The effects of thyroidectomy (Tx) and thyroxine replacement (T4Rx) on pituitary growth hormone (GH) secretion and hypothalamic GH-releasing hormone (GRH) concentration were compared to define the mechanism of hypothyroid-associated GH deficiency. Thyroidectomized rats exhibited a complete loss of pulsatile GH secretion with extensive reduction in GRH responsiveness and pituitary GH content. Cultured pituitary cells from Tx rats exhibited reduced GRH sensitivity, maximal GH responsiveness, and intracellular cyclic AMP accumulation to GRH, while somatostatin (SRIF) suppressive effects on GH secretion were increased. Hypothalamic GRH content was also markedly reduced. T4Rx completely restored hypothalamic GRH content and spontaneous GH secretion despite only partial recovery of pituitary GH content, GRH and SRIF sensitivity, and intracellular cyclic AMP response to GRH. The results indicate multiple effects of hypothyroidism on GH secretion and suggest that a critical role of T4 in maintaining normal GH secretion, in addition to restoring GH synthesis, is related to its effect on hypothalamic GRH.
H Katakami, T R Downs, L A Frohman
Normal blood-derived monocyte/macrophages were found to be susceptible to infection in vitro by human T lymphotropic virus type III (HTLV-III), the etiologic agent of the acquired immunodeficiency syndrome. In addition, HTLV-III was recovered from monocyte/macrophages of patients infected with this virus. The above findings raise the possibility that HTLV-III-infected monocyte/macrophages may serve as a vehicle for the dissemination of virus to target organs and as a reservoir for viral persistence, as has been shown for other lentiviruses including visna virus and caprine arthritis encephalitis virus.
D D Ho, T R Rota, M S Hirsch
The insulin binding characteristics and the structural components of the insulin receptor were studied in the purified liver plasma membranes from seven patients with noninsulin-dependent diabetes (NIDDM) and seven control subjects. In comparison to the controls, diabetic subjects had a 65% reduction in plasma insulin levels in response to an oral glucose load. Specific insulin binding by liver membranes from diabetic patients was, however, twofold greater than the binding activity by membranes from control subjects. This alteration resulted largely from an increase in the number of insulin receptors and a modest increase in receptor binding affinity. Holo (nonreduced) receptor species of similar molecular weights were detected by an affinity labeling technique in the two membrane preparations and sulfhydryl reduction demonstrated an insulin binding subunit of 125,000 mol wt. Overall, these results show that the hepatic insulin resistance of NIDDM cannot be explained by a deficiency in insulin binding.
P Arner, K Einarsson, S Ewerth, J Livingston
D A Williams, S H Orkin
We investigated the diminished natural killer (NK) activity in human T lymphotropic virus type III (HTLV-III) seropositive hemophiliacs. Despite normal percentages of NK cells, lymphocytes from five hemophiliacs showed impaired NK activity against K-562 tumor cells in 4-h chromium release microcytotoxicity assays. For example, at an effector-to-target cell ratio of 10:1, cells from patients caused 21.7 +/- 2.5% lysis of tumor targets compared with 47.9 +/- 5.1% lysis by cells from controls (mean +/- SEM, P less than 0.005). Cells from patients were as cytotoxic in 18 h as were cells from controls in 4 h. Binding to tumor targets was not impaired since 11.0 +/- 1.5% of cells from patients and 11.1 +/- 1.3% of cells from controls bound to K-562 cells. Patients' binding cells, however, showed defective killing of attached tumor cells at all time points tested from 0 to 18 h. At 4 h, for example, patients' cells had lysed 10.9 +/- 2.1% of attached tumor cells compared with 26.3 +/- 3.3% lysis by controls' cells (P less than 0.005). The percentage of lymphocytes which were active NK cells (i.e., cells that bound and lysed a tumor cell) was always lower for patients than for controls (1.17 +/- 0.25% vs. 2.82 +/- 0.33%, P less than 0.005). Two methods for estimating recycling of effector cells against multiple target cells demonstrated that active NK cells from patients could recycle as well as those from controls (approximately 3-4 times in 4 h). Mixing experiments showed no evidence for cellular suppression of NK activity. The lytic function of NK cells from HTLV-III seropositive hemophiliacs is thus heterogeneous. This is characterized by a defect in post-binding lysis, with relative sparing of binding capability and recycling capacity.
