Intrarenal administration of angiotensin II does not moderate afferent renal nerve mediated cardiovascular reflexes in the anaesthetized rabbit.

Stimulation of the afferent renal nerves in the anaesthetized rabbit by acute reduction in renal perfusion pressure results in a neurally mediated, reflex increase in hindlimb vascular resistance. To determine whether exogenous angiotensin II moderates the reflex, the kidneys of anaesthetized rabbits were vascularly isolated and renal blood flow was occluded acutely, following intrarenal administration of vehicle (0.9% saline) or angiotensin II (0.5 ng), and the hindlimb vascular response was measured. Occlusion of renal blood flow resulted in similar, significant increases in femoral perfusion pressure of 39.7 +/- 7.1 mmHg after vehicle and 21.3 +/- 8.9 mmHg (P < 0.05, n = 6) after angiotensin II. The viability of the preparation following repeated episodes of renal blood flow occlusion was tested by a series of three rapid (2-3 min delay) occlusions and three delayed (30 min delay) occlusions. Femoral perfusion pressure rose by 43.1 +/- 10.7 mmHg (rapid, P < 0.05, n = 11) and 64.4 +/- 12.3 mmHg (delayed, P < 0.05, n = 5) on the first occasion. On the second occasion, the rapid occlusion did not result in a significant increase in femoral perfusion pressure (29.1 +/- 8.1 mmHg), but the delayed group did (54.6 +/- 22.4 mmHg, P < 0.05). On the third occasion, neither group showed a significant change (20.9 +/- 16.3 and 30.8 +/- 13.5 mmHg). These data suggest that exogenous angiotensin II does not moderate the afferent renal nerve reflex. The decline in hindlimb response following rapid serial occlusion may be attributed to a diminution of an intermediary substance(s) at the nerve receptor site.

Evidence for a complex role of HLA class II genotypes in susceptibility to multiple sclerosis in Iceland.

We analyzed the association of HLA-DR and -DQ haplotypes and alleles with multiple sclerosis (MS) in 91 patients and 91 controls from Iceland using the relative predispositional effect method. The aim was to establish whether there is heterogeneity in HLA associations with MS, whether there are both predispositional and protective haplotypes, and whether sequence motifs also contribute to MS susceptibility. MS was positively associated with a DR2 haplotype (DRB5*0101-DQA1*0102-DQB1*0602), and empirical logistic analysis indicated that this haplotype is MS-associated because of a primary MS association with the DR2 allele. A DR13 haplotype (DRB1*1302-DQA1*0102-DQB1*0604) was negatively associated with MS, i.e., protective. Study of DR2-negative patients and controls confirmed this negative association and identified a second protective DR haplotype (DRB1*0701-DQA1*0201-DQB1*0201). Within these protective haplotypes in DR2-negative individuals, both DQA1 alleles and one DQB1 allele (*0604) were protective, but neither DR allele was protective, i.e., DQ loci may be more important than DR loci in encoding molecules protective against MS. Predispositional (Phe67) and protective (Ile67) DR beta sequence motifs were present in the total and DR2-negative patient and control groups. Since DQ but not DR alleles appear to be protective, DR beta Ile67 may confer additional protection against MS. Study of family-normal controls confirmed the MS association with the DR2 haplotype, and the transmission-disequilibrium test showed cosegregation and linkage of DR2 alleles and MS in families.

Mechanisms involved in the activation of ischemically sensitive, afferent renal nerve mediated reflex increases in hind-limb vascular resistance in the anesthetized rabbit.

Acute occlusion of the renal circulation in the anesthetized rabbit results in a neurally mediated, reflex increase in hind-limb vascular resistance, which is flow rather than pressure dependent. This suggests that the activating stimulus could be ischemia. In the present study vascularly isolated kidneys were perfused with hypoxemic or hypercapnic blood, and the hind-limb vascular response was measured. Renal perfusion with hypoxemic blood resulted in an increase in femoral perfusion pressure (FPP), which was negatively correlated with the oxygen tension of the blood. At a PO2 of 36.4 +/- 0.9 mmHg (1 mmHg = 133.3 Pa), FPP rose by 34.4 +/- 5.7 mmHg. Renal denervation abolished this effect. Renal perfusion with hypercapnic blood had no effect on FPP. Prostaglandin E2, bradykinin, and adenosine are released during renal ischemia and have been implicated in the mediation of afferent renal nerve activity; intrarenal administration (prostaglandin E2, 10 micrograms; bradykinin, 5 micrograms; adenosine, 20 micrograms; as a 1-mL bolus) during renal perfusion with normoxemic blood elicited increases in FPP of 32.4 +/- 13.2, 19.2 +/- 3.7, and 55.6 +/- 17.8 mmHg, respectively. Intrarenal indomethacin, aprotonin, and aminophylline all inhibited the increase in FPP observed during renal perfusion with hypoxemic blood. These data indicate that renal hypoxemia stimulates an afferent renal nerve mediated increase in FPP and suggest that prostaglandin E2, bradykinin, and adenosine may all be involved in the activation of ischemically sensitive R1 chemoreceptors.

