 2 subtypes were found to coexist in the left ventricle. The relative proportions of the two beta receptor subtypes were determined by the use of competition radioligand selective binding and computer modelling techniques employing the subtype selective antagonists ICI 118,551 (beta 2 selective) and atenolol (beta 1 selective) in rat or metoprolol (beta 1 selective) in man. The rat left ventricle contained about 74% beta 1 and 26% beta 2 adrenergic receptors, human left ventricle papillary muscles contained about 69% beta 1 and 31% beta 2. Human and rat left ventricles contain both beta 1 and beta 2 adrenergic receptors with similar affinities. Rat might be a model for the study of human myocardial beta adrenergic receptors.

Summary Specific dopaminergic receptors were found in the calf adrenal zona glomerulosa. Specific binding, as defined by the difference in 3H-ADTN (2-amino-6,7-dihydroxy-1,2,3,4 -tetrahydronaphthalene) binding in the presence of excess dopamine was saturable and of high affinity. Binding was rapid (t1/2=3.2 min) and rapidly reversible (t1/2=1.8 min). Stereospecificity of binding to the dopamine receptor was demonstrated by the fact that (R)-sulpiride, a proposed D-1 antagonist, was 50-fold more active at displacing 3H-ADTN than (S)-sulpiride, a D-2 antagonist. Among the agonists, SK&F 38393, a putative D-1 agonist, was more active than dopaminergic ergots, D-2 agonists. A Scatchard analysis of the data revealed a Kd=2.9±0.2 nM (m±SEM) and a Bmax=39±4 fmoles per mg of protein. Binding was not affected by guanyl nucleotides, nor was it affected by sodium ion. Binding was decreased by phosphatidic acid. No modification of cAMP production was observed in the presence of dopamine or of dopamine+GTP, whereas the cells showed an increase in cAMP after ACTH or β-adrenergic stimulation. These data suggest that the dopaminergic receptor identified is not linked to adenylate cyclase, and therefore its place is not in the D-2 dopamine receptor subclass.

The stimulatory effect of metoclopramide upon aldosterone secretion is independent of the known aldosterone-regulating mechanisms (renin, potassium, adrenocorticotropic hormone), is unrelated to its effect on prolactin and is absent when metoclopramide is directly added to isolated adrenal zona glomerulosa cells. To examine the possibility of a “humoral” mediation of aldosterone stimulation by metoclopramide, we evaluated the effect of serum of 10 normal subjects injected with metoclopramide (10 mg i.v.) on aldosterone production by collagenase-dispersed calf adrenal zona glomerulosa cells. Whereas no effect was observed with serum collected before the injection, serum collected from 5 to 30 min after the injection stimulated aldosterone production. The effect was seen 2.5 min after the injection, was significant at 5 min (P 0.05), 10,15,20 and 30 min (P 0.01). The effect disappeared 40 min after the injection, when plasma aldosterone in subjects was still elevated (P 0.01). The biological half-life of the factor ( t 1 2 ) is about 12.5 min. A significant correlation was found between the maximal aldosterone response to metoclopramide in vivo and the maximal effect of serum in vitro (r2=0.69; P 0.01). We suggest that metoclopramide stimulates aldosterone production in vivo by the increase in serum of a factor which, in turn, stimulates aldosterone and whose physiological significance remains to be evaluated.