M Katzman, M M Lederman
Analysis of 24-h urinary steroid excretion was performed by capillary gas chromatography in six patients (five men, one woman) with adrenocortical insufficiency. Ten healthy subjects (five men, five women) served as controls. A complete absence of all 21-hydroxylated steroid metabolites was seen in patients with adrenocortical insufficiency, whereas the excretion of several steroids lacking hydroxylation in the 21-position (pregnenolone, pregnenetriol, and 11-ketoandrosterone) was markedly increased. In addition, the presence of 11 beta-hydroxyandrosterone was confirmed by mass-spectrometry in the urine of three patients. This pattern of steroid excretion was unchanged in patients with adrenocortical insufficiency, both after stimulation by 1-24 adrenocorticotropin (ACTH) and after short-term (3-d) suppression with dexamethasone. We conclude that patients with adrenocortical insufficiency present a pattern of steroid excretion characterized by the absence of 21-hydroxylated metabolites. In the absence of functional adrenocortical tissue, long-term pathologically elevated concentrations of ACTH apparently stimulate early steps of steroid synthesis, most likely in the gonads. In addition, the presence of 11-hydroxylated steroid metabolites (11-ketoandrosterone, 11 beta-hydroxyandrosterone) in the urine of patients with adrenocortical insufficiency demonstrates that chronic ACTH excess in this disorder may induce some activity of 11 beta-hydroxylase, an enzyme not found in the gonads under physiological conditions.
H Vierhapper, P Nowotny, W Waldhäusl
Plasma cholesterol metabolism was investigated in normotriglyceridemic patients with end-stage renal disease treated by hemo- or continuous ambulatory peritoneal dialysis (CAPD), and compared with that in a control group with normal renal function. A reversed net transport of free cholesterol from plasma to cultured fibroblasts, as well as greatly reduced levels of plasma cholesterol esterification and cholesterol ester transfer rates to low and very low density lipoproteins (LDL and VLDL), was found in the hemodialysis group compared to the controls. The LDL and VLDL contained increased amounts of free cholesterol and inhibited cholesterol ester transfer when recombined with control plasma. The LDL triglyceride content was doubled in the hemodialysis group, whereas cholesterol esters were decreased. Patients treated by CAPD, in marked contrast, had cholesterol metabolic rates that were within the normal range, as well as normal lipoprotein composition.
H Dieplinger, P Y Schoenfeld, C J Fielding
The cerebral capillary endothelium is unique and functions as an effective blood-brain barrier (BBB) owing to its intercellular tight junctions and rare pinocytotic vesicles. To assess how bacterial meningitis alters the BBB, rats were inoculated intracisternally with three encapsulated meningeal pathogens (Escherichia coli K1+, Streptococcus pneumoniae type III, Haemophilus influenzae type b) and an unencapsulated mutant strain (H. influenzae Rd). After defined infection durations, the morphologic alterations of the cerebral capillary endothelium were quantitatively assessed by transmission electron microscopy. Results revealed a significant increase in pinocytotic vesicle formation (P less than 0.001) early after meningitis induction (4 h) that was sustained with longer infection durations (10 h, 18 h) for all encapsulated strains tested. In addition, there was a progressive increase in completely separated intercellular junctions with increasing infection duration, (P less than 0.05). 4 h after induction of meningitis with H. influenzae Rd, cerebrospinal fluid (CSF) bacterial concentrations, cerebral capillary morphologic changes, and functional BBB permeability to circulating 125I-albumin were similar to those observed with H. influenzae type b. However, prolonging the H. influenzae Rd infection to 18 h allowed for CSF clearance of the organism, thereby precluding the significant increase in separated junctions or progression of functional BBB permeability seen with the encapsulated H. influenzae type b. These data suggest a uniform morphologic explanation for altered BBB permeability in meningitis with a reproducible temporal sequence. Encapsulation does not appear essential for BBB injury, but may facilitate its progression by allowing the organism to evade host clearance.