The reflex effect of changes in renal perfusion on hindlimb vascular resistance in anaesthetized rabbits.

This study was designed to characterise the response of the hindlimb vasculature to reduced renal perfusion in the anaesthetized rabbit and to elucidate whether the stimulus was dependent upon reduced renal perfusion pressure (RPP) or blood flow (RBF). Acute decreases in renal perfusion resulted in rapid and reversible increases in femoral perfusion (FPP). This vascular response was completely abolished following renal denervation indicating that the afferent components of the reflex is neurally mediated. Acute hindlimb responses to changes in renal perfusion pressure were present whether the limb was perfused with homologous blood or cross-perfused with blood from a donor rabbit, demonstrating that the efferent component of the response is also neurally mediated. There was a 28-s latency for initiation of the hindlimb vasoconstriction, which is consistent with recent evidence for renal autocoid stimulation of the afferent renal nerve receptors. Decreasing RPP indirectly, by altering flow, resulted in a hindlimb vasoconstriction below approximately 55 mm Hg (7.3 kPa) RPP or 15 ml/min RBF. However, decreasing RPP by directly reducing pressure in graded steps resulted in increases in FPP, which reflected the changes in renal flow; thus during the autoregulatory phase, where flow did not change as pressure fell, FPP also remained stable. The results of these protocols suggest that a neurally mediated hindlimb vascular reflex is stimulated by decreased renal flow rather than pressure.

The inotropic effect of atrial natriuretic factor in the anesthetized rabbit.

This study was designed to investigate whether atrial natriuretic factor (ANF) administered over the physiological, pathological and pharmacological range has a negative inotropic action on the heart. Anesthetized rabbits were infused with increasing doses of ANF (0.05, 0.25 and 0.5 micrograms kg-1 min-1), while measuring hemodynamic variables including the maximum rate of change of left ventricular pressure (dP/dtmax) as an index of inotropic state. Plasma levels of immunoreactive ANF (iANF) were measured to relate the hemodynamic changes to actual plasma levels of the peptide. Administration of ANF was associated with decreases in blood pressure, left ventricular pressure and dP/dtmax so that after 0.5 micrograms kg-1 min-1 infusion, these variables had decreased by 21 +/- 2 mmHg, 21 +/- 5.3 mmHg and 925 +/- 175 mmHg/s, respectively (P less than 0.01). There were no significant changes in right atrial pressure, left ventricular end-diastolic pressure or heart rate. Since dP/dtmax can be influenced by changing hemodynamic variables and baroreflex changes, a second group of rabbits was studied in which afterload and heart rate were held artificially constant. Again, in this group of rabbits, infusions of AFN led to decreasing inotropic state, so that at the highest infusion rate, a 14% decrease in dP/dtmax was observed (P less than 0.05). By comparison, hydralazine, a drug which causes active vasodilatation but no direct inotropic action, significantly (P less than 0.01) decreased blood pressure, left ventricular pressure and dP/dtmax when infused at a rate of 10 micrograms kg-1 min-1. However, in animals in which afterload was controlled, hydralazine did not affect any of the variables measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of the desensitization of atrial natriuretic factor and nitroglycerin in rat aortic rings.

1. Atrial natriuretic factor (ANF) relaxes vascular smooth muscle through activation of particulate guanylate cyclase and generation of cyclic GMP. 2. From other laboratories, there is some evidence from cultured vascular smooth muscle cell studies for homologous desensitization of ANF-induced cGMP production and down-regulation of ANF receptors. 3. This series of studies demonstrates that homologous desensitization of ANF-induced relaxation of rat aortic ring preparations also occurs. 4. Heterologous desensitization could not be demonstrated to the vasoactive peptides angiotensin II or vasopressin, nor to nitroglycerin which has previously been shown to exhibit heterologous desensitization with other nitrovasodilators and shares some common elements in the pathway to vascular smooth muscle relaxation with ANF.

Characterization of a cell type-specific enhancer found in the human papilloma virus type 18 genome.

We have previously isolated long-range acting enhancer elements from the HeLa genome by functional selection. In this report, the structural and functional characteristics of one (GA1) of the enhancers are reported. By cloning various restriction fragments and by deletion mutagenesis, the activity of GA1 was located in a 230-bp region. The nucleotide sequence of GA1 and genomic Southern blot analysis indicated that GA1 is derived from human papilloma virus (HPV) 18 DNA that had been integrated into the HeLa genome. The enhancer is located in the non-coding region of the HPV 18 genome. The HPV 18 enhancer consists of two functional domains, both of which have full enhancer activity in HeLa cells. The enhancer does not contain enhancer core sequences but contains several blocks of potential Z-DNA sequence. Like SV40 and polyoma virus enhancers, the activity of the HPV 18 enhancer was repressed by adenovirus E1a products. The HPV 18 enhancer shows a narrow cell type specificity: it is active in some cervical carcinoma cell lines, but inactive in all non-cervical cells except for one neuroblastoma cell line. These results suggest that the HPV 18 enhancer plays an important role in regulation of the viral genes.