No abstract

The aim of this study was to investigate the effects of bradykinin on conventional outflow facility in relation to kinin effects on matrix metalloproteinase (MMP) secretion. Conventional outflow facility was measured in isolated bovine segments perfused at a constant pressure of 10 mmHg. Experiments were also performed in primary cultures of bovine trabecular meshwork cells to assess bradykinin effects on the secretion of MMP-9 assessed by western blot. Administration of bradykinin (10(-7) M) to perfused anterior segments produced a 50% increase in outflow facility above basal levels. The effect was slow to develop, requiring 100 min for a significant increase in facility and 4 h for the peak response to be observed. Pretreatment of anterior segments with the B(2) kinin receptor antagonist, HOE-140 (10(-6) M), or with the nonselective MMP inhibitor, GM6001 (10(-5) M) blocked the response to bradykinin (10(-7) M). Treatment of cultured trabecular meshwork cells with bradykinin (10(-7) M) for 120 min stimulated secretion of MMP-9 into the extracellular media, and this response was inhibited by HOE-140 (10(-6) M). These results demonstrate that bradykinin activates B(2) kinin receptors to increase conventional outflow in the perfused bovine eye and provide evidence that secretion and activation of MMPs within the conventional pathway may mediate the effect.

Adenylyl cyclases present a potential focal point for signal integration in vascular smooth muscle cells (VSMC) influencing contractile state and cellular responses to vessel wall injury. In the present study, we examined the influence of the vasoactive peptide arginine vasopressin (AVP) on cAMP regulation in primary cultures of rat aortic VSMC and in the A7r5 arterial smooth muscle cell line. In cultured VSMC and A7r5 cells, AVP had no effect on basal cAMP but differentially affected beta-adrenergic receptor-induced activation of adenylyl cyclase. AVP synergistically increased (twofold) isoproterenol-stimulated cAMP production in VSMC but inhibited the effect of isoproterenol (50%) in the A7r5 cell line. The effects of AVP in both preparations were blocked when cells were pretreated with a selective V(1) vasopressin receptor antagonist. Moreover, the actions of AVP in both models were dependent on release of intracellular Ca(2+) and were mimicked by elevation of Ca(2+) with the ionophore A23187, suggesting that the responses to AVP involve Ca(2+)-mediated regulation of adenylyl cyclase stimulation. Adenylyl cyclase types I, III, and VIII are stimulated by Ca(2+)/calmodulin, whereas types V and VI are directly inhibited by Ca(2+). RNA blot analysis for effector isotypes indicated that both VSMC and A7r5 cells expressed types III, V, and VI. VSMC also expressed mRNA for type IV and VIII effectors, which could account for the cell-specific responses to peptide hormone and Ca(2+).

The influence of arginine vasopressin (AVP) on agonist-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation was investigated in vascular smooth muscle cells (VSMC) cultured from rat thoracic aorta. Incubation of VSMC with AVP for 60 s produced a 2- to 2.5-fold enhancement of isoproterenol-induced cAMP formation. AVP also increased cAMP stimulation by the prostaglandin I2 analogue iloprost. The effect of AVP to enhance agonist-stimulated cAMP formation was completely inhibited in cells pretreated with a selective antagonist of V1 vasopressin receptors but was not affected by blockade of V2 receptors. Inhibition of protein kinase C activation failed to alter the action of AVP to potentiate cAMP stimulation, but treatment of cells with calmodulin antagonists significantly attenuated this effect of the peptide. Moreover, depletion of Ca2+ stores with thapsigargin decreased AVP enhancement of isoproterenol-stimulated cAMP by > 70%. The action of AVP to increase cAMP stimulation was also demonstrated in freshly isolated strips of rat aorta where treatment with peptide produced a twofold increase in isoproterenol-stimulated cAMP formation. RNA blot analysis indicated expression in VSMC of mRNA encoding type III adenylyl cyclase, a Ca(2+)-calmodulin-sensitive isoform of the effector. Furthermore, when detergent-solubilized membrane extract was subjected to calmodulin affinity chromatography, a peak of adenylyl cyclase activity was identified which had affinity for calmodulin matrix in the presence of Ca2+. The results indicate that AVP activates V1 receptors in VSMC to enhance agonist-stimulated cAMP formation by a Ca(2+)-calmodulin-dependent mechanism and suggest that type III adenylyl cyclase may provide a focal point in the VSMC for cross talk between constrictor and dilator pathways.

SUMMARY Early differences in hemodynamic variables and vasoactive substances between progeny of hypertensive and normotensive parents were sought in normotensive children aged 10-17 years. Forty-two black and 34 white children of hypertensive parents (cases) and an age-balanced group of 20 black and 45 white children of normotensive parents (controls) underwent exercise stress testing. Blood pressure, heart rate, urinary electrolytes, kallikrein, and prostaglandin E-like material, plasma renin activity, and norepinephrine were measured before, during, and after exercise. Analyses compared the findings of four subject groups: black cases with black controls, white cases with white controls, black cases with white cases, black controls with white controls. Based on a family history of hypertension, significant familial differences were found: Black cases "were larger" (p = 0.003) when compared to black control subjects and had higher resting systolic, dlastolic, and maximum exercise diastolic blood pressures, and higher postexercise plasma renin activity (p = 0.04); white cases also were larger (p = 0.004) in comparison with white controls and had higher postexercise heart rates, higher preexercise urinary prostaglandin E-like material, and lower plasma norepinephrine after exercise (p < 0.05). Significant racial differences were noted in heart rate, blood pressure, urinary electrolytes, and other biochemical substances. Among the cases, black/white comparisons showed that blacks had lower postexercise heart rates, and higher resting and maximum exercise systolic and diastolic blood pressures (p < 0.04 for these comparisons). Additionally, blacks had higher preexercise urinary sodium excretion, lower preexercise urinary potassium excretion (p < 0.003), and lower plasma renin activity before and after exercise (p < 0.003). Finally, urinary kallikrein excretion before and after exercise was lower in blacks (p < 0.03). While blood pressures were similar among the black and the white controls, comparisons revealed that the blacks had higher preexercise sodium and potassium excretion (p < 0.005), lower plasma renin activity at all levels of activity, and lower plasma norepinephrine 10 minutes after exercise (p < 0.05). Thus, significant intraracial and interracial differences in physiological and biochemical variables, thought to be related to the development of hypertensive diseases, have been detected in normotensive children categorized according to a family history of hypertension. With use of these variables, the black case children can be separated from the other three groups and may have increased risk for the development of adult onset hypertension. 57Considerable information has been published concerning the familial aggregation of hypertension. Paffenbarger et al. 5 in 1968 reported that a parental history of hypertension was correlated with the development of the disorder in youths followed into later years. Familial aggregation of blood pressures through childhood was established by Zinneretal. 6 in 1971. ...