V J Quagliarello, W J Long, W M Scheld
In passive Heymann nephritis (PHN) in rats, antibody (anti-Fx1A) reacts in situ with a glomerular epithelial antigen and induces complement (C)-mediated cell-independent proteinuria. To assess the role of the membrane attack complex (MAC), we determined the need for C8 in the pathogenesis of proteinuria in an autologous-phase model of PHN. Isolated rat kidneys, containing nonnephritogenic, non-C-fixing gamma 2 sheep anti-Fx1A (planted antigen), when perfused in vitro with C-fixing guinea pig anti-sheep IgG and a source of C (fresh human plasma 50% vol/vol in buffer containing bovine serum albumin), developed marked proteinuria after 20 min (0.58 +/- 0.08 mg/min X g, n = 8) that increased further to 3.20 +/- 0.93 mg/min X g after 80 min. In contrast, identical kidneys perfused with antibody and heat-inactivated or C8-deficient human plasma and normal kidneys perfused with antibody and fresh plasma excreted only 0.27 +/- 0.03 (n = 6), 0.27 +/- 0.04 (n = 5), and 0.40 +/- 0.05 mg/min X g (n = 6) after 20 min, and 0.13 +/- 0.02, 0.22 +/- 0.03, and 0.32 +/- 0.05 mg/min X g after 80 min, respectively. When C8-deficient plasma was reconstituted with sources of C8 (n = 3), proteinuria was restored to the level observed with fresh normal plasma. Differences in protein excretion could not be explained by quantitative differences in glomerular antigen or antibody content. Extensive ultrastructural damage to glomerular visceral epithelial cells was exclusively seen in antigen-containing kidneys perfused with antibody and C8-replete plasma. Thus, glomerular injury in this model results from an antigen-specific, antibody-directed, C8-dependent reaction involving assembly of the MAC. The ultrastructural findings argue in favor of MAC-induced cytotoxicity of the glomerular visceral epithelial cells.
A V Cybulsky, H G Rennke, I D Feintzeig, D J Salant
Aortic atheromatous plaques regress slowly in cholesterol-fed rabbits that have been returned to normal laboratory diet. To delineate metabolic factors potentially responsible for persistence of atherosclerosis under these conditions, the physical, chemical, and metabolic characteristics were determined for lipoproteins of d less than 1.006 g/ml; such lipoproteins are thought to be the major determinant of progression of atherosclerotic lesions in cholesterol-fed rabbits. At the time of return to a normal laboratory diet regimen after 3 mo of feeding with cholesterol-enriched laboratory diet, plasma cholesterol concentrations were 2,275 +/- 252 mg/dl, mostly attributable to cholesteryl ester-rich very low density lipoproteins (VLDL). On the hypercholesterolemic diet, fractional catabolic rates of plasma clearance of 125I-labeled VLDL were reduced (0.011 +/- 0.002 vs. 0.151 +/- 0.015 h-1), but the total VLDL catabolic rate was increased considerably (17.1 +/- 2.2 vs. less than 1.2 +/- 0.4 mg of protein/kg X d), because of the expansion of the endogenous pool of cholesteryl ester-rich VLDL. The total catabolic rate of VLDL was maintained above estimated control values (5.8 +/- 0.7 mg protein/kg X d) even 10 wk after return of the rabbits to a normal chow regimen, an effect attributable to continued high rates of cholesteryl ester-rich VLDL synthesis in liver. Accumulation of cholesteryl ester-rich VLDL into aortic tissue persisted at a high rate. Thus the persistence of aortic atheromatous lesions after cessation of cholesterol feeding was attributable in part to continued high rates of hepatic production of cholesteryl ester-rich VLDL and its persistent delivery into the aortic wall.
A Daugherty, G Schonfeld, B E Sobel, L G Lange